In general, automatic transmissions for vehicles are configured such that a shift range selected from among a parking range (P), a reverse range (R), a neutral range (N), a drive range (D), and the like is established due to a driver operating, for example, a shift lever disposed in the vicinity of the driver seat of a vehicle.
In general, range changing devices of recent years have been called by-wire systems, and when the driver operates the shift lever, a sensor or the like detects the range position selected by the shift lever, and based on this detection signal, the operating device described below changes the state of a parking mechanism and a manual valve, which is one constituent element of a hydraulic control device for shift range changing (e.g., see Patent Literature 1).
Here, the operating device includes a detent mechanism for positioning a spool of the manual value and a parking rod of the parking mechanism by pushing/pulling them in stages, an actuator for driving the detent mechanism, and an electronic control unit that controls the actuator.
The detent mechanism includes a detent plate that pushes/pulls the spool and the parking rod by being tilted by the actuator, and a detent spring that maintains the resting position of the detent plate.
A spindle that is coupled to an output shaft of the actuator is integrally attached to the detent plate at the center of tilt thereof, and the detent plate is provided with a wave part formed from a plurality of valleys that correspond to each rotation angle of the detent plate and mountains between the valleys.
A roller is provided on the free end side of the detent spring, as an engaging part that engages with any of the valleys of the wave part. Upon engaging the roller with a valley, the detent spring exerts elastic force on the detent plate so as to keep the engaged state.
The actuator includes an electric motor or the like, and a deceleration mechanism that decelerates the output of the electric motor, and transfers such output to the output shaft. In general, such an actuator has play (backlash, assembly error, or the like) in the rotation direction between the rotor of the electric motor and the output shaft.
Here, for reference, if the parking range P has been selected by the shift lever, the detent plate is tilted by a predetermined angle, and in conjunction with this tilting of the detent plate, the parking rod of the parking apparatus is, for example, pushed to the back, thus putting the output shaft of the automatic transmission in a locked state in which rotation is not possible.
Also, if the reverse range R, the neutral range N, or the drive range D has been selected, the detent plate is tilted by a predetermined angle, and in conjunction with this tilting of the detent plate, the parking rod is, for example, pulled forward, thus putting the output shaft of the automatic transmission in an unlocked state in which rotation is possible, and also, the spool of the manual value is displaced in the axial direction, thus engaging or freeing a frictional engaging element such as a clutch or a brake that is included in a transmission mechanism part of the automatic transmission, thereby establishing the requested range.
Incidentally, in any of the above situations, when the detent plate is at rest, the roller of the detent spring is engaged with any of the valleys of the wave part of the detent plate, thus positioning and maintaining the position of the detent plate.