Hydraulic machine with variable displacement

Abstract

A variable displacement hydraulic machine comprising an end cap configured to accommodate at least two different types of pistons, such as a maximum displacement servo piston or a minimum displacement servo piston. The assembly process involves selecting the appropriate servo piston type depending on whether the machine is configured for maximum or minimum displacement. The two servo piston types are interchangeable, maintaining the same position within the end cap's internal volume. This simplifies and streamlines assembly compared to conventional methods.The end cap has the same orientation and position relative to a housing, regardless of whether the machine is configured as a pre-tensioned maximum displacement or minimum displacement machine.

Description

TECHNICAL AREA

[0001] The present invention relates generally to variable displacement hydraulic machines and in particular to variable displacement hydraulic machines which can be configured to have a minimum displacement or maximum displacement when preloaded, and to methods for assembling such variable displacement hydraulic machines. BACKGROUND

[0002] Hydraulic machines with variable displacement, such as hydraulic pumps or hydraulic motors, are known. It is also known that the displacement of a hydraulic machine with variable displacement can be configured to vary as needed or desired. The displacement level of a hydraulic machine with variable displacement can be pre-set to a minimum level in the resting state, e.g., when stationary or idling, so that an actuating force is required to change the displacement level of the hydraulic machine with variable displacement to a maximum level or an intermediate level.Alternatively, the displacement level of a variable hydraulic machine may be biased to a maximum displacement level in a non-operating state of the variable hydraulic machine, so that an actuating force is required to change the displacement level of the variable hydraulic machine to a minimum displacement level or a level in between.

[0003] Although it is known that a hydraulic variable displacement machine can be configured at rest to be pre-tensioned for minimum displacement or maximum displacement, the differences in the configuration of parts and assembly steps between machines pre-tensioned for minimum displacement or maximum displacement are significant. SUMMARY

[0004] The present invention provides hydraulic machines with variable displacement and assembly methods which advantageously make it possible to realize the configuration of the hydraulic machine with variable displacement by replacing a single part.

[0005] According to some embodiments of the present invention, a variable displacement hydraulic machine comprises a housing and an end cap connected to the housing, which define an internal volume. The machine further comprises a servo piston biasing towards maximum displacement or a servo piston biasing towards minimum displacement, which are arranged at least partially within the internal volume of the end cap. The end cap is configured such that the servo piston biasing towards maximum displacement and the servo piston biasing towards minimum displacement can be arranged at a servo piston position within the internal volume. The variable displacement hydraulic machine is biased towards maximum displacement when the servo piston biasing towards maximum displacement is arranged at the servo piston position.The variable displacement hydraulic machine is biased in the direction of minimum displacement when the servo piston biasing for minimum displacement is located at the servo piston position.

[0006] According to some embodiments of the present disclosure, a servo unit is arranged at least partially within the internal volume in which the servo piston pre-tensioning the maximum displacement or the servo piston pre-tensioning the minimum displacement is located. The servo piston heads of the servo piston pre-tensioning the maximum displacement or the servo piston pre-tensioning the minimum displacement are, in a non-actuated state, pre-tensioned against a stop on the housing or the end cap by means of a servo piston spring.

[0007] In some embodiments, a variable-displacement hydraulic machine comprises a housing and an end cap connected to the housing, the end cap defining an internal volume. The end cap is configured to accommodate, at least partially within the internal volume, a servo preload piston for maximum displacement and a servo preload piston for minimum displacement, interchangeably positioned at a servo piston position within the internal volume. The variable-displacement hydraulic machine is preloaded toward a maximum displacement level when the servo preload piston for maximum displacement is positioned at the servo piston position, and preloaded toward a minimum displacement level when the servo preload piston for minimum displacement is positioned at the servo piston position.For this purpose, a swashplate is held / tilted at a maximum or minimum swivel angle by means of the servo piston rod of one of the selected servo preload pistons, the servo piston for maximum displacement, or the servo piston for minimum displacement, while the hydraulic machine is at rest. Accordingly, the hydraulic machine can be configured for either the maximum or minimum displacement configuration, depending on which servo preload piston has been selected to be arranged in the interior or in the servo unit.

