Variable displacement hydraulic motor

Abstract

The utility model relates to a variable displacement hydraulic motor. In one example, a hydraulic motor includes a swash plate having a tilt angle, a plurality of piston assemblies configured to rotate about a drive shaft. In the motor, each piston assembly includes an inner piston slidably coupled to an outer piston cooperating with a cylinder in a cylinder block, and a retention device configured to inhibit axial movement of the outer piston in a first position and to allow axial movement of the outer piston in a second position.

Description

Technical Field

[0001] The present invention relates to a variable displacement motor and a method for operating a hydraulic motor. Background Art

[0002] Previous variable displacement motors relied on a variable angle swash plate to vary the motor displacement. These motors include a drive shaft connected to a cylinder block containing pistons. The pistons interact with a swash plate that is angled relative to the piston block to drive the reciprocating motion of the pistons in the cylinders. The angle of the swash plate is adjusted to vary the displacement of the motor. Thus, for example, the displacement of the motor can be adjusted to match the operating conditions of the system in which it is deployed and to improve motor efficiency. Some motors utilize bushings to allow for adjustment of the angle of the swash plate.

[0003] US2019 / 0112926 A1 of Hemink discloses an axial piston machine (e.g., a pump or motor) having an adjustable displacement function in one embodiment. To change the displacement of the machine, a variable displacement assembly is used to rotate a swash plate to change the reciprocating displacement of the piston. The variable displacement assembly includes a swash plate and a piston and spring assembly designed to control the tilt of a wobble plate coupled to an inclined collar.

[0004] The inventors have recognized several problems with the Hemink machine, as well as other previous variable displacement motors and pumps. For example, the variable displacement components of the Hemink may be susceptible to wear and eventually deterioration. Thus, the useful life of the machine is shortened, requiring shorter maintenance intervals. Bushings used in other motors and pumps may also be susceptible to wear and deterioration, thereby affecting the reliability of the device. Utility Model Content

[0005] Faced with the above problems, the inventors have developed a variable displacement hydraulic motor to overcome at least some of the problems. In one example, the hydraulic motor includes a swash plate having an inclination angle (e.g., a fixed inclination angle). The hydraulic motor also includes a plurality of piston assemblies configured to rotate about a drive shaft. Each piston assembly includes an inner piston slidably coupled to an outer piston and a retaining device, the outer piston cooperates with a cylinder in a cylinder block, and the retaining device is configured to inhibit the axial movement of the outer piston in a first position and allow the axial movement of the outer piston in a second position. In this way, the displacement of the motor can be reliably changed using the piston in the piston assembly, which is less prone to wear and degradation than previous variable displacement mechanisms. Therefore, the service life and customization appeal of the motor are improved. In addition, the motor with the retaining device can achieve less complexity than a variable angle swash plate machine. In addition, when compared with an adjustable swash plate motor, the above hydraulic motor allows the motor to achieve higher efficiency, and the adjustable swash plate motor experiences reduced efficiency when operating in a reduced swash plate angle mode. In addition, if desired, the use of a fixing device to adjust the displacement of the motor allows the axial length of the motor to be reduced compared to a variable angle swash plate.

[0006] Furthermore, in one example, the retaining device may include a radially alignable pin. The pin may be hydraulically actuated such that the pin extends and retracts based on hydraulic line pressure. Extension of the pin axially limits movement of the outer piston, and retraction of the pin allows the outer piston and the inner piston to reciprocate axially in unison. In this way, the retaining device may reliably vary the displacement of the motor. Thus, the motor may be operated more efficiently over a wide range of operating conditions using a mechanism that is less susceptible to wear and eventual operational degradation.

[0007] In another example, the retaining device may include an axially displaceable body including a radial extension that axially confines the outer piston in the retracted position and allows reciprocating movement of the outer piston in the extended position. In this way, the retaining device is configured for axial actuation, thereby enabling the device to be effectively incorporated into the housing of the motor if desired.

[0008] It should be understood that the above utility model summary is provided to introduce a selection of concepts further described in the detailed description in a simplified form. It is not meant to identify key or essential features of the claimed subject matter, and the scope of the claimed subject matter is uniquely defined by the claims following the detailed description. In addition, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1A and Figure 1B A first example of a variable displacement hydraulic motor in a system is shown.

[0010] Figure 2 Shows Figure 1B A cross-sectional view of a hydraulic motor is depicted in FIG.

