The present disclosure relates to a hydraulic drive system having a hydraulic circuit architecture operable in first and second modes. In a first mode, a main hydraulic pump (22) is used to drive a hydraulic actuator (24) via a closed hydraulic circuit, and a charge pump (42) provides charge flow to the closed hydraulic circuit. In a second mode the main pump set to zero displacement and the charge pump (42) is used to drive the hydraulic actuator (24).

A traveling hydraulic stepless transmission (“HST”), ensures stopping of a vehicle on a slope under high load conditions, maintains stopping the vehicle on flat ground under low load conditions, and enables smooth starting from a stop. The HST includes a neutral check valve (“NCV”) and an internal damping system (“IDS”). The NCV includes a first orifice that opens a first oil passage to a transaxle case when a pressure in the first oil passage is equal to or less than a predetermined pressure, and that connects the second oil passage to the transaxle case when a pressure in a second oil passage is equal to or less than the predetermined pressure. The IDS includes second orifices that connect a high pressure side of the oil passages to the transaxle case when a discharge rate of the hydraulic pump is equal to or less than a predetermined discharge rate.

A traveling hydraulic stepless transmission (“HST”), ensures stopping of a vehicle on a slope under high load conditions, maintains stopping the vehicle on flat ground under low load conditions, and enables smooth starting from a stop. The HST includes a neutral check valve (“NCV”) and an internal damping system (“IDS”). The NCV includes a first orifice that opens a first oil passage to a transaxle case when a pressure in the first oil passage is equal to or less than a predetermined pressure, and that connects the second oil passage to the transaxle case when a pressure in a second oil passage is equal to or less than the predetermined pressure. The IDS includes second orifices that connect a high pressure side of the oil passages to the transaxle case when a discharge rate of the hydraulic pump is equal to or less than a predetermined discharge rate.

A hydraulic valve block for a hydraulic unit includes a high-pressure port, a low pressure port, a pilot valve having a pilot valve spool, and a bypass valve having a bypass valve spool. The pilot valve connects in an initial position a control line to a discharge area. The pilot valve is switched by means of a force whose height depends on the pressure level at the low pressure side to a shifted position in which the pilot valve conducts pressure from the high-pressure port to the control line. The bypass valve switches from a closed position in which a fluid connection between the high pressure port and low pressure port is disabled, to an open position in which a fluid connection between the high pressure port and low pressure port is enabled, if the control line connected to an opening surface of the bypass valve, is not connected to the high-pressure port.

A hydraulic valve block for a hydraulic unit includes a high-pressure port, a low pressure port, a pilot valve having a pilot valve spool, and a bypass valve having a bypass valve spool. The pilot valve connects in an initial position a control line to a discharge area. The pilot valve is switched by means of a force whose height depends on the pressure level at the low pressure side to a shifted position in which the pilot valve conducts pressure from the high-pressure port to the control line. The bypass valve switches from a closed position in which a fluid connection between the high pressure port and low pressure port is disabled, to an open position in which a fluid connection between the high pressure port and low pressure port is enabled, if the control line connected to an opening surface of the bypass valve, is not connected to the high-pressure port.

The invention relates to a hydraulic machine, in particular to a hydraulic motor with two working lines, from one of which a high pressure line and from the other one a low pressure line is branched off. An electronic control unit and a servo displacement unit are provided to control the displacement of the displacement volume of a drive mechanism of the hydraulic machine, wherein the displacement volume can be determinated by the displacement of a servo piston within the servo displacement unit. For this, the servo piston can be loaded at least on one side via a servo pressure line with hydraulic fluid under servo pressure, wherein the servo pressure level can be adjusted by a control spool arranged moveable within a control valve. For this, hydraulic fluid from the low pressure line or, perhaps, from the high pressure line is guidable via the control valve to the servo pressure line if a suitable control signal is available at a switching valve.

The invention relates to a hydraulic machine, in particular to a hydraulic motor with two working lines, from one of which a high pressure line and from the other one a low pressure line is branched off. An electronic control unit and a servo displacement unit are provided to control the displacement of the displacement volume of a drive mechanism of the hydraulic machine, wherein the displacement volume can be determinated by the displacement of a servo piston within the servo displacement unit. For this, the servo piston can be loaded at least on one side via a servo pressure line with hydraulic fluid under servo pressure, wherein the servo pressure level can be adjusted by a control spool arranged moveable within a control valve. For this, hydraulic fluid from the low pressure line or, perhaps, from the high pressure line is guidable via the control valve to the servo pressure line if a suitable control signal is available at a switching valve.

A hydrostatic drive, as a whole system, includes two fluidic displacement units (1, 3), which can be adjusted at least in respect of the volumetric flow. One unit is coupled to an input (9). The other unit is coupled to an output (11). The units can be connected to each other in the manner of a closed fluidic circuit, to which a storage circuit (23) is connected. The storage circuit has at least one storage device (33), is divided into a low-pressure side (27) and a high-pressure side (25), and has a valve control (17) for controlling the whole system.

A hydrostatic drive, as a whole system, includes two fluidic displacement units (1, 3), which can be adjusted at least in respect of the volumetric flow. One unit is coupled to an input (9). The other unit is coupled to an output (11). The units can be connected to each other in the manner of a closed fluidic circuit, to which a storage circuit (23) is connected. The storage circuit has at least one storage device (33), is divided into a low-pressure side (27) and a high-pressure side (25), and has a valve control (17) for controlling the whole system.

A drive, which permits a lowering in the feed pressure provided by the feed pump and, at the same time, effects a supply to the displacement unit of the drive which meets the demand with regard to pressure and delivery volume. This is achieved in that the displacement unit (5) is supplied with hydraulic energy by an electro-hydraulic supply unit (6) wherein the supply unit (6) comprises a hydraulic reservoir (9) and a non-return valve (18) and is connected to the feed pressure limiting valve (12), which is implemented as an electrically adjustable pressure limiting valve, wherein the hydraulic reservoir (9) is also connected to an electro-hydraulic pressure sensor (10), which outputs the electric signal thereof to an electric auxiliary controller (11), and wherein the electric auxiliary controller (11) drives the feed pressure limiting valve (12). These hydraulic drives are used for example, in self-propelled working machines.