GB2518831A

GB2518831A - Brake Compensation System and Acuator Using The Same

Info

Publication number: GB2518831A
Application number: GB1317333.1A
Authority: GB
Inventors: Niall Mccullough; Karin Krattinger
Original assignee: Johnson Electric SA
Current assignee: Johnson Electric SA
Priority date: 2013-10-01
Filing date: 2013-10-01
Publication date: 2015-04-08
Also published as: GB201317333D0

Abstract

A brake actuator 11 comprises an electric motor 30 which drives via gears 40 an output shaft 50 for operating a brake pad between a brake released position and a brake engaged position in response to a rotation of the output shaft 50. A compensation system comprises a marker 84, e.g. a magnet and Hall sensor connected to a printed circuit board, attached to the output shaft 50 and an encoder 85 configured to sense a first angular displacement of the output shaft 50 corresponding to a first brake stroke and a second angular displacement of the output shaft 50 corresponding to a second brake stroke. A control module, on the printed circuit board, is coupled to the encoder 85 and is configured to adjust a third angular displacement of the output shaft 50 corresponding to a third brake stroke in response to a variation between the first angular displacement and the second angular displacement. Reference is also made to a brake compensation system for a brake actuator.

Description

TITLE

[0001] Brake Compensation System and Actuator Using The Same

FIELD OF THE INVENTION

[0002] This invention generally relates to an automobile brake system, and particularly to a brake compensation system, a brake compensation method, and a brake actuator incorporating such brake compensation system.

BACKGROUND OF THE INVENTION

[0003] An automobile brake system is a key safety element in an automobile. In operation, the friction material of an automobile brake such as braking lining suffers from wear, and the brake stroke changes gradually due to the wear. A wear monitoring system is usually used to monitor the wear. For electromagnetic brakes, wear monitoring is accomplished via the measurement of the air gap between the armature and the solenoid coil. However, the method does not compensate for the increase of the brake stroke due to wear.

[0004] Accordingly, it would be advantageous to have a brake compensation system that is able to monitor the wear and compensate the variation of brake stroke. It would be desirable for the compensation system to be integrated with the brake actuator. It is also advantageous if the compensation system is able to indicate when the friction material is worn out and needs replacement.

SUMMARY OF THE INVENTION

[0005] Accordingly, in one aspect thereof, the present invention provides a brake actuator for operating a brake pad, comprising: a motor; ai output shaft driven by the motor; and a pushing member coupled to the output shaft and configured to operate the brake pad between a brake released position and a brake engaged position in response to a rotation of the output shaft; a measuring system configured to measure a first angular displacement of the output shaft corresponding to a first brake stroke and a second angular displacement of the output shaft corresponding to a subsequent second brake stroke; and a control module configured to adjust a third angular displacement of the output shaft conesponding to a third brake stroke in response to a variation between the first angular displacement and the second angular displacement.

[0006] Preferably, the measuring system comprises: a marker attached to the output shaft; and an encoder cooperating with the marker for sensing the first anguhr displacement and the second angular displacement.

[0007] Preferably. the marker includes a polarized permanent magnet; and the encoder includes a Hall sensor.

[0008] Preferably, the brake actuator comprises a printed circuit board; and the Hall sensor is mounted to the printed circuit board.

[0009] Preferably, the brake actuator comprises a printed circuit board; the Hall sensor is connected to the printed circuit board; and the control module is disposed on the printed circuit board.

[0010] Preferably. the brake actuator comprises a printed circuit board; the Hall sensor is connected to the printed circuit board; and the control module is a part of an engine flnsrnission control system.

[0011] Preferably, the brake actuator further comprises a gear assembly coupled between the motor and the output shaft.

[0012] In another aspect thereof, the present invention provides a brake compensation system for a brake actuator having an output shaft to operate a brake pad between a brake released position and a brake engaged position in response to a rotation of the output shaft, comprising: an measuring system configured to measure a first angular displacement of the output shaft colTesponding to a first brake stroke and a second angular displacement of the output shaft corresponding to a subsequent second brake stroke; and a control module configured to adjust a third angular displacement of the output shaft corresponding to a third brake stroke in response to a variation between the first angular displacement and the second angular displacement.

[0013] Preferably, the measuring system comprises: a marker attached to the output shaft; and an encoder cooperating with the marker and configured to sensing the first angular displacement, the second angular displacement and the third angular displacement.

