Disc brake

A disc brake (10) is described, comprising a brake disc (12) and two brake shoes (20), which are pressable against both sides of the brake disc (12) and which in relation to a peripheral force (C′) generated upon application of the brake shoes (20) against the brake disc (12) are supported against a vehicle-fixed carrier (14). The disc brake (10) moreover comprises at least one device (34) for measuring and/or converting the peripheral force (C′), which device is disposed in a force transmission chain between the brake shoe (20) and the carrier (14). A force transmission member in the form of e.g. a swivel element (30) is disposed between the brake shoe (20) and the device (34) for measuring and/or converting the peripheral force (C′) and is movable under guidance parallel to the brake disc (12).

BACKGROUND OF THE INVENTION

The invention relates to a disc brake comprising a brake disc and two brake shoes, which are pressable against both sides of the brake disc and in relation to a peripheral force generated upon application of the brake shoes against the brake disc are supported against a vehicle-fixed carrier, and comprising at least one device for measuring and/or converting the peripheral force, which device is disposed in a force transmission chain between at least one of the brake shoes and the carrier.

Modern brake systems, for control and feedback control purposes, require an exact measurement of the forces occurring during a braking operation. Usually, these forces are subdivided into transverse forces (also known as normal forces or clamping forces) and peripheral forces (also known as frictional forces). The component of force introduced by a brake shoe into the brake disc at right angles to the plane of the brake disc is described as a transverse force. By peripheral force, on the other hand, is meant the component of force, which on account of the brake friction between a friction lining of the brake shoe and the brake disc acts in peripheral direction of the brake disc upon the brake shoe. By multiplying the peripheral force by the distance of the application point of the peripheral force from the axis of rotation of the wheels, the braking torque may be determined.

Many applications require an exact knowledge of the actual magnitude of the braking torque and hence also an exact knowledge of the peripheral force. For example, the braking torque may be used to form a precise closed-loop control circuit for electrohydraulic and electromotive brake systems.

In the case of the disc brake known from DE-GM 90 10 026, and corresponding U.S. Pat. No. 5,279,394, both of which are incorporated by reference herein, measurement of the peripheral force is effected by means of a force sensor, which is disposed on or in a guide pin. This guide pin is firmly connected to the initially mentioned, vehicle-fixed carrier and engages into a slide groove. The slide groove is formed on a structural part connected rigidly to one of the brake shoes and is displaceable in relation to the guide pin.

A further disc brake, which for measuring the peripheral force comprises a force sensor disposed in a force transmission chain between at least one of the brake shoes and a vehicle-fixed carrier, is known from DE 196 39 686, and corresponding U.S. Pat. No. 6,059,379, both of which are incorporated by reference herein. The force sensor is disposed on a fastening screw, by means of which a caliper of the disc brake is connected to the vehicle-fixed carrier.

It has been found that measurement of the peripheral force in the disc brakes known from prior art is prone to error because of various influences. These errors make it difficult to achieve precise control or feedback control of brake systems.

The underlying object of the invention is to indicate a disc brake, which allows a more exact determination of the peripheral forces that occur during a braking operation.

SUMMARY OF THE INVENTION

In a disc brake of the initially described type this object is achieved according to the invention in that between at least one of the brake shoes and the device for measuring and/or converting the peripheral force at least one force transmission member is disposed, which is movable under guidance parallel to the brake disc.

Such an arrangement of the force transmission member guarantees that a transverse force introduced by a brake shoe into the force transmission member acts, not upon the device for measuring and/or converting the peripheral force, but upon a guide provided for the force transmission member. The device for measuring and/or converting the peripheral force is consequently acted upon exclusively by the peripheral force and is able to measure and/or convert the peripheral force precisely. The transverse force, on the other hand, is “filtered out” by means of the force transmission member and does not influence the measurement and/or conversion of the peripheral force.

As already explained, the transverse force introduced by a brake shoe into the force transmission member is advantageously taken up by a guide provided for the force transmission member. The guide may take the form of a groove, rail, bearing for a bolt coupled to the force transmission member etc. In an advantageous manner, the guide of the force transmission member is coupled rigidly to the vehicle-fixed carrier. The effect achieved thereby is that the transverse force introduced into the guide may be taken up by the carrier.

