Gear clash logic

A system and method for selectively engaging and disengaging auxiliary equipment to avoid gear clash in a vehicle is disclosed. The system includes a transmission, a transfer case, and a transmission controller. The transmission has a plurality of gears for establishing a plurality of gear ratios. The transfer case is coupled to the transmission by an output shaft. The transmission controller is in communication with a plurality of control devices for controlling the operation of the transmission. The controller includes control logic for controlling the engagement and disengagement of the auxiliary equipment. The control logic has a first control logic for determining whether an operator has actuated a selector switch, a second control logic for actuating a torque transmitting device to engage or disengage the auxiliary equipment and avoid gear clash, a third logic for monitoring the engagement or disengagement of the auxiliary equipment, and a fourth control logic determining whether the auxiliary equipment has been engaged or disengaged.

TECHNICAL FIELD

The present invention relates to systems and methods for preventing gear clash in vehicles having a transfer case that couples a transmission output shaft to auxiliary equipment.

BACKGROUND

Commercial vehicles such as fire truck pumpers, sewer cleaners, and oil field pumpers include an auxiliary gearbox or transfer case that is connected to the output shaft of the vehicle's transmission. In auxiliary equipment mode, the transfer case drives auxiliary equipment, and the transmission controller provides a secondary mode of operation. A secondary mode of operation could be a single forward range or all ranges with a shift schedule specific to the auxiliary equipment.

The process of transfer case engagement and disengagement with auxiliary equipment takes place with the transmission output shaft locked by applying locking clutches. The locking clutch application is referred to as Neutral Very Low (NVL) range. In NVL, auxiliary equipment engagement and disengagement is difficult to achieve when gear teeth do not line up properly such that a “gear-clash” condition exists. “Gear-clash” in the transfer case cannot be overcome with a transfer case actuator. Operators will attempt to eliminate “gear-clash” by selecting drive or reverse. A high failure rate of transfer case actuators is attributed to “gear-clash”. Another “gear-clash” condition exists when the gear teeth have been lined up properly, however, the gear teeth do not slide to full engagement due to transmission drag torque on the gear teeth.

Therefore, there is a need for a system and method to preventing “gear-clash” that addresses both gear teeth alignment and gear teeth engagement. The system and method for preventing “gear-clash” should operate during engagement and disengaging of the auxiliary equipment.

SUMMARY

In an aspect of the present invention, a system is provided for selectively engaging and disengaging auxiliary equipment to avoid gear clash in a vehicle. The system includes a transmission, a transfer case, and a transmission controller. The transmission has a plurality of gears for establishing a plurality of gear ratios. The transfer case is coupled to the transmission by an output shaft. The transmission controller is in communication with a plurality of control devices for controlling the operation of the transmission. The controller includes control logic for controlling the engagement and disengagement of the auxiliary equipment. The control logic has a first control logic for determining whether an operator has actuated a selector switch, a second control logic for actuating a torque transmitting device to engage or disengage the auxiliary equipment and avoid gear clash, a third logic for monitoring the engagement or disengagement of the auxiliary equipment, and a fourth control logic determining whether the auxiliary equipment has been engaged or disengaged.

In still another aspect of the present invention, a method for selectively engaging and disengaging auxiliary equipment to avoid gear clash in a transfer case of a vehicle is provided. The method includes determining whether an operator has actuated a selector switch, actuating a torque transmitting device to engage or disengage the auxiliary equipment and avoid gear clash, monitoring the engagement or disengagement of the auxiliary equipment, and determining whether the auxiliary equipment has been engaged or disengaged.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, wherein like reference numbers refer to like components, inFIG. 1a system10for selectively powering a first set of equipment12and a second set or auxiliary set of equipment14to avoid gear clash is schematically illustrated. Gear clash includes misalignment of gear teeth and the present invention contemplates that the teachings described herein may be most useful in vehicles having auxiliary power equipment that require a power transfer from the transmission. For example, commercial vehicles such as fire trucks, sewer cleaners and oil field pumpers all have auxiliary equipment that require a power transfer from the transmission to operate. Of course, one of ordinary skill in the art will appreciate that the teachings of the present invention can be applied not only to these types of vehicles but to other vehicles and systems as well.