[0011] Figure 3A and Figure 3B A second example of a variable displacement hydraulic motor is shown.

[0012] Figure 4A and Figure 4B A third example of a variable displacement hydraulic motor is shown.

[0013] Figure 5 A method for operating a variable displacement hydraulic motor is shown. DETAILED DESCRIPTION

[0014] A variable displacement hydraulic motor is described herein, which achieves higher reliability and efficiency and reduced complexity compared to motors using adjustable angle swash plates. In order to achieve improved reliability and efficiency, the motor is provided with piston assemblies, each of which has an inner piston and an outer piston. The axial movement of the outer piston is activated and deactivated to switch the motor between a reduced displacement configuration and a full displacement configuration. In order to achieve this motor displacement change function, the motor includes a retaining device (e.g., a hydraulic retaining device), which can take the form of a hydraulically actuated pin that extends and retracts in a radial direction. In the extended position, the pin axially restricts the movement of the outer piston, and in the retracted position, the inner piston and the outer piston reciprocate axially in series. In other examples, the retaining device may include an axially translatable body, the body including an extension, which axially defines the outer piston in a partial displacement configuration. In this way, the displacement of the motor can be reliably changed. In one example, the swash plate can have a fixed position. In this way, the reliability of the motor can be further improved and the complexity can be further reduced compared to previous adjustable displacement machines. Furthermore, the use of a retaining device to vary the displacement of the motor allows the axial length of the motor to be shortened, if desired, compared to motors using an adjustable angle swash plate.

[0015] Figure 1A and Figure 1B A first example of a variable displacement hydraulic motor is shown in a full displacement configuration and a partial displacement configuration indicated by a pin retaining arrangement. Figure 2 Shows Figure 1B A cross-sectional view of a hydraulic motor shown in FIG. 1 , in a partial displacement configuration with a pin extending and axially restricting movement of the outer piston. Figure 3A and Figure 3B Another example of a variable displacement hydraulic motor is shown having different hydraulic paths for a retaining device to facilitate motor displacement adjustment. Figure 4A and Figure 4BYet another example of a variable displacement hydraulic motor having a retaining device including an axially translatable body and an extension that also selectively axially constrains movement of an outer piston is shown. Figure 5 A method for regulating the displacement of a hydraulic motor is shown.

[0016] Figure 1A A variable displacement hydraulic motor 100 (eg, a multi-speed hydraulic motor) is shown in a system 102. The motor 100 may be deployed in a variety of systems including, but not limited to, transmissions (eg, hydromechanical transmissions), industrial systems, and the like.

[0017] The variable displacement hydraulic motor 100 includes a swash plate 104 and a drive shaft 106 having an input interface 108. Bearings (e.g., ball bearings, roller bearings, tapered roller bearings, etc.) may be coupled to the drive shaft 106 and enable the drive shaft to rotate and support. The input interface 108 serves as a mechanical coupling to an upstream component. For example, in one use case example, the input interface 108 may be coupled to a mechanical branch in a hydromechanical transmission. However, in other examples, the motor 100 may be rotationally coupled to a variety of suitable components.

[0018] The drive shaft 106 rotates about an axis 110 during operation of the motor. Figure 1B as well as Figure 2 , Figure 3A , Figure 3B , Figure 4A and Figure 4B Axis 110 is additionally shown in the figure for reference. In addition, the swash plate 104 is arranged to be inclined at an angle 112 relative to the axis 110. In the example shown, the inclination angle 112 is fixed. In one example, the inclination angle can be between 16 degrees and 20 degrees, and in one use case example can specifically be 18 degrees. Therefore, the swash plate inclination angle remains constant in various operating modes of the motor. Compared to motors that use bushings and / or other components that are prone to degradation to change the angle of the swash plate, the use of a fixed angle swash plate allows for increased reliability of the motor. Therefore, the service life of the motor is extended. However, in other examples, other suitable inclination angles may be used.

[0019] The motor 100 also includes a cylinder block 114 having a plurality of cylinders 116. The piston assemblies 118 are designed to reciprocate axially within the cylinders and cooperate therewith. Therefore, each cylinder 116 has an inner diameter 120 that is larger than the outer diameter 122 of the associated piston assembly 118.

