Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Reexamination Certificate
2000-01-18
2001-06-26
Marmor, Charles A (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
C475S303000, C074S339000
Reexamination Certificate
active
06251045
ABSTRACT:
BACKGGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates, generally, to two-speed (high-low) transfer cases and, more particularly, to a method and apparatus for shifting between low and high gearing arrangements for a two-speed transfer case.
2. Description of the Related Art
Transfer cases are used in full and part-time, four-wheel drive vehicles to distribute driving power received through an input shaft from the vehicle's transmission to a pair of output drive shafts. One of the drive shafts powers the vehicle's front wheels and the other of the drive shafts powers the vehicle's rear wheels. In vehicles that permit shifting between two-wheel drive and four-wheel drive modes, the input shaft of the transfer case provides continuous drive power to one of its output shafts and selectively provides drive power to the other output shaft via some type of disengageable or otherwise adjustable coupling, such as a viscous coupling, electromagnetic clutch, or positionable spur gearing. Other drive modes are sometimes provided, including four-wheel drive high (
4
H) for higher four-wheel drive speeds, four-wheel drive low (
4
L) for lower four-wheel drive speeds, neutral for disengaging the transmission from the front and rear axles to allow towing, and locked four-wheel drive for controlling wheel slippage. Historically, transfer cases were configured such that the vehicle had to be stopped before shifting between low and high gears. Typically, this requirement resulted from the lack of any type of synchronizer within the transfer case to facilitate this shift. In these cases, an adjustable coupling was used to manually shift between drive modes using a mechanical shift actuator.
On the other hand, synchronization of the input and output shafts of the transfer case prior to shifting between low and high gears and into and out of four-wheel drive facilitates shifts while the vehicle is moving. This mode of operation has been referred to as shift “on the fly.” Numerous synchronization devices have been proposed in the related art. For example, it is known to employ a clutch which is operable to translate torque either directly between the input and output shafts (high speed) or between the input and output shafts via a planetary gear reduction set. Clutches of this type may be spring-biased such that shifting is not fully accomplished until the relative speeds of the rotating members to be coupled have achieved a certain level of synchronization. However, some synchronization devices known on the related art have suffered from the disadvantage that they are overly complex and add excessive cost to the transfer case. Others have failed to achieve adequate synchronization prior to the shifting event resulting in slip and/or unacceptable noise.
Mechanical shift actuators gave way to electronically controlled shift actuators, particularly for shift actuators that can be operated by a rotational source, such as an electric motor. U.S. Pat. No. 4,664,217 issued to Welsh et al. on May 12, 1987 discloses such an electric shift actuator. More specifically, the Welsh et al. '217 patent teaches the use of a reversible dc electric motor to rotate a cammed shift actuator to selectively shift drive gearing within the transfer case between a neutral position, two-wheel drive mode and low and high speed four-wheel drive modes. Selection of a desired drive mode is accomplished by operating the motor under the control of a microprocessor-based control circuit. The microprocessor commands a motor drive circuit to energize the motor to run in either the clockwise or counterclockwise direction to achieve the desired drive mode. While this type of electronic shift control was an improvement in the related art, the problem of effectively and efficiently synchronizing the rotation of members to be coupled during any given shifting operation remained.
U.S. Pat. No. 5,771,477 issued to Showalter et al. on Jun. 23, 1998, proposed one solution for this problem. More specifically, the Showalter '477 patent discloses a method and apparatus for synchronizing low to high transfer case shifts using sensors to sense the speed of the input and output shafts of the transfer case. A microprocessor is employed to measure the change in speed over time of each of the input and output shafts and to make a prediction when the relative speeds of the shafts will be equal. The microprocessor then commands operation of a shift actuator at a predetermined time before the shafts are synchronized such that shifting is accomplished when the speeds of the input and output shafts are substantially equal.
While the '477 method and apparatus was an improvement over the related art, there still remains a need for greater control and more accurate synchronization prior to shifting between low and high speeds in a transfer case. In addition, there remains a need to achieve such synchronization in an efficient, cost-effective and relatively simply manner.
SUMMARY OF THE INVENTION
The present invention overcomes the disadvantages in the related art in a transfer case having synchronized low to high shift capabilities. More specifically, the transfer case includes an input shaft, an output shaft, and a gear set selectively operable to translate torque between the input and output shafts at reduced speeds. A clutch is operable to translate torque between the input and output shafts either directly or through the gear set. An actuator, having a rotational output, is operatively coupled to the clutch for moving the clutch between predetermined positions. A control unit is employed in connection with the transfer case to effect the method of synchronizing low to high shifts in the transfer case. To this end, the control unit calculates the speed of the actuator as it moves the clutch to a neutral position. The control unit further determines the additional time until the clutch will reach a predetermined synchronization point using the speed of the actuator and the remaining rotational distance through which the actuator must move for the clutch to reach the predetermined synchronization point. The control unit is further operable to stop the actuator when the clutch has reached the synchronization point for no longer than a predetermined time. The control unit then senses and compares the rotational speeds of the input and output shafts and signals the actuator to complete the shift from low to high by moving the clutch to provide direct torque translation between the input and output shafts when the difference in the rotational speeds of the input and output shafts is less than a predetermined value.
Accordingly, the present invention is a method and apparatus for providing synchronization of low to high shifts in a transfer case which allows for a high level of control and an accurate synchronization prior to shifting between low and high speeds. Furthermore, these objectives are achieved with the method and apparatus of the present invention in an efficient, cost effective and relatively simple manner.
Other objects, features and advantages of the present invention will be readily appreciated as the same becomes better understood after reading the subsequent description taken in connection with the accompanying drawings.
REFERENCES:
patent: 4664217 (1987-05-01), Welch et al.
patent: 4718303 (1988-01-01), Fogelberg
patent: 4828070 (1989-05-01), Maramatsu
patent: 5150637 (1992-09-01), Ninomiya et al.
patent: 5346442 (1994-09-01), Eastman
patent: 5389053 (1995-02-01), Steeby et al.
patent: 5407024 (1995-04-01), Watson et al.
patent: 5425284 (1995-06-01), Davis
patent: 5508916 (1996-04-01), Markyvech et al.
patent: 5653143 (1997-08-01), Langevin
patent: 5680308 (1997-10-01), Warren
patent: 5688205 (1997-11-01), Buhler
patent: 5699870 (1997-12-01), Warren
patent: 5704867 (1998-01-01), Bowen
patent: 5771477 (1998-06-01), Showalter et al.
patent: 5867092 (1999-02-01), Vogt
patent: 6022289 (2000-02-01), Francis
patent: 6164149 (2000-12-01), Ohmori et al.
patent: 6165103 (2000-12-01), Tenzor
Ficht John R.
Fosmoe Richard Thomas
Oliveira Gary A.
Bliss McGlynn P.C.
Borg-Warner Inc.
Dziegielewski Greg
Marmor Charles A
Pang Roger
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