In an embodiment of the present invention, system10includes a transmission16, a transfer case18, a transmission controller20and control logic embodied in hardware, software, or a combination of hardware and software within controller20. The transmission16is a conventional vehicle transmission and, generally, has a plurality of gears for establishing a plurality of gear ratios. For example, transmission16is the transmission shown and described in U.S. Pat. No. 4,070,927, hereby incorporated by reference. Transmission16may have six forward gear speeds or gear ratios and two reverse gear speeds or gear ratios. Of course, the present invention contemplates is operable with transmissions having other gear speeds. Transmission16typically has a plurality torque transmitting devices (not shown) for selectively transferring power between the plurality of gears and ultimately to a transmission output shaft22. Moreover, at least one of torque transmitting devices (C4) is configured to selectively prevent rotation of the transmission output shaft22. In order to transmit torque from an engine to the output shaft22, at least two torque transmitting devices must be engaged and the torque transmitting device C4must be disengaged. When the transmission16is in neutral, only one torque transmitting mechanism (C5) is engaged or activated. The torque transmitting devices are clutches or brakes as is well known in the field of transmissions.

The transfer case18includes a plurality of gears to transfer torque or power from the transmission to auxiliary equipment14. The transmission output shaft22couples the transfer case18to transmission16. The transmission controller20, generally, includes a processor (not shown) in communication with electronic memory storage devices (not shown). Further, control logic is also provided in controller20and may be implemented in hardware, software, or a combination of hardware and software. For example, a control logic may be in the form of program code that is stored on the electronic memory storage and executable by the processor. Generally, controller20receives transmission speed signals from transmission speed sensors23mounted to transmission16. Additionally, transmission controller20receives other inputs from other vehicle input devices24such as an auxiliary mode selection switch. The auxiliary mode selection switch provides an output to controller20indicative of an operator requesting auxiliary power mode or the engagement of the auxiliary equipment14. Further, a positive engagement switch or sensor26is in communication with the auxiliary equipment14and the transmission controller20. The positive engagement switch26provides an output to controller20indicative of engagement or disengagement of the auxiliary equipment14. The controller20receives these inputs and selectively activates a plurality of control devices such as the torque transmitting devices to control the operation of the transmission and the rotation of the transmission output shaft22.

For example, a control logic implemented in software program code that is executable by the processor of controller20includes a first control logic for determining whether an operator has actuated a selector switch, a second control logic for determining whether a transmission output speed is greater than an output speed threshold, a third control logic for engaging a torque transmitting device to lock the transmission output shaft, a fourth control logic for incrementing a first timer after the transmission output shaft is locked, a fifth control logic for comparing a first recorded time recorded by the first timer to a first time threshold, a sixth control logic for disengaging all torque transmitting devices so that no torque is transferred to the output shaft, a seventh control logic for incrementing a second timer, an eighth control logic for comparing a second recorded time recorded by the second timer to a second time threshold, a ninth control logic for engaging the torque transmitting device engaged during neutral and disengaging the torque transmitting device that locks the output shaft to allow the transmission output shaft to rotate, a tenth control logic for incrementing a third timer after the torque transmitting device has been disengaged to allow the transmission output shaft to rotate and an eleventh control logic for comparing a third recorded time recorded by the third timer to a third time threshold.

Referring now toFIG. 2, a flowchart of a method30for controlling the engagement of the second set or auxiliary set of equipment is illustrated, in accordance with an embodiment of the present invention. The method30is initiated at block32with the vehicle having the auxiliary equipment originally being in a normal mode of operation with the auxiliary equipment disengaged. At block34, the method30determines whether an auxiliary equipment mode has been selected by a vehicle operator indicative of a desire to engage the auxiliary equipment. If the method30has determined that an auxiliary equipment mode has been requested, then the method30enters an engage gear clash logic routine, as represented by block36, to prevent gear clash in the transfer case and engage the auxiliary equipment, as will be described in further detail hereinafter. Once the engage gear clash logic routine36has terminated the method30proceeds to block38. However, if the method30of the present invention determines that auxiliary equipment mode has not been requested then the method30returns to block32. At block38, the method30determines whether the auxiliary equipment is engaged by monitoring an auxiliary equipment engagement sensor. If the method30determines that the auxiliary equipment is engaged at block38, then the method30terminates in auxiliary equipment mode, as represented by block40. However, if the method30of the present invention determines that the auxiliary equipment has not been engaged then the method30returns to block36and re-enters the engage gear clash logic routine.

