GB2356686A

GB2356686A - Vehicle braking control systems

Info

Publication number: GB2356686A
Application number: GB9927991A
Authority: GB
Inventors: George Howard Mercer
Original assignee: Bayerische Motoren Werke AG; MG Rover Group Ltd
Current assignee: Bayerische Motoren Werke AG; MG Rover Group Ltd
Priority date: 1999-11-27
Filing date: 1999-11-27
Publication date: 2001-05-30
Anticipated expiration: 2019-11-27
Also published as: DE10052765A1; GB2356686B; GB9927991D0

Description

2356686 Vehicle Braking Control Systems The present invention relates to

control systems for vehicle brakes and in particular to anti-lock and traction control systems.

It can be a problem with both anti-lock braking and traction control systems that the pulsed application of the brakes used in them tends to set up vibrations in the vehicle. These can either be vibrations of the wheels vertically caused by reaction of the pulsed braking torque through the suspension, or vibrations in the drive train. These vibrations can reduce the effectiveness of the brakes by reducing the level of traction between the tyres and the ground, and can also be felt as vibrations by the driver.

Accordingly the present invention provides a vehicle comprising wheels, brakes for braking the wheels, a control unit arranged to control the brakes, controllable damping means for damping vibrations in a component of the vehicle, and sensing means wherein the control unit is arranged to detect the occurrence of vibrations in the vehicle using the sensing means, to determine whether the vibrations are being produced by control of the brakes and, of they are, to increase the damping provided by the damping means.

The damping means may comprise switchable or variable rate dampers in the vehicle suspension system. In this case they can be made stiffer if the vibrations are being produced by the control of the brakes than would be desirable if they were being produced by the surface over which the vehicle was travelling.

Alternatively the clamping means may form part of the engine mounting system of the vehicle. In this case it might also be beneficial to make the damping means stiffer if the vibrations are being produced by the control of the brakes than would be desirable if they were being produced directly by the engine.

Preferred embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a diagrammatic representation of a vehicle according to the invention.

A vehicle has a body 10 with wheels 12, 14 connected to it by respective suspension systems, each comprising a spring 16 and a damper 18. The dampers are controllable so that their damping rate can be varied. An engine 20 is mounted on the body 10 by means of active engine mounts 22. Hydraulically actuated brakes 24 are provided to apply a braking torque to the wheels, and the braking torque can be modified by a hydraulic valve block 26 using hydraulic pressure from a pump 28 under the control of a chassis control unit 30. The chassis control unit therefore performs the functions of conventional ABS control units, but also controls the vehicle's suspension system and the active engine mounts 22 as described below.

Wheel speed sensors 32, ride height sensors 34 and an accelerometer 36 mounted on the body 10, and a sensor 38 for sensing vibrations of the engine 20 all provide signals to the control unit 30, which determines from them the frequency and amplitude of vibrations of the wheels 12, 14 relative to the body 10, absolute vibrations of the body 10 and vibrations of the engine 20 relative to the body 10, and also the nature of the surface over which the vehicle is travelling.

Under normal driving conditions the control unit 30 controls the suspension dampers 18 and the engine mounts 22 in a conventional manner. For example, if the vehicle is travelling over rough ground the dampers are controlled so as to have a low level of damping so that the vibrations are not transmitted to the body.

Also of the engine is vibrating significantly the engine mounts 22 controlled so as to have a relatively low spring rate so that the vibrations are not transmitted into the body 10 more than is necessary.

The chassis control unit 30 is also arranged to provide an anti-lock brake (ABS) function and a traction control function. During ABS operation the valve block 26 is arranged to reduce the hydraulic pressure to the brakes if locking of any of the wheels 12, 14 is detected. During traction control the valve block is arranged to apply the brakes using pressure from the pump 28 of any of the wheels is spinning. Each of these functions tend to result in a pulsing of the braking torque, and they can therefore lead to vibrations being built up in the wheels 12, 14 or in the engine 20.

Therefore during ABS and traction control the control unit 30 is arranged to monitor for vibrations in the vehicle using the various sensors 32, 34, 36, 38 and to determine whether vibrations are being set up as a result of the brake control. This can be done by detecting that the frequency of the vibrations corresponds to that of the pulsed actuation of the brakes. Typically the vibrations produced are axle tramp where the wheels vibrate relative to the body, and driveline vibrations. If vibrations of the wheels are detected which are of the same frequency as the brake actuation pulses, or at least of such vibrations are detected as being predominant over those produced by other things, such as the surface over which the vehicle is travelling, then the control unit 30 stiffens the dampers 18 of the suspension to reduce the vibrations. This reduces the vibrations which will be felt by the driver and improves the effectiveness of the brakes by making the contact force between the tyres and the ground more constant. If vibrations in the engine 20 are detected which are of the same frequency as the brake actuation pulses, or at least of such vibrations are detected as being predominant, then the control unit st iffens the engine mounts 22 to reduce the vibrations.

Claims

-4CLAIMS

1. A vehicle comprising wheels, brakes for braking the wheels, a control unit arranged to control the brakes, controllable damping means for damping vibrations in a component of the vehicle, and sensing means wherein the control unit is arranged to detect the occurrence of vibrations in the vehicle using the sensing means, to determine whether the vibrations are being produced by control of the brakes and, of they are, to increase the damping provided by the damping means.

2. A vehicle according to claim I wherein the damping means form part of the vehicle suspension system connecting the wheels of the vehicle to its body.

3. A vehicle according to claim 1 or claim 2 wherein the vibrations are vibrations of at least one wheel of the vehicle.

4. A vehicle according to claim 1 wherein the damping means forms part of an engine mount.

5. A vehicle according to claim I or claim 4 wherein the vibrations are vibrations of at least a part of the power train of the vehicle.

6. A vehicle substantially as hereinbefore described with reference to the accompanying drawings.