Drum brakes

Abstract

In particular, for controlling electromechanically actuable brakes of the automatic brake assist type, it is necessary to sense the forces acting on the abutments (6) of the brake shoes (2, 3). The abutments (6) are therefore made of a solid material that deforms under load, and a measuring device is provided to sense this deformation. The shape of the abutments (6) is selected so that they have a measuring gap, the size of which changes when the abutments are subjected to load. The size of the measuring gap can be sensed, for example, by a Hall sensor or an AMR sensor.

Description

[Technical field]

[0001] The present invention relates to a drum brake of servo type structure having a brake drum and two brake shoes, the two brake shoes can be attached to the brake drum, the drum brake is arranged on the brake shoe side of a carrier plate, each having a pressure end and a support end, an extension device is present between the pressure ends, the extension device is mounted so as to float with respect to the carrier plate and supported at a force introduction point at the pressure ends to introduce force to the two pressure ends, and a ram is present between the support ends, the ram is mounted so as to float with respect to the carrier plate and supported on the two support ends to transmit force. [Background technology]

[0002] An electrically actuable drum brake of this type, in which the expansion device consists of an electric actuator, is described in WO 99 / 53214 A1.

[0003] Information about the amount of force acting on a drum brake is needed to be able to control or adjust the actuator when applying braking. According to WO 99 / 53214 A1, a load sensor is placed on the end face of the abutment to measure the force with which one of the brake shoes rests on the abutment.

[0004] However, this information is not accurate enough to control or adjust the electric actuator, because the frictional forces acting on the brake shoes when applying the brakes may be different, and therefore the support force affected by the frictional forces may also be different for each brake shoe, and therefore this support force of the brake shoes does not accurately reflect the total amount of force and braking torque acting on the drum brake. Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention is therefore based on the object of creating a drum brake with a load measuring device on the abutment that reflects the total amount of force acting on the drum brake during braking application. [Means for solving the problem]

[0006] To achieve this aim, it is proposed that each brake shoe has at its pressure end a pressure head adjacent to the force introduction point, both pressure heads being supportable on an abutment arranged between them and connected to a carrier plate, that the abutment as a whole is embodied as a mass component elastically deformable under load, and that one or more sensors are provided which detect the deformation of the abutment occurring under load in order to enable the braking torque generated in the drum brake to be determined by means of a sensor signal.

[0007] This configuration of the abutments makes it possible to determine the braking force of the drum brakes of servo-type construction.

[0008] A strain gauge attached to the abutment can be used to determine the deformation of the abutment.

[0009] To achieve a well-defined deformation, the abutment is preferably formed by a base connected via a web to a pedestal which is rigidly connected to the carrier plate, the pressure head resting against both edges of the base When the base is subjected to a load, it displaces or tilts relative to the pedestal, which can be detected by measurement.

[0010] In a first simple embodiment, the base is connected to the pedestal via a central web, and the mutually facing edges of the base and the pedestal run parallel to each other and enclose a measurement gap between them. When the base moves relative to the pedestal, the size of the measurement gap changes. The change in size of the measurement gap can be detected by measurement.

[0011] Another embodiment envisages the abutment having a U-shape with a base and two arms protruding from the base, on the outside of which the abutment ends of the brake shoe are supported, and one or more sensors are of a type capable of detecting the inclination of the arms as they change under load.

[0012] For this purpose, the base originates from a pedestal fixed to the carrier plate and is supported by a central web adjacent the inner edge of the base, so that the arms are directed towards the carrier plate.

[0013] In order to form the measurement gap in this embodiment as well, the invention provides for pins projecting laterally from the central web to reach the inner edges of the arms whilst forming the measurement gap.

[0014] Another embodiment of the abutment envisages that the base and pedestal are connected to each other via two posts located at the edges to form a frame, with at least one pin originating from the pedestal extending to the inner edge of the base to form a measurement gap.

[0015] In the case of unidirectional loading, the rectangular frame is bent into a parallelogram, with the result that the measurement gap is reduced proportionately.

[0016] To increase measurement accuracy, the pedestal, web, and base are preferably designed as a unitary component.

[0017] As already explained above, the measurement of the deformation of the abutment can be carried out with the aid of strain gauges.

[0018] The determination of the measurement gap size can be carried out, for example, by means of a Hall sensor or an AMR sensor based on the anisotropic magnetoresistance effect, for which purpose the arm is equipped with a magnet which serves as a signal transmitter for the Hall sensor or AMR sensor.