[0020] The piston assembly 118 is rotationally coupled to the drive shaft 106 and thus rotates in response to the rotation of the drive shaft. The piston assembly 118 includes a sliding member 124 that shares contact with a surface 126 of the swash plate 104. The sliding member 124 is attached to the inner piston 128 via a joint 130 (e.g., a ball joint). The piston assembly 118 also includes an outer piston 132. Each outer piston circumferentially surrounds and cooperates with a corresponding inner piston. Therefore, the cross-section of the outer piston is annular and includes a central opening. The size of the inner piston and the outer piston can be selected based on the partial displacement and full displacement target values ​​before manufacturing. For example, the geometric area of ​​the inner piston and the outer piston can be selected based on the expected final use operating environment of the pump.

[0021] An interface 134 is formed between the inner piston 128 and the outer piston 132. One or more materials used to construct the inner and outer pistons can be selected based on a trade-off between two operating conditions of the pistons ((i) reciprocating in unison, and (ii) causing the inner piston to reciprocate within the outer piston while the axial movement of the outer piston is constrained (e.g., inhibited)). For example, when the outer piston is axially restrained, a reduction in the amount of friction between the inner and outer pistons may be desirable. However, when the pistons move in unison, increased friction may be desired. In one example, the inner and outer pistons may be constructed of nitrided steel to reduce friction and increase mechanical properties. However, in other examples, the pistons may be constructed of additional or alternative suitable materials.

[0022] In the partial displacement mode, the inner piston 128 reciprocates axially independently of the axially restrained outer piston 132. The axial restraint of the outer piston 132 is extended herein. In contrast, in the full displacement mode, the inner piston 128 and the outer piston 132 reciprocate axially in unison within the cylinder.

[0023] The hydraulic motor 100 also includes a retaining device 136 corresponding to each piston assembly. In the example shown, the retaining device 136 is a hydraulically actuated pin device 138 that extends and retracts (e.g., radially extends and retracts) a pin 140 based on fluid pressure (e.g., oil pressure) in a hydraulic line 142. The working fluid in the hydraulic motor may be oil (e.g., natural oil or synthetic oil). The pin 140 may be radially aligned so that the outer piston can be securely retained.

[0024] The pin arrangement 138 comprises a pin 140, a spring 144 and an actuation chamber 146. The pins 140 are shown in a retracted position such that they do not interact with the outer piston 132 to axially constrain the piston.

[0025] The use of a retaining device and piston assembly to vary the displacement of the motor enables the motor to achieve higher efficiency and lower complexity than a variable angle swash plate machine. In addition, the use of a retaining device and piston assembly also allows the axial length of the motor to be shortened, if desired, compared to a machine with an adjustable angle swash plate.

[0026] In the example shown, the hydraulic line 142 is directed through the cylinder block 114 and the valve plate 152 in some examples. To elaborate, multiple conduits can be used to direct the fluid to the retaining device 136. At least a portion of these conduits can be pressurized in one example, or can be non-pressurized in another example. Since the hydraulic line may only allow fluid to pass during certain conditions, this internal hydraulic line guidance may require hydrostatic pressure balancing on the valve plate. If desired, arranging the hydraulic lines in this manner allows the size design of the motor to be relatively unaffected, but may require increased manufacturing complexity. However, in other examples, the hydraulic lines may be directed to the retaining device via the housing.

[0027] One or more valves 148 may be connected to the hydraulic line 142 to allow for regulation of pressure in the hydraulic line. Additionally, a pump and / or other hydraulic circuit may be in fluid communication with the valve.

[0028] In the example shown, the hydraulic motor 100 also includes a housing 150 and a valve plate 152. The valve plate 152 may include an inlet valve 154 and an outlet valve 156 ( Figure 1A ), which can be hydraulically coupled to upstream and downstream system components, respectively. The hydraulic actuator 100 can further include a cylinder spring 158.

[0029] The hydraulic motor 100 is shown as a two-speed motor. However, in alternative examples, the motor can be designed to have three or more speeds. In these examples, additional inner pistons can be added to the piston assembly to achieve greater displacement adjustment granularity.

[0030] The system 102 may also include a controller 190 (eg, a transmission control unit (TCU)), such as Figure 1A As shown. The controller 190 may include a microcomputer having components such as a processor 192 (e.g., a microprocessor unit), input / output ports, and an electronic storage medium 194 (e.g., a read-only memory chip, a random access memory, a keep-alive memory, a data bus) for executable programs and calibration values. The storage medium may be programmed with computer-readable data representing instructions that are executable by the processor to perform the methods and control techniques described herein, as well as other variations that are anticipated but not specifically listed. In this way, the control techniques, methods, etc. expanded herein may be stored as instructions in a non-transitory memory.

