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A device to measure wheel slip to improve the fuel efficiency of off road vehicles
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Journal of Terramechanics
ScienceDirect Journal of Terramechanics 70 (2017) 1–11
www.elsevier.com/locate/jterra
A device to measure wheel slip to improve the fuel efficiency of off road vehicles A. Ashok Kumar a,⇑, V.K. Tewari b, Chanchal Gupta b, C.M. Pareek b b
a College of Agricultural Engineering, Madakasira, India Agricultural and Food Engineering Department, IIT Kharagpur, India
Received 18 March 2016; received in revised form 24 September 2016; accepted 12 November 2016
Abstract A hall sensor based simple technique was introduced to measure wheel slip and a microcontroller based embedded digital system was developed to display wheel slip data and warn the operator with audible and visible warnings if the optimum range is exceeds. Hall sensor slip measurement system was validated in controlled soil bin condition, tar macadam surface and actual field condition and compared with the commercial radar sensor. The developed system is simple in construction and can be mounted to any make and model of agricultural tractors by entering the appropriate rolling radius via the computer interface. Field trials were conducted to measure wheel slip and fuel consumption on farm use with and without activation of slip indicator; it was observed that, the amount of fuel saving during various agricultural operation was up 1.3 l/h. Ó 2016 ISTVS. Published by Elsevier Ltd. All rights reserved.
Keywords: Hall effect sensor; Actual speed measurement; Radar sensor; Display unit; Soil bin; Wheel slip
1. Introduction The primary purpose of agricultural tractors is to perform drawbar work. This is defined by pull and travel speed. Research shows that about 20–55% of the available tractor energy is wasted at the tyre-soil interface (Burt and Bailley, 1982). This energy wears the tires and compacts the soil to a degree that may be detrimental to crop production. Efficient operation of farm tractors includes: (i) selecting an optimum travel speed for a given tractor-implement system (ii) maximizing the tractive advantage of the traction devices, and (iii) maximizing the fuel efficiency of the engine and drive train. Among these, the maximizing of fuel efficiency could be done with little efforts. Increasing costs of petroleum products, most possible efforts are needed to improve the fuel efficiency and also ⇑ Corresponding author.
E-mail address: [email protected] (A. Ashok Kumar). http://dx.doi.org/10.1016/j.jterra.2016.11.002 0022-4898/Ó 2016 ISTVS. Published by Elsevier Ltd. All rights reserved.
better environmental concern. Especially in agricultural tractors, matching size of implement and load to a given size of tractor place a vital role in optimizing the fuel efficiency. Brixius and Wismer (1987) suggested that wheel slip has a dominating role in improving the tractive performance. The tractors operate at peak efficiency if their slip is maintained in a certain optimum range (Zoz, 1972). In general wheel slip occurs when the tires are turning faster than the ground speed of the tractor. As a result, less than 60–70% of the power that a tractor engine develops is used to pull an implement through the soil, also it may be even drop to 50% on soft and sandy soils. As per the past studies, it is recommended that, tractors and tires should be maintained to optimize wheel slippage at 10–15% to get better tractive performance and less slippage than this results in the expenditure of too much fuel energy to move the wheels, whereas too much slippage (greater than 15%) can result in excessive tire spin and energy loss through the tire, which is nonproductive.
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Nomenclature b S nl no do d1 Vf Vr i Np
wheel width (in.) wheel slip (%) number of revolutions of drive wheels at load condition number of revolutions of drive wheels at no load condition distance travelled in fixed number of revolutions at no load condition distance travelled in fixed number of revolutions at load condition front wheel voltage rear wheel voltage wheel slip number of signal picks
Wheel slip is one of the major key indicators of efficient tractor operation. The level of wheel slip serves as a proxy to indicate whether the right combination of tire pressures, tractor weight (ballast) and tractor operating speed is selected, resulting in the correct traction required to perform efficiently and fuel save (Pranav et al., 2010). Further, wheel slip can determine the wear and expected lifetime of a tractor’s drive train and tyres. A wheel slip that is too low may be a sign that the drive train is being strained and excessive weight is being hauled. Conversely, a very high wheel slip suggests that the tyres are wearing excessively and wasted rotations are likely wasting fuel. The tractive effort can be basically enhanced by increasing the area of contact between the tractor wheels and the soil surface, and reducing the abnormal slippage. Knowing the importance of wheel slip, several attempts have been made to measure this parameter. Researchers have used different techniques like Doppler/microwave radar device (Stuchly et al., 1976; Freeland et al., 1988; Wang and Domier, 1989; Khalilian et al., 1989; Grisso et al., 1991; Reed and Turner, 1993) and electronic circuits using photo-transducer (Zoerb and Popoff, 1967; Lyne and Meiring, 1977; Clark and Gillespie, 1979; Jurek and Newendorp, 1983; Grevis-James et al., 1981; Erickson et al., 1982; Shropshire et al., 1983; Musonda et al., 1983) for accurate measurement of slip. Most of these techniques were tractor specific, costly and of unproven reliability for instantaneous measurement of slip. These techniques were based on calculation of theoretical velocity on test bed instead of operating on a hard surface which is essential for defining zero condition. Even though there a few device to measure wheel slip for a specific tractors with bulky in construction and own limitations and could not be able to display and warn the operator with audible and visible warnings, if the wheel slip exceeds the optimum values. By keeping all the above state-
rr r rf Nf rL rR NL NR t VrL VrR DAS tt tt
radius of the roller, m rolling radius of the test tyre, m rolling radius of the front tire number of revolutions of front tire rolling radius of the left rear wheel rolling radius of the right rear wheel number of revolutions of left rear wheel number of revolutions of right rear wheel refreshment time velocity of left rear wheel, rpm velocity of right rear wheel, rpm data acquisition system total time between 1st and last pick, s total time between 1st and last pick, s
ments in mind, an attempt was made to study and present the past research on wheel slip measurement techniques and to develop a simple technology and embedded system with simple, cheap and reliable materials to measure and display wheel slip digitally along with audible and visible warnings if the wheel slip exceeds the optimum values. 2. Materials and methods The above said methods are costly and bulky in construction with their own limitations and could not be able to display and warn the operator with audible and visible warnings, if the wheel slip exceeds the optimum values, hence a simple embedded system was developed to measure the wheel slip precisely and warn the operator with simple, cheap and reliable materials. The overall embedded system comprises of three Hall Effect sensors, three magnetic mounted round discs, magnetic pins, and LCD display unit, buzzer and LEDs. The detailed description of developed device as follows. 2.1. Development of wheel slip indicating device Three magnetic pins mounted round discs were developed and mounted to the tractor front and rear wheels to measure the actual and theoretical speed of operation (Fig. 1). These disc were placed at inner side of the tractor wheels to avoid interruptions and vibrations for accuracy. Three Hall effect sensors were mounted close to the developed magnetic pins mounted discs to detect and generate the number pulses from magnetic pins while facing each other. Hall effect sensor is an ideal sensing technology, the hall element is constructed from a thin sheet of conductive material with output connections perpendicular to the direction of current flow. When subjected to a magnetic field, it responds with an output voltage proportional to
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Magnetic Pins
Hall effect sensor
Fig. 3. Left rear wheel mounted magnetic pins disc with sensor. Fig. 1. Disc with magnetic pins.
the magnetic field strength. Hall effect sensor is a type of transducer that varies its output voltage in response to a magnetic field. When passed through a magnetic field, it in turn generates a voltage signal. The magnitude of the signal voltage depends on the relative size of the magnetic target, its speed of approach, and how close it is from the magnet. In a single revolution, the sensor generates number of pulses depending upon the number of magnets detected. Over comparison to any other sensing devices, it has true solid state, long life, high speed operation, no moving parts, cheap, reliable and accurate. Actual speed of operation was measured by front wheel mounted magnetic pins disc (Fig. 2) and the theoretical speed was measured by both of the tractor rear wheels mounted magnetic pins disc as shown in Fig. 3. Eighteen number of small pieces of magnets were fixed to the front wheel mounted disc at equal distances to facilitate the actual RPM measurement where as thirty six number of magnets were placed on the tractor each rear wheel mounted disc to measure theoretical speed for more accuracy since as the number of magnetic pins increases, the efficiency of wheel slip measurement increase. Three Hall
Hall effect sensor
Fig. 2. Front wheel mounted magnetic pins disc along with sensor.
