BRAKE PAD WEAR SENSOR
A brake pad wear measuring system for measuring brake pad wear for a vehicle disc brake system includes a first coil having a first coil face and is excitable to create a first magnetic field. A first target is spaced a fixed distance from the first coil face. The first coil and the first target are configured for movement relative to each other in response to application of the disc brake system so that the first target covers a portion of the first coil that varies with the amount of brake pad wear and varies the inductance of the first coil. The inductance of the first coil is indicative of the amount of brake pad wear. The brake pad wear measuring system also includes a second coil having a second coil face and is excitable to create a second magnetic field. A second target is configured to move toward the second coil face in response to application of the disc brake system so that the distance between the second target and the second coil face varies with the amount of brake pad wear and varies the inductance of the second coil. The inductance of the second coil is indicative of the amount of brake pad wear.
1 . A brake pad wear measuring system for measuring brake pad wear for a vehicle disc brake system, comprising:
a first coil having a first coil face and being excitable to create a first magnetic field;
a first target spaced a fixed distance from the first coil face, wherein the first coil and the first target are configured for movement relative to each other in response to application of the disc brake system so that the first target covers a portion of the first coil that varies with the amount of brake pad wear and varies the inductance of the first coil, the inductance of the first coil being indicative of the amount of brake pad wear;
a second coil having a second coil face and being excitable to create a second magnetic field;
a second target configured to move toward the second coil face in response to application of the disc brake system so that the distance between the second target and the second coil face varies with the amount of brake pad wear and varies the inductance of the second coil, the inductance of the second coil being indicative of the amount of brake pad wear.
2 . The brake pad wear measuring system recited in claim 1 , further comprising a controller configured to excite the first and second coils to produce the magnetic fields and for measuring the inductance of the first and second coils, wherein the controller is configured to respond to changes in inductance in the first and second coils caused by movement of the first and second targets in the magnetic field to provide a signal indicative of brake pad wear.
3 . The brake pad wear system recited in claim 1 , wherein the first and second coil faces are oriented perpendicular to each other, the first target is oriented parallel to the first coil face, and the second target is oriented parallel to the second coil face.
4 . The brake pad wear system recited in claim 1 , wherein the first coil and target are configured to measure brake pad wear at the beginning of the life of the brake pad, and the second coil and target are configured to measure brake pad wear beginning at a predetermined point toward the end of the life of the brake pad.
5 . The brake pad wear system recited in claim 1 , wherein the second coil is smaller than the first coil and the second target completely covers the second coil regardless of the amount of brake pad wear.
6 . The brake pad wear system recited in claim 1 , wherein the first target has a generally tapered configuration, and the second target has a generally rectangular configuration.
7 . The brake pad wear measuring system recited in claim 1 , the first and second targets are oriented perpendicular to each other.
8 . The brake pad wear measuring system recited in claim 1 , wherein the first target moves parallel to the first coil face in response to brake application, and the second target moves normal to the second coil face in response to brake application.
9 . The brake pad wear measuring system recited in claim 1 , wherein the second coil is sized so that movement of the second target toward the second coil face no effect on the inductance of the second coil until the brakes reach a predetermined amount of wear.
10 . A brake pad wear measuring system for measuring brake pad wear for a vehicle disc brake system, comprising:
a sensor comprising a housing supporting a first coil excitable to create a first magnetic field, a second coil excitable to create a second magnetic field, and a controller configured to excite the first and second coils and to measure the inductance in the first and second coils;
a first target configured to move within the first magnetic field and affect the inductance of the first coil in response to application of the disc brake system;
a second target configured to move toward the second magnetic field in response to application of the disc brake system and have no effect on the inductance of the second coil until the brake pad reaches a predetermined amount of wear.
11 . The brake pad wear measuring system recited in claim 10 , wherein the controller is configured to respond to changes in inductance of the first and second coils caused by movement of the first and second targets in the magnetic fields to provide a signal from the sensor indicative of brake pad wear.
12 . The brake pad wear system recited in claim 10 , wherein the controller is configured to calculate initial brake pad wear in response to the inductance of the first coil, and to calculate brake pad wear in response to changes in inductance of the second coil only after the brake pad reaches the predetermined amount of wear.
13 . The brake pad wear system recited in claim 10 , wherein the first and second coil faces are oriented perpendicular to each other, the first target is oriented parallel to the first coil face, and the second target is oriented parallel to the second coil face.
14 . The brake pad wear system recited in claim 10 , wherein the first coil and target are configured to measure brake pad wear at the beginning of the life of the brake pad, and the second coil and target are configured to measure brake pad wear beginning toward the end of the life of the brake pad.
15 . The brake pad wear system recited in claim 10 , wherein the second coil is smaller than the first coil and the second target completely covers the second coil regardless of the amount of brake pad wear.
16 . The brake pad wear system recited in claim 10 , wherein the first target has a generally tapered configuration, and the second target has a generally rectangular configuration.
17 . The brake pad wear measuring system recited in claim 10 , the first and second targets are oriented perpendicular to each other.
18 . The brake pad wear measuring system recited in claim 10 , wherein the first target moves parallel to the first coil face in response to brake application, and the second target moves normal to the second coil face in response to brake application.
19 . The brake pad wear measuring system recited in claim 10 , wherein the second coil is sized so that movement of the second target toward the second coil face has no effect on the inductance of the second coil until the brakes reach a predetermined amount of wear.