Oil pressure controlled vehicle transmission, power unit incorporating same, and method of using same

A transmission for transmitting power from a power unit of a vehicle to a drive train component of the vehicle,

• the power unit comprising
• a crankshaft;
• a first main shaft;
• and
• a second main shaft;
• the transmission comprising:
• a shift drum;
• a first hydraulic clutch;
• a first fluid damping member which is operatively fluidly connectable with said first hydraulic clutch for damping an initial application of oil pressure thereto;
• a second hydraulic clutch;
• a second fluid damping member which is operatively fluidly connectable with said second hydraulic clutch for damping an initial application of oil pressure thereto;
• a transmission output shaft;
• and
• a plurality of gear trains disposed between the transmission output shaft and the main shafts,
• wherein when the first hydraulic clutch is actuated, power is transmitted from the first main shaft to the output shaft through one of said gear trains which is either a first speed gear train, a third speed gear train, or a fifth speed gear train,
• and wherein when the second hydraulic clutch is actuated, power is transmitted from the second main shaft to the output shaft through one of said gear trains which is either a second speed gear train, a fourth speed gear train or a reverse gear train;
• and
• wherein the transmission further comprises an oil pressure control system for controlling oil pressures applied to the first and second hydraulic clutches, the oil pressure control system comprising:
• an oil pressure source;
• a common oil passage connected to the oil pressure source and supplying oil in common to both the first and second hydraulic clutches;
• a control valve provided in the common oil passage;
• a first individual oil passage communicating with the first hydraulic clutch;
• a second individual oil passage communicating with second hydraulic clutch;
• a selector valve, the selector valve configured so as to permit switching a connection between the common oil passage and one of the first and second individual oil passages,
• a first releasing passage communicating with the selector valve, and
• a second releasing passage communicating with the selector valve,
• wherein, when the selector valve is permitting communication of the first individual oil passage with the common oil passage the selector valve is also permitting communication of the second individual oil passage with the second releasing passage, and when the selector valve is permitting communication of the second individual oil passage with the common oil passage, the selector valve is also permitting communication of the first individual oil passage with the first releasing passage, and further
• wherein the control valve is operable to control oil pressures in said first and second hydraulic clutches so that during operation of the transmission, the oil pressure in one of said hydraulic clutches corresponding to a selected initial gear train is automatically maintained in a lowered state such that the clutch corresponding to the selected initial gear train is disengaged during and immediately following a shifting operation for shifting from a neutral condition to a movement-initiating engagement with the selected initial gear train which is either the first speed gear train or the reverse gear train, in order to initiate motion of the vehicle, and oil pressure in the hydraulic clutch corresponding to the selected initial gear train is thereafter increased after a predetermined time following the engagement of said selected initial gear train,
• wherein completion of engagement of said selected initial gear train is judged by a change in position due to turning of said shift drum;
• and wherein the oil pressure control system further comprises:
• a first solenoid valve interposed between the common oil passage and the oil pressure source at a location upstream of the control valve;
• a second solenoid valve interposed between the common oil passage and the selector valve at a location downstream of the control valve;
• a first pressure discharge valve in communication with the first individual oil passage;
• and
• a second pressure discharge valve in communication with the second individual oil passage;
• wherein
• when the transmission is in the neutral condition,
• the first solenoid valve is closed,
• the second solenoid valve is open,
• the control valve releases oil pressure in the common oil passage downstream of the control valve,
• the selector valve permits communication between the first individual oil passage and the common oil passage whereby pressure in the first individual oil passage is released and the first hydraulic clutch remains in a disconnected state, and further permits communication between the second individual oil passage and the second pressure discharge valve, such that pressure in the second individual oil passage is released and the second hydraulic clutch also remains in a disconnected state.