Interrelated power delivery controls – including engine control – Transmission control – Transmission controlled by engine
Reexamination Certificate
1999-12-20
2001-08-07
Marmor, Charles A (Department: 3681)
Interrelated power delivery controls, including engine control
Transmission control
Transmission controlled by engine
C477S155000, C477S158000, C475S127000
Reexamination Certificate
active
06270444
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The invention relates to a shift control apparatus for an automatic transmission. In particular, the invention relates to a technique for smoothly performing a shift requiring disengagement and engagement of two different engagement elements between shift stages (simultaneous grip change of four elements).
2. Description of Related Art
In an automatic transmission, it has been well known that a power transmission route via a shift element composed of planetary gears is switched by engaging and disengaging friction engagement elements, thereby achieving a plurality of shift stages by changing a gear ratio. Engagement and disengagement of the engagement elements during shifting must be performed under a hydraulic control that is as simple as possible while reducing shock resulting from shifting. Thus, in general, operation of engagement elements for up-shift and down-shift basically includes additional engagement of another engagement element or disengagement of at least one engagement element being engaged. If the operation cannot be performed because of the gear train construction, one engagement element that has been already engaged is disengaged so as to engage another engagement element, that is, a so called grip change operation of engagement elements is performed.
Recently, automatic transmissions have been increasingly employing a multi-stage shifting mechanism so as to improve drivability and reduce the fuel cost by decreasing energy consumption. Such multi-stage shifting has been generally achieved by adding an acceleration or deceleration stage using an overdrive or under-drive gear to a shift mechanism consisting of a multi-staged planetary gear set. As another aspect, there has been disclosed in U.S. Pat. No. 5,106,352 a technology for achieving multi-stages by employing an input to a Ravigneaux type planetary gear set as two systems of high/low to achieve multi-stages.
In the multi-stage gear train as described above, the shifting speed conforming to the running state of a vehicle can be selected from a wider range of choices, thus causing the requirement for a complicated grip change of four elements as well as a simple grip change of two elements. As an example requiring such a grip change of four elements, there is shown a so-called skip shift from a number of shift stages to a particular shift stage at one time. In any case, when such a multiple grip change of four elements is performed, how to control the sequence or timing of the engagement and disengagement of each engagement element becomes a key issue. The failure of this control, if any, may cause the problem of degrading smooth advancement of shift operations within the transmission mechanism. In addition, if shift continuity is lost, there are problems of stepwise shocks during shifting, worsening of shocks at the end of shifting or an unnecessary increase of a shifting time.
SUMMARY OF THE INVENTION
In order to solve the foregoing problems, it is an object of the invention to provide a shift control apparatus for automatic transmissions capable of preventing retardation of shifting while minimizing shock during shifting by smoothing the advancing shift that requires engagement and disengagement of four engagement elements.
Preferably, the automatic transmission has brakes, clutches and/or one-way-clutches as engaging elements.
In order to achieve the foregoing object, according to the invention, there is provided a shift control apparatus for an automatic transmission in which activation of four engagement elements is required for shifting from a first speed to a second speed, the first speed is achieved by engagement of first and second engagement elements, and the second speed is achieved by engagement of third and fourth engagement elements. The control apparatus includes shift control means in which disengagement of the second engagement element is started after the start of disengagement of the first engagement element; engagement of the fourth engagement element is completed after completing engagement of the third engagement element; and disengagement of the second engagement element is started before completing engagement of the third engagement element.
Specifically, the control means starts disengagement of the second engagement element just before completing engagement of the third engagement element.
More specifically, the second and third engagement elements are controlled by hydraulic pressures of respective hydraulic servos, and the shift control means starts engaging the second engagement element by lowering the hydraulic pressure of the hydraulic servo for the second engagement element after the start of engaging the third engagement element by increasing the hydraulic pressure of the hydraulic servo for the third engagement element, and further completes engaging the third engagement element by increasing the hydraulic pressure of the hydraulic servo for the third engagement element.
In the foregoing construction, the shift control means detects an advancing state of shifting from the first speed to the second speed, and controls each hydraulic pressure of the hydraulic servos for the second and third engagement elements in accordance with the advancing state. When the shift advancing state indicates a first reference value, engagement of the third engagement element is started by increasing the hydraulic pressure of the hydraulic servo for the third engagement element, and when the shift advancing state further indicates a second reference value, the third engagement element is engaged completely by further increasing the hydraulic pressure. When the shift advancing state indicates a third reference value indicating the advancing state between the first and the second reference values, disengagement of the second engagement element is started by decreasing the hydraulic pressure of the hydraulic servo for the second engagement element.
In addition, the shift control means controls a disengaging operation until the second engagement element starts disengaging in accordance with a state of the first engagement element.
Next, a state of the first engagement element indicates the shifting state that varies depending on the disengaging operation of said first engagement element, the second engagement element is controlled with respect to the operation until the start of disengagement thereof by decreasing the hydraulic pressure of the hydraulic servo for the second engagement element, and lowering characteristics of the hydraulic pressure is controlled based on a judgment with respect to the shifting state.
The state of said first engagement element indicates the shifting state that varies depending on the disengaging operation of the first engagement element, the second engagement element is controlled with respect to the operation until the start of disengagement thereof by decreasing the hydraulic pressure of the hydraulic servo for the second engagement element, and a timing for the start of lowering the hydraulic pressure is controlled based on the judgment of the shifting state.
Shifting from the first speed to the second speed is achieved via a third speed, the third speed is achieved by engaging one of the four engagement elements and disengaging the other engagement element simultaneously from the first speed, and the second speed is achieved by activating the remaining two engagement elements from the third speed, and the shifting state indicates the shifting state from the first speed to the third speed.
The shifting state is judged using an index indicating an input/output revolution of the transmission that varies during shifting to a predetermined speed, and lowering of the hydraulic pressure of the hydraulic servo for the second engagement element is started when the index becomes a predetermined value.
Alternatively, the shifting state is judged using an index indicating an engagement force of the third engagement element to be engaged, and lowering of the hydraulic pressure of the hydraulic servo for the second engagement
Kojima Kouichi
Teraoka Yutaka
Tsutsui Hiroshi
Aisin Aw Co. Ltd.
Ho Ha
Marmor Charles A
Oliff & Berridg,e PLC
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