Control system for automatic transmission

Interrelated power delivery controls – including engine control – Transmission control – Engine controlled by transmission

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Details

477109, B60K 4106, F16H 6100

Patent

active

054962307

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a control system for establishing a reverse gear stage in an automatic transmission having a main transmission portion and an auxiliary transmission portion.


BACKGROUND ART

There has been widely known in the prior art an automatic transmission which is equipped with a gear transmission mechanism and a plurality of frictional engagement elements to be selectively applied by the action of a hydraulic control unit so that any of a plurality of gear stages including a reverse stage may be established.
In this automatic transmission, a serious load torque is applied to the frictional engagement elements especially at the reverse time having a high gear ratio. Thus, there have been proposed a variety of counter-measures For the serious load torque.
Japanese Patent Laid-Open No. 129162/1991 has disclosed a system which is enabled to improve the durability of the frictional engagement elements and reduce the size of the frictional engagement elements by decreasing the engine torque when the reverse gear stage is established.
Moreover, Japanese Patent Laid-Open No. 166428/1992 has disclosed a system which is enabled to reduce the load torque when the reverse gear stage is established or maintained, by setting the auxiliary transmission portion to the high gear stage when the reverse stage is established.
incidentally, in case the engine torque-down to be effected when the reverse stage is established is executed by delaying the ignition time, for example, the timing for the delay is restricted of itself from the standpoint of preventing the overheat. This makes it impossible to continue the reduction of the load torque for a long time after the establishment of the reverse stage.
In case, moreover, the auxiliary transmission portion is set to the high gear stage, the number of the frictional engagement elements to be applied for the shift to the reverse stage is increased to drop the line pressure for the application thereby to elongate the time period till the application end (i.e., the establishment of the reverse stage) and to elongate the time period for the applications. As a result, the durability of the frictional engagement elements is not always improved.


DISCLOSURE OF THE INVENTION

The present invention has been conceived in view of the foregoing problems of the prior art and has an object to solve the problems by providing a control system for an automatic transmission, which is enabled to reduce the load torque of frictional engagement elements at a reverse time by solving the problems of the cases, in which the torque-down of an engine is to be executed and in which an auxiliary transmission portion is to be set to a high gear stage, and by extracting the individual advantages effectively.
According to the present invention having the gist, as shown in FIG. 1, the aforementioned problems are solved by providing a control system for an automatic transmission, comprising a gear transmission unit for establishing a predetermined gear stage by applying a plurality of frictional engagement elements selectively, wherein said gear transmission unit includes a main transmission portion capable of establishing at least a reverse gear stage, and an auxiliary transmission portion capable of switching a high gear stage and a low gear stage, and wherein said auxiliary transmission portion is set to the high gear stage at the shifting time to the reverse gear stage, wherein the improvement comprises: means for detecting generation of a command for shifting to the reverse gear stage; reverse stage establishment control means for establishing the reverse gear stage by controlling the application of predetermined ones of said frictional engagement elements of said main transmission portion when the reverse stage shifting command is generated; engine torque control means for executing a torque-down of an engine at the time of controlling the engagement of said frictional engagement elements for establishing the reverse gear stage; means for detecting establishment

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