Abstract: A lock-up clutch by way of which input/output shafts of a torque converter are operatively connected to each other is connected to an electronic type pressure control valve. During speed changing in a transmission, the problem of interruption of torque transmission can be solved by turning off the lock-up clutch at the time when filling of one of the speed changing clutches to be next brought into an operatively engaged state with hydraulic oil is completed. Hydraulic pressure (P.sub.t) in the torque converter is exerted on the back 100 pressure portion of a piston of the lock-up clutch while hydraulic pressure (P.sub.t) in the torque converter is exerted on the proportional solenoid side of the pressure control valve, making it possible to reduce the initial hydraulic pressure. During speed changing, the lock-up clutch is not fully released from the engaged state but maintains its operative state at low pressure, causing shock from shifting the lock-up state to be reduced.

Abstract: A lock-up clutch by way of which input/output shafts of a torque converter are operatively connected to each other is connected to an electronic type pressure control valve. During speed changing in a transmission, the problem of interruption of torque transmission can be solved by turning off the lock-up clutch at the time when filling of one of the speed changing clutches to be next brought into an operatively engaged state with hydraulic oil is completed. Hydraulic pressure (P.sub.t) in the torque converter is exerted on the back pressure portion of a piston of the lock-up clutch while hydraulic pressure (P.sub.t) in the torque converter is exerted on the proportional solenoid side of the pressure control valve, making it possible to reduce the initial hydraulic pressure. During speed changing, the lock-up clutch is not fully released from the engaged state but maintains its operative state at low pressure, causing shock from shifting the lock-up state to be reduced.

Abstract: A method of controlling speed changes in a hydraulically actuated type multiple-stage speed change gear, which renders it possible to prevent the occurrence of "shift hunting" without impairing the acceleration characteristics of the vehicle and also reduce the magnitude of shocks which occur at the time of speed changes even in case hydraulic clutches of small capacity are used. According to this method of controlling speed changes, a controller (30) is used to conduct speed changes when conditions for speed changes, i.e., upshift/downshift are satisfied, and in cases where a downshift is made after an upshift and an upshift is made after a downshift, speed changes are conducted after the lapse of a long speed change inhibiting time, and in other cases than the aforementioned, speed changes are conducted after the lapse of a short speed change inhibiting time.

Abstract: In a configuration in which electronically operated pressure control valves (31-36) are respectively connected to clutches of a two-stage transmission (3) composed of main transmissions (1st, 2nd, R, 4th, 3rd) and sub transmissions (L, H), when a downshift is effected from a present speed stage to a next speed stage with power on, the supply of oil pressure to a speed-changing clutch for the present speed stage is stopped on the basis of a speed-change command, the pressure control valve is actuated when a relative number of revolutions of the speed-changing clutch for the next speed stage becomes zero, which commences the supply of oil pressure to that speed-changing clutch, and the supply of oil pressure is gradually increased upon confirming the completion of a filling time of the speed-changing clutch. Thus discomfort owing to a speed-change shock is prevented in whatever state the amount of an accelerator operated and the state of operation of a brake are.

Abstract: During shift change, a discrimination is made as to a load, a quantity of residual hydraulic oil in respective shift change clutches (F, R, 1 to 4) and a state of shift change which has been effected from what speed stage to what speed stage so that a pattern of electrical commands to be issued to pressure control valves (51 to 56) for required shift change clutches is variably controlled depending on results derived from the above discrimination. Thus, smooth shift change can always be achieved regardless of running conditions. Electrical commands (C.sub.1 to C.sub.6) to be fed to the respective pressure control valves (51 to 56) are compared with electrical currents (I.sub.1 to I.sub.6) outputted from drive circuits and outputs (S.sub.1 to S.sub.6) from clutch pressure detecting means (101 to 106) for each clutch, whereby an abnormality is detected with the relevant clutch based on results derived from the comparison.

Abstract: The present invention provides an apparatus for controlling a hydraulic pressure usable for a clutch wherein the appratus is employed for a transmission mounted on a construction machine or the like in such a manner that it is provided separately for a plurality of clutches 1 and it is controlled individually. The apparatus includes a first valve 3 for allowing a large amount of hydraulic oil to flow in the clutch and a second valve 4 for electronically controlling a clutch pressure so that the termination of filling and the clutch pressure are detected by a simple structural arrangement on the basis of a displacement of a spool 21 for the first valve 3 and a separately disposed piston. In addition, appearing of an overshoot pressure on the termination of filling is prevented by providing a difference in pressue receiving areas on the spool 21 for the first valve.