[0031] The controller 190 may receive various signals from sensors 195 coupled to various areas of the system 102. For example, the sensors 195 may include a pedal position sensor designed to detect depression of an operator-actuated pedal such as an accelerator pedal and / or a brake pedal, one or more speed sensors at the transmission input and output shafts, a clutch position sensor, etc. Input devices 198 (e.g., an accelerator pedal, a brake pedal, a drive mode selector, a gear selector 199, combinations of these, etc.) may further provide input signals indicative of operator intent for system control.

[0032] Upon receiving Figure 1A When the controller 190 receives signals from various sensors 195, the controller 190 processes the received signals and uses various actuators 196 of the system components to adjust the components based on the received signals and the instructions stored on the memory of the controller 190. For example, the controller 190 can be designed to change the displacement of the hydraulic motor 100. For example, when the controller 190 determines that the displacement of the motor should be adjusted via operator input and / or based on system operating conditions. In response to this determination, the controller 190 can adjust the valve 148, pump and / or other hydraulic regulating device connected to the pipeline 142 to change the pressure in the pipeline, thereby adjusting the state of the holding device 136. For example, the pressure in the hydraulic pipeline 142 can be increased to extend the pin 140 and the pressure in the hydraulic pipeline 142 can be reduced to retract the pin. However, in other examples, the holding device can be electromechanically actuated via a solenoid actuator. For example, other controllable components in the system can function in a similar manner in terms of sensor signals, control commands and actuator adjustments.

[0033] exist Figure 1A and 1B, Figure 2 , Figure 3A , Figure 3B , Figure 4A and Figure 4B A coordinate system is provided for reference in . In one example, the z-axis can be a vertical axis (e.g., parallel to the gravity axis), the x-axis can be a lateral axis (e.g., a horizontal axis), and / or the y-axis can be a longitudinal axis. However, in other examples, these axes can have other orientations.

[0034] exist Figure 1A In the hydraulic motor configuration shown, inner piston 128 and outer piston 132 reciprocate in unison in the cylinder during motor operation. This configuration may be referred to as a full displacement configuration, in which the pistons displace a greater amount of fluid than a partial displacement configuration, as described herein.

[0035] Figure 1BThe hydraulic motor 100 is shown in a partial displacement configuration, wherein the pin 140 in the retaining device 136 extends into the cylinder 116 so as to axially limit (e.g., inhibit) the movement of the outer piston 132. Therefore, the side surface 160 of the pin 140 is in contact with or adjacent to the axial end 162 of the outer cylinder. In addition, in the partial displacement configuration, the axial end 164 of the outer piston 132 is adjacent to the end wall 166 of the cylinder. In this way, the inner piston 128 reciprocates within the outer piston that is held substantially axially stationary. Arrow 168 indicates the reciprocating motion of the inner piston 128. As shown, the axial length of the pin 140 is selected to avoid contact with the flange 170 of the inner piston 128 near the joint 130. Figure 1B The cutting plane 2-2 shown in FIG. Figure 2 Cross-sectional view shown.

[0036] Figure 2 A cross-sectional view of the variable displacement hydraulic motor 100 is shown. The inner piston 128 and the outer piston 132 in the piston assembly 118 and the retaining device 136 are shown again, with the pin 140 in its extended position, which prevents axial movement of the outer piston 132. Figure 2 Also shown in FIG. 1 is a spring 144 in the retaining device 136 .

[0037] Figure 3A and Figure 3B Another example of a variable displacement hydraulic motor 300 is shown in full displacement configuration and partial displacement configuration, respectively. The hydraulic motor 300 includes Figure 1A and 1B The hydraulic motors 100 shown in FIG. 1 overlap several structural and functional features. Therefore, for the sake of brevity, redundant descriptions of these shared features are omitted.

[0038] Figure 3A and Figure 3B Specifically shown is a hydraulic line 302 that provides hydraulic actuation for a retaining device 304 that is routed through a housing 305. To elaborate, the hydraulic line 302 may feed a retaining device 304 (e.g., a control pin) for the outer piston via a contact (e.g., a hydraulic interface) between the housing 305 and the cylinder block 307. However, as previously described, the hydraulic line may be routed internally through the cylinder block and / or the valve plate 306.

