Hydraulic control device for working vehicle

A hydraulic control device for a working vehicle including

• a transmission, a first pump, a second pump, and a third pump which are driven by a prime mover,
• a steering circuit for controlling discharge oil from said first pump by a steering priority valve and supplying the same preferentially to a steering changeover valve,
• a working machine circuit for supplying discharge oil from said second pump to a working machine changeover valve,
• an assistance circuit for making the remainder of discharge oil from said first pump controlled by said steering priority valve join said working machine circuit,
• a steering dedicated circuit for making discharge oil from said third pump join said steering circuit downstream of said steering priority valve, and
• a shift-down switch for shifting down said transmission to a first speed gear when being operated while said transmission is in a second speed gear, comprising:
• an unloading valve (14), connected to a circuit (6, 13) which connects a junction of said working machine circuit (9, 9a) and said assistance circuit (13) and said first pump (4) and includes said assistance circuit (13), for allowing discharge oil from said first pump (4) to be freely drained;
• a pressure increasing valve (22, 24), connected to said working machine circuit (9a) downstream of said junction, for increasing a set pressure of pressure oil in said downstream working machine circuit (9a);
• a check valve (17), provided in said connecting circuit (6, 13) between a portion connected to said unloading valve (14) and said junction, for checking back-flow of the pressure oil in said downstream working machine circuit (9a) toward said unloading valve (14);
• and
• a controller (16) for draining discharge oil from said first pump (4) by said unloading valve (14) and increasing the set pressure of said downstream working machine circuit (9a) by said pressure increasing valve (22, 24) when said transmission (3) is shifted down from the second speed gear to the first speed gear on receipt of an actuating signal from said shift-down switch (15).

A hydraulic control device for a working vehicle, including a transmission, a first pump, and a second pump which are driven by a prime mover,

• a steering circuit for controlling discharge oil from said first pump by a steering priority valve and supplying the same preferentially to a steering changeover valve,
• a working machine circuit for supplying discharge oil from said second pump to a working machine changeover valve,
• an assistance circuit for making the remainder of discharge oil from said first pump controlled by said steering priority valve join said working machine circuit, and
• a shift-down switch for shifting down said transmission to a first speed gear when being operated while said transmission is in a second speed gear, comprising:
• an unloading valve (14), connected to said working machine circuit (9) upstream of a junction of said working machine circuit (9, 9a) and said assistance circuit (13), for allowing discharge oil from said second pump (5) to be freely drained;
• a pressure increasing valve (22, 24), connected to said working machine circuit (9a) downstream of said junction, for increasing a set pressure of pressure oil in said downstream working machine circuit (9a);
• a check valve (17), provided in said upstream working machine circuit (9) between a portion connected to said unloading valve (14) and said junction, for checking back-flow of the pressure oil in said downstream working machine circuit (9a) toward said unloading valve(14);
• and
• a controller (16) for draining discharge oil from said second pump (5) by said unloading valve (14) and increasing the set pressure of said downstream working machine circuit (9a) by said pressure increasing valve (22, 24) when said transmission (3) is shifted down from the second speed gear to the first speed gear on receipt of an actuating signal from said shift-down switch (15);
• wherein said unloading valve (14) has a pilot pressure operated unloading valve (14) which is freely switched to onload condition or unloaded condition depending on presence or absence of pilot pressure and a first solenoid operated changeover valve (21) for switching said presence or absence of pilot pressure, and
• wherein said pressure increasing valve (22, 24) has a second relief valve (24) which is set at a higher pressure than a first relief valve (23) with normal set pressure and a second solenoid operated changeover valve (22) for switching the connection with said downstream working machine circuit (9a) from said first relief valve (23) to said second relief valve (24).

A hydraulic control device for a working vehicle, including

• a transmission, a first pump, and a second pump which are driven by a prime mover,
• a steering circuit for controlling discharge oil from said first pump by a steering priority valve and supplying the same preferentially to a steering changeover valve,
• a working machine circuit for supplying discharge oil from said second pump to a working machine changeover valve,
• an assistance circuit for making the remainder of discharge oil from said first pump controlled by said steering priority valve join said working machine circuit, and
• a shift-down switch for shifting down said transmission to a first speed gear when being operated while said transmission is in a second speed gear, comprising:
• an unloading valve (14), connected to said working machine circuit (9) upstream of a junction of said working machine circuit (9, 9a) and said assistance circuit (13), for allowing discharge oil from said second pump (5) to be freely drained;
• a pressure increasing valve (22, 24), connected to said working machine circuit (9a) downstream of said junction, for increasing a set pressure of pressure oil in said downstream working machine circuit (9a);
• a check valve (17), provided in said upstream working machine circuit (9) between a portion connected to said unloading valve (14) and said junction, for checking back-flow of the pressure oil in said downstream working machine circuit (9a) toward said unloading valve (14);
• a controller (16) for draining discharge oil from said second pump (5) by said unloading valve (14) and increasing the set pressure of said downstream working machine circuit (9a) by said pressure increasing valve (22, 24) when said transmission (3) is shifted down from the second speed gear to the first speed gear on receipt of an actuating signal from said shift-down switch (15);
• and
• a work mode switch (25) for selecting a work mode and outputting a signal for switching a hard earth mode or soft earth mode,
• wherein said controller (16)
• unloads said second pump (5) by said unloading valve (14) and increases the set pressure of said downstream working machine circuit (9a) by said pressure increasing valve (22, 24) when said transmission (3) is shifted down from the second speed gear to the first speed gear on receipt of an actuating signal from said shift-down switch (15) in the case where a signal for said hard earth mode is inputted, and
• unloads said second pump (5) by said unloading valve (14) and switches said pressure increasing valve (22, 24) to reduce the set pressure of said downstream working machine circuit (9a) to a normal pressure when said transmission (3) is shifted down from the second speed gear to the first speed gear on receipt of an actuating signal from said shift-down switch (15) in the case where a signal for said soft earth mode is inputted.

