Brake force transmission device for a brake force amplifier

[0001] The present invention relates to a brake force transmission device for a brake force booster with an elastic reaction element, an input member with an associated effective surface, an output member with an associated effective surface, and with a first transmission ratio defined by a ratio of the effective surfaces being in operative engagement with the reaction element.

[0002] Japanese utility model Sho 61-205858 e.g. discloses a transmission device of this type. The transmission device comprises a resiliently preloaded, moveable pressure member (38b) arranged on an inlet side (or an outlet side) and causing an abrupt increase of the boosting ratio due to a change of the surface ratio on the inlet side (or on the outlet side), with an input force predetermined.

[0003] In view of the above, the present invention is based on a transmission device of the type to be taken from the preamble of claim 1. It is an object of the invention to provide a transmission device that has a particularly small overall size and is easy to integrate into a standard type of brake force booster. Consequently, an objective is to permit employing the transmission device as desired also in already existing brake force boosters, without necessitating costly new constructions or modifications.

[0004] This object is achieved by the combination of features to be taken from the characterizing portion of claim 1.

[0005] In the solution of claim 1, the invention principally involves that deformation of the reaction element displaces the switching ring in opposition to the force of the spring towards the input member until the surface of the reaction element reacting on the control housing is increased by the annular surface of the switching ring. The result is a smaller effective surface at the input and, thus, also an increase of the transmission ratio of forces. More specifically, this means that after the switching ring has moved into abutment on the control housing, the reaction of the output member applied to the input member is reduced. Thus, the driver can reach the same braking effect, with a reduced pedal force.

[0006] A particularly simple design for the transmission device is achieved in an improvement of the invention by the combination of features of claim 2. The spring assembly may have a very simple design, as will be explained in the following. Further, the spring assembly may form a closed construction unit that is integrally inserted into the control housing when the brake force booster is assembled. The same applies to the switching ring that may be connected integrally to the spring assembly, yet forms a separate unit in an advantageous manner. The advantage of these measures in particular resides in the fact that both the spring assembly and the switching ring may be kept on stock in different types, and the control housing may then be equipped with them depending on the requirement and the desired course of boosting.

[0007] In a favorable improvement of the invention, it is advisable to use the features indicated in claim 3 with respect to the spring assembly. Essentially, the spring assembly may have a symmetrical design. It is only important in this regard that the two retaining elements can be displaced relative to each other in opposition to the force of the spring. Further, the stop element ensures that the two retaining elements are combined in a unit and none of the retaining elements can get lost. Besides, it is possible to clearly define the force with which the two retaining elements are preloaded towards each other by selecting the spring and the distance between the two retaining elements.

[0008] In accordance with the combination of features as in claim 4, the first retaining element can make catch directly on the reaction element by way of a projection that reaches through the second retaining element. It is, however, also feasible that the first retaining element acts on the reaction element only indirectly by way of a pressure member. This is advantageous inasmuch as the pressure member may be chosen corresponding to the variation of the desired amplification. As it is also possible to select the switching ring that can be inserted separately, as has been explained hereinabove, the combination of the switching ring and a pressure member permits largely varying the course of the characteristic curve of amplification. Thus, the boosting performance of the brake force booster can be adapted to a great extent to the respective requirements by the selection of the switching ring, the pressure member, and the spring element in dependence on the input force. It is also favorable that the mentioned elements may be retrofitted and thus allow an adaptation of the booster already in series production.

[0009] The features according to claim 5 describe as an improvement of the invention a particularly simple possibility of guiding the switching ring within the housing. In this arrangement, the switching ring with its inside surface may be guided both by way of the outside surface of the projection and by way of its outside peripheral surface on the inside peripheral surface of a projection on the control housing. However, only guiding of the switching ring on its outside peripheral surface is possible for the case that the first retaining element makes catch at the reaction element only indirectly by way of a pressure member.

[0010] In accordance with the combination of features in claim 6 it may be advisable that the switching ring abuts on the control housing and, thus, changes the characteristic curve of amplification. The features disclosed in claim 11 permit achieving a still simplified construction. In this arrangement, the switching ring does not abut directly on the control housing but indirectly by way of the second retaining element on which it is acting. This permits a very simple configuration of the switching ring, hence, it is made of a simple cylindrical ring. Further, a large stop surface may be achieved in a very simple fashion by the design according to claim 11 because the second retaining element anyway must have a sufficiently large extension in a radial direction for accommodating a sufficiently large spring.

[0011] The combination of features of claim 7 also permits achieving a simplified manufacture. Because the fixed ring may additionally be used as a guide for the switching ring, the strength of the switching ring and thus the course of the characteristic curve of the amplification may be influenced by correspondingly dimensioning the inside recess of the fixed ring and the outside diameter of the switching ring.

[0012] The provisions in claim 8 allow achieving further simplification for the design of the transmission device of the invention. The control housing serves for axially guiding the second retaining element and additionally as a stop. Thus, the walls of the guiding grooves are utilized twice because they are used for guiding in a longitudinal direction and as a stop.

