GB2070206A

GB2070206A - Automotive hydrostatic transmission

Info

Publication number: GB2070206A
Application number: GB8104916A
Authority: GB
Original assignee: Gyro Mining Transport Ltd
Current assignee: Gyro Mining Transport Ltd
Priority date: 1980-02-26
Filing date: 1981-02-17
Publication date: 1981-09-03
Also published as: ZA811116B; AU7317381A; GB2070206B

Abstract

A self-propelled vehicle, eg a locomotive, has a control unit (13) incorporating a micro processor and a diesel engine (5) driving a pump (11) whose output is varied by unit (13) according to signals representing the speed of the engine and individual where motors (15) and the pressure differential between delivery and return lines (14, 17) which indicates whether the vehicle is pulling or being pushed by its load. The unit (13) compares, the speed of a driven wheel at one side of the vehicle with a reference speed for that side and additionally compares, the speed of a driven wheel at one side of the vehicle with the speed of a driven wheel at the other side, the pump output being increased or decreased should the comparisons indicate speed differences outside allowable tolerances. <IMAGE>

Description

SPECIFICATION Self-propelled vehicle This invention relates to a self-propelled vehicle, e.g. a locomotive, having a hydrostatic transmission system, which system is capable of providing improved drive characteristics and imparting more responsive control of the vehicle by the driver than prior art proposals.

In prior art proposals, the technique has been to run a power unit, e.g. a diesel engine, at full speed, while manually controlling the output of a hydraulic pump driven by the power unit, the pump transmitting pressure fluid to one or more hydraulic motors for powering the driving wheels of the vehicle.

According to the present invention, a selfpropelled vehicle having a hydrostatic transmission system comprises at least two driven wheels, one located at each side of the vehicle, a speed transducer associated with each wheel to monitor the speed thereof and electrically connected to a control unit incorporating a micro processor carried by the vehicle, a rotary power unit carried by the vehicle, the speed of which is controllable by a driver, a speed transducer to monitor the output speed of the power unit and electrically connected to the control unit, the power unit driving a hydraulic pump, the stroke and hence output of which is controllable by the control unit, and the pump being connected by hydraulic fluid lines to each drivable wheel, each of the lines incorporating a pressure traiisducer to monitor whether the vehicle is pulling a load or is being pushed by its load, the pressure transducers being electrically connected to the control unit, the control unit serving to compare the speed of a driven wheel at one side of the vehicle with a reference speed for that side of the vehicle and additionally to compare the speed of a driven wheel at one side of the vehicle with the speed of a driven wheel at the other side of the vehicle, with the pump output being increased or decreased should the comparisons indicate speed differences outside allowable tolerances.

Thus, if slip at one or more wheels is sensed, as often occurs with friction driven vehicles, e.g. locomotives, the pump output is adjusted to eliminate slip, such adjustment being irrespective of the speed of the power unit, so that the vehicle of the invention eliminates wheel slip and also eliminates stall of the power unit. In effect, the pump is able to deliver the maximum horse power possible for any output speed of the power unit that can be applied to the wheels without slip or with an immediate correction when slip is sensed.

The power unit may be a diesel engine, while control of the pump by the control unit is conveniently effected by a servo-valve.

When the vehicle is a locomotive it may incorporate eight driving wheels located in two sets of four in four-wheeled bogies at each end of the vehicle, all eight wheels being driven. It is highly improbable that all eight wheels would slip together and hence a speed difference sensed at one of the wheels is sufficient to adjust the pump output. If slip occurs when the vehicle is pulling a load, the pump output is decreased. Conversely, if slip occurs when the vehicle is being pushed hy a load, e.g. when travelling down a gradient, then the pump output is increased. Thus. in effect the reference speed for any one wheel is determined from the speeds of the other seven wheels.However, to cater for the possibility of all four wheels at one side of the vehicle slipping simultaneously, the micro processor is preferably further employed to compare the speeds of the left hand side wheels with the speeds of the right hand side wheels. Again, if a speed difference is sensed outside an allowable tolerance (and in this case the tolerance would be related to that speed difference normally encountered between inner and outer wheels when negotiating a curve), the pump output is adjusted.

In the circumstance where there is only one driven wheel at each side of the vehicle, the reference speed for each side may be obtained from locating a speed transducer adjacent a non-driven wheel.

With the vehicle at rest, the driver's throttle would be in the idling position, and the pump at zero stroke. Additionally, a driver's brake control may be-connected to the control unit, again to effect adjustment of the pump output whereby the vehicle will come to rest without inducing skids at any retarded wheel.

The invention will now be described in greater detail, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a side elevation of a locomotive with eight driven wheels; Figure 2 is an end elevation of Fig. 1, and Figure 3 is a schemmatic diagram of a control circuit for the locomotive of Figs. 1 and 2.