[0019] The invention will now be explained in more detail based on three exemplary embodiments. [Brief description of the drawings]

[0020] [Figure 1] A brake drum comprising a first embodiment of an abutment. [Diagram 2] FIG. 2 is an enlarged view of the drum brake abutment shown in FIG. 1 . [Diagram 3] FIG. 4 is an enlarged view of a second embodiment of the abutment. [Figure 4] FIG. 4 is an enlarged view of a third embodiment of the abutment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0021] FIG. 1 shows in a perspective view a drum brake of a motor vehicle, said drum brake comprising a circular carrier plate 1 and two brake shoes 2 and 3 arranged concentrically about the central axis of the carrier plate 1 .

[0022] The brake shoes 2, 3 are concentrically surrounded by a brake drum (not shown here) which is connected to the wheel of the vehicle to be braked, and when the brake shoes 2, 3 are pressed against this brake drum a rotating wheel is slowed down (service braking) or a stationary wheel is prevented from rotating (parking brake).

[0023] The brake shoes 2, 3 each have a pressure end and a support end, and an expansion device 4 is disposed between the opposing pressure ends, which is typically a hydraulically, electromechanically or electrohydraulically actuable device.

[0024] Similarly, between the oppositely positioned support ends there is a ram 5 which transmits force from one brake shoe to the other.

[0025] Both the expander 4 and the ram 5 are mounted so as to float circumferentially relative to the carrier plate 1, so this is a "duo-servo" brake with a powerful automatic boosting effect.

[0026] To support the braking forces acting as frictional forces between the brake shoes 2, 3 and the brake drum, an abutment 6 is provided. It is located radially outside the expander 4, where, adjacent to the force introduction point of the expander 4 and also at the ends of the brake shoes 2, 3, there are pressure heads 7, 8, which are supported on both sides of the abutment 6. Both the expander 4 and the ram 5 are mounted so as to float, so that the braking forces are in each case transmitted only from the trailing brake shoe to the abutment 6.

[0027] Considering the counterclockwise rotation of the brake drum according to the arrow 9 shown, the brake shoe 2 shown on the left is the leading brake shoe and the brake shoe 3 shown on the right is the trailing shoe.

[0028] The expansion device 4 pushes the two brake shoes 2, 3 apart, the leading brake shoe 2 being carried by the brake drum in its rotational direction relative to the carrier plate 1. The frictional force exerted on it is also transmitted by the ram 5 to the trailing brake shoe 3, so that its pressure head 8 is supported on the abutment 6.

[0029] The invention now envisages that a support force is measured there, which force represents a measure of the damping force and can therefore be used to control the expansion device 4 .

[0030] For this purpose, in the simplest case, the abutment 6 shown in FIG. 2 consists of a massive but flat component which protrudes vertically from the carrier plate 1 and is fixed to it, thus allowing the pressure heads 7, 8 to rest on their edges facing in the circumferential direction.

[0031] Here, the abutment 6 comprises a pedestal 10, which is connected to the pedestal 10 via a narrow central web 11 is a base 12, against whose circumferentially facing edge the pressure heads 7, 8 of the brake shoes 2, 3 can be arranged. The mutually facing edges of the pedestal 10 and the base 12 run parallel to each other with a small gap, so that two measuring gaps 13, 14 are formed between the pedestal 10 and the base 12, starting from the web 11.

[0032] If the brake drum is rotated counterclockwise according to the arrow 9 shown, the brake shoe 2 shown on the left is the leading brake shoe and the one shown on the right is the trailing brake shoe 3. Due to the frictional forces between the brake shoes and the brake drum, the brake shoes, since they are mounted floating, are carried in the direction of rotation, so that the trailing brake shoe 3 is supported on the base 12 of the abutment 6, which is inclined relative to the pedestal 10, so that the measuring gap 14 facing it is widened and the measuring gap 13 facing away from it is narrowed, as shown in FIG.

[0033] These changes can be detected by suitable sensors and represent the value of the applied damping force, which can then be used to control the expansion device.

[0034] In the case of a different direction of rotation, the functions of the two brake shoes 2, 3 are reversed, the left brake shoe becomes the trailing shoe and the right brake shoe becomes the leading shoe, so that the latter is supported on the base 12 of the abutment 6, so that the measuring gap 13 on the left side facing it is widened and the measuring gap 14 on the right side facing away from it is narrowed.

[0035] Another possibility for the design of the abutment is shown in Figure 3. Extending from the pedestal 10 fixed to the carrier plate 1 is a central web 16 which merges into a transverse web 17 from each of whose ends extend respective arms 18, 19 directed towards the pedestal 10. The central web 16, the transverse web 17 and the two arms 18, 19 thus form a T. The pressure heads 7, 8 of the brake shoes 2, 3 are arranged against the outer edges of the arms 18, 19 facing in the circumferential direction.