Referring now toFIG. 3, a flowchart of a method50for controlling the disengagement of the second set or auxiliary set of equipment is illustrated, in accordance with an embodiment of the present invention. Method50is initiated at block52with the vehicle having the auxiliary equipment being in an auxiliary equipment mode of operation with the auxiliary equipment engaged. At block54, the method50determines whether normal operation mode has been selected by a vehicle operator indicative of a desire to disengage the auxiliary equipment. If the method50has determined that a normal operation mode has been requested, then the method50enters a disengage gear clash logic routine, as represented by block56, to prevent gear clash in the transfer case and disengage the auxiliary equipment, as will be described in further detail hereinafter. Once the disengage gear clash logic routine56has terminated the method50proceeds to block58. However, if the method50of the present invention determines that normal operation mode has not been requested then the method50returns to block52. At block58, the method50determines whether the auxiliary equipment is disengaged by monitoring an auxiliary equipment engagement sensor. If the method50determines that the auxiliary equipment is disengaged at block58, then the method50terminates in normal operation mode, as represented by block60. However, if the method50of the present invention determines that the auxiliary equipment has not been disengaged then the method50returns to block56and re-enters the disengage gear clash logic routine.

Referring now toFIG. 4, a flowchart of a method70for preventing “gear clash” during engagement of the auxiliary set of equipment14by the transfer case18is illustrated in accordance with an embodiment of the present invention. The method70operates by controlling the torque transferred to the output shaft22of the transmission16in order to control the amount of torque transferred to the transfer case18as the transfer case18engages the auxiliary equipment14. By controlling the torque through the output shaft22, the torque through gear teeth within the transfer case18is controlled to prevent gear clash. For example, the method70is initiated at block72with the vehicle operator requesting engagement of the auxiliary equipment. At block74, the method determines whether the transmission has been placed in neutral and compares the transmission output speed with a predefined speed threshold (Enter_NVL_Thresh). When the transmission has been placed in neutral, one torque transmitting device (C5) is applied and all other torque transmitting devices are disengaged. If the method70has determined that the transmission has been placed in neutral and that the transmission output speed is less than the predefined speed threshold, then a torque transmitting device (C4) is engaged to lock the transmission output shaft22and prevent further rotation in order to initiate a Neutral Very Low (NVL) condition, as represented by block76. However, if method70of the present invention determines that the transmission has not been placed in neutral or that the transmission output speed is greater than the predefined speed threshold (Enter_NVL_Thresh), then the method returns to block72. At block78, a first timer (NVL_Timer) is incremented and recorded. The time recorded by the NVL_Timer is compared to a predefined time threshold (Time_in_NVL_Thresh), as represented by block80. If the method70of the present invention determines that the time recorded by NVL_Timer is not greater than Time_in_NVL_Thresh, then the method70returns to block76and re-enters the gear clash logic routine. If at block80the method70determines that the time recorded by NVL_Timer is greater than Time_in NVL_Thresh, then the transmission is placed in a neutral no clutches (NNC) condition where the torque transmitting device (C5) operable to place the transmission in neutral is disengaged, as indicated by block81. In the NNC condition, no transmission drag torque is carried over to the output shaft22since all the torque transmitting devices that transmit torque to the output shaft22are disengaged. However, the torque transmitting device C4operable to lock the output shaft22remains engaged. At block82, a second timer (NNC_Timer) is incremented and recorded. The time recorded by the NNC_Timer is compared to a predefined time threshold (Time_in_NNC_Thresh), as represented by block83. If the method70of the present invention determines that the time recorded by NNC_Timer is not greater than Time_in_NNC_Thresh, then the method70returns to block81and re-enters the disengage gear clash logic routine. If at block83the method70determines that the time recorded by NNC_Timer is greater than Time_in_NNC_Thresh, then the method70proceeds to block84. At block84, the torque transmitting device (Clutch C5) that engages neutral is engaged and the torque transmitting device (Clutch C4) is disengaged to allow the transmission shaft22to rotate. At block85, a third timer NC5_Timer is incremented and the time is recorded. The time recorded by the NC5_Timer is compared to a predefined time threshold (Time_in_NC5_Thresh) and the transmission output speed is compared to a speed threshold (Immed_NVL_Thresh), as represented by block86. If at block86the method determines that the time recorded by NC5_Timer is greater than Time_in_NC5_Thresh or if the transmission output speed is greater than Immed_NVL_Thresh, then the method returns to block76or the method ends. However, if method70of the present invention determines that the time recorded by NC5_Timer is not greater than Time_in_NC5_Thresh or if the transmission output speed is not greater than Immed_NVL_Thresh, then the method returns to block84.

