Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
  • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
  • B60T8/32—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration
  • B60T8/34—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition
  • B60T8/36—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition including a pilot valve responding to an electromagnetic force
  • B60T8/3615—Electromagnetic valves specially adapted for anti-lock brake and traction control systems
  • B60T8/3655—Continuously controlled electromagnetic valves
  • B60T8/366—Valve details
  • B60T8/367—Seat valves, e.g. poppet valves
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
  • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
  • B60T8/32—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration
  • B60T8/321—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration deceleration
  • B60T8/3255—Systems in which the braking action is dependent on brake pedal data
  • B60T8/327—Pneumatic systems
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B60—VEHICLES IN GENERAL
  • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
  • B60T8/00—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force
  • B60T8/32—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration
  • B60T8/34—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition
  • B60T8/36—Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force responsive to a speed condition, e.g. acceleration or deceleration having a fluid pressure regulator responsive to a speed condition including a pilot valve responding to an electromagnetic force
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02H—EMERGENCY PROTECTIVE CIRCUIT ARRANGEMENTS
  • H02H9/00—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection
  • H02H9/04—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage
  • H02H9/045—Emergency protective circuit arrangements for limiting excess current or voltage without disconnection responsive to excess voltage adapted to a particular application and not provided for elsewhere
  • H02H9/047—Free-wheeling circuits