[0014] Preferably, the marker includes a polarized permanent magnet; and the encoder includes a Hall sensor.

[0015] Preferably. the brake actuator comprises a printed circuit board; the Hall sensor is mounted on the printed circuit board, and the contr& module is disposed on the printed circuit board.

[0016] Preferably, the control module is a part of an engine transmission control module.

[0017] Preferably, the marker includes a permanent magnet disc with diametral polarization.

[0018] In a further aspect thereot the present invention provides a brake compensation method for a brake actuator having an output shaft to drive a brake pad in brake strokes between a brake released position and a brake engaged position in response to a rotation of the output shaft, wherein the brake compensation method comprising: detecting a first angular displacement of the output shaft that corresponds to a first brake stroke; detecting a second angular displacement of the output shaft that corresponds to a subsequent second brake stroke; and adjusting a third angular displacement of the output shaft that colTesponds to a third brake stroke in response to a variation between the first angular displacement and the second angular displacement.

[0019] Preferably, detecting a first angular displacement and detecting a second angular displacement includes measuring an absolute angular position of the output shaft.

0020J Preferably. detecting a first angular displacement includes: mounting a marker to the output shaft so that the marker rotates with the output shaft; and using an encoder to detect a first angular position of the marker corresponding to a brake released position and a second angular position of the marker corresponding to a brake engaged position.

[0021] Preferably, adjusting a third angular displacement of the output shaft comprises: acquiring the variation between the first angular displacement and the second angular displacement; and shifting an angular position of the output shaft corresponding to a brake released position of the third brake stroke in response to the variation so that the adjusted third angular displacement is substantially equal to the first angular displacement.

[0022] Preferably. the first brake stroke is predefined as an initial brake stroke.

[0023] Preferably, the step of adjusting is peifoirned when the automobile is repowered on.

[0024] Preferably. the brake compensation method further comprises defining an initial brake stroke after an automobile power on as the first brake stroke.

[0025] Preferably. the brake compensation method further comprises determining an angular position of the output shaft corresponding to a brake engaged position of the brake stroke and generating an indication to indicate that friction material is worn out in response to the angubr position equal to a predefined value.

[0026] Preferably. adjusting a third angular displacement of the output shaft corresponding to a third brake stroke includes defining an initial brake stroke after a subsequent automobile power on as the third brake stroke.

[0027] Preferably, the method further comprises: checking if the angular position of the output shaft that corresponds to brake engaged position of a brake stroke is equal to a predefined value; if the angular position is equal to a predefined value, generating an indication to indicate that friction material is worn out.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Various embodiments of the present invention are described, by way of example only, with reference to the drawings, in which identical or related structures, elements, or parts may be labeled with the same reference numerals throughout the figures. Dimensions of components and features shown in the figures are generally chosen for convenience and clanty of presentation and are not necessanly to scale.

[0029] Figure 1 is an isometric view of an automobile brake system according to an exemplary embodiment of the present invention, with a half-housing removed; [0030] Figure 2 is a cross section view of the brake system shown in Figure 1; [0031] Figure 3 illustrates a bearing in the brake system shown in Figure 1; [0032] Figure 4 is a plan view of the brake system shown in Figure 1; [0033] Figure 5 is another plan view of the brake system shown in Figure 1; [0034] Figure 6 is a block diagram of a compensation system in the brake system shown in Figure 1; [0035] Figure 7 schematically illustrates an angle measuring system in the compensation system shown in Figure 1; and [0036] Figure 8 is a flowchart illustrating a compensation method for an automobile brake system according to an exemplary embodiment of the present invention.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS

[0037] Referring to Fig. I and Fig. 2, an automobile brake system 10 according to an embodiment of the present invention comprises a brake actuator 11 and a pushing member 70 driven by brake actuator 11. Pushing member 70 has a side face 71 serving as a friction surface. Alternatively, a brake lining (not shown) could be mounted on side face 71 of pushing member 70.

[0038] Brake actuator 11 includes a housing 20, a motor 30 fixed to housing 20, a gear assembly 40 driven by motor 30, two output shafts 50 driven by gear assembly 40, and two eccentric bearings 60 connected respectivdy to the two output shafts 50.

Pushing member 70 is connected to the two eccentric bearings 60. Pushing member 70 is driven to move along a circle so that an object such as a brake lining arranged nearby or directly connected thereto is forced to move laterally as shown by the arrow iii Fig. 1.

