Hydraulic axial piston unit and method for controlling of a hydraulic axial piston unit

Abstract

Hydraulic axial piston unit includes a rotatable cylinder block and a valve segment with two pressure ports. An IDC control port and an ODC control port are located on the valve segment in circumferential direction between the circumferential ends of the pressure ports such that a cylinder bore can be fluidly connected to the IDC control port or the ODC control port when the associated working piston is at or close to its inner dead center or outer dead center. The circumferential distance from the control ports to the pressure ports is smaller than the circumferential extension of the cylinder bores. A first and a second bypass line each connecting one of the control ports are provided with an adjustable orifice in the first bypass line, capable of continuously variably opening and closing the first bypass line in order to enable an adjustable fluid flow connection between the connected pressure port and the connected pressure port.

What is claimed is: 
     
         1 . A hydraulic axial piston unit with a rotating group whose displacement volume is set by means of a displacement element, the rotating group comprising a rotatable cylinder block with cylinder bores in which working pistons are mounted reciprocally moveable, and with a valve segment comprising a kidney-shaped first pressure port and a kidney-shaped second pressure port, wherein a cylinder bore can be fluidly connected to an IDC control port or an ODC control port when the associated working piston is at or close to its inner dead center (IDC) or at or close to its outer dead center (ODC), respectively, wherein the IDC control port and the ODC control port are located in circumferential direction between the respective circumferential ends of the first pressure port and the second pressure port, wherein the circumferential distance from the IDC control port to the first and second pressure ports and the circumferential distance from the ODC control port to the first and second pressure ports is smaller than the circumferential extension of the cylinder bores, and wherein a first bypass line and a second bypass line are provided, each connecting one of the control ports, with an adjustable orifice arranged in the first bypass line, capable of continuously variably opening and closing the first bypass line in order to enable an variably adjustable fluid flow connection between the connected control port and a connected pressure port, wherein, the first bypass line and the second bypass line each connects the next pressure port after the connected control port in rotational direction of the cylinder block. 
     
     
         2 . (canceled) 
     
     
         3 . (canceled) 
     
     
         4 . (canceled) 
     
     
         5 . The hydraulic axial piston unit according to  claim 1 , wherein the second bypass line is connected to a pressure compensation chamber. 
     
     
         6 . (canceled) 
     
     
         7 . The hydraulic axial piston unit according to  claim 1 , wherein the openings of the cylinder bores facing the valve segment show a kidney-shaped cross section, wherein the circumferential extensions of the kidney-shaped openings of the cylinder bores are smaller than the circumferential distance between the adjacent ends of the first and second kidney-shaped pressure ports. 
     
     
         8 . (canceled) 
     
     
         9 . The hydraulic axial piston unit according to  claim 1 , wherein an adjustable orifice is arranged in each of the bypass lines. 
     
     
         10 . (canceled) 
     
     
         11 . (canceled) 
     
     
         12 . The hydraulic axial piston unit according to  claim 1 , wherein a parallel bypass line comprising an adjustable orifice or a non-adjustable orifice establishes a fluid flow connection parallel to the fluid flow connection between the pressure port and the control port connected by the first bypass line or between the pressure port and the control port connected by the second bypass line. 
     
     
         13 . (canceled) 
     
     
         14 . The hydraulic axial piston unit according to  claim 1 , wherein each control port is additionally connected to the other pressure port via a third and a fourth bypass line, wherein an adjustable orifice is arranged in each of the four bypass lines. 
     
     
         15 . (canceled) 
     
     
         16 . (canceled) 
     
     
         17 . The hydraulic axial piston unit according to  claim 1 , wherein, in case the rotating group is at maximum displacement in its initial position, a safety pressure limiter switching valve is arranged in at least one of the bypass lines in order to close the associated bypass line when a system pressure level exceeds a threshold value. 
     
     
         18 . (canceled) 
     
     
         19 . The hydraulic axial piston unit according to  claim 1 , wherein the opening size of the orifices is controlled mechanically or by an electronic control unit (ECU) comprising a micro-controller, and being connected to at least one sensor selected from a group of sensors comprising a tilt angle sensor, a shaft position sensor, a pressure sensor, a flow sensor, a rotational speed sensor, a temperature sensor, a direction sensor, a torque sensor, an acceleration sensor or any other sensor capable of monitoring at least one operational parameter of the hydraulic unit. 
     
     
         20 . The hydraulic axial piston unit according to  claim 1 , comprising at least two adjustable orifices one provided in the first bypass line and one provided in the second bypass line, wherein the opening sizes of the two adjustable orifices are adjustable separately or by means of a shared mechanical, electromechanical, hydraulic or pneumatic mechanism. 
     
     
         21 . The hydraulic axial piston unit according to  claim 1 , wherein the IDC and/or the ODC control port comprise a circular shape, an elongated shape, an ellipse shape, a triangle shape, a kidney-shape or any other shape. 
     
     
         22 . The hydraulic axial piston unit according to  claim 1 , wherein the IDC control port and/or the ODC control port are located on the valve segment in circumferential direction with an angular offset to the rotational position on the valve segment at which the working pistons are at its inner dead center (IDC) and/or outer dead center (ODC), respectively. 
     
     
         23 . (canceled) 
     
     
         24 . The hydraulic axial piston unit according to  claim 22 , wherein a second ODC control port is located on the valve segment such that the first and second ODC control ports being located in circumferential direction on both sides of the rotational position on the valve segment which corresponds to the outer dead center (ODC) position of the working pistons. 
     
