Power plants – Pressure fluid source and motor – Pulsator
Reexamination Certificate
2000-02-18
2001-05-22
Ryznic, John E. (Department: 3745)
Power plants
Pressure fluid source and motor
Pulsator
C060S554000
Reexamination Certificate
active
06233932
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a fully hydraulic brake power generator/master cylinder unit according to the precharacterizing clause of claim
1
.
In contrast to the brake booster/master cylinder units still predominantly used today, in fully hydraulic brake power generator/master cylinder units the brake power is not boosted or generated with the aid of a vacuum, but purely hydraulically. In a similar way to conventional vacuum brake boosters, the actuating force normally introduced via a brake pedal by the vehicle driver is boosted proportionally, in that hydraulic fluid is supplied under pressure in a controlled manner by a valve to a booster stage which acts on the pressure chamber or pressure chambers of the master cylinder and thus builds up in the latter the brake pressure which is then transferred to the associated wheel brakes via the individual brake circuits of the vehicle brake system. When the brake pedal is released, this booster stage is then relieved of pressure again under the control of said valve.
In particular embodiments of fully hydraulic brake power generator/master cylinder units, normally, that is to say when the booster stage is functioning properly, their input member is no longer used for introducing power into the unit, but, instead, is employed only for actuating the unit, in that the input member is merely displaced, for example by the depression of a brake pedal connected to the input member. The displacement of the input member is sensed, and a corresponding hydraulic pressure is built up in the booster stage as a function of this displacement, in order to generate the brake power desired by the driver. In this case, the hydraulic pressure emanates from an external source, for example from a pressure accumulator or from a rapid-response hydraulic pump. Only when the hydraulic booster stage fails can the vehicle driver couple the input member mechanically, normally to the primary piston of the master cylinder, by vigorously depressing the brake pedal, so as then to build up at least some brake pressure by depressing the brake pedal further and by means of the resulting displacement of the primary piston.
Since the vehicle driver therefore normally actuates the brake power generator/master cylinder unit only indirectly, the unit itself, in contrast to brake power generator/master cylinder units conventional hitherto, does not give him any feedback on the brake pedal with regard to the brake pressure which has been built up in the unit, thus making it difficult to actuate the brake pedal in a metered manner.
In order to improve the meterability of the brake system in brake power generator/master cylinder units without direct brake pressure feedback to the brake pedal, it is known to simulate brake pressure feedback, for example by means of a spring arrangement, so that the customary behavior of a conventional brake booster/master cylinder unit, in which higher brake pressures require a higher pedal pressure, is imparted to the driver artificially. However, the problem of the known arrangements for artificially generated brake pressure feedback is that, when the hydraulic booster stage is not functioning, for braking purposes the spring force serving for artificial brake pressure feedback to the brake pedal first has to be overcome by the driver, before it is possible to build up brake pressure by a correspondingly more pronounced actuation of the brake pedal. On the basis of this behavior of the brake system, the driver may be given the feeling that his efforts are in vain and may therefore think, incorrectly, that the brake system is entirely inoperable.
SUMMARY OF THE INVENTION
The object on which the invention is based is to develop a brake power generator or a brake power generator/master cylinder unit with artificially generated brake pressure feedback, to the effect that, if the hydraulic booster stage fails, the unit can be actuated without any detectable hindrance by the spring force serving for artificial brake pressure feedback. Furthermore, according to one development, the meterability of such brake power generator/master cylinder units is to be further improved.
Proceeding from the brake power generator/master cylinder unit mentioned in the introduction, this object is achieved, according to the invention, in that the spring arrangement serving for artificial brake pressure feedback to the brake pedal has a first spring and a second spring which are connected in series, the spring force of the second spring being detectably greater than the spring force of the first spring, and in that, when the brake power generator/master cylinder unit is actuated, if the hydraulic booster stage fails essentially only the first spring carries out brake pressure feedback. Thus, when the brake power generator/master cylinder unit according to the invention is functioning properly, a user of said unit receives the desired simulated brake pressure feedback in the usual way, without having to overcome excessive resistance for braking purposes if the hydraulic booster stage fails.
The other advantage of the solution according to the invention is that, even if the hydraulic booster stage fails, the brake pedal does not execute an idle travel in the initial phase of actuation, but has to be actuated against the spring force of the first spring which, however, is markedly lower than that of the second spring. This avoids panic reactions on the part of the driver, which may occur when a driver notices the “slack travel” of the brake pedal, that is to say when he does not detect any resistance when he depresses the brake pedal.
The spring forces of the two springs are to be so different that a user of the brake power generator/master cylinder unit according to the invention can detect this difference clearly. If the hydraulic booster stage fails, the driver can then easily take note of this failure from the markedly lower resistance of the brake pedal in the initial phase. Detectably different spring forces can be achieved, for example, by means of detectably different spring constants of the two springs of the spring arrangement. Alternatively, it is also possible to use springs having an at least similar spring constant, the second spring being installed in the highly compressed state and the first spring in the fully expanded state.
According to a preferred embodiment of the brake power generator/master cylinder unit according to the invention, when the latter is actuated, the first spring remains ineffective in terms of brake pressure feedback if the hydraulic booster stage is functioning properly. This means that the simulated brake pressure feedback to the brake pedal is then brought about only by the second spring. On account of the markedly different spring forces of the two springs, if the hydraulic booster stage fails the second spring serves essentially for transmitting the actuating force exerted on the brake pedal to the first spring which is then compressed. In this case, the second spring is not, or in any event not appreciably, compressed.
In preferred embodiments of the brake power generator/master cylinder unit according to the invention, when the latter is actuated, if the hydraulic booster stage fails the second spring is just displaced, together with the input member, in particular, relative to the housing of the brake power generator/master cylinder unit. This constitutes an elegant method of rendering the second spring essentially ineffective in terms of simulated brake pressure feedback if the hydraulic booster stage has failed. Advantageously, in such an embodiment, the first spring is prevented from being compressed, when the hydraulic booster stage is functioning properly. Particularly preferably, the hydraulic pressure in the hydraulic booster stage is utilized to prevent the first spring from being compressed. When this hydraulic pressure lapses if the hydraulic booster stage fails, the force preventing compression of the first spring is no longer present and the changeover according to the invention between
Heibel Helmut
Knechtges Josef
Lucas Industries Public Limited Company
MacMillan Sobanski & Todd LLC
Ryznic John E.
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