effect sensors were used, placed close to the magnetic pins to avoid the errors and generate number of pulse from each of the magnets of mounted disc (Figs. 2 and 3). The used hall sensor could be able to detect the pin up to the distance of 2 cm, in the present study, a clearance of 0.5 cm was placed between sensor and pins. The outputs of the sensor was connected to the arduino based microcontroller unit which could process the signals and display the actual speed of operation, theoretical speed of operation and percentage slip on the LCD screen, also the data is sent to a laptop/SD card module for recording the data. It is also provided with two LEDs namely red, green and a buzzer to alert the operator when the slip exceeds the optimum range. In the present study, the optimum wheel slip considered in the range of 10–15%. The following equations were used to calculate actual speed and % slip from the received signal of pulses from each of the discs. 2prf N f t Total pulse generated during time t Nf ¼ Pulse generated per revolution ðN f Þ ðVrL þ VrR Þ Theoretical speed of operation ðV t Þ ¼ 2 ð2prL N L Þ VrL ¼ t ð2prR N R Þ VrR ¼ t
Actual speed of operation ðV a Þ ¼
ð1Þ
ð2Þ ð3Þ ð4Þ
where rf = rolling radius of the front tire, Nf = number of revolutions of front tire, rL = rolling radius of the left rear wheel, rR = rolling radius of the right rear wheel, NL = number of revolutions of left rear wheel, NR = number of revolutions of right rear wheel, t = refreshment time, VrL = velocity of left rear wheel, rpm, VrR = velocity of right rear wheel, rpm. 2.1.1. Development of embedded slip indicator To read and process the signals of Hall Effect sensors, a simple microcontroller based system was developed. It
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Fig. 4. Overall circuit diagram of slip indicating device.
mainly consists of an ATMEGA 2560 microcontroller to count the number of pulses, thereby calculating wheel slip. It has 54 digital input/output pins 16 analog inputs, 4 UARTs (hardware serial ports), a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button and a LCD screen to display the calculated actual speed, theoretical speed and percentage slip. The outputs of Hall sensors were fed to microcontroller unit to process and calculate the wheel slip according to the program and display it on the LCD screen, also send data to the laptop via USB cable/stores the data in SD card module. It is also provided with two LEDs, namely red, green and a buzzer to alert the operator when the slip exceeds the optimum range on farm use. The green led glows continuously to indicate the working of developed system, red LED glows and buzzer on when the slip value exceeds the optimum range. In this design, as per the reviews, the optimum value considered as 10–15% i.e. when the slip exceeds the 15%, red led glows along with continuous loud buzzer sound to alert the operator to reduce slip by reducing depth and speed of operation to increase the fuel efficiency. The overall circuit diagram of the signal processing unit is shown in Fig. 4 and the developed embedded system is shown in Fig. 5.
Fig. 5. Developed slip indicating device.
2.2. Validation of the slip indicating device For validation of the developed Hall Effect sensor based technique for wheel slip measurement, the front mounted
A. Ashok Kumar et al. / Journal of Terramechanics 70 (2017) 1–11
magnetic disc and rear wheel mounted discs were validated on tar macadam and field surface for actual speed measurement by mounting a commercial non contact type radar sensor. 2.2.1. Validation of actual speed measurement on tar macadam surface and field condition For validation of Hall Effect sensor based front wheel magnetic pins mounted disc (Fig. 1) for actual speed, the test tractor was operated for thirty meters distance on tar macadam surface, the time required to cover the distance was measured and recorded in different gears at different engine speeds and found good correlation between obtained and observed values. For more accuracy, and justification, a non–contact type radar sensor was also used to validate the actual speed measurement technique on tar macadam and field surface. The radar sensor was installed on a test tractor at a suitable place located below the right foot rest of the tractor (Fig. 6). The height of sensor was maintained 45 cm from the ground surface and rearward facing at an angle 38° depression from the horizontal. The actual speed recorded by the developed system was compared with the speed measured by the radar sensor and found a very good linearity with R2 value of 0.996. During testing, the output of the radar sensor was connected to Data Acquisition System (DAS) to record the data, prior to the test, radar sensor was calibrated with the DAS. The average values of the recorded data were used to calculate the actual speed. 2.3. Validation of slip indicator in controlled soil bin The facility of traction laboratory of Agricultural and Food Engineering Department, IIT Kharagpur was used to evaluate the developed slip indicator under controlled soil bin condition. The laboratory facility consisted of a 23.5 1.37 1.50 m soil bin filled with the locally available lateritic sandy clay loam soil, an electronic platform balance, a soil processing trolley, a tire test carriage (single wheel tester) and a drawbar pull loading device. The tire test carriage consisted of a main frame to accommodate
Radar Sensor
Fig. 6. Position of radar sensor on test tractor.
5
the various sizes of tires, a loading platform, a parallel bar linkage system and a power transmission system. The test carriage was attached to a towing trolley through fixed supports of parallel bar linkage. To vary horizontal pull of the test wheel, a drawbar–loading device with a shoe type braking arrangement was used. An electrical control panel was used to operate the soil processing trolley and the tire test carriage in forward and reverse directions. The overall view of the traction laboratory is shown in Fig. 7. 2.3.1. Slip measurement set up in traction lab In order to determine the wheel slippage, the actual and theoretical forward speed of the wheel was measured. The actual forward speed measuring device (Fig. 8a) consisted of a proximity switch attached to towing trolley and sensing the rotation of a roller moving over the steel rail. The radius of the roller is 0.0448 m. The number of signal pick from the proximity switch was counted using a program developed in matlab and the time corresponding to the 1st and last pick was also noted. The actual forward speed of the wheel was calculated as follows. Actual velocity ðV a Þ ¼
2p ðN p 1Þ rr tt
ð5Þ
where Np = number of signal picks, rr = radius of the roller, m and tt = total time between 1st and last pick, s. The theoretical forward speed of the wheel was also measured using another proximity switch, which senses the rotation of a disc connected to the wheel axle through chain and sprocket. The theoretical forward speed measuring device is shown in Fig. 8b. The theoretical forward speed of the wheel was calculated as follows. Theoritical velocity ðV t Þ ¼
2p ðN p 1Þ r 8 tt
ð6Þ
where Np = number of signal picks, r = rolling radius of the test tyre, m and tt = total time between 1st and last pick, s.
2.3.2. Installation of magnetic mounted discs in traction lab A small shaft was mounted with the help of two ball bearings and powered by the main shaft of single wheel tester. The discs were mounted in each side of the additional shaft which refers to the two rear wheels of the tractor. A rigid steel wheel of circumference 2 m was fabricated and attached with a hinge joint behind the single wheel tester. The third disc was mounted on the shaft of the fabricated rigid wheel which referred to the front wheel of a tractor. The slip indicator was kept on the wheel tester and the respective signal cables were connected to the Hall Effect sensors and power supply unit. For each test, slip was calculated on the basis of the recorded speed of the existing
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6
7
9
5 6
8
2 7
1
1. Soil bin 4. Rotating drum 7. Induction motor
2. Side rails 5. Steel rope 8. Test wheel
3
4
3. Motion drive mechanism 6. Rope supporting frame 9. Pull loading device
Fig. 7. Overall view of traction laboratory (Tiwari et al., 2010).