In the drawings, a locomotive 1 is provided with two bogies 2 each carrying four flanged and drivable wheels 3 seated on heads of rails 4. The locomotive 1 further comprises a 1 50 H.P. diesel engine 5 and housing 6, a clutch and hydraulic pump.

As shown in Fig. 3, the engine 5 is provided with a driver's, manual throttle control 7 to control the speed of the engine 5 which has a flywheel 8 monitored by a speed transducer 9. A driveshaft 10 from the engine 5 drives a variable stroke hydraulic pump 11 contained within the housing 6, the pump stroke being varied by means of a servo control valve 1 2 in turn controlled by a micro processor located within a control unit 1 3.

The pump 11 is provided with an output line 14, with individual lines 15 connected to a hydraulic motor (not shown) at each wheel 3 and individual lines 1 6 from each hydraulic motor connected to a return line 1 7 to the pump 11. A pressure transducer 1 8 is located in each line 14, 17 and electrically connected by lines 19 to the control unit 13, while a speed transducer 20 is associated with each wheel 3 and electrically connected by lines 21 to the control unit 1 3. Finally, a driver's manual brake control 22 is also provided and connected by line 23 to the control unit 1 3.

In use, with the engine 5 running at idling speed and the pump 11 at zero stroke and hence no fluid output, the driver releases the brakes and displaces the throttle control 7 to commence acceleration of the locomotive 1.

When running, the pressure transducers monitor whether the locomotive is pulling its load, e.g. when accelerating or running uphill or being pushed by its load, i.e. when decelerating or running downhill, which information is conveyed to the control unit 13, the latter comparing the speed of a driven wheel 3 at one side of the locomotive 1 with a reference speed for that side of the locomotive and additionally to compare the speed of a driven wheel 3 at one side of the locomotive with the speed of a driven wheel 3 at the other side of the locomotive, with the fluid output of the pump 11 being adjusted by the servo control valve 1 2 should the comparisons indicate speed differences outside allowable tolerances, e.g. such as the differences that would inevitably occur between inner and outer wheels when the locomotive 1 was negotiating a curve in the rails 4. Furthermore, as an additional precautionary measure, the micro processor of the control unit 1 3 also compares the speeds of the four wheels 3 at one side of the locomotive 1 with the four wheels 3 at the other side of the locomotive 1 and again adjustment of the output of the pump 11 is effected automatically should the differences exceed allowable tolerances. When it is desired to bring the locomotive 1 to rest, the driver operates brake control 22 to bring about the same control procedure as for accelerating viz. the output of the pump 11 is adjusted to preclude skidding of any retarded wheel.

Claims

1. A self-propelled vehicle having a hydrostatic transmission system comprising at ieast two driven wheels, one located at each side of the vehicle, a speed transducer associated with each wheel to monitor the speed thereof and electrically connected to a control unit incorporating a micro processor carried by the vehicle, a rotary power unit carried by the vehicle, the speed' of which is controllable by a driver, a speed transducer to monitor the output speed of the power unit and electrically connected to the control unit, the power unit driving a hydraulic pump, the stroke and hence output of which is controllable by the control unit. and the pump being connected by hydraulic fluid lines to each drivable wheel, each of the lines incorporating a pressure transducer to monitor whether the vehicle is pulling a load or is being pushed by its load, the pressure transducers being electrically connected to the control unit, the control unit serving to compare the speed of a driven wheel at one side of the vehicle with a reference speed for that side of the vehicle and additionally to compare the speed of a driven wheel at one side of the vehicle with the speed of a driven wheel at the other side of the vehicle, with the pump output being increased or decreased should the comparisons indicate speed differences outside allowable tolerances.

2. A vehicle as claimed in Claim 1, wherein the power unit is a diesel engine.

3. A vehicle as claimed in Claim 1 or Claim 2, wherein control of the pump by the control unit is effected by a servo-valve.

4. A vehicle as claimed in any preceding Claim, in the form of a locomotive incorporating eight driving wheels located in two sets of four in four-wheeled bogies at each end of the vehicle, all eight wheels being driven.

5. A vehicle as claimed in Claim 4, wherein a speed difference sensed at one of the wheels is employed to adjust the pump output.

6. A vehicle as claimed in Claim 4 or Claim 5, wherein the micro processor is further employed to compare the speeds of the left hand side wheels with the speeds of the right hand side wheels.

7. A vehicle as claimed in any one of Claims 1 to 3, wherein, with only one driven wheel at each side of the vehicle, the reference speed for each side is obtained from locating a speed transducer adjacent a nondriven wheel.

8. A vehicle as claimed in any preceding Claim, wherein a driver's brake control is connected to the control unit, again to effect adjustment of the pump output whereby the vehicle will come to rest without inducing skids at any retarded wheel.

9. A self-propelled vehicle having a hydrostatic transmission system, substantially as hereinbefore described with reference to the accompanying drawings.