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

Abstract

A hydraulic axial piston unit includes a rotatable cylinder and a valve section having two pressure ports. The IDC control port and the ODC control port are located on the valve section between the circumferential ends of the pressure port in the circumferential direction such that the cylinder bore may be fluidly connected to the IDC control port or the ODC control port when the associated working piston is at or near its inner or outer dead center. A circumferential distance from the control port to the pressure port is less than a circumferential extent of the cylinder bore. A first bypass line and a second bypass line are provided, each connecting one of the control ports, with an adjustable orifice in the first bypass line, the adjustable orifice being capable of continuously variably opening and closing the first bypass line, and the adjustable orifice being capable of continuously variably opening and closing the second bypass line. In this way, an adjustable fluid flow connection between the connected pressure port and the connected pressure port can be achieved.

Description

[0001] The present invention relates to a hydraulic axial piston unit and a method for controlling a hydraulic axial piston unit. More specifically, the present invention relates to a hydraulic axial piston unit of the swash plate type and a hydraulic axial piston unit of the slanted axis type configuration. The present invention also relates to a method for controlling both types of hydraulic axial piston units. The hydraulic axial piston unit to which the present invention relates can be used in open hydraulic circuits as well as in closed hydraulic circuits and can include a fixed displacement volume or a variable displacement volume.

[0002] Hydraulic axial piston units of swash plate type or swash shaft type construction are well known in the prior art and are used as fixed or variable displacement units. These hydraulic axial piston units can all be operated in pumping mode or motor drive mode. The displacement volume of the hydraulic axial piston unit can be set / controlled by setting / changing the inclination angle of the displacement element (i.e., swash plate or yoke). In order to convert mechanical power into hydraulic power (and vice versa), the hydraulic axial piston unit includes a rotating group. The rotating group has a rotatable cylinder body with a cylinder bore, and the working piston is reciprocatingly arranged in these cylinder bores for conveying hydraulic fluid from a kidney-shaped inlet port to a kidney-shaped outlet port located on the valve section of the hydraulic axial piston unit. When the displacement element is tilted relative to the drive shaft axis of the hydraulic unit, when the cylinder body rotates, the working piston is forced to reciprocate between its inner dead center (IDC) and its outer dead center (ODC). Thus, when the movement direction of the piston changes from moving toward the valve section to moving toward the displacement element, the piston is at its inner dead center. When the movement direction of the piston changes from movement toward the displacement element to movement toward the valve section, the piston is at its outer dead center. As is known, one of the inlet port or the outlet port is used as a high-pressure port and the corresponding other port is used as a low-pressure port. Which port is used as a high-pressure port and which port is used as a low-pressure port is determined according to the operating mode of the hydraulic unit and the hydraulic flow direction.

[0003] In order to manually set the inclination angle of the displacement element of the hydraulic axial piston unit, a hydraulic or electronic control unit is used. In order to set / adjust the displacement volume of the hydraulic axial piston unit, these control units selectively guide the hydraulic pressure into the pressure chamber of the servo unit by displacing the control valve core, thereby frequently controlling the movement of the servo piston in the servo unit. Due to the high requirements for manufacturing and operating precision, these control and servo arrangements are complex and prone to errors. Therefore, they are expensive in terms of manufacturing and installation work. In addition, the control and servo units known in the art are bulky and occupy a large space due to the number of their parts, which increases the overall size of the hydraulic axial piston unit. The known controls of the hydraulic axial piston unit are developed for specific applications and require specific adaptation of the control parts for each application, such as specific valve plates and / or valve sections and specifically adapted servo and control valve cores and springs, which require small tolerances. The components of the displacement control unit are prone to wear and therefore require continuous maintenance or replacement. Furthermore, these specific components are not suitable for in-service changes, ie once installed they cannot be adapted to the individual load case, and furthermore they cannot usually be used in different hydraulic axial piston units of different volume dimensions / cubic capacities.

[0004] The object of the present invention is therefore to provide a hydraulic axial piston unit with a control system for setting and controlling the displacement volume of the hydraulic axial piston unit, which hydraulic axial piston unit comprises a smaller number of components or at least components of a simpler design than the solutions in the prior art, but which nevertheless enables the displacement volume of the hydraulic axial piston unit to be set and controlled reliably. The hydraulic axial piston unit according to the invention is therefore less expensive and requires less construction space than the solutions known in the art. The control system for the hydraulic axial piston unit according to the invention is intended to be adaptable to different hydraulic axial piston units even during operation, i.e. without the hydraulic axial piston unit having to be disassembled.

[0005] This object is achieved by a hydraulic axial piston unit according to claim 1 and a method for controlling the displacement volume of a hydraulic rotary group according to claim 35. Preferred embodiments are presented in the dependent claims thereof.

[0006] The hydraulic axial piston unit according to the present invention comprises a rotating group, the displacement volume of which is set by means of a displacement element. The rotating group comprises a rotatable cylinder body having a cylinder bore, in which a working piston is reciprocatingly mounted. When the cylinder body rotates and the displacement element is tilted relative to the rotation axis of the cylinder body, the piston moves forward and backward in the corresponding cylinder bore. When the cylinder bore and the working piston arranged in the cylinder bore are observed to rotate a full circle, the piston changes the direction of movement twice. At the inner dead center (IDC), the working piston changes its direction of movement from moving toward the fluid exchange opening of the cylinder bore to moving away from the fluid exchange opening of the cylinder bore. Accordingly, within one rotation, the inner dead center is the position of the working piston closest to the fluid exchange opening of the cylinder bore, that is, the working piston is inserted the farthest into the cylinder bore and the fluid volume in the cylinder bore is the smallest. At the outer dead center (ODC), the movement of the working piston changes from moving away from the fluid exchange opening of the cylinder bore to moving toward the fluid exchange opening of the cylinder bore. Therefore, when considering one complete rotation of the cylinder body, at the outer dead center, the working piston is at the position farthest from the fluid exchange opening of the corresponding cylinder bore, that is, at this position, the working piston is withdrawn farthest from the cylinder bore and the fluid volume in the cylinder bore is the maximum value allowed by the set inclination angle.

[0007] For example, when the working piston of a hydraulic axial piston pump is at ODC, the pressure in the corresponding cylinder bore changes from low inlet pressure to high outlet pressure, while when the piston is at IDC, the cylinder bore pressure changes from high outlet pressure to low inlet pressure. For a hydraulic motor, the situation is the opposite: at ODC, the pressure of the working piston and the pressure in the corresponding cylinder bore change from high inlet pressure to low outlet pressure, while at IDC, the pressure of the piston and the pressure in the corresponding cylinder bore that accommodates the piston change from low outlet pressure to high inlet pressure.

[0008] Thus, it is known in the art that the adjustable longitudinal position of the inner and outer dead centers of the working piston (i.e. the position as seen along the axis of rotation of the rotating group) depends on the inclination / inclination angle of the displacement element. However, the angular position of the inner and outer dead centers is fixedly set by the rotating group design, i.e. independently of the inclination angle of the displacement element, as long as the orientation and position of the inclination axis of the displacement element do not change.

[0009] The hydraulic axial piston unit according to the present invention further comprises a valve section having a kidney-shaped first pressure port and a kidney-shaped second pressure port. When the cylinder bore overlaps with the first pressure port or the second pressure port, the hydraulic fluid can be conducted to the cylinder bore and discharged from the cylinder bore. Further, according to the present invention, the IDC control port and the ODC control port are located on the valve section, between the corresponding circumferential ends of the kidney-shaped first pressure port and the kidney-shaped second pressure port in the circumferential direction. In other words, the pressure ports and the control ports are alternately arranged in the circumferential direction, such as the ODC control port, the first pressure port, the IDC control port, and the second pressure port.

[0010] The IDC control port and the ODC control port are arranged on the valve section in such a way that the cylinder bore can be fluidly connected to the IDC control port or the ODC control port when the associated working piston is at or near its inner dead center (IDC) or at or near its outer dead center (ODC), respectively. As mentioned above, the circumferential position of the IDC and ODC of the working piston is constant. Therefore, according to the present invention, regardless of the tilt angle, the circumferential position of the IDC control port on the valve section is always at or near the IDC of the working piston, and similarly, the ODC control port on the valve section is always at or near the circumferential position of the ODC of the working piston.

[0011] According to the present invention, the circumferential distance of the IDC control port to the first pressure port and the second pressure port and similarly the circumferential distance of the ODC control port to the first pressure port and the second pressure port are less than the circumferential range of the cylinder bore or its opening toward the valve section. When the cylinder bore leaves the circumferential area where the cylinder bore overlaps with the first pressure port or the second pressure port during the rotational motion of the cylinder body, the hydraulic fluid retained in the cylinder bore can be further compressed due to the continuous motion of the piston. When the piston approaches its inner stop point but has not yet reached its inner stop point, this effect can, for example, occur in a hydraulic pump. Since the hydraulic fluid in the cylinder bore cannot be discharged via the first kidney-shaped pressure port or the second kidney-shaped pressure port, further compressing the hydraulic fluid in the cylinder bore will bring about a pressure shock or pressure peak in the cylinder bore and therefore a pressure shock or pressure peak on the valve section. In addition, in other scenarios and situations, there may be a pressure peak, shock, or uneven distribution of pressure on the valve section, such as a certain cavitation near the ODC. In order to weaken these effects, in the extension of the pressure kidney-shaped portion, a circumferentially oriented pressure elongation groove (also referred to as a "fishtail") is usually provided in the valve section.

[0012] Furthermore, according to the invention, when the cylinder bore stops overlapping with the first pressure port or the second pressure port, the cylinder bore is simultaneously in contact with the IDC control port or with the ODC control port, for example in the case of a hydraulic axial piston pump, overpressure or excess hydraulic fluid can be discharged via the IDC control port, or cavitation can be avoided by an additional hydraulic fluid supply via the ODC control port. In the case of a hydraulic axial piston motor, cavitation may occur at the ODC of the working piston, so that in this case, the cavitation effect can be avoided or at least reduced by the hydraulic fluid supply via the ODC control port. Therefore, according to the invention, pressure peaks and unfavorable pressure distribution on the valve section are avoided, and the aforementioned elongated groove (fishtail) is avoided.

[0013] According to the present invention, a first bypass line and a second bypass line are provided, each of which connects one of the control ports (i.e., the IDC control port or the ODC control port) to one of the first pressure port or the second pressure port or to a pressure compensation chamber. An adjustable orifice is arranged in the first bypass line, which is capable of continuously and variably opening and closing the first bypass line so as to enable an adjustable fluid flow connection between the connected pressure port and the cylinder bore passing through via the first bypass line and the allocated control port. The second bypass line is connected to the corresponding other control port. The orifice in the first bypass line can be provided as an additional part, for example in the form of a flow valve or the like, and an adjustable flow opening is particularly preferred. However, it is also possible that the non-adjustable orifice is formed integrally with the first bypass line and / or the second bypass line in which these orifices are arranged.

[0014] The opening of at least one orifice and its opening size affect the sum of the static pressures at the displacement element. The pressures at the IDC control port and the ODC control port each generate a force acting on the displacement element via a working piston. The ODC control port and the IDC control port are arranged on the valve section, on the opposite side of the tilt axis of the displacement element, and each has a lateral offset relative to the tilt axis. These offsets can be the same, but not necessarily so. Therefore, the pressures at the ODC control port and the IDC control port each generate a moment group / torque group relative to the tilt axis of the displacement element, wherein the torque at the ODC control port includes an algebraic sign different from the torque at the IDC control port. The torque group generated (including the torque group generated by the pressure port) sets the tilt angle of the displacement element, and thus realizes the corresponding displacement of the displacement element according to the tilt direction. If the pressure level at the ODC control port is adjusted relative to the pressure level at the IDC control port, the torque group generated will change. The torque group generated is also affected by other parameters and forces, which will be explained later.