[0013] To achieve a sufficient degree of spring force despite small dimensions, the combination of features as disclosed in claim 9 is advisable in an improvement of the invention. The spring may influence the course of the characteristic curve of amplification by a corresponding selection of the characteristic curve of the spring. The projection may be integrally connected directly to the first retaining element corresponding to the features of claim 10. The retaining element may also be riveted to the projection for saving material and for the suitable combination of construction materials.

[0014] It is an important aspect for the invention that it is integrated into a controlled brake system in an especially appropriate manner, as is explained in connection with claim 11. This applies in particular when in the controlled brake system the distribution of the brake forces to the individual wheels or wheel groups is controlled in dependence on the slip at the respective wheel or the wheels. It is thereby rendered possible with low effort that a sufficiently high amount of brake pressure can be generated even if a driver actuates the brake with a too weak depression of the pedal. On the other hand, the controlled distribution of brake forces ensures that the vehicle will not leave track as a result of slip on one or more wheels.

[0015] The advantage of the invention is basically due to the following facts. The present function principle essentially and simply relates to a biased spring that is interposed between the valve piston and the piston in an axial function. Functionally required stops are provided, with a direct transmission being ensured when the booster is operated. The preferred constructive features are as follows: There is provision of a compression spring that is captivated in a straightforward fashion, and a very simply designed spring element is used. The control housing includes a fixed ring that is configured very simply as a disc taking up force. This fixed ring can move to abut on the end surface of a stepped bore in the control housing, with grooves being indented into the wall of the stepped bore that serve for guiding and as a stop at the same time. In other words, the following features are especially important in the construction described herein.

[0016] The present function principle is basically and simply related to a preloaded spring that is interposed between the valve piston and the annular piston in an axial function, with some functionally induced stops, with a direct force transmission being ensured during operation. Construction features to be especially emphasized are the straightforwardly captivated compression spring(s) (5), an inexpensive force-transmission member. A control housing area (4) behind the disc (1) taking up forces receives multi-functionally the forces of the switching ring (2) and additionally serves for guiding a stop plate as second retaining element (6) with stop. The stop plate (6) biases the spring, conducts the reaction forces of the annular piston (2) to the spring, represents the stop of the annular piston as well as a transmission member during operation.

[0017] The invention is especially efficient in connection with an electronically controlled brake force distribution because in the event of failure of the ABS (anti-lock system) usually also the electronic brake force distribution (EDB) will fail. In this case, the driver can still properly dose the brake pressure in the steep branch of the booster characteristic curve. This is in contrast to systems with a panic braking function such as a brake assistant (BA) or mechanical brake assistant (MBA) which are considerably more difficult to master during change-over to an infinite (steep) characteristic curve of brake force boosting.

[0018] Two embodiments of the present invention will be explained in the following by way of the accompanying drawings. In the drawings,

[0019]
FIG. 1 shows a first embodiment of a transmission device of the invention in cross-section and a broken-out illustration.

[0020]
FIG. 2 is a broken-out cross-sectional view of the embodiment of FIG. 1 at the level of the line of intersection A-A in FIG. 1.

[0021]
FIG. 3 shows a second embodiment of the invention.

[0022] The design and the function of the transmission device 1 will be described in detail in the following, and the basic function of a brake force booster as disclosed exemplarily in PCT/EP98/07314 is assumed as being known.

[0023] In an idealized view, brake force boosters principally known in the art have a constant transmission ratio over the entire operating range up to the so-called point of maximum boosting, with the produced output force (pedal force and boosting force) rising linearly above the input force (pedal force). In principle, the transmission ratio essentially influencing the pedal feeling of the driver is defined by the ratio of the effective surface (d4) associated with the output member to the effective surface (d3) associated with the input member. For greater braking effects, that means, at a higher brake force level, it is considered positive to support the driver to a stronger degree. More specifically, a higher transmission ratio is caused, as can be taken e.g. from JP-Sho-61-205858.

[0024] In addition to other parts to be assigned to the brake force booster, which do not have any major influence and therefore will not be described in the following, a transmission device 20 of the invention comprises an input member 22 with a valve piston 23, said input member being movably arranged in a control housing 8 with a first sealing seat 21, as well as an output member 24 for actuating a master brake cylinder (not shown). Interposed between the input member 22 and the output member 24 is a preferably disc-shaped elastic element 7 which is made of plastic material or rubber material and is encompassed on all sides by surfaces of parts of the transmission device 20, in other words, is quasi encapsulated between movable walls. When pressurized the elastic reaction element 7 behaves like an incompressible fluid according to the laws of constancy of volume and acts quasi as a mediator between the pedal forces introduced by way of the input member 22 and the brake reaction forces which are fed back from the vehicle brake system to the vehicle operator. Consequently, balanced forces prevail at the reaction element 7 in each position of brake actuation.

