Method and apparatus for providing momentary torque reversal for a transmission having an automated shift system

An automated vehicle transmission having a wet clutch and an auxiliary motor that is operatively connected to the transmission to overcome residual torque forces in the wet clutch. Residual torque forces in the wet clutch may prevent disengagement of a gear train and also prevent the transmission from shifting into neutral. A control system determines whether residual torque is resisting the disengagement of the gear train for more than a predetermined time period. According to the method, if a shift is delayed for more than the predetermined time period, the auxiliary motor is actuated to apply an oppositely oriented torque to the transmission gear train to overcome the residual torque and allow the transmission to shift into neutral.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to transmissions having an automated shift system.

2. Background Art

Transmissions for vehicles having an automated shift mechanism have been developed that automatically shift a shift lever mechanism similar to a manual transmission shift mechanism. One example of such a transmission has been developed for medium and heavy-duty trucks is known as the “AutoShift” transmission by Applicants' assignee primarily for medium and heavy-duty trucks. This system uses an electronic control that operates X-Y motors in a shift actuator to shift between a plurality of different gear trains to provide a range of gear ratios. Using this technique, operation of a vehicle is simplified and shifting performance may be optimized by reducing or minimizing human error. While the AutoShift system has proven effective in higher gear ratios, in lower gear ratios when the truck is operated at slow speeds, it would be desirable to provide quicker shift response when shifting from gear to gear.

In some transmission applications, it may be preferred to provide a wet clutch to disengage the transmission from the vehicle engine or source of drive torque to provide superior clutch durability. The torque load to the transmission is relieved by disengaging the clutch. Disengaging the clutch theoretically permits the torque load to go to zero and allows the transmission system to shift into neutral and prior to changing gears. However, with a wet clutch, even a small amount of rotation between the transmission and engine may cause the wet clutch to remain sufficiently engaged to prevent the transmission from being shifted into neutral. A wet clutch resists pulling to neutral as a result of “torque lock” caused by viscous drag in the wet clutch which may be as little as seven foot pounds of torque. The viscous drag is caused by the shearing of fluid between members that have a speed differential in the clutch pack.

If an X-Y shifter is provided, it may not be able to overcome the residual torque. If the X-Y shifter motors cannot overcome the residual torque, shifting will be delayed until the torque is reduced sufficiently to be overcome by the X-Y shifter motors. The time required to fully disengage the clutch may lead the operator to believe that the transmission is sticking or not properly shifting. A delay of a half a second or more may be noticeable to an operator.

There is a need for a control system and method of operating a vehicle transmission system that breaks, or reverses, the torque load resulting from wet clutch viscous drag. By counteracting the torque load from the wet clutch, one gear set can be disengaged allowing the transmission to be shifted into neutral. These and other problems facing prior art vehicle transmission systems are addressed by Applicants' invention as summarized below.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a vehicle transmission is provided that provides a plurality of selectable speed ratios. The transmission comprises an input shaft that receives torque in a first direction of rotation that is directed to a plurality of gear sets that each selectively provide one of the plurality of gear ratios. Each gear set comprises a plurality of gears that are arranged in a drivetrain. A wet master clutch is disengaged to facilitate sufficient disengagement of the engine from the transmission allowing the transmission to change from one gear set to another. Residual viscous drag torque may be created by the wet clutch that, in some circumstances, resists disengagement of the transmission. The transmission may also include at least one shift motor that shifts the transmission from one gear set to a neutral position between gear sets and then to another gear set. The control system determines whether shifting the transmission into neutral is delayed for more than a predetermined time period. If so, an auxiliary motor may apply torque in a second direction of rotation that is opposite to the first direction of rotation when the control system determines that shifting into a neutral position is delayed for more than the predetermined period of time. Applying torque in the second direction overcomes the residual clutch drag torque and thereby facilitates shifting the transmission into the neutral position by creating a torque reversal across the transmission.

