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Hydrostatic Drive Gives Advantages to Works Vehicles

21st November 1958
Page 60
Page 60, 21st November 1958 — Hydrostatic Drive Gives Advantages to Works Vehicles
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INTERESTING transmission • contrasts were provided by three vehicles equipped with hydrostatic transmission at the • Public Works Exhibition at Olympia last week.

Shown in prototype form, I he Bagnall Burns BB90 crawler tractor exhibited by W. G. Bagnall, Ltd., Stafford, was fitted with two Lucas 1.P.

3,000 variable output swashplate pumps from which the drive is transmitted to two B.B. wheel motors of the seveneylindered radial type. The pumps are driven by a Meadows 4DC 420 oil engine developing 90 b.h.p. at the power unit's rated speed of 2,000 r.p.m.

Maximum hydraulic pressure is 3,000 p.s.i. and the motors transmit a maximum combined torque of 10,500 lb-ft. The rated draw-bar pull of the tractor is 15,000 lb.

Outstanding advantages of the transmission include the elimination of clutch, gearbox, reverse gear and transmission • shafts, positive independent Control of the speed. of both tracks, and stepless variation of :the tractor speed up to 7 m.p.h. in either. direction.

It is claimed by the makers that an overall average efficiency of 80 per eent. is afforded by the transmission. This is compared with an average efficiency of mechanical crawler transmissions of 75 per cent. and a torque converter .transmission efficiency of 70 per cent.

A Road-Marshall RD series 2 roller has been converted by the makers, Marshall, Sons, and Co., Gainsborough, to operate on a Dowty hydrostatic system, in which both the pump and the motor are of the 12-cylindered axial piston type. The angle of the pump swash plate can be altered to give infinitely variable drive in both directions over the complete speed range.

The units take the place of the clutch and gearbox and their use obviates the need for a braking system apart from a parking brake. The vehicle is driven by an oil engine developing 35 b.h.p.

A representative of The Commercial Motor, who drove the roller, reports that its simplicity and range of ratio control would provide obvious. advantages in the case of a road vehicle, given an acceptable efficiency and favourable cost and weight factors.

Tests of the roller have not been sufficiently prolonged to obtain accurate fuel-consumption figures, but the results indicate that there is no loss of efficiency.

A favourable consumption is also Claimed by Reliance Trucks, Ltd.. Heckmondwike, for their hydrostatically c22 driven Bantam Mark II three-wheeled works truck, which is shown as a production model following full-scale tests of prototypes under arduous conditions in a quarry. The result has shown that the transmission reduces fuel consumption.

In this case, the power of a J.A.P. single-cylindered petrol engine, developing b.h.p. at 1.800 r.p.m., is transmitted direct to a gear-type pump which supplies oil to two .wheel motors, mounted on sides of the single driving wheel.

These are also of the gear type and can be employed individually or in parallel to provide two speed ranges. Ease of control is comparable, if not superior, to that provided by a battery electric power unit.

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