Electric vehicle with regenerative and anti-lock braking

• US 5,615,933 A
• Filed: 05/31/1995
• Issued: 04/01/1997
• Est. Priority Date: 05/31/1995
• Status: Expired due to Fees

• Current Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Original Assignee: General Motors Corporation (Motors Liquidation Co. GUC Trust)
• Inventors: Conlon, Brendan M., Kidston, Kevin S.
• Primary Examiner(s): Poon, Peter M.
• Application Number:
  US08/456,094
• Time in Patent Office: 671 Days
• Field of Search: 303/3, 303/15, 303/152, 364/426.02, 180/65.1, 180/265, 180/65.5, 180/65.3, 180/65.4, 318/364, 318/371, 188/156, 188/158, 188/159
• US Class Current: 303/152
• CPC Class Codes: B60L 2260/30 Engine braking emulation
• CPC Class Codes: B60L 3/102 of individual wheels
• CPC Class Codes: B60L 3/108 whilst braking, i.e. ABS
• CPC Class Codes: B60L 7/26 Controlling the braking effect
• CPC Class Codes: B60T 1/10 by utilising wheel movement for accumulating energy, e.g. driving air compressors
• CPC Class Codes: B60T 13/586 the retarders being of the electric type
• CPC Class Codes: B60T 2270/602 ABS features related thereto
• CPC Class Codes: B60T 8/00 Arrangements for adjusting wheel-braking force to meet varying vehicular or ground-surface conditions, e.g. limiting or varying distribution of braking force by changing number of effective brake cylinders in power brake systems B60T17/10
• CPC Class Codes: B60T 8/267 for hybrid systems with different kind of brakes on different axles

Abstract

A vehicle has an electric propulsion motor, a regenerative brake control and an anti-lock friction brake system which responds to excess wheel slip of a front wheel during braking to modulate friction braking torque to reduce the excess wheel slip. It further has a control responsive to activation of the anti-lock brake system to prevent the application of regenerative braking during such activation. The regenerative braking may be blended with the friction braking when anti-lock braking is not activated so that battery charge is conserved. When the anti-lock braking is activated, however, the regenerative braking is ramped down to preserve smoothness in the braking. The regenerative braking may be applied to create drag during vehicle coastdown. When anti-lock braking is activated, if it is sensed that the wheel is on a low friction (μ) surface, the regenerative braking is removed immediately. The low friction surface may be identified from the brake fluid pressure levels during the modulation process of the anti-lock brake system. The coastdown drag may be applied at more than one operator controlled level or, when cruise control is active, automatically at a higher level for more accurate vehicle speed control on downgrades.

Claims

1. A vehicle having an electric power supply, a front wheel, an electric propulsion motor mechanically coupled to the front wheel and electrically coupled to the electric power supply, a control for applying coastdown regenerative braking to the front wheel when the vehicle is in a coastdown mode, and a hydraulically activated friction brake system with an anti-lock apparatus which, when activated, responds to excess wheel slip of the front wheel during braking to modulate hydraulic pressure and thus control braking torque to reduce the excess wheel slip, the control comprising, in combination:

hydraulic pressure responsive means for determining when the front wheel is on a low friction road surface; and

means for eliminating the coastdown regenerative braking when the anti-lock apparatus is active and the hydraulic pressure responsive means determines that the front wheel is on a low friction road surface but maintaining the coastdown regenerative braking when the anti-lock apparatus is active and the hydraulic pressure responsive means determines that the front wheel is not on a low friction road surface.

2. The vehicle of claim 1 in which the control further comprises means for applying blend regenerative braking and friction braking in response to an operator initiated brake signal to maximize the return of energy to the electric power supply and means for ramping down the blend regenerative braking to zero when the anti-lock apparatus is active.

3. In an electric vehicle comprising a front wheel, an electric propulsion motor having a rotor coupled to the front wheel for rotation therewith, an electric power source, an inverter electrically connecting the electric propulsion motor and electric power source for motoring or regenerative braking operation, a friction braking system for the front wheel, and an anti-lock braking control for the friction braking system, a control comprising, in combination:

means for deriving a total motor torque signal from a requested accel torque signal and a coastdown regen decel torque signal;

means for, if the total motor torque signal represents a net decel torque, determining from the total motor torque signal an achieved blend regen decel torque signal and outputting the achieved blend regen decel torque signal to the inverter for regenerative braking operation;

means for determining if the front wheel is on a low friction road surface; and

means for, when the anti-lock braking control is active and the front wheel is on a low friction road surface, changing the coastdown regen decel torque signal to zero but, when the anti-lock control is active and the front wheel is not on a low friction surface, maintaining the coastdown regen decel torque signal.

