GB2065837A

GB2065837A - Vehicle transmission control system

Info

Publication number: GB2065837A
Application number: GB8039619A
Authority: GB
Original assignee: Honeywell Inc
Current assignee: Honeywell Inc
Priority date: 1979-12-17
Filing date: 1980-12-10
Publication date: 1981-07-01
Also published as: CA1164973A; DE3047025A1; GB2065837B; SE8007068L; FR2471879A1

Abstract

A system for controlling a a transmission (20) of a vehicle includes a sensor (30, 32) for sensing the speed of the engine, a controller (33, 37) connected to the sensor for controlling the output of the transmission dependent upon engine speed, and a threshold circuit (REF) connected to the controller for inhibiting transmission output until the engine speed has attained a predetermined level, above that normally required to drive auxiliary functions of the vehicle. In the system shown, the output of amplifier (33) is fed via reversing switch (37) to a valve (38) controlling displacement of pump (21). <IMAGE>

Description

SPECIFICATION Vehicle transmission control system This invention relates to a system for controlling the operation of a vehicle's transmission.

Many modern day vehicles are fully capable of utilizing the vehicle engine for providing both auxiliary functions and vehicle drive. Such vehicles can include, as examples, aerial lift trucks, grade trimmers, fork lifts, dozers, trenchers and front end loaders. In the control of such vehicles, the operator sets engine speed at a predetermined governed value for powering all functions of the machine. Thus, when the bucket of a front end loader is to be operated, for example, the levers for controlling the orientation of the bucket are operated and, when the machine is to be driven in the forward or reverse direction, the forward and reverse drive pedals are operated to in turn operate the transmission of the vehicle.Such an operation means that when the vehicle is standing still and the bucket is being operated as one of the auxiliary functions of the vehicle, the vehicle's engine is quite likely supplying excessive horsepower and, therefore, consuming excessive fuel.

According to the present invention there is provided an improved system for controlling a transmission of a vehicle, the system comprising a sensor operable to sense the output of the vehicle engine; control means responsive to said sensor for controlling the transmission output in dependence upon the engine output; and threshold means for inhibiting transmission output until said engine output has attained a predetermined level.

Thus the engine is allowed to run fast enough for supplying the auxiliary functions without providing transmission output. At higher engine speeds, the transmission output adapts to engine rpm in a load control manner; that is, if the engine speed drops because of excess load, the transmission "downshifts". This "downshift" also occurs as a result of throttle reduction.

An embodiment of the invention will now be described by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows one type of machine on which the present invention can be used; Figure 2 shows a control system according to the present invention for use in the machine of Figure 1; and Figure 3 is a graph showing swash plate angle of the pump in the hydrostatic transmission of the system of Figure 2 as a function of engine output.

Referring to Figure 1, a front end loader vehicle 10 comprises bucket 1 operator's cab 12 and engine 13. Inside operator's cab 12 are the various levers and pedals for controlling the forward and reverse progress of vehicle 10 and the orientation ordinary design, the details of it will not be specifically shown herein. However, the control system for propelling vehicle 10 is shown in detail in Figure 2.

As shown in Figure 2, vehicle 10 has its engine 13 controlled by lever 14 (which alternatively may be a foot pedal) connected to engine 13 by shaft 15. Lever 14 controls the amount of fuel supplied to engine 13 and therefore controls the rotational speed of engine output shaft 16. Output shaft 16 is then connected to hydrostatic transmission 20 in the form of hydraulic pump 21 and hydraulic motor 22 interconnected by hydraulic lines 23 and 24. Hydraulic motor 22 than has an output shaft 25 connected to the drive train of the vehicle for propulsion.

The control system comprises pulse pickup unit 30 sensing the speed of rotation of disc 31 affixed to engine output shaft 16 and providing a series of output pulses the frequency of which is dependent upon the engine speed. Typically, disc 31 has a plurality of teeth which interact with a magnetic field established by pulse pickup unit 30 to induce the pulses which are supplied to frequency-tovoltage converter 32. Pulse pickup unit 30 may be an SB100A manufactured by Honeywell Inc.