[0039] Figure 4A and Figure 4B Another example of a variable displacement hydraulic motor 400 is shown in a full displacement configuration and a partial displacement configuration. The hydraulic motor 400 includes Figure 1A and 1B The hydraulic motors 100 shown in FIG. 1 overlap many structural and functional features. Therefore, for the sake of brevity, redundant descriptions of these shared features are omitted.

[0040] Figure 4A and Figure 4B The retaining device 402 shown in FIG. 4 includes a body 404 designed to translate axially within a chamber 406 of a housing 408. A seal 409 is provided at the interface of the chamber 406 and the body 404 to enable a fluid to be contained in the chamber and pressurized to allow for actuation of the device. In addition, a hydraulic line 411 extends through the housing and opens into the chamber to enable hydraulic actuation of the retaining device. A valve, pump, etc. may be coupled to the hydraulic line to enable hydraulic actuation of the retaining device.

[0041] The extension 410 is connected to the end of the body 404. Figure 4A In the axially retracted position shown, the extension 410 serves to axially confine the outer piston 412. In one example, the extension 410 can be radially aligned and arranged substantially perpendicular to the body 404. Conversely, when the body 404 is in the Figure 4B In the extended position shown, when the motor is operated, the outer piston 412 can move in unison with the inner piston 414. In this way, different mechanisms can be provided to retain the outer piston to adjust the motor displacement. Figure 4A and Figure 4B The geometry of the displacement adjustment mechanism in uses retaining devices that can be external to the cylinder block 415 to anchor the outer piston. In addition, in different examples, these retaining devices can be hydraulically fed from lines leading through the cylinder block or from the housing to the cylinder block. In one specific example, a single pressurized line can be used to feed each retaining device, thereby simplifying the design of the system and therefore simplifying manufacturing.

[0042] Figure 5 A method 500 for operating a variable displacement hydraulic motor is shown. In one example, the method 500 may be performed by Figures 1A-4B The method 500 may be implemented by any of the hydraulic motors or combinations of motors described. In other examples, the method may be implemented by other suitable variable displacement hydraulic motors. In addition, as previously described, the method 500 may be implemented by a controller including a memory storing instructions for method steps executable by a processor, as previously indicated.

[0043] Figure 5 The method 500 shown in FIG. 5 includes determining operating conditions at 502. The operating conditions may include the position of an input device (e.g., the position of a shift lever), clutch configuration, accelerator pedal position, transmission input / output speed, motor speed, vehicle speed, vehicle load, ambient temperature, etc. The operating conditions may be determined via sensor input, modeling, lookup tables, and / or other suitable techniques.

[0044] Next at 504, the method includes determining whether the displacement of the motor should be adjusted. The determination may take into account system operating conditions, such as motor efficiency, target motor output oil flow, etc. For example, when the motor efficiency drops below a threshold or rises above a threshold, the displacement of the motor may be adjusted. However, other techniques for determining when to switch the displacement of the motor have been contemplated.

[0045] If it is determined that the displacement of the motor should not be adjusted (“NO” at 504 ), the method moves to 506 where the method includes maintaining the current displacement of the motor. For example, the motor may remain in a full displacement configuration or a partial displacement configuration.

[0046] Conversely, if it is determined that the displacement of the motor should be adjusted ("yes" at 504), the method moves to 508 where the method includes performing a motor displacement adjustment, which may include step 510 or step 512. At 510, the method includes transitioning the retaining device to a position that axially confines the outer piston. Conversely, at 512, the method includes transitioning the retaining device to a position that allows movement of the outer piston.

[0047] The technical effect of the hydraulic motor operation method described herein is to improve motor reliability while achieving a displacement adjustment function. In this way, the displacement of the motor can be adjusted to more appropriately adapt to operating conditions using a mechanism that is less prone to degradation than previous displacement adjustment mechanisms.

