Electric vehicle regenerative antiskid braking and traction control system

• US 5,450,324 A
• Filed: 01/07/1993
• Issued: 09/12/1995
• Est. Priority Date: 01/07/1993
• Status: Expired due to Term

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Motor Company
• Inventors: Cikanek, Susan R.
• Primary Examiner(s): Teska, Kevin J.
• Assistant Examiner(s): NGUYEN, TAN QUANG
• Application Number:
  US08/001,603
• Time in Patent Office: 978 Days
• Field of Search: 364/426.02, 364/426.03, 364/424.05, 364/426.01, 180/197, 180/165, 180/65.3, 188/156, 188/159, 188/181 T, 303/3, 303/93, 303/103, 303/112, 303/113.2, 303/20
• US Class Current: 701/108
• CPC Class Codes: B60L 15/2009 for braking
• CPC Class Codes: B60L 2240/12 Speed
• CPC Class Codes: B60L 2240/14 Acceleration
• CPC Class Codes: B60L 2240/421 Speed
• CPC Class Codes: B60L 2240/423 Torque
• CPC Class Codes: B60L 2250/26 by pedal actuation
• CPC Class Codes: B60L 2260/24 Coasting mode
• CPC Class Codes: B60L 3/102 of individual wheels
• CPC Class Codes: B60L 7/18 Controlling the braking effect B60L7/12, B60L7/14, B60L7/16 take precedence
• CPC Class Codes: B60L 7/24 with additional mechanical or electromagnetic braking
• CPC Class Codes: B60T 13/58 Combined or convertible systems
• CPC Class Codes: B60T 2270/602 ABS features related thereto
• CPC Class Codes: B60T 2270/603 ASR 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 8/175 Brake regulation specially adapted to prevent excessive wheel spin during vehicle acceleration, e.g. for traction control safety devices for propulsion unit control responsive to, or preventing, skidding of wheels B60K28/16
• CPC Class Codes: B60T 8/17636 Microprocessor-based systems
• CPC Class Codes: B60T 8/3205 acceleration B60T8/34, B60T8/52, B60T8/54, B60T8/56, B60T8/58, B60T8/72, B60T8/86, B60T8/88 take precedence
• CPC Class Codes: B60W 10/04 including control of propulsion units
• CPC Class Codes: B60W 10/08 including control of electric propulsion units, e.g. motors or generators
• CPC Class Codes: B60W 10/18 including control of braking systems
• CPC Class Codes: B60W 2552/40 : Coefficient of friction
• CPC Class Codes: B60W 30/18127 : Regenerative braking
• CPC Class Codes: B60W 30/1819 : Propulsion control with control means using analogue circuits, relays or mechanical links
• CPC Class Codes: Y02T 10/64 : Electric machine technologies in electromobility
• CPC Class Codes: Y02T 10/72 : Electric energy management in electromobility

Abstract

An antiskid braking and traction control system for an electric or hybrid vehicle having a regenerative braking system operatively connected to an electric traction motor, and a separate hydraulic braking system includes one or more sensors for monitoring present vehicle parameters and a processor, responsive to the sensors, for calculating vehicle parameters defining the vehicle behavior not directly measurable by the sensors and determining if regenerative antiskid braking control, requiring hydrualic braking control, or requiring traction control are required. The processor then employs a control strategy based on the determined vehicle state and provides command signals to a motor controller to control the operation of the electric traction motor and to a brake controller to control fluid pressure applied at each vehicle wheel to provide the appropriate regenerative antiskid braking control, hydraulic braking control, and traction control.

Claims

1. An antiskid braking and traction control system for a vehicle having at least two driven wheels, a regenerative braking system operatively connected to an electric traction motor having motor control means for controlling the operation of said motor, and a separate hydraulic braking system having brake control means for controlling fluid pressure applied at each wheel by said hydraulic braking system, said antiskid braking and traction control system comprising:

sensing means for sensing vehicle parameters representative of vehicle behavior; and

processing means, responsive to said sensing means, for calculating vehicle parameters defining said vehicle behavior not directly measurable by said sensing means,

for determining a vehicle state of said vehicle based on said vehicle parameters, said vehicle state being any of requiring regenerative antiskid braking control, requiring hydraulic braking control, and requiring traction control,

for employing a real time control strategy based on said vehicle state, and

for providing command signals to said motor control means to control the operation of said electric traction motor and to said brake control means to control fluid pressure applied at each wheel to provide said regenerative braking control, hydraulic braking control, and traction control.