Definitions

• the present invention relates to the art of vehicle control systems, and more particularly to a method and apparatus for controlling the operation of vehicle brakes on a vehicle equipped with an electronic braking system (EBS) having an electronic control unit (ECU) with a drive circuit (for example, a pulse width modulated (PWM) drive circuit) controlling a solenoid in a modulating valve of an anti-lock braking system (ABS) .
• EBS electronic braking system
• ECU electronic control unit
• a drive circuit for example, a pulse width modulated (PWM) drive circuit
• ABS anti-lock braking system
• the invention relates to a drive circuit that operates effectively in both a steady state control mode and a quick current dissipation mode .
• ABS anti-lock brake systems
• a brake modulator valve is connected between a source of pressurized air and a brake actuator.
• the modulator is typically a three-way valve that under normal service conditions receives pressurized air upon activation of the brakes (e.g., upon operator depression of a brake pedal) and conveys the air to the brake actuators. If an anti-lock event -- i.e., impending wheel lock -- is sensed by the associated ECU, the ECU sends electronic control signals to a solenoid valve assembly associated with the relevant modulator.
• the ECU controls the solenoid valve assembly so that the modulator valve controls the flow of pressurized air to the brake actuators in a manner that simulates brake pedal "pumping" at a repetition rate not obtainable by a human operator.
• the result is improved braking efficiency without loss of vehicle control associated with wheel lock or skid.
• the modulator is a proportional pressure control valve. To use this valve for both service brake applications and ABS control it must be able to provide a smooth and consistent pressure and be able to quickly change from one pressure to another.
• PWM is used to control the current, and therefore the force, produced by the solenoid.
• a diode is placed in parallel with the solenoid to produce smooth current and force profiles and minimize power dissipation. Though the diode is beneficial during steady-state operation, it limits the rate at which the current and force can dissipate.
• Conventional PWM drive circuits cannot perform optimally during the anti-lock brake control because the diode does not allow for rapid dissipation of the current .
• the present invention is directed to a new and improved apparatus and method which overcomes the above- referenced problems and others and provides for a PWM drive circuit that is able to operate in both the quick dissipation mode and steady-state control mode.
• a brake pedal sends an activation signal to an ECU and at least one sensor sends situational data to the ECU.
• the ECU outputs a control signal to a solenoid m a modulator valve to control air to the brake cylinder.
• the drive circuit includes a diode connected m parallel with the solenoid when operating in a steady-state control mode. When the EBS system is operating m a quick dissipation mode the diode is removed from the circuit .
• the current path to the diode is opened and the diode is effectively removed from the circuit when the ECU determines that a quick dissipation mode is required.
• a primary advantage of the present invention is found in the ability to effectively operate the braking system in both a steady state control mode and a quick dissipation mode without limiting the current and force dissipation rate.
• Another advantage of the invention resides m the use of a PWM drive circuit that optimally performs during an ABS event, as well as when the braking system demands a rapid brake pressure decrease. Still other benefits and advantages of the present invention will become apparent to those of ordinary skill m the art upon reading and understanding the following detailed description of the preferred embodiments.
• FIGURE 1 illustrates a schematic representation of a braking system in accordance with the subject invention
• FIGURE 2 is an elevational view, partly in cross-section of a typical solenoid operated, proportional modulator valve
• FIGURE 3 is a circuit representation of the pulse width modulating drive circuit
• FIGURE 4 illustrates the drive circuit's incorporation into a schematic representation of the ECU and the modulator valve ;
• FIGURES 5a and 5b are graphical representations of the steady- state mode of operation
• FIGURES 6a and 6b are graphical representations of the operation with a conducting diode m the drive circuit.
• FIGURES 7a and 7b are graphical representations of the quick dissipation mode of operation with diode effectively removed from the drive circuit .
• FIGURE 1 schematically illustrates an ABS/EBS braking system in which a brake cylinder 10 applies a braking force to a wheel (not shown) .
• the brake cylinder is m communication with a source of pressurized air 12 through modulator valve 20 having a solenoid actuator 30.
• the valve 20 is electrically actuated when solenoid actuator 30 receives a control signal from a pulse width modulator circuit (PWM) , which is described m more detail below in reference to FIGURE 3, in an electronic control unit (ECU) 22.
• PWM pulse width modulator circuit
• ECU 22 electronice control unit
• the onboard ECU 22 receives various electrical signal inputs from one or more sensors 24 and a signal from a foot pedal 26.
• the electronic signals are input to the ECU and, in response, a suitable control signal is provided through line 28 to the solenoid actuator 30 in modulator valve 20.
• the sensors for example, monitor wheel skid conditions (anti-lock brake systems or ABS systems) and/or wheel slippage such as a traction control system.
• the pressure supplied to the brake cylinder may also be monitored and a suitable signal provided to the ECU 22 to prevent over pressure conditions.
• General details of these types of units are well known in the art (for example, U.S. Patent No. 5,404,303 which is commonly owned by the assignee of the present application and incorporated herein by reference) so that further description is deemed unnecessary to a full and complete understanding of the present invention.
• a typical proportional modulator 20 includes a solenoid actuator 30 having a piston 32 with an O-ring seal 34 at one end.
• the piston extends into valve cavity or supply chamber 36 in the modulator housing where the seal selectively engages valve seat 38 on one end of a spool valve 40.
• the spool valve is a hollow cylindrical arrangement having first and second seals 42, 44 defined at opposite ends thereof.
• a central, small diameter passage 50 extends through the spool valve and provides communication between a first or delivery port 52 and a small diameter exhaust port 54.
