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Vehicle and machinery design; Implements
Journal ofTerramechanics, Vol. 24, No. 2, pp. 141-152, 1987.
Printed in Great Britain.
VEHICLE
AND
MACHINERY
DESIGN;
0022--4898/8753.00+0.00 Pergamon Journals Ltd. © 1987ISTVS
IMPLEMENTS*
U. D. PERDOK~f
Summary--Aftera general introduction the papers presentedat SessionIV of the 9th International ISTVSConferenceconcernedwith "Vehicleand MachineryDesign", are discussedin groups, based on field of application. Special attention is paid to instrumentation and implementation of measurements. INTRODUCTION THE GENERALtheme of the 9th international ISTVS conference, "Terramechanics, mobility and unconventional vehicles" is subdivided into the following themes for five sessions. Session Session Session Session Session
I: Terrain Evaluation, Morphology, Soil, Snow, Ice and Frost. II: Soil-Vehicle Interaction. Tyres and Tracks. III: Vehicle Dynamics. Stearing. IV: Vehicle and Machinery Design. Implements/Instruments. V: Non-Conventional Land Transport Systems.
The theme description of session IV allowed a variety of papers on design aspects of vehicles, implements, control instruments and measuring instruments for soil and machine parameters to be handed in. The 15 papers classified for Session IV form the basis for this "state-of-the-art" report on vehicle and machinery design including implements and instruments. Preceding the review of submitted papers, some present time considerations and limitations are mentioned, related to research and development on design of off-road and field machinery. -
-
-
-
--
-
Presently, off-road vehicles and machinery are an integral part of the total production system (e.g. transport or farming system). A flexible design, permitting considerable adjustments in the production system is needed more than ever. A multi-disciplinary R&D approach therefore has become indispensible. Complex variations in soil-properties and vegetation characteristics exist amongst others. This is due to weather and climate and terrain history. Along with the analytical design method (with the help of simplified models of reality), the empirical testing of prototypes in the field will remain necessary. An old but ever so relevant problem is the high investment costs per hour of operation, due to season bound usage. Off-road and field operations require by definition mobile instead of stationary machines. For the primary function and the mobility, conflicting requirements of design
*State-of-the-artreport presentedat the 9th International Conferenceof the International Societyfor TerrainVehicle Systems, Barcelona,Spain, 31 August-4 September 1987. tlnstitute of Agricultural Engineering,(IMAG), P.O. Box 43, 6700AA Wageningen, The Netherlands. 141
142
[l. D. PERDOK
will remain a problem in many applications. Some relatively new concerns are soil degradation on agricultural fields and terrains with the aim of conserving nature. Here. a light construction for conservation of the soil on the one hand and strength, durability and large capacity for economical operation on the other hand obviously are conflicting design requirements. Many off-road machines have a limited potential with respect to the number of machines required. This can be a disadvantage for manufacturing costs and application of innovations developed in other disciplines. The application of micro-electronics offers new opportunities for research (data acquisition and management), product development (CAD), manufacturing (CAM) and optimization of operation (process control). Research and development on off-road vehicles and machinery will continue to be directed to improvements in functionality, strength, safety, reliability, durability, cost and energy factors, possibilities for repair, ergonomic aspects and interaction with the environment. With these considerations and limitations in mind, groups of papers are divided according to function (vehicle versus machinery) and further subdivided into fields of application. VEHICLE DESIGN Papers in this group have been subdivided into subgroups according to type of wheel equipment (running gear) and field of application (army, earthmoving, farming, forestry) in Table 1. TABLE 1. CLASSIFICATIONOF VEHICLES Running gear Application
tracks 1.1, 1.2.
tank (rubber) bulldozer (steel)
tyres 2.1. 2,2.
agricultural tractor logging tractor
1.1. Tank (papers 7 and 13) This vehicle belongs to the "heaviest species" as a result of the necessary armour protection. Nevertheless, high mobility is required for performing the road and field function. Some characteristics are: (i) The rubber tracks are more designed for speed than for traction; (ii) Resulting from its large weight, a powerful engine is needed to reach a favourable power to weight ratio; (iii) The large mass requires large acceleration forces. This is also caused by rotating parts. An increase of the power to weight ratio of 10 to 15 kw/ton halves the required time to accelerate from 0 to 40 km/h. Gas turbines are considered as a future alternative for diesel engines; (iv) Low ground pressure is required for soft soil conditions. This leads to wider and especially longer tracks, which causes problems for steering and manoeuvrability. In practice, higher vehicle weights appear to cause a higher ground pressure level (about 1 bar). See Fig. 1, (paper 13; Fig. 10). A uniform distribution of ground pressure under the track could be reached by the application of many small rollers. However, this results in more internal power losses. A high speed requires large rollers which
VEHICLE AND MACHINERY DESIGN 1.1
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have the disadvantage of a high non-damped weight and a low clearance within the track construction. The compromise will be medium sized rollers with additional track supporting rollers. Good suspension and damping systems are needed on rough terrai~ to spare the operators and the vehicle. Hydropneumatic springs still have to be improved compared to the torsional spring bar as far as reliability is concerned. In the near future improved rotary shock absorbers will push aside the telescope type. Slope climbing capacity (up to 60%) is improved by a wide speed range if a hydrodynamic torque converter is used. Total vehicle weight and outer dimensions (width, silhouette) must be kept in accordance with existing (rail)roads, bridges etc. The future can bring quite radical changes in vehicle design; e.g. the tower tank concept and the location of the drive train have to be checked again. The S-tank may offer a good example of an alternative design. The wear of a track as a result of its contamination with soil (dirt) and heat development should be further reduced.
