System and method for braking an electric drive vehicle on a low Mu surface

• US 6,709,075 B1
• Filed: 08/07/2000
• Issued: 03/23/2004
• Est. Priority Date: 08/07/2000
• Status: Active Grant

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Pate, Steven Otis, Crombez, Dale Scott
• Primary Examiner(s): Lavinder, Jack
• Assistant Examiner(s): KING, BRADLEY T
• Application Number:
  US09/635,183
• Time in Patent Office: 1,324 Days
• Field of Search: 303/3, 303/15, 303/150, 303/152, 701/80, 701/81
• US Class Current: 303/152
• CPC Class Codes: B60L 15/2009 for braking
• CPC Class Codes: B60L 3/102 of individual wheels
• CPC Class Codes: B60L 7/10 Dynamic electric regenerative braking B60L7/22 takes precedence
• CPC Class Codes: B60T 2270/602 ABS features related thereto
• CPC Class Codes: B60T 8/17636 Microprocessor-based systems
• CPC Class Codes: Y02T 10/64 Electric machine technologies in electromobility
• CPC Class Codes: Y02T 10/72 Electric energy management in electromobility

Abstract

Strategies other than immediate elimination of regenerative braking (FIG. 2) are invoked when an incipient wheel lock-up is detected, the ABS becomes active, and/or incipient wheel slip is detected. The strategies include: reducing the regenerative braking torque as a function of the coefficient of friction of a surface on which the vehicle is traveling (FIG. 3); and adjusting regenerative braking in relation to the rate at which wheel slip is changing (FIG. 4). Some of the strategies may be applied on an individual wheel basis (FIG. 5), and some of the strategies may be applied in conjunction with operating friction brakes of the vehicle to apply at least some of the reduction in regenerative braking torque as friction brake torque (FIG. 1).

Claims

1. An electric motor vehicle comprising:

road-engaging wheels;

friction brakes for the wheels;

a powerplant comprising a rotary electric machine that is operatively coupled through a drivetrain to driven ones of the road-engaging wheels and that is capable both of delivering traction torque to the driven wheels and of imposing regenerative braking torque on the driven wheels;

a throttle request source operated by a throttle that is depressed to accelerate the vehicle; and

a brake request source operated by a brake pedal that is depressed to brake the vehicle; and

a processing system for processing data useful in operating both the friction brakes and the electric machine, including data from the throttle request source requesting the electric machine to operate as a generator imposing regenerative braking on the drivetrain simulating compression braking that would be imposed by an internal combustion engine on the drivetrain when the throttle ceases to be depressed and data from the brake request source requesting the electric machine to operate as a generator imposing regenerative braking on the drivetrain when the brake pedal is depressed, and calculating desired regenerative braking torque and desired friction brake torque when braking torque requires both regenerative braking torque and friction brake torque;

wherein the processing system executes a strategy comprising reducing, but not completely eliminating, the torque that is being applied to the drivetrain as regenerative braking torque when a wheel-condition-initiated triggering event occurs.