Development of an on-board gradient data acquisition system

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Technical Notes.'JSAE Review 18 (19971 301 322

Technical Notes

Development of an on-board gradient data acquisition system Masao Takasugi, Yasuhisa Sonoda, Toshiyuki Isaka, Masaharu Oshima, Toshihiro Watanabe l'eehnical Center, Nissan Motor Co. Ltd. 560-2 ()katsukokT~. Atsugi-city, Kanagawa, 243-01 Japan

Received 24 December 1996

i. Introduction Road gradient is a critical load condition for assessing the reliability and cooling performance of vehicles, so there is need for a simple and accurate method of measuring gradients of roads under all sorts of terrain conditions. This report describes the development of an on-board gradient data acquisition system that adopts a gradient calculation method based on vehicle acceleration and velocity. The acquisition system provides excellent long-term measurement stability, is econo-mical, compact, lightweight and is capable of real-time calculations.

celeration sensors have somewhat less short-term accuracy than optical fiber gyroscopes, they provide perfectly acceptable accuracy for the purpose of measuring road gradients, so this method was adopted in the present system.

2.2. Measurement principle Figure 1 illustrates the principle of the acceleration sensor-based measurement method. The acceleration of a running vehicle ~ can be represented by = g sin 0 + dv/dt, where O is the vehicle gradient, v is velocity and g is gravitational acceleration. The vehicle gradient 0 is therefore given by

2. Calculation method

2.1. Calculation method selection

0 = sin - 1((2 - dv/dt)/,q) A range of different methods are available for measuring gradients including the use of optical fiber gyroscopes, mechanical gyroscopes, acceleration sensors and global positioning sensors (GPS). Table 1 summarizes the attributes of these various approaches. Although ac-

2.3. Correction The bodies of actual vehicles, however, are not necessarily parallel to the surface of the road, with the offset

Table 1 Attributes of gradient measurement methods Requirements

and 0 can be easily derived by measuring :~ and v.

Measurement method sin 0

Short-term accuracy l.ong-term accuracy Vibration resistance Dimensions. weight Cost

Acceleration Optical sensor gyroscope

Mechanical gyroscope

GPS

Fair

Excellent

Fair

Fair

Excellent

Fair

Fair

Fair

Excellent

Excellent

Poor

Excellent

Excellent Excellent

Fair Fair

Poor Poor

Fair Poor

_.~

v

Fig. 1. Measurement principle.

0389-4304:97.517.00 ¢ 1997 Society of Automotive Engineers of Japan. Inc. and Elsevier Science B.V. All rights reserved PII S 0 3 8 9 - 4 3 0 4 1 9 7 ) 0 0 0 2 5 - 8

JSAE9733738

Technical Notes/JSAE Review 18 (1997) 301 322

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Main instrument unit • LCD ] [ Operation [Operator switchies module ]Alarms ] Condition setting '~ I Conditionrecording Graphic display [ Data n~co~.'ng Data 'll~'"l~ SRA M c~-'-~'"lP p/~teb°°k

Sensors Acceleration [sensor ]! Height

[..].....

sensors II

acquisitioncalculation module

Velocity ~ . ,

| .~ Analog output

sensor

Floppy disk Data storage

Fig. 2. Data acquisition system contiguration.

defined by the pitch angle, 0p. In order to compensate for this offset, the pitch angle is first determined by measuring the vehicle-to-road distance at the front and at the rear of the vehicle, Ht and Hr, using height sensors, then subtracting this value from the vehicle gradient described in the previous section to obtain the true road gradient 0o.

LCD

Operator switchies

\

!

OOOOO

B

Input/output devices a r e installed from the back

/

J

3. Acquisition system overview 3.1. Specifications

(1) Accuracy: Adopting chassis-dynamometer control based on gradient data, system data is accurate within +0.Y', and this precision is sustained over long periods. (2) Temperature environment: Designed for use in cold as well as hot regions, the system can be applied in ambient temperature environments ranging from - 2 0 to + 60'~C. (3) Resistance to vibration: The system is ruggedly designed for installation on vehicles, and can withstand vibrations up to 19.6 m/s 2 (2G). (4) Real-time cah'ulation: Data from the acceleration, velocity and vehicle height sensors are required and processed, then displayed and recorded as road gradient data in real time. 15) Memory medium: An SRAM card (PCMCIA type 1) is provided for the memory medium, considering the need for data recording under high-vibration conditions. 3.2. Con]qguration

As shown in Fig. 2, the data acquisition system consists of various sensors, the main instrumentation unit (the appearance of which is shown in Fig. 3) including a data acquisition-calculation module and an operation module, a notebook PC for setting measurement parameters

SRAM card slot

W320 × Ill 18 × D250mm

Fig. 3. Appcarance of the main instrument unit.

and graphically displaying measurement results, and an SRAM card as memory medium for storing measurement results• To perform measurements, the sampling rate and other measurement parameters are written to the SRAM card using the notebook PC, then transferred to the main instrumentation unit. The main instrumentation unit acquires signal data from the acceleration, height and velocity sensors; calculates the road gradient and pitch angle: and displays the results on the PC while recording the data to the SRAM card in real time. The results can also be output in analog form at the same time. The data stored on the SRAM card can be graphically displayed on the notebook PC.

4. Gradient accuracy testing The accuracy of initial static tests performed in the laboratory were within +0.2' over a measurement range of +_30", well within the target accuracy required. Actual on-road measurements were then performed with the system mounted on a test vehicle driven over roads of known gradient. The results arc shown in Fig. 4. Measured values ranging from 11 ~ to 12: were obtained for an

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Technical Notes/JSAE Review 18 (1997) 301 322

(Degrees) 20 r--

.......

400

1 o5

10 ~ - - ' 1 ~E

(m) 800 -

Actual gradient

'~

0 -10 -20

v ,

/J

" v -,.4-

---~-.-.--. I

-400

-14.5 l

I(m)

75 Distance

0 /I

150

Fig. 4. Measurement result of up and downhill gradients.

-800

0

i

I

6250 Distance

I

I(m)

12500

Fig. 6. Measurement results of clevation gain of a Public Mountain Road.

(De ;rees) 10 5 E .o 2 r~

0 -5 -10

i

0

I

6250 Distance

,

I (m)

12500

Figure 5 reveals that the gradient data measured by the on-board gradient data acquisition system correlates very closely with the actual gradients (indicated by the solid dots in the figure) as measured with a spirit level. In Fig. 6, the cumulative elevation gain of 800 m derived by integrating the gradient samples is fairly close to the actual 830 m shown on a topographical map, and should not present any practical limitation on the system.

Fig. 5. Measurement result of uphill gradient of a Public Mountain Road. 6. Conclusions

actual uphill gradient of 11.5: and values ranging from - 14¢~to - 1 5 were obtained for a downhill gradient of -14.5 ~. Again, these results are within our target accuracy requirements.

5. Measurement

example

Actual gradient measurement results recorded for a public mountain road are shown in Figs. 5 and 6.

This report described a rugged on-board gradient data acquisition system that collects data from acceleration, height and velocity sensors; then calculates and stores road gradient, vehicle pitch, vehicle speed, and other data in real time while the vehicle is moving. Accurately reflecting experimental load conditions and evaluation criteria, the data measured by this system is useful for assessing the reliability and cooling performance of vehicles, so that they can be designed to better meet the needs of the marketplace.