[0015] By controlling the opening size of at least one variable orifice or the ratio of the opening sizes of more than one orifice in the bypass line, the inclination angle of the displacement element of the hydraulic unit can be adjusted and set. The opening size of the orifice can be controlled, for example, by an electronic control unit. As a result, it is not necessary to inject hydraulic fluid into the cylinder bore passing through in short time intervals (for example, in the range of milliseconds). On the contrary, static pressure is used to control and set the pressure distribution encountered by the cylinder bore when passing through one of the control ports. The inclination angle of the displacement element and the opening of the adjustable orifice do not change regularly at a high frequency. In particular, not every time when the cylinder bore passes through an IDC control port or an ODC control port. Since static pressure is used to influence the pressure distribution along the valve section to control the inclination angle of the displacement element, the frequency required to adjust the opening of the orifice is relatively low.

[0016] The hydraulic axial piston unit according to the invention may comprise a variable displacement volume which is controlled by adjusting the opening size of an adjustable orifice (i.e. the size of its opening). The adjustable orifice is arranged at least in the first bypass line so as to adjust the pressure at one control port relative to the pressure at the other control port. Thus, during the transition of the cylinder bore from one pressure port to the other, the pressure distribution may be modified, so that the torque set acting on the displacement element may be changed / varied.

[0017] The hydraulic axial piston unit according to the invention may alternatively comprise a fixed displacement volume. In such an embodiment of the invention, the displacement volume is set by setting the opening of an adjustable orifice in a first bypass line so as to adjust the pressure at one control port relative to the pressure at the other control port. The fixed displacement volume is maintained throughout the operation of the hydraulic unit. Even if the displacement volume of the hydraulic unit remains constant, the opening of the adjustable orifice can still be adjusted or controlled during the operation of the hydraulic unit. Thus, the pressure distribution in the cylinder bore overlapping with the control port connected to the bypass line with the adjustable orifice can be adjusted. Thus, vibrations of the displacement element as well as pressure peaks, oscillations or cavitations can be reduced or even eliminated. Thus, the noise generated during the operation of the hydraulic unit can be reduced and the operating behavior of the hydraulic unit according to the invention can be improved, so that the life of the hydrostatic unit can be extended.

[0018] According to the invention, a second bypass line connected to the other control port can be connected to the pressure compensation chamber. In such an embodiment, the second bypass line establishes a fluid connection between the other control port and the pressure compensation chamber. The pressure compensation chamber can be adapted to dampen pressure peaks and cavitation in the passing cylinder bore, respectively on the valve section, thereby avoiding pressure oscillations.

[0019] In one embodiment of the present invention, the second bypass line is connected to the first pressure port or the second pressure port so as to establish a fluid flow connection between the connected pressure port and the cylinder bore passing through via one of the control ports. Preferably, the first bypass line having an adjustable orifice connects the IDC control port or the ODC control port to the first pressure port or the second pressure port, and the second bypass line connects the other corresponding control port to the corresponding other pressure port.

[0020] Preferably, according to the present invention, the first bypass line and the second bypass line are each connected to the next pressure port after the connected control port as seen in the rotation direction of the cylinder body. For example, in an open-circuit pump, the control port at the IDC is preferably connected to a pressure port at a low system pressure via an allocated bypass line, and the control port at the ODC is connected to a pressure port at a higher system pressure via an allocated bypass line. Since a closed-circuit pump, as opposed to an open-circuit pump, is also typically operated in a motor-driven mode, the present invention may additionally provide a possible solution for switchably connecting the ODC control port to the corresponding high system pressure port, for example, via a switching valve or a shuttle valve. As known to those skilled in the relevant art, when the hydrostatic unit changes from a pumping mode to a motor-driven mode, the system pressure ports at the valve section are swapped, and vice versa.

[0021] If the hydraulic unit is configured as a hydraulic pump, one bypass line may, for example, connect the ODC control port with a pressure port at a higher system pressure, and another bypass line may connect the IDC control port with a pressure port at a lower system pressure. If the hydraulic unit is operated as a hydraulic motor, the situation may be reversed, and one bypass line may, for example, connect the IDC control port with a high pressure port, wherein another bypass line connects the ODC control port with a low pressure port.

[0022] The connection of the control port to the next upcoming pressure port (seen in the intended rotational direction of the rotating group) helps to avoid setting a "fishtail" in the valve section, as described above, because the next / upcoming pressure is directed back to the control port that is located before the valve section in the rotational direction. As a result, pressure peaks or cavitations as described above can be at least reduced or even avoided, because the circumferential path / distance of the cylinder bore opening from the end of one pressure port to the beginning of the control pressure port with another system pressure is shortened. To this end, it is preferred in the present invention that the circumferential extent of the cylinder bore opening is sized so that the opening intersects the pressure port on its way out and at least partially overlaps with both ports, namely the control port and the next upcoming pressure port. According to the present invention, when the cylinder bore opening overlaps with the control port connected to the next system pressure, the pressure level in the cylinder bore can be adjusted / adjusted / trimmed to reduce the noise and vibration caused by the step in the pressure distribution. Preferably, these small adjustments are done during constant tilt angle operation of the hydrostatic unit, where these small adjustments may not result in a change in the displacement volume, but improve the operating behavior of the hydrostatic unit.

[0023] In one embodiment of the present invention, the opening of the cylinder bore facing the valve section exhibits a kidney-shaped cross section. According to the prior art, the cylinder bore generally comprises a circular opening, the diameter of which is substantially equal to the radial extension of the kidney-shaped pressure port on the valve section. If the opening of the cylinder bore comprises a kidney-shaped cross section and the longer dimension of the kidney-shaped opening is oriented in the circumferential direction, the opening covers a larger area in the circumferential direction than the circular opening. Therefore, considering the requirement that the opening of the cylinder bore should be able to overlap with the departing pressure port and the upcoming control port at the same time, the distance between the control port and its adjacent pressure port can also be increased, thereby improving the robustness of the valve section.

[0024] Further preferably, the circumferential extent of the kidney-shaped opening of the cylinder bore is less than the circumferential distance between adjacent ends of the first kidney-shaped pressure port and the second kidney-shaped pressure port. Otherwise, there will be a rotational position of the cylinder bore where the cylinder bore may short-circuit the first pressure port with the second pressure port.

[0025] According to the present invention, an orifice with an adjustable opening size (hereinafter referred to as "adjustable orifice") can be arranged in each of two or more bypass lines, that is, in the first bypass line and the second bypass line and in the additional bypass line that may exist. Alternatively, a non-adjustable orifice can be arranged in any of the bypass lines if the bypass line does not include an adjustable orifice. Therefore, both the first bypass line and the second bypass line can include an adjustable orifice, or only the first bypass line can include an adjustable orifice. In this case, the other, i.e., the second bypass line, preferably includes a non-adjustable orifice so as to provide a constant hydraulic resistance to the hydraulic flow in the bypass line. Depending on the selected arrangement, the inclination angle of the displacement element can be adjusted or set by affecting the ratio of the opening of the orifice in the first bypass line relative to the opening of the orifice in the second bypass line, or by affecting the ratio of the opening of the adjustable orifice in one bypass line relative to the opening of the non-adjustable orifice in another bypass line. In the case of an adjustable orifice (eg a proportional flow valve), the pressure at the assigned control port can be variably adjusted so that the pressure difference between the two control ports and thus the force and torque set conditions on the valve section can be controllably influenced.

[0026] In one embodiment of the invention, one or two additional parallel bypass lines including adjustable orifices or non-adjustable orifices can establish an additional fluid flow connection in parallel with the fluid flow connection between the pressure port connected by the first bypass line and the control port or between the pressure port connected by the second bypass line and the control port. When two parallel connections are provided between the same pressure port and the same control port, it is allowed to divide the operating range of the adjustable orifice required to operate the hydraulic unit into two parts. The design of the orifices in the parallel bypass lines can be selected accordingly. For example, a non-adjustable orifice providing a small constant pressure drop can be combined with an adjustable orifice providing an adjustable pressure drop in addition to the constant pressure drop. This makes the design of the orifices arranged in the bypass line cost-effective. Compared with a single orifice with a wide operating range, each operating range of the parallel orifices can be reduced, thereby maintaining the total operating range of the orifice arrangement, which is the sum of the control ranges of the two orifices.

[0027] According to the present invention, the present disclosure covers a variety of different arrangements of bypass lines. For example, the two control ports can be connected to the same pressure port via a first bypass line and a second bypass line. In addition, each control port can be connected to another pressure port via a third bypass line and a fourth bypass line, wherein an adjustable orifice can be arranged in each of the four bypass lines.

[0028] As known in the art, the displacement element can be biased to an initial position by means of an elastic force, in which the displacement volume of the rotating group is maximum, minimum or zero. The displacement element can also be biased to an initial position by means of an offset of the tilting axis of the displacement element relative to the rotation axis of the cylinder body. Therefore, the pistons on both sides of the tilting axis include different lever arms relative to the tilting axis. Even if a small pressure (e.g., charging pressure) is provided to the pressure port / cylinder bore and the pressure on all pistons is the same, due to the different lever arms, the piston will generate a torque group on the valve section relative to the tilting axis. Therefore, once pressure is supplied to the cylinder bore, the displacement element begins to tilt, and there is a pressure difference at the first pressure port and the second pressure port, which can be conducted to the IDC control port and the ODC control port via the first bypass line and the second bypass line.

[0029] According to the present invention, the hydraulic axial piston unit may further include a return mechanism that is capable of generating a restoring force on the displacement element when the displacement element pivots away from its initial position. The restoring force may generate a torque that is directed to be opposite to the resultant torque generated by the pressure at the IDC control port and the ODC control port. For example, the return mechanism may include an elastic component that provides a restoring force / torque that increases when the tilt angle of the displacement element increases. For each tilt angle of the displacement element, the moment balance between the pressure at the IDC control port and the ODC control port and the restoring force of the return mechanism determines the movement of the displacement element, thereby determining the tilt angle of the displacement element. By arranging the control port on the valve section circumferentially located between the pressure ports, the moment group on the valve section can be affected / changed so that the restoring moment from the return mechanism can be transversely displaced and the displacement element can increase its stroke, that is, its tilt angle increases. Therefore, for each tilt angle, the balance / equilibrium of the force / torque can be adjusted, and the displacement volume of the hydrostatic unit can be controlled. Thus, when increasing or decreasing the pressure difference at the control port, the stroke of the displacement element can be increased or decreased simply by adjusting the opening size of at least one variable orifice arranged in one or both bypass lines connected to the control port with the upcoming pressure level in the rotational direction.

[0030] The valve section may be formed integrally with the housing of the hydraulic axial piston unit, or an end cap of the hydraulic axial piston unit, or a housing cover or another component within the housing of the hydraulic unit. Alternatively, the valve section may be provided as a separate part.

[0031] The first pressure port at the valve section may include more than one kidney-shaped pressure port opening, and / or the second pressure port of the valve section may include more than one kidney-shaped pressure port opening. This may improve the mechanical stability of the valve section in the region of the first pressure port and / or the second pressure port while minimizing negative impacts on the flow of hydraulic fluid to the cylinder bore overlapping the first pressure port and / or the second pressure port.

[0032] According to the present invention, the opening of orifice can be mechanically controlled or controlled by an electronic control unit (ECU). The electronic control unit can include a microcontroller and can be connected to at least one sensor selected from the sensor group including the following items: an inclination angle sensor, an axle position sensor, a pressure sensor, a flow sensor, a rotation speed sensor, a temperature sensor, a direction sensor, a torque sensor, an acceleration sensor or any other sensor that can monitor at least one operating parameter of a hydraulic unit. The control unit can control the opening of the orifice based on the measured value provided by the at least one sensor. For this purpose, the control unit can perform calculations (e.g., calculating an error signal) and can adjust the opening of the orifice so that, for example, the error signal is reduced by applying a PID control rule. The opening of the orifice can be calculated based on the circumferential position of the first kidney-shaped pressure port and the second kidney-shaped pressure port, the circumferential position of the IDC control port and the ODC control port, the diameter of the orifice, the restoring force of the return mechanism, the angular velocity of the shaft of the hydraulic unit, the pressure at the first kidney-shaped pressure port and the second kidney-shaped pressure port, operating temperature and / or other parameters.

