Patent Application
20120198926
The invention relates to a measuring arrangement for measuring the application force of a disc brake. The invention also relates to a corresponding disc brake.
Disc brakes can have different measuring arrangements for measuring an application force, wherein for this purpose, for example, pressure sensors are used in a hydraulic brake. However, a disc brake on a vehicle is subject to relatively extreme operating conditions which can influence in different ways a measurement variable which correlates with the application force of the disc brake.
The object of the present invention is therefore to make available an improved measuring arrangement. A further object is to provide an improved corresponding disc brake.
This and other objects are achieved by a measuring arrangement, and a disc brake incorporating said measuring arrangement, for measuring the application force of a disc brake, comprising: two components of the disc brake which can be moved, in particular displaced, relative to one another along a displacement distance when an application force is applied; at least one application force sensor having a housing; a measuring object, which is one of the two components or can be permanently connected to one of the two components and comprises at least one metallic end face or at least one target object with at least one metallic end face for contactless interaction with the application force sensor; and an evaluation unit. The application force sensor is an eddy current sensor for sensing displacement along the displacement distance with the evaluation unit for converting the sensed displacement into a measurement variable as a measure of the application force. The application force sensor and the measuring object are attachable to the respective component of the two components so as to also be removable.
An advantageous feature of the invention consists in the fact that the application force sensor and the measuring object can be attached to the respective component of the two components in such a way that they can be removed again. This results in easy mounting and a short replacement time when performing maintenance and service, wherein at the same time accuracy of the determined measurement variable is maintained. The range of application is made larger and includes disc brakes of any design, even those with self-energization.
Accordingly, a measuring arrangement for measuring the application force of a disc brake preferably has the following: two components of the disc brake which can be moved, in particular displaced, relative to one another along a displacement distance when an application force is applied, at least one application force sensor having a housing; a measuring object which is one of the two components or can be permanently connected to one of the two components, and comprises at least one metallic end face or at least one target object with at least one metallic end face for contactless interaction with the application force sensor; and an evaluation unit, wherein the application force sensor is an eddy current sensor for sensing displacement along the displacement distance with the evaluation unit for converting the sensed displacement into a measurement variable as a measure of the application force, and wherein the application force sensor and the measuring object can be attached to the respective component of the two components in such a way that they can be removed again.
The application force sensor and the measuring object can be attached to the respective component of the two components in a centered fashion and/or in a positively locking fashion in such a way that they can be removed again. This provides the advantage that the mounting time is shortened, with orientation times being reduced to a minimum.
The application force sensor can be permanently connected to the other component of the two components and is arranged at a distance from the end face along the displacement distance, wherein one of the two components is a caliper back of a brake caliper of the disc brake, and the other of the two components is a caliper head of the brake caliper of the disc brake.
A pickup device having a coil and a booster device are arranged in the housing of the application force sensor. This arrangement is advantageous since, in this way, the detected measurement variable signal can be boosted over the shortest possible displacement distance without interference influences from the outside due to electromagnetic fields. In order to increase the immunity to interference additionally with respect to moisture and dust, the housing can be hermetically sealed. In one embodiment, the housing is manufactured, for example, from a plastic such as, for example, glass-fiber-reinforced polyamide.
The application force sensor is oriented with the coil of the pickup device on a pickup longitudinal axis at a right angle to the end face. This may, for example, be carried out in an easy way by means of a centering device which forms a positively locking engagement by way of faces, edges, centering pins, centering bolts or the like.
The application force sensor has a measuring range which is larger, by an amount equal to installation tolerances which occur and thermally induced changes of length, than the maximum relative displacement of the two components with respect to one another, which is brought about by the application force.
As a result, influence due to interference variables such as changes in length and installation tolerances are largely reduced.
An end face of the application force sensor can be arranged at a distance from the end face of between 0 mm and 10 mm, preferably between 0.5 mm and 6.5 mm. Eddy current sensors are available which also supply a highly accurate signal over a very short distance.
For adaptation to the surroundings, the application force sensor can be designed to output a sensor signal which can be calibrated to the material of the measuring object, of the target object, the material of the surroundings of the measuring object and/or of the target object and/or the geometry of the measuring object and/or of the target object. In this context, surface coatings of the end faces are also taken into account. The material of the housing of the application force sensor can also be included in the calibration. For this purpose, the evaluation device has, for example, a memory device in which corresponding values are stored in table form, on the basis of which values calibration is made easily possible. This storage device can also include values which can be used to output a temperature-compensated sensor signal and/or for zero point alignment of a sensor signal which is to be output.