     
         25 . The hydraulic axial piston unit according to  claim 24 , wherein a second IDC control port is located on the valve segment such that the first and second IDC control ports being located in circumferential direction on both sides of the rotational position on the valve segment which corresponds to the inner dead center (IDC) position of the working pistons. 
     
     
         26 . The hydraulic axial piston unit according to  claim 24 , wherein the second IDC control port and/or the second ODC control port are respectively connected to a third bypass line and/or a fourth bypass line, wherein at least one of the third and fourth bypass lines comprises an adjustable orifice capable of continuously and variably opening and closing the associated bypass line. 
     
     
         27 . (canceled) 
     
     
         28 . The hydraulic axial piston unit according to  claim 1 , operated in a closed hydraulic circuit and comprising a shuttle valve having two inlets and one outlet, which inlets are in fluid connection with the first and second pressure ports and which outlet is in fluid connection with the IDC control port or the ODC control port, such that the shuttle valve is capable of conducting the higher system pressure from one of the first and second pressure ports to the IDC control port or to the ODC control port and/or to a control valve. 
     
     
         29 . The hydraulic axial piston unit according to  claim 28 , wherein a control valve is provided with a first inlet connected to the outlet of the shuttle valve, and a second inlet connected to lower system pressure or to a hydraulic reservoir, and with a first outlet connectable to the IDC control port or the ODC control port, and a second outlet connectable to the other control port, wherein the control valve is capable of selectively connecting the first inlet with the first outlet and the second inlet with the second outlet, or of connecting the first inlet with the second outlet and the second inlet with the first outlet, or of short-circuiting the first outlet with the second outlet. 
     
     
         30 . The hydraulic axial piston unit according to  claim 28 , comprising a charge pump capable of providing a hydraulic fluid flow to one of the first or second pressure port to generate an initial pressure difference between the first and second pressure ports and/or to switch the shuttle valve when the hydraulic axial piston unit is in its neutral position. 
     
     
         31 . (canceled) 
     
     
         32 . The hydraulic axial piston unit according to  claim 1  any of the preceding claims, wherein the at least one adjustable orifice is controlled by the electronic control unit (ECU) based on a pressure and/or displacement feedback of at least one adjustable orifice. 
     
     
         33 . The hydraulic axial piston unit according to  claim 1 , wherein the control ports are inclined with respect to a rotational axis of the hydraulic axial piston unit. 
     
     
         34 . (canceled) 
     
     
         35 . A method for variably controlling the displacement volume of a hydraulic rotating group driving or being driven by a driving shaft, having a displacement element tiltable for adjusting the displacement volume of the rotating group, wherein the rotating group comprises a rotatable cylinder block in which working pistons are mounted reciprocally moveable in cylinder bores, and a valve segment with a kidney-shaped first pressure port and with a kidney-shaped second pressure port, wherein an IDC control port and an ODC control port are located on the valve segment in circumferential direction between the respective circumferential ends of the first pressure port and the second pressure port, wherein a cylinder bore can be fluidly connected to the IDC control port or the ODC control port when the associated working piston is at or close to its inner dead center (IDC), or is at or close to its outer dead center (ODC), respectively, wherein the circumferential distance from the IDC control port to the first and second pressure ports and the circumferential distance from the ODC control port to the first and second pressure ports is smaller than the circumferential extension of the cylinder bores,
 wherein the method comprises the following steps:
 draining or supplying of hydraulic fluid from or to the passing cylinder bores via the IDC control port by means of a first bypass line having a first orifice, 
 supplying or draining of hydraulic fluid to or from the passing cylinder bores via the ODC control port by means of a second bypass line having a second orifice, 
 adjusting an opening size of the first orifice, or an opening size of the second orifice, or adjusting both opening sizes of the first orifice and the second orifice in order to set or adjust the angle of tilt of the displacement element and to control the displacement volume of the hydraulic rotating group, wherein the hydraulic fluid from the ODC and IDC control ports is supplied or drained with the pressure level of the next pressure port in rotational direction of the cylinder block. 
   
     
     
         36 . (canceled) 
     
     
         37 . The method according to  claim 35 , further comprising the step of:
 processing a command of a control unit or an operator by means of an electronic control unit (ECU) having a microcontroller for adjusting the opening sizes of the orifices in the first bypass line and/or in the second bypass line, in order to control the pressure in the cylinder bores for controlling the displacement volume of the hydraulic axial piston unit.   
     
     
         38 . (canceled) 
     
     
         39 . The method according to  claim 35 , further comprising the step of:
 continuously monitoring the operational parameters of the hydraulic axial piston unit in order to smoothen pressure transition between the first and second pressure ports and vice versa, and/or for controlling the pressure in the cylinder bores, and/or for adjusting the tilt angle of the displacement element.   
     
     
         40 . The method according to  claim 35 , further comprising in case the rotating group is used in a closed circuit hydraulic application having a charge pump, the steps of:
 supplying charge pressure to one of the first or second pressure ports via a charge pressure valve, when the rotating group is in its neutral position   guiding of hydraulic fluid by means of one of the first or the second bypass line from the pressure port with the higher pressure to the associated control port;   draining of hydraulic fluid by means of the other bypass line from the other control port to a hydraulic fluid reservoir.