GB2270961A

GB2270961A - An automatic gearbox with a gear engagement inhibitor

Info

Publication number: GB2270961A
Application number: GB9319889A
Authority: GB
Inventors: Friedrich Graf; Dieter Brueckner
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 1992-09-29
Filing date: 1993-09-27
Publication date: 1994-03-30
Anticipated expiration: 2013-09-27
Also published as: GB2270961B; FR2696225A1; FR2696225B1; DE4232649C2; DE4232649A1; GB9319889D0

Abstract

A safety device prevents a sudden increase in torque on the gearbox with transition from an interrupted drive train to an engaged drive train. Such transitions occur if the driver depresses the accelerator 4 and at the same time shifts the selection lever 10 of the automatic gearbox 2 from the neutral position or parking position into a driving position, or if the force transfer in the automatic gearbox is delayed owing to influences conditional on the temperature. This can lead to an abrupt acceleration of the motor vehicle and damage to parts of the drive train. A gearbox control unit 3 compares the throttle valve position, the engine speed and the engine torque with respective predetermined limiting values. If a limiting value is exceeded then the gearbox control unit 3 delivers a blocking signal to the gearbox 2 and prevents the drive engagement. <IMAGE>

Description

2270961 A MOTOR VEHICLE WITH AN AUTOMATIC GEARBOX The invention relates to

a motor vehicle having an automatic gearbox.

In motor vehicles with an automatic gearbox the problem can occur that when there is a transition from an interrupted drive train, namely a neutral or parking position of the gearbox, to a engaged drive train, a sudden increase in the torque occurs at the gearbox output. Such an increase occurs, for example, if the driver moves the lever from the select position "N" (neutral position or idle-running position) or "P" (parking position) into a drive position and presses the accelerator at the same in order to demand power. A sudden increase in the torque also occurs if the gearbox only produces the frictional connection in a delayed manner, such as, for example, occurs with low temperatures in the gearbox owing to the increased viscosity of the hydraulic fluid.

A sudden increase in the torque at the gearbox output results, however, in dangerous abrupt acceleration of the vehicle. Moreover, the gearbox is greatly stressed in the short term. Parts in the drive train (gearbox, differential etc.) can be damaged.

In a known safety device (DE 34 21 247 C2), when introducing a driving gear, an increase in the motor power is prevented if the brake of the motor vehicle is not activated, as either the accelerator pedal is locked, the fuel supply to the engine blocked, or the quantity of air sucked-in by the engine is greatly reduced by a second throttle valve. This type of reduction in power demands high expenditure especially since an individual control apparatus for the known blocking devices is required.

The underlying object of the invention is to create a safety device which prevents sudden undesirable increases in torque at the gearbox output and incurring as little expense as possible.

According to the present invention there is provided a motor vehicle with an automatic gearbox having inhibiting means for preventing a sudden increase in gearbox output torque when there is a transition from an interrupted drive train to an engaged drive train, the inhibiting means being responsive to a transition of a drive-selection lever from a neutral or parking position to a driving position, and comprising means for comparing at least one engine operating parameter with a predetermined limiting value when such a transition occurs, and for transmitting a blocking signal to the gearbox to prevent engagement of the drive train when the limiting value is exceeded.

Preferably, a signal representing the torque at the input of the gearbox is supplied to the inhibiting means for comparison with a torque limiting value. A signal representing the engine speed and/or a signal representing the throttle valve position may also be supplied to the inhibiting means for comparison with respective limiting values. The inhibiting means is preferably connected to the gearbox by a line conveying the blocking signal.

For a better understanding of the present invention and to show how it may be carried into effect reference will now be made by way of example to the accompanying drawing, which shows, in a diagrammatical manner, the most important drive elements of a motor vehicle with an automatic gearbox.

The drive of a motor vehicle consists substantially of an engine 1, an automatic gearbox 2 and an electronic gearbox control unit 3. The driver requests power from the engine 1 using an accelerator 4, which is connected to the engine 1 by a mechanical coupling or by or an electric line 5.

The rotational movement of the engine reaches the input of the gearbox 2 by way of a shaft 6. The gearbox output is connected to the driven wheels 9 of the motor vehicle by means of a drive member 8 which is 5 represented here in a simplified manner by a shaft.

The driver can select one of the following different known gear positions by way of a selection lever 10: "R" for reverse travel and "D", @'V', "2" and possibly 'W' for one or several forward driving stages.

The position of the selection lever 10 is conveyed by way of a line 11 to the gearbox 2 and to the gearbox control unit 3. The gearbox control unit monitors the signals arriving at the line 11 and determines when a transition takes place from an interrupted drive train, for example idle-running, to a engaged drive train, for example drive D. The gearbox control unit receives, by way of signal lines 12, 14 and 15, the values of the following motor operating parameters: the actual value of the throttle valve position which conforms with the position of the accelerator, the engine speed and/or the engine torque. It processes these parameters and the selection lever position and produces a control signal which is conveyed by way of a line 16 to the gearbox 2 and effects introduction of the suitable gear-change procedure.

If a transition to an engaged drive train, such as described above, is established, the gearbox input torque, which corresponds to the engine torque, is compared by the gearbox control unit 3 with a predetermined limiting value. The limiting value depends on the respective type of motor vehicle and possibly on the foreseen driving conditions or use of the vehicle. For common types of motor vehicle it lies in the region of 30 to 50 Nm.

The engine speed is compared by the gearbox control unit 3 moreover with a predetermined limiting value, which lies at approximately 2000 revolutions per minute.

Finally the throttle valve position is also compared, by means of the gearbox control unit 3, with a limiting value which corresponds to an angle of approximately 10'.

If one of the engine operating parameters exceeds the predetermined limiting value then the gearbox control unit produces a blocking signal which is conveyed by way of a signal line 18 to the gearbox and which prevents engaged drive from being introduced in the gearbox. It blocks, as it were, the effect of the selection lever on the gearbox. The blocking signal is not cancelled until all of the operating parameters have fallen below the predetermined limiting values.

In this way the above-described safety device prevents with simple means sudden increases in the torque at the gearbox output and the dangers associated with this.

Claims

1. A motor vehicle with an automatic gearbox having inhibiting means for preventing a sudden increase in gearbox output torque when there is a transition from an interrupted drive train to an engaged drive train, the inhibiting means being responsive to a transition of a drive-selection lever from a neutral or parking position to a driving position, and comprising means for comparing at least one engine operating parameter with a predetermined limiting value when such a transition occurs, and for transmitting a blocking signal to the gearbox to prevent engagement of the drive train when the limiting value is exceeded.

2. A vehicle as claimed in claim 1, in which a signal representing the torque at the input of the gearbox is supplied to the inhibiting means for comparison with a torque limiting value.

3. A vehicle as claimed in claim 1 or 2, in which a signal representing the engine speed is supplied to the inhibiting means for comparison with an engine speed limiting value.

4. A vehicle as claimed in any one of claims 1 to 3, in which a signal representing the throttle valve position is supplied to the inhibiting means for comparison with a throttle valve position limiting value.

5. A vehicle as claimed in any preceding claim, in which the inhibiting means is connected to the gearbox by a line conveying the blocking signal.

6. A vehicle substantially as described herein with reference to and as shown in the accompanying drawing.