The zero point corresponds here to the state of the inactivated brake, which serves as a reference for every braking operation. This zero point can be slightly displaced during operation (due to shocks, thermal expansion etc.) and can be displaced to a relatively large degree during maintenance and servicing (for example change of pads). The absolute value of the zero point is not significant owing to linearization of the sensor signal. The application force sensor can therefore also be designed to output a linearized sensor signal by storing the associated values in the evaluation unit. The linearization of the sensor signal can be implemented with respect to a change in position of the measuring object, target object and/or the application force.
In one embodiment, the pickup device, the booster device and the evaluation unit can be arranged in the housing, which results in a compact design.
In an alternative embodiment, the pickup device can be arranged in the housing. It is then possible only for the coil to be present in the housing, which is then considerably reduced in size. In this context, further switching units of the pickup device, the booster device and the evaluation unit can be arranged separately therefrom. This may be integrated, for example, into a wear sensor unit of the brake or into a control unit. As a result, simplified routing of cables can be obtained, with a combination means which reduces expenditure on installation.
In another alternative, the pickup device and the booster device can be arranged in the housing, wherein the evaluation unit can be arranged in a wear sensor unit of the disc brake. In this context, the software of the evaluation unit can be a component of the software of the wear sensor unit, which entails savings in terms of space and components.
The application force sensor can therefore be provided with at least one connecting line and/or output line, which can be connected permanently, and/or at least one connecting line and/or output line, which can be connected via plug-type connector devices. The combination of cables which therefore result with the wear sensor unit or other units of the brake can be led on as a common cable to an EBS control unit.
A combination of cables of the sensor cable and a wear sensor cable is also possible, and in turn reduces expenditure on installation and installation space. The sensor cable can, of course, also be connected directly to a brake control unit.
The housing can easily be attached directly and/or via at least one clip to one of the components and/or to a bottom plate of the disc brake by use of at least one attachment element. The housing can be screwed for the purpose of rapid mounting and dismounting.
The measuring object can be embodied as a pad-mounting bracket, which can be permanently connected to one of the two components of the disc brake and which has the at least one end face or the at least one target object with at least one end face. The target object can be connected to the pad-mounting bracket directly or via a mounting element. In this context, the target object, which is metallic or has a metallic end face, can be screwed on, riveted on, welded on or attached in some other way. It can also be embodied in one piece with the pad-mounting bracket. Of course, the pad-mounting bracket can have more than one end face or more than one target object.
In order to increase the measuring accuracy, the pad-mounting bracket can be attached with a centering device to one of the components. Nevertheless, the pad-mounting bracket can be replaced and removed with simple means. Such a securing process should be at least in the measuring direction of the sensor. The measuring direction is the direction in which displacement of the sensor along its pickup longitudinal axis is detected.
In order to bring about forced guidance, i.e. without lateral offset, sagging, etc., the pad-mounting bracket can be guided in a displaceable fashion with a guide device on the other component in the direction of the displacement distance for the purpose of positive guidance. The pad-mounting bracket is therefore not rigidly fastened to the other component of the disc brake and is freely movable at least in the measuring direction of the sensor with the result that the target object is removed from the coil of the sensor when the application force is built up. This design can be embodied in such a way that the pad-mounting bracket is restricted in its freedom of movement and/or in its degrees of freedom with respect to the brake disc in the radial direction and/or circumferential direction by, for example, correspondingly shaped faces on the brake caliper and/or bottom plate of the disc brake. The fastening of the pad-mounting bracket on the caliper backside can therefore prevent pivoting movements of the target object on the bracket in the transverse direction with respect to the pickup longitudinal axis of the coil of the sensor. As a result, the freedom of movement of the target object can be restricted in the radial and/or circumferential direction with respect to the brake disc.
The fastening of the pad-mounting bracket on the caliper back may be, for example, by way of a bolt connection, a screw connection, a combination thereof or with additional positive engagement.
For the sake of simplified calibration, the pad-mounting bracket and the target object can be manufactured from a material which has properties which are fixed for the calibration.