Fig. 8. (a) Actual forward speed measuring device, (b) theoretical forward speed measuring device.
slip measurement setup and compared with the corresponding value of the slip measured directly by the slip indicator with different normal loads. 2.4. Validation of slip indicator on tar macadam surface To validate the developed slip indicator under real practical use, number of experiments were conducted to compare the manual observed slip (So) with the measured slip (Sm) of developed system on tar macadam surface under loaded condition. On tar macadam surface, the test tractor (towing tractor) pulled by an auxiliary tractor (towed tractor) in different gears for ten revolutions of the rear wheel (Fig. 9). The time required, distance covered and the force required to pull the towing tractor was measured. The force required to pull the tractor was measured with the help of dynamometer. Initially the tractor was operated without load and then with load, and the observed slip was calcu-
lated by using an Eq. (7). Each experiment was replicated three times for more accuracy. Vl S ð%Þ ¼ 1 100 ð7Þ Vnl where Vl is the velocity of rear wheel with load in m/s and Vnl is the velocity of rear wheel without load in m/s. 2.5. Validation of slip indicator on actual field condition To test and validate the developed devices under field condition, a field of one hectare fallow land was selected and subdivided into two plots to validate the developed slip sensing device in actual field condition. The cone index of the soil was measured with help of cone penetromer at various places of selected field as per ASABE S.313.3 and found an average cone index value of 1328,826 and 764 kPa during ploughing, harrowing and tillering opera-
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between fuel filter and fuel injection pump (supply line) and another one was placed between over flow line (return line) and fuel tank as shown in Fig. 11. The two fuel meters were connected with the help of adapters and Nylon pipe and placed on the right side of the tractor with the help of L iron sheet, iron plate and bolts. The output of fuel meters were recorded with help of data logger. The difference in fuel quantity in between Supply line flow rate (l/ h) and Return line flow rate (l/h) give the fuel consumption.
Towing tractor Towed tractor Dynamometer
2.7. Effect of slip indicator on operator performance Fig. 9. Slip measurement on tar macadam surface with towing and towed tractor.
tion respectively. Several tests were conducted with test tractor with three implements, namely, mould board (MB) plough, cultivator and disc harrow (Fig. 10). The depth of operation was varied from 15 to 30 cm for MB plough, 9 to 15 cm for cultivator and 8 to 12 cm for harrow. Manual slip measurement was based on measuring the distance traveled for fixed number of revolution of the drive wheels at load and no load conditions and measured by using Eq. (8). S¼
do d1 100 do
ð8Þ
To know the effect of slip indicator on operator, a study was conducted by considering ten well experienced agricultural drivers those who are free from cardiac and other ailments were selected. A plot of one hectare agricultural land was selected and divided into number plots and all the selected tractor drivers were asked to operate the tractor without activation and with activation of wheel slip indicator. The tests were conducted with all the selected implements and operators and proper care was taken to keep all the operating parameters uniformly and the fuel consumption was measured in both the cases of operation (with and without activation of slip indicator). 3. Results and discussion
where
3.1. Actual speed validation on tar macadam surface
do = distance travelled in fixed number of revolutions at no load condition; dl = distance travelled in fixed number of revolutions at load condition.
The actual speed recorded by the developed system was compared with the speed measured by the radar sensor and
2.6. Measurement of fuel consumption To know the effect of slip indicator on operator performance, the fuel consumption was measured with the help of two fuel meters. One of the fuel meters was placed
Fig. 10. Validation of developed system under actual field operation.
Fig. 11. A view of fuel meters on test tractor, (a) supply fuel meter, (b) return fuel meter.
A. Ashok Kumar et al. / Journal of Terramechanics 70 (2017) 1–11
3.2. Slip indicator validation in controlled soil bin condition Under controlled soil bin condition, the simultaneous results obtained by the developed slip indicator and the existing system was compared at different normal loads and the sample picture of slip characteristics with normal loading of 8500N and 10,500N in soft soil is shown in Figs. 13 and 14 the percentage deviation slip values measured by both the device is ±2.5%. The numerical values within the brackets above the bar diagrams indicate percentage deviation. The data indicated a maximum error in slip measurement of 1%. However, in 74% of the sample data, the error in slip measurement was less than ±0.5%. The results were analyzed statistically and observed that the variation between speed values measured by both the sensors was not significant. 3.3. Validation of slip indicator on tar macadam surface The developed slip indicator was also tested on tar macadam surface by mounting the developed wheel slip
60
(-2.7)
Measured Indicated
50
Slip, %
found good linearity with R2 value of 0.996. The average actual speed measured by the two systems in different gears and throttle position on tar macadam surface was presented in Fig. 12, it showed that the indicated actual speed is very close to the measured actual speed by the radar sensor. To observe the effect of skid and deflection on the front tire in actual field condition, the actual speed measured through front wheel was compared with that measured by the radar sensor. It was observed that, the radar sensor values varied from 0.98 to 1.42 m/s with an average reading of 1.19 m/s, whereas, the slip indicating device values varied from 1.1 to 1.44 m/s with an average reading of 1.18 m/s. This shows the suitability of hall effect sensor with magnetic pins mounted discs to measure actual speed over the costly devices like radar sensor. The results were analyzed statistically and observed that the variation between speed values measured by both the sensors was not significant.
(2.6)
40 30
(3.9)
20 10
(3.8)
(-1.4)
(0.8)
1113.5
2194.2
0 0
3193.1
3749.8
4093.7
Dra, N Fig. 13. Comparison of measured and indicated slip at 8500 N load in soft soil. 40
(2.0)
Measured Indicated
35 30
Slip, %
8
(4.7)
25
(0.6)
20 15
(-4.4)
10 5
(4.5)
(-4.2)
0 0
1277.2
2227
3193.1
3897.2
4306.6
Dra, N Fig. 14. Comparison of measured and indicated slip at 10,500 N load in soft soil.
measurement system to the tires and indicator near the dash board of the operator. The results obtained by the developed system were compared with the manual measured slip values. The manual measured slip values at different loads were compared with slip values obtained by the developed slip indicator simultaneously using a statistical term, relative deviation (RD), which is defined as follows (Kumar and Pandey, 2012). N 1X SO Sm RD ¼ 100 ð9Þ N i¼1 Sm
L1=1st low gear; L2=2nd low gear; L3=3rd low gear; L4=4th low gear; H1=1st high gear; H2=2nd high gear; H3=3rd high gear; R1= 1000 RPM; R2=1500; R3=2000
Fig. 12. Validation of actual speed on tarmacadam road without load.
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Table 1 Comparison of indicated slip and measured slip on tar macadam surface. S. No.
Towed tractor gear position
Towing tractor gear
Average draft, N
Manual measured slip (Sm), %
Slip indicated by indicator, (So), %
RD, %
1 2 3
L4 H1 H2
Neutral
1200 1570 1930
3.82 4.65 5.33
3.81 4.63 5.31
0.357
4 5 6
H1 H2 H3
L1
4679 4921 5374
7.47 7.96 8.52
7.49 8.01 8.54
0.375
7 8 9
H1 H2 H3
L2
6300 6900 7100
8.73 8.94 9.79
8.71 8.95 9.80
0.148
10 11 12
H1 H2 H3
L3
7900 8500 9100
11.34 12.13 13.82
11.33 12.15 13.85
0.156
13 14 15
H1 H2 H3
L4
10,456 11,342 12,476
13.94 14.53 15.21
13.91 14.51 15.19
0.162
45 Measured Slip
40
where So is the experimental value measured by the developed slip indicator, Sm is the manual measured slip values and N the number of observations. The RD values for the entire test observations were found less than +0.4 percent (Table 1). This shows that, the suitability of developed system to measure wheel slip of tractor.
Manual Measured slip
35
Slip, %
30 25 20 15 10
3.4. Validation of slip indicator on actual field condition
5 0 15.5
18.5
21.5
24.5
25.5
28.5
Depth, cm
18
Measured Slip
a
Manual Measured slip
15
Slip, %
12 9 6 3 0 9.5
10.5
12.3
13.5
14.2
15
b
Depth, cm Measured Slip
18
The results obtained by the developed system under field condition were compared with the manual measured slip value. During ploughing operation it was observed that, the slip values ranges between 13.5 and 41.68% as the depth varies from 15 to 30 cm measured by the slip indicator where as the slip values ranges between 12.9 and 42.37% measured by manual measurement and 6.3–24.17% of slip during harrowing and tillering operation measured by the indicator where as 6.7–25.78% of slip during harrowing and tillering operation measured by manual measurement. The comparison of slip values indicated by the slip indicating device and manually measured slip under ploughing, harrowing and tillering operation is shown in Fig. 15a–c.
Manual Measured slip
15
Slip, %
12 9 6 3 0 8
9
10
11
Depth, cm
11.5
12
c
Fig. 15. Comparison between measured and obtained slip values: (a) tractor with MB plough, (b) tractor with cultivator, (c) tractor with disc harrow.
