Motors: expansible chamber type – Working member position feedback to motive fluid control – Plural input signal means for single motor valve
Reexamination Certificate
2002-06-13
2004-03-16
Look, Edward K. (Department: 3745)
Motors: expansible chamber type
Working member position feedback to motive fluid control
Plural input signal means for single motor valve
Reexamination Certificate
active
06705200
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to vacuum brake boosters having a vacuum chamber and a working chamber separated from one another in a pressure-proof manner by a movable wall, having a control valve, which comprises a housing workingly coupled to the movable wall and containing a valve seat, which to achieve a pressure difference at the movable wall is capable of controlling the supply of atmospheric pressure or above-atmospheric pressure to the working chamber in dependence upon the displacement of an input element of the brake booster, as well as having an emergency braking aid comprising a permanent magnet and an armature, which cooperates with the permanent magnet and is spring-biased counter to the actuating direction and in the event of an emergency braking operation is pulled into abutment with the permanent magnet, with the result that the control valve is opened for the supply of atmospheric pressure or above-atmospheric pressure to the working chamber.
Vacuum brake boosters have been known for some time and millions of them are in use for boosting the actuating forces of a vehicle hydraulic brake system and therefore keeping them at a comfortably low level for the driver of a vehicle.
Also known are so-called brake assists. By said term is usually meant a system, which in the event of an emergency braking operation for substantially the same actuating force may provide a driver with an increased braking power. Systems of said type were developed because studies have shown that the majority of vehicle users during an emergency braking operation do not press as hard on the brake pedal as would be necessary to achieve the maximum braking power. The stopping distance of the vehicle is therefore longer than necessary.
Systems of said type already in production employ an electromagnetically actuable brake booster in conjunction with a device capable of determining the actuating speed of the brake pedal. If said device detects an actuating speed above a defined threshold value, it is assumed that an emergency braking situation exists and the brake booster is set to saturation point by the electromagnetic actuating device, i.e. the brake booster supplies its maximum boosting power.
Brake boosters with an electromagnetic actuating facility are however too expensive for motor vehicles in the low to medium price category. There was therefore a demand for solutions, which achieve a brake assist function with a lower outlay.
An, in said respect, improved vacuum brake booster with brake assist function is known from JP 175 373 A. The known vacuum brake booster has a vacuum chamber and a working chamber separated in a pressure-proof manner from one another by a movable wall. A control valve, which has a housing workingly coupled to the movable wall, has an atmosphere valve seat, which is rigidly connected to the housing and which to achieve a pressure difference at the movable wall is capable of controlling the supply of atmospheric pressure to the working chamber in dependence upon the displacement of an input element of the brake booster. For improved braking force assistance during emergency braking operations, an armature cooperating with a permanent magnet is provided in the control valve housing and is coupled in actuating direction rigidly to the actuating element. The armature is spring-biased counter to actuating direction and in the normal position of the control valve is held at a first distance from the permanent magnet. In the course of an approach towards the permanent magnet the armature, when it is less than a previously defined second distance away, which is smaller than the first distance, is pulled by the permanent magnet counter to the spring bias acting on the armature and with simultaneous cancellation of an, in actuating direction, rigid coupling to the actuating element into abutment with the permanent magnet.
The armature substantially takes the form of a hollow cylinder, on the opposite ends of which radially outwardly projecting flanges are disposed. The flange facing the permanent magnet is pulled into abutment with the permanent magnet upon undershooting of the second distance. The flange of the armature remote from the permanent magnet has at its greatest diameter a vacuum valve seat. The permanent magnet is fastened in a mounting, which is connected counter to the actuating direction of the actuating element rigidly to the control valve housing.
In the case of the vacuum brake booster known from JP 175 373 A it was discovered that, in order to achieve a uniform performance of the brake assist, the components configuring the emergency braking aid should have only extremely narrow component tolerances. Otherwise, it is in particular impossible to guarantee the tripping threshold of the brake assist with the required constancy. The close component tolerances of the brake assist resulting from said requirement make mass production difficult and add to the cost of manufacture of the vacuum brake booster.
SUMMARY OF THE INVENTION
The object of the invention is to provide a vacuum brake booster of the described type with a mechanical brake assist, which despite generous component tolerances makes it possible to guarantee a uniform performance of the vacuum brake booster.
Said object is achieved according to the invention by a vacuum brake booster having the features indicated in claim
1
. The sub-claims relate to advantageous refinements and developments of the invention.
According to the invention it is proposed, for adjusting the distance between the armature and the permanent magnet particularly in the non-actuated state of the vacuum brake booster, to make the axial position of the permanent magnet relative to the control valve housing and/or the distance between the armature and the valve seat adjustable. This has the advantage that all of the components of the vacuum brake booster and, in particular, the components of the brake assist may be manufactured with generous component tolerances. According to the invention, the purposeful adjustment of the distance between armature and permanent magnet is not effected until during or after assembly of the vacuum brake booster.
The adjustment of the distance between the armature and the permanent magnet may be realized in various ways. If, for example, armature and valve seat are of an integral construction, the axial position of the permanent magnet relative to the housing may be adjusted. If, on the other hand, the axial position of the permanent magnet relative to the housing is permanently defined, then armature and valve seat may be provided in the form of separate components, which are connected to one another at a defined maximum distance from one another. Naturally, it is also possible to combine said options for adjusting the distance between the armature and the permanent magnet.
If armature and valve seat are provided in the form of separate components, a defined distance between said two components may be realized in various ways. For example, a distance element may be disposed between armature and valve seat. A set of distance elements of different defined lengths may then be provided and during assembly of the vacuum brake booster, depending on the desired distance between armature and valve seat, the appropriate distance element may be selected and disposed between armature and valve seat. An alternative form of construction provides that deformable standard distance elements are provided, which in accordance with the desired distance between armature and valve seat are reshaped to the required dimension prior to assembly of the vacuum brake booster. The reshaped distance element is then disposed between the armature and the valve seat.
A defined distance between armature and valve seat may also be realized in that armature and valve seat have mutually complementary threads. During assembly of the vacuum brake booster a screw connection is therefore established between the armature and the valve seat, wherein by means of the length of the screw connection the distance between
Possmann Michael
Schlüter Peter
Leslie Michael
Look Edward K.
Lucas Varity GmbH
MacMillan Sobanski & Todd LLC
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