Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
1998-10-06
2001-03-27
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
Reexamination Certificate
active
06205905
ABSTRACT:
FIELD OF THE INVNETION
The invention relates to a brake booster, and more particularly, to a brake booster which is provided with reaction transmitting means including a spring.
DESCRIPTION OF THE PRIOR ART
A brake booster is known in the art which exhibits a reduced servo ratio during the initial phase of the braking operation of the brake booster and exhibits an increased servo ratio during a later phase of the braking operation.
In a brake booster of the kind described, reaction transmitting means is interposed between a reaction disc and a valve plunger, and comprises 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 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 being spaced apart beyond a given spacing (Japanese Lead-Open Patent Application No. 85,442/1996).
With this construction, when a brake pedal is depressed to actuate 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 within the reaction transmitting means is compressed, whereby the prevailing servo ratio can be maintained relatively low. This improves the maneuverability in a range where a braking force of a reduced magnitude is required.
On the other hand, when the spring within the reaction transmitting means is compressed, the second retainer and the valve plunger will be advanced relative to the first retainer and the plate plunger by an amount corresponding to the compression of the spring, and accordingly, this is equivalent to a further depression of the brake pedal by an amount corresponding to the compression of the spring. The prevailing servo ratio can be chosen relatively high, thereby allowing a braking force of an increased magnitude to be obtained with a reduced force of depression.
Because the reaction disc comprises a viscoelastic member such as rubber, the brake booster incorporating the reaction disc exhibits a hysteresis, a phenomenon that the magnitude of an output from the brake booster becomes different upon depression and upon release of the brake pedal if the force with which the brake pedal is depressed is maintained same.
In the presence of the hysteresis, if a driver unconsciously decreases the force of depression slightly after he has ceased to increase the force with which the brake pedal is depressed, a braking force of the same magnitude is maintained, bringing forth an advantage that the brake feeling is improved.
However, in the brake booster which is provided with the reaction transmitting means, when the spring within the reaction transmitting means is compressed, a flow path switching action takes place within the valve mechanism of the brake booster as the spring changes its length, whereby the hysteresis caused by the reaction disc is accommodated by the spring, resulting in the magnitude of an output from the brake booster which remains substantially equal upon depression and upon release of the brake pedal.
As a consequence, if a driver unconsciously decreases the force of depression slightly after he has ceased to increase the force with which the brake pedal is depressed, the braking force will be immediately reduced, and a driver then feels as if the brake is ineffective, thus disadvantageously degrading the brake feeling.
SUMMARY OF THE INVENTION
In view of the foregoing, the invention provides a brake booster which is provided with reaction transmitting means including a spring, but which is capable of maintaining a brake feeling in good condition.
Thus, the invention relates to a brake booster including a valve body slidably disposed within a shell, a valve mechanism disposed within the valve body, an input shaft for driving 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 mounted 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. In accordance with the invention, the reaction transmitting means includes a first and a second reaction transmitting path disposed in parallel for transmitting a brake reaction from the reaction disc to the valve plunger, the first reaction transmitting path including a spring charged to a preset load so that the brake reaction from the reaction disc is transmitted through the spring to the valve plunger while the second reaction transmitting path includes a viscoelastic member so that the brake reaction from the reaction disc is transmitted to the valve plunger through the viscoelastic member.
With the described construction, when the pedal is depressed to actuate the brake booster, the servo ratio can be maintained relatively low in the similar manner as in the prior art until the spring within the reaction transmitting means becomes compressed.
At this time, since the valve plunger causes a compression of the reaction disc through the reaction transmitting means and moves forward, the reaction disc is effective to produce a hysteresis which provides an output from the brake booster of a differing magnitude upon depression and upon release of the brake pedal.
On the other hand, as the spring within the reaction transmitting means becomes compressed, the valve plunger will be advanced relative to the valve plunger by an amount corresponding to the compression of the spring, equivalently resulting in an effect that the brake pedal is further depressed by an amount corresponding to the compression of the spring, thus increasing the servo ratio.
At this time, as the spring within the reaction transmitting means is compressed, the brake reaction from the reaction disc is transmitted to the valve plunger through the spring in the first reaction transmitting path while simultaneously the brake reaction from the reaction disc is transmitted to the valve plunger through the viscoelastic member in the second reaction transmitting path.
When the brake reaction acts upon the viscoelastic member in the second reaction transmitting path, the viscoelastic member is compressed in accordance with the magnitude of the brake reaction, whereby the viscoelastic member is effective to provide the hysteresis in the similar manner as the reaction disc.
As a consequence, the hysteresis is provided during an initial phase of operation of the brake booster which is prior to the commencement of the compression of the spring and during which the servo ratio is in a low range and during a later phase which is after the commencement of compression of the spring and during which the servo ratio is in a greater range, thus enabling the brake feeling to be maintained in good condition.
Above and other objects and advantages of the invention will become apparent from the following description of several embodiments of the invention with reference to the attached drawings.
REFERENCES:
patent: 5823089 (1998-10-01), Inoue et al.
patent: 5943937 (1999-09-01), Endo
patent: 8-85442 (1996-02-01), None
Konishi Masaru
Satoh Tohru
Shingyoji Shigeo
Watanabe Makoto
Flynn ,Thiel, Boutell & Tanis, P.C.
Jidosha Kiki Co. Ltd.
Lazo Thomas E.
Look Edward K.
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