[0008] According to some embodiments of the invention, the swashplate of the hydraulic machine is biased in its initial position towards a maximum swivel angle when the servo preload piston is positioned for maximum displacement in the servo unit. The swashplate is biased in its initial position towards a minimum swivel angle when the servo preload piston is positioned for minimum displacement in the servo unit. This applies regardless of whether the hydraulic machine is to be operated as a pump or as a motor.

[0009] According to the invention, pairs of servo pistons, one for maximum displacement and one for minimum displacement, can be provided for one or more volumetric machine sizes, which have the same servo piston head and the same servo piston shell, but differ in their servo piston rods, in particular at the connection point to the swashplate.Since, according to the invention, the same hydraulic machine can be converted from an initial configuration with maximum displacement to an initial configuration with minimum displacement by exchanging the servo pistons, the connection points of the servo piston rods to the swashplate must have different distances to the servo piston head, such that the servo piston for maximum displacement preloads the swashplate to the maximum swivel angle in the unactuated state, and the servo preload piston for minimum displacement preloads the swashplate to the minimum swivel angle in the unactuated state.

[0010] In some embodiments of the variable displacement hydraulic machine according to the invention, the same end cap can be used in the same relative orientation and position with respect to the housing, regardless of whether the servo preload piston for maximum displacement or the servo preload piston for minimum displacement is arranged in the servo piston unit. This allows for cost reduction, since identical parts for the end cap and the housing can be used for both types of initial configuration, thereby reducing the number of part variants, at least for these two parts, which are costly to manufacture.

[0011] In some embodiments of the variable displacement hydraulic machine according to the invention, the servo preload piston for maximum displacement or the servo preload piston for minimum displacement has a contact surface configured such that, in an actuated position when the maximum travel of the servo piston is reached, it comes into contact with a stop on the end cap. With such a contact surface for the servo piston rod on the end cap, the maximum confirmation position of the servo piston can be predetermined. This contact surface on the end cap can be located in the same position for both types of initial displacement configuration, since only the position of the connection point of the servo piston with the swashplate on the servo piston rod varies with respect to the distance to the servo piston head and / or the contact area for contacting the corresponding contact surface on the end cap.

[0012] In a further embodiment according to the invention, the size of the swashplate's swivel angle is variably adjustable during operation of the hydraulic machine by applying variable pressure levels to the servo piston head between a minimum and a maximum swivel angle. Thus, the servo piston head, pre-tensioned by a servo piston spring, can be positioned at any point between the initial position (unactuated) and the maximum actuated position by applying variable / controlled servo pressure to the servo piston head, e.g., by means of a control unit that can be actuated in a known manner, e.g., hydraulically, electromechanically, manually, or pneumatically.

[0013] As is evident, at least to a person skilled in the relevant field of technology, the concept according to the invention is not limited to hydraulic machines with unidirectional adjustment, since it is also applicable to hydraulic machines whose swashplate is adjustable in both directions of inclination in order to change the direction of rotation of the hydraulic machine. For example, when the hydraulic machine is in its initial position with maximum displacement, increasing servo pressure tilts the swashplate to smaller pivot angles. However, this tilting movement must not be limited to a position of 0° of the swashplate with respect to the axis of rotation of the hydraulic machine, since the swashplate can also be tilted beyond zero up to "negative" pivot angles. Similarly, an initial configuration with minimum displacement must not have a minimum angle of 0° with respect to the axis of rotation, since this angle can also deviate from zero degrees.

