The present disclosure relates to axial piston pumps. In particular, the present disclosure relates to the control of an axial piston pump.
An axial piston pump generally comprises a plurality of pistons arranged within a cylinder block. The cylinder block may be driven to rotate about its axis by a shaft, which is typically connected to an internal combustion engine, or other mechanical drive means.
A diagram of an axial piston pump known in the art is shown in
Each piston 12 is connected to the swash plate 11 via a connector, typically a ball and socket joint. The swash plate 11 is moveable about a pivot point such that the angle of inclination of the swash plate 11 can be varied. In
The pistons 12 within the piston barrel 3 are arranged to bear against a swashplate.
The variable displacement of the cylinders within the piston barrel 3 is typically provided by variation in an angle of a swash plate. The angle of the swash plate may be controlled by a solenoid valve, which in turn controls the displacement of the cylinders.
As the piston barrel 3 rotates, the pistons reciprocate within the piston barrel 3. A valve plate provided on the opposite end of the piston barrel 3 to the swashplate defines an at least one inlet 40 and at least one outlet 42 for fluid being pumped through the axial piston pump.
In some known axial piston pumps, the rotational position of the valve plate inlets 40 and outlets 42 may be adjusted by providing an adjustable valve plate. An example of the adjustment of an adjustable valve plate using timing screws 30, 31 is shown in
The change in timing brought by adjustment of an adjustable valve plate in turn affects the “stiffness” of the axial piston pump. The stiffness of the axial piston pump reflects the relationship between the pump displacement and the output pressure. Axial piston pumps with increased stiffness require a greater pressure to destroke the pump. By adjusting the timing of an axial piston pump (via an adjustable valve plate) the stiffness of the axial piston pump can be calibrated mechanically.
Against this background, the present disclosure aims to provide an improved, or at least commercially relevant alternative axial piston pump or axial piston pump controller.
According to a first aspect of the disclosure an axial piston pump controller for an axial piston pump having a fixed valve plate and a variable displacement is provided. The axial piston pump controller is configured to:
The controller of the first aspect is configured to control an axial piston pump having a fixed valve plate. The controller of the first aspect calculates a pump stiffness adjustment factor which is used to modify the nominal value for the pump displacement current determined based on the pump rotational speed. In effect, the pump stiffness adjustment factor can increase or decrease the stiffness by increasing or decreasing the pump displacement control current output with respect to the nominal value calculated based on the pump rotational speed. Thus, rather than determining the pump displacement control current using a one dimensional control map based on engine speed, the controller of the first aspect uses a three dimensional control strategy (pump rotational speed, pump output pressure, and pump displacement). The effect of changing the stiffness of the axial piston pump is similar to the effect achieved by adjusting the timing of the pump based on the position of an adjustable valve plate. Accordingly, the controller of the first aspect allows an axial piston pump having a fixed valve plate to be controlled as if it had an adjustable stiffness similar to an axial piston pump having a variable-position valve plate.
According to a second aspect of the disclosure an axial piston pump having a fixed valve plate and a variable displacement is provided. The axial piston pump comprises:
The axial piston pump of the second aspect has a fixed valve plate. The controller of the axial piston pump includes a control map which can be used calculate a pump stiffness adjustment factor in order to effectively the stiffness of the axial piston pump. Accordingly, the axial piston pump of the second aspect can be controlled as if it had an adjustable stiffness similar to an axial piston pump having a variable-position valve plate. In contrast to an axial piston pump with a variable-position valve plate, the axial piston pump of the second aspect has an adjustable stiffness that does not require any mechanical adjustment of the axial piston pump.
A specific embodiment of the disclosure will now be described, by way of example only, with reference to the accompanying drawings in which:
According to an embodiment of the disclosure, an axial piston pump is provided. A schematic diagram of the axial piston pump 100 is shown in
The axial piston pump 100 shown in
The axial piston pump 100 may be installed in a closed-loop hydraulic system. As such, the hydraulic fluid pumped through the axial piston pump 100 is pumped though a closed circuit (ignoring any hydraulic fluid losses or leakages from the closed loop) and essentially returns back to the axial piston pump 100.
The plurality of pistons 12 of the axial piston pump 100 are located in a circular array within the piston barrel 3. The pistons 12 may be spaced at equal intervals about the rotational shaft 8 which is located at a longitudinal centre of the piston barrel 3. The piston barrel 3 is compressed against the fixed valve plate 6 by a spring 13. The spring 13 is shown in a cut-away portion of
Each piston 12 is connected to the swash plate 11 via a connector, typically a ball and socket joint. The swash plate 11 is moveable about a pivot point such that the angle of inclination of the swash plate 11 can be varied. In
The fixed valve plate 6 comprises at least one arcuate inlet port (not shown) and at least one arcuate outlet port (not shown). For example, the fixed valve plate 6 may be provided with similar inlet and outlet ports to the valve plate shown in
During operation of the axial piston pump 100, the piston barrel 3 rotates so that each piston 12 periodically passes over the each of the arcuate inlet port and the arcuate outlet port of the fixed valve plate 6. The rotation of the piston barrel is driven by rotation of the rotation shaft 8, which in turn may be connected to a source of motive power. For example, in the embodiment of
The angle of inclination of the swash plate 6 causes the pistons to undergo an oscillatory displacement in and out of the cylinder block, thus drawing the hydraulic fluid into the arcuate inlet port and subsequently expelling the hydraulic fluid out of the arcuate outlet port. The volume of hydraulic fluid expelled is related to the magnitude of the angle of inclination of the swash plate 6. For small angles of inclination, the stroke of each piston 12 is relatively small, and thus the volume of hydraulic fluid discharged is relatively low. As the angle of inclination increases, the piston stroke increases, thus increasing the volume of hydraulic fluid expelled.