Frequency-to-voltage converter 32 converts the frequency of the pulses received from pulse pickup unit 30 into a voltage proportional to that frequency and supplies that voltage to the positive input of amplifier 33. The output of amplifier 33 is connected through resistor 34 to one input of summing junction 36. The junction of summing junction 36 and resistor 34 is connected to ground through diode 35 and resistor 41. The other input to summing junction 36 is a reference input which establishes a threshold level below which output shaft 25 of hydrostatic transmission 20 will not rotate and above which the revolutions per minute of output shaft 25 is governed by the output of engine 13. The output from summing junction 36 is connected to the negative input of amplifier 33.

Frequency-to-voltage converter 32 and amplifier 33 may be a package manufactured by Honeywell Inc. under the number W883A. Resistor 41 and diode 35 are included in the feedback circuit of amplifier 33 for characterizing the output of amplifier 33 as will be discussed with respect to Figure 3.

The output from amplifier 33 is connected through forward/reverse switch 37 the output of which is then connected to valve 38. Valve 38 may be a V7058A manufactured by Honeywell Inc. and receives the electrical signal from forwardireverse switch 37 to provide a hydraulic output for controlling the swash plate of pump 21 and, therefore, the output thereof.

Forward/reverse switch 37 controls the polarity of the signal supplied to valve 38 for driving vehicle 10 in a forward or a reverse direction.

As described above, the reference input to summing junction 36 provides a threshold level for operation of hydrostatic transmission 20.

Figure 3 is a graph showing the operation of hydrostatic transmission 20 as a function of engine speed rpm. The idle point is the lowest setting of engine 13 providing the lowest speed of shaft 16. As the engine is throttled upward, the speed of shaft 16 increases and, as a result, the pulses from pulse pickup unit 30 increase in frequency. This increased frequency results in an increased voltage to the positive input of amplifier 33. However, the output from amplifier 33 and forward/reverse switch 37 will not begin to change until the voltage to the positive input of amplifier 33 exceeds the input to the negative input terminal which is a function of the reference setting.Once this reference setting has been attained by the output from frequency-to-voltage converter 32, the angle of the swash plate of pump 21 will follow line A of Figure 3 for the forward direction and line B for the reverse direction. Curves C and D are provided by the resistor 41 and diode 35 circuit to characterize lines A and B.

It can be seen from Figures 2 and 3 that as the loading on the machine increases, the speed of output shaft 16 of engine 33 reduces which will proportionally reduce the pump swash plate angle and reduce the speed of rotation of output shaft 25 from hydrostatic transmission 20 resulting in a "downshift". If the forward or reverse progress of vehicle 10 is to be maintained, throttle 14 must be increased to accommodate the increased load up to the point where engine 13 is at its horsepower limit. When vehicle 10 is at a standstill during a time when the auxiliary functions of the vehicle are being utilized, engine speed need only be operated between the idle point I and the reference point R as shown in Figure 3 instead of the higher setting at which present prior art systems are operated This operation results in an efficient and economical utilization of engine output.

Claims

1. A system for controlling a transmission of a vehicle, the system comprising a sensor operable to sense the output of the vehicle engine; control means responsive to said sensor for controlling the transmission output in dependence upon the engine output; and threshold means for inhibiting transmission output until said engine output has attained a predetermined level.

2. The system of Claim 1, wherein said sensor comprises a speed sensor for sensing engine output speed.

3. The system of Claim 2, wherein said speed sensor includes a pulse pickup unit for providing an output signal having a frequency dependent upon engine output speed.

4. The system of Claim 3, wherein said sensor includes a frequency-to-voltage converter receiving said output signal from said pulse pickup unit and providing a voltage output dependent upon said frequency.

5. The system of Claim 4, wherein said control means comprises an amplifier having a first input connected to said frequency-to-voltage converter for receiving said voltage output thereof.

6. The system of Claim 5, wherein said threshold means comprises a reference means connected to a second input of said amplifier and operable to establish the threshold level below which the transmission is not operated.

7. The system of Claim 5 or 6, wherein said control means further comprises a forward/reverse circuit connected to an output of said amplifier for determining the forward and reverse direction of travel for said vehicle.

8. The system of any one of the preceding claims, wherein the transmission is hydrostatic, wherein the control means controls the flow of hydraulic fluid from a hydraulic pump to a hydraulic motor dependent upon engine speed; and wherein the threshold means prevents the flow of hydraulic fluid from said pump to said hydraulic motor until the speed of said engine output has attained a predetermined level.

9. The system of Claim 8, wherein said control means includes a valve connected to said sensor to control said hydraulic motor output as a function of engine speed.