[0014] In some embodiments, a method for assembling a variable displacement hydraulic machine comprises: providing an end cap, wherein the end cap defines an internal volume; determining whether the variable displacement hydraulic machine is to be configured as preset to a maximum displacement level or as preset to a minimum displacement level; selecting a servo preload piston for maximum displacement if the determination step indicates that the variable displacement hydraulic machine is to be configured preset to maximum displacement; and selecting a servo preload piston for minimum displacement if the determination step indicates that the variable displacement hydraulic machine is to be configured preset to minimum displacement.The arrangement of the selected servo preload piston for maximum displacement or the selected servo preload piston for minimum displacement at least partially at a servo piston position within the internal volume, and the connection of the end cap to a housing. BRIEF DESCRIPTION OF THE FIGURES Fig. Figure 1A is a side sectional view of a state-of-the-art variable displacement hydraulic machine configured to be pre-tensioned to a maximum displacement level. Fig. Figure 1B is a side view of the state-of-the-art variable displacement hydraulic machine. Fig. 1A; Fig. Figure 1C is a front view of the state-of-the-art variable displacement hydraulic machine. Fig. 1A; Fig. 2A is a sectional view from the left of the state-of-the-art variable displacement hydraulic machine. Fig. 1A, which, however, is configured to be biased to a minimum displacement level; Fig. 2B is a left side view of the state-of-the-art variable displacement hydraulic machine. Fig. 2A; Fig. 2C is a front view of the state-of-the-art variable displacement hydraulic machine. Fig. 2A; Fig. Figure 3A is a sectional view of the left side of a variable displacement hydraulic machine configured according to the present invention to be pre-tensioned to a maximum displacement level. Fig. 3B is a left-hand sectional view of the variable displacement hydraulic machine made of Fig. 3A, wherein a servo piston was moved into an actuated position. Fig. Figure 4A is a left-hand sectional view of a variable displacement hydraulic machine configured according to the present invention to be pre-tensioned to a minimum displacement level; and Fig. 4B is a left-hand sectional view of the variable displacement hydraulic machine made of Fig. 4A, wherein a servo piston was moved into an actuated position. DETAILED DESCRIPTION

[0015] Before various embodiments are described in detail, it should be noted that the invention is not limited to the embodiments described. It should also be noted that the terminology used serves only to describe certain embodiments and not to limit the scope of the claims of the present application.

[0016] According to the Fig. Figure 1A-1C describes a hydraulic machine 10 with variable displacement according to the prior art, designed to be pre-tensioned to a maximum displacement level. The previously known machine 10 has an end cap 12, a housing 14, and an actuator 16, which has an electrical proportional control element 18 that interacts with a spring 19. The housing 14 defines a first fluid port 20A and a second fluid port 20B.

[0017] The variable displacement hydraulic machine 10 is designed to be biased to a maximum displacement, meaning that an actuating force of the actuator 16 is required to change the displacement level to a lower displacement level, e.g., to a minimum displacement level or an intermediate displacement level. In this arrangement, the electrical proportional control element 18 and the spring 19 are shown extending towards the lower part of the machine 10 (from the perspective of the Fig. 1A-1C), wherein the first terminal 20A is located on the right side of the machine 10 and the second terminal 20B is located on the left side of the machine 10 ( Fig. 1C).

[0018] According to the Fig. 2A-2C is the hydraulic machine 10 with variable displacement known from the prior art. Fig. 1A-1C is shown, but modified so that it is preset to a minimum displacement level. The modification of the prior art machine 10 requires a reversal of the orientation of the actuator 16, such that the electrical proportional control element 18 and the spring 19 run towards a top side of the machine 10 (from the perspective of the Fig. 2A-2C) and the first terminal 20A is located on the left side of machine 10 and the second terminal 20B is located on the right side of machine 10 ( Fig. 2C). The end cap 12 must be rotated to accommodate the reconfiguration of the preload for displacement.

[0019] Referring to the Fig. 3A and Fig. Figure 3B shows a variable displacement hydraulic machine 100, which, according to embodiments of the present invention, is configured to be pre-tensioned to a maximum displacement level. The machine 100 has an end cap 112 defining an internal volume 113, the end cap 112 being connected to a housing 114. The machine 100 has a maximum displacement servo pre-tension piston 122A, which is arranged at a servo piston position within the internal volume 113 of the end cap 112, and a servo piston spring 124, which is arranged to pre-tension the maximum displacement servo pre-tension piston 122A to a position defined in Fig. Figure 3A shows that in the maximum displacement position, the servo preload piston 122A causes a swashplate 123, connected to the servo piston rod 129 at a swashplate connection point 125, to move into a maximum displacement position in which the machine 100 dispenses a maximum amount of fluid per stroke. The maximum amount of fluid per stroke can be determined by the maximum tilt angle of the swashplate, thus setting the upper limit for the fluid output of the machine 100 per stroke.

