Motors: expansible chamber type – Working member position feedback to motive fluid control – Follower type
Reexamination Certificate
2000-02-18
2001-04-10
Lopez, F. Daniel (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Follower type
Reexamination Certificate
active
06212993
ABSTRACT:
The invention relates to a vacuum brake booster for a hydraulic vehicle braking system. A vacuum brake booster of this type is known from EP-B-0 173 333.
BACKGROUND OF THE INVENTION
Brake boosters of said type are nowadays employed as large-scale production products for the amplification of the actuation force which is applied by the driver of a vehicle to the brake pedal during a braking operation. An input member of the brake booster, which is connected to the brake pedal, transmits the actuation force applied by the driver to the brake booster which amplifies said force and supplies it via an output member to a downstream master cylinder which is connected to the brake booster.
The brake booster is to respond as directly as possible to a variation of the actuation force exerted by the driver and correspondingly increase or decrease, respectively, the force assistance. This means that the air volume which is required for venting the working chamber of the brake booster must be supplied as rapidly as possible. Due to the rapidly incoming air undesired noise may occur, and it is known to reduce this noise to an extent which no longer constitutes a disturbance by means of sound-absorbing material, for example in the form of a sound-absorbing liner (see also DE-B-29 18 734).
SUMMARY OF THE INVENTION
The invention is based on the object to provide a vacuum brake booster the working chamber of which can be vented as rapidly as possible without being provided with sound-absorbing material and without the occurrence of disturbing noise.
According to the invention, the vent duct in the control valve housing is therefore not used to mechanically limit the stroke of the sensing piston which is displaced by the input member, as is common in the state of the art, but rather at least the edge of the slot provided in the guide sleeve for the sensing piston which is closer to the master cylinder is used as a stop for the stop bar. This enables the vent duct to have a significantly larger axial extension in that area where the stop bar protrudes through the slot of the guide sleeve into the vent duct as compared to the axial extension of the slot. In one embodiment of a brake booster according to the invention, the stop for the stop bar, which determines the rest position of the sensing piston, i.e. the position which the sensing piston assumes when the brake booster is not actuated, is formed by an inner shoulder of the brake booster housing. When the brake booster is actuated, however, the axial extension of the slot in the guide sleeve defines the maximum possible stroke of the sensing piston in that the, in the axial direction, front and rear edges of the slot form one stop each for the stop bar which is securely connected to the sensing piston and protrudes through the slot.
According to the invention, the vent duct thus no longer fulfils a mechanical stop function but only serves to route the air and can therefore be better optimised in this respect. In particular, the cross-section of the vent duct in that area into which the stop bar protrudes is selected much larger than hitherto usual which reduces the flow rate and thus the noise generation during the flow. In addition, the larger axial dimension of the vent duct in the mentioned area makes it possible to orient this area of the vent duct obliquely towards the working chamber, which results in a less defined deflection of the air flowing in coaxially with the input member and, as a consequence thereof, in a less defined whirling as well as simultaneously in the generation of less noise. The above-mentioned measures also provide for a discernible reduction of the pressure loss of the vent duct which leads to an improved flow through same and thus to an improved response of the brake booster to variations of the actuating force.
In a preferred embodiment of the brake booster according to the invention the control valve housing is made of plastic material and the guide sleeve is made of metal. A control valve housing made of plastic material can be manufactured economically, for example by injection moulding, while the guide sleeve made of metal as an insert of simple design for receiving the sensing piston ensures the required good dimensional accuracy and a high wear resistance. Advantageously, the guide sleeve comprises a collar which is oriented essentially radially outwardly, by means of which the guide sleeve is anchored in the control valve housing. It is particularly advantageous to have this collar coated with plastic material which can easily be achieved by inserting the guide sleeve into the mould for the control valve housing at an appropriate location prior to injection moulding. Alternatively, the collar can be adhered to, melted with the control valve housing, or attached to same in another manner.
In order to further improve the flow through the vent duct, according to a preferred embodiment of the brake booster according to the invention, an essentially funnel-shaped narrowing air guiding element is arranged coaxially with the input member in the air inlet area of the vent duct, which element bears upon a shoulder of the input member. The support of the air guiding element on a shoulder of the input member renders a separate support unnecessary. The air guiding element directs the air flowing into the vent duct to the valve seats of the control valve and thus prevents unnecessary deflections; of the air stream with the resulting eddy and noise generation.
In a constructively advantageous manner the air guiding element is urged by a spring against the shoulder formed at the input member and is thus securely positioned, which spring simultaneously serves to return the input member to the initial position after termination of a brake booster actuation.
In one embodiment the air guiding element is penetrated by a series of flow openings which taper conically in the flow direction and extend obliquely towards the main axis (centre longitudinal axis) of the brake booster. The flow openings are arranged equidistantly to each other in the circumferential direction of the air guiding element. Such a configuration of the air guiding element offers, while providing high stability, a large flow cross-section and thus a relatively low flow resistance.
REFERENCES:
patent: 4350076 (1982-09-01), Thiel
patent: 4718326 (1988-01-01), Sugiura et al.
patent: 5564326 (1996-10-01), Gautier et al.
patent: 2918734 C2 (1989-11-01), None
patent: 9005629 U 1 (1990-05-01), None
patent: 3924672 (1991-01-01), None
patent: 173338 B1 (1988-03-01), None
patent: 2258022 (1993-01-01), None
Lopez F. Daniel
Lucas Industries Public Limited Company
MacMillan Sobanski & Todd LLC
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