Electronically commutated hydraulic machine and method of operation for reducing the occurrence of resonance effects - Patents.com

Abstract

A hydraulic system including an electronically commutated machine having multiple working chambers controlled in each cycle of working chamber volume to perform an active or inactive cycle of the working chamber volume allows only multiple defined portions of the cycle to be active to avoid creating active cycle frequencies that cause low frequency resonance. The demand signal may be quantized to a fraction m / n, where n is an integer below a threshold selected to avoid repeating patterns of active cycles that exceed a cutoff length.

Description

[Technical field]

[0001] The present invention relates to the field of electronically commutated hydrolic machines. [Background technology]

[0002] Electronically commutated hydraulic machines are known in which the displacement of working fluid per working chamber is controlled for each discrete cycle of working chamber volume in step-wise correlation with the cycle of working chamber volume, at least by active control of low pressure valves connecting each working chamber to a low pressure manifold, and in some embodiments (e.g., when the machine functions as a motor) by active control of high pressure valves connecting each working chamber to a high pressure manifold. Such machines are capable of responding rapidly to changes in demand and can closely match output to fluctuating demand signals.

[0003] The invention particularly relates to electronically commutated machines in which active cycles of a working chamber volume in which a net displacement of working fluid occurs are interspersed with inactive cycles of a working chamber volume in which no net displacement of working fluid occurs. Typically, most or all of the active cycles are full stroke cycles in which the working chamber displaces a predetermined maximum displacement of working fluid by suitable control of the timing of the valve actuation signals. It is also known to adjust the low pressure valve and optionally the high pressure valve to adjust the fraction of the maximum displacement achieved during an active cycle by manipulating so-called partial stroke cycles. However, typically such machines intersperse active and inactive cycles, the active cycles being full stroke cycles, and the fraction of the cycle that is active (active cycle fraction) being varied to achieve the demand fractional displacement, instead of operating with only partial stroke cycles.

[0004] Problems have been found to occur when such machines are operated at certain percentages of maximum power. Examples of this are found at low percentages of maximum power and at high percentages of maximum power. At low percentages, the machine may accidentally perform only active cycles interspersed with inactive cycles resulting in high pulsating flow. Such pulsating flow has been found to sometimes cause vibrations (especially low frequency vibrations) and resonant effects. For example, if such a machine is operated at 5% of maximum displacement per shaft revolution and performs operations by performing one active cycle followed by 19 inactive cycles in succession and then repeating this pattern, with the working chambers being equally spaced and in phase, vibrations will occur at 1 / 20th the frequency of the working chamber selection (how often the working chambers commit to either an active or inactive cycle). If this coincides with the resonant frequency of the equipment components, it may lead to undesirable vibrations or damage. For example, if the equipment is an excavator, the low frequency pulsating flow may vibrate the operator's cabin. Thus, repeating patterns of working chamber (eg, cylinder) activation (ie, the working chamber going through an activation cycle) leads to the generation of a corresponding operating frequency (and possibly harmonics thereof).

[0005] Resonance effects can also occur due to the pattern of cylinders undergoing inactive cycles. For example, if a similar machine is operating at 95% of its maximum displacement, it will mainly perform active cycles, with one in every 20 cycles being an inactive cycle. Such a cylinder inactive pattern can again cause resonance effects at a frequency equal to 1 / 20th the frequency of the working chamber operation. Strong resonances can also occur just above and just below 50% of the maximum displacement.

[0006] The present invention therefore seeks to provide an electronically commutated hydraulic machine which intersperses active and inactive cycles of the working chamber volume which reduces or avoids the generation of certain resonant frequencies, particularly low frequencies.

