Abstract:
The present invention relates to an electromagnetic antilock brake system 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.

Description:
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&#39;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&#39;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&#39;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&#39;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. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     FIG. 1 a  is a front view of the present invention in the deenergized mode. 
     FIG. 1 b  is a front view of the present invention in the energized mode. 
     FIG. 2 is a side view of the present invention. 
     FIG. 3 a  is a front view of a preferred embodiment of the release arm, electromagnet, cam and return spring mbly of the present invention. 
     FIG. 3 b  is cross sectional front view of the brake drum, backing plate and brake shoe of the present invention. 
     FIG. 4 is a block diagram of the control system of the present invention. 
     FIG. 5 is a preferred embodiment of the control circuitry of the present invention. 
     FIGS. 6A-6F are a block diagram of a first preferred embodiment of the control system logic of the present invention. 
     FIGS. 7A and 7B are a block diagram of a second preferred embodiment of the control system logic of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention is directed to an electromagnetic ABS. The invention comprises a backing plate  10  comprising a central opening  11 , a front face  12 , and an outer region  13 , as shown in FIG. 1 a  and  1   b . The invention further comprises an axle  14  extending through the central opening, as shown in FIG.  2 . The axle comprises an end region  15 , as shown in FIGS. 2 and 3 b . In a preferred embodiment, the axle is rotatable. A rotatable hub  16  is attached to the end region of the axle, as shown in FIG.  2 . The rotatable hub comprises a front face  17  and a rear face. In one preferred embodiment, the rotatable hub comprises a ferromagnetic material. In another preferred embodiment, the invention further comprises a steel plate  20  attached to the rotatable hub, as shown in FIG.  2 . In a preferred embodiment, the rotatable hub comprises a multiplicity of extension arms  19  or lugs projecting outward from the front face having a sufficient thickness to support a brake drum. 
     The invention further comprises a brake shoe spring  22  having a first end  23  attached to the backing plate and having a second end  24 . In a preferred embodiment, the brake shoe spring is a helical spring, as shown in FIGS. 1 a  and  1   b . A brake shoe  26  is mounted 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, as shown in FIGS. 1 a  and  1   b.    
     In a preferred embodiment, the invention comprises a first brake shoe and a second brake shoe placed on opposite sides of the outer region of the front face of the backing plate, as shown in FIGS. 1 a  and  1   b . In this preferred embodiment, the first and second brake shoes are connected to the second ends of a first brake shoe spring and a second brake shoe spring, respectively, such that each brake shoe is moveable radially inward or radially outward. 
     In a preferred embodiment, the invention further comprises a brake drum  30  mounted on the hub. The brake drum comprises an inner braking surface  31  facing the brake shoe, as shown in FIG. 3 b . In the embodiment where there are two brake shoes, the inner braking surface faces each brake shoe. The brake drum is attached to the hub such that the brake drum rotates with the hub. 
     The invention further comprises a pivotable release  40  arm having a first end region  41  and a second end region  42 , as shown in FIGS. 1 a ,  1   b  and  3   a . The release arm is positioned such that its movement can cause or permit the brake shoe to move radially inward or outward. In a preferred embodiment, the release arm is positioned such that its movement traverses a maximum arc length of 30 degrees. In an embodiment where there are two brake shoes, the release arm is positioned such that its movement can cause or permit each brake shoe to move radially inward or outward. 
     In a preferred embodiment, the invention further comprises a movement linkage  43  connected to the second end region of the release arm and to the brake shoe. In a preferred embodiment, the movement linkage comprises a rotatable cam. As shown in FIGS. 1 a  and  1   b , the cam rotates in response to rotation of the release arm. When the first end region of release arm rotates in the rotational direction of the hub, the cam is rotated, thereby permitting inward radial movement of the brake shoe, as shown in FIGS. 1 a  and  1   b . In a preferred embodiment, the release arm is sized, shaped and positioned to traverse a maximum arc length of 30 degrees as the cam rotates through its entire range of motion. 
     The invention further comprises an electromagnet  44  connected to the first end region of the release arm, 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, as shown in FIGS. 1 b  and  3   a . The movement of the release arm opposite to the rotational direction of the hub causes the brake shoe to move radially outward, as shown in FIG. 1 a.    