According to other aspects of the invention as they relate to the vehicle transmission embodiment of the invention, the auxiliary motor is provided with an axially shifted gear that engages a gear in the transmission. An example of such an auxiliary motor and an axially shifted gear combination is commonly referred to as a Bendix motor. The auxiliary motor may be a fluid driven motor such as a hydraulic or pneumatic motor. Alternatively, the auxiliary motor could be an electric motor, or the like. The auxiliary motor may engage a gear that is attached to the input shaft or, if the transmission is provided with a counter shaft, the auxiliary motor may engage a gear that is attached to the counter shaft or is meshed to the counter shaft. The auxiliary motor may be connected to the transmission through a power take off connection or may be connected in another location on the housing of the transmission.

According to another aspect of the invention as it relates to the transmission, the control system may signal the auxiliary motor to disengage the gear after the transmission shifts to neutral. According to another aspect of the invention as it relates to the transmission, at least one shifter motor may further comprise a set of X-Y shifter motors. A position sensor may be disposed in the set of X-Y shifter motors when the position sensor provides a signal to the control system that is used to determine whether the transmission is in the neutral position.

According to another aspect of the invention, a method of controlling an automated vehicle transmission system is provided. The transmission system receives torque in the first direction of rotation from an engine. A multiple speed transmission that has a wet clutch, disengages the wet clutch to permit shifting the transmission into a neutral position that is subject to a residual torque in the first direction of rotation. A control unit is provided for shifting the transmission. The method comprises the steps of determining if the residual torque is delaying movement of the transmission into the neutral position for more than the predetermined period of time. If so, a reverse output torque is applied to the transmission in a second direction of rotation to counteract the residual torque and allow the transmission to be placed into neutral.

According to another aspect of the invention as it relates to the method of controlling the automated vehicle transmission, the method may further include the step of determining if a transmission neutral mode or gear change has been selected but not achieved within the predetermined time period.

According to another aspect of the method, the step of applying a reverse output torque further comprises providing an auxiliary motor that engages a gear that is attached to the input shaft. Alternatively, reverse output torque may be applied by the auxiliary motor engaging a gear that is attached to a counter shaft.

Another aspect of the method may comprise the step of stopping the application of reverse output torque when the control system determines that the transmission is in the neutral position.

According to another aspect of the method, the step of determining whether the residual torque is delaying movement may further comprise monitoring the position sensor disposed in the set of X-Y shifter motors and by providing a signal to the control system to determine whether the transmission is in the neutral position.

These and other aspects of the vehicle transmission and method of controlling the vehicle transmission of the present invention will be better understood in view of the attached drawings when taken in connection with the detailed description of the illustrated embodiments of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

Referring now toFIG. 1, a vehicle transmission10and engine12of a vehicle (not shown) are connected by a wet clutch14. The wet clutch14connects the drive shaft16of the engine12to an input shaft18of the transmission10. The wet clutch14allows for hydrostatic engagement and disengagement of the transmission10by the engine12.

The wet clutch14provides increased durability in comparison to a dry clutch. The wet clutch14is of conventional design and relies upon fluids such as oil (natural, synthetic or any other combination) to cool the clutch pack that may become heated as a result of repeated engagements and disengagements. While the wet clutch14provides an interrupt mechanism for drive line torque, in certain applications, if a limited amount of residual torque is present in the clutch due to viscous drag, it will make the gear train difficult to disengage and pull to neutral. Residual torque of seven foot pounds or more in the wet clutch14may be sufficient to prevent the gear train from being pulled to neutral.

According to one embodiment of the invention, an auxiliary motor20(that may be of the type that is commonly referred to as a “Bendix” motor) may be provided to overcome the residual torque counteracting the residual torque generated by a wet clutch. Counteracting the residual viscous torque allows the gear train to disengage. A control system22is provided on the transmission to control shifting the transmission into different gear ratios. The control system22may comprise a shifter motor or a set of X-Y shifter motors24that provide automated shifting of a transmission. The X-Y shifter motors24act upon a shift bar housing (not shown) to move the gear selection mechanism in a shift pattern comparable to a manual shift pattern of a conventional manual transmission.