[0036] Protruding laterally from the central web 16 are two pins 20, 21 which terminate immediately before the inner edges of the arms 18, 19 and which in each case form measuring gaps 13, 14.

[0037] The respective leading brake shoe 2, 3 bends inwards the arm 19 or 18 on which it is supported, so that the associated measuring gap 14 or 13 decreases in size, which can be detected by measurement.

[0038] At the same time, the pins 20, 21 act as overload protection devices: if the braking forces become too great, the arms 17, 18 rest against the associated pins 20, 21.

[0039] The third embodiment shown in Figure 4 comprises a pedestal 10 and a base 12, which are connected to each other via two posts 22, 23 located at the two edges, thus forming a frame with a central opening. Extending from the inner edge of the pedestal 10, which delimits the opening, are two pins 20, 21, which extend to the inner edge of the base 12, leaving measurement gaps 13, 14.

[0040] When the base 12 is loaded in the circumferential direction, it displaces parallel to the pedestal 10, causing the rectangular frame to deform into a parallelogram, with the base 12 approaching the ends of the pedestal 10 and the pins 20, 21, causing the measurement gaps 13, 14 to correspondingly decrease in size.

[0041] In all embodiments, there are different possibilities available for measuring the change in the measurement gap: sensors using the anisotropic magnetoresistance effect (AMR effect) or, alternatively, linear Hall sensors can be used.

[0042] Independently of the measurement of the measured gap size, the respective changes in the shape of the abutment can be detected by the strain gauges.

[0043] The sensor allows the measurement of the braking torque acting on the drum brake, which is used to control the braking effect of the drum brake. The present invention may also include the following aspects: 1. A drum brake of servo type structure having a brake drum and two brake shoes (2, 3), the two brake shoes (2, 3) can be attached to the brake drum, the drum brake is arranged on the brake shoe side of a carrier plate (1), each having a pressure end and a support end, an extension device (4) is present between the pressure ends, the extension device (4) is attached to the carrier plate (1) so as to float, and is supported at a force introduction point at the pressure ends to introduce force to the two pressure ends, a ram (5) is present between the support ends, the ram (5) is attached to the carrier plate (1) so as to float, and is supported at a force introduction point at the pressure ends to transmit force. 1. A drum brake supported on said two support ends for braking a drum brake, characterized in that each brake shoe (2, 3) has at its pressure end a pressure head adjacent to the force introduction point, both pressure heads (7, 8) being supportable on an abutment (6) arranged between them and connected to the carrier plate (1), and in that the abutment (6) is embodied as a whole as a mass component elastically deformable under load, and in that one or more sensors are provided which detect the deformation of the abutment (6) occurring under load in order to enable the braking torque generated by the drum brake to be determined by means of a sensor signal. 2. A drum brake as described in claim 1, characterized in that the abutment (6) is formed by a base terminating in a pedestal (10) rigidly connected to the carrier plate (1) via a web (11), and the pressure heads (7, 8) rest against both edges of the base (12). 3. The drum brake described in claim 2, wherein the base (12) is connected to the pedestal (10) via a central web (16), and the mutually facing edges of the base (12) and the pedestal (10) extend parallel to each other and enclose a measurement gap therebetween. 4. The drum brake described in 2. above, characterized in that the abutment (6) has a U-shape with a base (12) and two arms (18, 19) protruding from the base and capable of supporting the pressure head (7, 8) at their outer edges, and the one or more sensors are of a type capable of detecting the inclination of the arms (18, 19) which changes under load. 5. A drum brake described in any one of 1. to 4. above, characterized in that the base (12) is supported by a central web (20) that originates from a pedestal fixed to the carrier plate (1) and is adjacent to the inner edge of the base (10), so that the arms (11, 12) are directed toward the carrier plate (1). 6. A drum brake as described in 4. or 5. above, characterized in that the pins (20, 21) protruding laterally from the central web (16) reach the inner edges of the arms (18, 19) while forming a measuring gap. 7. The drum brake described in 5. above, characterized in that the base and the pedestal are connected to each other via two posts (22, 23) located at their edges to form a frame, and at least one pin originating from the pedestal extends to the inner edge of the base (12) to form a measurement gap. 8. The drum brake according to claim 5, wherein the pedestal (10), the web (20) and the base (12) form an integral component. 9. A drum brake as described in any one of 1. to 8. above, characterized in that a strain gauge is attached to the abutment (6) to detect deformation of the abutment (6). 10. A drum brake described in any one of 1. to 8. above, characterized in that a sensor based on the anisotropic magnetoresistance effect or the Hall effect is used to detect deformation of the abutment (6). [Explanation of symbols]