[0007] WO2015 / 040360 (Abrahams et al.) disclosed a machine in which the pattern of valve actuation signals was adjusted such that the frequency of one or more intensity peaks in the frequency spectrum of the active and inactive cycle patterns of the actuation chambers did not remain within one or more ranges of undesirable frequencies. The present invention seeks to provide an alternative approach, which is typically simpler to implement. Summary of the Invention [Means for solving the problem]

[0008] According to a first aspect of the present invention there is provided a method of operating an apparatus comprising a prime mover and a plurality of hydraulic actuators, the hydraulic machine having a rotatable shaft in driving engagement with the prime mover and comprising a plurality of working chambers having volumes which vary cyclically with rotation of the rotatable shaft (e.g. each chamber may be defined by a cylinder within which a piston reciprocates in use), a hydraulic circuit extending between a group of one or more working chambers of the hydraulic machine and one or more of the hydraulic actuators, each working chamber of the hydraulic machine comprising a low pressure valve regulating the flow of hydraulic fluid between the working chamber and a low pressure manifold, and a high pressure valve regulating the flow of hydraulic fluid between the working chamber and the high pressure manifold. and a high pressure valve configured to actively control at least the low pressure valves (and in some embodiments also the high pressure valves) of one or more groups of working chambers to select a net displacement of hydraulic fluid per working chamber in each cycle of working chamber volume, thereby selecting a net displacement of hydraulic fluid per group of one or more working chambers in response to a demand signal, the method comprising controlling said valves to cause each working chamber to perform either an active cycle or an inactive cycle of the working chamber volume during each cycle of working chamber volume, wherein the fraction of the working chambers performing an active cycle is variable and selected from a plurality of discrete fractions.

[0009] According to a second aspect of the present invention there is provided an apparatus comprising a prime mover and a plurality of hydraulic actuators, the hydraulic machine having a rotatable shaft in driving engagement with the prime mover and comprising a plurality of working chambers having volumes which vary cyclically with rotation of the rotatable shaft (e.g. each chamber may be defined by a cylinder within which a piston reciprocates in use), a hydraulic circuit extending between a group of one or more working chambers of the hydraulic machine and one or more of the hydraulic actuators, each working chamber of the hydraulic machine comprising a low pressure valve regulating the flow of hydraulic fluid between the working chamber and a low pressure manifold and a high pressure valve regulating the flow of hydraulic fluid between the working chamber and the high pressure manifold, the hydraulic machine comprising a working chamber volume control means for controlling the volume of the working chamber volume control means for controlling the volume of the working chamber volume control means. a controller configured to actively control at least the low pressure valves (and in some embodiments also the high pressure valves) of one or more groups of working chambers to select a net displacement of hydraulic fluid per working chamber during each cycle of pressure, thereby selecting a net displacement of hydraulic fluid per group of one or more working chambers in response to a demand signal, the controller being configured (e.g. programmed) to control said valves to cause each working chamber to perform either an active cycle or an inactive cycle of the working chamber volume during each cycle of the working chamber volume, the apparatus being characterized in that the fraction of the working chambers performing an active cycle is variable and configured to be selected from a plurality of discrete fractions.

[0010] The controller of the hydraulic machine can be configured such that the fraction of the working chamber that executes an active cycle is variable and can be one of a plurality of discrete fractions. The apparatus can be configured such that the controller of the hydraulic machine receives only a demand signal selected from a plurality of discrete values, whereby the fraction of the working chamber that executes an active cycle is variable and selected from a plurality of discrete fractions.

[0011] An "active cycle" refers to a cycle of the working chamber volume during which a net displacement of the working fluid occurs. An "inactive cycle" refers to a cycle of the working chamber volume during which no net displacement of the working fluid occurs (usually one or both of the low and high pressure valves remain closed throughout the cycle). The active and inactive cycles are usually interspersed to satisfy the demand indicated by the demand signal. This is in contrast to machines that only perform active cycles, the displacement of which may be variable. A working chamber selection decision refers to a decision as to whether a working chamber undergoes an active or inactive cycle of the working chamber volume. These usually occur when the rotatable shaft is at each of a number of discrete angles. An "active cycle fraction" refers to the fraction of the working chamber performing an active cycle. This is also known as the effective fraction. The demand signal is usually processed as a "displacement fraction," Fd, which is a target fraction of the maximum displacement of the working fluid per revolution of the rotatable shaft. The demand in volume terms (amount of working fluid per second) can be converted to a displacement fraction by taking into account the current rotational speed of the rotatable shaft and the number of working chambers connected in a group to the same high pressure manifold and actuator. The demand signal relates to the demand for composite fluid displacement of a group of one or more working chambers fluidly connected to said one or more of the hydraulic actuators via a hydraulic circuit. There may be one or more other groups of working chambers fluidly connected to one or more other hydraulic actuators with respective demand signals.

