The measurement of tractor transmission losses

J. agric. Engng Res. (1974) 19, 71-75

The Measurement of Tractor Transmission Losses T. T. MCCARTHY*; Z. KOLOZSl~ The method of measurement and results are presented for the losses in the transmission of an agricultural tractor. The results describe the effect of oil temperature and gear setting on the level of loss. 1.

Introduction

The prediction of tractor field performance based on the minimum amount of measurement and the maximum amount of computation highlights two main difficulties. These are the limitations on performance due to (a) the tractor as an individual unit and (b) the tractor/surface/ activity as an interacting system. Since each tractor type, both in isolation and as part of a system, exhibits characteristics peculiar to a particular configuration it seems unlikely that field measurement will be eliminated. If, therefore, one accepts that measurement is necessary then one needs to decide which parameters to measure to provide the maximum benefit for the minimum effort. In this paper a specific measurement exercise is described which relates to the tractor as a unit. It will be seen, however, that the results are applicable to the "system" situation and in fact suggest how certain "system" measurements should be performed. All measurements are reported in metric units and the abbreviation hp implies hp (metric). 125

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Fig. 1. Temperature increase in oil due to transmission rotation

2. Measurement of transmission losses If one considers a tractor engine as a source of torque then there are basically two sources of torque loss. These are losses which are directly proportional to engine torque and represent metal/metal contact in gear teeth, etc., and those losses which go towards heating and churning * Department of Agricultural Engineering, University of Newcastle upon Tyne. ~" Farm Machinery Research Institute, Hungary. 71

THE MEASUREMENT OF TRACTOR TRANSMISSION I,OSSES

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the transmission oil. Only the latter losses were of interest and were measured on a Massey Ferguson 165. The transmission oil was Esso Tractor Lube. 2.1. Method of measurement To perform the measurements two tractors were necessary, the second one being used as a power source to drive the tractor under test. Both tractors had their rear wheels removed, were jacked up and had their rear axles coupled through a torque transducer. The rear axle, and thus the transmission, of the tractor under test was driven in the normal sense for forward travel. During the tests it was necessary to ensure that the engine of the tractor under test was disengaged from the gearbox. -

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Fig. 2. Torque and hp losses in neutral gear

With a gear selected on the test tractor the torque applied to the rear axle at a given speed was measured by the torque transducer and recorded on magnetic tape. This was later replayed onto a u.v. recorder and the average torque for a given speed was noted. At all times the p.t.o, lever on the test tractor was set so that the p.t.o, speed was proportional to ground speed, i.e. axle speed in this case. The average p.t.o, speed was measured by tachometer and, knowing the p.t.o, speed/ axle speed ratio, the axle speed was calculated. From the axle speed the engine speed corresponding to the selected gear could be calculated. So the parameters measured were torque and p.t.o. speed. All other parameters, except temperature of course, were calculated as follows: axle speed, rev/min

= p.t.o, speed (rev/min) × K where K ( = 0.127) is the ratio of

axle speed for the test p.t.o, speed

tractor engine speed (rev/min) horsepower (hp)

= axle speed (rev/min)x gear ratio torque ( m k p ) x axle speed (rev/min) 716-2

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Y. M C C A R T H Y ;

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KOLOZSI

theoretical travelling speed (km/h) =

2~r x rolling radius (m) × axle speed (rev/min) ,~ 60 1000

For the test tractor the rolling radius was 710 mm. While the authors were specifically interested in the torque the experimental results have, where appropriate, been quoted in hp. This permits convenient comparison of the magnitude of losses with the rated output of the tractor. 3. 3.1.

Results

Losses vs temperature

It is to be expected that transmission rotation will produce a temperature increase in the oil thus affecting the torque required to produce rotation. Fig. 1 illustrates this effect. The measurements were made in gear L2 at rated engine speed (2000 rev/min). One can see that the transmission loss at 10°C is approximately twice that at 40°C and in fact that the loss is reasonably constant above 40°C. Obviously when measuring the level of loss it is desirable to do so when the oil temperature has stabilized. In the results presented here all measurements were done at approximately 30°C ; this reduced the time required to perform the tests. It is obvious from Fig. 1 that with the particular transmission oil tested one would expect greatly increased losses under winter operating conditions. 3.2. Losses in neutral Fig. 2 illustrates the torque and horsepower losses when the test tractor was in neutral. The independent variable is theoretical travelling speed (km/h) which takes no account of slip. In this case an extra dependent variable is plotted--"Equivalent towing force, kp". This force is that which exists when the axle torque is converted to a force at the ground contact point: axle torque (mkp) equivalent towing force, kp = rolling radius (m) This force is relevant when one is measuring the rolling resistance of a tractor. If the rolling resistance is to be measured by towing the tractor in neutral then this transmission equivalent towing force is included in the measurement. For a given towing speed, Fig. 2 will give an estimate of the error in rolling resistance due to the tractor transmission.

3.3. Losses in gear Figs 3 and 4 show the effect of different gears on losses. The following points are apparent: (a) In a given gear the losses increase with engine speed. At rated engine speed (2000 rev/min) in gear H3 the losses are 96.5 mkp or 3'7 hp. The N.I.A.E. engine test 1 gives 57.8 hp at rated speed. Hence at rated engine speed in gear H3 the transmission loss accounts for about 6.4 °o of the engine output. (b) Within either the high or low gear ranges the higher the gear the higher the losses for a given engine speed. It is apparent, however, that the losses in gear L3 are greater than those in HI. (c) Over the engine speed range 1000-2000 rev/min the losses may be approximated by a straight line. This is a useful feature when using the information in the prediction of tractor field performance and will be reported in a future publication.

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Fig. 3. Axle torque losses in various gears. L, low; H. high

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Fig. 4. Transmission power losses in various gears. L, low; H, high

LOSSES

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4. Conclusions The results reported in this paper may be summarized in the following points: (a) oil temperature is an important consideration when measuring transmission losses; (b) the transmission losses contribute to an error in the measurement of rolling resistance; the lower the speed at which the measurement is made the smaller the error; (c) the higher the gear the more significant are the transmission losses; (d) for prediction work the losses in different gears can be approximated by straight lines. REFERENCE

t Test report no. 458,

N.I.A.E., Silsoe, 1965