[0020] The servo preload piston for maximum displacement 122A has a contact surface 126A designed to abut a bearing surface 128 of the end cap 112. When the contact surface 126A of the servo preload piston for maximum displacement 122A abuts the bearing surface 128 (see Fig. The displacement element of machine 100 (e.g., the swashplate) moves into a position of minimum displacement, in which machine 100 dispenses a minimal amount of fluid per stroke. Machine 100 is designed such that an actuating force moves the servo preload piston for maximum displacement 122A into the position indicated in Fig. The servo piston is moved to the position shown in Figure 3B or to any position in between. In a preferred embodiment, the actuating force is a servo pressure acting on the servo piston head 127, which is biased into its initial position by means of the servo piston spring 124. When the actuating force on the servo piston head exceeds the bias force of the servo piston spring 124, the servo piston is moved towards the stop surface 128, which is located inside 113 of the end cap 112. This also moves the connection point 125 on the servo piston rod 129 towards the stop surface 128 and tilts the swashplate 123 to smaller pivot angles.

[0021] With reference to the Fig. 4A and Fig. 4B is the hydraulic machine 100 with variable displacement from the Fig. 3A and Fig. 3B is shown, but designed such that it is pre-tensioned to a minimum displacement level according to embodiments of the present invention. The machine 100 is identical to the machine 100 from the Fig. 3A and Fig. 3B, except that at the servo piston position, the servo preload piston 122A for maximum displacement is replaced by a servo preload piston for minimum displacement 122B. The servo piston spring 124 is arranged to preload the servo preload piston for minimum displacement 122B into a minimum displacement position, which is in Fig. As shown in Figure 4A. In the minimum displacement position, the minimum displacement servo preload piston 122B causes the displacement element of the machine 100, for example a swashplate, to move into a minimum displacement position in which the machine 100 delivers a minimum amount of fluid per stroke. A minimum amount of fluid per stroke can also include zero delivery of fluid per stroke.

[0022] The servo preload piston for minimum displacement 122B has a contact surface 126B designed to contact a bearing surface 128 of the end cap 112. When the contact surface 126B of the servo piston 122B for minimum displacement contacts the bearing surface 128 (see Fig. 4B), the displacement element of the machine 100 (e.g., the swashplate) moves into a position of maximum displacement, in which the machine 100 dispenses a maximum amount of fluid per stroke. The machine 100 is designed such that an actuating force moves the servo preload piston for minimum displacement 122B into the position shown in Fig. 4B can move to the position shown or to any position in between.

[0023] The same end cap 112 defines the internal volume 113 such that the internal volume 113 is designed to accommodate the servo preload piston 122A for maximum displacement and the servo preload piston for minimum displacement. It should be noted that the end cap 112 is suitable for accommodating both piston 122A and piston 122B, but this does not mean that the end cap 112 accommodates or arranges both pistons 122A and 122B simultaneously. Rather, the end cap 112 is suitable for accommodating or arranging both pistons 122A and 122B in such a way that the pistons 122A and 122B are interchangeable within the end cap 112 to effect a change in the preload configuration of the machine 100 with respect to displacement.

[0024] The end cap 112 has the same relative orientation with respect to the housing 114, regardless of whether the machine 100 is configured for a preload with maximum displacement, as in the Fig. 3A and Fig. 3B shown, or for a preload with minimal displacement, as in the Fig. 4A and Fig. 4B shown. In other words, no rotation of the end cap 112 is required to change the preload for the displacement level of the machine 100, as is the case with the machine 10 according to the prior art in the Fig. 1A-2C is required. After connecting the end cap 112 to the housing 114, the relative orientation and position of the end cap 112 with respect to the housing 114 is the same, regardless of whether the servo preload piston 122A for maximum displacement or the servo preload piston 122B for minimum displacement is selected and is located at the servo piston position within the inner volume 113 of the end cap 112.

