Fluid-pressure and analogous brake systems – Multiple systems – Fluid pressure and electric
Patent
1994-07-01
1995-08-15
Butler, Douglas C.
Fluid-pressure and analogous brake systems
Multiple systems
Fluid pressure and electric
188156, 303160, 3031134, 303 20, B60T 800, B60T 1000, B60T 1358, B60T 1366
Patent
active
054413354
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
Vehicle brakes including an acutable wear-free auxiliary brake are known. The engine brake, retarder or constant throttles, for example, can be considered an auxiliary brake.
An electronically controlled motor vehicle brake (ELB), for utility vehicles for example, has an electrical braking value pick-up which emits an electrical output signal (for example, a potentiometer voltage) depending on the actuation path of the brake pedal to an electronic control unit. A required value U.sub.R (for example pressure) for the control of the friction brakes and a required value U.sub.D for the control of the auxiliary brakes (for example engine brake, constant throttle, electrical or hydrodynamic retarder) are in turn derived from this electrical output signal U. FIG. 1 shows the characteristic.
In order to preserve the friction brakes as much as possible and to keep the wear low, only the auxiliary brakes are now activated in the initial region s.sub.01 of the actuation path (U.sub.D). It is only when their braking effect is not sufficient that the friction brakes are added. The characteristic of the friction brakes U.sub.R is also still relatively flat at the beginning in order to achieve good graduation.
In the case of rapid braking or emergency braking, however, this arrangement has the disadvantage that the friction brake only comes into use relatively late (after s.sub.01).
Because of this, longer response times and pressure build-up times occur with the consequence of a longer braking distance.
The auxiliary brakes react so sluggishly that they only become effective too late in the case of emergency braking. Furthermore, their braking effect is limited; it is, furthermore, dependent on speed and rotational speed and it does not remain effective until the vehicle is at rest.
SUMMARY OF THE INVENTION
The following advantages are provided by the invention.
The required value characteristic for the activation of the friction brakes depends on the actuation rate ##EQU1## at the braking value pick-up.
In the case of slower actuation rate (less than a limiting value G), a late and slow activation of the friction brake is effected because the auxiliary brake comes into use first (no wear!).
In the case of rapid actuation rate (greater than G), rapid response of the friction brakes is effected and the auxiliary brakes may even be switched off.
There is a short braking distance with integrated activation of the friction brake and auxiliary brake with an electrical braking value pick-up.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 plots various output signals versus actuation path
FIG. 2 shows a block circuit diagram of a vehicle brake according to the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
An electronically controlled motor vehicle brake (ELB) is represented in a block circuit diagram in FIG. 2. An electrical braking value pick-up 1 generates an electrical output signal U (a potentiometer voltage, for example) as a function of the actuation path s, of the brake pedal and is connected to an electronic control unit 2. A required value U.sub.R for the control of the friction brakes and a required value U.sub.D for controlling the auxiliary brakes (engine brake, constant throttle, electrical or hydrodynamic retarder, for example) corresponding to the characteristics of FIG. 1 is in turn generated from this electrical output signal U.
In order to preserve the friction brakes as much as possible and to keep the wear low, only the sustained-action brakes 11 (via an actuator 10) are now activated in the initial range s.sub.01 of the actuation path (U.sub.D). It is only when its braking effect is no longer sufficient that the friction brakes 9 are added (U.sub.R). The characteristic of the friction brakes U.sub.R is also still relatively flat at the beginning in order to achieve good graduation (block 6).
As already mentioned above, however, this arrangement alone has the disadvantage that the friction brake only comes into use relatively late (after s.sub.01) in the case of rapid braking or
REFERENCES:
patent: 4962969 (1990-10-01), Davis
patent: 5184875 (1993-02-01), Wrede
patent: 5378053 (1995-01-01), Patient et al.
Stumpe Werner
Wrede Jurgen
Butler Douglas C.
Robert & Bosch GmbH
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