Clutch control device for four-wheel drive vehicle

Patent metadata

Field	Value
Publication number	US-9981552-B2
Application number	US-201515118259-A
Country	US
Kind code	B2
Filing date	Feb 24, 2015
Priority date	Feb 28, 2014
Publication date	May 29, 2018
Grant date	May 29, 2018

Abstract

A clutch control device is provided for a four-wheel drive vehicle for transmitting drive force to the rear wheels. The clutch control device includes a dog clutch and a friction clutch, and a 4WD control unit that controls the engagement and disengagement of the dog clutch and the friction clutch. The 4WD control unit is switchable between a two-wheel drive mode and a four-wheel drive mode. The 4WD control unit is programmed to control engagement of the dog clutch so that the dog clutch is engaged after the friction clutch is engaged and the dog clutch is synchronized. During engagement of the dog clutch, the 4WD control unit is programmed to reduce a transmission torque of the friction clutch when the dog clutch engagement standby state is detected.

First claim

The invention claimed is:

1. A clutch control device for a four-wheel drive vehicle having a pair of main drive wheels, a pair of auxiliary drive wheels, and a drive source configured to output a drive force, the clutch control device comprising:
a dog clutch operatively disposed in a transmission path between the main drive wheels and the auxiliary drive wheels to separate a system for transmitting the drive force to the auxiliary drive wheels from a system for transmitting the drive force to the main drive wheels by releasing the dog clutch;
a friction clutch operatively disposed in the transmission path between the main drive wheels and the auxiliary drive wheels to allocate a portion of the drive force from the drive source to the auxiliary drive wheels in accordance with a clutch engagement capacity of the friction clutch;
an engagement standby state sensor configured to detect an engagement standby state in which engagement of the dog clutch is incomplete at a time of an engagement operation of the dog clutch; and
a clutch control unit operatively coupled to the dog clutch and the friction clutch to selectively carry out an engagement and disengagement control of the dog clutch and an engagement and disengagement control of the friction clutch in accordance with a vehicle state that is detected by the engagement standby state sensor such that the four-wheel drive vehicle is switched between a two-wheel drive state in which only the main drive wheels are driven and a four-wheel drive state in which the main drive wheels and the auxiliary drive wheels are driven,
the clutch control unit being further programmed such that when the dog clutch will be engaged, the clutch control unit carries out a control to engage the friction clutch and synchronize the dog clutch before engaging the dog clutch, and
the clutch control unit being further programmed to reduce a transmission torque of the friction clutch when the engagement standby state is detected during the engagement of the dog clutch, the clutch control unit further executing a waiting step before reducing the transmission torque of the friction clutch if the four-wheel drive vehicle is decelerating when the engagement standby state is detected during the engagement of the dog clutch.

2. The clutch control device as recited in claim 1 , wherein
the clutch control unit is further programmed to execute a control to switch from a disconnected two-wheel drive mode in which the dog clutch and the friction clutch are released to a drive mode in which the dog clutch is engaged, when the vehicle is accelerating.

3. The clutch control device according to claim 2 , wherein
the clutch control unit is further programmed to reduce the transmission torque to a degree that a differential rotation is generated between a drive source side and an auxiliary drive source side of the dog clutch when reducing the transmission torque of the friction clutch.

4. The clutch control device according to claim 2 , wherein
the clutch control unit is further programmed to carry out the reduction gradually over time when reducing the transmission torque of the friction clutch.

5. The clutch control device according to claim 2 , wherein
the clutch control unit is further programmed to wait for a vehicle speed to go below a vehicle speed threshold value that is set in advance in the waiting step.

6. The clutch control device according to claim 5 , wherein
the clutch control unit is further programmed to carry out a drive mode switch control in accordance with the vehicle speed, wherein the drive mode is controlled to the disconnected two-wheel drive mode when the vehicle speed is in a higher vehicle speed region than a mode switch vehicle speed that is set in advance, and the drive mode is switched to a four-wheel drive mode in a lower vehicle speed region than the mode switch vehicle speed, and
the clutch control unit is further programmed to set the vehicle speed threshold value to a value that is below the mode switch vehicle speed.

7. The clutch control device according to claim 6 , wherein
the clutch control unit is further programmed to set the vehicle speed threshold value to a value at which an engagement shock is generated when engaging the dog clutch is suppressed.

8. The clutch control device according to claim 5 , wherein
the clutch control unit is further programmed to carry out the reduction with a gradient that decreases with time when reducing the transmission torque of the friction clutch in the engagement standby state during deceleration.

9. The clutch control device according to claim 2 , wherein
the dog clutch is disposed upstream of a transfer mechanism provided at a drive branch position to the auxiliary drive wheels, and
the friction clutch is disposed in a drive shaft of one of the auxiliary drive wheels which extends from the transfer mechanism that is connected to a propeller shaft and a differential.

10. The clutch control device according to claim 2 , wherein
the friction clutch is disposed upstream of a transfer mechanism provided at a drive branch position to the auxiliary drive wheels, and
the dog clutch is disposed in a drive shaft of one of the auxiliary drive wheels which extends from the transfer mechanism that is connected to a propeller shaft and a differential.

11. The clutch control device as recited in claim 1 , wherein
the clutch control unit is further programmed to reduce the transmission torque to a degree that a differential rotation is generated between a drive source side and an auxiliary drive source side of the dog clutch when reducing the transmission torque of the friction clutch.

12. The clutch control device as recited in claim 1 , wherein
the clutch control unit is further programmed to carry out the reduction gradually over time when reducing the transmission torque of the friction clutch.

13. The clutch control device as recited in claim 1 , wherein
the dog clutch is disposed upstream of a transfer mechanism provided at a drive branch position to the auxiliary drive wheels, and
the friction clutch is disposed in a drive shaft of one of the auxiliary drive wheels which extends from the transfer mechanism that is connected to a propeller shaft and a differential.

14. The clutch control device as recited in claim 1 , wherein
the friction clutch is disposed upstream of a transfer mechanism provided at a drive branch position to the auxiliary drive wheels, and
the dog clutch is disposed in a drive shaft of one of the auxiliary drive wheels which extends from the transfer mechanism that is connected to a propeller shaft and a differential.

15. A clutch control device for a four-wheel drive vehicle having a pair of main drive wheels, a pair of auxiliary drive wheels, and a drive source configured to output a drive force, the clutch control device comprising:
a dog clutch operatively disposed in a transmission path between the main drive wheels and the auxiliary drive wheels to separate a system for transmitting the drive force to the auxiliary drive wheels from a system for transmitting the drive force to the main drive wheels by releasing the dog clutch;
a friction clutch operatively disposed in the transmission path between the main drive wheels and the auxiliary drive wheels to allocate a portion of the drive force from the drive source to the auxiliary drive wheels in accordance with a clutch engagement capacity of the friction clutch;
an engagement standby state sensor configured to detect an engagement standby state in which engagement of the dog clutch is incomplete at a time of an engagement operation of

Assignees

• Nissan Motor

Inventors

• Ogawa Katsuyoshi
• Mori Atsuhiro
• Mitsuishi Shunichi
• Morita Makoto
• Takaishi Tetsu

Classifications

• B60K2023/0825

  for adding torque to the front wheels · CPC title

• B60K2023/0833

  for adding torque to the rear wheels · CPC title

• F16D2500/10462

  Dog-type clutch · CPC title

• B60K23/08 Primary

  for changing number of driven wheels {, for switching from driving one axle to driving two or more axles (B60K17/3515 takes precedence)} · CPC title

• B60K17/02

  characterised by arrangement, location, or kind of clutch · CPC title