Instruments. In paper 7 much attention is paid to measuring techniques for stress-strain and thermal behaviour of tracks (Fig. 2; paper 7, Fig. 2). /2omputer models which are developed for this behaviour were checked by field measurements. The strain-gauges used worked well; the thermocouples however appeared to lack durability. 1.2. Bulldozer (papers 5 and 11) These vehicles, equipped with steel tracks, are designed for developing large forces in the horizontal direction in order to pull rippers or to push blades. Loaders have to be designed for large vertical forces as well. Research and development activities reported here are directed to the wear aspects of tracks [11] and ergonomic improvement for the operator [5] of tracked vehicles. Special attention is paid to: (i) Material behaviour under occurring stresses and strains. (ii) The relation of wear properties of construction materials to lifetime of the components (improved durability). (iii) Improvement of the steerability of the tracked vehicle by the application of hydrostatic transmission. Despite the large torsional forces (Fig. 3; paper 5, Fig. 2), the described !ransmission system enables the operator to steer the vehicle in a stable way: straight and m turns. An important advantage of the described system is the better ergonomical
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condition for the operator, now even comparable to the situation found on wheel tractors.
Instruments. Stress, strain and displacement are measured [ 11] in relation to reduced wear (in sand) and increased durability. Mathematical and physical relationships between the measured parameters should help in determining reliability criteria for the analysis and design of tool components. 2.1. Agricultural tractor (papers 1, 4, 8 and 9) These power units replaced animal traction in agriculture. At first the same tools, adapted to the tractor, were used. Tractors were at that time designed to generate pull (large power to weight ratio). The development of the phenomenon of weight transfer from tool to tractor rear axle
VEHICLE AND MACHINERY DESIGN
145
through hydraulic hitching and control systems gave relatively lighter tractor designs still having good traction performance. Engine power meanwhile was raised by the application of engines with increased compression ratio, engine speed etc. The application of p.t.o.driven tools for many field jobs has further enlarged the efficiency of power transfer from the engine to the working parts. In increasing numbers, the bigger tractors for arable farming are equipped with additional front wheel drive (4-w drive). In horticulture and rice-farming, single axle tractors are even more replaced by tractors with two axles (2- or 4-w drive). Safety, ease of operation and ride comfort are much improved by the introduction of low-noise level, air-conditioned safety cabs, semi-automatic transmissions, automatic lift control etc. Present-day, sometimes contradictory design requirements for agricultural tractors are reviewed in one of the submitted papers. The other three papers contribute to further improvement in safety, ride comfort and efficiency of power transfer from engine to working parts. Designs and testing of new instrumentation are presented. Some outcomes are summarized below. -
-
-
-
The use of agricultural tractors in the field as well as on the road has resulted in some characteristic design solutions as, for instance, the broad speed range of the transmission and the application of flexible, lugged tyres giving good grip in the field and additional suspension and shock absorption on the road. In paper 4, such design features are treated in more detail. For prevailing field conditions on slopes, loss of control by sliding and subsequent overturning can be prevented by an operator warning system (paper 9). The system uses some automatically recorded field-specific data from a brake test. The brake test is done before starting the actual work. (See under "instruments"). Measured rotational vibrations, as one of the characteristics of the dynamic behaviour of the small tractor, appear to depend strongly on tyre type (high lugs versus turf-type), forward speed and the type of tool attached to it (trailer or rotary tiller). Some results can be seen in Fig. 4 (paper 8, Fig, 6).
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A given tractor-implement combination is most efficiently operated in terms of work rate and specific fuel consumption if the engine operates continuously close around the point of rated torque. It can be achieved by an automatic load control system (paper 1).
146
U.D. PERDOK
Instruments. Rotational vibrations of a small tractor (paper 8) are measured by nine accelerometers in a special arrangement. Results are presented as Power Spectrum Density graphs. The slope monitor (paper 9) includes a damped pendulum based sensor and a datalogger. It senses and stores (max. 21 weeks!) actual slopes and deceleration-test data. Based on a deceleration test in the field, the critical slope limit is calculated and warned for. The monitor was tested in practice on 2-w drive tractors (slopes smaller than 20%) and on 4-w drive tractors (slopes 20-30%). The automatic engine load control system (paper 1) is based on torque measurement by an inductive sensor, attached to the governor housing. The sensor controls the automatic shifting of gears by means of hydraulically operated clutches. It assures operation of the tractor engine in the full load range. 2.2. Logg&g tractor (paper 3) In this paper (paper 3), the commercially available forestry tractors, skidders and forwarders are reviewed. The design of forestry tractors has developed from adapted agricultural tractors (half tracks) to special designs with 4-w drive, big wheels and articulated steering. The skidder was developed originally from a conventional tractor (front axle removed), attached to a trailer (frame steering). Later on, the axles were driven through hydrostatic-mechanical transmission and were equipped with bigger wheels or (smaller) wheels in tandem configuration. Those machines were provided with winches, hydraulic knuckle booms etc. as well. Figure 5 (paper 3, Fig. 1) shows characteristic form-indices of the present day, commercially available three types of forestry vehicles, i.e. adapted agricultural tractors, skidders and forwarders. Width and length are related to total vehicle mass and to installed engine power. Against this background of data and trends, the various types (actual and future design) of machinery made in Yugoslavia (IMT) have been evaluated.
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VEHICLE AND MACHINERY DESIGN
147
MACHINERY DESIGN
The papers in this group could be subdivided into subgroups according to discipline and field of application as presented in Table 2. TABLE 2. CLASSIFICATIONOF MACHINERY Discipline
Civil engineering
Agricultural engineering
Application
3.1. 3.2.