Fig. 16. Effect of fuel consumption on draft force under ploughing operation with and without activation of slip indicator.
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Table 2 Effect of slip indicator on operator performance. Operator. No.
1 2 3 4 5
Fuel consumption (l/h) without activation of slip indicator
Fuel consumption (l/h) with activation of slip indicator
Fuel saving, %
P
H
T
P
H
T
P
H
T
3.45 3.38 3.41 3.34 3.51
1.24 1.29 1.42 1.32 1.39
1.21 1.34 1.49 1.39 1.43
2.43 2.39 2.32 2.31 2.52
1.01 1.04 1.12 1.09 1.1
1.00 1.11 1.21 1.06 1.12
29.56 29.28 31.96 30.83 28.21
18.54 19.37 21.13 17.42 20.86
17.355 17.164 18.791 23.741 21.678
P = ploughing, H = harrowing and T = tillering
3.5. Measurement of fuel consumption To know the effect of slip indicator on fuel consumption, initially, the test tractor was operated in first plot with selected three implements at a specified depth without activation of embedded slip indicator and measured the fuel consumption. It was observed that, as the draft increase, fuel consumption was increased. It was also observed that, the fuel consumption was varied from 3.23 l/h to 7.86 l/h for ploughing operation as the draft force changes from 7760 N to 12,760 N, where as it varied from 1.24 l/h to 5.68 l/h with the draft force changes from 5500 N to 7710 N under tillering operation and 1.26 l/h to 5.39 l/h with the draft force changes from 5150 N to 7470 N under harrowing operation. Further, the test tractor was tested with various implements in another plot with activation of wheel slip indicator and same procedure was followed and found that, the fuel consumption was varied from 2.53 l/h to 6.56 l/h for ploughing operation as the draft force varied from 7890 N to 12870 N, where as it varied from 1.23 l/h to 5.15 l/h with the draft force changes from 5590 N to 7860 N under tillering operation and 1.25 l/h to 4.71 l/h with the draft force changes from 5250 to 7330 N under harrowing operation. Hence it is clearly indicating that, with the developed device the fuel efficiency can be improved. The effect of draft force on fuel consumption of tractor during ploughing operation with and without activation of developed slip indicator is shown in Fig. 16. To know the effect of slip indicator on operator performance, a study was conducted by considering ten well experienced agricultural drivers those who are free from cardiac and other ailments. It was observed that, the driver reaction to the warnings slip indicator was not uniform and observed a slight variation in the response to the audible warnings. The fuel consumption and individual responses of selected drivers during operation with selected implements with and and without activation of slip indicator is presented in Table 2. It was also observed that, the fuel consumption during various operations with different drivers is not uniform; however there is no much difference in between the fuel consumptions values with and without activation of slip indicator. It also observed that, the fuel savings of different operations with various drivers is in
the range of 17–32% on farm use. It is clearly indicating that, the developed device help the operator to operate the tractor in minimum fuel consumption zone. 4. Conclusions A Hall Effect sensor and microcontroller based embedded digital system was developed and mounted to the tractor to measure wheel slip under various agricultural operations. A digital display unit was provided to display the actual speed, theoretical speed, wheel slip of operation, a safe green zone and warning red zone. A buzzer was also provided to buzz the sound to alert the operator when the slip values exceed the optimum limit. These zones help the operator to operate the tractor at optimum slip values so to achieve better tractive performance and increasing the fuel efficiency. The programme was written editable format and the optimum limits of wheel slip can be changed as per need by uploading limit range of wheel slip via computer interface of the microcontroller program. The developed system was rigorously tested under laboratory as well as in the field condition and found a maximum variation of 1.6–2% of wheel slip as compared with the commercial radar sensor and manual measurement system. This device can be applied to any make and model of 2WD tractor by entering the appropriate value of rolling radius via the computer interface. Based on the test results, it was concluded that, with this developed device the fuel can be saved up to a maximum of 32% on farm use. Hence, it is clearly indicated that, this development should bring improved fuel efficiency to tractor operations, especially if it is incorporated as standard equipment by tractor manufacturers. Also this digital slip indicator may also be useful for research and development works especially in tillage research. References Brixius, W.W., Wismer, R.D., 1978. The Role of Slip in Traction, ASAE Paper No. 78-1538. Burt, E.C., Bailley, A.C., 1982. Load and inflation pressure effects on tyres. Trans. ASAE 25 (4), 881–884. Clark, J.S., Gillespie, J.R., 1979. Development of a Tractor Performance Meter. ASAE Paper No. 79-1616, St. Joseph, Michigan.
A. Ashok Kumar et al. / Journal of Terramechanics 70 (2017) 1–11 Erickson, L., Larsen, W., Rust, S., 1982. Four-Wheel Drive Tractor Axle and Drawbar Horsepower: Field Evaluation and Analysis. ASAE Paper No. 82-1057, St. Joseph, Michigan. Freeland, R., Tompkins, F., Wilhelm, L., 1988. Portable Instrumentation to Study Performance of Lawn and Garden Ride-On Tractors. ASAE Paper No. 88-1079, St. Joseph, Michigan. Grisso, R., Taylor, R., Way, T., Bashford, L., 1991. Tractive Performance of 18.4R46 and 18.4R42 Radial Tractor Tires. ASAE Paper No. 911589, St. Joseph, Michigan. Grevis-James, I.W., DeVoe, D.R., Bloome, P.D., Batchelder, D.G., 1981. Microcomputer Based Data Acquisition System for Tractors. ASAE Paper No. 81-1578, St. Joseph, Michigan. Jurek, R.L., Newendorp, B.C., 1983. In-Field Fuel Efficiency Comparisons of Various John Deere Tractors. ASAE Paper No. 83-1563, St. Joseph, Michigan. Khalilian, A., Hale, S., Hood, C., Garner, T., Dodd, R., 1989. Comparison of Four Ground Speed Measurement Techniques. ASAE Paper No. 89-1040, St. Joseph, Michigan. Kumar, A., Pandey, K.P., 2012. A device to measure dynamic front wheel reaction to safeguard rearward overturning of agricultural tractors. J. Comput. Electron. Agric. 87 (2012), 152–158. Lyne, P.W., Meiring, P., 1977. A wheel slip meter for traction studies. Trans. ASABE 20 (2), 238–242.
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Musonda, N.G., Bigsby, F.W., Zoerb, G.C., 1983. Four Wheel Drive Tractor Instrumentation. ASAE Paper No. 83-1546, St. Joseph, Michigan. Pranav, P.K., Pandey, K.P., Tewari, V.K., 2010. Digital slip meter for agricultural 2WD tractors. Comput. Electron. Agric. 73 (2), 188–193. Reed, J., Turner, P.E., 1993. Slip Measurement Using Dual Radar Guns. ASAE/CASE, Paper No. 93-1031. Stuchly, S.S., Townsend, J.S., Thansandote, A., 1976. Travel Reduction Measurement by Doppler Radar Methods. ASAE Paper No. 76-1070, St. Joseph, Michigan. Shropshire, G.J., Woerman, G.R., Bashford, L.L., 1983. A Microprocessor Based Instrumentation System for Traction Studies. ASAE Paper No. 83-1048, St. Joseph, Michigan. Tiwari, V.K., Pandey, K.P., Pranav, P.K., 2010. A review on traction prediction equations. J. Terramechanics 47, 191–199. Wang, Z., Domier, K.W., 1989. Prediction of Drawbar Performance for a Tractor with Dual Tires. Transactions of the ASAE, vol. 32, No. 5, St. Joseph, Michigan. Zoerb, G.C., Popoff, J., 1967. Direct indication of tractor-wheel slip. Canad. Agric. Eng. 9 (2), 91–93. Zoz, F.M., 1972. Predicting tractor field performance. Trans. ASAE 15, 249–255.
