Current control method for a solenoid operated fluid control valve of an antilock braking system

• US 6,019,441 A
• Filed: 10/09/1997
• Issued: 02/01/2000
• Est. Priority Date: 10/09/1997
• Status: Expired due to Fees

• Current Assignee: BWI Company Limited SA (Shougang Corporation)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Lloyd, Earl Wayne, Cornwell, William Dale
• Primary Examiner(s): Le, Mark T.
• Assistant Examiner(s): YEAGLEY, DANIEL S
• Application Number:
  US08/946,909
• Time in Patent Office: 845 Days
• Field of Search: 303/116.1, 303/156, 303/157, 303/158, 303/161, 303/119.2
• US Class Current: 303/156
• CPC Class Codes: B60T 8/36 including a pilot valve responding to an electromagnetic force
• CPC Class Codes: B60T 8/363 in hydraulic systems B60T8/3655, B60T8/3675 and B60T8/369 take precedence
• CPC Class Codes: B60T 8/5006 Pressure reapplication by pulsing of valves B60T8/5012, B60T8/5018, B60T8/505, B60T8/5056 take precedence

Abstract

The solenoid control valves of a solenoid-operated automotive antilock braking system are cyclically controlled to enable the valves to operate in a stable, partially open position that provides a desired fluid flow while minimizing noise associated with acceleration and deceleration of the controlled fluid. After an incipient lock-up condition is detected and the solenoid valve has been energized to hold and/or permit a partial release of the brake pressure, the solenoid is initially de-energized for a defined interval designed to reduce the current to a scheduled value. In this interval, the solenoid current is re-circulated through a free-wheeling diode for a smooth decay, allowing the valve to slowly open in a smooth and stable fashion. Then the solenoid is pulse-width modulated (PWM) at a frequency and duty cycle designed to maintain the solenoid current at the scheduled value. The interval of PWM is relatively brief to avoid any instability associated with the current pulsation. At this point, the solenoid is re-energized just long enough to reach its steady state value, thereby returning the valve to a closed or nearly closed position, and completing the current control cycle. The solenoid is then de-energized and the cycle is repeated, allowing the controller to smoothly return the brake pressure to the system pressure while minimizing any attendant hydro-mechanical noise.

Claims

1. A method of operation for an automotive anti-lock braking system in which an electrically controlled solenoid valve in a hydraulic line coupling a master cylinder to a braking device is electrically activated to a first position to permit unimpeded fluid flow in said hydraulic line or a second position to interrupt fluid flow in said hydraulic line, the method comprising the steps of:

energizing the solenoid to move the valve to the second position to interrupt fluid flow in said hydraulic line;

de-energizing the solenoid for a first interval that allows its current to decay to a scheduled value for moving the valve to a desired position intermediate said first and second positions;

maintaining the solenoid current at said scheduled value for a second interval to maintain said valve at said desired position;

re-energizing said solenoid for a third interval that allows the solenoid current to return to a steady state value, thereby substantially returning said valve to said second position; and

repeating said de-energizing, maintaining, and re-energizing steps with successively lower scheduled current values to gradually re-establish unimpeded fluid flow in said hydraulic line.

2. The method of operation defined in claim 1, wherein the step of maintaining the solenoid current comprises the step of:

repeatedly energizing and de-energizing said solenoid at a frequency too high to substantially change the position of said valve, and at duty cycle chosen to maintain the solenoid current at said scheduled value.

3. The method of operation defined in claim 2, wherein said second interval has a duration sufficiently short to maintain stable control of said valve position.

4. The method of operation defined in claim 1, wherein said successively lower scheduled current values correspond to a succession of desired positions intermediate said first and second positions.

5. The method of operation defined in claim 1, wherein the re-energizing of said solenoid for said third interval returns said valve substantially to said second position.

6. A method of operation for an automotive anti-lock braking system in which an electrically energizable fluid valve in a hydraulic line coupling a master cylinder to a braking device has an armature which is biased to an open position when the valve is de-energized to permit unimpeded fluid flow in said hydraulic line and to a closed position when the valve is energized with current to interrupt fluid flow in said hydraulic line, the method comprising the steps of:

energizing the valve with current to move the armature to the closed position to interrupt fluid flow in said hydraulic line;

de-energizing the valve for a first interval that allows said current to decay to a scheduled value for retracting the armature to a desired position intermediate said open and closed positions;

rapidly energizing and de-energizing said valve to maintain said current at said scheduled value for a second interval, thereby to maintain said armature at said desired position;

re-energizing said valve for a third interval that allows said current to return to a steady state value, thereby substantially returning said armature to said closed position to substantially interrupt fluid flow in said hydraulic line; and

repeating said de-energizing, maintaining, and re-energizing steps with successively lower scheduled current values to gradually re-establish unimpeded fluid flow in said hydraulic line.

7. The method of operation defined in claim 6, wherein said second interval has a duration sufficiently short to maintain stable control of said valve position.

8. The method of operation defined in claim 6, wherein said successively lower scheduled current values correspond to a succession of desired positions intermediate said open and closed positions.

9. A method of operation for an automotive anti-lock braking system in which an electrically energizable fluid valve in a hydraulic line coupling a master cylinder to a braking device has an armature which is biased to an open position when the valve is de-energized to permit unimpeded fluid flow in said hydraulic line and to a closed position when the valve is energized with current to interrupt fluid flow in said hydraulic line, the method comprising the steps of:

pulse-width-modulating said valve for a first interval to maintain its current at a current command value which moves the armature to a desired position intermediate said open and closed positions, thereby establishing a desired fluid flow rate in said hydraulic line;

energizing said valve for a second interval to increase said current to a steady state value, thereby moving said armature substantially to said closed position to substantially interrupt fluid flow in said hydraulic line;

de-energizing the valve for a third interval that allows said current to decay to said current command value for returning the armature to said desired position, thereby re-establishing said desired fluid flow rate; and

repeating said pulse-width-modulating, energizing, and de-energizing steps with successively lower current command values corresponding to successively higher fluid flow rates to gradually re-establish unimpeded fluid flow in said hydraulic line.

10. The method of operation defined in claim 9, wherein said first interval has a duration sufficiently short to maintain stable control of said armature position.