4. The electric vehicle of claim 3 in which the friction brake system is a hydraulic brake system, the anti-lock brake control modulates a hydraulic pressure when activated and the means for determining if the front wheel is on a low friction road surface comprises sensing apparatus responsive to the hydraulic pressure.

5. The electric vehicle of claim 4 in which the anti-lock brake control modulates the hydraulic pressure between a first value for which wheel slip is detected and a second value for which wheel slip is not detected and the means for determining if the front wheel is on a low friction road surface repeatedly compares the first value as sensed by the sensing apparatus to a low pressure reference value.

6. The electric vehicle of claim 3 in which the coastdown regen decel torque signal has a value simulating the coastdown feel of an internal combustion engine with an automatic transmission.

7. The electric vehicle of claim 6 further comprising a cruise control for automatically maintaining a predetermined vehicle velocity in which the coastdown regen decel torque signal has a first value when the cruise control is not activated and a second, larger value when the cruise control is activated.

8. The electric vehicle of claim 3 in which the coastdown regen decel torque signal has a value simulating the coastdown feel of an internal combustion engine with an automatic transmission in DRIVE.

9. The electric vehicle of claim 3 in which the coastdown regen decel torque signal has a value simulating the coastdown feel of an internal combustion engine with an automatic transmission in OVERDRIVE.

10. In an electric vehicle comprising a front wheel, an electric propulsion motor having a rotor coupled to the front wheel for rotation therewith, an electric power source, an inverter electrically connecting the electric propulsion motor and electric power source for motoring or regenerative braking operation, a friction braking system for the front wheel, and an anti-lock braking control for the friction braking system, a control comprising, in combination:

means for deriving a total motor torque signal from a requested accel torque signal, a coastdown regen decel torque signal, and a requested regen decel torque signal;

means for determining, if the total motor torque signal represents a net decel torque, an achieved blend regen decel torque signal and outputting the latter to the inverter for regenerative braking operation;

means for determining a friction brake decel torque signal and outputting the latter to the friction brake system for friction braking;

means for determining if there is a low friction road surface in contact with the front wheel;

means for, when the anti-lock braking control is active and there is not a low friction road surface in contact with the front wheel, ramping down the requested regen decel torque signal to zero but maintaining the coastdown regen torque signal; and

means for, when the anti-lock braking control is active and there is a low friction road surface in contact with the front wheel, changing the requested regen decel torque signal and the coastdown regen decel torque signal to zero immediately.

11. The electric vehicle of claim 10 in which the friction brake system is a hydraulic brake system, the anti-lock brake control modulates a hydraulic pressure when activated and the means for determining if the front wheel is on a low friction road surface comprises sensing apparatus responsive to the hydraulic pressure.

12. The electric vehicle of claim 11 in which the anti-lock brake control modulates the hydraulic pressure between a first value for which wheel slip is detected and a second value for which wheel slip is not detected and the means for determining if the front wheel is on a low friction road surface repeatedly compares the first value as sensed by the sensing apparatus to a low pressure reference value.

13. The electric vehicle of claim 10 in which the coastdown regen decel torque signal has a value simulating the coastdown feel of an internal combustion engine with an automatic transmission.

14. The electric vehicle of claim 13 further comprising a cruise control for automatically maintaining a predetermined vehicle velocity in which the coastdown regen decel torque signal has a first value when the cruise control is not activated and a second, larger value when the cruise control is activated.

15. The electric vehicle of claim 10 in which the coastdown regen decel torque signal has a value simulating the coastdown feel of an internal combustion engine with an automatic transmission in DRIVE.

16. The electric vehicle of claim 10 in which the coastdown regen decel torque signal has a value simulating the coastdown feel of an internal combustion engine with an automatic transmission in OVERDRIVE.