Journal of Terramechanics
ScienceDirect Journal of Terramechanics 70 (2017) 1–11
www.elsevier.com/locate/jterra
A device to measure wheel slip to improve the fuel efficiency of off road vehicles A. Ashok Kumar a,⇑, V.K. Tewari b, Chanchal Gupta b, C.M. Pareek b b
a College of Agricultural Engineering, Madakasira, India Agricultural and Food Engineering Department, IIT Kharagpur, India
Received 18 March 2016; received in revised form 24 September 2016; accepted 12 November 2016
Abstract A hall sensor based simple technique was introduced to measure wheel slip and a microcontroller based embedded digital system was developed to display wheel slip data and warn the operator with audible and visible warnings if the optimum range is exceeds. Hall sensor slip measurement system was validated in controlled soil bin condition, tar macadam surface and actual field condition and compared with the commercial radar sensor. The developed system is simple in construction and can be mounted to any make and model of agricultural tractors by entering the appropriate rolling radius via the computer interface. Field trials were conducted to measure wheel slip and fuel consumption on farm use with and without activation of slip indicator; it was observed that, the amount of fuel saving during various agricultural operation was up 1.3 l/h. Ó 2016 ISTVS. Published by Elsevier Ltd. All rights reserved.
Keywords: Hall effect sensor; Actual speed measurement; Radar sensor; Display unit; Soil bin; Wheel slip
1. Introduction The primary purpose of agricultural tractors is to perform drawbar work. This is defined by pull and travel speed. Research shows that about 20–55% of the available tractor energy is wasted at the tyre-soil interface (Burt and Bailley, 1982). This energy wears the tires and compacts the soil to a degree that may be detrimental to crop production. Efficient operation of farm tractors includes: (i) selecting an optimum travel speed for a given tractor-implement system (ii) maximizing the tractive advantage of the traction devices, and (iii) maximizing the fuel efficiency of the engine and drive train. Among these, the maximizing of fuel efficiency could be done with little efforts. Increasing costs of petroleum products, most possible efforts are needed to improve the fuel efficiency and also ⇑ Corresponding author.
E-mail address: [email protected] (A. Ashok Kumar). http://dx.doi.org/10.1016/j.jterra.2016.11.002 0022-4898/Ó 2016 ISTVS. Published by Elsevier Ltd. All rights reserved.
better environmental concern. Especially in agricultural tractors, matching size of implement and load to a given size of tractor place a vital role in optimizing the fuel efficiency. Brixius and Wismer (1987) suggested that wheel slip has a dominating role in improving the tractive performance. The tractors operate at peak efficiency if their slip is maintained in a certain optimum range (Zoz, 1972). In general wheel slip occurs when the tires are turning faster than the ground speed of the tractor. As a result, less than 60–70% of the power that a tractor engine develops is used to pull an implement through the soil, also it may be even drop to 50% on soft and sandy soils. As per the past studies, it is recommended that, tractors and tires should be maintained to optimize wheel slippage at 10–15% to get better tractive performance and less slippage than this results in the expenditure of too much fuel energy to move the wheels, whereas too much slippage (greater than 15%) can result in excessive tire spin and energy loss through the tire, which is nonproductive.
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A. Ashok Kumar et al. / Journal of Terramechanics 70 (2017) 1–11
Nomenclature b S nl no do d1 Vf Vr i Np
wheel width (in.) wheel slip (%) number of revolutions of drive wheels at load condition number of revolutions of drive wheels at no load condition distance travelled in fixed number of revolutions at no load condition distance travelled in fixed number of revolutions at load condition front wheel voltage rear wheel voltage wheel slip number of signal picks
Wheel slip is one of the major key indicators of efficient tractor operation. The level of wheel slip serves as a proxy to indicate whether the right combination of tire pressures, tractor weight (ballast) and tractor operating speed is selected, resulting in the correct traction required to perform efficiently and fuel save (Pranav et al., 2010). Further, wheel slip can determine the wear and expected lifetime of a tractor’s drive train and tyres. A wheel slip that is too low may be a sign that the drive train is being strained and excessive weight is being hauled. Conversely, a very high wheel slip suggests that the tyres are wearing excessively and wasted rotations are likely wasting fuel. The tractive effort can be basically enhanced by increasing the area of contact between the tractor wheels and the soil surface, and reducing the abnormal slippage. Knowing the importance of wheel slip, several attempts have been made to measure this parameter. Researchers have used different techniques like Doppler/microwave radar device (Stuchly et al., 1976; Freeland et al., 1988; Wang and Domier, 1989; Khalilian et al., 1989; Grisso et al., 1991; Reed and Turner, 1993) and electronic circuits using photo-transducer (Zoerb and Popoff, 1967; Lyne and Meiring, 1977; Clark and Gillespie, 1979; Jurek and Newendorp, 1983; Grevis-James et al., 1981; Erickson et al., 1982; Shropshire et al., 1983; Musonda et al., 1983) for accurate measurement of slip. Most of these techniques were tractor specific, costly and of unproven reliability for instantaneous measurement of slip. These techniques were based on calculation of theoretical velocity on test bed instead of operating on a hard surface which is essential for defining zero condition. Even though there a few device to measure wheel slip for a specific tractors with bulky in construction and own limitations and could not be able to display and warn the operator with audible and visible warnings, if the wheel slip exceeds the optimum values. By keeping all the above state-
rr r rf Nf rL rR NL NR t VrL VrR DAS tt tt
radius of the roller, m rolling radius of the test tyre, m rolling radius of the front tire number of revolutions of front tire rolling radius of the left rear wheel rolling radius of the right rear wheel number of revolutions of left rear wheel number of revolutions of right rear wheel refreshment time velocity of left rear wheel, rpm velocity of right rear wheel, rpm data acquisition system total time between 1st and last pick, s total time between 1st and last pick, s
ments in mind, an attempt was made to study and present the past research on wheel slip measurement techniques and to develop a simple technology and embedded system with simple, cheap and reliable materials to measure and display wheel slip digitally along with audible and visible warnings if the wheel slip exceeds the optimum values. 2. Materials and methods The above said methods are costly and bulky in construction with their own limitations and could not be able to display and warn the operator with audible and visible warnings, if the wheel slip exceeds the optimum values, hence a simple embedded system was developed to measure the wheel slip precisely and warn the operator with simple, cheap and reliable materials. The overall embedded system comprises of three Hall Effect sensors, three magnetic mounted round discs, magnetic pins, and LCD display unit, buzzer and LEDs. The detailed description of developed device as follows. 2.1. Development of wheel slip indicating device Three magnetic pins mounted round discs were developed and mounted to the tractor front and rear wheels to measure the actual and theoretical speed of operation (Fig. 1). These disc were placed at inner side of the tractor wheels to avoid interruptions and vibrations for accuracy. Three Hall effect sensors were mounted close to the developed magnetic pins mounted discs to detect and generate the number pulses from magnetic pins while facing each other. Hall effect sensor is an ideal sensing technology, the hall element is constructed from a thin sheet of conductive material with output connections perpendicular to the direction of current flow. When subjected to a magnetic field, it responds with an output voltage proportional to
A. Ashok Kumar et al. / Journal of Terramechanics 70 (2017) 1–11
3
Magnetic Pins
Hall effect sensor
Fig. 3. Left rear wheel mounted magnetic pins disc with sensor. Fig. 1. Disc with magnetic pins.
the magnetic field strength. Hall effect sensor is a type of transducer that varies its output voltage in response to a magnetic field. When passed through a magnetic field, it in turn generates a voltage signal. The magnitude of the signal voltage depends on the relative size of the magnetic target, its speed of approach, and how close it is from the magnet. In a single revolution, the sensor generates number of pulses depending upon the number of magnets detected. Over comparison to any other sensing devices, it has true solid state, long life, high speed operation, no moving parts, cheap, reliable and accurate. Actual speed of operation was measured by front wheel mounted magnetic pins disc (Fig. 2) and the theoretical speed was measured by both of the tractor rear wheels mounted magnetic pins disc as shown in Fig. 3. Eighteen number of small pieces of magnets were fixed to the front wheel mounted disc at equal distances to facilitate the actual RPM measurement where as thirty six number of magnets were placed on the tractor each rear wheel mounted disc to measure theoretical speed for more accuracy since as the number of magnetic pins increases, the efficiency of wheel slip measurement increase. Three Hall
Hall effect sensor
Fig. 2. Front wheel mounted magnetic pins disc along with sensor.