4.1. 4.2.
earth moving cable laying
soil tillage land leveling
The discussion is concentrated on the ripper, subsoiler and loader bucket for civil engineering and on soil tillage tools for agricultural engineering. Two papers are of a more fundamental nature. They are based mainly on measurements with scale models in soil bins (papers 2 and 15). The other papers deal with research and development work using practical conditions (outdoor) and full-scale tools (papers 6, 10, 12 and 14). For the tools working in rock mass and in soil, proper depth control is of common interest. In several papers it was identified as a subject of importance. Think, for instance, of the loader bucket where adequate depth control assures an even filling. Other examples are the depth uniformity of a seedbed and the precision of cable and drain laying. The performance of conventional (passive) depth control by support wheels or tracks (either those of the vehicle itself or additional ones on tools) is especially bad as the rut depth variation of the supporting wheels increases. This can be the case if bearing capacity fails at weak spots in the field, but also if pulling wheels with a support function meet field spots failing grip; this will result in increased "digging action". Improved depth control could be achieved by a larger supporting area and a considerable reduction of the required pulling force. Draft can often be reduced by the use of p.t.o, powered tools (rotary or vibratory).
3.1. Earth moving (papers 6 and 15) The handling of strong material like rock mass is very special. Ripping and dozing performance in different directions on a test site could be correlated successfully to standard rock properties (modulus of deformation) and to the anisotropy of the terrain, determined on the basis of a bore hole test (paper 6). Prediction of pulling force and depth of the fracture zone was realized with the help of the Finite Elements Method (FEM). The results corresponded with the field measurements. This method opens possibilities to predict the performance of these operations for other sites with different (physical) material properties (Fig. 6; paper 6, Fig. 8). × 10-3 2.0-o 1°'~M ) pa
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mass (FEM analysis).
148
U.D. PERDOK
Instruments. Value and direction of the resultant force on the tip of the ripper werc measured through strain gauges (paper 6). A piston type penetration tester is used to determine the coefficient of penetration and modulus of deformation in the wall of a bore-hole in specific directions. Optimization of loader bucket design is the theme of paper 15. Four basic geometric bucket parameters are introduced. They are bucket opening, bottom arc ratio, inclination of side edge, and coefficient of fender height. Other parameters, when needed, can be derived from these basic values. Therefore, this parameter set is potentially suitable for application in Computer Aided Design systems. Principal research was directed to determine the correlation between the basic geometric parameters and inserting resistance (considerable influence) on the one hand and the so called filling factor (minor influence) on the other hand. Nine scale models of buckets were used. Measurements on full scale models corresponded well with the predictions on the basis of the research mentioned above. Instruments. A movable bin (length 3 m, width 0.8 m) and a stationary bin (length 44 m, width 2 m) were used for the tests on scale models and full scale buckets, respectively. Inserting resistance component forces were measured with two octagon ring dynamometers. A displacement sensor was used for the measurement of inserting depth. 3.2. Cable laying (paper 12) For this important activity in civil engineering practice, it is important to design for the least possible soil disturbance (next to laying the cable at the required location). This contrasts with the objectives of tillage and excavating operations. The research described here is concerned with optimization of the cable laying tool for high output, precision of cable placement and ease of operation. The influence of the relevant design and operational parameters on the performance is summarized below. --
-
---
-
Increased working depth from 0.7 to 0.8 m means that the feasible forward speed is halved. The optimum inclination (attack) angle of the blade appears to range from 25-30 °. The vertical component of tool vibration influences the performance most of all. Vibration frequency should be high for resonance to occur. Raising the frequency from 27 to 42 Hz gave an increase in forward speed of 40%. The influence of the amplitude is considerable as well. It has an optimum at about 5 mm. The combined effect of frequency and amplitude, expressed as peak vertical acceleration is clearly shown in Fig. 7 (paper 12, Fig. 5). The effect of vibratory energy input is most distinct on cohesive and heterogeneous soils (clay soils). Sandy soils are the easiest to handle. Compacted, coherent and relatively dry soils are difficult ones. The parallelogram design improved the performance (factor 2 in speed!) as compared to the conventional rear arm construction. Some relevant data derived from the presented diagram are a maximum speed of about 1.0 k m / h in difficult soils and a required tractor power of about 100 kW, fifty/fifty divided over generating pull (draft) and maintaining a vibratory movement of the tool (p.t.o.).
Instruments. Measurement of forces, speed and vibration (frequency and amplitude) was done in the conventional way. Automatic depth control appears to be desirable. It will be
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VEHICLE AND MACHINERY DESIGN
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Relation between maximum speed of translation and acceleration of the blade for different tractive efforts (depth 80 cm--medium difficulty soil).
possible with the use of appropriate gauges. The authors point out that there is a need for proper classification of soils according to the degree of (operational) difficulty and also to predict the soil condition on the basis of continuous identification (by means of electrical resistance) and by dynamic penetrometer readings. 4.1. Soil tillage (papers 2, 10 and 14) Under this heading, soil deformations (paper 2), energy requirement under field conditions (paper 10), and wear aspects of tool components (paper 14) are discussed. The phenomenon of soil cutting is characterized by large deformations of the soil. A generally accepted, satisfactory analytical or experimental technique to clarify the mechanism of large deformations does not exist. In paper 2, the authors acknowledge techniques such as the "Soil Pressure Theory" (soil mechanics), "Limit Equilibrium Theory" (plastic mechanics) and FEM-analysis. Although these techniques offer an effective means for estimation of, for instance, cutting resistance, they cannot be used to explain the mechanism of large deformations. The experiments described in paper 2 are conducted using a flat edge with a relatively large cutting angle (ranging from 45-75 degrees) and a small working depth--blade height ratio. The relative displacement was determined with the help of tracers. Next (cumulative) strain has been calculated. -
-
--
Typical cutting phenomena are described in Fig. 8 (paper 2, Fig. 10); a soil wedge tends to be formed and "intake by shear plain failure" can be distinguished. The strain analysis in the failure zone shows that (among others) volumetric expansion (dilatancy) occurs.
