Clutch Control System For Power Transfer Unit in Four-Wheel Drive Vehicle

• US 20070255473A1
• Filed: 04/25/2007
• Published: 11/01/2007
• Est. Priority Date: 04/26/2006
• Status: Active Grant

• Current Assignee: Magna Steyr Fahrzeugtechnik AG & Company KG (Magna International Incorporated)
• Original Assignee: Magna Steyr Fahrzeugtechnik AG & Company KG (Magna International Incorporated)
• Inventors: Parigger, Martin, Teuschel, Andreas, Christofl, Thomas
• Granted Patent: US 7,873,457 B2
• Time in Patent Office: Days
• US Class Current: 701/67
• CPC Class Codes: B60K 17/3462 with means for changing distribution of torque between front and rear wheels
• CPC Class Codes: B60K 23/0808 for varying torque distribution between driven axles, e.g. by transfer clutch
• CPC Class Codes: B60K 28/16 responsive to, or preventing, skidding of wheels brake control systems for vehicle drive stability B60T8/1755; arrangements responsive to a speed condition for adjusting wheel braking force B60T8/32; control of vehicle driving stability otherwise than by controlling the propulsion unit only B60W30/02; preventing wheel slippage by reducing power in rail vehicles B61C15/00
• CPC Class Codes: B60K 28/165 acting on elements of the vehicle drive train other than the propulsion unit and brakes, e.g. transmission, clutch, differential acting on brakes B60T8/17
• 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: F16D 2500/10425 Differential clutch
• CPC Class Codes: F16D 2500/10431 4WD Clutch dividing power between the front and the rear axle
• CPC Class Codes: F16D 2500/30406 Clutch slip
• CPC Class Codes: F16D 2500/3115 Vehicle wheel speed
• CPC Class Codes: F16D 2500/5075 Prevention or regulation of vehicle's wheel slip

Abstract

A power transfer assembly for use in a four-wheel drive vehicle has a torque transfer mechanism equipped with a power-operated clutch actuator for controlling adaptive engagement of a friction clutch and a control system for controlling actuation of the clutch actuator. The control system and its method of operation are adapted to control actuation of the clutch actuator based on whether the vehicle is operating in an engine drive mode or an engine coast/braking mode.

Claims

1. A transfer case for use in a motor vehicle having a powertrain and first and second drivelines, comprising:

a first output shaft transmitting torque from the powertrain to the first driveline;

a second output shaft adapted to drive the second driveline;

a clutch assembly operably disposed between said first and second output shafts;

a power-operated clutch actuator having a force generating mechanism for causing a clutch engagement force to be applied to said clutch assembly and an electric controlled device operable to move said force generating mechanism in response to a control signal; and

a control system operable to generate said control signal based on certain operating characteristics of the vehicle and including a first slip control program and a second slip control program, said first slip control program operable for determining a torque gradient value when the powertrain transmits drive torque to said first output shaft and said second slip control program is operable for determining torque gradient value when the powertrain transmits coast torque to said first output shaft.

2. A method of controlling torque transfer in an all-wheel drive vehicle having a powertrain, first and second drivelines, a clutch for controlling the distribution of torque to the first and second drivelines, sensors for determining the wheel speeds for both drivelines, a control unit for calculating a new command torque value, and a clutch actuator energized by the control unit for engaging the clutch to generate the new command torque, said method comprising the steps of:

calculating a speed difference value based on the wheel speeds detected by the sensors;

comparing the speed difference value to a threshold value;

integrating the deviation between the speed difference value and the threshold value once the speed difference exceeds the threshold value;

continue integration of the deviation until the integral reaches a limit value which is a function of the last command torque value;

calculating the new command torque value once the integral exceeds the limit value as a function of the last command torque and a gradient value of the speed difference; and

outputting a control signal to the clutch actuator corresponding to the new command clutch for engaging the clutch.

3. The method of claim 2 wherein the threshold value is a function of the vehicle speed.

4. The method of claim 2 further comprising the step of initiating a hold time once the speed difference value is less than the threshold value.

5. A method for controlling transfer of drive torque in an all-wheel drive vehicle having a powertrain, first and second drive axles, a controllable clutch operable to control the distribution of drive torque to the axles, sensors for the wheel speeds of both axles, a control unit for determining a new command torque capacity of the clutch, and an actuator to set the torque capacity with the following, sequentially repeated steps:

(a) calculate a speed difference value from the sensors based on the wheel speeds of the first and second drive axles;

(b) if the speed difference value passes a threshold value, then integrate the deviation between the speed difference value and the threshold value until the integral reaches a limit value, which is a function of the last command torque capacity of the clutch; and

(c) if the integral reaches this limit value, determine a new command torque capacity as a function of the last command torque capacity and a gradient of the speed difference value, which new command torque capacity is set by the actuator engaging the clutch.

6. The control method according to claim 5 wherein the threshold value is a function of the speed of the vehicle.

7. The control method according to claim 5 wherein:

(a) a vehicle speed is calculated based on signals of the wheel speed sensors of the first and the second drive axles;

(b) the speed difference value of the wheels is compared with a threshold value which is a function of the vehicle speed; and

(c) if the speed difference value becomes less than this threshold value, the torque capacity is reduced by a value determined as a function of the difference between the speed difference value and the threshold value.

8. The control method according to claim 5 wherein a hold time starts if the first threshold value is passed downwards, and a second threshold value is determined as function of vehicle speed;

(a) if the second threshold value is passed downwards after the hold time, then the torque capacity is derived as a first function of the deviation between the speed difference value from the second threshold value;

or

(b) if the second threshold is passed within the hold time, starting after expiration of the hold time the torque capacity is derived as a second function of the deviation between the speed difference from the second threshold value;

or

(c) if the second threshold value is not passed, the new command torque capacity is set equal to the last command torque capacity.

9. The control method according to claim 8 wherein when the first threshold is passed downwards, integration of the deviation between the speed difference value and the second threshold value is started, whereby the speed difference values lower than the first threshold are taken as negative, and it is continued until the integral reaches a limit value which is a function of the last command torque capacity of the clutch, and the new command torque capacity of the clutch is derived according to a function of the last command torque capacity and the gradient of the speed difference according to a third function, which new command torque capacity is set by the clutch actuator of the clutch.

10. The control method according to claim 8 wherein if the speed difference value is lower than the second threshold, the new command torque capacity is derived according to a function of the deviation between the speed difference and the second threshold or as a function of the steering angle.

11. The control method according to claim 8 wherein the speed difference of the wheels of the first and second driven axles is derived from the signals of the sensors using a 1^st order filter with a defined filter-constant.

12. The control method according to claim 8 wherein the first and second threshold values are modified using the speed difference during cornering.

13. The control method according to claim 8 wherein the first and second threshold values are modified using the speed difference resulting from differences in tire diameters.

14. The control method according to claim 8 wherein pursuant to the sign of the speed difference value and the engine torque it is distinguished between a drive-slip condition and a coast-slip condition, and if

(a) the sign of the speed difference value and the engine torque are positive, then the function of the vehicle speed follows a first curve, and if

(b) the sign of the speed difference value and the engine torque are negative, then the function of the vehicle speed follows a second curve.

15. The control method according to claim 8 wherein the new command torque capacity is compared with the actual torque capacity set by the actuator of the clutch, and if the deviation therebetween exceeds a defined tolerance value the new command torque capacity is set equal to the sum of the actual torque capacity and the tolerance value.