[0012] The multiple discrete fractions are selected to avoid the generation of resonant vibrations at undesirable frequencies, particularly resonances at frequencies below a predetermined minimum frequency. The multiple discrete fractions are typically selected to avoid the generation of any repeating patterns of active and inactive cycles of the working chamber volume having a length that exceeds a predetermined maximum repeating pattern length. The multiple discrete fractions, when expressed in irreducible fractions, typically do not include any fractions having a denominator greater than a predetermined maximum denominator.

[0013] This avoids or reduces the adverse effects of sympathetic vibrations that would otherwise occur, such as component damage, unacceptable noise and vibration as experienced by an operator. Equipment that includes hydraulic pumps and motors can be damaged by vibrations resulting from the operation of the hydraulic pump or motor.

[0014] The selection of the multiple discrete fractions typically takes into account a predetermined operating rotational speed of the rotatable shaft (which may be a standard or minimum standard operating speed) (as the rotational speed of the rotatable shaft determines the frequency of the working chamber cycles).

[0015] Typically, the demand signal to which a hydraulic machine responds is quantized and has one of a number of discrete values. The discrete values ​​may also be discrete fractions (e.g., active cycle fractions). These discrete values ​​may be the same as discrete fractions. However, this depends on the units of the demand signal and the manner in which the demand signal is processed to determine whether the working chamber undergoes an active or inactive cycle. Thus, at least the low pressure valves (and in some embodiments also the high pressure valves) of the working chambers are controlled to select the net displacement of hydraulic fluid per working chamber in each cycle of the working chamber volume, thereby making the fraction of the working chambers performing an active cycle variable, but a selected fraction from a number of discrete fractions.

[0016] The discrete fractions (and, where applicable, the discrete values) can be viewed as a group of (a finite number of) discrete fractions (values) from which one value is selected at any one time. The discrete fractions (or values) are typically stored in a solid-state memory device in electronic communication with the machine's controller, and are read from the solid-state memory as needed.

[0017] A (optionally continuous) demand signal may be received and the demand signal may be quantized, for example, by selecting the closest discrete value to the received demand, or the next discrete value above or below the received demand signal. Hysteresis may be applied to the quantization step to avoid chattering.

[0018] The multiple discrete values ​​and multiple discrete fractions may represent corresponding fractions of the maximum displacement of the working fluid per revolution of the rotatable shaft (displacement fraction, Fd) for each group of one or more working chambers.

[0019] There may be a step of determining a discrete value, e.g. calculating a value or reading a value from a memory, and the value may be variable, for example depending on the rotational speed of a rotatable shaft.

[0020] When the demand signal is quantized, the pattern of active and inactive cycles at these discrete displacement fractions (the "quantized displacements") produces a cylinder actuation pattern (i.e., a pattern of cylinders performing active or inactive cycles) whose frequency content is known, and as a result, the minimum frequency repeating cylinder actuation pattern that exists is known.

[0021] Thus, the pattern of the valve command signal is controlled to reduce unwanted vibrations by avoiding a certain range of Fd. This means that the target net displacement may not be met exactly. However, some closed loop feedback systems can correct any errors resulting from this, as the machine may operate at discrete fractions above the requested displacement fraction, and at discrete fractions below the requested displacement fraction.

[0022] An example of a system that cannot tolerate volumetric error is one based on open loop displacement control, which requires the pump to deliver the exact fluid demand. Closed loop pressure control with an integral term, such as LS (Load Sense) systems, also suffer from quantization. The displacement demand can cycle between two discrete displacement levels when the continuous displacement demand level is between two discrete levels from a quantization table. For example, say you are controlling to 20 bar at steady state. At a lower displacement level it will be 18 bar and at a higher displacement level it will be 25 bar. Consider the case where the closest discrete level is below the continuous displacement level. The selected discrete level will be a flow rate from the pump that is lower than the flow rate due to the continuous displacement level demand. It is 18 bar. This causes the integral term of the pressure control loop to increase. At some point, this integral term will become large enough to move the continuous displacement demand level closer to the higher discrete displacement level, and the selected discrete displacement will increase to this higher level. As the delivery pressure becomes 25 bar, the integral term will start to decrease. At some point, it will be low enough to drop the pump's demand displacement level. This cycle may continue indefinitely and may occur at a low frequency, introducing low frequency content into the hydraulic lines.