Instruments. A three-component load cell is used to measure the forces on the cutting blade. Lead markers (2 mm in diameter) proved to be adequate tracers for soil movement determination. This was checked by the use of lead-oxide powder. The X-ray radiography method (here applied in a vertical plane) will, in the near future, also be applied to three-dimensional phenomena. A practical method to predict the energy requirement of soil tillage tools roughly is described in paper 10. Specific ploughing resistance is used as the exclusive input parameter for soil type and condition. Tool parameters are only soil-cutting intensity and tool velocities (relevant for p.t.o.-powered machinery). The tool parameters can be derived from tool design and operational data. Recently, this method has been successfully applied to existing
150
U.D. PERDOK
machinery (p.t.o.-powered harrows, rotary tillers etc.) and is now used on a relatively l~ew tool, the so called crankshaft digger, which is shown in Fig. 9 (paper 10, Fig. 2).
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A typical outcome for this machine is: E= 1.23 A + 18.7 k J / m 3.
--
--
E is the specific energy required; A is the same for mouldboard ploughing (= 70 k J / m 3 for medium soil). Typical bite dimensions are a length, width and depth of 0.25 m, a tool-shaft speed of 2.25 rev/s and a forward speed of 0.5 m/s. F r o m specific energy, other relevant data such as p.t.o, and drawbar power, tractor fuel consumption and task times can be derived in a relatively simple way. Estimated absolute values appeared to be about 20% higher than those measured. The effect of changes in operation (speed, r.p.m.) are reasonably well explained.
VEHICLE AND MACHINERY DESIGN
151
Wear of tool components (Zs) as a function of relative speed (v) and load intensity (p) (Zs = tip,v)) is the research subject of paper 14. This relation is determined empirically. Figure 10 (paper 14, Fig. 1) shows some results. The following explanations are given for wear behaviour in relation to load intensity and speed.
Zs [mg/km]
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-
-
-
-
-
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-
-
Soil particle behaviour in the soil-tool contact area (in particular rolling versus sliding) is seen as the essential factor determining the rate of wear. Rolling particles cause less wear than sliding ones. Increase of wear with load intensity is explained by the fact that particles have more resistance to rolling in a denser soil matrix (caused by higher load intensities). Increase of speed appeared to stimulate the rolling action of artificial soil material i.e. gravel and marked ceramic cylinders (about 6 mm in diameter). A decrease in wear rate may therefore be expected at an increase of speed. In a particular situation, the tendency of soil particles to roll instead ofslide over the tool surface will also depend on tool surface roughness, particle geometry, soil moisture content etc.
PAPERS PRESENTED IN SESSION IV: VEHICLE AND MACHINERY DESIGN; IMPLEMENTS l 1] A. FEKETE, Tractor engine operation under full-load conditions. Hungarian Institute of Agricultural Engineering, Hungary. [2] S. ICHmA,K. HYODOand Y. OOISHI,Visualization of the cutting mechanism of soils by the X_ray radiography. Mitsubishi Heavy Industries Ltd, Japan. [3] D. KORNICER,Application of morphological analysis for reconstruction and design of logging tractors. Industrija Masina i Traktora, Yugoslavia. [4] P. LINARES,Land mechanics and its influence on agricultural vehicles. Polytechnical University of Madrid, Spain. 15] S. MILIDRAG,M. GAVRIC,M. DAUTOVICand R. HERBEZ, Optimisation selection of a system solution of hydromechanical transmission with a hydrostatic transformer for operating agricultural tracked tractors. Mechanical faculty, Sarajevo. SOUR "BNT", Pucarevo. Yugoslavia. [6] T. MURO, Excavating performance of bulldozer for a layered rock mass. Department of Ocean Engineering, Faculty of Engineering, Ehime University, Japan. [7] N.R. MURPHY,JR, A. S. LESSEMand B. E. REED,Experimental and analytical determination of structural and thermal behavior of tank tracks. U.S. Army Engineering Waterways Experiment Station, U.S.A. lSl K. OHMIYA,Analysis of the rotational vibrations of a small tractor. Faculty of Agriculture, Hokkaido University, Japan.
152
U.D. PERDOK
[9] G. M. OWEN and A. G. M. HUNTER, A safe slope monitor for agricultural tractors: survey of use on farms. Scottish Institute of Agricultural Engineering, Scotland. [10] U. D. PERDOK and G. D. VERMEULEN, Design parameters of multi-powered soil tillage tools in relation to energy demand. Institute of Agricultural Engineering (IMAG), the Netherlands. [11] W. POPPY, Reducing wear on crawlers. The Technical University of Berlin, Federal Republic of Germany. [ 12] A. QUmEL and E. PONCERRY, Output improvement of machines with vibrating blade for pipe or cable laying. Centre d'Experimentations Routibres, France. Centre National d'Etudes des T616communications, France. [13] 1. C. SCHMID,Some aspects on high mobility development of tracked vehicles. University of the Federal Armed Forces, Federal Republic of Germany. [14] A. SELENTA, The physical interpretation of relationships between the rate of wear of digging elements and parameters of friction process. Warsaw University of Technology, Poland. [ 15] L. SHUXUE,J. WANJUN, G. LINGFENand N. JlxIN, Experimental research of geometric shape and its working resistance of loading bucket. Jilin University of Technology, China.
Printed in Great Britain.
VEHICLE
AND
MACHINERY
DESIGN;
0022--4898/8753.00+0.00 Pergamon Journals Ltd. © 1987ISTVS
IMPLEMENTS*
U. D. PERDOK~f
Summary--Aftera general introduction the papers presentedat SessionIV of the 9th International ISTVSConferenceconcernedwith "Vehicleand MachineryDesign", are discussedin groups, based on field of application. Special attention is paid to instrumentation and implementation of measurements. INTRODUCTION THE GENERALtheme of the 9th international ISTVS conference, "Terramechanics, mobility and unconventional vehicles" is subdivided into the following themes for five sessions. Session Session Session Session Session
I: Terrain Evaluation, Morphology, Soil, Snow, Ice and Frost. II: Soil-Vehicle Interaction. Tyres and Tracks. III: Vehicle Dynamics. Stearing. IV: Vehicle and Machinery Design. Implements/Instruments. V: Non-Conventional Land Transport Systems.