[0025] While the in the Fig. The hydraulic machines 100 shown are used as motors; the principles of preload for displacement are equally applicable to pump devices. Fig. Figures 3A-4B also show that the two illustrated housings 114 and end caps 113 of the respective hydraulic machines are identical parts and that the initial displacement configuration - maximum or minimum initial displacement preload - is achieved either by using a preload piston 122A for maximum displacement ( Fig. 3A and Fig. 3B) or a preload piston 122B for minimal displacement ( Fig. 4A & 4B) is reached.

[0026] Further comparison of the two different initial displacement configurations reveals the following: Fig. 3A and Fig.3B recognize that the swashplate connection point 125A on the preload piston 122A for maximum displacement is closer to the servo piston head than on the preload piston 122B for minimum displacement, where the swashplate connection point 125B is closer to the contact surface 126B.

[0027] The range of motion of the displacement element in variable displacement hydraulic machines can be virtually any range required or desired for the specific application. For example, and without limitation, the range of motion for the configuration preset to the maximum displacement value can be a swashplate angle of 18° when no pressure is applied (i.e., without actuation by a force) and a swashplate angle of 0° when pressure is applied; conversely, for the configuration preset to the minimum displacement value, a swashplate angle of 0° when no pressure is applied and a swashplate angle of 18° when pressure is applied.

[0028] Advantageously, the variable displacement hydraulic machines and methods for assembling variable displacement hydraulic machines according to the invention offer advantages to both the customers / users of the machines and the manufacturers of the machines. For example, customers / users of the machines do not notice any difference in the external mounting (or housing) of the machine, since the same housing and / or end cap can be used for a machine preloaded for minimum displacement and a machine preloaded for maximum displacement. Thus, a customer / user does not have to consider different sizes and / or shapes due to the selected preload state of the variable displacement hydraulic machine. Furthermore, the customer does not have to consider different connection positions, since the connection positions are identical regardless of the selected preload state.Furthermore, if required, the customer / user can change the preload state of the variable displacement hydraulic machine by replacing a single part, thereby reducing complexity and cost as important factors in deciding whether or not to change the preload state of the machine.

[0029] Manufacturers can reduce costs and complexity by producing variable-displacement hydraulic machines and applying the assembly methods described in the present invention. Manufacturers may only need to change a single part in the manufacturing process depending on whether the customer orders a machine with minimum preload or maximum preload. The manufacturer does not need to stock and select different housing and / or end cap designs to accommodate the different preload configurations. Furthermore, the manufacturer achieves cost savings because the assembly methods for the different preload states of the machines are virtually identical, differing only in the selection of a single different part.Furthermore, manufacturers can use the same assembly tools for both configurations, which also leads to a reduction in costs and complexity.

[0030] While one of the advantages of the variable displacement hydraulic machines and assembly method described in the present invention is that only a single part needs to be replaced (namely the servo piston 122A, 122B), it is also within the scope of the present invention that other parts can be exchanged or replaced if necessary or desired. For example, in some embodiments, in addition to replacing the servo piston 122A, 122B, a swashplate of the machine can be replaced or modified.

[0031] As is known to those skilled in the art, numerous modifications and adaptations of the embodiments of the present invention described above can be made without deviating from the basic concept of the invention as defined in the appended claims. Accordingly, the described embodiments are to be understood merely as examples and not as limitations. REFERENCE MARK LIST 10 hydraulic machine 12 End cap 14 cases 16 Actuator 18 Control element 19 springs 20A First connection 20B Second connection 100 hydraulic machines 112 End cap 113 internal volume 114 cases 120 servo unit 122A Servo preload piston for maximum displacement 122B Servo preload piston for minimal displacement 123 Slanted disc 124 Servo piston spring 125A, 125B Swashplate connection point 126A, 126B Contact surface 127 Servo piston head 128 site area 129 Servo piston rod