[0023] However, the opening and closing timing of at least the low pressure valve (and in some embodiments the high pressure valve as well) may be adjusted to change the fraction of maximum stroke volume displaced per working chamber during each active cycle. The fraction of maximum stroke displaced is coordinated (e.g., by the machine controller) with the active cycle fraction to allow the hydraulic machine to displace a fraction of the displacement indicated by the demand signal while limiting the active cycle fraction to only one of a number of discrete fractions.

[0024] This may allow for a continuous range of displacements per revolution of the rotatable shaft to be generated, although the fraction of the working chambers performing an active cycle is limited to one of a number of discrete fractions. This allows all displacements (from zero to full) per revolution of the rotatable shaft to be valid, effectively creating a (complete) variable displacement hydraulic machine (full continuous displacement is possible using a finite number of discrete active cycle fractions). All fractions of the maximum displacement may be achieved by allowing a range of maximum stroke volume variation from 0 to 100%, although limits of 0 to 5% and 95 to 100%, or 0 to 10% and 90 to 100% of the maximum stroke volume variation are also possible. The fraction of the maximum stroke volume displaced per working chamber during each cycle may vary between 0 to x% and y% to 100%, with x<25 and y>75, or x≦10 and y≧90. The reason is that such ranges of partial stroke displacement can be produced by actuating the valve only near the beginning or end of the stroke (within a cycle of the working chamber volume) when fluid flow into or out of the working chamber is restricted.

[0025] The discrete fractions and / or values ​​of the demand signal may be equally spaced or not equally spaced. The discrete fractions and / or values ​​of the demand signal may or may not vary with the rotational speed of the rotatable shaft. If they vary with the rotational speed of the rotatable shaft, they may be selected to reduce the generation of low frequency components. For example, the discrete values ​​may be less than 1000, or less than 100. If the demand signal is digital, they do not refer to possible values ​​imposed by binary logic, but rather to a subset of values ​​that can be represented digitally, given the bit size of the demand signal. Thus, the discrete values ​​typically represent less than 10%, less than 1%, or less than 0.1% of the digital values ​​that the demand signal may have, given its bit length.

[0026] The controller is capable of receiving a demand signal (usually a continuous demand signal) and determining a corresponding series of values, said series of values ​​corresponding to a pattern of active and / or inactive cycles of the working chamber volume, thereby satisfying the demand signal (i.e., the demand signal (F) resulting from the pattern of active and / or inactive cycles of the working chamber volume). d ) averaged over a period of time. The method can include receiving a demand signal (typically a continuous demand signal) and determining a corresponding series of values, said series of values ​​corresponding to a pattern of active and / or inactive cycles of the working chamber volume thereby satisfying the demand signal (i.e., determining a demand signal (F) resulting from the pattern of active and / or inactive cycles of the working chamber volume). d ) averaged over a period of time.

[0027] For example, the controller may receive a continuous demand signal of 90% of maximum displacement and determine a sequence of values ​​including at least 100 values, or desirably at least 500 values, and more preferably at least 1000 values. The sequence of values ​​may include a repeating sequence, such that the pattern of active and / or inactive cycles may include a period of time that corresponds to the repeating sequence. The active cycles averaged over a period of time fill as close to 90% as possible without generating low frequency content in the sequence.

[0028] In some embodiments, the net displacement of the working fluid during each active cycle is the same, which is typically the maximum displacement of the working fluid per working chamber.

[0029] A fraction is a number between 0 and 1 expressed as a ratio between an integer numerator and an integer denominator. An irreducible fraction is a fraction expressed such that the numerator and denominator have no integer common factors. For example, 3 / 6 is the same as the irreducible fraction 1 / 2.

