Fluid-pressure and analogous brake systems – Speed-controlled – Having a valve system responsive to a wheel lock signal
Reexamination Certificate
2000-12-01
2002-09-17
Graham, Matthew C. (Department: 3613)
Fluid-pressure and analogous brake systems
Speed-controlled
Having a valve system responsive to a wheel lock signal
C303S115200, C303S116200, C303S010000
Reexamination Certificate
active
06450589
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a brake pressure transducer (brake pressure generator) for a hydraulic vehicle brake system. Furthermore, the invention relates to a hydraulic vehicle brake system that is equipped with such a brake pressure transducer and also to a method of operating such a brake pressure transducer and a vehicle brake system equipped therewith.
It is generally known that, in hydraulic vehicle brake systems, the brake pressure transducer comprises a so-called main brake cylinder in order to generate a brake pressure for the wheel brake that is proportional to the actuating force initiated via the actuating element—normally a brake pedal. It is likewise generally known also to equip the brake pressure transducer with a brake force booster that superimposes a servo force to boost the actuating force initiated via the actuating element. Suitable as brake force boosters for this purpose are both pneumatic boosters, which operate on the underpressure principle, and hydraulic boosters, which employ a hydraulic pump.
Such a pneumatic brake force booster is disclosed, for example, in DE 28 45 794 C2, while such a hydraulic-brake force booster is disclosed, for example, in DE 44 43 869 A1. Both the pneumatic and the hydraulic brake force boosters have a movable partition that subdivides an internal housing space into two chambers and transmits a force via a transmission element to the main brake cylinder if the chambers are subjected to a pressure difference as a function of a force acting on the actuating element. In the unactuated state, the chambers are pressure-equalized, with the result that the movable partition does not transmit a force to the output member. In the case of the pneumatic booster, the pressure difference is produced by an underpressure being generated in one chamber by means of an underpressure source, while the other chamber is subject to atmospheric pressure. In contrast, in the hydraulic booster, the pressure difference is generated by means of a hydraulic pump whose suction side is connected to the one chamber and whose pressure side is connected to the other chamber, with the result that the hydraulic pump pumps in the direction from the one chamber to the other chamber in order to achieve a brake force boost.
Nevertheless, such a hydraulic vehicle brake system is open to improvement. Thus, the full brake force boost is needed only in about 10% of all braking actions relating to a vehicle. It is now clear that the design of the brake force boost is overdimensioned for the remaining about 90% of the braking actions. This overdimensioning has the disadvantage that a relatively large installation space is necessary in the motor vehicle, as a result of which complexity and costs occur.
Especially if a pneumatic brake force booster is used, there is a direct relationship between booster power and overall size, that is to say the greater the booster power required, the larger is the brake force booster. Since the required booster power depends substantially on vehicle weight, so-called tandem boosters—that is to say, in principle, two brake force boosters arranged behind one another—have to be predominantly used in higher vehicle classes, as a result of which further installation space is needed in addition. A pneumatic brake force booster furthermore has the disadvantage that an underpressure source has to be provided in the vehicle. True, in the case of a vehicle equipped with a petrol engine, the underpressure generated in the intake system can in principle be used. However, severe fluctuations in the underpressure generated in this way can adversely affect the performance of the brake system, in particular with regard to the ever-increasing performance requirements in the future, so that complexity and costs of providing an independent underpressure source are unavoidable.
The object of the invention is therefore to provide an improved hydraulic vehicle brake system that can be produced in more compact form and with a lower cost expenditure and can also be actuated comfortably.
This object is achieved according to the invention with a brake pressure transducer that has the features disclosed herein.
SUMMARY OF THE INVENTION
According to the invention, the quantity of brake fluid that accrues because of the reduction in the volume of the additional hydraulic chamber at the input side of the pump is additionally fed, when the brake pressure transducer is actuated, by means of the pump to the quantity of brake fluid accruing in the wheel brake because of the reduction in the volume of the hydraulic chamber. The said quantity of brake fluid additionally fed into the wheel brake by means of the pump has the effect that a higher brake pressure than the brake pressure originally generated in the hydraulic chamber is established in the wheel brake or in the hydraulic chamber. In this way, a secondary servo force is provided by means of which a boost in the actuating force initiated via the actuating element and/or the primary servo force provided by the brake force booster can be achieved in a particularly advantageous way. The total actuating force of the brake pressure transducer is consequently made up of the initiated actuating force, the primary and the secondary servo force.
Under these circumstances, the disadvantages explained above in the case of the use of a generally known brake force booster are avoided since the brake force booster providing the primary servo force has to apply a substantially lower boost. In the case of a pneumatic brake force booster, this means specifically that a single booster having a diameter of 6 inches is adequate for a vehicle that, in the case of a conventional brake force system, would have to be equipped at least with one tandem booster having a diameter of 8 and 9 inches. In addition, because a substantially “weaker” pneumatic brake force booster is adequate, the underpressure source can also be “weaker” and to that extent can be designed more simply and with a lower cost expenditure. Since a “weaker” pneumatic brake force booster is also less sensitive to fluctuations in the underpressure, the underpressure generated by reason of principle in the intake system can be utilized in a less critical way in the case of a vehicle equipped with a petrol engine.
A further substantial advantage is that two servo forces are applied that are independent of one another. This consequently comprises a redundancy should a failure occur either of the brake force booster providing the primary servo force or the pump providing the secondary servo force, as a result of which a decisive contribution is made to increasing the safety of the vehicle brake system.
The brake force booster may be a brake force booster in the conventional sense that superimposes a fixed primary servo force on the actuating force initiated via the actuating element. On the other hand, it may be an electronically controllable brake force booster that can be controlled by means of an electrical actuator in order, firstly, to actuate the brake pressure transducer instead of or in addition to an actuation via the actuating element and, secondly, to adjust the primary servo force. Suitable as an electrical actuator is, preferably, a solenoid valve arrangement that is incorporated in the electronically controllable brake force booster in an installation space-saving manner. As a result of the use of an electronically controllable brake force booster, the vehicle brake system becomes particularly suitable for emergency or spot braking actions and also automatic braking procedures, for example, for regulating vehicle dynamics, drive slip and distance.
In an advantageous manner, the regulating behaviour of the vehicle brake system with regard to actuating comfort, which means reactions on the actuating element (brake pedal), and metering capability are improved if the delivery rate of the pump can be controlled by means of an electrical actuator in order to adjust the secondary servo force. To be preferred here as an electrical actuator is
Dieringer Werner
Kinder Ralf
Graham Matthew C.
Lucas Industries plc
MacMillan Sobanski & Todd LLC
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