The theme description of session IV allowed a variety of papers on design aspects of vehicles, implements, control instruments and measuring instruments for soil and machine parameters to be handed in. The 15 papers classified for Session IV form the basis for this "state-of-the-art" report on vehicle and machinery design including implements and instruments. Preceding the review of submitted papers, some present time considerations and limitations are mentioned, related to research and development on design of off-road and field machinery. -
-
-
-
--
-
Presently, off-road vehicles and machinery are an integral part of the total production system (e.g. transport or farming system). A flexible design, permitting considerable adjustments in the production system is needed more than ever. A multi-disciplinary R&D approach therefore has become indispensible. Complex variations in soil-properties and vegetation characteristics exist amongst others. This is due to weather and climate and terrain history. Along with the analytical design method (with the help of simplified models of reality), the empirical testing of prototypes in the field will remain necessary. An old but ever so relevant problem is the high investment costs per hour of operation, due to season bound usage. Off-road and field operations require by definition mobile instead of stationary machines. For the primary function and the mobility, conflicting requirements of design
*State-of-the-artreport presentedat the 9th International Conferenceof the International Societyfor TerrainVehicle Systems, Barcelona,Spain, 31 August-4 September 1987. tlnstitute of Agricultural Engineering,(IMAG), P.O. Box 43, 6700AA Wageningen, The Netherlands. 141
142
[l. D. PERDOK
will remain a problem in many applications. Some relatively new concerns are soil degradation on agricultural fields and terrains with the aim of conserving nature. Here. a light construction for conservation of the soil on the one hand and strength, durability and large capacity for economical operation on the other hand obviously are conflicting design requirements. Many off-road machines have a limited potential with respect to the number of machines required. This can be a disadvantage for manufacturing costs and application of innovations developed in other disciplines. The application of micro-electronics offers new opportunities for research (data acquisition and management), product development (CAD), manufacturing (CAM) and optimization of operation (process control). Research and development on off-road vehicles and machinery will continue to be directed to improvements in functionality, strength, safety, reliability, durability, cost and energy factors, possibilities for repair, ergonomic aspects and interaction with the environment. With these considerations and limitations in mind, groups of papers are divided according to function (vehicle versus machinery) and further subdivided into fields of application. VEHICLE DESIGN Papers in this group have been subdivided into subgroups according to type of wheel equipment (running gear) and field of application (army, earthmoving, farming, forestry) in Table 1. TABLE 1. CLASSIFICATIONOF VEHICLES Running gear Application
tracks 1.1, 1.2.
tank (rubber) bulldozer (steel)
tyres 2.1. 2,2.
agricultural tractor logging tractor
1.1. Tank (papers 7 and 13) This vehicle belongs to the "heaviest species" as a result of the necessary armour protection. Nevertheless, high mobility is required for performing the road and field function. Some characteristics are: (i) The rubber tracks are more designed for speed than for traction; (ii) Resulting from its large weight, a powerful engine is needed to reach a favourable power to weight ratio; (iii) The large mass requires large acceleration forces. This is also caused by rotating parts. An increase of the power to weight ratio of 10 to 15 kw/ton halves the required time to accelerate from 0 to 40 km/h. Gas turbines are considered as a future alternative for diesel engines; (iv) Low ground pressure is required for soft soil conditions. This leads to wider and especially longer tracks, which causes problems for steering and manoeuvrability. In practice, higher vehicle weights appear to cause a higher ground pressure level (about 1 bar). See Fig. 1, (paper 13; Fig. 10). A uniform distribution of ground pressure under the track could be reached by the application of many small rollers. However, this results in more internal power losses. A high speed requires large rollers which
VEHICLE AND MACHINERY DESIGN 1.1
143
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I o Germany " USA a Great Britain aFranee v UdSSR
~ 0.6
~^ 30
40 W
50
dO
[to] gross-weight
FIG. 1. Ground pressure p of real vehicles versus their gross weight W.
(v)
(vi) (vii) (viii)
(ix)
have the disadvantage of a high non-damped weight and a low clearance within the track construction. The compromise will be medium sized rollers with additional track supporting rollers. Good suspension and damping systems are needed on rough terrai~ to spare the operators and the vehicle. Hydropneumatic springs still have to be improved compared to the torsional spring bar as far as reliability is concerned. In the near future improved rotary shock absorbers will push aside the telescope type. Slope climbing capacity (up to 60%) is improved by a wide speed range if a hydrodynamic torque converter is used. Total vehicle weight and outer dimensions (width, silhouette) must be kept in accordance with existing (rail)roads, bridges etc. The future can bring quite radical changes in vehicle design; e.g. the tower tank concept and the location of the drive train have to be checked again. The S-tank may offer a good example of an alternative design. The wear of a track as a result of its contamination with soil (dirt) and heat development should be further reduced.
Instruments. In paper 7 much attention is paid to measuring techniques for stress-strain and thermal behaviour of tracks (Fig. 2; paper 7, Fig. 2). /2omputer models which are developed for this behaviour were checked by field measurements. The strain-gauges used worked well; the thermocouples however appeared to lack durability. 1.2. Bulldozer (papers 5 and 11) These vehicles, equipped with steel tracks, are designed for developing large forces in the horizontal direction in order to pull rippers or to push blades. Loaders have to be designed for large vertical forces as well. Research and development activities reported here are directed to the wear aspects of tracks [11] and ergonomic improvement for the operator [5] of tracked vehicles. Special attention is paid to: (i) Material behaviour under occurring stresses and strains. (ii) The relation of wear properties of construction materials to lifetime of the components (improved durability). (iii) Improvement of the steerability of the tracked vehicle by the application of hydrostatic transmission. Despite the large torsional forces (Fig. 3; paper 5, Fig. 2), the described !ransmission system enables the operator to steer the vehicle in a stable way: straight and m turns. An important advantage of the described system is the better ergonomical
144
U. D. P E R D O K 340 /
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Thermocouple responses in relation to variation in speed.