[0030] Typically, when discrete fractions are expressed in reduced fractions, the denominators range up to a maximum value selected to avoid generating a repeating pattern of actuation chamber actuation at a frequency below a predetermined minimum value. Typically, when discrete fractions are expressed in reduced fractions, they include fractions with integer denominators up to the maximum denominator. When discrete fractions are expressed as reduced fractions, they may include fractions with integer denominators that are multiples of an integer i up to the maximum denominator. (For example, for i=3, the denominators are 3, 6, 9, 12... and many such fractions have smaller integers when expressed in reduced fractions, but the fractions typically include 1 / i, 1 / 2i, 1 / 3i...(3i-1) / 3i, (2i-1) / 2i, i-1 / i).

[0031] Each of the plurality of fractions may include or consist of irreducible fractions having a denominator from 1 to n (usually with 0 and 1) and a corresponding numerator m from 1 to n-1 (m and n are integers).

[0032] Each of the multiple integers may include or consist of an irreducible fraction with a denominator that is a multiple of an integer i from i to n (usually with 0 and 1) and a numerator m from 1 to n-1 (i>1). i may be equal to redundancy if each working chamber has the same redundancy. Redundancy refers to the number of working chambers in the same working chamber group that operate in phase (and therefore have the same fluid displacement as the shaft angle).

[0033] 10. The method of any one of the preceding claims, wherein the smallest non-zero fraction of the plurality of discrete fractions is 1 / n, and the second smallest non-zero fraction of the plurality of discrete fractions is typically 1 / (n-1), where n is an integer.

[0034] A minimum non-zero fraction of the plurality of discrete fractions may be selected such that at a target rotational operating speed of the rotatable shaft, the frequency of the repeating pattern of active cycles of the working chamber volume exceeds a predetermined minimum allowable frequency.

[0035] The smallest non-zero fraction of the plurality of discrete fractions may be selected taking into account that two or more actuation chambers have the same phase or that there is a non-uniform phase difference between two or more actuation chambers. This may include processing data representative of the relative phases of the actuation chambers and / or taking into account that some actuation chambers may have cycles of synchronized actuation chamber volumes. The method may include calculating the number of consecutive actuation chambers in a group of actuation chambers required to generate a repeating pattern, typically taking into account phase differences and / or redundancy of actuation chambers within the group.

[0036] However, the discrete fractions (active cycle fractions) and / or discrete values ​​(if applicable) of the quantized demand signal may be determined by simulation or experiment. In this case, the discrete fractions and / or values ​​of the quantized demand signal are included in the discrete fractions (or values) responsive to simulation or experiment that indicate that the frequency content of the resulting high pressure manifold pressure, or valve actuation current, or other signal meets one or more acceptable frequency spectrum criteria, and / or that the frequency content below the cutoff frequency is below a threshold, or that the effect of the selection of active and inactive cycles is acceptable (e.g., responsive to operator feedback, or measurements or calculations of the movement of one or more parts of the instrument), or that they are excluded if they do not meet such criteria. Thus, the discrete fractions and / or values ​​may be constructed by trial and error. A minimum frequency may be determined by experiment or simulation (whether during design, manufacturing, or run-time) and used to calculate the maximum denominator n.

[0037] The discrete fraction (active cycle fraction) and / or the plurality of discrete values ​​of the quantized demand signal (if applicable) do not have to be determined prior to manufacture or commissioning of the machine or even prior to operation, but may be calculated during run-time and / or in real time, taking into account pre-determined parameters (e.g. phase and redundancy data of the working chambers, minimum frequency) and / or current measurement parameters (e.g. shaft rotation speed).

[0038] The plurality of discrete fractions and / or the plurality of discrete values ​​(where applicable the demand signal is quantized) may vary in response to a rotational speed of the rotatable shaft or another operating parameter of the apparatus. That is, the plurality of discrete fractions (or values) may be groups of discrete fractions (or values), and different groups of discrete fractions (or values) may be used at different rotational speeds of the rotatable shaft, or different values ​​or ranges of another operating parameter of the apparatus. The method may include switching from using a first plurality of discrete fractions (or values) to a second plurality of discrete fractions (or values) when the rotational speed of the rotatable shaft exceeds a threshold value.