• an inlet or supply port 56 selectively communicates with the delivery port 52 for applying a pneumatic braking force to the brake cylinder associated with the wheel.
• a second or enlarged diameter exhaust port 70 is also provided and is in selective communication with the delivery port 52 via diaphragm 72.
• the diaphragm includes a bleed or pilot opening 74 that provides constant communication between the delivery port and the supply chamber 36.
• the solenoid 30 may be of any known type in the art, and is preferably shown as being comprised of a series connected inductor 102 and resistor 104 for modeling purposes only.
• the solenoid 30 is connected to a pulse width modulating input controlled voltage source 106, which is controlled by the ECU software, through a low side switching circuit 110.
• the low side switching circuit 110 includes a low side switch 120, preferably a field effect transistor (FET) or MOSFET, which is connected to the solenoid through its drain and is connected m parallel with series connected zener diode 122 and diode 124 at its gate.
• FET field effect transistor
• the pulse width modulator input voltage 106 flows to the switching circuit through a resistor 130.
• Resistor 132 is connected to ground.
• the solenoid 30 is connected to a second voltage source 140 through a second switching system, which is series connected with the solenoid 30.
• the second switching circuit includes a zener diode 142, which goes to ground, and a high side switch 144, which is also controlled by the ECU software.
• the high side switch 144 and diode 146 connect at node 148, and a third input to the node 148 includes a diode 150 m series with the voltage source 140.
• the method of effectively removing diode 146 from circuit 100 during the quick dissipation mode and allowing diode 146 to be m parallel connection with the solenoid 30 during the steady- state control mode will be discussed.
• the ECU 22 applies a pulse width modulated signal from source 106 to the gate of the low side switch 120 through the switching circuit 110.
• the ECU also energizes high side switch 144. In this manner, both switches are closed, completing the circuit to connect diode 146 in parallel with proportional solenoid 30.
• the diode 146 is optimally removed from the drive circuit 100.
• the ECU de- energizes the high side switch 144 and de-energizes the low side switch 110. This opens circuit 100, as is best shown in FIGURE 4, effectively removing the diode 146 from the circuit 100.
• Zener diode 122 is at approximately twenty volts, for example, which allows the lower side of the coil 102 to reach approximately twenty to twenty four volts.
• the energy stored in the coil is more quickly dissipated since there is a greater voltage across it.
• the lower side of the coil rises to the clamp voltage of zener diode 122.
• the top side of the coil is free to go to a negative voltage when switch 144 opens.
• the top side of the coil 102 in the steady state mode was at twelve volts.
• opening the switch 144 in the quick dissipation mode and the provision of zener diode 142 allows the top side of the coil to drop from, for example, twelve volts to a negative level.
• the higher voltage potential across the coil thereby dissipates the energy more quickly - - which is desired with the rapid pulsing/actuating of the brakes in an ABS mode.
• the reason the lower side of the coil can reach an elevated level is based in part on the provision of diode 150.
• the reverse bias of the diode 150 allows node 148 to go to a higher voltage. Opening high switch 144 starts the process, breaks the recirculating current path with diode 146, and permits the increased voltage potential across the coil to be attained which, in turn, more quickly dissipates the energy therefrom. This allows the current to rapidly dissipate through solenoid 30 as will be described in greater detail with reference to FIGURES 7a and 7b.
• FIGURES 5a and 5b graphically represent a steady- state mode of voltage and current through the proportional solenoid 30.
• channel 1 represents the current flowing through the proportional solenoid 30 and channel 2 represents the low side voltage at the proportional solenoid 30.
• channel 1 represents the current flowing through the solenoid 30 and channel 2 represents the pressure sensor output, which is approximately 2.3 V in the exemplary arrangement, although it will be understood that other values may be advantageously used without departing from the scope and intent of the subject invention.
• FIGURES 7a and 7b the difference between the current flowing though the solenoid 30 with the recirculating diode 146 conducting (FIGURES 6a-b) and without the recirculating diode 146 conducting (FIGURES 7a-b) during the quick dissipation mode of the system is more clearly illustrated.
• Channel 1 in both FIGURES 6a and 6b represents the current through the solenoid during quick dissipation mode with the diode 146 conducting.
• Channel 2 in FIGURE 6a is the pressure sensor output, while channel 2 in FIGURE 6b is the low side voltage at the proportional solenoid 30.
• channel 1 is a graphical representation of the current through the solenoid 30 during quick dissipation mode with the diode 146 out of the circuit 100 based on the present invention' s ability to open the circuit by de-energizing the high side switch 144.
• the signal on channel 2 in FIGURE 7a is the low side voltage at the proportional solenoid 30 and the signal on channel 2 in FIGURE 7b is the pressure sensor output.
• FIGURES 7a and 7b It is evident from FIGURES 7a and 7b that by opening the switches 120, 144 and effectively removing the diode 146 from the circuit during quick dissipation mode, the current can dissipate remarkably faster than when the diode is left to conduct in the drive circuit, as in seen in FIGURES 6a and 6b.
• this pulse width modulator drive circuit 100 in the ECU to drive the solenoid, a smooth and consistent pressure is provided for both service brake and ABS brake control, and the valve is able to quickly change from one pressure to another.

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• Engineering & Computer Science (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Transportation (AREA)
• Mechanical Engineering (AREA)
• Fluid Mechanics (AREA)
• Regulating Braking Force (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=23455318

Family Applications (1)

Country Status (3)

Cited By (4)

Citations (6)

• 2000
  • 2000-08-04 CA CA002379266A patent/CA2379266A1/en not_active Abandoned
  • 2000-08-04 WO PCT/US2000/021448 patent/WO2001010692A1/en active Application Filing
  • 2000-08-04 MX MXPA02001284A patent/MXPA02001284A/es unknown

Patent Citations (6)

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