effect sensors were used, placed close to the magnetic pins to avoid the errors and generate number of pulse from each of the magnets of mounted disc (Figs. 2 and 3). The used hall sensor could be able to detect the pin up to the distance of 2 cm, in the present study, a clearance of 0.5 cm was placed between sensor and pins. The outputs of the sensor was connected to the arduino based microcontroller unit which could process the signals and display the actual speed of operation, theoretical speed of operation and percentage slip on the LCD screen, also the data is sent to a laptop/SD card module for recording the data. It is also provided with two LEDs namely red, green and a buzzer to alert the operator when the slip exceeds the optimum range. In the present study, the optimum wheel slip considered in the range of 10–15%. The following equations were used to calculate actual speed and % slip from the received signal of pulses from each of the discs. 2prf N f t Total pulse generated during time t Nf ¼ Pulse generated per revolution ðN f Þ ðVrL þ VrR Þ Theoretical speed of operation ðV t Þ ¼ 2 ð2prL N L Þ VrL ¼ t ð2prR N R Þ VrR ¼ t
Actual speed of operation ðV a Þ ¼
ð1Þ
ð2Þ ð3Þ ð4Þ
where rf = rolling radius of the front tire, Nf = number of revolutions of front tire, rL = rolling radius of the left rear wheel, rR = rolling radius of the right rear wheel, NL = number of revolutions of left rear wheel, NR = number of revolutions of right rear wheel, t = refreshment time, VrL = velocity of left rear wheel, rpm, VrR = velocity of right rear wheel, rpm. 2.1.1. Development of embedded slip indicator To read and process the signals of Hall Effect sensors, a simple microcontroller based system was developed. It
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A. Ashok Kumar et al. / Journal of Terramechanics 70 (2017) 1–11
Fig. 4. Overall circuit diagram of slip indicating device.
mainly consists of an ATMEGA 2560 microcontroller to count the number of pulses, thereby calculating wheel slip. It has 54 digital input/output pins 16 analog inputs, 4 UARTs (hardware serial ports), a 16 MHz crystal oscillator, a USB connection, a power jack, an ICSP header, and a reset button and a LCD screen to display the calculated actual speed, theoretical speed and percentage slip. The outputs of Hall sensors were fed to microcontroller unit to process and calculate the wheel slip according to the program and display it on the LCD screen, also send data to the laptop via USB cable/stores the data in SD card module. It is also provided with two LEDs, namely red, green and a buzzer to alert the operator when the slip exceeds the optimum range on farm use. The green led glows continuously to indicate the working of developed system, red LED glows and buzzer on when the slip value exceeds the optimum range. In this design, as per the reviews, the optimum value considered as 10–15% i.e. when the slip exceeds the 15%, red led glows along with continuous loud buzzer sound to alert the operator to reduce slip by reducing depth and speed of operation to increase the fuel efficiency. The overall circuit diagram of the signal processing unit is shown in Fig. 4 and the developed embedded system is shown in Fig. 5.
Fig. 5. Developed slip indicating device.
2.2. Validation of the slip indicating device For validation of the developed Hall Effect sensor based technique for wheel slip measurement, the front mounted
A. Ashok Kumar et al. / Journal of Terramechanics 70 (2017) 1–11
magnetic disc and rear wheel mounted discs were validated on tar macadam and field surface for actual speed measurement by mounting a commercial non contact type radar sensor. 2.2.1. Validation of actual speed measurement on tar macadam surface and field condition For validation of Hall Effect sensor based front wheel magnetic pins mounted disc (Fig. 1) for actual speed, the test tractor was operated for thirty meters distance on tar macadam surface, the time required to cover the distance was measured and recorded in different gears at different engine speeds and found good correlation between obtained and observed values. For more accuracy, and justification, a non–contact type radar sensor was also used to validate the actual speed measurement technique on tar macadam and field surface. The radar sensor was installed on a test tractor at a suitable place located below the right foot rest of the tractor (Fig. 6). The height of sensor was maintained 45 cm from the ground surface and rearward facing at an angle 38° depression from the horizontal. The actual speed recorded by the developed system was compared with the speed measured by the radar sensor and found a very good linearity with R2 value of 0.996. During testing, the output of the radar sensor was connected to Data Acquisition System (DAS) to record the data, prior to the test, radar sensor was calibrated with the DAS. The average values of the recorded data were used to calculate the actual speed. 2.3. Validation of slip indicator in controlled soil bin The facility of traction laboratory of Agricultural and Food Engineering Department, IIT Kharagpur was used to evaluate the developed slip indicator under controlled soil bin condition. The laboratory facility consisted of a 23.5 1.37 1.50 m soil bin filled with the locally available lateritic sandy clay loam soil, an electronic platform balance, a soil processing trolley, a tire test carriage (single wheel tester) and a drawbar pull loading device. The tire test carriage consisted of a main frame to accommodate
Radar Sensor
Fig. 6. Position of radar sensor on test tractor.
5
the various sizes of tires, a loading platform, a parallel bar linkage system and a power transmission system. The test carriage was attached to a towing trolley through fixed supports of parallel bar linkage. To vary horizontal pull of the test wheel, a drawbar–loading device with a shoe type braking arrangement was used. An electrical control panel was used to operate the soil processing trolley and the tire test carriage in forward and reverse directions. The overall view of the traction laboratory is shown in Fig. 7. 2.3.1. Slip measurement set up in traction lab In order to determine the wheel slippage, the actual and theoretical forward speed of the wheel was measured. The actual forward speed measuring device (Fig. 8a) consisted of a proximity switch attached to towing trolley and sensing the rotation of a roller moving over the steel rail. The radius of the roller is 0.0448 m. The number of signal pick from the proximity switch was counted using a program developed in matlab and the time corresponding to the 1st and last pick was also noted. The actual forward speed of the wheel was calculated as follows. Actual velocity ðV a Þ ¼
2p ðN p 1Þ rr tt
ð5Þ
where Np = number of signal picks, rr = radius of the roller, m and tt = total time between 1st and last pick, s. The theoretical forward speed of the wheel was also measured using another proximity switch, which senses the rotation of a disc connected to the wheel axle through chain and sprocket. The theoretical forward speed measuring device is shown in Fig. 8b. The theoretical forward speed of the wheel was calculated as follows. Theoritical velocity ðV t Þ ¼
2p ðN p 1Þ r 8 tt
ð6Þ
where Np = number of signal picks, r = rolling radius of the test tyre, m and tt = total time between 1st and last pick, s.
2.3.2. Installation of magnetic mounted discs in traction lab A small shaft was mounted with the help of two ball bearings and powered by the main shaft of single wheel tester. The discs were mounted in each side of the additional shaft which refers to the two rear wheels of the tractor. A rigid steel wheel of circumference 2 m was fabricated and attached with a hinge joint behind the single wheel tester. The third disc was mounted on the shaft of the fabricated rigid wheel which referred to the front wheel of a tractor. The slip indicator was kept on the wheel tester and the respective signal cables were connected to the Hall Effect sensors and power supply unit. For each test, slip was calculated on the basis of the recorded speed of the existing
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A. Ashok Kumar et al. / Journal of Terramechanics 70 (2017) 1–11
6
7
9
5 6
8
2 7
1
1. Soil bin 4. Rotating drum 7. Induction motor
2. Side rails 5. Steel rope 8. Test wheel
3
4
3. Motion drive mechanism 6. Rope supporting frame 9. Pull loading device
Fig. 7. Overall view of traction laboratory (Tiwari et al., 2010).
