Hydraulically driven vehicle

A hydraulically driven vehicle, comprising:

• a hydraulic pump driven by an engine;
• a variable displacement hydraulic motor for traveling driven by pressure oil from the hydraulic pump;
• a motor displacement control device that adjusts a displacement of the hydraulic motor in correspondence to a drive pressure at the hydraulic motor;
• a forward/backward operating member through which a forward travel command, a backward travel command and a neutral command for the vehicle are issued;
• a traveling operation member through which a command for acceleration and deceleration for the vehicle is issued in accordance with an extent to which the traveling operation member is operated;
• a pilot valve configured to provide a pilot pressure oil in response to an operation of the traveling operation member;
• a control valve configured to be driven by the pilot pressure oil from the pilot valve to control a flow of pressure oil from the hydraulic pump to the hydraulic motor;
• a counterbalance valve, that is disposed between the control valve and the hydraulic motor, configured to be switched to an opening position by the pressure oil supplied from the hydraulic pump so as to open a return path for oil to return from the hydraulic motor to the control valve, and to be switched to a closing position so as to close the return path as the pressure oil from the hydraulic pump is stopped;
• a directional control valve that controls a flow of the pilot pressure oil which acts on the control valve in response to an operation of the forward/backward operating member;
• a reverse operation detection device that detects a reverse operation of the forward/backward operating member performed to a reverse side opposite from a direction along which the vehicle is advancing;
• a rotation speed detection device that detects a physical quantity having a correlation to a rotation speed of the hydraulic motor;
• and
• a control device that stops supply of the pressure oil from the hydraulic pump to the hydraulic motor by interrupting the flow of the pilot pressure oil to the control valve in response to the neutral command issued from the forward/backward operating member, regardless of the operation of the traveling operation member, wherein:
• when the neutral command is not issued from the forward/backward operating member, the control device (a) stops supply of the pressure oil from the hydraulic pump to the hydraulic motor by interrupting the flow of the pilot pressure oil to the control valve if the physical quantity detected by the rotation speed detection device exceeds a reference value and the reverse operation at the forward/backward operating member is detected by the reverse operation detection device, and (b) allows the pilot pressure oil to flow to the control valve, even if the reverse operation at the forward/backward operating member is detected, if the physical quantity detected by the rotation speed detection device is equal to or smaller than the reference value.

A hydraulically driven vehicle, comprising:

• a hydraulic pump driven by an engine;
• a variable displacement hydraulic motor for traveling driven by pressure oil from the hydraulic pump;
• a motor displacement control device that adjusts a displacement of the hydraulic motor in correspondence to a drive pressure at the hydraulic motor;
• an operating member through which a forward travel command and a backward travel command for the vehicle and a command for acceleration and deceleration for the vehicle are issued;
• a pilot valve configured to provide a pilot pressure oil in accordance with an extent to which the operating member is operated;
• a control valve configured to be driven by the pilot pressure oil from the pilot valve to control a flow of pressure oil from the hydraulic pump to the hydraulic motor;
• a counterbalance valve, that is disposed between the control valve and the hydraulic motor, configured to be switched to an opening position by the pressure oil supplied from the hydraulic pump so as to open a return path for oil to return from the hydraulic motor to the control valve, and to be switched to a closing position so as to close the return path as the pressure oil from the hydraulic pump is stopped;
• a first directional control valve that is disposed between the control valve and the counterbalance valve and controls a flow of the pressure oil from the hydraulic pump to the hydraulic motor;
• a neutral command device that issues a command for switching the control valve to a neutral position;
• a second directional control valve configured to be switched to interrupt the pilot pressure oil which acts on the control valve in response to the command issued from the neutral command device, regardless of operation of the operating member, and configured to be switched to allow the pilot pressure to flow to the control valve when the command is not issued from the neutral command device;
• a reverse operation detection device that detects a reverse operation of the operating member performed to a reverse side opposite from a direction along which the vehicle is advancing;
• a rotation speed detection device that detects a physical quantity having a correlation to a rotation speed of the hydraulic motor;
• and
• a control device that controls the first directional control valve such that the first directional control valve (a) stops the flow of the pressure oil from the hydraulic pump to the hydraulic motor when the physical quantity detected by the rotation speed detection device exceeds a reference value and the reverse operation at the operating member is detected by the reverse operation detection device, and (b) allows the pilot pressure oil to flow to the control valve, even if the reverse operation at the operating member is detected, when the physical quantity detected by the rotation speed detection device is equal to or smaller than the reference value.