GB2112089A

GB2112089A - Inhibitor for transmission control systems

Info

Publication number: GB2112089A
Application number: GB08235339A
Authority: GB
Inventors: Roland Kenneth Borton
Original assignee: AE PLC
Current assignee: AE PLC
Priority date: 1981-12-16
Filing date: 1982-12-10
Publication date: 1983-07-13
Also published as: ES518222A0; GB2112089B; IT8224765A1; FR2518027B1; ES8401390A1; IT1155386B; FR2518027A1; PT75989A; PT75989B; IT8224765A0

Abstract

An inhibitor is provided which compares at 17 the engine speed 16 with a predetermined engine speed 18 and, if the transmission is sought to be engaged while the predetermined speed is exceeded, prevents transmission engagement. The driver has to select disengagement of the transmission and reduce the engine speed below the predetermined speed before the transmission can be re-engaged. <IMAGE>

Description

SPECIFICATION Transmission control systems The invention relates to transmission control systems and in particular to transmission engagement inhibitors and to vehicles including such inhibitors.

Those vehicles which have an engine which drives the vehicle through a transmission which can be engaged and disengaged by a driver, commonly allow the driver to increase the engine speed when the transmission is disengaged and then engage the transmission. This causes the vehicle to accelerate suddenly and this is undesirable both because it can endanger persons close to the vehicle, where this is a road vehicle, and because it strains the engine and transmission system.

According to a first aspect of the invention, there is provided a transmission engagement inhibitor for use with a an engine which drives through a transmission which can be selectively engaged and disengaged, and comprising means for producing an overspeed signal when the engine speed exceeds a pre-set speed, the overspeed signal means being connected to a control system for producing an inhibit signal when engagement of a disengaged transmission is selected and when an overspeed signal is received, the inhibit signal preventing engagement of the transmission system.

The following is a more detailed description of one embodiment of the invention, by way of example, reference being made to the accompanying drawing which is a block diagram of a transmission engagement inhibitor.

The inhibitor to be described with reference to the drawing is for use with a vehicle such as an omnibus or coach where the engine drives the vehicle through an automatic transmission. The gears are selected by the driver whose selection is relayed electrically to the transmission to engage the selected gear. The driver can also select a disengaged or "neutral" position of the transmission. The inhibitor acts to prevent engagement of a gear when the engine speed is above a predetermined level.

In the inhibitor shown in the drawing, the selector 10 has three "gear engaged" positions 1 0a, lOb, 1 0c and a neutral position 11. The output from each gear engaged position is connected to the transmission 12 by a respective line and the lines from the gear engaged positions are interrupted by respective switches R1, R2, R3.

The outputs of the gear engaged and the neutral positions are fed to a control system 1 3 whose output is fed to a relay 14 which controls the switches R1, R2, R3. A second output from the control system 13 fed to a warning device 1 5.

An engine speed signal producing device 16, which may be a tacho-generator or may be an electronic engine revolution counter of the vehicle, produces a signal representative of the engine speed which is fed to a frequency-to-voltage converter 20 whose output is fed to a comparator 1 7. A variable resistor 1 8 is used to produce a signal corresponding to a pre-set engine speed above which a gear is not to be engaged and this signal is also fed to the comparator 1 6. The output 1 9 of the comparator 1 6 is fed to the control system 13.

In use, the inhibitor operates as follows to prevent the transmission being engaged when the engine speed exceeds a pre-set level.

The variable resistor 1 7 is set to produce the pre-set speed signal which may, for example, correspond to 700 or 750 rpm. The engine speed signal from the device 20 and this pre-set speed signal are received by the comparator 1 7 which produces an overspeed signal when the engine speed signal exceeds the pre-set speed signal and an underspeed signal when the engine speed signal is less than the pre-set speed signal. There may be some hysterisis between the levels of the speed signals.

When the selector 10 is in "neutral" and the driver selects one of the gear positions 1 0a, 1 Ob, 1 0c, the engage signal so produced is received by the control system 13. If the signal received by the control system 1 3 from the comparator 1 7 is an overspeed signal, the control system 1 3 produces an inhibit signal which does not allow the relay 14 to operate. At the same time, the warning device 1 5 operates to warn the driver. This warning may be a visual warning or an audible warning such as a buzzer and may be given for a pre-set time determined by a monostable circuit in the control system 1 3.

