1. Field of the Invention
The present invention relates to a control device for an automatic transmission and more particularly to a control device for an automatic transmission suitable for a vehicle such as an automobile.
2. Description of the Prior Art
This kind of control device for an automatic transmission is provided with a shift-locking device which locks a shift lever for safety when the shift lever is positioned in a parking position and a brake pedal is not depressed.
The shift lever comprises a control lever pivotably mounted on a base bracket, and a compression rod contained by the control lever in a slidable manner in the axial direction and mounted with a positioning pin in the direction vertical to the above axis. The control lever is provided with a guide slot at the peripheral portion for guiding the movement of the positioning pin.
The control device also comprises a positioning plate with a plurality of positioning recesses for engaging the positioning pin to keep the shift lever in the parking position or in the driving positions.
The shift lever is mounted with a ball selectively and elastically engaged in a plurality of check recesses of the positioning plate secured to the base bracket to moderate the motion of the shift lever.
The shift-lock device comprises a rotary bushing fitted on the control lever in a freely pivotable and axially immovable manner, and a shift-lock solenoid for pivoting the rotary bushing to a lock release position, mounted on the control lever through a mounting bracket.
According to this configuration when the shift lever is positioned in the parking position, the descent of the positioning pin is blocked by the rotary bushing, so that the shift lever is shift-locked. In this shift-locking condition, when the break pedal is pressed, the shift-lock solenoid acts to pivot the rotary bushing to the lock release position to release the shift-lock.
However, in the conventional control device for an automatic transmission, because the rotary bushing is mounted on the shift lever as a movable member, the shape of the rotary bushing is restricted by the shape of the shift lever. In addition, because the diameter of the shift lever as a pivot is large, the pivotal friction is large and the rotary bushing is inclined to produce a noise during operation resulting from a wobble.
Moreover, because the shift-lock solenoid is mounted on the shift lever as a movable member, the wire must be long enough to prevent breakage. Therefore, the number of clips increases, thus raising the production costs. In addition, because the shift-lock solenoid moves together with the shift lever, the shift-lock solenoid requires enough space to move, and hence, the whole device must be a large size.
Further, because the positioning pin of the positioning plate and the positioning recesses are made of metal, when shifting the shift lever, the positioning pin contacts the positioning recesses causing an unpleasant metallic noise, which can distract the driver.
Furthermore, when the shift lever is shifted, the ball of the shift lever contacts the check recess causing an unpleasant metallic noise.