FIG, 2.
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The plan of the forces in turning a tracked motor vehicle.
condition for the operator, now even comparable to the situation found on wheel tractors.
Instruments. Stress, strain and displacement are measured [ 11] in relation to reduced wear (in sand) and increased durability. Mathematical and physical relationships between the measured parameters should help in determining reliability criteria for the analysis and design of tool components. 2.1. Agricultural tractor (papers 1, 4, 8 and 9) These power units replaced animal traction in agriculture. At first the same tools, adapted to the tractor, were used. Tractors were at that time designed to generate pull (large power to weight ratio). The development of the phenomenon of weight transfer from tool to tractor rear axle
VEHICLE AND MACHINERY DESIGN
145
through hydraulic hitching and control systems gave relatively lighter tractor designs still having good traction performance. Engine power meanwhile was raised by the application of engines with increased compression ratio, engine speed etc. The application of p.t.o.driven tools for many field jobs has further enlarged the efficiency of power transfer from the engine to the working parts. In increasing numbers, the bigger tractors for arable farming are equipped with additional front wheel drive (4-w drive). In horticulture and rice-farming, single axle tractors are even more replaced by tractors with two axles (2- or 4-w drive). Safety, ease of operation and ride comfort are much improved by the introduction of low-noise level, air-conditioned safety cabs, semi-automatic transmissions, automatic lift control etc. Present-day, sometimes contradictory design requirements for agricultural tractors are reviewed in one of the submitted papers. The other three papers contribute to further improvement in safety, ride comfort and efficiency of power transfer from engine to working parts. Designs and testing of new instrumentation are presented. Some outcomes are summarized below. -
-
-
-
The use of agricultural tractors in the field as well as on the road has resulted in some characteristic design solutions as, for instance, the broad speed range of the transmission and the application of flexible, lugged tyres giving good grip in the field and additional suspension and shock absorption on the road. In paper 4, such design features are treated in more detail. For prevailing field conditions on slopes, loss of control by sliding and subsequent overturning can be prevented by an operator warning system (paper 9). The system uses some automatically recorded field-specific data from a brake test. The brake test is done before starting the actual work. (See under "instruments"). Measured rotational vibrations, as one of the characteristics of the dynamic behaviour of the small tractor, appear to depend strongly on tyre type (high lugs versus turf-type), forward speed and the type of tool attached to it (trailer or rotary tiller). Some results can be seen in Fig. 4 (paper 8, Fig, 6).
~
12
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With Trailer Unladen
With Trailer Laden
./YI
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5
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Comparison of PSD of pitch angular accelerations for tractor with implement and for tractor alone.
A given tractor-implement combination is most efficiently operated in terms of work rate and specific fuel consumption if the engine operates continuously close around the point of rated torque. It can be achieved by an automatic load control system (paper 1).
146
U.D. PERDOK
Instruments. Rotational vibrations of a small tractor (paper 8) are measured by nine accelerometers in a special arrangement. Results are presented as Power Spectrum Density graphs. The slope monitor (paper 9) includes a damped pendulum based sensor and a datalogger. It senses and stores (max. 21 weeks!) actual slopes and deceleration-test data. Based on a deceleration test in the field, the critical slope limit is calculated and warned for. The monitor was tested in practice on 2-w drive tractors (slopes smaller than 20%) and on 4-w drive tractors (slopes 20-30%). The automatic engine load control system (paper 1) is based on torque measurement by an inductive sensor, attached to the governor housing. The sensor controls the automatic shifting of gears by means of hydraulically operated clutches. It assures operation of the tractor engine in the full load range. 2.2. Logg&g tractor (paper 3) In this paper (paper 3), the commercially available forestry tractors, skidders and forwarders are reviewed. The design of forestry tractors has developed from adapted agricultural tractors (half tracks) to special designs with 4-w drive, big wheels and articulated steering. The skidder was developed originally from a conventional tractor (front axle removed), attached to a trailer (frame steering). Later on, the axles were driven through hydrostatic-mechanical transmission and were equipped with bigger wheels or (smaller) wheels in tandem configuration. Those machines were provided with winches, hydraulic knuckle booms etc. as well. Figure 5 (paper 3, Fig. 1) shows characteristic form-indices of the present day, commercially available three types of forestry vehicles, i.e. adapted agricultural tractors, skidders and forwarders. Width and length are related to total vehicle mass and to installed engine power. Against this background of data and trends, the various types (actual and future design) of machinery made in Yugoslavia (IMT) have been evaluated.
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O( FORM INDEX H/L F[~3.5.
Relationship between the quoted values for logging tractors.
VEHICLE AND MACHINERY DESIGN
147
MACHINERY DESIGN
The papers in this group could be subdivided into subgroups according to discipline and field of application as presented in Table 2. TABLE 2. CLASSIFICATIONOF MACHINERY Discipline
Civil engineering
Agricultural engineering
Application
3.1. 3.2.