Claims

Hydraulic machine (100) with variable displacement of swashplate design, comprising: • a housing (114); and • an end cap (112) connected to the housing (114), wherein the end cap (112) defines an internal volume (113); and • a servo unit (120) which is arranged at least partially within the internal volume (113), wherein a servo piston (122A) for maximum displacement or a servo preload piston for minimum displacement (122B) is arranged, the servo piston head (127) of which is preloaded in an unloaded state by means of a servo piston spring (124) against a stop (115) on the housing (114) or on the end cap (112); • a swashplate (123) which is pivotable from a maximum to a minimum pivot angle and vice versa by means of a servo piston rod (129) of one of the two preload servo pistons (112A or 122B);wherein the swashplate (123) is biased in its initial position in the direction of a maximum swivel angle when the servo bias piston for maximum displacement (122A) is arranged in the servo unit (120); and wherein the swashplate (123) is biased in its initial position in the direction of a minimum swivel angle when the servo bias piston for minimum displacement (122B) is arranged in the servo unit (120). Hydraulic machine with variable displacement according to claim 1, wherein the hydraulic machine with variable displacement (100) is a motor or a pump. Hydraulic machine with variable displacement according to one of claims 1 or 2, wherein the servo preload piston (122A) for maximum displacement and the servo preload piston (122B) for minimum displacement differ from each other with respect to a distance between the servo piston head (127) and the respective connection point to the swashplate (125A or 125B) on the servo piston rod (129) for tilting the swashplate (123). Hydraulic machine with variable displacement according to one of claims 1 to 3, wherein the servo preload piston (122A) for maximum displacement or the servo preload piston (122B) for minimum displacement has a contact surface (126A, 126B) which is designed such that it abuts a contact surface (128A, 128B) of the end cap (112) in an actuated position. Hydraulic machine with variable displacement according to one of claims 1 to 4, wherein the same end cap (112) can be used in the same relative orientation and position with respect to the housing (114), regardless of whether the servo preload piston (122A) for maximum displacement or the servo preload piston (122B) for minimum displacement is arranged in the servo piston unit (120). Hydraulic machine with variable displacement according to one of claims 1 to 5, which further comprises a first connection point and a second connection point, wherein the first connection point and the second connection point are identical, regardless of whether the servo piston (122A) for maximum displacement or the servo preload piston for minimum displacement is arranged on the servo piston unit (120). Hydraulic machine with variable displacement according to one of claims 1 to 6, wherein the swashplate (130) in the position with maximum displacement forms a pivot angle of less than 45° to the axis of rotation of the hydraulic machine with variable displacement (100). Hydraulic machine with variable displacement according to one of claims 1 to 7, wherein the swashplate (123) in the position with minimum displacement forms an angle of 0° to the axis of rotation of the hydraulic machine with variable displacement (100). Hydraulic machine with variable displacement according to one of claims 1 to 8, wherein during operation of the hydraulic machine the size of the swivel angle of the swashplate (123) is variably adjustable by applying variable pressure levels to the servo piston head (127) between a minimum and a maximum swivel angle. Hydraulic machine with variable displacement according to one of claims 1 to 9, wherein, when the servo preload piston for maximum displacement (122A) is arranged on the servo piston unit (120), the hydraulic machine can be pivoted from 0° to a negative swivel angle during operation of the hydraulic machine. Hydraulic machine with variable displacement according to one of claims 1 to 10, wherein when the servo piston (122B) is positioned on the servo piston unit (120) for servo preload for minimum displacement, the minimum swivel angle of the swashplate (123) in the initial preload position deviates from 0°. Hydraulic machine with variable displacement according to claim 9, wherein the pressure on the servo piston head (127) is transmitted by a manually, electrically, magnetoelectrically, hydraulically or pneumatically actuated control unit. Hydraulic transmission with at least one hydraulic machine with variable displacement according to one of claims 1 to 12, which is arranged in an open or closed hydraulic circuit.

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