[0048] Figure 1A , 1B, 2, 3A, 3B, 4A and 4B show example configurations with relative positioning of various components. If shown as directly contacting or directly connecting each other, such elements can be respectively referred to as directly contacting or directly connecting in at least one example. Similarly, in at least one example, elements shown as continuous or adjacent to each other can be respectively continuous or adjacent to each other. As an example, components placed as face-shared contact with each other can be referred to as face-shared contact. As another example, in at least one example, elements positioned to be spaced apart from each other, with only spacing space between them and without other components can be referred to as such. As another example, elements shown as above / below each other, on opposite sides or on the left / right of each other can be referred to as such relative to each other. In addition, as shown in the accompanying drawings, in at least one example, the topmost element or the point position of the element can be referred to as the "top" of the component, and the bottommost element or the point position of the element can be referred to as the "bottom" of the component. As used herein, top / bottom, upper / lower, above / below can be relative to the vertical axis of the accompanying drawings and used to describe the positioning of the elements of the accompanying drawings relative to each other. Therefore, in one example, the element shown as above other elements is positioned vertically above the other elements. As another example, the shape of the element depicted in the accompanying drawings may be referred to as having such a shape (e.g., such as circular, straight, planar, curved, blunt, chamfered, angled, etc.). In addition, in one example, elements coaxial with each other may be referred to as such. In addition, in at least one example, elements shown as intersecting with each other may be referred to as intersecting elements or intersecting with each other. Further, in one example, elements shown as being in another element or outside another element may be referred to as such. In other examples, elements offset from each other may be referred to as such. Further, elements coaxial or parallel to another element may be referred to as such. Further, the axis about which the part rotates may be referred to as the axis of rotation.

[0049] The utility model will be further described in the following paragraphs. In one aspect, a variable displacement hydraulic motor is provided, which includes a swash plate having an inclined angle; a plurality of piston assemblies configured to rotate about a drive shaft; wherein each of the plurality of piston assemblies includes: an inner piston slidably coupled to an outer piston and a retaining device, the outer piston cooperates with a cylinder in a cylinder block, the retaining device being configured to inhibit axial movement of the outer piston in a first position and to allow axial movement of the outer piston in a second position.

[0050] On the other hand, a method for operating a variable displacement hydraulic motor is provided, which includes selectively adjusting the displacement of the variable displacement hydraulic motor by adjusting a hydraulic holding device; wherein the hydraulic holding device is configured to: in a first position, limit axial movement of an outer piston in a piston assembly including an inner piston; and in a second position, allow simultaneous axial movement of the outer piston and the inner piston.

[0051] On the other hand, a multi-speed hydraulic motor is provided, which includes a swash plate having a fixed tilt angle; a plurality of piston assemblies configured to rotate about a drive shaft; wherein each of the plurality of piston assemblies includes: an inner piston slidably connected to an outer piston, the outer piston cooperating with a cylinder in a cylinder block; and a hydraulic retaining device, which limits the axial displacement of the outer piston in a reduced displacement configuration and allows full axial displacement of the outer piston in a full displacement configuration.

[0052] In any of these aspects or combinations of these aspects, the tilt angle can be fixed.

[0053] In any of these aspects or combinations of these aspects, the retaining device may include a pin.

[0054] In any of these aspects or combinations of these aspects, the pins can be radially aligned.

[0055] In any of these aspects or combinations of these aspects, the hydraulic motor may further include a hydraulic line in fluid communication with the retaining device.

[0056] In any of these aspects or combinations of these aspects, the hydraulic line may extend through the housing.

[0057] In any of these aspects or combinations of these aspects, the hydraulic line may extend through the valve plate.

[0058] In any of these aspects or combinations of these aspects, the retaining device may include an axially displaceable body including a radial extension that axially confines the outer piston in the retracted position.

[0059] In any of these aspects or combinations of these aspects, the hydraulic motor may further include a controller including instructions that, when executed by the controller, cause the controller to: transition the retaining device between the first position and the second position.

[0060] In any of these aspects or combinations of these aspects, the controller may be a transmission control unit in a hydromechanical transmission.

[0061] In any of these aspects or combinations of these aspects, selectively adjusting the displacement of the variable displacement hydraulic motor can include moving or maintaining the hydraulic holding device to the second position during the second operating condition.

[0062] In any of these aspects or combinations of these aspects, adjusting the hydraulic holding device may include increasing a pressure of a hydraulic fluid in a hydraulic line coupled to the hydraulic holding device to transition the hydraulic holding device between the first position and the second position.

[0063] In any of these aspects or combinations of these aspects, the hydraulic retaining device may include radially aligned pins that extend and retract.

[0064] In any of these aspects or combinations of these aspects, the inner piston can be coupled to a slider that shares contact with the swash plate surface.