[0033] According to the present invention, the adjustable orifice can be a rotary slide valve or a linear slide valve housed in a valve chamber. The rotary valve core or linear valve core of the valve can include a recess or opening overlapping with a passage (i.e., a valve port) in the valve chamber, wherein the size of the overlap can be continuously adjusted by rotating the rotary valve core or by moving the linear valve core longitudinally. The orifice can be a linearly operated valve / orifice, a rotary valve / orifice, or a flow valve. Flow valves are generally less expensive than linear or rotary operated orifices. Here, a person skilled in the art will find a large number of solutions on how to provide an adjustable orifice (i.e., an orifice with an adjustable opening size).

[0034] As described above, the hydraulic axial piston unit according to the present invention may include two adjustable orifices, one adjustable orifice is arranged in the first bypass line, and the other adjustable orifice is arranged in the second bypass line. The openings of the two adjustable orifices can be adjusted by means of a shared mechanism, which can be mechanical, electromechanical, hydraulic or pneumatic. For example, a common (i.e. shared) valve core can be provided, which is used as a shared valve core for the adjustable orifice in the first bypass line and the adjustable orifice in the second bypass line. Such a single valve core can, for example, include a recess for adjusting the fluid flow in the first bypass line, and another recess for adjusting the fluid flow in the second bypass line.

[0035] According to the invention, the shape of the control port is associated with achieving good controllability of the tilt angle of the displacement element. A circular / annular shaped control port is easy to manufacture and therefore represents a low-cost solution. However, the shape of the control port can also be adapted to the shape of the opening of the cylinder bore. Basically, the control port can include any desired shape. For example, the control port can show an elongated shape in the circumferential direction of the valve section, and its radial extension matches the radial extension of the cylinder bore. This design increases the overlap between the opening of the cylinder bore and the control port. The control port can also include a kidney shape, wherein the longer side of the kidney-shaped portion preferably extends in the circumferential direction. The control port can also include an elliptical shape, a triangular shape or any other shape, wherein even the manufacturing direction must not coincide with the axis of rotation of the valve section.

[0036] Not only the shape of the IDC control ports and the ODC control ports is considered relevant for setting and adjusting the displacement of the hydraulic axial piston unit, but also the position of the IDC control ports and the ODC control ports on the valve section. According to the present invention, the IDC control ports and / or the ODC control ports can be located on the valve section, angularly offset in the circumferential direction from the rotational position, in which the working piston is at its inner dead center and / or outer dead center, respectively. This arrangement is generally referred to as "indexing" and is particularly preferred for hydraulic pumps. The specific position of the IDC control ports and / or the ODC control ports is selected based on the type of use of the hydraulic unit and the requirements derived therefrom. In an exemplary embodiment, the IDC control ports and / or the ODC control ports can be located slightly clockwise behind the actual rotational / circumferential position of the IDC or ODC.

[0037] Thus, continuing the example of a hydraulic pump, the pressure at the ODC control port affects the movement of the working piston when the piston enters the cylinder bore (i.e., at the beginning of the pressure phase), and the pressure at the IDC control port affects the movement of the piston when the piston is withdrawn from the cylinder bore (i.e., at the beginning of the suction phase). In an exemplary case, the ODC port can be connected to a high-pressure line, wherein the IDC port can be connected to a low-pressure line. Increasing the opening of the orifice in the bypass line connected to the ODC control port will produce a higher pressure in the pressure chamber enclosed by the working piston in the cylinder bore. Since this higher pressure must be supported by the displacement element, the inclination angle of the displacement element increases. Increasing the opening size of the orifice arranged in the bypass line connected to the IDC control port will reduce the hydraulic resistance that must be overcome when the hydraulic fluid is sucked into the above-mentioned pressure chamber when passing through the IDC control port. The reaction force generated acting on the displacement element in the inner dead center (IDC) area is reduced and the inclination angle of the displacement element is increased.

[0038] In another embodiment of the invention, the IDC control port and / or the ODC control port can be located exactly on the valve section at that rotational position in which the working piston is at its inner dead center (IDC) and / or its outer dead center (ODC), respectively. This arrangement can be preferred, for example, for hydraulic units, especially hydraulic motors, which operate with a changing fluid flow direction but whose displacement element can be tilted in only one direction. Since the algebraic sign of the tilting angle remains unchanged, the rotational position of the inner and outer dead centers remains unchanged even if the fluid flow direction changes. However, when the direction of fluid flow is reversed and the tilting direction remains unchanged, the rotational direction of the hydraulic motor is reversed. If the IDC pressure port and the ODC pressure port on the valve section do not coincide with the IDC or ODC, but show an angular offset from the IDC and ODC positions, the behavior of the hydraulic unit will be different depending on the rotational direction of the cylinder, because - considering only one of the control ports by way of example - the control port will be in one rotational direction before the corresponding dead center position and in another rotational direction after the corresponding dead center position.

[0039] In another embodiment of the invention, the first ODC control port can be located on the valve section, angularly offset from the rotational position at the valve section, in which the working piston is at its outer dead center, and the second ODC control port can be located on the valve section, so that the first and second ODC control ports are located on both sides of the rotational position on the valve section corresponding to the outer dead center position of the working piston. This arrangement increases the options for controlling the tilt angle of the displacement element of the hydraulic unit, because the pressure in the cylinder bore can be influenced before reaching the outer dead center position and after leaving the outer dead center position (i.e. when the working piston moves outward) and after leaving the inner dead center (i.e. when the working piston moves inward). This increases the angular range over which the displacement control according to the invention can affect the tilt angle.

[0040] Similar to the above embodiment, according to the present invention, the second IDC control port can be located on the valve section. If the first IDC control port is located on the valve section, angularly offset from the rotational position at the valve plate, in which the working piston is at its inner dead center, the first and second IDC control ports can be located on either side of the rotational position on the valve plate corresponding to the inner dead center position of the working piston. This can be implemented as an additional feature or an alternative to providing the second ODC control port on the valve section.

[0041] Providing a second IDC control port and a second ODC control port can be particularly useful when the direction of the fluid flow delivered / supplied by another hydrostatic unit can be reversed. In this case, the direction of rotation of the cylinder block and therefore the direction in which the cylinder bore moves from ODC to IDC is interchanged. When the four control ports are symmetrically arranged on the valve plate / valve section, the control feasibility remains unchanged regardless of the fluid flow direction.

[0042] According to the invention, the second ODC control port and / or the second IDC control port can be connected to the fourth bypass line and / or the third bypass line, respectively, wherein at least one of the third bypass line and the fourth bypass line comprises an adjustable orifice capable of continuously and variably opening and closing the associated bypass line. Providing an additional orifice with an adjustable opening in a separate additional bypass line increases the feasibility of adjusting the pressure ratio at the control port and improves the feasibility of influencing / controlling / adapting the hydraulic pressure distribution acting on the working piston during one rotation of the cylinder, thereby further enhancing the controllability of the hydraulic unit.

[0043] The hydraulic axial piston unit according to the present invention can be operated in an open hydraulic circuit or in a closed hydraulic circuit. The hydraulic unit can be operated as a hydraulic motor or a hydraulic pump. The person skilled in the art is aware of the fact that a hydraulic pump arranged in an open hydraulic circuit usually includes only one direction of rotation of the cylinder and therefore shows only one delivery direction. A hydraulic pump arranged in a closed hydraulic circuit typically includes only one direction of rotation, wherein the displacement element of the hydraulic pump can be tilted bidirectionally so that the hydraulic fluid can be delivered through the closed hydraulic circuit in two directions / bidirectionally. In many embodiments, the cylinder of the hydraulic motor in the closed hydraulic circuit can be rotated in two directions depending on which of the pressure ports of the hydraulic motor is connected to a higher system pressure and which is connected to a lower system pressure. In most applications according to the prior art, the tilt angle of the hydraulic motor in the closed circuit can only adjust the stroke / be adjusted in one direction.

[0044] When the hydraulic unit according to the invention is operated in a closed hydraulic circuit and the direction of fluid flow is reversed, the pressure at the first and second pressure ports and therefore also in the first and second bypass lines will change. However, depending on the type of use, it may be preferred that the same type of system pressure is always present in the first bypass line and at the connected control port (e.g. a high system pressure is always present at the IDC control port) and also in the second bypass line and at the connected control port (e.g. a low system pressure is always present at the ODC control port). This is particularly preferred for hydraulic motors whose displacement elements are tiltable in only one direction and whose outer and inner dead centers are not interchanged during operation of the hydraulic unit, neither in one nor in the other direction of rotation.

[0045] In this case, the hydraulic unit may include a component that can always conduct one pressure level to the IDC control port and another pressure level to the ODC control port regardless of the direction of rotation of the hydraulic unit. This function can be achieved, for example, by a shuttle valve having two inlets and one outlet, wherein the inlet of the shuttle valve is in fluid connection with the first pressure port and the second pressure port, and the outlet is in fluid connection with the IDC control port, the ODC control port or the control valve (its function is explained later) or the like. For example, for a hydraulic motor, the outlet of the shuttle valve can be connected to the IDC control port. According to this arrangement, the shuttle valve can conduct a higher system pressure from the first pressure port or the second pressure port to the IDC control port or the ODC control port or the control valve. For example, for a hydraulic motor, the IDC control port is connected to a higher pressure (e.g., inlet pressure), and the ODC control port can be connected to a lower pressure (e.g., outlet pressure) or a hydraulic reservoir in this case. Therefore, the unidirectional tilt angle of the displacement element can be controlled independently of the direction of rotation of the hydraulic unit (here exemplarily a hydraulic motor). According to the invention, the opening of an orifice in the second bypass line, which can be connected, for example, to an ODC control port, can be adjusted in order to influence the tilt angle of the hydraulic unit. Additionally or alternatively, the opening of an orifice in the first bypass line, which is connected to an IDC control port, can be adjusted so that the pressure level at the IDC control port can be controlled. This influences the pressure distribution acting on the working piston during one rotation around the cylinder axis, at least until the working piston reaches another control port.

[0046] If the displacement element of the hydraulic unit can be tilted in two directions, the IDC and ODC can be interchanged according to the tilting direction of the displacement element. According to the present invention, a control valve or similar device capable of directing high system pressure to the ODC control port and low pressure to the IDC control port (and vice versa) can be provided. The control valve may include a first inlet connected to the outlet of the shuttle valve and a second inlet connected to the hydraulic reservoir. In this way, the first inlet of the control valve is connected to a high pressure level and the second inlet is connected to a lower pressure level, wherein the first outlet of the control valve can be connected to the IDC control port or the ODC control port, and the second outlet can be connected to the corresponding other control port. The control valve can selectively connect the first inlet to the first outlet and the second inlet to the second outlet, or connect the first inlet to the second outlet and the second inlet to the first outlet, or short-circuit the first outlet to the second outlet. Therefore, regardless of the actual rotational position of the ODC and the IDC, a higher pressure can always be conducted to the ODC control port (for the hydraulic pump) or the IDC control port (for the hydraulic motor), and a lower pressure can always be conducted to the corresponding other control port.

[0047] In order to facilitate the starting of the hydraulic unit according to the invention, the hydraulic unit may comprise an (additional) charging pump capable of providing an initial starting pressure, which initial starting pressure may be conducted to one of the control ports via one of the bypass lines, for example by means of a valve arrangement. For such a start, the charging pressure provided by the charging pump is sufficient to initially tilt the displacement element towards a starting position in which a small pressure difference is generated between the first pressure port and the second pressure port. Via the bypass line, the pressure difference is conducted to the IDC control port and the ODC control port via the bypass line and may be used to initially tilt the displacement element at approximately a small angle. Thereby, a flow of hydraulic fluid from the charging pump to one of the control ports is no longer necessary, in particular when a high system pressure at one of the pressure ports exceeds the charging pressure, the pressure difference generated by the started hydraulic unit is sufficient to control the tilting angle by means of at least one variable adjustment orifice.

