Patent Application
20110169323
1. Field of the Invention
This invention relates generally to controlling the powertrain of a motor vehicle while launching the vehicle on a grade.
2. Description of the Prior Art
A vehicle that is stopped on a grade can be held stationary using wheel brake torque until propulsion torque, transmitted from the engine through a transmission and final drive mechanism to the wheels, exceeds brake torque. It is important to avoid unnecessary transmission clutch slip when brake torque is holding the hill, particularly when the transmission lacks a torque converter.
An electronic signal representing estimated propulsion torque can be used as a measure of propulsion torque at the wheels to release brake torque. In this case, either a brief timeout occurs after neither the brake pedal nor accelerator pedal is depressed by the driver, or the brakes are applied indefinitely if the driver depresses the accelerator pedal greater than a small amount. In the latter case, the resulting propulsion torque is smaller than brake torque.
The period during which propulsion torque is less than brake torque can be significant especially in heavy traffic on a grade, and would cause excessive, unnecessary clutch wear.
A method for controlling a vehicle powertrain includes establishing first and second functions relating desired engine torque and driver demand torque corresponding to hill start assist being active and inactive, respectively; while hill start assist is active, holding the vehicle stopped on a grade by automatically producing wheel brake torque and producing engine torque derived from the first function; automatically releasing wheel brake torque when driver demand torque equals or exceeds wheel brake torque; launching the vehicle using engine torque derived from the first function and corresponding to said pedal displacement; and while hill start assist is inactive, launching the vehicle using engine torque derived from the second function.
The method reduces clutch wear by lower engine torque levels when the driver is pressing the accelerator pedal to a level insufficient to launch the vehicle on the current grade.
The scope of applicability of the preferred embodiment will become apparent from the following detailed description, claims and drawings. It should be understood, that the description and specific examples, although indicating preferred embodiments of the invention, are given by way of illustration only. Various changes and modifications to the described embodiments and examples will become apparent to those skilled in the art.
The invention will be more readily understood by reference to the following description, taken with the accompanying drawings, in which:
Referring now to the drawings, there is illustrated in
A vehicle controller comprising a transmission module (TCM) 42 and an engine control module ECM 50 communicates through electronic signals mutually and with battery 26, transmission 16, the clutch actuator 25, and a gear selector 44, which moves among (P)ARK, (R)REVERSE, (N)EUTRAL, and (D)RIVE positions in an automatic mode channel 46 and between upshift (+) and downshift (−) positions in a manual mode channel 48. The engine control module (ECM) 50 is powered by battery 26, receives and sends signals to the starter 14 and engine 12 and receives input signals from an accelerator pedal 52 and brake pedal 54.
The accelerator pedal 52 and brake pedal 54 are controlled manually by depressing the respective pedal through a distance from a reference state, in which the pedal is not depressed. The accelerator pedal 52 provides input demand, i.e., drive demand torque, to the vehicle controller for changes in engine torque. Engine torque, transmitted through the transmission 16, 60 and final drive mechanism 24 to the wheels, powers the driven wheels 30, 31 with wheel torque. The accelerator pedal 54 provides demands to the vehicle controller for changes in wheel brake torque. Under certain conditions, the controller can actuate the brake system automatically to produce wheel brake torque that holds the vehicle stationary on a grade without actuating the brake pedal 54.
The vehicle controller, a microprocessor-based controller accessible to a control algorithm 76, communicates through electronic signals transmitted on a communication bus with the engine 12, starter 14, transmission 16, 60, gear selector 40, accelerator and brake pedals 52, 54, and a wheel brake system, which supplies brake pressure to the wheel brakes to produce the wheel brake torque that holds the vehicle stationary on a grade. The controller is accessible to data stored in electronic memory relating engine torque and accelerator pedal displacement, which indicated the magnitude of driver demand torque.
As illustrated in
If the result of test 82 is true, control advances to 84 where a test is made to determine whether the road grade is greater than a reference road grade, and whether brake torque is greater than a reference brake torque that will hold the vehicle stationary on the grade, indicating that hill start assist (HSA) control is active. When hill start assist (HSA) control is active, the vehicle controller actuates the brake system to produce wheel brake torque automatically at a wheel torque magnitude that holds the vehicle stationary on the road grade.
If the result of test 84 is logically true, control advances to step 86 where, as illustrated in
If current accelerator pedal displacement 88 is greater than 94, where hill-start-assist brake release torque 96 is less than the engine torque that will produce wheel torque equal to the brake release torque, then brake torque is released and the vehicle is launched using engine torque alone.
If the result of test 84 is false, indicating that hill start assist (HSA) control is inactive, control advances to step 98 where current accelerator pedal displacement 88 is used to index a function 100 to determine the desired engine output torque 102 while HSA is inactive.
When the transmission includes at dual input clutches 18, 20 such as the powershift transmission 16 of
In accordance with the provisions of the patent statutes, the preferred embodiment has been described. However, it should be noted that the alternate embodiments can be practiced otherwise than as specifically illustrated and described.