[0039] Gear assembly 40 is received in housing 20, and mechanically coupled between motor 30 and the two output shafts 50 to enable output shafts 50 to have lower rotation speed and greater output torque. In the present embodiment, gear assembly 40 includes a primary gear 42 coupled to motor 30, a middle gear 44 meshed with primary gear 42, and an ultimate gear 46 meshed with middle gear 44.

0040J The two output shafts 50 are assembled to the housing 20 and engaged with opposite sides of ultimate gear 46 so that the two output shafts 50 rotate synchronously in the same direction.

[0041] The two eccentnc bearings 60 are respectively mounted to the two output shafts 50. Referring also to Fig. 3, each of eccentric bearings 60 includes a cup 62, a cone 64 surrounded by cup 62, and a plurality of rollers 66 sandwiched between cup 62 and cone 64. Cup 62 is substantially ring-shaped. Each cone 64 is substantially ring-shaped with the center 01 of the inner surface thereof being offset from the center 02 of the outer surface thereof. The inner surface of cone 64 is tightly fitted to a distal end of a corresponding output shaft 50, so that the eccentric bearing 60 is connected to the output shaft 50.

[0042] Refening also to Fig. 4, pushing member 70 defines two through holes 72.

The two eccentric bearings 60 are fixed into conesponding through holes 72. ffi this way, the pushing member 70 is fixedly coupled to the two eccentric bearings 60.

[0043] Referring to Fig. 3, Fig. 4 and Fig. 5, when motor 30 drives gear assembly 40 to cause ultimate gear 46 to rotate clockwise, the two output shafts 50 rotates counterclockwise synchronously. At one moment, the two eccentric bearings 60 are both arranged at the highest position they can reach, as shown in Fig. 4. At a subsequent moment, the two eccentric bearings 60 are at the leftmost position they can reach, as shown in Fig. 5. As such, a lateral movement of the pushing member 70 is generated.

[0044] In accordance with a specific embodiment of the present invention, cup 62 in one of the two eccentric bearings 60 is shaped to have two flat surfaces 68 opposite to each other as shown in Fig. 3. The two through holes 72 in pushing member 70 comprises a round through hole and a rectangular through hole. The inner surface of the square through hole 72 contacts the two flat surfaces 68 of the corresponding bearing 60 received therein. The length of the square through hole 72 is slightly greater than the diameter of cup 62 of bearing 60. In this way, the corresponding cup 62 can slightly slide within the square through hole 72, which makes it easier to assemble pushing member 70 to bearing 60.

[0045] It should be understood that, during braking operation, pushing member 70 and the friction material such as a brake Uning mounted on pushing member 70 is driven to move between a brake released position and a brake engaged position. When the brake is thcated at the brake engaged position, the brake lining applies a predetermined force to a brake drum or a brake disc (not shown in the figures). Brake stroke is defined as the rotation angle of output shaft 50 that corresponds an angular displacement from the brake released position to the brake engaged position. Brake stroke generafly increases over time due to the wear of the friction material. For example, an initial brake stroke may be equal to an absolute rotation angle of 70 degree, and a subsequent brake stroke may be equal to an absolute rotation angle of 72 degree.

In this case, the variation of brake stroke is 2 degree. To maintain the same brake stroke, the brake released position would need to be shifted by 2 degree to compensate for the change in the brake engaged position due to the wear of the friction material.

[0046] Referring to Fig. 2, Fig. 6, and Fig. 7, the actuator 11 comprises a compensation system 80 for detecting the wear of the friction material and compensating the variation in the brake stroke. Compensation system 80 comprises a measuring system 82 for detecting angular position of output shaft 50 and a control module 88 for adjusting the angular position of the output shaft 50 to compensate brake stroke variation caused by the wear of the fnction matena according to the output of the measuring system 82. Measuring system 82 includes an angle-measuring system.

preferably an absolute angle-measuring system, comprising an angular position indicator or marker 84 fixed to one of output shafts 50 and rotatable therewith, and an encoder 85 mounted inside housing 20. In accordance with a specific embodiment, angular position marker 84 is a polarized permanent magnet. preferably a permanent magnet disc with diametral polarization, fixed to and rotatable with the output shaft 50.

The encoder 85 is a Hall system comprising a Hall sensor mounted on a printed circuit board (not shown).

[0047] During braking operation, output shafts 50 rotate to drive pushing member 70. Angular position marker 84 rotates with output shafts 50. The angu'ar position of the angular position marker 84 is detected by the encoder 85. Specifically.

both x component Bx and y component By of the rotation are measured by the encoder 85, and then the angular position is yield by arctan (Bx/By).