Referring now toFIG. 5, a flowchart of a method90for preventing “gear clash” during disengagement of the auxiliary set of equipment14by the transfer case18is illustrated in accordance with an embodiment of the present invention. The method90operates by controlling the output shaft22of the transmission16in order to control the amount of torque transferred to the transfer case18as the transfer case18disengages the auxiliary equipment14. By controlling the torque through the output shaft22, the torque through gear teeth within the transfer case18is controlled to prevent gear clash. For example, the method90is initiated at block92with the vehicle operator requesting normal operation mode or disengagement of the auxiliary equipment. At block94, the method determines whether the transmission has been placed in neutral and compares the transmission output speed with a predefined speed threshold (Exit_NVL_Thresh). If method90has determined that transmission has been placed in neutral and that the transmission output speed is less than Exit_NVL_Thresh then, then a torque transmitting device (C4) is engaged to lock the transmission output shaft22and prevent further rotation in order to initiate a Neutral Very Low (NVL) condition, as represented by block96. However, if the method90of the present invention determines that the transmission has not been placed in neutral or that the transmission output speed is greater than the predefined speed threshold (Exit_NVL_Thresh), then the method returns to block92. At block98, a first timer (NVL_Timer) is incremented and recorded. The time recorded by the NVL_Timer is compared to a predefined time threshold (Time_in_NVL_Thresh), as represented by block100. If the method90of the present invention determines that the time recorded by NVL_Timer is not greater than Time_in_NVL_Thresh, then the method90returns to block96and re-enters the disengage gear clash logic routine. If at block100the method90determines that the time recorded by NVL_Timer is greater than Time_in_NVL_Thresh, then the transmission is placed in a neutral no clutches (NNC) condition where the torque transmitting device (C5) operable to place the transmission in neutral is disengaged, as indicated by block101. In the NNC condition, no transmission drag torque is carried over to the output shaft22since all the torque transmitting devices that transmit torque to the output shaft22are disengaged. However, the torque transmitting device C4operable to lock the output shaft22remains engaged. At block102, a second timer (NNC_Timer) is incremented and recorded. The time recorded by the NNC_Timer is compared to a predefined time threshold (Time_in_NNC_Thresh), as represented by block103. If the method90of the present invention determines that the time recorded by NNC_Timer is not greater than Time_in_NNC_Thresh, then the method90returns to block101and re-enters the disengage gear clash logic routine. If at block103the method90determines that the time recorded by NNC_Timer is greater than Time_in_NNC_Thresh, then the method90proceeds to block104. At block104, the torque transmitting device (Clutch C5) that engages neutral is engaged and the torque transmitting device (Clutch C4) is disengaged to allow the transmission shaft22to rotate. At block105, a third timer NC5_Timer is incremented and the time is recorded. The time recorded by the NC5_Timer is compared to a predefined time threshold (Time_in_NC5_Thresh) and the transmission output speed is compared to a speed threshold (Immed_NVL_Thresh), as represented by block106. If at block106the method90determines that the time recorded by NC5_Timer is greater than Time_in_NC5_Thresh or if the transmission output speed is greater than Immed_NVL_Thresh, then the method returns to block96or the method ends. However, if method90of the present invention determines that the time recorded by NC5_Timer is not greater than Time_in_NC5_Thresh or if the transmission output speed is not greater than Immed_NVL_Thresh, then the method returns to block104.

While the best modes for carrying out the invention have been described in detail, it is to be understood that the terminology used is intended to be in the nature of words and description rather than of limitation. Those familiar with the art to which this invention relates will recognize that many modifications of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced in a substantially equivalent way other than as specifically described herein.