GB2282861A

GB2282861A - Methods and systems for controlling automatic transmission systems to allow engine braking

Info

Publication number: GB2282861A
Application number: GB9321300A
Authority: GB
Inventors: Kenneth Leonard Smith
Original assignee: Lucas Industries Ltd
Current assignee: ZF International UK Ltd
Priority date: 1993-10-15
Filing date: 1993-10-15
Publication date: 1995-04-19
Also published as: GB9321300D0

Abstract

A method and system for controlling an automatic transmission system employ a control strategy causing the transmission system to select a higher gear ratio, to effect engine braking, if preselected operational conditions are sensed. The operational parameters sensed include vehicle speed, throttle position and an operation condition of the vehicle brake. The system preferably acts to select a higher ratio if either the brake is applied or the vehicle is constant, and the throttle is closed. Engine speed could alternatively or additionally be used as an input parameter. The strategy may require that one or more of the parameters has satisfied the required condition for a minimum time period. <IMAGE>

Description

METHODS AND SYSTEMS FOR CONTROLLING AUTOMATIC TRANSMISSION SYSTEMS This invention relates to methods and systems for controlling vehicle automatic transmission systems.

According to one aspect of the invention there is provided a method of controlling the gear ratio of a vehicle automatic transmission system to cause engine braking.

The invention provides a control strategy for causing the vehicle automatic transmission system to select a higher gear ratio, to effect engine braking, if certain preselected operational conditions are sensed, overriding the normal operation of the automatic transmission system. More specifically, the control strategy may be designed to initiate engine braking if it is determined that prolonged braking is needed, as, for example, when the vehicle is moving downhill.

The method may comprise sensing different operational parameters of the vehicle, including an operational parameter indicative of an operating condition of the vehicle brake, and controlling the gear ratio of the vehicle automatic transmission system in dependence on the operational parameters sensed.

The sensed operational parameters may further include parameters indicative of vehicle speed and throttle position.

In a particular implementation of the invention, a higher gear ratio of the vehicle automatic transmission system is selected if either the vehicle brake is applied or the vehicle speed is constant or is increasing and the vehicle throttle is closed.

According to another aspect of the invention there is provided a control system for controlling the gear ratio of a vehicle automatic transmission system to cause engine braking.

The control system may comprise sensor means for sensing different operational parameters of the vehicle, including an operational parameter indicative of an operating condition of the vehicle brake, and control means for controlling the gear ratio of the vehicle automatic transmission system in response to an output from the sensor means.

The operational parameters sensed by the sensor means may further include vehicle speed and throttle position.

An embodiment of the invention is now described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a control system in accordance with the invention and Figure 2 shows a logic circuit representing the control strategy used in the control system of Figure 1.

The control system shown in Figure 1 provides a control strategy for causing the vehicle automatic transmission system to select a higher gear ratio, to effect engine braking, whenever certain preselected operational conditions prevail. More specifically, the control strategy is designed to initiate engine braking if it is determined that prolonged braking is needed, as, for example, when the vehicle is moving downhill.

In the illustrated embodiment, the control system has three sensors S1, S2, S3, each sensitive to a different operational parameter.

Sensor S1 senses vehicle speed and produces two outputs 01 and 02. Output 01 is produced if the vehicle speed is determined to be increasing, whereas output 02 is produced if vehicle speed is determined to be constant.

Sensor S2 senses throttle position and produces an output 03 if the throttle is determined to be closed.

Sensor 53 senses an operating condition of the vehicle brake and produces an output 04 if it is determined that the brake is being applied. The operating condition of the brake may be sensed in various ways; for example, by sensing movement of the brake mechanism itself or by sensing a change in brake fluid pressure.

Outputs 01 to 04 are supplied to the vehicle engine management system control unit CU which is arranged to operate in accordance with a predetermined control strategy. The control strategy adopted in this embodiment of the invention is represented by the logic circuit shown in Figure 2 of the drawings.

Referring to Figure 2, outputs 01 and 02, derived from sensor S1, are supplied to respective input terminals of a logical OR gate G1, and the output from gate G1 is connected to one input of a logical AND gate G2.

Output 03, from sensor S2, is supplied to the other input of gate G2, and the output from gate G2 is connected to one input of a second logical OR gate G3. Output 04 from sensor S3 is supplied to the other input of gate G3.

With this control strategy, the output 05 from gate G3 will be high whenever, (i) output 04 is high (i.e. the vehicle brake is being applied), or (ii) output 03 is high (i.e. the vehicle throttle is open) and either 01 or 02 is high (i.e. vehicle speed is increasing or is constant).

Gate G3 is connected to the automatic shift control actuator SC. If either condition (i) or condition (ii) is satisfied the need for engine braking will have been established, and the resulting output 05 causes the shift control actuator SC to select a higher gear ratio. In this way, the control system overrides the normal operation of the automatic transmission system.

The above-described control strategy may be implemented by means of a processor which is programmed to carry out the logical operations represented by the circuit shown in Figure 2, in response to the outputs 01-04. Typically, the same processor could be used to carry out the other engine management functions of the control unit CU.

Alternatively, the control strategy could be implemented in hard-wired form.

It will be understood that the control strategy described with reference to Figures 1 and 2 is given by way of example only, and that the present invention embraces alternative control strategies. For example, although the described control system has three sensors, for sensing vehicle speed, throttle position and an operating condition of the vehicle brake, other forms of sensor (e.g. for sensing engine revolutions) could alternatively or additionally be used.

Furthermore, the control strategy may require that one or more of the sensed operational parameters (e.g.

application of the vehicle brake) has satisfied the relevant condition for a minimum time period before a higher gear ratio is initiated.

Claims

1. A method of controlling the gear ratio of a vehicle automatic transmission system to cause engine braking.

2. A method as claimed in claim 1 including sensing for preselected operational conditions and selecting a higher gear ratio if said preselected operational conditions are sensed whereby to override normal operation of the automatic transmission system to cause engine braking.

3. A method as claimed in claim 2 wherein the sensing step includes sensing different operational parameters of the vehicle including an operational parameter indicative of an operating condition of the vehicle brake.

4. A method as claimed in claim 3 wherein the sensed operational parameters further include operational parameters indicative of vehicle speed and throttle position.

5. A method as claimed in claim 4 wherein said higher gear ratio is selected if either the vehicle brake is being applied or the vehicle speed is constant or is increasing, and the vehicle throttle is closed.

6. A control system for controlling the gear ratio of a vehicle automatic transmission system to cause engine braking.

7. A control system as claimed in claim 6 comprising sensing means sensing for preselected operational conditions and selection means for selecting a higher gear ratio if said preselected operational conditions are sensed whereby to override normal operation of the automatic transmission system to cause engine braking.

8. A control system as claimed in claim 7 wherein the sensing means senses different operational parameters of the vehicle including an operational parameter indicative of an operating condition of the vehicle brake.

9. A control system as claimed in claim 8 wherein the sensing means also senses an operational parameter indicative of vehicle speed and throttle position.

10. A control system as claimed in claim 9 wherein the selection means selects the higher gear ratio if either the vehicle brake is being applied or the vehicle speed is constant or is increasing, and the vehicle throttle is closed.

11. A method according to claim 1 substantially as herein described with reference to the accompanying drawings.

12. A control system according to claim 6 substantially as herein described with reference to the accompanying drawings.