[0048] According to the invention, at least one of the adjustable orifices may provide a pressure and / or displacement feedback signal. Displacement or pressure feedback means that the hydraulic displacement unit includes a feedback loop so that the pressure level in the cylinder bore or at the control port or the tilt angle of the displacement element is transmitted to the adjustable orifice mechanically, electrically or hydraulically, or from the adjustable orifice to the control unit of the hydraulic system. According to the invention, a mechanical feedback or an electronic feedback signal may be provided by the orifice to the electronic control unit. Additionally or alternatively, the opening of at least one adjustable orifice may be affected by the magnitude of the feedback signal. For example, when the tilt angle of the displacement element increases, and the increased tilt angle is sent directly to the adjustable orifice as a feedback signal or to the electronic control unit that controls the opening of the adjustable orifice as a feedback signal, the opening of the adjustable orifice may be reduced so as to limit or stop the movement of the displacement element. Thus, the pressure in the cylinder bore and the tilt angle of the displacement element may be controlled by means of the adjustable orifice in the bypass line. Thus, at least in some cases, the servo piston / servo unit according to the prior art may be omitted.

[0049] According to the invention, the control port can pass through the valve section perpendicularly to the front surface of the valve section. However, the control port can also pass through in a direction oblique to the rotation axis of the valve section or the hydraulic axial piston unit, respectively. This means that the orientation and position of the hydraulic bypass line in which the adjustable or non-adjustable orifice is arranged can be selected according to the space constraints imposed by the design of the components of the hydrostatic unit around the rotating group, for example, the control port can be drilled and the drilling direction can be oriented perpendicularly to the front surface of the valve section or can be oriented at an angle to the front surface that is different from being perpendicular to the plane of the valve section.

[0050] In one embodiment, the radial position of the control port may be offset from the pitch diameter defined by the circumferential extent of the first and second pressure ports. In other words, the radial distance of the control port to the rotation axis of the hydraulic unit must not be equal to the pitch radius of the pressure port.

[0051] According to the present invention, a method for controlling the displacement volume of a hydraulic rotating group driven by a drive shaft or a drive shaft is further provided. The hydraulic rotating group includes a displacement element, which can be tilted to adjust the displacement volume of the rotating group. The rotating group includes: a rotatable cylinder body, the rotatable cylinder body has a cylinder bore, and a working piston is reciprocatingly mounted in the cylinder bore; and a valve section, the valve section has a kidney-shaped first pressure port and a kidney-shaped second pressure port. The IDC control port and the ODC control port are located on the valve section, between the corresponding circumferential ends of the first pressure port and the second pressure port in the circumferential direction. When the associated working piston is at or near its inner dead center (IDC) or at or near its outer dead center (ODC), the cylinder bore can be fluidly connected to the IDC control port or the ODC control port. The circumferential distance from the IDC control port to the first pressure port and the second pressure port and the circumferential distance from the ODC control port to the first pressure port and the second pressure port are less than the circumferential range of the cylinder bore.

[0052] The method for controlling the displacement volume of a hydraulic rotating group comprises the following steps:

[0053] - exhausting hydraulic fluid from or supplying hydraulic fluid to a passing cylinder bore via an IDC control port by means of a first bypass line having a first orifice,

[0054] - supplying hydraulic fluid to or exhausting hydraulic fluid from a passing cylinder bore via the ODC control port by means of a second bypass line having a second orifice,

[0055] - Adjusting the size of the opening of the first orifice or the second orifice, or both, in order to control the pressure level in the cylinder bore through the control port, thereby setting or adjusting the tilt angle of the displacement element and thus the displacement volume of the hydraulic rotary group. In some cases, in particular when the control ports are arranged symmetrically on the valve section with respect to the tilt axis, a supplementary (additional) amount of hydraulic fluid is discharged from another control port that is not supplied with hydraulic fluid. This is due to the incompressibility of the hydraulic fluid and the stiffness of the displacement element, in order to allow the displacement element to move tiltingly around the tilt axis.

[0056] When hydraulic fluid under high pressure is supplied to the passing cylinder bore at the ODC control port (for hydraulic pumps) or at the IDC control port (for hydraulic motors), the pressure in the cylinder bore can increase. Due to the higher pressure, the force on the working piston sealing the cylinder bore increases. This increased force is transmitted by the piston to the displacement element and is supported there. According to the principle of "action force = reaction force", the supporting force affects the balance of forces and torques present at the displacement element. When high pressure is supplied to the passing cylinder bore at the ODC control port, an increased tilting force acting on the displacement element is generated. If the tilting moment (group) at the displacement element is higher than the reset force / torque that forces the displacement element to return to its initial position or neutral position, the tilt angle of the displacement element increases.

[0057] In the exemplary case of a hydraulic pump, increasing the opening of the adjustable orifice in the bypass line connecting the pressure port with a higher system pressure to the ODC control port results in a higher pressure at the ODC control port and in the cylinder bore passing through, resulting in a greater tilt angle. In short, opening the adjustable orifice in the bypass line increases the tilt angle of the displacement element. Conversely, closing the adjustable orifice in the bypass line or reducing the size of the adjustable orifice in the bypass line results in a decrease in the tilt angle of the displacement element as the force on the working piston passing through the ODC control port decreases.

[0058] At the IDC control port, a similar / similar situation exists at low system pressure levels. Continuing with the case of the pump, the increased pressure in the cylinder bore through the IDC control port causes a neutralization / destroke torque that can reduce the tilt angle of the displacement element due to the transmission of the above-mentioned force. Therefore, the higher the pressure in the cylinder bore through the IDC control port, the greater the neutralization / destroke torque generated, thereby destroke / tilting the displacement element toward zero displacement. In contrast to the situation when the pressure in the cylinder bore through the IDC is reduced, the tilt angle of the displacement element can be increased. The pressure at the IDC control port can be affected by an adjustable orifice arranged in the connected bypass line. Preferably for a hydraulic pump, the bypass line connected to the IDC control port is connected to a low (system) pressure level. An orifice with an adjustable opening size can be arranged in the bypass line. Therefore, the flow resistance or back pressure in the bypass line connecting the IDC control port to the low-pressure port can be adjusted. Therefore, increasing the opening size of the variable orifice in the bypass line can increase the tilt angle of the displacement element.

[0059] According to the invention, the supply or discharge of hydraulic fluid is done at the pressure level of the subsequent / next upcoming pressure port (seen in the direction of rotation of the cylinder or rotating group). For example, in a hydraulic pump, the pressure level at the IDC changes from a high system pressure to a low system pressure, so that according to the invention, an IDC control port located between two pressure kidneys at or near the IDC is preferably connected to the low system pressure kidney via a bypass line. Optionally, an adjustable orifice is arranged in the bypass line, in particular for hydraulic pumps that can be operated at positive and negative tilt angles, because in this case, by tilting the displacement element beyond zero, the IDC changes with the ODC and vice versa, so that the control port can be both an IDC control port and an ODC control port.

[0060] In summary, according to the present invention, controlling the pressure in the cylinder bore through the control port at the ODC and the pressure in the cylinder bore through the control port at the IDC can make an additional servo system for adjusting the tilt angle of the displacement element redundant, because the tilt angle of the displacement element of the hydraulic unit can be adjusted by means of controlled opening or closing of a variable orifice provided in a first bypass line and / or a second bypass line connected to the ODC control port and the IDC control port, so as to change the pressure level in the cylinder bore through the control port in a controlled manner.

[0061] The invention is also applicable to hydraulic units equipped with a servo system for supporting the regulation of the displacement volume and / or for adjusting and / or balancing the operating behavior of the hydraulic unit when there is a pressure step during a change in pressure in the cylinder bore from a high system pressure to a low system pressure and vice versa. The pressure transition can be smoothed by the arrangement of a control port on the valve section, by which a preferred variable regulating pressure can be supplied via a bypass line connected to the two system pressure ports. For this purpose, preferably at least one adjustable orifice is arranged in one of the two bypass lines. It is therefore further preferred that two or more bypass lines are arranged in such a way that for each direction of rotation, the next upcoming system pressure level can be directed back to a control port on the valve section that is located in the direction of rotation before the pressure port connected to the bypass line.

[0062] The method according to the invention may further comprise the step of processing the command of the control unit or the operator by means of an electronic control unit (ECU). The electronic control unit may comprise a microcontroller for adjusting the size of the opening of the orifice in the first bypass line and / or the second bypass line in order to adapt / control the pressure in the cylinder bore and thereby control the displacement volume of the hydraulic axial piston unit. According to the invention, any of the adjustable orifices may be controlled by the electronic control unit, regardless of whether the bypass line in which the adjustable orifice is arranged connects one of the control ports to one of the pressure ports, to a hydraulic reservoir, or to a pressure compensation chamber or a closed cavity.

[0063] The method according to the invention may further comprise the step of sensing at least one operating parameter of the hydraulic axial piston unit by means of a sensor. The sensor may be selected from the group of sensors comprising: an inclination angle sensor, a shaft position sensor, a pressure sensor, a flow sensor, a rotation speed sensor, a temperature sensor, a direction sensor, a torque sensor, an acceleration sensor or any other sensor capable of monitoring at least one operating parameter of the hydraulic unit.

[0064] According to the invention, the method may further comprise the steps of continuously monitoring the operating parameters of the hydraulic axial piston unit in order to smooth the pressure transition between the kidney-shaped first pressure port and the kidney-shaped second pressure port and vice versa, and / or for controlling the pressure level in the cylinder bore, thereby controlling the pressure distribution in the cylinder bore during its operation around the axis of rotation of the hydraulic axial piston unit, i.e. the pressure course based on the rotation angle of the cylinder body. The method according to the invention further enables the pressure level at the control port to be controlled by opening and closing the opening size of the adjustable orifice, thereby adjusting the inclination angle of the displacement element. For this purpose, the measured operating parameters of the hydraulic unit may be processed by an electronic control unit.

[0065] With the aid of the accompanying drawings, a preferred embodiment of the hydraulic axial piston unit according to the invention is explained in more detail in order to improve the understanding of the basic concept of the invention. This embodiment does not limit the scope of the inventive concept, but only represents possible design alternatives, which can be modified within the knowledge of a person skilled in the relevant art without departing from the scope of the invention. Therefore, all these modifications and changes are covered by the claimed invention. In the drawings:

[0066] Figure 1 shows the design of a first embodiment of a hydraulic axial piston unit according to the invention;

[0067] Figure 2 A first embodiment of a hydraulic axial piston unit according to the invention is schematically shown;

[0068] Figure 3Schematically shows a valve section of a first embodiment of a hydraulic axial piston unit according to the invention;

[0069] Figure 4 Schematically shows a valve section of a second embodiment of a hydraulic axial piston unit according to the invention;

[0070] Figure 5 Schematically shows a valve section of a third embodiment of a hydraulic axial piston unit according to the invention;

[0071] Figure 6 Schematically shows a valve section of a fourth embodiment of a hydraulic axial piston unit according to the invention;

[0072] Figure 7 Schematically shows a valve section of a fifth embodiment of a hydraulic axial piston unit according to the invention;

[0073] Figure 8 Schematically shows a valve section of a sixth embodiment of a hydraulic axial piston unit according to the invention;

[0074] Fig. 9 Schematically shows a valve section of a seventh embodiment of a hydraulic axial piston unit according to the invention;

[0075] Fig.10a Schematically shows a hydraulic circuit of an eighth embodiment of a hydraulic axial piston unit according to the invention;

[0076] Fig.10b Schematically shows a hydraulic circuit of a ninth embodiment of a hydraulic axial piston unit according to the invention;

[0077] Fig.11 Schematically shows a valve section of an eighth embodiment of a hydraulic axial piston unit according to the invention;

[0078] Fig.12 Schematically shows a valve section of a tenth embodiment of a hydraulic axial piston unit according to the invention;

[0079] Fig.13 A first embodiment of an adjustable orifice according to the present invention is shown in an open position;

[0080] Fig.14 A first embodiment of an adjustable orifice according to the invention is shown in a closed position;

[0081] Fig.15 A second embodiment of an adjustable orifice according to the invention is shown in an open position;

[0082] Fig.16A second embodiment of an adjustable orifice according to the invention is shown in a closed position.