[0048] It should be understood that the measuring system 82 is not limited to being a FlaIl sensor measuring system. Other angle-measuring systems that deliver absolute angular position could also be used. For example, the measuring system 82 could be an angle-measuring system comprising an optical shaft encoder system or an electromagnetic rotary resolver. Preferably, the angle-measuring system 82 has an accuracy of one degree or better.

[0049] Referring to Fig. 8, in step S 101, detecting a first angular displacement of marker 84 that colTesponds to a first brake stroke. In the present embodiment, the first angular displacement is acquired by detecting a first angular position of marker 84 corresponding to the brake released position of the first brake stroke, and a second angular position of marker 84 corresponding to the brake engaged position of the first brake stroke. It is contemplated that the first brake stroke may be an initial brake stroke.

The first angular position of marker 84 correspondiiig the brake released position of the initial brake stroke could be detected or predefined.

[0050] In step S 103, detecting a second angular displacement of marker 84 that corresponds to a second brake stroke. It is contemplated that the second brake stroke could be any one of the subsequent brake strokes. In the present embodiment, the second angular displacement is acquired by detecting a third angular position of marker 84 conesponding to the brake released position of the second brake stroke, and a fourth angular position of marker 84 corresponding to the brake engaged position of the second brake stroke. Due to the wear of friction material such as a brake lining, the second angular displacement is usually slightly or significantly larger than the first angular displacement.

[0051] In step SIOS. acquiring angular variation between the first brake stroke and the second brake stroke. For example, if the first angular displacement of the first brake stroke is 70 degree, and the second angular displacement of the second brake stroke is 72 degree, then the angular variation between the first brake stroke and the second brake stroke is 2 degree.

[0052] It is contemplated that the angular variation colTesponds to the variation of the brake stroke. Therefore, the variation of brake stoke is compensated by the control module 88 based on the angular variation, as illustrated in step Sl07 shown in Fig. 8.

The brake stroke compensation is accomplished by adjusting the angular displacement of the third brake stroke based on the angular variation. Specifically, shifting the brake released position of the third brake stroke by the angular variation. It is contemplated that the third brake stroke could be any brake stroke following the second brake stroke.

For example, if the angular vanation is 2 degree, to maintain the brake stroke (i.e., making the subsequent brake stroke basically equal to the first brake stroke), the brake released position is shifted by 2 degree for the next brake stroke.

[0053] Furthermore, the worn out of the friction material such as a brake lining is also detected by comparing the angular position of marker 84 corresponding a brake engaged position with a predefined value that corresponds to a predefined friction material thickness. The friction material such as a brake lining is worn out and needs replacement when the angular position of marker 84 corresponding a brake engaged position is detected to reach a predefined value. Preferably, in this case, the predefined angular position indicates that the friction material is worn out and needs replacement, as illustrated in steps S 109 and Sill respectively, it should be understood that steps S109 and Sill could be performed immediately after step 5105.

[0054] The compensation operation in S107 could be performed immediately after each brake operation to maintain the brake strokes substantially constant in the brake operation. Alternatively, the compensation operation could be performed periodically.

In accordance with one embodiment, the variation of brake stroke is detected and registered at automobile's current power-on, and the compensation operation is performed at the next power-on. In other words, the compensating step is performed only when the automobile is repowered on, to make sure that the compensating step does not interfere with the braking function in urgent braking situations.

[0055] In the present embodiment, the Hall sensor is mounted to a printed circuit board (PCB). Alternatively, the Hall sensor may be mounted to housing 20 and connected to a PCB. The control module 88 is mounted or integrally embedded to the PCB. The drive circuit of motor 30 may also be integrated to the PCB. making brake actuator ii more compact. Alternatively, the control module 88 could be a part of ETC (engine transmission control) system. As is known, an ETC system is a system to control engine speed, engine power. engine torque, etc..

[0056] In accordance with an embodiment of the present invention, brake actuator 11 is an electro-mechanical actuator. Due to the small number of parts between angular position marker 84 mounted on output shaft 50 and pushing member 70 the accumulated tolerance (essentially play/backlash in bearing 60) between marker 84 and pushing member 70 is small and the positioning error is low. Therefore, the accuracy is improved.

[0057] Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. Therefore, the scope of the invention is to be determined by reference to the claims that follow.