The angle of inclination of the swash plate 11 is controlled by a servo piston 2. The servo piston 2 is configured to control the flow of hydraulic fluid for biasing the angle of inclination of the swash plate 11. The flow of hydraulic fluid is proportional to the degree the servo piston 2 is opened. As such, the angle of inclination of the swash plate 11 is controlled based on the degree of opening of the servo piston 2.
The degree of opening of the servo piston 2 is in turn controlled by pump control valve 5. Pump control valve 5 comprises a solenoid actuator (not shown). The solenoid actuator controls a pilot pressure which in turn is used to control the degree of opening of the servo piston 2. As such, a pump displacement control current supplied to the solenoid actuator of the pump control valve 5 controls the angle of inclination of the swash plate 11, and thus the displacement of the axial piston pump.
The skilled person will appreciate that electro-hydraulic actuators for controlling the position of a swash plate 11 are well known to the skilled person. Accordingly, the skilled person will appreciate that the present disclosure may be applied to any axial piston pump having an electro-hydraulic actuator configured to control the variable displacement of the axial piston pump 100.
The solenoid actuator of the pump control valve 5 is controlled by controller 20 which is configured to supply a pump displacement control current to the pump control valve 5. The controller 20 may be a dedicated processor configured to perform the control scheme discussed below. In some embodiments, the controller 20 of this disclosure may be combined with other control functions. For example, an engine control unit (ECU) of a hydraulic machine may be used to provide the controller 20 according to this disclosure. As such, the controller 20 may be provided separately (i.e. not directly mounted on or incorporated into) from the axial piston pump 100.
In some axial piston pumps known in the art, the pump displacement control current provided to the axial piston pump is, essentially, the nominal pump current. That is to say, it is known in the art to calculate the pump displacement control current based on the pump rotational speed driving the pump. This calculation is typically performed using a one dimensional control map which provides a nominal pump current for different pump rotational speeds.
The controller according to the embodiment of
It will be appreciated from
According to the embodiment of
As shown in
In the embodiment of
In such a case, the pump displacement (DP), pump rotational speed (SP), motor rotational speed (SM) and motor displacement (DM) are related by the following equation:
DPSP=DMSM
The motor rotational speed SM can be measured using a suitable sensor, the output of which is provided to the controller 20. The pump rotational speed SP may also be measured and provided to the controller 20. The motor displacement can be inferred from the motor speed based on a calibration of the motor at a range of different motor speeds. As such, a control map for estimating the pump displacement can be generated having as inputs: motor rotational speed and pump rotational speed which allows the pump displacement to be estimated. The estimated pump displacement can then be provided to the pump stiffness control map in order to determine the pump stiffness adjustment factor.
A graph showing the effect of the pump stiffness adjustment factor is shown in
The dashed line in
An example of a pump stiffness control map is shown in
In some embodiments, a single pump stiffness control map may be provided separately from the calculation of the nominal pump current based on the engine speed. As such, the pump stiffness adjustment to the pump displacement control current may be applied independently of the pump rotation speed. In some embodiments, the pump stiffness adjustment to the pump displacement current may also be dependent on pump rotation speed. As such, in some embodiments, a plurality of pump stiffness control maps may be provided. Each of the plurality of pump stiffness control maps may provide a map of values for the pump stiffness adjustment factor at a respective pump rotation speed. The controller 20 may be configured to select one of the pump stiffness control maps for calculating the pump stiffness adjustment factor based on the engine speed.
While the embodiment of
Thus, according to this disclosure, the controller 20 may be configured to perform a method of controlling a displacement of an axial piston pump having a fixed valve plate and a variable displacement. In a first step of the method, a displacement of the axial piston pump is determined. As discussed above, the displacement may be determined by estimation using the pump displacement estimation module or by direct measurement using a suitable sensor.
A pump displacement control current to be supplied to the axial piston pump to control the displacement of the axial piston pump is also calculated. This step comprises calculating a nominal value for the pump displacement control current based on a rotational speed of the axial piston pump and calculating a pump stiffness adjustment factor based on a pump stiffness control map having as inputs: an output pressure of the axial piston pump; and the estimated pump displacement. The pump displacement control current to be supplied to the axial piston pump is then calculated based on the nominal value and the pump stiffness adjustment factor.
Once calculated, the controller 20 outputs an instruction to output the calculated pump displacement control current to the axial piston pump in order to control the displacement of the axial piston pump.
Thus, according to embodiments of this disclosure a controller 20 for controlling the displacement of an axial piston pump 100 is provided.
According to this disclosure, an axial piston pump controller is provided. The axial piston pump controller may be used to control an axial piston pump. The axial piston pump may be installed in a closed-loop hydraulic system. For example, the axial piston pump may be provided as part of a hydraulic system for a machine (i.e. a hydraulic machine).
Number | Date | Country | Kind |
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2111611.6 | Aug 2021 | GB | national |