The force transmission member may be guided parallel to the brake disc along different paths. It is, for example, conceivable for the force transmission member to be guided in a translatory manner, e.g. along a straight line, or rotary manner, e.g. along a circular path. Rotary guidance of the force transmission member is preferred. In said case a possible option is, for example, to design the force transmission member as a swivel element in the manner of a rocker. The swivel element preferably has a swivelling axis parallel to an axis of rotation of the brake disc and may be coupled to the carrier. If, on the other hand, the force transmission member is to be guided in a translatory manner, it may be provided e.g. in the form of a sliding element.

A force transmission member movable under guidance parallel to the brake disc may be disposed at a single side or at opposite sides of the brake disc. In the latter case, a total of two force transmission members are provided, wherein each force transmission member interacts with one brake shoe.

When two force transmission members are provided, a separate device for measuring and/or converting the peripheral force may be provided for each force transmission member. In said manner, the peripheral force may be separately measured and/or converted for the, in relation to the brake disc, vehicle-inner brake shoe and for the vehicle-outer brake shoe.

Two force transmission members disposed at opposite sides of the brake disc may be coupled to one another. This coupling is preferably designed in such a way that the forces, which are introduced in each case by the vehicle-inner and vehicle-outer brake shoe into the force transmission members, are combined, i.e. added together. In said case, it is sufficient to provide for the coupled force transmission members a common device for measuring and/or converting the peripheral force.

The coupling of the force transmission members disposed at opposite sides of the brake disc is preferably of a rigid design, e.g. in the manner of a bridge. Such a rigid coupling has the advantage that the brake shoes are stabilized relative to one another and markedly reduces the oblique wear of the friction linings.

The device for measuring and/or converting the peripheral force may be disposed in any desired manner, provided it is guaranteed that the device is disposed downstream of the force transmission member in the force transmission chain of the peripheral force from at least one of the brake shoes to the vehicle-fixed carrier. A possible option is to integrate the device into the force transmission member. This is effected e.g. in such a way that the force force transmission member acted upon by the peripheral force may be supported by means of the device against the vehicle-fixed carrier. On the vehicle-fixed carrier there may be formed, for said purpose, a stop for the force force transmission member equipped with the device for measuring and/or converting the peripheral force.

The device for measuring and/or converting the peripheral force may comprise a force sensor. The force sensor is designed e.g. as a piezoelectric element. Such a piezoelectric element may also be actively controlled in order, in the manner of an actuator, to generate a positive feedback so that guidance noises occurring during a braking operation are compensated. According to an alternative development, the device for measuring and/or converting the peripheral force comprises a force transducer and a sensor for detecting the converted force. The force transducer may be e.g. a force/pressure transducer, downstream of which a pressure sensor is functionally connected. A downstream pressure sensor may by virtue of a hydraulic connection be disposed remote from the brake, e.g. on the steering knuckle or shock-absorbing strut, so that it is not subject to the thermal load at the brake.

So that the forces occurring during a braking operation may be reliably introduced by the brake shoe into the force transmission member, a keyed connection may be established at least during a braking operation between the brake disc and the force transmission member. For this purpose, the force transmission member may be profiled at a region interacting with the at least one brake shoe, and the at least one brake shoe may have a complementary profiling. In an advantageous manner, the profiling of the brake shoe or the profiling of the force transmission member is designed in the manner of a groove, which extends parallel to the axis of rotation of the brake disc and into which a complementary profiling of the respective other element engages in a movable manner.

The disc brake according to the invention is suitable for use in a wide variety of brake systems. A use of the disc brake in electrohydraulic or electromotive vehicle brake systems is preferred. In such vehicle brake systems, the measured peripheral force is advantageously used for feedback control purposes.

DETAILED DESCRIPTION OF THE INVENTION

FIGS. 1 to 4show a first embodiment of a disc brake10according to the invention of a vehicle brake system. The disc brake10has a brake disc12, which during forward travel of the vehicle moves in the direction of the arrows A in the side view according toFIG. 2. The disc brake10is supported in a conventional manner on a brake carrier14, which is mounted in a vehicle-fixed manner, i.e. does not move in relation to the vehicle. A caliper16overlaps the brake disc12.

Two brake shoes18,20are disposed on both sides of the brake disc12and each have a friction lining22,24, which for braking purposes is pressable against the brake disc12. In the customary manner the friction linings22,24are fastened in each case on carrier plates26,28.