The auxiliary motor20engages a gear26within the transmission10to exert a reverse torque that counteracts the residual torque and permits the control system22to shift the transmission out of one gear into neutral and into a new gear ratio.

Referring now toFIG. 2, a transmission10is shown that has an auxiliary motor20mounted to a side mounting plate28. The side mounting plate28secures the auxiliary motor20to a housing30of the transmission10. The input shaft18of the transmission10is provided at the engine end of the transmission10while the auxiliary motor20is secured to a transmission housing30and extends radially relative to the input shaft18.

Referring now toFIG. 3, the auxiliary motor20is shown with the side mounting plate28. An axially shifted gear36having a plurality of gear teeth38is secured to a shaft40. The shaft40is axially shiftable relative to the auxiliary motor20to cause the gear teeth38of the axially shifted gear36to engage axially extending gear teeth42that extend in an axial direction relative to the gear26. The axially extending gear teeth42are provided on a side wall44, or flange, that is associated with the gear26. The gear26may be an input shaft gear or any other gear that may transmit reversely oriented torque through the transmission to the wet clutch14.

In operation, the auxiliary motor20is actuated by the control system22of the transmission10when it is desired to shift a transmission but residual torque present in the wet clutch prevents disengagement of the gear train. If the residual torque present in the wet clutch prevents disengagement, the gear train may not disengage and the transmission10may not shift into neutral within the predetermined time period. If, for example, residual torque prevents the gear train from disengaging for a period of more than one half of a second, the control system22may actuate the auxiliary motor20. When the auxiliary motor20is actuated, the shaft40shifts the axially shifted gear36causing gear teeth38to engage gear teeth38of the gear26. The auxiliary motor20applies torque to the gear26that in turn imparts torque to the wet clutch14countering the residual torque. When the control system determines that the transmission is in neutral, application of torque to the gear26is stopped by turning off the auxiliary motor20and retracting the axially shifted gear36.

Referring now toFIG. 4, an alternative embodiment of the present invention is shown wherein a transmission50is provided with a power take off (PTO) mounted auxiliary motor52. The auxiliary motor52is secured to a PTO connection port54. The PTO connection port54in the illustrated embodiment is disposed on the opposite end of the transmission from input shaft56. Input shaft56is adapted to be operatively connected to an engine (not shown). The PTO mount auxiliary motor52is secured to the PTO connection port54by a PTO connector58. The PTO mount auxiliary motor52is disposed in the same axial orientation as the input shaft56.

Referring toFIG. 5, the PTO mounted auxiliary motor52is shown with the PTO connector58. The auxiliary motor52has an axially shifted gear60that is mounted on an extensible shaft62that is driven by the auxiliary motor52. The extensible shaft62shifts the axially shifted gear60into engagement with a gear66that is located adjacent to the PTO. The gear66may be mounted on a counter shaft of the transmission or, alternatively, may be mounted on the input shaft of a transmission. It may also be any other gear of the transmission that is continuously and constantly meshed with the gear train connected to the input shaft. A plurality of gear teeth68are provided on the gear60that engage gear teeth70on the gear66.

In operation, the auxiliary motor52is actuated when the engine control system22determines that the gear train is locked up as a result of residual torque forces within the wet clutch. The control system22actuates the auxiliary motor52causing the motor to operate and also axially shift the gear60into engagement with the gear66. Rotation of the gear60provides torque that is applied to the gear66. The torque applied to the gear66is directed in the opposite direction relative to the residual torque in the wet clutch14to overcome the residual torque. This creates a torque reversal across the transmission and allows the transmission to shift into neutral. After the transmission is shifted into neutral, the control system may stop the application of torque to the gear66. The control system22may then act through the X-Y shift motor24to shift the transmission into the next desired gear ratio.