[0058] In the description and claims of the present application, each of the verbs "comprise", "include", "contain" and "have", and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items.

Claims

CLAiMS: 1. A brake actuator for operating a brake pad, comprising: a motor; an output shaft driven by the motor; and a pushing member coupled to the output shaft and configured to operate the brake pad between a brake released position and a brake engaged position in response to a rotation of the output shaft; a measuring system configured to measure a first angular displacement of the output shaft corresponding to a first brake stroke and a second angular displacement of the output shaft colTesponding to a subsequent second brake stroke; and a control module configured to adjust a third angular displacement of the output shaft corresponding to a third brake stroke in response to a variation between the first angular displacement and the second angular displacement.
2. The brake actuator of claim 1, wherein the measuring system comprises: a marker attached to the output shaft; and an encoder cooperating with the marker for sensing the first angular displacement and the second angular displacement.
3. The brake actuator of claim 2, wherein: the marker indudes a polarized permanent magnet; and the encoder includes a Hall sensor.
4. The brake actuator of claim 3, further comprising a printed circuit board, wherein the Hall sensor is mounted to the printed circuit board.
5. The brake actuator of claim 3. further comprising a printed circuit board, wherein: the Hall sensor is connected to the printed circuit board; and the control module is disposed on the printed circuit board.
6. The brake actuator of claim 3. further comprising a printed circuit board, wherein: the Hall sensor is connected to the printed circuit board; and the control module is a part of an engine transmission control system.
7. The brake actuator of claim I, further comprising a gear assembly coupled between the motor and the output shaft.
8. A compensation system for a brake actuator having an output shaft to operate a brake pad between a brake released position and a brake engaged position in response to a rotation of the output shaft, comprising: a measuring system configured to measure a first angular displacement of the output shaft corresponding to a first brake stroke and a second angular displacement of the output shaft colTesponding to a subsequent second brake stroke; and a control module configured to adjust a third angular displacement of the output shaft colTespondrng to a third brake stroke in response to a variation between the first angular displacement and the second angular displacement.
9. The compensation system of claim 8, wherein the measuring system comprises: a marker attached to the output shaft; and an encoder cooperating with the marker and configured to sense the first angular displacement and the second angular displacement.
10. The compensation system of claim 9, wherein: the marker includes a polarized permanent magnet; and the encoder includes a Hall sensor.
11. The compensation system of claim 10, further comprising a printed circuit board, wherein: the Hall sensor is mounted on the printed circuit board, and the control module is disposed on the printed circuit board.
12. The compensation system of claim 10, wherein the control module is a part of an engine transmission control modu'e.
13. The compensation system of claim 9. wherein the marker includes a permanent magnet disc with diametral polarization.
14. A brake compensation method for a brake actuator having an output shaft to drive a brake pad in brake strokes between a brake released position and a brake engaged position in response to a rotation of the output shaft, comprising: detecting a first angular displacement of the output shaft colTespondmg to a first brake stroke; detecting a second angular displacement of the output shaft corresponding to a subsequent second brake stroke; and adjusting a third angular displacement of the output shaft colTesponding to a third brake stroke in response to a variation between the first angular displacement and the second angular displacement.
15. The brake compensation method of claim 14, wherein detecting a first angular displacement includes measuring an absolute angular position of the output shaft.
16. The brake compensation method of claim 14, wherein detecting a first angular displacement includes: mounting a marker to the output shaft so that the marker rotates with the output shaft; and using an encoder to detect a first angular position of the marker corresponding to a brake released position and a second angular position of the marker corresponding to a brake engaged position.
17. The brake compensation method of claim 16, wherein adjusting a third angular displacement of the output shaft comprises: acquiring the variation between the first angular displacement and the second angular displacement; and shifting an angular position of the output shaft corresponding to a brake released position of the third brake stroke in response to the variation so that the adjusted third angular displacement is substantially equal to the first angular displacement.
18. The brake compensation method of claim 14, further comprising defining an initia' brake stroke after an automobile power on as the first brake stroke.
19. The brake compensation method of claim 18, wherein adjusting a third angular displacement of the output shaft corresponding to a third brake stroke includes defining an initial brake stroke after a subsequent automobile power on as the third brake stroke.
20. The brake compensation method of claim 14, further comprising: determining an angular position of the output shaft colTespondrng to a brake engaged position of the brake stroke and generating an indication to indicate that friction material is worn out in response to the ang&ar position equal to a predefined value.