Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Patent
1989-04-28
1990-10-16
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
180233, 180244, 180249, 303 96, B60K 2308, B60T 866, B60T 832
Patent
active
049629700
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
Motor vehicles are known which can be shifted from rear-wheel drive to four-wheel drive, for example, and in which the drives of the two axles can be rigidly coupled to each other by locking the associated differential. In addition, one or two differential locks may be provided for the rigid coupling of the wheel drives of one axle.
Moreover, anti-lock braking systems for motor vehicles are known which, for the control of the wheel slip, form a reference value whose curve optimally approximates that of the vehicle speed. In such system this reference value is formed by the use of different gradients.
The formation of the reference value is particularly difficult in the case of vehicles with four-wheel drive, and especially when, in addition, a central lock is engaged.
SUMMARY OF THE INVENTION
The principal object of the invention and its embodiments is to provide possible solutions for the problem outlined above. In this connection, it is important that the central lock and any further locks which may be used, as well as the four-wheel drive, be disengaged or defeated as the brakes are applied. This may be done in response to the brake light switch signal.
This object, as well as other objects which will become apparent from the discussion that follows, are achieved, in accordance with the present invention, by varying the reference value in dependence upon whether the motor vehicle is shifted into two-wheel or four-wheel drive, in dependence upon the engagement of a central lock, and/or in dependence upon the engagement of a differential lock.
For a full understanding of the present invention, reference should now be made to the following detailed description of the preferred embodiments of the invention and to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of the power train and electronic control system for a four-wheel drive vehicle.
FIG. 2 is a block diagram of an anti-lock braking system according to the present invention, as applied to the vehicle of FIG. 1.
FIG. 3 is a block diagram showing a typical evaluation circuit which may be used in the system of FIG. 2.
FIG. 4 is a time diagram illustrating the operation of the anti-lock braking system of FIGS. 2 and 3 in one driving situation.
FIG. 5 is a time diagram illustrating the operation of the anti-lock braking system of FIGS. 2 and 3 in another driving situation.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
An exemplary embodiment of the invention is illustrated in FIGS. 1 to 3, and various possible solutions are illustrated in FIGS. 4 and 5 in terms of two driving situations.
In FIG. 1, the front wheels of a motor vehicle are designated by 1 and 2, and its rear wheels by 3 and 4. An engine 5 is normally connected through a drive shaft 10 with a differential 6 through which the rear wheels 3 and 4 are driven.
In the vehicle shown in FIG. 1, provision is made for shifting to four-wheel drive, to which end a longitudinal differential 7 can be switched so that in addition to the shaft 10 for the rear-wheel drive a shaft 8 is driven, through which and through a further differential 9 the front wheels are driven.
The shafts 8 and 10 can be rigidly coupled to the engine through a central lock contained in the differential 7. The differentials 6 and 9 may also have differential locks that can be engaged.
The assumption is here made that the shifting to four-wheel drive and the engagement of the locks are brought about automatically by means of a control circuit 11 to which signals corresponding to the speeds of the wheels 1 to 4 are fed. (This is indicated in FIG. 1 only by the wheel speed sensors 2a and 4a for the wheels 2 and 4, respectively. Corresponding wheel speed sensors 1a and 3a are also connected to the control circuit 11.) On the basis of the wheel-speed differences ascertained, a shifting to four-wheel drive and/or an engaging of the differential locks occurs, triggered by means of lines 13. A brake light switch signal is fed to the terminal 12 for releasing the locks a
REFERENCES:
patent: 4675819 (1987-06-01), Fennel
patent: 4702337 (1987-10-01), Burckhardt et al.
patent: 4746173 (1988-05-01), Fennel et al.
patent: 4762376 (1988-08-01), Matsubara
patent: 4832145 (1989-05-01), Fujii et al.
Braschel Volker
Demel Herbert
Jonner Wolf-Dieter
Roller Dieter
Butler Douglas C.
Robert & Bosch GmbH
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