[0083] In the drawings, the same reference numerals are used for the same components of different embodiments throughout the specification to improve readability.

[0084] Figure 1 An exemplary design of a first embodiment of a hydraulic axial piston unit according to the invention is shown. The hydraulic pump comprises a displacement element 4 which can be tilted relative to a tilting axis 9 in order to adjust the displacement volume of a rotating group 2 of the hydraulic unit. The rotating group 2 comprises a cylinder block 3 rotatable about a rotation axis 13, the cylinder block having a cylinder bore 5, in which a working piston 6 is mounted reciprocatingly between an outer dead center (ODC) and an inner dead center (IDC). The working piston 6 abuts the displacement element 4 via a sliding shoe. A valve section 20 is located on the other side of the cylinder block 3, the valve section comprising a first pressure port 21 and a second pressure port 22, which are used as interfaces for connecting the hydraulic unit to an open hydraulic circuit or a closed hydraulic circuit. The valve section 20 further comprises an IDC control port 23 arranged near the rotational position of the IDC of the working piston 6 of the hydraulic unit and an ODC control port 24 arranged near the rotational position of the ODC of the working piston 6 of the hydraulic unit.

[0085] Figure 2 The hydraulic scheme of a first embodiment of a hydraulic axial piston unit (here exemplarily a hydraulic axial piston pump) is depicted. The ODC control port 24 is fluidly connected to the second pressure port 22 via a first bypass line 27. The IDC control port 23 is fluidly connected to the hydraulic reservoir 100 via a second bypass line 28.

[0086] In accordance with Figure 2 In an embodiment of, the hydraulic unit operates, for example, in an open hydraulic circuit. The first pressure port 21 is connected to a low system pressure, for example to a hydraulic reservoir 100. The second pressure port 22 is connected to a high-pressure line. Therefore, a high system pressure is present at the ODC control port 24, while a low system pressure is present at the IDC control port 23. An orifice 29 whose opening size can be variably adjusted is arranged in the first bypass line 27 for adjusting the fluid flow in the bypass line 27 and thereby adjusting the pressure level at the ODC control port 24. Since the first bypass line 27 is connected to the second pressure port 22, i.e. to the outlet of the hydraulic pump and therefore to the high-pressure side, opening the adjustable orifice 29 increases the flow and pressure at the ODC control port 24. The second bypass line 28 includes an orifice 31, the opening size of which is not adjustable in this embodiment. Therefore, in Figure 2 In the embodiment shown, the flow resistance in the second bypass line 28 is not adjustable.

[0087] The hydraulic unit further comprises a return mechanism 10, which forces the displacement element 4 of the hydraulic unit to return to the initial position when the displacement element 4 is tilted away from its initial position. The initial position of the displacement element 4 can be at an inclination angle of zero degrees, for example. However, for a hydraulic unit operating as a hydraulic pump or hydraulic motor in an open hydraulic circuit, it is particularly preferred that the displacement element 4 can be initially tilted to a non-zero inclination angle. For this purpose, the rotation axis 12 of the displacement element 4, respectively the rotation axis 12 of the sliding surface of the shoe on the displacement element 4, can include an offset relative to the rotation axis 13 of the drive shaft or cylinder 3 in the direction of the tilting axis 9 of the displacement element 4 (see Figure 1 ). Alternatively, the displacement element 4 of the hydraulic unit may be biased to a non-zero displacement angle by means of a resilient force, for example provided by a spring.

[0088] Figure 3 The valve section 20 of a first embodiment of a hydraulic axial piston unit according to the present invention is schematically shown. The valve section 20 comprises a first pressure port 21 and a second pressure port 22. Both pressure ports are kidney-shaped. As described above, the first pressure port 21 (in accordance with Figure 2 and Figure 3 The first embodiment of the present invention is shown in Figure 1. ...

[0089] The working piston 6 of the hydraulic unit (see Figure 1 ) abuts against the displacement element 4 via a sliding shoe. On the other side, the working piston 6 is sealed against a pressure chamber, which is formed by the combination of the cylinder bore 5 and the valve section 20. When the cylinder body 3 rotates and the displacement element 4 includes a non-zero inclination angle, the working piston 6 reciprocates in the cylinder bore 5, and when the piston 6 moves away from the valve section 20, the volume of the pressure chamber in the cylinder bore 5 increases. When the piston 6 moves toward the valve section 20, the volume of the pressure chamber decreases. At the outer dead center (ODC), the volume of the pressure chamber is the largest because the distance between the piston 6 and the valve section 20 is the largest. At the inner dead center (IDC), the distance between the piston 6 and the valve section 20 and therefore the volume of the pressure chamber is the smallest.

[0090] In the first embodiment, considering the (open circuit) hydraulic pump, at the position of the ODC, the working piston 6 extends from the pressure chamber and the suction phase, in which the hydraulic fluid enters the pressure chamber, changes to the pressure phase, in which the hydraulic fluid is pressed out of the pressure chamber. At the IDC, the phases are reversed, i.e. the working piston 6 changes from the pressure phase to the suction phase.

[0091] According to the present invention, the ODC control port 24 is arranged at or near the rotational position of the ODC. Similarly, the IDC control port 23 is arranged at or near the rotational position of the IDC. In the first embodiment of the present invention, both the control ports 23 and 24 are arranged in a position where the rotational position of the working piston 6 at the ODC and IDC (dead center plane 17) and the rotational position of the ODC control port 24 and the IDC control port 23 have an offset angle γ respectively. O / γ i The positions of the ODC control port 24 and the IDC control port 23 are crucial to the function of the present invention, especially the offset angle γ O / γ i According to the algebraic symbol and the angle γ O / γ i The size of can affect the time points at which the control ports 23, 24 start and end overlapping with the cylinder bore 5 passed. When the pressure in the cylinder bore 5 passing through one of the control ports 23, 24 / overlapping with one of the control ports can be changed / adjusted in a controlled manner, modifying the positions of the ODC and IDC control ports 23, 24 affects the timing and time span. According to the present invention, for example, for a hydraulic pump, the IDC control port 23 and the ODC control port 24 can be preferably arranged behind the corresponding IDC rotational position or the ODC rotational position (as seen from the rotational direction of the pump). According to Figure 3 , the IDC control port 23 is connected to the hydraulic reservoir 100 and the first pressure port 21 (here, the low system pressure side (inlet side or suction side) of the hydraulic pump) via a second bypass line 28 having a non-adjustable orifice 31. The ODC control port 24 is connected to the second pressure port 22 (here, the high system pressure side (outlet side or pressure side) of the hydraulic pump) via a first bypass line 27 including an adjustable orifice 29.

[0092] The opening of the cylinder bore 5 facing the valve section 20 (shown in dashed lines in the figures) comprises a kidney shape, for example, whose circumferential extension τ is smaller in most applications than the circumferential distance between the first pressure port 21 and the second pressure port 22. The circumferential distance between the first pressure port 21 and the second pressure port 22 is the circumferential distance σ between the first pressure port 21 and the location of the ODC / IDC O / σ i and the circumferential distance β between the second pressure port 22 and the location of the ODC / IDC O / βi If the extension τ is greater than σ O +β O The sum or σ i +β i The first pressure port 21 can be hydraulically short-circuited to the second pressure port 22 via the cylinder bore 5 .

[0093] The inclination angle of the displacement element 4 can be adjusted by controlling the opening size of the adjustable orifice 29. When the opening of the orifice 29 increases, the high pressure is conducted to the ODC control port 24. Therefore, the pressure in the cylinder bore 5 passing through the ODC control port 24 can be increased. The increase in the cylinder bore pressure causes a greater force on the working piston 6 arranged in the passing cylinder bore 5. Since this force is supported / abutted by the displacement element 4 and acts on the displacement element 4 via the sliding shoe, respectively, the inclination angle of the displacement element 4 can be increased by increasing the pressure in the cylinder bore 5 passing through the ODC control port. If the opening size of the variable orifice 29 in the first bypass line 27 is reduced, the pressure on the working piston 6 is reduced and the force of the working piston 6 acting on the displacement element 4 is also reduced. Therefore, the return mechanism 10 (see Figure 2 ) can apply a return / neutralizing force that is higher than the stroke-increasing force of the displacement element 4 and tilt / destroke the displacement element 4 toward its initial position until the return force and the pressure exerted by the working piston 6 on the displacement element 4 are balanced again. In summary, adjusting the opening size of the variable / adjustable orifice 29 affects the balance of forces / torques on the displacement element 4 relative to the tilt axis, which is established between the stroke-increasing pressure of the displacement element 4 and the neutralizing force of the return mechanism 10. The torque generated by the pressure is maximum when the adjustable orifice 29 is fully opened.

[0094] A person skilled in the art will appreciate that the inventive concept can be applied to set the displacement volume of a fixed displacement unit and to set and adjust the displacement volume of a variable displacement hydraulic unit. Furthermore, the inventive concept can be used to improve and / or smooth the operating behavior of a hydraulic unit, since the pressure conversion steps can be reduced, thereby eliminating the need to provide a "fishtail". Thus, the inventive concept can be applied to a hydraulic unit equipped with a servo unit or to a hydraulic unit without a servo unit, to set / adjust the displacement volume.

[0095] Figure 4 The valve section 20 of a second embodiment of a hydraulic axial piston unit according to the invention is schematically shown. The arrangement according to the second embodiment of the invention is similar to Figure 1 and Figure 2The arrangement shown. The second embodiment comprises an adjustable orifice 29 in the first bypass line 27 in order to control the pressure at the IDC control port 23. A non-adjustable orifice 31 is provided in the second bypass line 28. Therefore, in this exemplary embodiment, the tilt angle of the displacement element 4 is controlled by adjusting the opening / flow resistance in the first bypass line 27 and thus the pressure at the IDC control port 23. In the rotational area of ​​the IDC control port 23, the pressure in the cylinder bore 5 passing the IDC control port 23 generates a moment relative to the tilt axis of the displacement element 4, which moment is able to reduce the tilt angle. At the IDC, the working piston 6 is at its maximum introduction point in the cylinder bore 5 passing the IDC, so that increasing the pressure in the cylinder bore 5 passing the IDC will reduce the tilt angle of the displacement element 4. Conversely, reducing the pressure in the cylinder bore 5 passing the IDC can increase the tilt angle of the displacement element 4 because the reaction force of the displacement element 4 is reduced.

[0096] As previously mentioned, the first pressure port 21 and therefore the first bypass line 27 are connected to the low pressure side of the hydraulic unit, here to the hydraulic reservoir 100. Therefore, opening the adjustable orifice 29 provides a reduced pressure (back pressure) at the IDC control port 23, because the hydraulic fluid can be pushed out of the cylinder bore 5 with less resistance, and the pressure in the passing cylinder bore 5 is reduced. Therefore, the inclination angle of the displacement element 4 is increased. Closing the adjustable orifice 24 increases the resistance that the hydraulic fluid can be discharged, and a higher back pressure is accumulated, thereby increasing the pressure in the passing cylinder bore 5 by limiting the pressure relief. At the same time, due to the non-adjustable orifice 31 in the second bypass line 28, the pressure distribution at the ODC pressure port 24 is not actively adjusted.

[0097] Figure 5 The valve section of a third embodiment of a hydraulic axial piston unit according to the invention is schematically shown. The third embodiment can be regarded as a combination of the first and second embodiments. Therefore, an adjustable orifice 29 is provided in the second bypass line 29 and an adjustable orifice 30 is provided in the first bypass line 27. The working principle of the hydraulic axial piston unit according to the third embodiment is similar to that explained above. Increasing the pressure at the ODC control port 24 causes the tilt angle of the displacement element 4 to increase, due to the increase in the force on the displacement element 4 in the tilt direction. Increasing the pressure at the IDC control port 24 causes the tilt angle of the displacement element 4 to decrease, due to the corresponding pressure acting in the direction of reducing the tilt angle. Therefore, by providing an adjustable orifice 29, 30 in each of the two bypass lines 27, 28, the tilt angle of the displacement element 4 can be adjusted with high precision. In addition, by adjusting the opening size of the orifices 29, 30 relative to each other, vibrations and noise can be reduced so as to smooth the pressure distribution and reduce or even avoid pressure peaks or cavitation near or at the dead points IDC and ODC.