An actuation of the disc brake10results in the friction linings22,24being pressed in the direction of the arrows B, B′ against the brake disc12. The arrows B, B′ therefore symbolize the clamping or transverse force. The clamping force is generated in a manner known from prior art by means of an actuating mechanism, which is not illustrated in the drawings. The clamping action between the friction linings22,24of the clamping jaws18,20and the brake disc12generates a frictional force (peripheral force), which is denoted by the arrow C′ inFIG. 2for the brake shoe20. The brake shoe18, which is not shown inFIG. 2, is also acted upon by a corresponding peripheral force.

As is evident fromFIGS. 1 to 4, the forces generated during a braking operation are introduced in the direction of the arrow C′ and, in part, also in the direction of the arrows B, B′ into force transmission members30,32, which are supported against the vehicle-fixed carrier14in each case by means of a device34,36for measuring and/or converting the peripheral force. The vehicle-fixed carrier14is in turn rigidly connected to the vehicle by means of suitable fastening bolts40.

Each of the two force transmission members is designed as a swivel element30,32in the manner of a rocker. The swivel elements30,32are coupled in each case by means of a fastening bolt44,46pivotally to the carrier14. The swivelling axes of the swivel elements30,32defined by the bolts44,46extend parallel to the axis of rotation D (FIG. 2) of the brake disc12. The bolts44,46therefore allow a guided rotational movement of the swivel elements30,32parallel to the brake disc12, i.e. parallel to a plane containing the brake disc12.

As a result of the previously described mounting of the swivel elements30,32, the component of transverse force loading the swivel elements30,32in the direction of the arrows B, B′ (FIG. 1) is introduced by the swivel elements30,32via the bolts44,46into the carrier14. In contrast thereto, the component of peripheral force introduced in the direction of the arrow C′ (FIG. 2) into the swivel elements30,32is transmitted directly into the devices34,36for measuring and/or converting the peripheral force, which are supported against the carrier14. In other words, the fact that the swivel elements30,32are mounted in a manner that takes up transverse force guarantees that the forces introduced into the swivel elements30,32are cleared of transverse force when they act upon the devices34,36for measuring the peripheral force.

The carrier plates26,28interact in a positive manner with the swivel elements30,32. To said end, there is formed in each swivel element30,32a groove-shaped indentation50,52, which extends parallel to the axis of rotation D of the brake disc12and in which in each case a journal-like projection of the carrier plates26,28engages. InFIG. 3this is illustrated by the example of engagement of the journal-like projection54of the carrier plate28into the groove50of the swivel arm30.

The devices for measuring and/or converting the peripheral force, which are illustrated inFIGS. 2 to 4, are piezoceramic force sensors30,32, into which the peripheral force is introduced by means of the swivel elements30,32and which convert this peripheral force into an electric signal.

The electric signal produced by the force sensors34,36may be supplied by means of electric lines to an electronic control or feedback control system, which is not illustrated in the drawings.FIG. 3shows by way of example the electric line60of the force sensor34. The force sensors34,36in the present embodiment are integrated into the carrier14. It might however also conceivable to integrate the force sensors34,36into the swivel element30,32. It would also in principle be conceivable to dispose additional elements workingly between the force transmission members in the form of the swivel elements30,32and the devices for measuring and/or converting the peripheral force in the form of the force sensors34,36or between these devices and the carrier14.

In the first embodiment of a disc brake according to the invention described with reference toFIGS. 1 to 4, the force transmission members and the devices for measuring and/or converting the peripheral force are disposed in such a way that the forces arising during braking of a forward motion of the vehicle may be measured. It is however also possible, in addition to or instead of the forces arising during braking of a forward motion, to measure and/or convert the forces arising during braking of a reverse motion. Thus, in addition to the device for measuring and/or converting the peripheral force disposed at the right side of the carrier plate28inFIG. 2and to the force transmission member, such components might also be provided at the opposite side of the carrier plate28.

In the disc brake10according to the first embodiment, which is illustrated inFIGS. 1 to 4, the two swivel elements30,32are not coupled to one another. For this reason, the two force sensors34,36measure the peripheral force for the vehicle-inner brake shoe18and the vehicle-outer brake shoe20(FIG. 1) separately. According to the second embodiment of a disc brake according to the invention, which is illustrated inFIGS. 5 and 6, the peripheral force for the two brake shoes18and20is measured by means of only a single force sensor34.