2. An antiskid braking and traction control system according to claim 1 wherein said sensing means includes:

driven wheel speed sensors for measuring wheel speed of said at least two driven wheels;

two nondriven wheel speed sensors for measuring the wheel speed of two nondriven wheels;

brake pressure sensors for measuring brake pressure on said at least two driven wheels and for measuring pressure in brake line of said two nondriven wheels;

a master cylinder pressure sensor for measuring hydraulic pressure of a master cylinder;

a brake switch sensor for sensing the operation of said brakes;

a motor speed sensor for measuring speed of said electric traction motor; and

means for sensing the operation of an acceleration pedal switch.

3. An antiskid braking and traction control system according to claim 1 wherein said command signals include a rear hydraulic braking control signal, a front hydraulic braking control signal, and a regenerative antiskid braking control signal for modulating said brake control means and said motor control means when said vehicle is in said vehicle state requiring regenerative antiskid braking control.

4. An antiskid braking and traction control system according to claim 1 wherein said command signals include a front hydraulic braking control signal and a rear hydraulic braking control signal for modulating said brake control means when said vehicle is in said vehicle state requiring hydraulic braking.

5. An antiskid braking and traction control system according to claim 1 wherein said command signals include a reduction in motor torque control signal for modulating said motor control means when said vehicle is in said vehicle state requiring traction control.

6. An antiskid braking and traction control system according to claim 1 wherein said processing means further provides means for determining a worst case wheel slip condition among said driven wheels and for generating said command signals based on said worst case wheel slip condition.

7. An antiskid braking and traction control system according to claim 6 wherein said processing means further determines said worst case wheel slip condition by determining a driven wheel critical adhesion coefficient and a driven wheel critical slip for each of said driven wheels, deriving a critical adhesion coefficient equal to a lowest value of said driven wheel critical adhesion coefficient for each of said driven wheels, and deriving a critical wheel slip equal to a value of said driven wheel critical slip associated with said critical adhesion coefficient.

8. An antiskid braking and traction control system according to claim 1 wherein said processing means further includes a braking strategy for determining the optimum proportionality between regenerative braking and hydraulic braking while providing a required braking demand.

9. An antiskid braking and traction control system according to claim 1 wherein said processing means calculates vehicle acceleration, Dv, as one of said vehicle parameters according to the following equation whenever hydraulic brake pressure is applied to nondriven wheels:

##EQU2## wherein;

k is a spring rate of a drive axle of said vehicle,

Θ

_e is an integral of the speed of said motor,

G_r is a combined gear ratio of a differential and transmission of said vehicle,

Θ

_rd and Θ

_ld are integrals of the speeds of right and left driven wheels of said vehicle respectively,

J_r is wheel inertia,

α

_rd and α

_ld are time derivatives of the speeds of said right and left driven wheels respectively,

τ

_br and τ

_bl are hydraulic brake torques applied to said right and left driven wheels respectively,

R_w is a radius of one of said driven wheels,

W_rd and W_ld are speeds of the right and left driven wheels,

W_e is the motor speed,

β

is the damping rate between the motor shaft and wheel, and

M_v is the mass of said vehicle; and

according to the following equation whenever hydraulic braking is not applied to said nondriven wheels;

##EQU3## wherein;

v(t) is vehicle speed at time t,

T is sampling rate, and

v(t-T) is vehicle speed at time t minus sampling rate, T.

10. An antiskid braking and traction control system according to claim 1 wherein said processing means calculates an adhesion-coefficient μ

_d between a road surface and tire surface for each one of said driven wheels as one of said vehicle parameters, according to the following equation;

##EQU4## wherein;

k is a spring rate of a drive axle of said vehicle,

Θ

_e is an integral of the speed of said electric motor,

G_r is a combined gear ratio of a differential and a transmission of said vehicle,

Θ

_rd and Θ

_ld are integrals of the speeds of right and left driven wheels respectively,

τ

_d is hydraulic brake torque applied to said one of said driven wheels respectively,

J_r is wheel inertia,

α

_d is a time derivative of the speed of said one of said driven wheels,

R_w is the radius of said one of said driven wheels,

N_v is a normal force on said one of said driven wheels

β

is the damping rate between the motor shaft and wheel,

W_e is the motor speed, and

W_rd and W_ld are speeds of the right and left driven wheels, respectively.

11. A method for providing antiskid braking and traction control for a vehicle having at least two driven wheels, a regenerative-braking system operatively connected to an electric traction motor having motor control means for controlling the operation of said motor, and a separate hydraulic braking system having brake control means for adjusting the fluid pressure applied at each wheel by said hydraulic braking system, said method for providing antiskid braking and traction control comprising the steps of:

sensing vehicle parameters to obtain real-time measurements defining vehicle behavior;

calculating additional vehicle parameters describing vehicle behavior not directly measured in said step of sensing vehicle parameters;

determining whether regenerative antiskid braking control, hydraulic braking control, or traction control is required based on said vehicle behavior;

generating command signals, in response to said vehicle behavior, for controlling said motor control means of said electric traction motor and said brake control means of said hydraulic braking system such that said regenerative antiskid braking control, hydraulic braking control, or traction control is provided; and

controlling said motor control means of said electric traction motor and said brake control means of said hydraulic braking system in accordance with said command signals.

