Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Reexamination Certificate
1999-11-26
2001-10-30
Marmor, Charles A (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
C477S906000
Reexamination Certificate
active
06309324
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the invention
This invention relates to a control system for an automatic transmission for vehicles, and, more particularly, to an automatic transmission control system in which a timing at which two friction coupling elements are alternately locked and unlocked to provide a specific gear is determined based on a turbine speed.
2. Description of Related Art
Typically, an automatic transmission for an automobile has a torque converter and a transmission gear mechanism including a plurality of friction coupling elements, such as clutches and brakes, which are selectively locked and unlocked to place automatically the automatic transmission into desired gears according to driving conditions. In such an automatic transmission, a target gear to which the automatic transmission is shifted is ordinarily determined according to driving conditions including a vehicle speed and an engine load or throttle opening. Specifically, the target gear is determined based on predetermined gear shift patterns so as to become higher with an increase in vehicle speed and/or a decrease in engine load. Selectively locking and unlocking the frictional coupling elements is controlled by means of a hydraulic control circuit such as to place the transmission gear mechanism in the target gear. In this instance, in order to prevent or significantly reduce shift shock, locking or unlocking an friction coupling element is controlled not to be momentarily achieved but to progress gradually with slippage so that the speed of a turbine of the torque converter (which is hereafter referred to as the turbine speed) smoothly changes to a speed to be attained at completion of a gear shift following a target speed during the gear shift. Such a friction coupling element locking/unlocking control is known from, for example, Japanese Unexamined Patent Publication No. 1-1 99083. Further, during, for example, a specific gear shift which is provided as result of alternately locking and unlocking specific two friction coupling elements, either one of the two friction coupling elements is locked or unlocked ahead of unlocking or locking the other one to provide an inertia phase. In the inertia phase, hydraulic pressure for locking the friction coupling element is feedback controlled to rise gradually such that the turbine speed drops to a specified turbine speed when the gear is up-shifted or rises to a specified turbine speed when the gear is down-shifted and the two friction coupling element is completely locked and unlocked timely when the specified turbine speed is attained or almost attained. This control prevents a coincidental lock or interlock of the two friction coupling elements which result in an occurrence of shift shock.
In order to cause timely the alternate lock and unlock operation of the two friction coupling elements to provide the specific gear shift, it is necessary to detect a turbine speed. If a meters associated to turbine speed, such as a turbine speed sensor, breaks down, it is impossible to determine a timing at which locking or unlocking the other friction coupling element is to commence, as a result of which an untimely lock or unlock of the other friction coupling element occurs with an adverse effect of causing interlock or shift shock and an abrupt rise in engine speed.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a control system for an automatic transmission which causes a gear shift without producing shift shocks and putting a driver and passengers unpleasant feeling.
The control system of the invention is applied to an automatic transmission of the type having a transmission gear mechanism equipped with a torque converter and a plurality of hydraulically operated friction coupling elements, such as clutches and brakes, which are selectively locked and unlocked to change a power transmission path so as to place the automatic transmission into desired available gears according to scheduled gear shift patterns defined as maps based on vehicle driving conditions. The available gears includes a first group of gears which are provided by locking one of specific two hydraulically operated friction coupling elements and unlocking another specific hydraulically operated friction coupling elements and a second group of gears which are provided by locking only one of the hydraulically operated friction coupling elements. The automatic transmission control system comprises speed monitoring means for monitoring an input speed to the transmission gear mechanism, i.e. a speed of a turbine of the torque converter, hydraulic control circuit means for hydraulically locking and unlocking the hydraulically operated friction coupling elements to provide any one of the available gears, and control means comprising a microcomputer programmed to determine one of the available gears to which the automatic transmission is shifted according to the scheduled gear shift pattern selected based on a driving condition, to detect an failure of the input speed monitoring means based on the input speed, and to control the hydraulic control circuit means so as to prohibit a gear shift only to the first group of gears when detecting a failure of the input speed monitoring means.
The gear shift to be prohibited may be upshifts to the first group of gears. In this case, the automatic transmission control system unlocks the other specific hydraulically operated friction coupling element at a timing that the input speed drops and reaches a specified speed. The gear shift to be prohibited may be downshifts to the first group of gears made with an accelerator pedal remaining released. In this case, the automatic transmission control system unlocks the other specific hydraulically operated friction coupling element at a timing that the input speed rises and reaches a specified speed. The gear shift to be prohibited may further be downshifts to said first group of gears made with an accelerator pedal remaining stepped down. In this case, the automatic transmission control system controls a locking timing of one of the specific two hydraulically operated friction coupling elements based on the input speed during a gear shift to the first group of gears.
With the automatic transmission control system of the invention by which, when a failure of the input speed monitoring means is detected, a gear shift to the first group of gears which are provided by causing alternate lock and unlock operation of the specific two hydraulically operated friction coupling elements is prohibited while a failure of the input speed monitor is detected, there is no occurrence of interlock between the two hydraulically operated friction coupling elements due to untimely alternate lock and unlock operation of the two hydraulically operated friction coupling elements and an abrupt rise in engine speed which are felt as shift shocks by the driver and passengers. However, when the gear shift to one of the first group gears provided by causing alternate lock and unlock operation of the two hydraulically operated friction coupling elements is permitted when it is accompanied by actuating or releasing operation of the one-way clutch. Since the one-way clutch is spontaneously locked or released by a reversal in rotational direction of rotational elements of planetary gear mechanism occurring with progress of locking or unlocking operation of the other friction coupling element and the alternate lock and unlock operation of the two hydraulically operated friction coupling elements is timely caused without using an input speed, consequently, the gear shift is preferred to be permitted.
The automatic transmission control system of the invention may be applied to an automatic transmission of the type having a transmission gear mechanism equipped with a torque converter and a plurality of hydraulically operated friction coupling elements which are selectively locked and unlocked to change a power transmission path including a one-way clutch so as to place the automatic transmission into desired available gear
Kamada Shinya
Sawa Kenji
Ho Ha
Marmor Charles A
Mazda Motor Corporation
Nixon & Peabody LLP
Studebaker Donald R.
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