Fig. 8. (a) Actual forward speed measuring device, (b) theoretical forward speed measuring device.
slip measurement setup and compared with the corresponding value of the slip measured directly by the slip indicator with different normal loads. 2.4. Validation of slip indicator on tar macadam surface To validate the developed slip indicator under real practical use, number of experiments were conducted to compare the manual observed slip (So) with the measured slip (Sm) of developed system on tar macadam surface under loaded condition. On tar macadam surface, the test tractor (towing tractor) pulled by an auxiliary tractor (towed tractor) in different gears for ten revolutions of the rear wheel (Fig. 9). The time required, distance covered and the force required to pull the towing tractor was measured. The force required to pull the tractor was measured with the help of dynamometer. Initially the tractor was operated without load and then with load, and the observed slip was calcu-
lated by using an Eq. (7). Each experiment was replicated three times for more accuracy. Vl S ð%Þ ¼ 1 100 ð7Þ Vnl where Vl is the velocity of rear wheel with load in m/s and Vnl is the velocity of rear wheel without load in m/s. 2.5. Validation of slip indicator on actual field condition To test and validate the developed devices under field condition, a field of one hectare fallow land was selected and subdivided into two plots to validate the developed slip sensing device in actual field condition. The cone index of the soil was measured with help of cone penetromer at various places of selected field as per ASABE S.313.3 and found an average cone index value of 1328,826 and 764 kPa during ploughing, harrowing and tillering opera-
A. Ashok Kumar et al. / Journal of Terramechanics 70 (2017) 1–11
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between fuel filter and fuel injection pump (supply line) and another one was placed between over flow line (return line) and fuel tank as shown in Fig. 11. The two fuel meters were connected with the help of adapters and Nylon pipe and placed on the right side of the tractor with the help of L iron sheet, iron plate and bolts. The output of fuel meters were recorded with help of data logger. The difference in fuel quantity in between Supply line flow rate (l/ h) and Return line flow rate (l/h) give the fuel consumption.
Towing tractor Towed tractor Dynamometer
2.7. Effect of slip indicator on operator performance Fig. 9. Slip measurement on tar macadam surface with towing and towed tractor.
tion respectively. Several tests were conducted with test tractor with three implements, namely, mould board (MB) plough, cultivator and disc harrow (Fig. 10). The depth of operation was varied from 15 to 30 cm for MB plough, 9 to 15 cm for cultivator and 8 to 12 cm for harrow. Manual slip measurement was based on measuring the distance traveled for fixed number of revolution of the drive wheels at load and no load conditions and measured by using Eq. (8). S¼
do d1 100 do
ð8Þ
To know the effect of slip indicator on operator, a study was conducted by considering ten well experienced agricultural drivers those who are free from cardiac and other ailments were selected. A plot of one hectare agricultural land was selected and divided into number plots and all the selected tractor drivers were asked to operate the tractor without activation and with activation of wheel slip indicator. The tests were conducted with all the selected implements and operators and proper care was taken to keep all the operating parameters uniformly and the fuel consumption was measured in both the cases of operation (with and without activation of slip indicator). 3. Results and discussion
where
3.1. Actual speed validation on tar macadam surface
do = distance travelled in fixed number of revolutions at no load condition; dl = distance travelled in fixed number of revolutions at load condition.
The actual speed recorded by the developed system was compared with the speed measured by the radar sensor and
2.6. Measurement of fuel consumption To know the effect of slip indicator on operator performance, the fuel consumption was measured with the help of two fuel meters. One of the fuel meters was placed
Fig. 10. Validation of developed system under actual field operation.
Fig. 11. A view of fuel meters on test tractor, (a) supply fuel meter, (b) return fuel meter.
A. Ashok Kumar et al. / Journal of Terramechanics 70 (2017) 1–11
3.2. Slip indicator validation in controlled soil bin condition Under controlled soil bin condition, the simultaneous results obtained by the developed slip indicator and the existing system was compared at different normal loads and the sample picture of slip characteristics with normal loading of 8500N and 10,500N in soft soil is shown in Figs. 13 and 14 the percentage deviation slip values measured by both the device is ±2.5%. The numerical values within the brackets above the bar diagrams indicate percentage deviation. The data indicated a maximum error in slip measurement of 1%. However, in 74% of the sample data, the error in slip measurement was less than ±0.5%. The results were analyzed statistically and observed that the variation between speed values measured by both the sensors was not significant. 3.3. Validation of slip indicator on tar macadam surface The developed slip indicator was also tested on tar macadam surface by mounting the developed wheel slip
60
(-2.7)
Measured Indicated
50
Slip, %
found good linearity with R2 value of 0.996. The average actual speed measured by the two systems in different gears and throttle position on tar macadam surface was presented in Fig. 12, it showed that the indicated actual speed is very close to the measured actual speed by the radar sensor. To observe the effect of skid and deflection on the front tire in actual field condition, the actual speed measured through front wheel was compared with that measured by the radar sensor. It was observed that, the radar sensor values varied from 0.98 to 1.42 m/s with an average reading of 1.19 m/s, whereas, the slip indicating device values varied from 1.1 to 1.44 m/s with an average reading of 1.18 m/s. This shows the suitability of hall effect sensor with magnetic pins mounted discs to measure actual speed over the costly devices like radar sensor. The results were analyzed statistically and observed that the variation between speed values measured by both the sensors was not significant.
(2.6)
40 30
(3.9)
20 10
(3.8)
(-1.4)
(0.8)
1113.5
2194.2
0 0
3193.1
3749.8
4093.7
Dra, N Fig. 13. Comparison of measured and indicated slip at 8500 N load in soft soil. 40
(2.0)
Measured Indicated
35 30
Slip, %
8
(4.7)
25
(0.6)
20 15
(-4.4)
10 5
(4.5)
(-4.2)
0 0
1277.2
2227
3193.1
3897.2
4306.6
Dra, N Fig. 14. Comparison of measured and indicated slip at 10,500 N load in soft soil.
measurement system to the tires and indicator near the dash board of the operator. The results obtained by the developed system were compared with the manual measured slip values. The manual measured slip values at different loads were compared with slip values obtained by the developed slip indicator simultaneously using a statistical term, relative deviation (RD), which is defined as follows (Kumar and Pandey, 2012). N 1X SO Sm RD ¼ 100 ð9Þ N i¼1 Sm
L1=1st low gear; L2=2nd low gear; L3=3rd low gear; L4=4th low gear; H1=1st high gear; H2=2nd high gear; H3=3rd high gear; R1= 1000 RPM; R2=1500; R3=2000
Fig. 12. Validation of actual speed on tarmacadam road without load.
A. Ashok Kumar et al. / Journal of Terramechanics 70 (2017) 1–11
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Table 1 Comparison of indicated slip and measured slip on tar macadam surface. S. No.
Towed tractor gear position
Towing tractor gear
Average draft, N
Manual measured slip (Sm), %
Slip indicated by indicator, (So), %
RD, %
1 2 3
L4 H1 H2
Neutral
1200 1570 1930
3.82 4.65 5.33
3.81 4.63 5.31
0.357
4 5 6
H1 H2 H3
L1
4679 4921 5374
7.47 7.96 8.52
7.49 8.01 8.54
0.375
7 8 9
H1 H2 H3
L2
6300 6900 7100
8.73 8.94 9.79
8.71 8.95 9.80
0.148
10 11 12
H1 H2 H3
L3
7900 8500 9100
11.34 12.13 13.82
11.33 12.15 13.85
0.156
13 14 15
H1 H2 H3
L4
10,456 11,342 12,476
13.94 14.53 15.21
13.91 14.51 15.19
0.162
45 Measured Slip
40
where So is the experimental value measured by the developed slip indicator, Sm is the manual measured slip values and N the number of observations. The RD values for the entire test observations were found less than +0.4 percent (Table 1). This shows that, the suitability of developed system to measure wheel slip of tractor.
Manual Measured slip
35
Slip, %
30 25 20 15 10
3.4. Validation of slip indicator on actual field condition
5 0 15.5
18.5
21.5
24.5
25.5
28.5
Depth, cm
18
Measured Slip
a
Manual Measured slip
15
Slip, %
12 9 6 3 0 9.5
10.5
12.3
13.5
14.2
15
b
Depth, cm Measured Slip
18
The results obtained by the developed system under field condition were compared with the manual measured slip value. During ploughing operation it was observed that, the slip values ranges between 13.5 and 41.68% as the depth varies from 15 to 30 cm measured by the slip indicator where as the slip values ranges between 12.9 and 42.37% measured by manual measurement and 6.3–24.17% of slip during harrowing and tillering operation measured by the indicator where as 6.7–25.78% of slip during harrowing and tillering operation measured by manual measurement. The comparison of slip values indicated by the slip indicating device and manually measured slip under ploughing, harrowing and tillering operation is shown in Fig. 15a–c.