A hydraulic control device for a working vehicle, including

• a transmission, a first pump, a second pump, and a third pump which are driven by a prime mover,
• a steering circuit for controlling discharge oil from said first pump by a steering priority valve and supplying the same preferentially to a steering changeover valve,
• a working machine circuit for supplying discharge oil from said second pump to a working machine changeover valve,
• an assistance circuit for making the remainder of discharge oil from said first pump controlled by said steering priority valve join said working machine circuit,
• a steering dedicated circuit for making discharge oil from said third pump join said steering circuit downstream of said steering priority valve, and
• a shift-down switch for shifting down said transmission to a first speed gear when being operated while said transmission is in a second speed gear, comprising:
• an unloading valve (14), connected to a circuit (6, 13) which connects a junction of said working machine circuit (9, 9a) and said assistance circuit (13) and said first pump (4) and includes said assistance circuit (13), for allowing discharge oil from said first pump (4) to be freely drained;
• a pressure increasing valve (22, 24), connected to said working machine circuit (9a) downstream of said junction, for increasing a set pressure of pressure oil in said downstream working machine circuit (9a);
• a check valve (17), provided in said connecting circuit (6, 13) between a portion connected to said unloading valve (14) and said junction, for checking back-flow of the pressure oil in said downstream working machine circuit (9a) toward said unloading valve (14);
• a controller (16) for draining discharge oil from said first pump (4) by said unloading valve (14) and increasing the set pressure of said downstream working machine circuit (9a) by said pressure increasing valve (22, 24) when said transmission (3) is shifted down from the second speed gear to the first speed gear on receipt of an actuating signal from said shift-down switch (15);
• and
• a work mode switch (25) for selecting a work mode and outputting a signal for switching a hard earth mode or soft earth mode,
• wherein said controller (16)
• unloads said first pump (4) by said unloading valve (14) and increases the set pressure of said downstream working machine circuit (9a) by said pressure increasing valve (22, 24) when said transmission (3) is shifted down from the second speed gear to the first speed gear on receipt of an actuating signal from said shift-down switch (15) in the case where a signal for said hard earth mode is inputted, and
• unloads said first pump (4) by said unloading valve (14) and switches said pressure increasing valve (22, 24) to reduce the set pressure of said downstream working machine circuit (9a) to a normal pressure when said transmission (3) is shifted down from the second speed gear to the first speed gear on receipt of an actuating signal from said shift-down switch (15) in the case where a signal for said soft earth mode is inputted.

A hydraulic control device for a working vehicle including a transmission, a first pump, a second pump, and a third pump which are driven by a prime mover,

• a steering circuit for controlling discharge oil from said first pump by a steering priority valve and supplying the same preferentially to a steering changeover valve,
• a working machine circuit for supplying discharge oil from said second pump to a working machine changeover valve,
• an assistance circuit for making the remainder of discharge oil from said first pump controlled by said steering priority valve join said working machine circuit,
• a steering dedicated circuit for making discharge oil from said third pump join said steering circuit downstream of said steering priority valve, and
• a shift-down switch for shifting down said transmission to a first speed gear when being operated while said transmission is in a second speed gear, comprising:
• an unloading valve (14), connected to a circuit (6, 13) which connects a junction of said working machine circuit (9, 9a) and said assistance circuit (13) and said first pump (4) and includes said assistance circuit (13), for allowing discharge oil from said first pump (4) to be freely drained;
• a pressure increasing valve (22, 24), connected to said working machine circuit (9a) downstream of said junction, for increasing a set pressure of pressure oil in said downstream working machine circuit (9a);
• a check valve (17), provided in said connecting circuit (6, 13) between a portion connected to said unloading valve (14) and said junction, for checking back-flow of the pressure oil in said downstream working machine circuit (9a) toward said unloading valve (14);
• and
• a controller (16) for draining discharge oil from said first pump (4) by said unloading valve (14) and increasing the set pressure of said downstream working machine circuit (9a) by said pressure increasing valve (22, 24) when said transmission (3) is shifted down from the second speed gear to the first speed gear on receipt of an actuating signal from said shift-down switch (15);
• wherein said unloading valve (14) has a pilot pressure operated unloading valve (14) which is freely switched to unload condition or unloaded condition depending on presence or absence of pilot pressure and a first solenoid operated changeover valve (21) for switching said presence or absence of pilot pressure, and
• wherein said pressure increasing valve (22, 24) has a second relief valve (24) which is set at a higher pressure than a first relief valve (23) with normal set pressure and a second solenoid operated changeover valve (22) for switching the connection with said downstream working machine circuit (9a) from said first relief valve (23) to said second relief valve (24).