Electromagnetic antilock brake system

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.

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.

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. 1a and 1b. 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 3b. 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. 1a and 1b. 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. 1a and 1b.
 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. 1a and 1b. 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. 3b. 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. 1a, 1b and 3a.
 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. 1a and 1b, 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. 1a and 1b. 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. 1b and
 3a. 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. 1a.
 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. 3a. 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.
 1b. 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. 3a. 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. 1a and 1b. 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. 1a and 1b.
 The invention further comprises a sensor 60 positioned to measure the
 rotational speed or deceleration of the hub, as shown in FIG. 1b. 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. 1b 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.