[0065] In any of these aspects or combinations of these aspects, the hydraulic motor may further include a hydraulic line that is led through the housing or the valve plate and is coupled to the hydraulic holding device.

[0066] In any of these aspects or combinations of these aspects, the multi-speed hydraulic motor can be a two-speed hydraulic motor.

[0067] In any of these aspects or combinations of these aspects, the inner piston and the outer piston can be constructed of nitrided steel.

[0068] In another formulation, a two-speed hydraulic machine is provided that includes an adjustable volume piston disposed in a cylinder block and designed to vary the displacement of the hydraulic machine.

[0069] It should be noted that the example control and estimation routines included herein can be used with various system (e.g., transmission) configurations. The control methods and routines disclosed herein can be stored in non-transitory memory as executable instructions and can be executed by a control system including a controller combined with various sensors and actuators, and other system hardware combined with an electronic controller. Therefore, the actions, operations and / or functions described can graphically represent the code in the non-transitory memory of a computer-readable storage medium that will be programmed into the vehicle and / or powertrain control system. The various actions, operations and / or functions shown can be performed in the order shown, in parallel, or omitted in some cases. Similarly, the processing order for implementing the features and advantages of the examples described herein is not necessary, but is provided for ease of illustration and description. Depending on the specific strategy used, one or more of the actions, operations and / or functions shown can be repeatedly performed. If desired, one or more method steps described herein can be omitted.

[0070] Although various embodiments have been described above, it should be understood that they are presented as examples rather than limitations. It will be apparent to those skilled in the relevant art that the disclosed subject matter may be implemented in other specific forms without departing from the spirit of the subject matter. Therefore, the above embodiments are considered to be illustrative and not restrictive in all respects. Therefore, the configurations and routines disclosed herein are exemplary in nature, and these specific examples should not be considered restrictive, as many variations are possible. For example, the above technology can be applied to a powertrain including different types of propulsion sources, including different types of traction motors, internal combustion engines, transmissions, and other non-vehicle systems. The subject matter of the present disclosure includes all novel and non-obvious combinations and sub-combinations of the various systems and configurations disclosed herein and other features, functions, and / or characteristics.

[0071] The appended claims particularly point out certain combinations and subcombinations believed to be novel and non-obvious. These claims may refer to "an" element or a "first" element or the equivalent thereof. Such claims should be understood to include combinations of one or more such elements, neither requiring nor excluding two or more such elements. Other combinations and subcombinations of the disclosed features, functions, elements, and / or characteristics may be claimed in this or a related application by amendment of the present claims or by presentation of new claims. Such claims, whether broader, narrower, equal, or different in scope to the original claims, are deemed to be included in the subject matter of the present disclosure.

Claims

1. A variable displacement hydraulic motor, characterized in that: include: A swash plate having an inclined angle; as well as a plurality of piston assemblies configured to rotate about a drive shaft; Wherein, each of the plurality of piston assemblies comprises: an inner piston slidably coupled to an outer piston, the outer piston cooperating with a cylinder in a cylinder block; and A retaining device is configured to inhibit axial movement of the outer piston in a first position and to allow axial movement of the outer piston in a second position.

2. The variable displacement hydraulic motor according to claim 1, characterized in that: The tilt angle is fixed.

3. The variable displacement hydraulic motor according to claim 1, characterized in that: The retaining means comprises a pin.

4. The variable displacement hydraulic motor according to claim 3, characterized in that: The pins are radially aligned.

5. The variable displacement hydraulic motor according to claim 1, characterized in that: Also included is a hydraulic line in fluid communication with the retaining device.

6. The variable displacement hydraulic motor according to claim 5, characterized in that: The hydraulic line extends through the housing.

7. The variable displacement hydraulic motor according to claim 5, characterized in that: The hydraulic line extends through the valve plate.

8. The variable displacement hydraulic motor according to claim 1, characterized in that: The retaining device comprises an axially displaceable body including a radial extension which axially constrains the outer piston in a retracted position.

9. The variable displacement hydraulic motor according to claim 1, characterized in that: The inner and outer pistons are constructed of nitrided steel.

10. The variable displacement hydraulic motor according to claim 1, characterized in that: Also included is a controller, the controller comprising instructions that, when executed, cause the controller to: The retaining device is transitioned between the first position and the second position.

11. The variable displacement hydraulic motor according to claim 10, characterized in that: The controller is a transmission control unit in a hydromechanical transmission.

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