To allow the selected gear to be engaged, the driver must reduce the engine speed to below the predetermined speed and select "neutral" before re-selecting the required gear. This causes the comparator 1 7 to produce an underspeed signal and causes the control system 13 to re-set. When the gear is re-selected, the control system 13 actuates the relay 14 to close the switches R1, R2, R3 and allow the selected gear to be engaged by the transmission. The warning device 1 5 is not operated.

Of course, if the initial gear selection of the driver is made with the engine speed beiow the predetermined engine speed, the inhibitor will operate the relay 14 and allow the gear to be engaged. In addition, once the relay 14 has been operated, it is held until neutral is again selected, thus allowing gear changes to be made without opening the switches R1, R2, R3.

The inhibitor described above with reference to the drawings thus prevents a disengaged transmission being engaged when the engine speed is above say, 700 or 750 rpm. This prevents the vehicle being accelerated rapidly which can be dangerous to pedestrians, where the vehicle is an omnibus or coach, and also prevent undue strain on the engine and transmission.

This inhibitor can be readily connected between the most commonly used types of selectors and transmissions whether they use a controller or have direct connections to gearbox solenoids. In some systems, only one line between the selector 10 and the transmission 12 needs to be used to keep the transmission in neutral and, in this case, switches R2 and R3 are left unused.

It will be appreciated that the inhibitor need not be used with an omnibus or coach. It may be used in automobiles, or in any other form of vehicle or in static installations.

Claims

1. A transmission engagement inhibitor for use with an engine which drives through a transmission which can be selectively engaged and disengaged, and comprising means for producing an overspeed signal when the engine speed exceeds a pre-set speed, the overspeed signal means being connected to a control system for producing an inhibit signal when engagement of a disengaged transmission is selected and when an overspeed signal is received, the inhibit signal preventing engagement of the transmission system.

2. An inhibitor according to claim 1, wherein an underspeed signal is produced when the engine speed is less than the pre-set speed, the control system, on receipt of the underspeed signal and when engagement of a disengaged transmission is selected, producing an allow signal for allowing engagement of the transmission.

3. An inhibitor according to claim 1 or claim 2, wherein the overspeed signal producing means comprise a comparator for receiving a signal corresponding to the engine speed and a signal corresponding to the pre-set engine speed and for producing the overspeed signal when the engine speed signal exceeds the pre-set speed signal.

4. An inhibitor according to claim 3, when dependent on claim 2, wherein the comparator produces the underspeed signal when the engine speed signal is smaller than the pre-set speed signal.

5. An inhibitor according to any one of claims 1 to 4, when disengagement of the transmission is selected after the production of an inhibit signal, the control system produces a re-set signal for re-setting the inhibitor to permit subsequent engagement of the transmission if, on such engagement, no inhibit signal is again produced.

6. An inhibitor according to any one of claims 1 to 5 and in which the transmission system is controlled electrically from a selector, wherein the inhibitor further comprises a relay for insertion between the selector and the transmission system and for receiving the inhibit signal to prevent engagement of the transmission system by operation of the selector.

7. An inhibitor according to any one of claims 1 to 6 and including a warning device connected to the coì1tlol system for producing a warning and the overspeed signal.

8. An inhibitor according to claim 7, wherein the warning device includes a monostable circuit which causes the warning to be given for a predetermined time.

9. An inhibitor according to claim 7 or claim 8, wherein the warning is an audible warning or a visual warning.

10. An inhibitor according to any one of claims 1 to 9 and connected in a vehicle between a transmission system of the vehicle engine and a driver-controlled selector for selectively engaging and disengaging the transmission system.

11. An inhibitor according to claim 10 wherein the selector has a position in which the transmission system is disengaged and at least one transmission engaged position, and wherein the selector produces an electrical signal when neutral is selected and an electrical signal when the at least one transmission engaged position is selected, said signals being fed to the control system to indicate when engagement of a disengaged transmission is selected.

12. A transmission engagement inhibitor substantially as hereinbefore described with reference to the accompanying drawing.