[0098] Figure 6 The valve section 20 of a fourth embodiment of a hydraulic axial piston unit according to the invention is schematically shown. The fourth embodiment is a further development of the above-mentioned embodiments. In the ODC region, the valve section 20 of the hydraulic unit comprises a second ODC control port 26. Compared to the first ODC control port 24, the second ODC control port 26 is arranged on the opposite side of the ODC / IDC connection line of the dead center plane 7 (seen in the circumferential direction). This means, for example, that the first ODC control port 24 is arranged behind the ODC in the clockwise direction, while the second ODC control port 26 is arranged in front of the ODC in the clockwise direction. The second ODC control port 26 is connected to the second pressure port 22 via an additional bypass line 33, which may include, for example, an adjustable orifice 30 and a non-adjustable orifice. This arrangement enables better precise adjustment of the pressure distribution provided to the cylinder bore 5 via the first ODC control port 24 and the second ODC control port 26 when the cylinder bore 5 travels on its circular path due to the rotation of the cylinder block 3. As a result, noise and vibrations may also be reduced when operating the hydraulic unit, and reaction times to control signals may be shortened due to the higher flow rates that may pass through the two ODC control ports 24 , 26 .

[0099] Figure 7 The valve section 20 of a fifth embodiment of a hydraulic axial piston unit according to the invention is schematically shown. The fifth embodiment of the hydraulic unit may, for example, represent a hydraulic motor that may be arranged in a closed circuit. Unlike the embodiments described above, which all include an offset angle between the rotational position of the ODC / IDC control ports 23, 24 and the actual rotational position of the IDC and ODC, the ODC control port 24 and the IDC control port 23 of the hydraulic unit according to the fifth embodiment are arranged at the exact corresponding rotational position of the IDC and ODC, i.e. on the dead center plane 7. This means that the offset angle γ O / γ I Therefore, when adjusting the tilt angle of the displacement element 4 , the control behavior of the hydraulic unit is independent of the rotation direction of the cylinder 3 .

[0100] In the fifth embodiment, an adjustable orifice 29 is provided in the first bypass line 27. The orifice 31 arranged in the second bypass line 28 comprises a non-adjustable constant opening size. Typically, hydraulic motors used in closed circuit applications are capable of rotating in both directions. Even if the displacement element 4 of such a hydraulic motor is tiltable in only one direction, the pressure levels at the first pressure port 21 and the second pressure port 22 can be interchanged in order to reverse the direction of rotation of the rotating group 2 of the hydraulic unit. Figure 7In the embodiment shown, the ODC control port 24 is connected to the hydraulic reservoir 100 via the second bypass line 28. Therefore, a lower system pressure is present at the ODC control port 24 regardless of the direction of rotation. According to the invention, a high pressure can be provided to the IDC control port 23. For this purpose, a shuttle valve 35 is provided, whose outlet 38 is connected to the first bypass line 27. The first inlet 36 of the shuttle valve 35 is connected to the second pressure port 22. The second inlet 37 of the shuttle valve 35 is connected to the first pressure port 21. The shuttle valve 35 is able to always conduct the higher pressure level of the first pressure port 21 or the second pressure port 22 to the first bypass line 27 via its outlet 38. Therefore, regardless of the direction of rotation of the hydraulic unit, the adjustment of the opening size of the adjustable orifice 29 is always related to the high pressure level. The control of the inclination angle of the displacement element 4 of the hydraulic unit is similar to the control of the hydraulic unit according to embodiments 1 to 4. For the sake of brevity of this explanation, it will not be repeated.

[0101] Figure 8 The valve section 20 of a sixth embodiment of a hydraulic axial piston unit according to the invention is schematically shown. The sixth embodiment is similar to the fifth embodiment. However, the adjustable orifice in the bypass line 27 connecting the IDC control port 23 with the outlet 38 of the shuttle valve 35 is replaced by a non-adjustable orifice 31. An adjustable orifice 29 is provided in the first bypass line 28 connecting the ODC control port 24 to the hydraulic reservoir 100. Figure 4 The pump of the second embodiment in has similarly described the working principle of displacement control by means of the adjustable orifice 29 in the first bypass line 28 connected to the ODC control port 24, wherein the IDC control port 23 is connected to the low system pressure side. Therefore, for the sake of brevity of this explanation, repetition is avoided.

[0102] Fig. 9 The valve section 20 of a seventh embodiment of a hydraulic axial piston unit according to the present invention is schematically shown. The valve section 20 according to the seventh embodiment comprises a first ODC control port 24 and a second ODC control port 26, both connected to the second pressure port 22 via bypass lines 27 and 33, wherein each bypass line 27 and 33 comprises an adjustable orifice 29 and 30. In addition, the hydraulic unit comprises a first IDC control port 23 and a second IDC control port 25, both connected to the first pressure port 21 via bypass lines 28 and 32. These bypass lines also each comprise an adjustable orifice 34 and 39. The first ODC control port 24 and the second ODC control port 26 and the first IDC control port 23 and the second IDC control port 25 are arranged on both sides of the rotational position of the dead center plane 7 (including the rotational positions of the ODC and the IDC) in the rotational direction. If the hydraulic unit is capable of bidirectional rotation, such as Fig. 9As indicated by the double-headed arrow 80 in the figure, the circumferential distance from the first IDC / ODC control ports 23 and 24 to the IDC / ODC position on the valve section 20 can be equal to the circumferential distance from the second IDC / ODC control ports 25 and 26 to the rotational IDC / ODC position on the valve section 20. Therefore, the control behavior of the hydraulic unit is symmetrical and independent of the rotational direction. During operation of the hydraulic unit, the pressure levels at the first pressure port 21 and the second pressure port 22 can be interchanged, for example due to a change in operating mode (e.g., from motor mode to pump mode), or because it is desired to change the rotational direction of the hydraulic unit. Therefore, a technician in the relevant field can arrange a shuttle valve 35 in the bypass line 27 and 33, if the hydraulic unit is operated as a hydraulic pump, the shuttle valve is used to conduct high pressure to the ODC pressure ports 24, 26, or if the hydraulic unit is operated as a hydraulic motor, the shuttle valve is used to conduct high pressure to the IDC pressure ports 23, 25.

[0103] Fig.10a , Fig.10b and Fig.11 An eighth embodiment of a hydraulic axial piston unit according to the invention is schematically shown, which can be used, for example, as a pump in a closed hydraulic circuit. Similar to the above examples, the hydraulic unit according to the eighth embodiment comprises a first pressure port 21 and a second pressure port 22. Preferably, the hydraulic pump comprises only one direction of rotation, as shown by the arrow on the drive shaft 8 in FIG. 10 and Fig.10b and Fig.11 Indicated by the arrow 80 on the valve section 20 shown in FIG. In order to be able to supply hydraulic fluid in both directions, the displacement element 4 of the hydraulic unit can be tilted at positive and negative angles. The displacement element 4 is forced into its neutral position by the return mechanism 10, and the neutral position is usually also the initial position of the displacement element 4.

[0104] Fig.10bIn addition, a valve arrangement is shown, which includes charging pressure valves 51 and 52 as common check valves, each of which is combined with a proportional flow valve and discharges to a hydraulic reservoir 100. By means of this valve arrangement, a starting mechanism of a hydraulic pump with a neutral return mechanism 10 can be realized. When one of the flow valves (e.g., the flow valve next to the charging pressure valve 52) is opened, the charging pressure is directed to the corresponding other charging pressure valve, in this example, to the charging pressure valve 51, whose flow valve is closed. Therefore, when the charging pump starts working, an initial pressure difference is generated at the valve plate 20. At the same time, by opening the two adjustable orifices 29 and 30, a system pressure difference is established between the two control ports 23 and 24, thereby enabling the initial tilting of the displacement element 4. Due to this initial tilting of the displacement element 4, a system pressure is generated by the hydraulic pump, which increases the pressure difference between the two control ports 23 and 24 as long as the higher system pressure is higher than the charging pressure, and the adjustable orifice 29 remains at least partially open. By varying the flow passage through the adjustable orifices 29 and 30, the displacement volume may be set / adjusted as described above.

[0105] Due to the potential bidirectional tilting of the displacement element 4, the rotational position of the IDC and the rotational position of the ODC are not fixed, but interchange when the algebraic sign of the tilting angle of the displacement element 4 changes. Therefore, the assignment of the control ports 23 and 24 to the ODC and IDC is not constant throughout the operation of the hydraulic unit, but varies with the displacement of the displacement element 4 beyond zero. In certain operating states, the rotational position of the ODC can be located on the left side of the valve section 20, for example Fig.11 As shown. Accordingly, the rotational position of the IDC can be located at Fig.11 , and the corresponding control ports are labeled ODC control port 24 and IDC control port 23. Control ports 23, 24 are connected to pressure ports 21, 22 via first bypass line 27 and second bypass line 28, each of which includes an adjustable orifice 29 and 30.

[0106] The inlets 36 and 37 of the shuttle valve 35 are fluidly connected to the first pressure port 21 and the second pressure port 22, and the working principle of the shuttle valve has been explained above. The outlet 38 of the shuttle valve 35 is fluidly connected to the first inlet 41 of the control valve 40, which further includes a second inlet 42 connected to the hydraulic reservoir 100 or another low system pressure source. Therefore, the first inlet 41 of the control valve 40 is always connected to the high system pressure provided via the shuttle valve 35. The second inlet 42 of the control valve 40 is always connected to the low system pressure. The control valve 40 further includes a first outlet 43 connected to the first bypass line 27, and a second outlet 44 connected to the second bypass line 28. The position of the control valve 40 is selected according to the algebraic sign of the inclination angle of the displacement element 4 and according to the use of the hydraulic unit as a hydraulic pump or a hydraulic motor. The control valve 40 can connect the first inlet 41 to the first outlet 43 and the second inlet 42 to the second outlet 44. Therefore, the high pressure is conducted to the first bypass line 27 and the low pressure is conducted to the second bypass line 28. Alternatively, the control valve 40 can connect the first inlet 41 with the second outlet 44, thereby conducting high pressure to the second bypass line 28, and can connect the second inlet 42 to the first outlet 43, thereby conducting low pressure to the first bypass line 27. The control valve 40 can further include a third position, in which the bypass lines 27 and 28 are hydraulically short-circuited and the connection between the inlets 41 and 42 and the outlets 43 and 44 is blocked. Depending on the type of use, the displacement of the control valve 40 can be discrete or continuous. If the control valve 40 can be continuously positioned, the control valve 40 can even be used as a variable regulating orifice.

[0107] exist Fig.11 In the illustrated operating state of the control valve 40, the pressure at the ODC control port 24 and the pressure at the IDC control port 23 are equal, because the control valve 40 is in its third position, in which the ODC control port 23 is connected to the IDC control port 24. Therefore, the pressure difference between the ODC control port 24 and the IDC control port 23 does not generate a tilting moment. Therefore, only the usually relatively high force of the neutralization / return mechanism 10 and the usually relatively low torque group of the piston in the cylinder bore 5 of the hydraulic unit contribute to the torque balance on the displacement element 4, and the displacement element 4 is forced into its neutral position.