4.1. 4.2.
earth moving cable laying
soil tillage land leveling
The discussion is concentrated on the ripper, subsoiler and loader bucket for civil engineering and on soil tillage tools for agricultural engineering. Two papers are of a more fundamental nature. They are based mainly on measurements with scale models in soil bins (papers 2 and 15). The other papers deal with research and development work using practical conditions (outdoor) and full-scale tools (papers 6, 10, 12 and 14). For the tools working in rock mass and in soil, proper depth control is of common interest. In several papers it was identified as a subject of importance. Think, for instance, of the loader bucket where adequate depth control assures an even filling. Other examples are the depth uniformity of a seedbed and the precision of cable and drain laying. The performance of conventional (passive) depth control by support wheels or tracks (either those of the vehicle itself or additional ones on tools) is especially bad as the rut depth variation of the supporting wheels increases. This can be the case if bearing capacity fails at weak spots in the field, but also if pulling wheels with a support function meet field spots failing grip; this will result in increased "digging action". Improved depth control could be achieved by a larger supporting area and a considerable reduction of the required pulling force. Draft can often be reduced by the use of p.t.o, powered tools (rotary or vibratory).
3.1. Earth moving (papers 6 and 15) The handling of strong material like rock mass is very special. Ripping and dozing performance in different directions on a test site could be correlated successfully to standard rock properties (modulus of deformation) and to the anisotropy of the terrain, determined on the basis of a bore hole test (paper 6). Prediction of pulling force and depth of the fracture zone was realized with the help of the Finite Elements Method (FEM). The results corresponded with the field measurements. This method opens possibilities to predict the performance of these operations for other sites with different (physical) material properties (Fig. 6; paper 6, Fig. 8). × 10-3 2.0-o 1°'~M ) pa
~ 1.5-
~\
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~ o.5] L
100 FIG. 6.
L
200
1
300 Ed (Mpa)
I
400
I
500
Relations between VRD'/Pand modulus o f deformation Ed for various compressive strengths c o f rock
mass (FEM analysis).
148
U.D. PERDOK
Instruments. Value and direction of the resultant force on the tip of the ripper werc measured through strain gauges (paper 6). A piston type penetration tester is used to determine the coefficient of penetration and modulus of deformation in the wall of a bore-hole in specific directions. Optimization of loader bucket design is the theme of paper 15. Four basic geometric bucket parameters are introduced. They are bucket opening, bottom arc ratio, inclination of side edge, and coefficient of fender height. Other parameters, when needed, can be derived from these basic values. Therefore, this parameter set is potentially suitable for application in Computer Aided Design systems. Principal research was directed to determine the correlation between the basic geometric parameters and inserting resistance (considerable influence) on the one hand and the so called filling factor (minor influence) on the other hand. Nine scale models of buckets were used. Measurements on full scale models corresponded well with the predictions on the basis of the research mentioned above. Instruments. A movable bin (length 3 m, width 0.8 m) and a stationary bin (length 44 m, width 2 m) were used for the tests on scale models and full scale buckets, respectively. Inserting resistance component forces were measured with two octagon ring dynamometers. A displacement sensor was used for the measurement of inserting depth. 3.2. Cable laying (paper 12) For this important activity in civil engineering practice, it is important to design for the least possible soil disturbance (next to laying the cable at the required location). This contrasts with the objectives of tillage and excavating operations. The research described here is concerned with optimization of the cable laying tool for high output, precision of cable placement and ease of operation. The influence of the relevant design and operational parameters on the performance is summarized below. --
-
---
-
Increased working depth from 0.7 to 0.8 m means that the feasible forward speed is halved. The optimum inclination (attack) angle of the blade appears to range from 25-30 °. The vertical component of tool vibration influences the performance most of all. Vibration frequency should be high for resonance to occur. Raising the frequency from 27 to 42 Hz gave an increase in forward speed of 40%. The influence of the amplitude is considerable as well. It has an optimum at about 5 mm. The combined effect of frequency and amplitude, expressed as peak vertical acceleration is clearly shown in Fig. 7 (paper 12, Fig. 5). The effect of vibratory energy input is most distinct on cohesive and heterogeneous soils (clay soils). Sandy soils are the easiest to handle. Compacted, coherent and relatively dry soils are difficult ones. The parallelogram design improved the performance (factor 2 in speed!) as compared to the conventional rear arm construction. Some relevant data derived from the presented diagram are a maximum speed of about 1.0 k m / h in difficult soils and a required tractor power of about 100 kW, fifty/fifty divided over generating pull (draft) and maintaining a vibratory movement of the tool (p.t.o.).
Instruments. Measurement of forces, speed and vibration (frequency and amplitude) was done in the conventional way. Automatic depth control appears to be desirable. It will be
m,mn
VEHICLE AND MACHINERY DESIGN
,Transl ation speed
Rt= 10000daN
i ~
Rt=7500daN
149
Rt=5000daN
5 FIG. 7.
10
15
20
vertical I b of the 25 vcc (g) Peak acceleration blade
Relation between maximum speed of translation and acceleration of the blade for different tractive efforts (depth 80 cm--medium difficulty soil).
possible with the use of appropriate gauges. The authors point out that there is a need for proper classification of soils according to the degree of (operational) difficulty and also to predict the soil condition on the basis of continuous identification (by means of electrical resistance) and by dynamic penetrometer readings. 4.1. Soil tillage (papers 2, 10 and 14) Under this heading, soil deformations (paper 2), energy requirement under field conditions (paper 10), and wear aspects of tool components (paper 14) are discussed. The phenomenon of soil cutting is characterized by large deformations of the soil. A generally accepted, satisfactory analytical or experimental technique to clarify the mechanism of large deformations does not exist. In paper 2, the authors acknowledge techniques such as the "Soil Pressure Theory" (soil mechanics), "Limit Equilibrium Theory" (plastic mechanics) and FEM-analysis. Although these techniques offer an effective means for estimation of, for instance, cutting resistance, they cannot be used to explain the mechanism of large deformations. The experiments described in paper 2 are conducted using a flat edge with a relatively large cutting angle (ranging from 45-75 degrees) and a small working depth--blade height ratio. The relative displacement was determined with the help of tracers. Next (cumulative) strain has been calculated. -
-
--
Typical cutting phenomena are described in Fig. 8 (paper 2, Fig. 10); a soil wedge tends to be formed and "intake by shear plain failure" can be distinguished. The strain analysis in the failure zone shows that (among others) volumetric expansion (dilatancy) occurs.
