Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
1999-07-14
2001-02-27
Lopez, F. Daniel (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
Reexamination Certificate
active
06192783
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a brake booster, and more particularly, to a brake booster which is constructed in a manner to permit a brake ratio to be changed in two stages.
DESCRIPTION OF THE PRIOR ART
A brake booster is known in the art which comprises a valve body slidably disposed within a shell, a valve plunger slidably fitted into the valve body and coupled to an input shaft for movement therewith, a first plunger plate slidably fitted into a front tubular portion of the valve plunger, a first spring for urging the first plunger plate forwardly relative to the valve plunger, and a reaction disc interposed between one end of an output shaft and an end face of the valve body for transmitting a reaction which is acting on the output shaft through the first plunger plate and the first spring to the valve plunger and the input shaft (see, for example, Utility Model Publication No. 8337/1995).
In the conventional booster mentioned above, in the inoperative condition of the brake booster, the front end face of the first plunger plate slightly projects forwardly of the front end face of the valve plunger. When the brake booster is actuated, a reaction which is acting on the output shaft causes the reaction disc to bulge, thus causing it to abut against the front end face of the first plunger plate. Subsequently, as the reaction increases to compress the first spring, the reaction disc abuts against the first plunger plate and the end face of the valve plunger. As a consequence, an output rises with a greater booster ratio under the condition that the reaction disc abuts against only the first plunger plate, and the output rises with a reduced booster ratio under the condition that the reaction disc abuts against both the first plunger plate and the valve plunger. In this manner, a conventional arrangement permits a booster ratio to be changed in two stages corresponding to a region of a reduced and a greater depression of a brake pedal (input).
It is known in a brake booster that there exists a hysteresis, meaning a difference in the input between when a brake pedal is depressed and when it is released for an output of an equal magnitude. In the conventional booster mentioned above, the hysteresis occurs not only in a greater booster ratio region, but also in a smaller booster ratio region or in a region where the depression applied to a brake pedal is greater.
However, the presence of a hysteresis in a region where the depression of the brake pedal is greater results in fact that a driver feels that the controllability of a brake is uncomfortable. Accordingly, when a brake booster is premised in which a booster ratio can be changed in two stages, it is desired for the brake booster that the hysteresis be substantially equal to null in a region where the depression of the brake pedal is greater.
SUMMARY OF THE INVENTION
In view of the foregoing, the present invention provides a brake booster of the type initially mentioned in which an annular, second plunger plate is slidably fitted around the outer periphery of the first plunger plate at its front end, and a second spring having a greater resilience than the first spring is disposed between the second plunger plate and the valve plunger, so that in the inoperative condition of the brake booster, the front end face of the second plunger plate is located rearward of the front end face of the first plunger plate, such that as the brake booster is actuated, in a region of a smaller depression of the brake pedal, the reaction disc is brought into abutment against the front end face of the first plunger plate to allow a reaction acting upon the output shaft to be transmitted to the valve plunger through the first plunger plate and the first spring and in a region of a greater depression of the brake pedal, the reaction disc is brought into abutment against the front end faces of the both plunger plates to allow a reaction which is acting upon the output shaft to be transmitted to the valve plunger through the both plungers and the first and the second spring.
With this arrangement, as the brake booster is actuated, a reaction which is acting upon the output shaft causes the reaction disc to bulge rearwardly, initially abutting against the front end face of the first plunger plate. An output rises with a greater booster ratio under this condition.
Subsequently, as the depression applied to the brake pedal increases to cause an increase in the reaction, the first spring is compressed, whereupon the reaction disc abuts against the second plunger plate also, in addition to against the first plunger plate. The output rises with a reduced booster ratio from this point on.
In a region where the output rises with a reduced booster ratio as mentioned above, or in a region where the depression applied to the brake pedal is greater, as the brake pedal is released from depression, the reaction disc operates in a manner such that a fluid circuit is switched by a valve mechanism which is mechanically coupled to the valve plunger, thus immediately causing a reduction in the output. However, because the second plunger plate and the valve plunger are mechanically coupled together through the second spring by this time, the input cannot be reduced until the reaction disc which has bulged rearward is restored forwardly. Accordingly, in a region where the output rises with a reduced booster ratio, it follows that the hysteresis is substantially null.
In this manner, a brake controllability can be improved in a region of a greater depression (or input) of the brake pedal.
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: 3548595 (1970-12-01), Pech et al.
patent: 5699713 (1997-12-01), Mortimer
patent: 5794506 (1998-08-01), Inoue et al.
patent: 7-8337 (1995-03-01), None
Flynn, Theil, Boutell & Tanis, P.C.
Jidosha Kiki Co. Ltd.
Lopez F. Daniel
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