The disc brake according to the second embodiment, details of which are illustrated inFIGS. 5 and 6, corresponds substantially to the disc brake of the first embodiment. In a departure from the first embodiment, however, in the disc brake according to the second embodiment the swivel elements30,32disposed at opposite sides of the brake disc12are bridged by means of a central portion62and therefore rigidly coupled to one another (FIG. 6). The single force sensor34is disposed in the region of this central portion62bridging the two swivel elements30,32.

InFIGS. 5 and 6the force sensor34has been offset relative to its position in the first embodiment (seeFIGS. 3 and 4) upwards in the direction of the bridging portion62. As a result, the point of application of the force denoted by the arrow C′ on the swivel arm30no longer lies on one and the same horizontal straight line as the point of application of the counterforce symbolized by the arrow E (cf.FIG. 3).

The effect of the bridging62of the two swivel elements30,32, which is illustrated inFIGS. 5 and 6, is a summing of the peripheral forces acting upon the two brake shoes18,20. A further effect of the bridging62of the two swivel elements30,32is a stabilizing of the brake shoes18,20relative to one another and hence a reduction of the oblique wear of the friction linings22,24.

FIGS. 7 and 8show details of a third embodiment of a disc brake according to the invention. The disc brake according to the third embodiment is similar to the disc brake of the second embodiment. Once again, a common device70for measuring and/or converting the peripheral force is provided, so that this device70determines the sum of the peripheral force caused by the vehicle-inner and the vehicle-outer brake shoe.

The device70for measuring and/or converting the peripheral force comprises two subassemblies, namely a force/pressure transducer72, on the one hand, and a pressure sensor74, on the other hand. The force/pressure transducer72comprises a cylindrical bore76, which is formed in the carrier14and in which a piston78comprising a piston head80and a piston rod82is displaceably guided. The cylindrical bore76is closed at the rear, i.e. at its end remote from the piston head80, by an insert84. Inside the cylindrical bore76a hollow-cylindrical guide86permeable to a liquid medium is formed for the piston rod82and a liquid medium, e.g. oil, is disposed. The cylindrical bore76is connected to two liquid lines90,92, which penetrate the carrier14. The cylindrical bore76is connected by the first liquid line90to a supply system for the liquid and by the second liquid line92to the pressure sensor74. The function of the device70for measuring and/or converting the peripheral force is described in greater detail further below.

The disc brake according to the third embodiment comprises two force transmission members movable under guidance parallel to the brake disc, namely, on the one hand, a swivel element32coupled to the carrier14and, on the other hand, a plate-shaped force transmission member94, which is coupled to the piston head80. This coupling of the plate-shaped force transmission member94to the piston78guarantees a guided movement of the plate-shaped force transmission member94parallel to the brake disc because of the interaction of the piston rod82with the guide86provided for the piston rod82and the interaction of the piston head80with the inner wall of the cylindrical bore76. Because of this translatory guidance of the plate-shaped force transmission member94, a transverse force introduced into the force transmission member94is transmitted by means of the piston78to the vehicle-fixed carrier14. The peripheral force introduced into the plate-shaped force transmission member94, on the other hand, effects a displacement of the piston78to the right inFIG. 7. Because of this displacement of the piston78the liquid medium disposed in the region of the cylindrical bore76is compressed, and the pressure inside the cylindrical bore76rises. This pressure rise proportional to the peripheral force is detected by the pressure sensor74and supplied by means of electric lines60as an electric signal to an electronic control or feedback control system, which is not illustrated in the drawings.

Forces are introduced into the plate-shaped force transmission member94not only by the brake shoe associated with this force transmission member94but also by a second brake shoe lying, in relation to the brake disc, opposite this first brake shoe, and are introduced namely by means of a transmission arrangement98. The transmission arrangement98comprises a transmission element in the form of a swivel element32, which is associated with the second brake shoe, a bearing bolt44penetrating the carrier14parallel to the axis of rotation of the brake disc, and an arm100interacting with the plate-shaped force transmission member94. Both the swivel element32and the arm100are connected by means of laser welding to the bolt44and disposed at right angles thereto.

A transverse force acting upon the swivel element32is introduced via the bolt44, which is rigidly coupled to the swivel element32, into the carrier14. A peripheral force introduced into the swivel element32, on the other hand, is transmitted by means of the bolt44to the arm100and from the latter to the plate-shaped force transmission member94. The transmission arrangement98therefore allows a coupling of swivel element32and plate-shaped force transmission member94.