Surrogate engine speed signal for controlling a dual clutch powershift transmission

A method for launching a vehicle having an engine shaft, first and second transmission input shafts, first and second input clutches, a coupler, a power path, and an output, the method including engaging the coupler to connect the first input shaft and the first output shaft through the power path, engaging the second input clutch to connect the engine shaft and the second input shaft mutually, using a speed of the second input shaft to determine a desired clutch torque capacity of the first input clutch, and actuating the first input clutch to produce the desired clutch torque capacity of the first input clutch and to complete a drive connection between the first input shaft and the output.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a dual clutch powershift transmission, and to launching a vehicle having such a transmission.

2. Description of the Prior Art

A powershift transmission is a geared mechanism that includes no torque converter, but instead employs two input clutches driveably connected to an engine crankshaft. A powershift transmission produces multiple gear ratios in forward and reverse drive and transmits power continuously using synchronized clutch-to-clutch shifts.

The transmission incorporates gearing arranged in a dual layshaft configuration between the transmission input and its output. One input clutch transmits torque between the input and a first layshaft associated with even-numbered gears; the other input clutch transmits torque between the transmission input and a second layshaft associated with odd-numbered gears. The transmission produces gear ratio changes by alternately engaging a first input clutch and running in a current gear, disengaging the second input clutch, preparing a power path in the transmission for operation in the target gear, disengaging the first clutch, engaging the second clutch and preparing another power path in the transmission for operation in the next gear.

A need exists for continuing to operate a dual clutch powershift transmission when communication between a transmission controller and an engine controller is lost, because shifting the transmission to neutral gear operation is considered a very high severity failure.

SUMMARY OF THE INVENTION

A method for launching a vehicle having an engine shaft, first and second transmission input shafts, first and second input clutches, a coupler, a power path, and an output, the method including engaging the coupler to connect the first input shaft and the first output shaft through the power path, engaging the second input clutch to connect the engine shaft and the second input shaft mutually, using a speed of the second input shaft to determine a desired clutch torque capacity of the first input clutch, and actuating the first input clutch to produce the desired clutch torque capacity of the first input clutch and to complete a drive connection between the first input shaft and the output.

In the event that communication between a transmission controller and an engine controller is lost or flawed, the control method and system engage an input clutch to connect the engine shaft and a second input shaft other than the first input shaft, which is associated with the on-coming gear to be engaged during the vehicle launch. In this way, the speed signal of the second input shaft accurately represents engine speed, is transmitted to the transmission controller, and is used to produce a desired torque capacity of the first input clutch.

The strategy requires an engine speed signal only during launch. Output speed is used to schedule gear shifts. All even gears are deselected during vehicle launch and the even-numbered gear clutch is closed. Under those conditions, the even-numbered gear input shaft speed sensor is used as the engine speed sensor.

The control strategy launches a vehicle equipped with a dual clutch transmission when communications between the engine controller and the transmission controller have been interrupted.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now toFIG. 1, a dual clutch power shift transmission10is driveably connected to the crankshaft12of an engine or a shaft driven by another power source, such as an electric motor. A first input friction clutch14alternately connects and disconnects shaft12and a first input shaft16as clutch14is engaged and disengaged, respectively. A second input friction clutch18alternately connects and disconnects shaft12and a second input shaft20as clutch18is engaged and disengaged, respectively.

A first set of selectable power paths, which produce the odd-numbered gears of the transmission, connect first input shaft16to a load, such as the driven wheels of a motor vehicle, through a powertrain that may include a drive shaft, differential mechanism and axle shafts. The first or third gear power paths are activated by moving coupler44to connect gear34or38, respectively, to output shaft22. Similarly, the fifth gear power path is activated by moving coupler52to connect gear42to output shaft24. A second set of selectable power paths, which produce the even-numbered gears of the transmission, connect second input shaft20to the load. The second or fourth gear power paths are activated by moving coupler46to connect gear46or50, respectively, to output shaft22. The reverse gear power path is activated by moving coupler52to connect gear54to output shaft24. When couplers46and52are in the neutral position, no drive connection between input shaft20and the load exists.

A first speed sensor26produces an electronic signal representing the rotational speed of input shaft16. The second speed sensor28produces an electronic signal representing the rotational speed of input shaft20, which produce the even-numbered gears and reverse gear. A third speed sensor30produces an electronic signal representing the rotational speed of output shaft24.

The first gear power path, one of the first set of power paths, includes a pinion32, secured to input shaft16; a first gear output34, journalled on output shaft22and in continuous meshing engagement with pinion32; and a coupler44. A third gear power path includes pinion36, secured to input shaft16; a third gear output38, journalled on output shaft22and in continuous meshing engagement with pinion36; and coupler44. A fifth gear power path includes pinion40, secured to input shaft16; a fifth gear output42, journalled on output shaft24and in continuous meshing engagement pinion40; and a coupler52.

The second gear power path, one of the second set of power paths, includes a pinion44, secured to input20; gear46and idler48, which are secured mutually and journalled on output shaft22, gear46being in continuous meshing engagement with pinion44; and coupler46. A fourth gear power path includes pinion48, secured to input shaft20; a fourth gear output50, journalled on output shaft22and in continuous meshing engagement pinion48; and coupler46. The reverse gear power paths includes pinion44, gear46, idler48and reverse output gear54, which is journalled on output shaft24and in continuous meshing engagement with idler48, and coupler52.