[0025] The reaction element 7 is seated in a bowl 25 that is open to the left in FIG. 1 and is formed by a first bore 26 in control housing 8 and a fixed ring 1 that is supported at edge 28 of a second bore 27 of the control housing 8. The bowl has an inlet opening 29, wherein the front end of the output member 24 in the drawing is guided. Said output member 24 at its right-hand end in FIG. 1 passes over into a plate 10 that closes the bowl 25 and bears against the wall of the reaction element 7 that points to the left in FIG. 1. Towards the right hand, the reaction element 7 is supported on the fixed ring 1 which, in turn, abuts on the circumferential edge 28 or step between the first bore 26 and the second bore 27. The surface for the plate 10 is indicated by value d4. The fixed ring 1 has an opening inside that is indicated by the value d3 as area of the opening. In opening (d3) a switching ring 2 is guided which is moveable relative to the fixed ring 1 in the longitudinal direction of the booster. A spring element is composed of a first retaining element 3, a second retaining element 6 and a spring 5. Said spring 5 preloads the two retaining elements 3 and 6 in relation to each other so that they can only be displaced against each other with a defined force. The maximum distance of the two retaining elements is determined by a stop 12 that is arranged at a projection 13 of the first retaining element 3.

[0026] The first retaining element 3 is furnished with projection 13 which can be configured as one single continuous piece along with the retaining element. However, it is also suitable to design the projection 13 as a rivet part, as illustrated in FIG. 1. To this end, the rivet part may be made of a material with appropriate strength, while the first retaining element 3 is made of a formable metal sheet. At the end of the rivet part 13, stop 12 is provided that is configured as a circumferential nose. It is ensured by this stop that the second retaining element 6 can move only a predetermined distance away from the first retaining element 3. The projection 13 may project until into the interior of the switching ring 2. As in the present embodiment, however, the rivet part 13 may also be succeeded by a pressure member 31, which extends through the switching ring 2 and acts on the reaction element 7.

[0027] Guiding the second retaining element 6 in the control housing 8 is important for the present invention. This guiding arrangement is effected by means of guiding grooves 4 which are machined into the inside peripheral surface of the second bore 27, distributed over the periphery of said bore. For guiding purposes, the second retaining element 6 includes correspondingly designed guiding projections 15 that engage into the grooves 4, as shown in FIG. 2. An end wall 11 in each groove forms a stop for the guiding projections 15 so that when the guiding projections 15 abut on the respective end wall 11, a force directed to the right to the second retaining element 6 in FIG. 1 is taken up by the control housing 8. All other components illustrated in FIG. 1 are not essential for the present invention and will not be described more closely herein.

[0028] The mode of operation according to the embodiment of FIG. 1 is as follows. When the input member 22 in FIG. 1 is displaced to the left in the position shown in FIG. 1, the pressure member 31 and the switching ring 2 will make catch at the reaction element 7. This renders a surface d3 active at the reaction element 7, while the reaction element 7 acts with surface d4 towards the output member 24. The ratio of these two surfaces defines the boosting ratio of the booster in this operating condition. The switching ring and pressure member 31 then move together in parallel because the spring 5 is so stiff that it will not yield to the input force acting on the input member 22 in this area.

[0029] With rising input force, the force exerted by the output member 24 and acting in the direction of the inlet will increase, with the proportionate force acting on the switching ring 2 rising as well. Said proportionate force finally becomes so high that the second retaining element 6 is lifted from stop 12 by the force applied by the switching ring 2 because the spring 5 starts to give way. Thus, the switching ring 2 displaces in relation to pressure member 31 to the right in FIG. 1. This displacement continues with rising input force until the guiding projections 15 finally come to bear against the associated end wall 11. As this occurs, the spring 5 is compressed and correspondingly shortened. Upon further rise of the input force, the additional forces acting on the switching ring 2 in the direction of the input are only taken up by the end wall 11 and, hence, by the control housing 8. Starting from this time, only surface d2 acts as a reactive force of the reaction element 7 on input member 22. The amplification of the booster dependent on the effective surfaces is thus the result of the ratio of surface d4 to surface d2. An abrupt increase of the boosting effect of the booster is achieved by abutment of the guiding projections 15 on the end wall 11.

[0030] The operations described will be carried out in reverse direction with declining input force. The pressure member 13 moves in relation to the fixed switching ring 2 in FIG. 1 so far to the right until finally spring 5 will displace the switching ring 2 to the left away from the end wall 11 by way of the second retaining element 6. Thus, the switching ring 2 acts in the direction of the input again and transmits a corresponding counterforce onto the input member 22 by way of spring 5. As a result, the boosting ratio has decreased by an amount corresponding to the growth of the reactive force.

[0031] The second embodiment shown in FIG. 3 is only slightly modified compared to the embodiment of FIG. 1. The basic difference is that instead of one spring 5 two parallel connected springs 5 and 32 are used. The internally seated second spring 32 has a lower spring constant compared to first spring 5. This way, a higher spring force that is more precise to proportion can be adjusted in the same space.

Number	Date	Country	Kind
101 07 57.1	Feb 2001	DE
101 44 619.5	Sep 2001	DE

Brake force transmission device for a brake force amplifier

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