[0108] According to the invention, there is no additional servo piston in the hydraulic unit, and the return mechanism 10 forces the displacement element 4 to reach a tilting angle of zero degrees. However, in order to be able to start the hydraulic unit, an initial pressure difference must be provided at the control ports 23 and 24, so that the hydraulic axial piston unit according to the invention can generate a hydraulic flow and the tilting angle of the displacement element 4 can be controlled by means of different pressure levels at the ODC / IDC control ports 23 and 24 generated at the pressure ports 21 and 22 with different pressure levels. For this purpose, in order to start the hydraulic axial piston unit, a charging pump 50 is provided that is capable of providing a pressure level to the shuttle valve 35, which pressure level is sufficient to generate a force at one of the control ports 23, 24 that overcomes the neutralizing force of the return mechanism 10. This charging pressure is necessary as long as the pressure difference generated in the working line of the hydraulic axial piston unit during the starting phase is not high enough to generate a tilting moment on the displacement element 4 via the pressure level at the control ports 23 and 24 that is sufficient to overcome the neutralizing force of the return mechanism 10. Once a sufficiently high pressure difference is reached, the supply of hydraulic fluid from the charging pump 50 to the shuttle valve 35 can be stopped. Furthermore, the charging pump 50 is able to replace hydraulic fluid which has been discharged, for example from the closed circuit due to leakage or for cooling purposes, via the low-pressure side.

[0109] Fig.12 FIG. 10 shows a ninth embodiment of a hydraulic axial piston unit according to the invention. The embodiment presented can be used, for example, as a hydraulic pump in a closed hydraulic circuit. Fig.11 The embodiment shown, the hydraulic unit comprises only one direction of rotation, but the displacement element 4 of the hydraulic unit can be tilted in two directions relative to its tilting axis 9 (see Figure 1 ). Therefore, when the algebraic sign of the inclination angle of the displacement element 4 is changed, the positions of the IDC and ODC and the positions of the corresponding control ports 23 and 24 may be reversed.

[0110] The valve arrangement 55 is fluidly arranged between the first and second pressure ports 21, 22 and the IDC control port 23 and the ODC control port 24. By means of the valve arrangement 55, when the pump is operated, appropriate pressure levels can be provided to the control ports 23 and 24, such as providing a high pressure to the ODC control port 24 and providing a low pressure to the IDC control port 23. The function of the valve arrangement 55 is similar to the function of the shuttle valve 35 combined with the control valve 40 described previously. The valve arrangement 55 includes a pressure-operated valve 57, which includes two inlets and two outlets. The pressure-operated valve 57 is adapted to conduct a higher pressure to one outlet (e.g., the first outlet) and conduct a lower pressure to the other outlet (e.g., the second outlet), regardless of whether the higher pressure is present at the first inlet or the second inlet.

[0111] The outlet of the pressure operated valve 57 is connected to the inlet of the start valve 59. Fig.12 In the embodiment of the present invention, the start valve is a three-position five-way reversing valve. The outlet of the start valve 59 is connected to the first bypass line 27 and the second bypass line 28. In the operating position of the start valve 59 (in Fig.12 ), the high and low pressures at the outlet of the pressure-operated valve 57 are further conducted to the bypass lines 27 and 28 by the start valve 59 without changing the direction of the fluid flow.

[0112] However, when there is no pressure difference between the first pressure port 21 and the second pressure port 22, for example when the hydraulic unit is started, there is no pressure difference at the control ports 23 and 24, and therefore no force can be generated to tilt the displacement element 4 of the hydraulic unit. In order to solve this problem, the third inlet of the start valve 59 is connected to a hydraulic reservoir 100 (e.g., a tank) at a low pressure level. A charging pump 50 is provided, which is capable of providing charging pressure to the inlet of the pressure-operated valve 57. This charging pressure is also present at the first inlet and the second inlet of the start valve 59. When the hydraulic unit is started, the cylinder 3 is forced to rotate and the start valve 59 can be displaced so as to conduct the charging pressure to one of the bypass lines 27 or 28 and conduct the low pressure from the hydraulic reservoir 100 to the other bypass line 28 or 27.

[0113] Thus, a pressure difference is established between the two bypass lines 27 and 28 and thus between the ODC / IDC control ports 23 and 24, which pressure difference is able to generate a sufficiently high torque on the displacement element 4 to tilt the displacement element 4 out of the initial position. After the initial tilting of the displacement element 4, a pressure difference is generated at the first pressure port 21 and the second pressure port 22 by the back and forth movement of the working piston 6 in the cylinder bore 5. When the valve arrangement 55 is operated to Fig.12 In the operating position shown, this pressure difference can be conducted via the valve arrangement to the control ports 23 and 24 and the hydraulic unit can operate as described in the context of the previous embodiments.

[0114] Figures 13 to 16 Two embodiments of an adjustable orifice 29 according to the invention are shown.

[0115] Fig.13 A first embodiment of an adjustable orifice 29 in an open position according to the present invention is shown. The orifice 29 comprises a valve body 60 in which a first valve port 66 and a second valve port 68 are arranged. The rotary valve core 62 comprises a recess on its circumferential surface, which overlaps with the first valve port 66 and the second valve port 68 so that a fluid connection is established between the two valve ports.

[0116] Fig.14A first embodiment of an adjustable orifice 29 in a closed position according to the present invention is shown. When the rotary spool 62 rotates, the first valve port 66 and the second valve port 68 no longer overlap the recess in the rotary spool 62, and the fluid connection is interrupted. Needless to say, the rotary spool 62 can be replaced by a linearly movable spool having corresponding recesses on the spool surface without departing from the scope of the present invention.

[0117] Fig.15 A second embodiment of adjustable orifices 29 and 30 according to the invention is shown in an open position. Fig.16 This second embodiment of the adjustable orifices 29 and 30 according to the invention is shown in a closed position. Fig.13 and Fig.14 Compared to the embodiment shown, Fig.15 and Fig.16 A linear spool valve is presented, however, the inventive concept can also be applied to a rotary spool valve. The adjustable orifices 29 and 30 include a common valve body 60 having a first valve port 66, a second valve port 68, a third valve port 70, and a fourth valve port 72. A linearly movable valve core 64 is slidably received in a central bore of the valve body 60 and includes two circumferential recesses that can overlap with the valve ports to establish a fluid connection between the first valve port 66 and the second valve port 68 and between the third valve port 70 and the fourth valve port 72. The adjustable connection of the first valve port 66 and the second valve port 68 represents the first adjustable orifice 29. The adjustable connection of the third valve port 70 and the fourth valve port 72 represents the second adjustable orifice 30. Since the first orifice 29 and the second orifice 30 share the common valve core 62, the opening of the first adjustable orifice 29 and the opening of the second adjustable orifice 30 are mechanically coupled to each other. Therefore, only one actuator / actuating mechanism is required to adjust the openings of the two orifices. Preferably, the pressure levels present at the valve ports 66, 68, 70, and 72 are symmetrical with respect to the plane between the second valve port 68 and the third valve port 70. For example, the second valve port 68 and the third valve port 70 can be connected to a higher pressure, and the first valve port 66 and the fourth valve port 72 can be connected to a lower pressure level, or vice versa. For example, this requirement can be met when the ODC control port 24 of a hydraulic unit (e.g., a hydraulic pump) is connected to the second valve port 68 and the IDC control port 23 of the hydraulic unit (e.g., a hydraulic pump) is connected to the fourth valve port 72. Then, the force generated by the hydraulic flow on the spool 62 (by Figures 11 to 14 The valve core 62 is balanced with respect to each other (as shown by the arrow in FIG. 1 ), and only a small force is required to hold the valve core 62 in place or to displace the valve core 62.

[0118] Based on the above disclosure as well as the accompanying drawings and claims, it can be understood that the hydraulic axial piston unit according to the present invention provides many possibilities and advantages compared to the prior art. Those skilled in the relevant art will further understand that further modifications and changes known in the art can be made to the hydraulic axial piston unit according to the present invention without departing from the spirit of the present invention. Therefore, all these modifications and changes are within the scope of the claims and are covered by the claims. It should be further understood that the examples and embodiments described above are for illustrative purposes only, and various modifications, changes or combinations of the embodiments proposed by those skilled in the relevant art are included in the spirit and scope of the present application.

[0119] List of reference numerals

[0120] 2 Rotating group 43 Control valve first outlet

[0121] 3 Cylinder 44 Second outlet of control valve

[0122] 4 Displacement components

[0123] 5 cylinder bore 50 charging pump

[0124] 6 Working piston 51 Filling pressure valve

[0125] 7 Dead point plane 52 Filling pressure valve

[0126] 9 Tilt axis

[0127] 10 Return mechanism 55 Valve arrangement

[0128] 12 Axis of rotation of valve section 57 Pressure operated valve

[0129] 13 Rotation axis of cylinder 59 Start valve

[0130] 20 Valve Section 60 Orifice Body

[0131] 21 First kidney pressure port 62 Rotary valve core

[0132] 22 Second kidney pressure port 64 Linear spool

[0133] 23 IDC control port 66 first valve port

[0134] 24 ODC control port 68 second valve port

[0135] 25 2nd IDC control port 70 3rd valve port

[0136] 26 2nd ODC control port 72 4th valve port

[0137] 27 First bypass line

[0138] 28 Second bypass line 80 Direction of rotation

[0139] 29 Adjustable orifice

[0140] 30 Adjustable orifice 100 Hydraulic reservoir

[0141] 31 Non-adjustable orifice

[0142] 32 Third bypass line ECU Electronic control unit

[0143] 33 Fourth bypass line IDC inner dead center

[0144] 34 Adjustable orifice ODC External stop point 35 Shuttle valve

[0145] βi Angle between the second pressure port and the inner dead center 36 Shuttle valve first inlet 37 Second inlet of shuttle valve βΟ Angle between the second pressure port and the outer dead center

[0146] γi Angle between IDC control port and IDC 38 Shuttle valve outlet

[0147] γΟ Angle between ODC control port and ODC 39 Adjustable orifice

[0148] σi Angle between the first pressure port and the inner dead center 40 Directional valve

[0149] σΟ Angle between the first pressure port and the outer dead center 41 First inlet of control valve 42 Second inlet of control valve τ Angular extension of the cylinder bore

Claims

1. A hydraulic axial piston unit, comprising: a rotary group (2), the displacement volume of which is set by means of a displacement element (4), the rotary group (2) comprising a rotatable cylinder body (3) with cylinder bores (5), in which a working piston (6) is reciprocatingly mounted; and a valve section (20), which comprises a kidney-shaped first pressure port (21) and a kidney-shaped second pressure port (22), wherein: When the associated working piston (6) is at or near its inner dead center (IDC) or at or near its outer dead center (ODC), respectively, the cylinder bore (5) can be fluidly connected to the IDC control port (23) or the ODC control port (24), wherein the IDC control port (23) and the ODC control port (24) are located between the respective circumferential ends of the first pressure port (21) and the second pressure port (22) in the circumferential direction, wherein the circumferential distance from the IDC control port (23) to the first and second pressure ports (21, 22) and the circumferential distance from the ODC control port (24) to the first pressure port (21, 22) are equal to the circumferential distance from the IDC control port (23) to the first and second pressure ports (21, 22). The circumferential distance between the first and second pressure ports (21, 22) is smaller than the circumferential extent of the cylinder bores (5), and wherein a first bypass line (27) and a second bypass line (28) are provided, each of which is connected to one of the control ports (23, 24), wherein an adjustable orifice (29) is arranged in the first bypass line (27), the adjustable orifice being able to continuously variably open and close the first bypass line (27) so as to enable a variably adjustable fluid flow connection between the connected control port (23, 24) and the connected pressure port (21, 22).

2. The hydraulic axial piston unit according to claim 1, wherein: The first bypass line (27) and / or the second bypass line (28) are each connected to the next pressure port (21, 22) after the connected control port (23, 24) in the rotation direction of the cylinder (3).

3. A hydraulic axial piston unit according to any one of claims 1 or 2, having a variable displacement volume, which is controlled by adjusting the opening size of the adjustable orifice (29) so as to control the pressure at the connected control port (23, 24) relative to the pressure at the other control port (24, 23).

4. A hydraulic axial piston unit according to claim 1, having a fixed displacement volume, which is set by setting the opening of the adjustable orifice (29) so as to set the pressure at the connected control port (23, 24) relative to the pressure at the other control port (24, 23).

5. The hydraulic axial piston unit according to any one of the preceding claims, wherein: The second bypass line (28) is connected to the pressure compensation chamber.

