Fluid-pressure and analogous brake systems – Multiple fluid-receiving devices – Multiple motors
Patent
1991-03-19
1993-10-12
Oberleitner, Robert J.
Fluid-pressure and analogous brake systems
Multiple fluid-receiving devices
Multiple motors
303 97, 303100, 3031135, 188349, B60T 826, B60T 832
Patent
active
052519686
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a brake apparatus for a two-axle vehicle having rotational speed sensors at least at the rear wheels of the vehicle, a circuit for evaluating the rotational speeds and for determining the rotational deceleration of the wheels, and control means for controlling the braking pressures or braking moments obtained at the brakes of the front and rear wheels.
Brake apparatuses having the sensors, circuits and control means referred to above are generally known from conventional antilock brake systems (ALB brake systems).
In conventional brake systems, whether or not they are electronically controlled, irregular wear of the brake linings at the brakes of the front and rear wheels occurs. The brake pads or linings of the front wheel brakes are subjected to a higher load than the brake linings of the rear wheel brakes due to the partial shift of the vehicle weight which as a rule takes place on braking. This leads to irregular wear of the brake pads or linings and consequently the frequency of pad change is higher than in a vehicle in which all the brake linings wear uniformly and can be replaced all at once.
The objective of the invention is to further develop a brake apparatus of the type set forth at the beginning in such a manner that the brake pads or linings have a life which is as long and uniform as possible.
A brake apparatus according to the invention for achieving this objective is described in claim 1. Advantageous further developments are set forth in subsidiary claims 2 to 8.
The invention is based on the recognition that in motor vehicles, in particular automobiles, during normal driving operation far more than 90% of all braking operations subject the brakes to a relatively low stress. Typically, far less than 10% of all braking operations take place with a braking force of magnitude such that the retardation of the vehicle lies in a range above 0.2 g. With the usual adhesion coefficients (also referred to as braking force coefficients and denoted by .mu.) above 0.4 it would therefore be possible for practically, all common automobile models to effect the brakings with a vehicle retardation of less than 0.2 g solely, via the rear axle of the vehicle.
The invention utilizes this knowledge and achieves a uniform wear of all the brake linings or pads of the vehicle in that the brakes of the rear wheels of the vehicle in "noncritical" braking situations are subjected to a braking force which is greater than the braking force obtained at the brakes of the front wheels at the same time. If the "noncritical" braking state ceases to be present, for example because the driver actuates the brake with more force and/or because due to the road conditions a tendency to lock occurs at the braked wheels, the increased loading of the rear wheel brakes provided according to the invention is immediately cancelled and all the brakes of the vehicle subjected to maximum braking, possibly under the control of a conventional antilock system.
A preferred further development of the invention provides that the brakes of the rear wheels of the vehicle have larger and/or more wear-resistant brake linings than the brakes of the front wheels. The greater loading of the brakes of the rear wheels according to the invention compared with the brakes of the front wheels then leads to the brake linings as a whole after a great number of braking operations with statistical distribution of the braking forces being uniformly, worn and it therefore being possible to replace them all at once after a relatively long life.
To implement the idea of the invention it is necessary to determine when the braking leaves the aforementioned "noncritical" state and becomes critical, i.e. requires an optimum use of all the braking means to obtain the shortest possible stopping distance. To determine such a transition from a noncritical to a critical state various criteria are available. These are mainly the rotational or angular retardations of the rear wheels subjected at the start of a braking according to the invention initia
REFERENCES:
patent: 2975871 (1961-03-01), Eckardt et al.
patent: 4735279 (1988-04-01), Sato
Lucas Industries Public Limited Company
Oberleitner Robert J.
Poon Peter M.
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