Manual Measured slip
15
Slip, %
12 9 6 3 0 8
9
10
11
Depth, cm
11.5
12
c
Fig. 15. Comparison between measured and obtained slip values: (a) tractor with MB plough, (b) tractor with cultivator, (c) tractor with disc harrow.
Fig. 16. Effect of fuel consumption on draft force under ploughing operation with and without activation of slip indicator.
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A. Ashok Kumar et al. / Journal of Terramechanics 70 (2017) 1–11
Table 2 Effect of slip indicator on operator performance. Operator. No.
1 2 3 4 5
Fuel consumption (l/h) without activation of slip indicator
Fuel consumption (l/h) with activation of slip indicator
Fuel saving, %
P
H
T
P
H
T
P
H
T
3.45 3.38 3.41 3.34 3.51
1.24 1.29 1.42 1.32 1.39
1.21 1.34 1.49 1.39 1.43
2.43 2.39 2.32 2.31 2.52
1.01 1.04 1.12 1.09 1.1
1.00 1.11 1.21 1.06 1.12
29.56 29.28 31.96 30.83 28.21
18.54 19.37 21.13 17.42 20.86
17.355 17.164 18.791 23.741 21.678
P = ploughing, H = harrowing and T = tillering
3.5. Measurement of fuel consumption To know the effect of slip indicator on fuel consumption, initially, the test tractor was operated in first plot with selected three implements at a specified depth without activation of embedded slip indicator and measured the fuel consumption. It was observed that, as the draft increase, fuel consumption was increased. It was also observed that, the fuel consumption was varied from 3.23 l/h to 7.86 l/h for ploughing operation as the draft force changes from 7760 N to 12,760 N, where as it varied from 1.24 l/h to 5.68 l/h with the draft force changes from 5500 N to 7710 N under tillering operation and 1.26 l/h to 5.39 l/h with the draft force changes from 5150 N to 7470 N under harrowing operation. Further, the test tractor was tested with various implements in another plot with activation of wheel slip indicator and same procedure was followed and found that, the fuel consumption was varied from 2.53 l/h to 6.56 l/h for ploughing operation as the draft force varied from 7890 N to 12870 N, where as it varied from 1.23 l/h to 5.15 l/h with the draft force changes from 5590 N to 7860 N under tillering operation and 1.25 l/h to 4.71 l/h with the draft force changes from 5250 to 7330 N under harrowing operation. Hence it is clearly indicating that, with the developed device the fuel efficiency can be improved. The effect of draft force on fuel consumption of tractor during ploughing operation with and without activation of developed slip indicator is shown in Fig. 16. To know the effect of slip indicator on operator performance, a study was conducted by considering ten well experienced agricultural drivers those who are free from cardiac and other ailments. It was observed that, the driver reaction to the warnings slip indicator was not uniform and observed a slight variation in the response to the audible warnings. The fuel consumption and individual responses of selected drivers during operation with selected implements with and and without activation of slip indicator is presented in Table 2. It was also observed that, the fuel consumption during various operations with different drivers is not uniform; however there is no much difference in between the fuel consumptions values with and without activation of slip indicator. It also observed that, the fuel savings of different operations with various drivers is in
the range of 17–32% on farm use. It is clearly indicating that, the developed device help the operator to operate the tractor in minimum fuel consumption zone. 4. Conclusions A Hall Effect sensor and microcontroller based embedded digital system was developed and mounted to the tractor to measure wheel slip under various agricultural operations. A digital display unit was provided to display the actual speed, theoretical speed, wheel slip of operation, a safe green zone and warning red zone. A buzzer was also provided to buzz the sound to alert the operator when the slip values exceed the optimum limit. These zones help the operator to operate the tractor at optimum slip values so to achieve better tractive performance and increasing the fuel efficiency. The programme was written editable format and the optimum limits of wheel slip can be changed as per need by uploading limit range of wheel slip via computer interface of the microcontroller program. The developed system was rigorously tested under laboratory as well as in the field condition and found a maximum variation of 1.6–2% of wheel slip as compared with the commercial radar sensor and manual measurement system. This device can be applied to any make and model of 2WD tractor by entering the appropriate value of rolling radius via the computer interface. Based on the test results, it was concluded that, with this developed device the fuel can be saved up to a maximum of 32% on farm use. Hence, it is clearly indicated that, this development should bring improved fuel efficiency to tractor operations, especially if it is incorporated as standard equipment by tractor manufacturers. Also this digital slip indicator may also be useful for research and development works especially in tillage research. References Brixius, W.W., Wismer, R.D., 1978. The Role of Slip in Traction, ASAE Paper No. 78-1538. Burt, E.C., Bailley, A.C., 1982. Load and inflation pressure effects on tyres. Trans. ASAE 25 (4), 881–884. Clark, J.S., Gillespie, J.R., 1979. Development of a Tractor Performance Meter. ASAE Paper No. 79-1616, St. Joseph, Michigan.
A. Ashok Kumar et al. / Journal of Terramechanics 70 (2017) 1–11 Erickson, L., Larsen, W., Rust, S., 1982. Four-Wheel Drive Tractor Axle and Drawbar Horsepower: Field Evaluation and Analysis. ASAE Paper No. 82-1057, St. Joseph, Michigan. Freeland, R., Tompkins, F., Wilhelm, L., 1988. Portable Instrumentation to Study Performance of Lawn and Garden Ride-On Tractors. ASAE Paper No. 88-1079, St. Joseph, Michigan. Grisso, R., Taylor, R., Way, T., Bashford, L., 1991. Tractive Performance of 18.4R46 and 18.4R42 Radial Tractor Tires. ASAE Paper No. 911589, St. Joseph, Michigan. Grevis-James, I.W., DeVoe, D.R., Bloome, P.D., Batchelder, D.G., 1981. Microcomputer Based Data Acquisition System for Tractors. ASAE Paper No. 81-1578, St. Joseph, Michigan. Jurek, R.L., Newendorp, B.C., 1983. In-Field Fuel Efficiency Comparisons of Various John Deere Tractors. ASAE Paper No. 83-1563, St. Joseph, Michigan. Khalilian, A., Hale, S., Hood, C., Garner, T., Dodd, R., 1989. Comparison of Four Ground Speed Measurement Techniques. ASAE Paper No. 89-1040, St. Joseph, Michigan. Kumar, A., Pandey, K.P., 2012. A device to measure dynamic front wheel reaction to safeguard rearward overturning of agricultural tractors. J. Comput. Electron. Agric. 87 (2012), 152–158. Lyne, P.W., Meiring, P., 1977. A wheel slip meter for traction studies. Trans. ASABE 20 (2), 238–242.
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Musonda, N.G., Bigsby, F.W., Zoerb, G.C., 1983. Four Wheel Drive Tractor Instrumentation. ASAE Paper No. 83-1546, St. Joseph, Michigan. Pranav, P.K., Pandey, K.P., Tewari, V.K., 2010. Digital slip meter for agricultural 2WD tractors. Comput. Electron. Agric. 73 (2), 188–193. Reed, J., Turner, P.E., 1993. Slip Measurement Using Dual Radar Guns. ASAE/CASE, Paper No. 93-1031. Stuchly, S.S., Townsend, J.S., Thansandote, A., 1976. Travel Reduction Measurement by Doppler Radar Methods. ASAE Paper No. 76-1070, St. Joseph, Michigan. Shropshire, G.J., Woerman, G.R., Bashford, L.L., 1983. A Microprocessor Based Instrumentation System for Traction Studies. ASAE Paper No. 83-1048, St. Joseph, Michigan. Tiwari, V.K., Pandey, K.P., Pranav, P.K., 2010. A review on traction prediction equations. J. Terramechanics 47, 191–199. Wang, Z., Domier, K.W., 1989. Prediction of Drawbar Performance for a Tractor with Dual Tires. Transactions of the ASAE, vol. 32, No. 5, St. Joseph, Michigan. Zoerb, G.C., Popoff, J., 1967. Direct indication of tractor-wheel slip. Canad. Agric. Eng. 9 (2), 91–93. Zoz, F.M., 1972. Predicting tractor field performance. Trans. ASAE 15, 249–255.