According to the known automatic transmission, when a shift lever of an automatic transmission is switched from a non-running range to a running range, a known garage controlling for transmitting a clutch of the automatic transmission to be in a running condition is executed. An engine rotation when such garage controlling is executed is usually equivalent to an idling rotation, and input torque is usually small, however; a setting range for a controlling hydraulic pressure is set to be large in consideration of a case that the input torque becomes large when an engine starts under a cold atmosphere. Thus, accuracy of the hydraulic pressure within the low pressure range which is often used is reduced, and fluctuation of the vehicle behavior such as a shift shock and a time-lag occurrence until a vehicle stars traveling are marked.
Setting a target time when the shift shock and the time-lag occurrence become compatible, a known learning control is executed by changing the hydraulic pressure up and down so as to make a time from the garage control starting time to the shift starting time or transmission ending time (transmission time period) to be the target time. For example, a known method disclosed in JP3055346B1 corrects a tightening operating fluid up and down in response to a length of a tightening required time relative to a setting time.
To abolish an accumulator and downsize a parts number, cost and size, an automatic transmission includes an electromagnetic valve for producing a clutch pressure by directly controlling a hydraulic pressure from a source of the hydraulic pressure. Such automatic transmission applies a high pressure charge during a predetermined time in an allowance area at the front portion of a piston stroke, and then executes a standby controlling for standing ready at low hydraulic pressure for moving a clutch piston (piston) rapidly.
A pre-charge pressure and a pre-charge time for a pre-charge controlling, and a standby pressure for standby pressure controlling are called as hydraulic pressure characteristic values. Thus, to change the transmission time period, such hydraulic pressure characteristic values related to the pre-charge control need to be considered as controlling factors at least as well as the controlling the hydraulic pressure up and down.
Further, considering a wear of the clutch or an various environments where the transmission is provided, the known means without the considering the hydraulic characteristic values related to the pre-charge control has a limitation to converge the transmission time period to a target time period. Specifically, the known automatic transmission includes a hard structure comprising a combination of the accumulator and an orifice, and such hard structure is applicable to a transmission which is having an function to adjust a clutch pressure increasing speed depending on a level of the provided hydraulic pressure, and not applicable to a transmission having a means for forming the clutch pressure by directly controlling the hydraulic pressure provided from the hydraulic pressure source by means of a electromagnetic valve.
FIG. 6A illustrates graphs indicating results of the starting control with a new friction engaging element C1. FIG. 6B illustrates graphs indicating results of the starting control with an aged friction engaging element C1 (0.4 mm/piece). A shift start time period T in FIG. 6B is longer than a shift start time period T in FIG. 6A. In addition, a time lag is found in FIG. 6B. Further, each torque in FIG. 6B has a sharp inclination, so that a transmission shock may be occurred under such condition. Thus, the leaning controlling needs to be executed.
Thus, a need exists for a hydraulic pressure controlling device of an automatic transmission or an automatic transmission using a method for forming a clutch pressure by directly controlling a hydraulic pressure provided from a source of the hydraulic pressure using an electromagnetic valve.