Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
1999-03-04
2001-04-03
Lopez, F. Daniel (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
C091S37600A
Reexamination Certificate
active
06209441
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a brake booster, and more particularly, to a brake booster including a reaction transmitting means having a spring.
DESCRIPTION OF THE PRIOR ART
A brake booster is known in the art which is designed to produce a reduced servo ratio during an initial phase of a braking operation of the brake booster while increasing the servo ratio during a later phase of the braking operation.
A brake booster of the kind described includes reaction transmitting means disposed between a reaction disc and a valve plunger and comprising a first and a second retainer disposed to be displaceable relative to each other, a spring disposed between the first and the second retainer and resiliently charged to a preset load to maintain the both retainers spaced apart normally, and a stop member which prevents the first and the second retainer from becoming spaced beyond a given distance (see Japanese Laid-Open Patent Application No. 85,442/1996).
With such an arrangement, if a brake pedal is depressed to operate the brake booster, the reaction transmitting means merely transmits a brake reaction which is transmitted from the reaction disc to the valve plunger through the first retainer, the spring and the second retainer until the spring in the reaction transmitting means is compressed, whereby a prevailing servo ratio can be chosen to be relatively low to improve the maneuverability in a range where a low braking force is required.
On the other hand, when the spring in the reaction transmitting means is compressed, the second retainer and the valve plunger are advanced relative to the first retainer and a plate plunger by an amount corresponding to the compression of the spring, and this is equivalent to a further depression of the brake pedal by an amount corresponding to the compression of the spring. This allows the prevailing servo ratio to be set to a relatively high value to allow a braking force of an increased magnitude to be obtained with a reduced force of depression.
In the brake booster employing the reaction disc, the reaction disc is formed of an elastic material such as rubber to cause a hysteresis, a phenomenon that the magnitude of an output from the brake booster becomes different between upon depression and release of the brake pedal if the force with which the brake pedal is depressed is maintained constant.
In the presence of the hysteresis, there results an advantage that the brake feeling is improved in that if a driver ceases to increases the force to depress the brake pedal and slightly decrease the force unintentionally, the braking force of an equal magnitude is obtained.
However, with the brake booster mentioned above which includes the reaction transmitting means, as the spring in the reaction transmitting means is compressed, a compressive deformation of the reaction disc is reduced in a relative sense, whereby the flow path switching action of a valve mechanism in the brake booster takes place almost entirely through the expansion and shrinkage of the spring. As a consequence, because the hysteresis which the reaction disc exhibits becomes reduced during the expansion and shrinkage of the spring, there results a disadvantage that a change in the output from the brake booster becomes sensitive to a change in the force with which the brake pedal is depressed.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the invention to provide a brake booster which assures a good brake feeling if it includes reaction transmitting means having a spring.
Thus, the invention relates to a brake booster comprising a valve body slidably disposed within a shell, a valve mechanism disposed within the valve body, an input shaft for causing a valve plunger, which forms part of the valve mechanism, back and forth to switch a flow path in the valve mechanism, an output shaft slidably disposed on the valve body, a reaction disc interposed between one end of the output shaft and the valve plunger, and reaction transmitting means interposed between the reaction disc and the valve plunger for transmitting a brake reaction from the reaction disc to the valve plunger, and wherein the valve mechanism comprises an annular first valve seat formed on the inner periphery of the valve body, an annular second valve seat formed on a rear portion of the valve plunger at a location radially inward of the first valve seat, a valve element adapted to be seated upon either valve seat, and a backup plate formed by a rigid body embedded into the valve element. In accordance with the invention, the external diameter of the backup plate is chosen to be less than the internal diameter of the first valve seat and greater than the external diameter of the second valve seat.
With the described arrangement, as a brake pedal is depressed to drive the valve plunger and the valve element which is seated on the second valve seat which is formed on the valve plunger forward, the valve element will become seated upon the first valve seat on the valve body which remains stationary at a forward position and become removed from the second valve seat, thereby allowing the brake booster to be operated in the similar manner as in the conventional arrangement.
The valve element is not provided with a backup plate in an area thereof which is adapted to be seated upon the first valve seat, whereby the elastic deformation becomes increased in comparison to the elastic deformation which occurs when such area is provided with a backup plate.
As a consequence, the hysteresis that an output from the brake booster has different magnitudes between upon depression and release of the brake pedal can be enhanced by the area of the valve element which is adapted to be seated upon the first valve seat, thereby allowing a change in the output which has been sensitive to a change in the force with which the brake pedal is depressed to be moderated in a region where the expansion and shrinkage of the spring in the reaction transmitting means occurs. In this manner, an improved brake feeling can be obtained as compared with the conventional arrangement.
Above and other objects, features and advantages of the invention will become apparent from the following description of an embodiment thereof with reference to the attached drawings.
REFERENCES:
patent: 4399736 (1983-08-01), Schubert
patent: 4793242 (1988-12-01), Kobayashi
patent: 5111734 (1992-05-01), Suzuki
patent: 5121674 (1992-06-01), Uyama
patent: 5386760 (1995-02-01), Goto et al.
patent: 5520086 (1996-05-01), Ikeda
patent: 5699713 (1997-12-01), Mortimer
patent: 5794506 (1998-08-01), Inoue et al.
patent: 5819633 (1998-10-01), Satoh
patent: 5823089 (1998-10-01), Inoue et al.
patent: 5893316 (1999-04-01), Inoue et al.
patent: 8-85442 (1996-02-01), None
Morimitsu Yasumasa
Nakamura Shuichi
Takaku Hitoshi
Flynn ,Thiel, Boutell & Tanis, P.C.
Jidosha Kiki Co. Ltd.
Lopez F. Daniel
LandOfFree
Brake booster does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Brake booster, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Brake booster will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2466158