     An electromagnetic energy source  46  is operatively coupled to the electromagnet, as shown in FIG.  4 . In a preferred embodiment, the electromagnetic energy source is capable of sending an electrical current signal to the electromagnet in response to a control signal from the controller. 
     The invention further comprises a return spring  48  having a first end  47  and a second end  49  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, as shown in FIG. 3 a . In one preferred embodiment, the first end of the return spring is attached to the face of the backing plate. 
     In an embodiment comprising a movement linkage connected to the release arm, the first end of the return spring is attached to the brake shoe or the backing plate. In another preferred embodiment, where the mechanical linkage is a cam and the system comprises two brake shoes, there is a return spring and a brake shoe connecting spring  51 . In this embodiment, the return spring has a first end attached to the release arm and a second end attached to the face of the backing plate. The brake shoe connecting spring is connected to the first and second brake shoes, as shown in FIG. 1 b . In a preferred embodiment, the brake shoe connecting spring is connected to the lower region of each brake shoe. 
     The return spring may be a compression spring, a torsional spring, or a tension spring. In a preferred embodiment, the return spring is a helical spring. In a preferred embodiment, the first end of the return spring is attached to the face. 
     The invention further comprises a wheel brake cylinder  50  mounted on the face, as shown in FIG. 3 a . A hydraulically actuated piston  52  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  54  having a first end  55  connectable to a reservoir of hydraulic fluid and a second end  56  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, as shown in FIGS. 1 a  and  1   b . A solenoid valve  58  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, as shown in FIGS. 1 a  and  1   b.    
     The invention further comprises a sensor  60  positioned to measure the rotational speed or deceleration of the hub, as shown in FIG. 1 b . The sensor is also capable of transmitting a signal indicative of hub rotational speed or deceleration. In a preferred embodiment, the sensor is capable of transmitting pulses indicative of wheel speed to the controller. In this embodiment, the controller also comprises a pulse accumulator  61  capable of counting pulses received from the sensor. 
     In a preferred embodiment, the controller is a Motorola Model 68HC11 microcontroller, as shown in FIG.  5 . In a preferred embodiment, the pulses are classified into the binary logic states of zero or one using transistor transistor logic (TTL). In a preferred embodiment, a logic zero is between negative 1.5 volts and 0.2 volts, and a logic one is between 2.0 volts and 5.0 volts. In a preferred embodiment, the sensor was an Airpax Model 1-0007. 
     The invention further comprises a controller  62  capable of receiving a signal from the sensor indicative of the hub rotational speed or deceleration, as shown in FIGS. 1 b  and  4 . 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, as shown in FIG.  4 . In a preferred embodiment, the processing carried out by the controller comprises calculating any deceleration of the hub. 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. 
     In a preferred embodiment, the controller comprises feedback control system  64  that is capable of varying the magnitude of the output signal from the electromagnetic energy source in proportion to a control signal received from the controller, as shown in FIGS. 4 and 7. In this embodiment, the strength of the electromagnetic field produced by the electromagnet is proportional to hub rotational speed or deceleration, as shown in FIG.  7 . This proportionality encompasses both linear and nonlinear proportionality. Another preferred embodiment of the control system logic is shown in FIG.  6 . This proportional control system provides the ability to vary the braking torque of the present invention in proportion to the rotational speed or deceleration of the hub. 
     In a preferred embodiment, the invention further comprises a brake switch  66  that is configured to be in the on position when the brake pedal is applied and configured to be in the off position when the brake pedal is not applied, as shown in FIG.  5 . The brake switch is coupled to send a signal indicative of its position to the controller, as shown in FIG.  4 . In a preferred embodiment, the controller will not send a control signal to energize the electromagnetic energy source unless the controller receives a signal from the brake switch indicating that the brake switch is on. In this same preferred embodiment, the controller will not send a control signal to close this solenoid valve unless the brake switch is on, thereby indicating that the brake pedal is applied, as shown in FIG.  6 . 
     The foregoing disclosure and description of the invention are illustrative and explanatory. Various changes in the size, shape, and materials, as well as in the details of the illustrative construction may be made without departing from the spirit of the invention.