Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
1998-05-13
2001-09-18
Oberleitner, Robert J. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S010000
Reexamination Certificate
active
06290307
ABSTRACT:
The present invention relates to a braking system with a master cylinder which comprises at least one cylinder/piston arrangement which can be actuated by a brake pedal in order to supply hydraulic fluid to at least one brake circuit.
Problems inherent in such braking systems are that it is difficult to enable also a brake power generation which is independent of the brake pedal actuation by the driver. This, however, is necessary for antislip control systems, driving dynamics control systems, automatic vehicle-to-vehicle ranging control. Generally, the brake pressure in the individual wheel brakes is modulated by ABS systems which are arranged in the brake circuit(s).
In conventional vehicle braking systems for motor vehicles the auxiliary energy required for braking is generated by pneumatic brake boosters which are coupled with the intake pipe of the motor in order to provide a vacuum with respect to atmospheric pressure in the brake booster. In modern engines, however, the vacuum is relatively low so that the required auxiliary energy can be provided to the desired extent and with the necessary dynamics.
The present invention is therefore based on the principle of providing the auxiliary energy required for braking by a controllable pressure source. This controllable pressure source can be activated by electrical energy.
Surprisingly, the renunciation of the previous pneumatic brake boosters and the inventive use of a controllable pressure source which is preferably activated by electrical energy in order to subject the piston of the cylinder/piston arrangement in the master cylinder under the control of an electronic control unit in the sense of supplying hydraulic fluid to the brake circuit offers the following considerable advantages.
In the area of the engine compartment rear bulk of the passenger cell considerable installation space becomes available because the previous large-size pneumatic brake boosters are no longer present. In addition, vacuum lines to the intake pipe are omitted. Moreover, a considerably higher pressure difference than in conventional brake boosters can be achieved which enables enhanced dynamics with controlled and/or boosted brake operations to be achieved. Finally, the controlled pressure source can be remotely arranged from the cylinder/piston arrangement of the master cylinder. This has positive effects on the crash behaviour.
According to a first embodiment of the invention the controllable pressure source is formed by a cylinder/piston arrangement whose piston can be axially moved by a motor in order to change the volume of a hydraulic chamber of the cylinder/piston arrangement, with the hydraulic chamber being hydraulically connected with a pressure chamber arranged in the master cylinder, whose change in volume causes an actuation of the master cylinder. The arrangement can be made in such a manner that the motor is operatively connected via a pinion and rack arrangement with the piston of the cylinder/piston arrangement. Alternatively, the arrangement can also be made in such a manner that the motor is operatively connected via a screw spindle
ut arrangement with the piston of the cylinder/piston arrangement.
In this context, it is crucial that a highly dynamic modulation of the pressure acting on the piston of the cylinder/piston arrangement in the master cylinder is enabled by the chosen arrangement.
This is also achieved by another inventive embodiment in which the controllable pressure source is formed by a cylinder/piston arrangement whose piston can be moved by a piezoelectric motor in order to change the volume of a hydraulic chamber of a cylinder/piston arrangement, with the hydraulic chamber being hydraulically connected with a pressure chamber arranged in the master cylinder, whose change in volume causes an actuation of the master cylinder. Due to the fact that piezoelectric motors can generally exert high forces but can perform only small axial strokes, the piezoelectric motor may comprise a transmission member, e.g. a diaphragm transmission.
In order to render the braking system suitable for the application in an antislip control, a driving dynamics control or a hill hold control it should be possible to bring the pressure source into a pressure build-up, pressure holding or pressure relief position. The controllable pressure source may be a hydraulic pump whose inlet side is hydraulically connected with a hydraulic fluid reservoir and whose outlet side is hydraulically connected with a pressure chamber arranged in the master cylinder, the volume change of which causes an actuation of the master cylinder. This applies in particular to hydraulic pumps with a high delivery rate and high pump dynamics.
Preferably the inlet side of the hydraulic pump is hydraulically connected with the outlet side of the hydraulic pump via a pressure limiting valve in order to prevent the burst pressure of the hydraulic system from not being exceeded.
Because some types of hydraulic pumps are not suited for building up the required pressure in the desired and/or required short time, in one embodiment of the invention the outlet side of the hydraulic pump is hydraulically connected with a pressure accumulator. This pressure accumulator can be charged by the pump to approx. 160 bar so that the required pressure level is directly available.
If the hydraulic pump is adapted to supply hydraulic fluid in two delivery directions, the pressure build-up phase as well as the pressure relief phase can be effected by the hydraulic pump. If the hydraulic pump is adapted to supply hydraulic fluid in one sense of delivery and if a pressure relief valve which can be controlled by the electric control unit is arranged between the inlet side and the outlet side of the hydraulic pump, with hydraulic fluid being able in at least one position of the pressure relief valve to flow from the pressure outlet side to the hydraulic fluid reservoir or to the inlet side, respectively, basically the same effect is achieved as in the case of a hydraulic pump which can supply hydraulic fluid in two delivery directions. However, the dynamics in the pressure relief phase are lower.
Some types of hydraulic pump are not self-locking so that a pressure holding phase cannot be effected in an easy manner with such hydraulic pumps. In such cases, a valve which can be controlled by the electronic control unit is arranged between the outlet side of the hydraulic pump and the pressure chamber arranged in the master cylinder, which at least in a first position connects the outlet side of the hydraulic pump with the pressure chamber in the master cylinder, and which at least in a second position connects the pressure chamber in the master cylinder with the hydraulic fluid reservoir.
Preferably the valve which can be controlled by the electronic control unit comprises a third position in which the outlet side of the hydraulic pump, the hydraulic fluid reservoir, and the pressure chamber of the master cylinder are shut off relative to one another.
According to another embodiment the pressure relief valve which can be controlled by the electronic control unit is a rheomagnetic valve, with the inlet side of the hydraulic pump being connected with a hydraulic fluid reservoir into which a rheomagnetic hydraulic fluid can be introduced.
In preferred embodiments of the braking system according to the invention a pressure sensor arrangement is provided which senses the fluid pressure acting on the pressure chamber of the master cylinder and which outputs an electrical signal which is representative of the current fluid pressure to the electronic control unit. Moreover, a sensor arrangement is preferably provided which senses an actuation of the brake pedal and which outputs an electrical signal which is representative of said actuation to the electronic control unit.
Thus the electronic control unit can effect an actuation of the master cylinder as a function of the actuation of the brake pedal but also independent of same. This may either be a boosting of the pedal actuation initiated by the dr
Mohr Kurt
Poertzgen Gregor
Lucas Industries Public Limited Company
MacMillan Sobanski & Todd LLC
Oberleitner Robert J.
Torres Melanie
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