6. The hydraulic axial piston unit according to any one of claims 1 to 4, wherein: The second bypass line (28) is connected to the first pressure port (21) or the second pressure port (22) so as to enable fluid flow connection between the connected pressure port (21, 22) and the passing cylinder bore (5) via the second bypass line (28).

7. A hydraulic axial piston unit according to any one of the preceding claims, wherein: The openings of the cylinder bores (5) facing the valve section (20) exhibit a kidney-shaped cross section.

8. The hydraulic axial piston unit according to claim 7, wherein: The circumferential extent of the kidney-shaped openings of the cylinder bores (5) is smaller than the circumferential distance between adjacent ends of the first and second kidney-shaped pressure ports (21, 22).

9. The hydraulic axial piston unit according to any one of the preceding claims, wherein: An adjustable orifice (29, 30) is arranged in each of these bypass lines (27, 28).

10. The hydraulic axial piston unit according to claims 1 to 8, wherein: If the second bypass line (28) does not comprise an adjustable orifice (29, 30), a non-adjustable orifice (31) is arranged in the second bypass line (28).

11. The hydraulic axial piston unit according to any one of the preceding claims, wherein: The adjustable orifice (29, 30) is a proportional flow valve whose flow passage can be adjusted by means of a force generated hydraulically, pneumatically or electromechanically.

12. A hydraulic axial piston unit according to any one of the preceding claims, wherein: A parallel bypass line including an adjustable orifice (29, 30) or a non-adjustable orifice (31) establishes a fluid flow connection in parallel with a fluid flow connection between a pressure port (21, 22) and a control port (23, 24) connected by the first bypass line (27) or between a pressure port (21, 22) and a control port (23, 24) connected by the second bypass line (28).

13. A hydraulic axial piston unit according to any one of the preceding claims, wherein: The two control ports (23, 24) are connected to the same pressure port (21, 22) via the first and second bypass lines (27, 28).

14. The hydraulic axial piston unit according to claim 13, wherein: Each control port (23, 24) is additionally connected to another pressure port (21, 22) via a third and a fourth bypass line (32, 33), wherein an adjustable orifice (29, 30) is arranged in each of these four bypass lines (27, 28, 32, 33).

15. A hydraulic axial piston unit according to any one of the preceding claims, wherein: The displacement element (4) is biased to an initial position by means of elastic force and / or by means of an offset of the tilting axis of the displacement element (4) relative to the rotation axis of the cylinder (3), in which initial position the displacement volume of the rotating group is maximum, minimum or zero.

16. The hydraulic axial piston unit according to any one of the preceding claims, further comprising a return mechanism (10) capable of generating a restoring force on the displacement element (4) when the displacement element (4) is pivoted away from its initial position.

17. A hydraulic axial piston unit according to claim 15 or 16, wherein: When the rotating group (2) is in its initial position at maximum displacement, a safety pressure limiter switching valve is arranged in at least one of the bypass lines (27, 28, 32, 33) in order to close the associated bypass line when the system pressure level exceeds a threshold value.

18. A hydraulic axial piston unit according to any one of the preceding claims, wherein: The valve section (20) is formed integrally with the housing, the end cover or the housing cover of the hydraulic axial piston unit.

19. A hydraulic axial piston unit according to any one of the preceding claims, wherein: The opening size of these orifices (29, 30) is controlled mechanically or by an electronic control unit (ECU) comprising a microcontroller and connected to at least one sensor selected from a group of sensors comprising: an inclination angle sensor, a shaft position sensor, a pressure sensor, a flow sensor, a rotation speed sensor, a temperature sensor, a direction sensor, a torque sensor, an acceleration sensor or any other sensor capable of monitoring at least one operating parameter of the hydraulic unit.

20. The hydraulic axial piston unit according to any of the preceding claims, comprising at least two adjustable orifices (29, 30), one adjustable orifice being arranged in the first bypass line (27) and one adjustable orifice being arranged in the second bypass line (28), wherein The opening sizes of the two adjustable orifices (29, 30) can be adjusted individually or by means of a shared mechanical, electromechanical, hydraulic or pneumatic mechanism.

21. A hydraulic axial piston unit according to any one of the preceding claims, wherein: The IDC and / or ODC control ports (23, 24) include a circular shape, an elongated shape, an elliptical shape, a triangular shape, a kidney shape, or any other shape.

22. A hydraulic axial piston unit according to any one of the preceding claims, wherein: The IDC control port (23) and / or the ODC control port (24) are located on the valve section (20) and are angularly offset in the circumferential direction from a rotational position on the valve section (20) at which the working pistons (6) are respectively at their inner dead center (IDC) and / or outer dead center (ODC).

23. A hydraulic axial piston unit according to claims 1 to 21, wherein: The IDC control port (23) and / or the ODC control port (24) are located on the valve section (20) at a rotational position on the valve section (20) at which the working pistons (6) are respectively at their inner dead center (IDC) and / or outer dead center (ODC).

24. The hydraulic axial piston unit according to claim 22, wherein: The second ODC control port (26) is located on the valve section (20) so that the first and second ODC control ports (24, 26) are located on both sides of the rotational position on the valve section (20) corresponding to the outer dead center (ODC) position of the working pistons (6) in the circumferential direction.

25. The hydraulic axial piston unit according to claim 24, wherein: The second IDC control port (25) is located on the valve section (20) so that the first and second IDC control ports (23, 25) are located on both sides of the rotational position corresponding to the inner dead center (IDC) position of the working pistons (6) on the valve section (20) in the circumferential direction.

26. A hydraulic axial piston unit according to claim 24 or 25, wherein: The second IDC control port (25) and / or the second ODC control port (26) are respectively connected to a third bypass line (32) and / or a fourth bypass line (33), wherein at least one of the third and fourth bypass lines (32, 33) includes an adjustable orifice (34, 39) capable of continuously and variably opening and closing the associated bypass line.

27. The hydraulic axial piston unit according to any of the preceding claims, which is operated as a hydraulic pump or a hydraulic motor in an open or closed hydraulic circuit.

28. A hydraulic axial piston unit according to claim 27, which operates in a closed hydraulic circuit and includes a shuttle valve (35), which has two inlets (36, 37) and one outlet (38), the inlets (36, 37) being fluidly connected to the first and second pressure ports (21, 22), and the outlet (38) being fluidly connected to the IDC control port (23) or the ODC control port (24), so that the shuttle valve (35) can conduct a higher system pressure from one of the first and second pressure ports (21, 22) to the IDC control port (23) or the ODC control port (24) and / or the control valve (40).

29. A hydraulic axial piston unit according to claim 28, wherein: The control valve (40) is provided with a first inlet (41) connected to the outlet (38) of the shuttle valve (35) and a second inlet (42) connected to a lower system pressure or a hydraulic reservoir (100), and a first outlet (43) connectable to the IDC control port (23) or the ODC control port (24) and a second outlet (44) connectable to the other control port (24, 23), wherein the control valve (40) is capable of selectively connecting the first inlet (41) to the first outlet (43) and the second inlet (42) to the second outlet (44), or connecting the first inlet (41) to the second outlet (44) and the second inlet (42) to the first outlet (43), or short-circuiting the first outlet (43) to the second outlet (44).

30. A hydraulic axial piston unit according to claim 28 or 29, comprising a charging pump (50) capable of providing a flow of hydraulic fluid to one of the first or second pressure ports (21, 22) to create an initial pressure difference between the first and second pressure ports (21, 22) and / or to switch the shuttle valve (35) when the hydraulic axial piston unit is in its neutral position.

31. A hydraulic axial piston unit according to any one of the preceding claims, wherein: The at least one adjustable orifice (29, 30, 34, 39) provides pressure feedback and / or displacement feedback to an electronic control unit (ECU).

32. A hydraulic axial piston unit according to any one of the preceding claims, wherein: The at least one adjustable orifice (29, 30) is controlled by the electronic control unit (ECU) based on pressure and / or displacement feedback of the at least one adjustable orifice (29, 30, 34, 39).

33. A hydraulic axial piston unit according to any one of the preceding claims, wherein: The control ports (23, 24) are inclined relative to the axis of rotation of the hydraulic axial-piston unit.

34. A hydraulic axial piston unit according to any one of the preceding claims, wherein: The radial positions of the control ports (23, 24) are offset from a pitch diameter defined by the circumferential extent of the first and second pressure ports (21, 22).

35. A method for variably controlling the displacement volume of a hydraulic rotary group (2) driving a drive shaft (8) or driven by the drive shaft, the hydraulic rotary group having a displacement element (4) which can be tilted for adjusting the displacement volume of the rotary group (2), wherein: The rotary group (2) comprises: a rotatable cylinder body (3), a working piston (6) being reciprocatingly mounted in a cylinder bore (5); and a valve section (20), the valve section having a kidney-shaped first pressure port (21) and a kidney-shaped second pressure port (22), wherein an IDC control port (23) and an ODC control port (24) are located on the valve section (20) and between the respective circumferential ends of the first pressure port (21) and the second pressure port (22) in the circumferential direction, wherein when the associated working piston (6) is reciprocatingly mounted in a cylinder bore (5), the valve section (20) has a kidney-shaped first pressure port (21) and a kidney-shaped second pressure port (22), wherein the IDC control port (23) and the ODC control port (24) are located on the valve section (20) and between the respective circumferential ends of the first pressure port (21) and the second pressure port (22) in the circumferential direction. The cylinder bore (5) is fluidly connectable to the IDC control port (23) or the ODC control port (24) when the piston (6) is at or near its inner dead center (IDC) or at or near its outer dead center (ODC), respectively, wherein the circumferential distance from the IDC control port (23) to the first and second pressure ports (21, 22) and the circumferential distance from the ODC control port (24) to the first and second pressure ports (21, 22) are smaller than the circumferential extent of the cylinder bores (5), The method comprises the following steps: - draining hydraulic fluid from or supplying hydraulic fluid to passing cylinder bores (5) via the IDC control port (23) by means of a first bypass line (27) having a first orifice (29), - supplying hydraulic fluid to or exhausting hydraulic fluid from the passing cylinder bores (5) via the ODC control port (24) by means of a second bypass line (28) having a second orifice (30), - Adjusting the opening size of the first orifice (29) or the opening size of the second orifice (30), or adjusting both the opening size of the first orifice (29) and the opening size of the second orifice (30), so as to set or adjust the inclination angle of the displacement element (4) and control the displacement volume of the hydraulic rotating group (2).

36. The method of claim 35, wherein: Hydraulic fluid from the ODC and IDC control ports (23, 24) is supplied or exhausted at the pressure level of the next pressure port (21, 22) in the rotational direction of the cylinder (3).

37. The method according to any one of claims 35 or 36, further comprising the steps of: - commands of a control unit or an operator are processed by means of an electronic control unit (ECU) having a microcontroller for adjusting the opening size of orifices (29, 30) in the first bypass line (27) and / or in the second bypass line (28) in order to control the pressure in the cylinder bores (5) and thus the displacement volume of the hydraulic axial piston unit.

38. The method according to any one of claims 35 to 37, further comprising the steps of: - Sensing at least one operating parameter of the hydraulic axial piston unit with the aid of a sensor selected from the group of sensors comprising: an inclination 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 operating parameter of the hydraulic unit.

39. The method according to any one of claims 34 to 37, further comprising the steps of: - Continuously monitoring the operating parameters of the hydraulic axial piston unit in order to smooth the pressure transition between the first and second pressure ports (21, 22) and vice versa, and / or for controlling the pressure in the cylinder bores (5), and / or for adjusting the inclination angle of the displacement element (4).

40. The method according to any one of claims 34 to 37, in the case where the rotating group (2) is used in a closed circuit hydraulic application with a charging pump (50), the method further comprising the steps of: - supplying charging pressure to one of the first or second pressure ports (21, 22) via a charging pressure valve (51, 52) when the rotating group (2) is in its neutral position; - directing hydraulic fluid from the pressure port (21, 22) having a higher pressure to the associated control port (23, 24) by means of one of the first or second bypass lines (27, 28); - Discharging the hydraulic fluid from the other control port (24, 23) to the hydraulic fluid reservoir (100) by means of the other bypass line (28, 27).

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