In order to at least partially compensate for possible pivoting movements of the target object or of the pad-mounting bracket, the end face can have a convex design.
An application force sensor is embodied for an above-described measuring arrangement as described above.
A pad-mounting bracket can be used for an above measuring arrangement as described.
A disc brake has a brake caliper which engages over a brake disc and which has a caliper head and caliper back connected thereto, wherein brake pads which can be pressed against the brake disc on both sides and are secured radially by means of a pad-mounting bracket are mounted in the brake caliper. The disc brake includes the measuring arrangement specified above.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.
Identical components and/or functional units with the same function are characterized with the same reference symbols in the figures.
The target object 3 is arranged in a target object section 8 of the measuring object 7. In this example, the target object 3 is a metal plate with specific known properties such as, for example, thermal expansion. The movement of the measuring object 7 is transmitted to the target object 3, with the result that the latter moves along a pickup longitudinal axis 22 to the same degree as the measuring object 7. The target object 3 has an end face 23 which is arranged at a right angle to the pickup longitudinal axis 22 and is arranged lying opposite the application force sensor 2.
The pickup longitudinal axis 22 is, at the same time, a longitudinal axis of the application force sensor 2. The application force sensor 2 includes in this example a housing 21, a pickup device 5 and a booster device 6. The pickup device 5 and the booster device 6 are located in the housing 21. The pickup device 5 has a longitudinal axis which is at the same time the pickup longitudinal axis 22. The housing 21 is hermetically sealed in this design.
The application force sensor 2 is embodied as an eddy current sensor in this example. In this context, the pickup device 5 has a coil which generates an electromagnetic alternating field which penetrates the target object 3 and brings about eddy currents in the material of the metallic target object 3. The intensity of the eddy currents is dependent on the displacement distance S in such a way that in the case of relatively short displacement distance values S the intensity is larger than in the case of relatively large displacement distance values. The alternating electromagnetic field which is generated in the coil is generated by applying electrical energy with a specific magnitude and a specific frequency to the coil from the pickup device 5. Depending on the intensity of the eddy currents generated in the target object 3 and the energy consumed in the process, the pickup device 5 determines an electrical variable as a sensor signal, which variable is proportional to the displacement distance S. This electrical variable, for example current or voltage, is then boosted by the booster device 6 and passed on to the evaluation unit 4 via a connecting line 24. The evaluation unit 4 has here a memory device 26 in which, for example, table values with which the evaluation unit 4 can process the electrical variable supplied by the application force sensor 2 are stored. These may be, for example, a linearization, calibration, temperature compensation, zero point alignment etc. For this purpose, the evaluation unit 4 may have at least one temperature sensor and/or may use a temperature signal, for example that from the application force sensor 2 or some other source (for example, brake control unit, pad wear sensor) for the evaluation.
The application force sensor 2 can either be permanently connected or connected in a pluggable fashion by its connecting line 24 to the evaluation unit 4. It is also possible for the evaluation unit 4 to be arranged completely in the application force sensor 2. However, the evaluation unit 4 can also be accommodated in wear sensor electronics (not shown) of the brake (see
Depending on the arrangement described above, the connecting line 24 and/or the output line 25 can be connected directly to a brake system, can be connected to a wear sensor system (permanently or via plug-type connections), and can be led on from there in a common cable to, for example, an EBS, and/or can be combined with a cable of a wear sensor.
The end face 23 of the target object 3 and the assigned end face of the pickup device 5 of the application force sensor 2 are arranged, for example, at a distance between 0 and 10 mm, preferably 0.5 and 6.5 mm.
The measuring range of the application force sensor 2 is made larger, by an amount equal to the installation tolerances which occur and thermally induced changes in length, than is brought about by a maximum displacement which is caused by the application force of the brake.
The calibration properties of the evaluation unit 4 are configured in such a way that the application force sensor 2 and/or its generated sensor signal is calibrated to the material of the target object 3. Calibration of the target object 3 when the latter is coated, for example with paint or other layers, is also possible, as is calibration to the surroundings thereof, for example the geometry of the measuring object 7 or of the target object section 8.