Coupler44includes a selector sleeve, which moves leftward to engage clutch teeth on the first gear output34, and moves rightward to engage clutch teeth on the third gear output38. Coupler44produces a drive connection between gears34and38, and output shaft22, depending on the direction that the selector sleeve is moved. Similarly, coupler46includes a selector sleeve that moves leftward to produce a drive connection between fourth gear output50and output shaft22, and moves rightward to produce a drive connection between idler48and output shaft22. Idler48is secured to a sleeve shaft54, on which output gear46is journalled on output shaft22. Coupler52includes a selector sleeve that moves leftward to produce a drive connection between fifth gear output42output shaft24, and moves rightward to produce a drive connection between reverse gear output54and output shaft24.

Gears56,58are both in continuous meshing engagement with a common output ring gear (not shown), thereby mutually connecting upper output shaft24and lower output shaft22such that the transmission includes a single output connected to a driven load.

Couplers44,46and52are preferably synchronizers of the type used in automotive manual transmissions to connect a gear or pinion to a shaft, after synchronizing the speed of the shaft and that of the pinion or gear. Each coupler may also disconnect the shaft and the associated pinion or gear. Alternatively, each coupler may be a dog clutch having teeth that are engaged with dog teeth on a gear or pinion. This invention may use couplers in any combination of synchronizers and dog clutches. Each coupler is composed of a hub secured to the shaft and a sleeve which is supported on the hub for sliding movement leftward or rightward into engagement with dog teeth on the adjacent gear or pinion. In the case where a coupler is a synchronizer, it is provided with a conical surface, which engages mutually with a corresponding conical surface located on the gear or pinion. When the synchronizer is engaging either of its adjacent gears, these conical surfaces are forced together into frictional contact, and that frictional engagement synchronizes the speed of the gear to that of the shaft before the dog teeth engage. Other types of synchronizers or couplers may also be used.

Referring now toFIG. 2, the vehicle can be launched, i.e. accelerated from a stopped or nearly stopped condition, using the first gear power path beginning with an initial transmission state60, in which input clutches14,18and couplers44,46,52are disengaged, thereby connecting no power path to the output shafts22,24.

Transmission10is prepared to launch the vehicle when placed in a second state62, in which the selector sleeve of coupler44is moved leftward to connect first gear output34to the output shaft22, input clutch18is engaged, all couplers associated with the even numbered gears remain disengaged, and input clutch14remains disengaged.

In the next state64, transmission10completes the engagement of first that launches the vehicle. Coupler44remains engaged and connecting first gear output34to output shaft22, input clutch18remains engaged and driving input shaft20at the speed of engine shaft12, couplers46and52remain disengaged, and the torque capacity of the first input clutch14is increased as a function of the speed of the second input shaft20, as represented by the signal produced by speed sensor28. The speed of first input shaft16is then equal to the speed of second input shaft20.

Speed sensor28is a surrogate for an engine speed sensor. It is assumed that the engine throttle is either mechanically connected to the accelerator pedal or is controlled by an engine controller as a function of accelerator pedal position.

A forward launch of the vehicle is completed in transmission state66, in which the even-numbered and odd-numbered gears are selected sequentially based on the speed of the output shaft as represented by the signal produced by speed sensor30. The output shaft speed, which is less than a reference speed for the current gear, is fed forward to select the next gear.

When a gear is selected, its corresponding coupler connects the selected gear to its output shaft, the input clutch associated with the off-going gear is disengaged, and the input clutch associated with the oncoming gear is engaged.

Although the method has been described with reference to a vehicle launch in first gear, the launch can be executed using the reverse gear power path beginning with an initial transmission state, in which input clutches14,18and couplers44,46,52are disengaged, thereby connecting no power path to the output shafts22,24.

Transmission10is prepared to launch the vehicle in reverse when the selector sleeve of coupler52is moved rightward to connect reverse gear output54to the output shaft24, input clutch14is engaged, all couplers associated with the odd-numbered gears remain disengaged, and input clutch18remains disengaged.

The transmission10completes the engagement that launches the vehicle in reverse when coupler52remains engaged and connecting reverse gear output54to output shaft22, input clutch14remains engaged and driving input shaft16at the speed of engine shaft12, couplers44and46remain disengaged, and the torque capacity of the second input clutch18is increased as a function of the speed of the first input shaft16, as represented by the signal produced by speed sensor26.

FIG. 3illustrates schematically an engine70controlled by an electronic engine control module72(ECM), which issues commands that control operation of the engine. Engine controller72receives input from various sensors including a sensor74, which produces an electronic signal representing the degree to which an accelerator pedal76is depressed, and a sensor78, which produces a signal representing the speed of engine crankshaft12.

The engine controller72communicates by a data bus80with an electronic transmission control module82(TCM), which issues commands that control operation of the input clutches14,18and couplers44,46,52in response to the results produced by executing transmission control algorithms. Data used in the execution of the algorithms is received as input from various electronic signals including speed sensors26,28,30and engine speed transmitted on bus80from ECM72. Stored in electronic memory accessible to the CPU of TCM82is a function84in the form of a lookup table indexed by engine speed and the oncoming gear in which the vehicle will be launched, the function containing a desired torque capacity of the input clutch that corresponds to the oncoming gear.

A conventional control strategy would set the torque capacity of the launch clutch as a function of engine speed. But, in the event communication of the current engine speed to TCM82is faulty or absent, the control strategy for launching the vehicle using the surrogate input signals from sensor28for a launch in first gear, or sensor26for a launch in reverse, is used.