12. A method for providing antiskid braking and traction control according to claim 11 wherein said step of sensing vehicle parameters measures wheel speed of both driven wheels and both nondriven wheels, brake pressure applied at both driven wheels and at least brake pressure in the brake line of nondriven wheels, master cylinder pressure, activation of a brake light switch, electric motor speed electric motor current, and activation of accelerator pedal switch.

13. A method for providing antiskid braking and traction control according to claim 11 wherein said step of generating command signals includes the step of generating a rear hydraulic braking control signal, a front hydraulic braking control signal, and a regenerative antiskid braking control signal for modulating said motor control means, if said vehicle is in a state requiring regenerative antiskid braking control.

14. A method for providing antiskid braking and traction control according to claim 11 wherein said step of generating command signals includes the step of generating a front hydraulic braking control signal and a rear hydraulic braking control signal for modulating said brake control means, if said vehicle is in a state requiring hydraulic braking control.

15. A method for providing antiskid braking and traction control according to claim 11 wherein said step of generating command signals includes the step of generating a reduction in motor torque control signal for modulating said motor control means, if said vehicle is in a state requiring traction control.

16. A method for providing antiskid braking and traction control according to claim 11 wherein if said vehicle requires regenerative antiskid braking control or traction control, said step of generating command signals further comprises the step of determining a worst case slip condition among said at least one driven wheel.

17. A method for providing antiskid braking and traction control according to claim 16 wherein said step of determining a worst case slip condition comprises the steps of:

estimating a critical adhesion coefficient μ

*_d for each driven wheel;

estimating a critical slip λ

*_d for each driven wheel;

deriving a critical adhesion coefficient μ

* for each driven wheel equal to a lowest value among said driven wheel critical adhesion coefficient for each driven wheel; and

deriving a critical slip λ

* equal to said critical slip associated with said critical adhesion coefficient.

18. A method for providing antiskid braking and traction control according to claim 14 wherein if said vehicle is in said state requiring regenerative antiskid braking control, said step of generating a command signal further includes the step of determining the optimum proportionality between regenerative braking and hydraulic braking necessary to maximize regenerative braking while providing a required braking demand.

19. A method for providing antiskid braking and traction control according to claim 11 wherein said step of calculating vehicle parameters includes calculating a vehicle acceleration, Dv, as one of said vehicle parameters according to the following equation whenever hydraulic brake pressure is applied to nondriven wheels:

##EQU5## wherein;

k is a spring rate of a drive axle of said vehicle,

Θ

_e is an integral of the speed of said electric motor,

G_r is a combined gear ratio of a differential and a transmission of said vehicle,

Θ

_rd and Θ

_ld are integrals of right and left driven wheels of said vehicle respectively,

J_r is wheel inertia,

α

_rd and α

_ld are time derivatives of said right and left driven wheel speeds respectively,

τ

_br and τ

_bl are hydraulic brake torques applied to said right and left driven wheels respectively,

R_w is a radius of said at least one driven wheel, and

M_v is the mass of said vehicle;

β

is the damping rate between the motor shaft and wheel,

W_e is the motor speed, and

W_rd and W_ld are speeds of the right and left driven wheels, respectively; and

according to the following equation whenever hydraulic braking is not applied to said nondriven wheels;

##EQU6## wherein;

v(t) is vehicle speed at time t,

T is sampling rate, and

v(t-T) is vehicle speed at time t minus sampling rate T.

20. A method for providing antiskid braking and traction control according to claim 11 wherein said step of calculating vehicle parameters includes calculating an adhesion coefficient μ

_d between a road surface and tire surface at each one of said driven wheels, as one of said vehicle parameters, according to the following equation;

##EQU7## wherein;

k is a spring rate of a drive axle of said vehicle,

Θ

_e is an integral of the speed of said electric motor,

G_r is a combined gear ratio of a differential and a transmission of said vehicle,

Θ

_rd and Θ

_ld are integrals of the speeds of right and left driven wheels of said vehicle respectively;

τ

_d is a hydraulic brake torque applied to said one driven wheel;

J_r is wheel inertia;

α

_d is a time derivative of the speed of said one driven wheel;

R_w is a radius of said one driven wheel;

N_v is a normal force on said one driven wheel;

β

is the damping rate between the motor shaft and wheel;

W_e is the motor speed; and

W_rd and W_ld are speeds of the right and left driven wheels, respectively.