In the case of zero point alignment, the zero point corresponds here to the state of the inactivated brake, which serves as a reference for every braking operation. This zero point can, to a small degree, be displaced during operation (by shocks, thermal expansion etc.) and to a larger extent during servicing of the brakes (for example changing of the pads). The absolute value of the zero point is not significant owing to the linearization of the sensor signal by the evaluation unit 4.
The sensor signal can be linearized with respect to the change in position of the target object 3 and/or to the application force of the brake by way of the evaluation unit 4.
The housing 21 of the application force sensor 2 is manufactured from a resistant material, for example plastic of a glass-fiber-reinforced polyamide type. Examples of attachment to a brake are shown in
The disc brake can be operated pneumatically, hydraulically or electrically. It has a brake caliper 10 which engages over a brake disc 11. On both sides of the brake disc 11, brake pads 15 are arranged, which brake pads 15 can be pressed against the brake disc 11 by way of an application device in order to bring about braking.
The brake caliper 10 is composed of a caliper back 13 and a caliper head 14 which are connected to one another by two tie bars 12. The tie bars 12 run in the axial direction of the brake disc 11 and bound a mounting opening 17 formed in the brake caliper 10 in the circumferential direction of the brake disc 11.
The brake pads 15 are held under prestress in the brake caliper 10, for which purpose each brake pad 15 has a pad-mounting spring 16 (
In its end region, facing the receptacle pocket 19, the pad-mounting bracket 7′ has a U-shaped measuring bracket 27 with two ends running in the axial direction of the brake disc 11. In this second exemplary embodiment, the measuring arrangement 1 includes two measuring points 9, which are arranged parallel to one another and which each have an application force sensor 2 and a target object 3. The target objects 3 are located here at the ends of the measuring bracket 27 which form target object sections 8. Here, in this embodiment, the measuring object 7 is permanently connected to the caliper back 13 in the form of the pad-mounting bracket 7′.
Here also, the application force sensors 2 are permanently connected to the caliper head 14 and are oriented with their pickup longitudinal axes 22 (
The application force sensors 2 are attached here with their housings 21 on the caliper head 14 by use of a clip 28 and two screws. Such a clip 28 is attached in the longitudinal direction to the housing 21 and runs parallel to the axis of the brake disc 11. In another embodiment, the clip 28 can also surround the housing 21 as a type of sleeve. The housings 21 have faces for the purpose of centering and orientation with the target objects 3, said faces interacting with faces of the caliper head 14. Other fastening and centering possibilities are, of course, possible. This results in simple replacement possibilities when performing maintenance and servicing of the brake.
In this design, the target objects 3 are embodied in one piece with the measuring bracket 27, and the measuring bracket 27 is permanently connected to the pad-mounting bracket 7′ by a screwed connection. Another exemplary embodiment of the measuring arrangement 1 according to the invention is shown in
In the exemplary embodiment of
In a multi-component design of the pad-mounting bracket 7′ and target object 3, there is an advantage in that the material of the target object 3 can be matched better to sensor parameters since the pad-mounting bracket 7′ does not have to have all the functional properties of the target object 3.
The pad-mounting bracket 7′ can also be attached in a positively locking fashion to the brake caliper 10 via a centering device, for example faces and/or pins/bolts, provided in addition to the fastening.
The receptacle pocket 19 can be embodied such that it permits the pad-mounting bracket 7′ to be guided so that it cannot carry out any movements in the transverse direction with respect to the pickup longitudinal axis 22 when braking operations occur.
In
A distance between the end face 23 of the target object 3 and the end face of the application force sensor 2 is provided both in
The invention is not restricted to the exemplary embodiments described above. It is, for example, contemplated for the target object 3 to have a convex design at its end face 23 in order to at least partially compensate for possible pivoting movements of the pad-mounting bracket 7′ and/or of the measuring object 7. The pad-mounting bracket 7′ can be embodied, for example, as a punched/bent part. The target object 3 can also be embodied as at least one end face on the measuring object 7 or pad-mounting bracket 7′.
The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 041 951.9 | Sep 2009 | DE | national |
This application is a continuation of PCT International Application No. PCT/EP2010/063485, filed Sep. 14, 2010, which claims priority under 35 U.S.C. §119 from German Patent Application No. DE 10 2009 041 951.9, filed Sep. 17, 2009, the entire disclosures of which are herein expressly incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2010/063485 | Sep 2010 | US |
| Child | 13421284 | US |