Instruments. A three-component load cell is used to measure the forces on the cutting blade. Lead markers (2 mm in diameter) proved to be adequate tracers for soil movement determination. This was checked by the use of lead-oxide powder. The X-ray radiography method (here applied in a vertical plane) will, in the near future, also be applied to three-dimensional phenomena. A practical method to predict the energy requirement of soil tillage tools roughly is described in paper 10. Specific ploughing resistance is used as the exclusive input parameter for soil type and condition. Tool parameters are only soil-cutting intensity and tool velocities (relevant for p.t.o.-powered machinery). The tool parameters can be derived from tool design and operational data. Recently, this method has been successfully applied to existing
150
U.D. PERDOK
machinery (p.t.o.-powered harrows, rotary tillers etc.) and is now used on a relatively l~ew tool, the so called crankshaft digger, which is shown in Fig. 9 (paper 10, Fig. 2).
i t
__
~
~)f
)
FIG. 8.
F1
Comparison of strain circles.
270 225
1
316
-
V_
.--
*0
90
l ~ spade cutting area
"///////////////Z///////Z//Z/~
/~_.~/q
FIG. 9. Cutting path of a crankshaft digger.
A typical outcome for this machine is: E= 1.23 A + 18.7 k J / m 3.
--
--
E is the specific energy required; A is the same for mouldboard ploughing (= 70 k J / m 3 for medium soil). Typical bite dimensions are a length, width and depth of 0.25 m, a tool-shaft speed of 2.25 rev/s and a forward speed of 0.5 m/s. F r o m specific energy, other relevant data such as p.t.o, and drawbar power, tractor fuel consumption and task times can be derived in a relatively simple way. Estimated absolute values appeared to be about 20% higher than those measured. The effect of changes in operation (speed, r.p.m.) are reasonably well explained.
VEHICLE AND MACHINERY DESIGN
151
Wear of tool components (Zs) as a function of relative speed (v) and load intensity (p) (Zs = tip,v)) is the research subject of paper 14. This relation is determined empirically. Figure 10 (paper 14, Fig. 1) shows some results. The following explanations are given for wear behaviour in relation to load intensity and speed.
Zs [mg/km]
I
t 1 501
F V
/
I k'
1 3 0 ~ . . . . ~ vim/rainI FIG. 10. The graph of the function Zs =f(p,v).
-
-
-
-
-
-
-
-
Soil particle behaviour in the soil-tool contact area (in particular rolling versus sliding) is seen as the essential factor determining the rate of wear. Rolling particles cause less wear than sliding ones. Increase of wear with load intensity is explained by the fact that particles have more resistance to rolling in a denser soil matrix (caused by higher load intensities). Increase of speed appeared to stimulate the rolling action of artificial soil material i.e. gravel and marked ceramic cylinders (about 6 mm in diameter). A decrease in wear rate may therefore be expected at an increase of speed. In a particular situation, the tendency of soil particles to roll instead ofslide over the tool surface will also depend on tool surface roughness, particle geometry, soil moisture content etc.
PAPERS PRESENTED IN SESSION IV: VEHICLE AND MACHINERY DESIGN; IMPLEMENTS l 1] A. FEKETE, Tractor engine operation under full-load conditions. Hungarian Institute of Agricultural Engineering, Hungary. [2] S. ICHmA,K. HYODOand Y. OOISHI,Visualization of the cutting mechanism of soils by the X_ray radiography. Mitsubishi Heavy Industries Ltd, Japan. [3] D. KORNICER,Application of morphological analysis for reconstruction and design of logging tractors. Industrija Masina i Traktora, Yugoslavia. [4] P. LINARES,Land mechanics and its influence on agricultural vehicles. Polytechnical University of Madrid, Spain. 15] S. MILIDRAG,M. GAVRIC,M. DAUTOVICand R. HERBEZ, Optimisation selection of a system solution of hydromechanical transmission with a hydrostatic transformer for operating agricultural tracked tractors. Mechanical faculty, Sarajevo. SOUR "BNT", Pucarevo. Yugoslavia. [6] T. MURO, Excavating performance of bulldozer for a layered rock mass. Department of Ocean Engineering, Faculty of Engineering, Ehime University, Japan. [7] N.R. MURPHY,JR, A. S. LESSEMand B. E. REED,Experimental and analytical determination of structural and thermal behavior of tank tracks. U.S. Army Engineering Waterways Experiment Station, U.S.A. lSl K. OHMIYA,Analysis of the rotational vibrations of a small tractor. Faculty of Agriculture, Hokkaido University, Japan.
152
U.D. PERDOK
[9] G. M. OWEN and A. G. M. HUNTER, A safe slope monitor for agricultural tractors: survey of use on farms. Scottish Institute of Agricultural Engineering, Scotland. [10] U. D. PERDOK and G. D. VERMEULEN, Design parameters of multi-powered soil tillage tools in relation to energy demand. Institute of Agricultural Engineering (IMAG), the Netherlands. [11] W. POPPY, Reducing wear on crawlers. The Technical University of Berlin, Federal Republic of Germany. [ 12] A. QUmEL and E. PONCERRY, Output improvement of machines with vibrating blade for pipe or cable laying. Centre d'Experimentations Routibres, France. Centre National d'Etudes des T616communications, France. [13] 1. C. SCHMID,Some aspects on high mobility development of tracked vehicles. University of the Federal Armed Forces, Federal Republic of Germany. [14] A. SELENTA, The physical interpretation of relationships between the rate of wear of digging elements and parameters of friction process. Warsaw University of Technology, Poland. [ 15] L. SHUXUE,J. WANJUN, G. LINGFENand N. JlxIN, Experimental research of geometric shape and its working resistance of loading bucket. Jilin University of Technology, China.