Brakes – Operators – Multiple
Reexamination Certificate
2000-03-17
2001-09-18
Butler, Douglas C. (Department: 3613)
Brakes
Operators
Multiple
C303S003000, C303S015000
Reexamination Certificate
active
06290030
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electromagnetic antilock brake system (“ABS”) which comprises an electromagnetically actuated release arm capable of adjusting the position of a cam or other motion linkage to result in a controlled application of brake shoes to a brake drum. The invention further comprises a control system for controlling the actuation and release of the ABS.
2. Description of the Prior Art
Prior art drum brake systems comprise hydraulically actuated brake shoes which can be radially extended in order to exert a friction force against a rotating drum thereby decelerating and/or stopping a motor vehicle. Prior art ABS's comprise sensors, wheel brake cylinders, pressure modulator assemblies, a master cylinder, and an electronic control unit. Prior art wheel sensors comprise sensor units which are capable of sensing the wheel speed. Prior art pressure modulator assemblies may comprise solenoid valves, accumulators, damper chambers, orifices, and return pumps. Pressure modulators are expensive due to the number of expensive components which they comprise.
One or more prior art ABS's comprise one accumulator, one damper chamber, one orifice, and one return pump for both front brakes of a motor vehicle and one accumulator, one damper chamber, one orifice, and one return pump for both rear brakes of a motor vehicle.
In a prior art ABS, the wheel sensor detects the speed of wheel rotation. This speed is monitored by the electronic control unit. When the wheel speed decreases at a rate that would cause wheel lock up due to pressure being applied from the master cylinder, the electronic control unit uses the pressure modulator to release and reapply the pressure to the wheel cylinder to prevent complete wheel lockup.
In one or more prior art ABS's, the pressure modulator operates at a rate of 4 to 10 cycles per second (cps). In such systems, the accumulator absorbs the surge in hydraulic fluid; the damping chamber suppresses pressure oscillations; and the orifice acts as a flow restrictor. When the rate of deceleration decreases to an acceptable level, one of the solenoid valves opens such that pressure is reapplied from the master cylinder to the wheel cylinder.
In practice, current ABS's may not completely prevent wheel lockup. The wheels may alternate between lockup and rolling as the wheel cylinder pressure is modulated using prior art antilock braking systems. This wheel lock up decreases braking performance by providing a discontinuous braking torque. The frequency of modulation is limited by the response time of the mechanical parts used to control the wheel cylinder. The pulsation of fluid being pumped back to the master cylinder poses problems for some drivers who decrease pressure on the brake pedal when prior art antilock braking systems are activated. Such drivers often decrease this pressure in response to the pulsation of hydraulic fluid. The resulting decrease in pressure may turn off the antilock braking system and may reduce braking performance.
The present invention overcomes the problems of prior art antilock braking systems by employing a system that does not rely upon a pressure modulator and does not therefore result in the pulsation of hydraulic fluid present in prior art antilock braking systems.
SUMMARY OF THE INVENTION
The present invention is directed to an electromagnetic ABS. The invention comprises a backing plate comprising a central opening, a front face, and an outer region. The invention further comprises and axle extending through the central opening. The axle comprises and end region. A rotatable hub is attached to the end region of the axle. The term “attached to,” as used herein, encompasses direct attachment of two components as well as indirect attachment of two components comprising intermediate components connected between the two components. The rotatable hub comprises a front face, a rear face, and ferromagnetic material.
The invention further comprises a brake shoe spring having a first end attached to the backing plate and having a second end. A brake shoe is positioned adjacent to the outer region of the front face of the backing plate and connected to the second end of the brake shoe spring, in such a manner that the brake shoe is movable radially inward or radially outward.
The invention further comprises a pivotable release arm having a first end region and a second end region. The release arm is positioned such that its movement can cause or permit the brake shoe to move radially inward or outward.
The invention further comprises an electromagnet connected to the first end region of the release arm, and positioned in close axial proximity to the hub such that the movement of the electromagnet in the rotational direction of the hub displaces the release arm, thereby causing the brake shoe to move radially inward. The term “connected to,” as used herein, encompasses direct connection of two components as well as indirect connection of two components comprising intermediate components connected between the two components. The movement of the electromagnet opposite to the rotational direction of the hub causes the brake shoe to move radially outward. An electromagnetic energy source is operatively coupled to the electromagnet.
The invention further comprises a return spring having a first end attached to the face and a second end attached to the release arm, such that the movement of the electromagnet in the rotational direction of the hub places a force or moment on the spring in opposition to the force of the spring.
The invention further comprises a wheel brake cylinder mounted on the face. A hydraulically actuated piston is longitudinally mounted within the wheel brake cylinder such that the piston is extendable to push the brake shoe radially outward.
The invention further comprises a hydraulic fluid delivery line having a first end connectable to a reservoir of hydraulic fluid and a second end connected to the wheel brake cylinder such that the pressurized injection of hydraulic fluid through the line is capable of extending the hydraulically actuated piston. A solenoid valve is installed in the delivery line such that when the solenoid valve is open, pressurized hydraulic fluid can flow through the valve to the brake cylinder and when the solenoid valve is closed, pressurized hydraulic fluid cannot flow through the valve to the brake cylinder.
The invention further comprises a sensor positioned to measure the rotational speed or deceleration of the hub. The sensor is also capable of transmitting a signal indicative of hub rotational speed or deceleration. The invention further comprises a controller capable of receiving a signal from the sensor indicative of the hub rotational speed or deceleration. The controller is capable of processing this signal, comparing the signal to a predetermined value and transmitting a control signal to energize the electromagnetic source and to close the solenoid valve when the compared signal exceeds a predetermined value. The controller is further capable of deenergizing the electromagnetic energy source and opening the solenoid valve when the compared signal does not exceed a predetermined value.
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Ridnour James A.
Speckhart Frank H.
Butler Douglas C.
Duane Morris & Heckscher LLP
Pezzlo Benjamin A.
The University of Tennessee Research Corporation
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