Abstract: During shift change, a discrimination is made as to a load, a quantity of residual hydraulic oil in respective shift change clutches (F, R, 1 to 4) and a state of shift change which has been effected from what speed stage to what speed stage so that a pattern of electrical commands to be issued to pressure control valves for required shift change clutches is variably controlled depending on results derived from the above discrimination. Thus, smooth shift change can always be achieved regardless of running conditions. Electrical commands to be fed to the respective pressure control valves are compared with electrical currents outputted from drive circuits and outputs from clutch pressure detecting means for each clutch, whereby an abnormality is detected with the relevant clutch based on results derived from the comparison. Once an abnormality is detected, an adequate disposal for processing the abnormality is executed so as to reliably prevent double engagement from taking place with clutches.

Abstract: The present invention is concerned with a transmission constructed in the two-staged structure including main speed changing units (1st, 2nd) and auxiliary speed changing units (H, L) which are provided with clutches (H, L, 1st, 2nd) which in turn are individually connected to electronic type pressure control valves (21 to 24) so as to enable the respective clutches to be controlled separately. When it is found that pressurized hydraulic oil delivered from a hydraulic pump has a shortage in amount at the time of starting of forward movement of a vehicle, feeding of hydraulic oil to the clutches (H, L) on the main speed changing unit side and the clutches (1st, 2nd) on the auxiliary speed changing unit side is effected with a certain time difference kept therebetween in order to suppress fluctuation in filling time due to reduction of an amount of hydraulic oil delivered from the hydraulic pump.

Abstract: A method for controlling a transmission system mounted on such as a traveling machine or a construction machine, the transmission system having a two-stage clutch configuration in which a speed is selected through a combination of a plurality of sub transmission clutches and a plurality of main transmission clutches. At the time of speed change, engagement is started beginning with the main transmission clutch side, and the engagement of the sub transmission clutch is commenced upon completion of the filling of the oil in the main transmission clutch, thereby reducing the two speed-change shocks, including a reverse shock, which are conventionally experienced.

Abstract: The present invention provides an apparatus for controlling a hydraulic pressure usable for a clutch wherein the apparatus is employed for a transmission mounted on a construction machine or the like in such a manner that it is provided separately for a plurality of clutches and it is controlled individually. The apparatus includes a first valve for allowing a large amount of hydraulic oil to flow in the clutch and a second valve for electronically controlling a clutch pressure so that the termination of filling and the clutch pressure are detected by a simple structural arrangement on the basis of a displacement of a spool for the first valve and a separately disposed piston. In addition, appearing of an overshoot pressure on the termination of filling is prevented by providing a difference in pressure receiving areas on the spool for the first valve.

Abstract: The present invention is concerned with a transmission constructed in the two-staged structure including main speed changing units (1st, 2nd) and auxiliary speed changing units (H, L) which are provided with clutches (H, L 1st, 2nd) which in turn are individually connected to electronic type pressure control valves (21 and 24) so as to enable the respective clutches to be controlled separately. When it is found that pressurized hydraulic oil delivered from a hydraulic pump has a shortage in amount at the time of starting of forward movement of a vehicle, feeding of hydraulic oil to the clutches (H, L) on the main speed changing unit side and the clutches (1st, 2nd) on the auxiliary speed changing unit side is effected with a certain time difference kept therebetween in order to suppress fluctuation in filling time due to reduction of an amount of hydraulic oil delivered from the hydraulic pump.

Abstract: A plurality of clutch hydraulic pressure gradual increase patterns for maintaining jerk value at a level of a target value are previously determined in dependence on vehicle weight and speed stages; a clutch hydraulic pressure gradual increase pattern corresponding to the vehicle weight and speed stage selected at the time of speed change is selected from the aforesaid plurality of clutch hydraulic pressure gradual increases patterns. Then, hydraulic pressure in a speed change clutch to be engaged is caused to increase gradually in accordance with the thus selected clutch hydraulic pressure gradual increase pattern.At the time point when a speed change command is issued, a speed change clutch to be subsequently brought in the engaged state is fed with hydraulic oil and gradually increasing hydraulic pressure is exerted on the speed change clutch after the time point when termination of filling time is confirmed with respect to this speed change clutch.