[0044] 1 Carrier Plate 2 Brake shoes 3 Brake shoes 4 Expansion Unit 5. Ram 6 Abutment 7 Pressure Head 8 Pressure Head 9 Arrows 10 Pedestal 11. Web 12 Base 13 Measurement Gap 14 Measurement Gap 16 Central Web 17 Cross web 18 Arm 19 Arm 20-pin 21 pin 22 Edge-located supports 23 Edge-located supports

Claims

1. A drum brake of servo type construction having a brake drum and two brake shoes (2, 3), the two brake shoes (2, 3) being capable of contacting the brake drum and being arranged on the brake shoe side of a carrier plate (1), the two brake shoes (2, 3) each having a pressure end at its uppermost part and a support end at its lowermost part, an extension device (4) being present between the pressure ends, the extension device (4) being floatingly mounted with respect to the carrier plate (1) and supported at the pressure ends at a force introduction point for introducing a force to the two pressure ends, a ram (5) being present between the support ends, the ram (5) being floatingly mounted with respect to the carrier plate (1) and supported at the two support ends for transmitting a force, each brake shoe (2, 3) having at its pressure end a pressure head adjacent to the force introduction point, Between both pressure heads (7, 8) there is provided an abutment (6) having a pedestal (10), a base (12) and a central web (11) connecting the pedestal (10) and the base (12); A measurement gap (13, 14) is formed between the pedestal (10) and the base (12); The brake shoes (2, 3) are supported by the base (12), and when the base (12) tilts relative to the pedestal (10) during braking, one of the measurement gaps (13, 14) widens and the other narrows, and one or more sensors are provided to detect this change.

2. A drum brake of servo type structure having a brake drum and two brake shoes (2, 3), the two brake shoes (2, 3) being capable of contacting the brake drum and being arranged on the brake shoe side of a carrier plate (1), the two brake shoes (2, 3) each having a pressure end at its uppermost part and a support end at its lowermost part, an extension device (4) being present between the pressure ends, the extension device (4) being floatingly attached to the carrier plate (1) and supported at a force introduction point at the pressure ends to introduce a force to the two pressure ends, a ram (5) being present between the support ends, the ram (5) being floatingly attached to the carrier plate (1) and supported at the two support ends to transmit a force, wherein each brake shoe (2, 3) has a pressure head at its pressure end adjacent to the force introduction point, Between both pressure heads (7, 8) is provided an abutment (6) having a pedestal (10), a central web (16) extending from the pedestal (10), lateral webs (17) joining the central web (16), and arms (18, 19) extending from the ends of the lateral web (17); pins (20, 21) projecting laterally from the central web (16) reach the inner edges of the arms (18, 19) while defining a measuring gap (13, 14); The brake shoes (2, 3) bend inwards, during braking, the arms (18, 19) on which they are supported, as a result of which the measuring gap (13, 14) decreases in size, and one or more sensors are provided to detect this change in the measuring gap (13, 14).

3. A drum brake of servo type structure having a brake drum and two brake shoes (2, 3), the two brake shoes (2, 3) being capable of contacting the brake drum and being arranged on the brake shoe side of a carrier plate (1), the two brake shoes (2, 3) each having a pressure end at its uppermost part and a support end at its lowermost part, an extension device (4) being present between the pressure ends, the extension device (4) being floatingly attached to the carrier plate (1) and supported at a force introduction point at the pressure ends for introducing a force to the two pressure ends, a ram (5) being present between the support ends, the ram (5) being floatingly attached to the carrier plate (1) and supported at the two support ends for transmitting a force, wherein each brake shoe (2, 3) has a pressure head at its pressure end adjacent to the force introduction point, Between both pressure heads (7, 8) there is an abutment (6) having a pedestal (10), a base (12) and two posts (22, 23) connecting the edges of the pedestal (10) and the base (12), At least one pin (20, 21) originating from the pedestal (10) extends to an inner edge of the base (12) while forming at least one measurement gap (13, 14); The drum brake is characterized in that when the base (12) is loaded in the circumferential direction during braking, it is displaced parallel to the pedestal (10), as a result of which the rectangular frame is deformed into a parallelogram, the base (12) approaching the ends of the pedestal (10) and the pins (20, 21), as a result of which the size of the at least one measuring gap (13, 14) is reduced, and one or more sensors are provided to measure this change in the measuring gap.

4. Drum brake according to any one of claims 1 to 3, characterised in that a strain gauge is attached to the abutment (6) for detecting the deformation of the abutment (6).

5. 4. Drum brake according to claim 1, characterized in that a sensor based on the anisotropic magnetoresistance effect or the Hall effect is used to detect the change in the measuring gap (13, 14).

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