Device and method for controlling a hydraulic machine

A variable hydraulic motor comprising:

• two working lines, from one of which a high pressure line and from the other one a low pressure line is branched off, and
• a control valve, within which a spool is arranged movable by means of a first actuator, such that a servo displacement unit can be provided with hydraulic fluid under pressure via a servo pressure line arranged at the output side of the control valve such that the displacement volume of the hydraulic motor is adjustable in a controlled manner, and
• wherein the spool includes means by which hydraulic fluid under pressure is guidable either from the low pressure line or the high pressure line to the servo displacement unit via the control valve and via the servo pressure line,
• wherein the inlet side of the control valve is connected to the low pressure line, and in that hydraulic fluid from the low pressure line can be forwarded to the servo pressure line via the control valve,
• wherein the inlet side of the control valve is connected to the high pressure line, and in that hydraulic fluid from the high pressure line can be forwarded to the servo pressure line via the control valve, and
• wherein the control valve is connected to a pressure relief valve, the pressure relief valve being configured to open a connection line if a predefined pressure level in the high pressure line is exceeded, and wherein the connection line hydraulically connects the high pressure line with a front face of the spool of the control valve.

A method for the controlled adjustment of the displacement volume of a variable hydraulic motor having a low pressure line and a high pressure line and having an electronic control unit and a servo displacement unit,

• wherein the adjustment of the displacement volume is made by the displacement of a control spool arranged in a control valve and by means of a first actuator according to a control signal of the electronic control unit such that hydraulic fluid under pressure can be conducted from the outlet side of the control valve via a servo pressure line to the servo displacement unit such that by means of the servo displacement unit the displacement volume of the hydraulic motor is adjusted in a controlled manner,
• wherein hydraulic fluid under pressure from the low pressure line is supplied to the inlet side of the control valve,
• wherein hydraulic fluid under pressure from the high pressure line is supplied to the inlet side of the control valve, if a predetermined threshold value for the pressure in the high pressure line is exceeded or a further control signal is generated by the electronic control unit that switches a switching valve such that hydraulic fluid under pressure from the high pressure line is conducted to the control valve, and
• wherein the switching valve is connected to a pressure relief valve, the pressure relief valve being configured to open a connection line if a predefined pressure level in the high pressure line is exceeded, and wherein the connection line hydraulically connects the high pressure line with a front face of the switching valve.

A method for the controlled adjustment of the displacement volume of a variable hydraulic motor, the variable hydraulic motor comprising a low pressure line, a high pressure line, an electronic control unit, a servo displacement unit, and a control valve having a control spool arranged therein, the method comprising:

• displacing the control spool by means of a first actuator according to a control signal of the electronic control unit such that hydraulic fluid under pressure can be conducted from the outlet side of the control valve via a servo pressure line to the servo displacement unit such that by means of the servo displacement unit the displacement volume of the hydraulic motor is adjusted in a controlled manner,
• wherein hydraulic fluid under pressure from the low pressure line is supplied to the inlet side of the control valve,
• wherein hydraulic fluid under pressure from the high pressure line is supplied to the inlet side of the control valve, if a predetermined threshold value for the pressure in the high pressure line is exceeded or a further control signal is generated by the electronic control unit that switches a switching valve such that hydraulic fluid under pressure from the high pressure line is conducted to the control valve, and
• wherein the switching valve is connected to a pressure relief valve, the pressure relief valve being configured to open a connection line if a predefined pressure level in the high pressure line is exceeded, and wherein the connection line hydraulically connects the high pressure line with a front face of the switching valve.