[0039] The number of discrete fractions (or values) used may be altered in response to changes in the number and phase of working chambers within a group of working chambers connected to a high pressure manifold.

[0040] Whether the working chamber is undergoing an active or inactive cycle of working chamber volume may be determined by comparing a time history of displacement demand (e.g., a received displacement demand signal) with a time history of actual displacement, for example, by incrementing an accumulator in response to the displacement demand signal and decrementing an accumulator in response to the amount of working fluid displaced.

[0041] A method of a third aspect extends to a method of calculating a plurality of discrete fractions for use in the method of the first aspect or the apparatus of the second aspect, the method comprising inputting a minimum allowable frequency, a target rotational operating speed of the rotatable shaft, and data indicative of the number and / or phase difference between working chambers of the machine and / or the phase difference between working chambers in groups (said groups being defined such that the grouped working chambers share a common hydraulic output), calculating an integer number n (usually the largest integer) of working chamber decision points between active cycles that result in the occurrence of a frequency of cylinder actuation only if it exceeds the minimum allowable frequency, and including 1 / n in the plurality of discrete fractions.

[0042] The method may further include, after removing duplicate values, including in the plurality of discrete fractions a plurality of fractions having denominators that are integers up to n and numerators that are integers up to n-1.

[0043] The method may include forming a plurality of discrete fractions from a plurality of fractions having denominators that are all integer multiples (greater than one) of an integer.

[0044] The method may include forming a number of discrete fractions, including fractions 1 / i, 1 / 2i, and typically also 1 / 3i where i is an integer, where i may be equal to the redundancy of the working chamber.

[0045] Usually, duplicate values ​​are removed. Fractions can be re-expressed as irreducible fractions. Fractions can be converted to binary.

[0046] The method may include removing one or more discrete fractions from the plurality of discrete fractions to avoid generating a repetitive cylinder actuation pattern having a frequency component below a particular value, the frequency component possibly occurring with unbalanced cylinder phasing.

[0047] The method may further include verifying whether the candidate discrete fractions (e.g., active cycle fractions) are associated with discrete levels of resulting output fluid displacement that have sufficient resolution to enable one or more operational smoothness criteria to be satisfied. If the candidate fractions do not result in sufficiently smooth operation (due to gaps between the discrete fractions), the method may include generating an error or fault strategy that recalculates the discrete fractions or re-specifies the hydraulic machine (e.g., determines the use of a hydraulic machine with more working chambers). The discrete fractions may be used as values ​​of the discrete fractions and / or quantized demand signal, if applicable.

[0048] The method may include storing a plurality of discrete fractions in a solid-state memory device for reading during operation.

[0049] The active and inactive cycles of the actuation chamber volumes performed by the actuation chamber include a pattern of finite duration for a given active cycle fraction, for example, the pattern of active and inactive cycles may have a minimum duration of at least 0.001 seconds, or at least 0.005 seconds, or at least 0.01 seconds, and / or a maximum duration of at most 0.1 seconds, or at most 0.5 seconds.

[0050] In one example machine, the minimum period may be 2.4 milliseconds (due to the frequency of actuation of all 12 evenly spaced cylinders at a maximum speed of 2500 RPM).Those skilled in the art will appreciate that with higher prime mover speeds or more cylinders, the minimum period may be 1 millisecond (or less).

[0051] In a first embodiment, it is preferable to remove all frequencies below 5 Hz, which corresponds to a period of 0.2 seconds.

[0052] Typically, a range of acceptable periods is selected depending on the acceptable frequency content. In applications where all frequencies below a certain value must be removed, a maximum acceptable period must be specified. From this maximum acceptable period, an acceptable range of active cycle fractions is selected depending on the number of cylinders and the operating range of the prime mover. For example, the acceptable range of active cycle fractions may be selected to include a number of discrete active cycle fractions generated using integer denominator values ​​and integer numerator values. The denominators of the multiple active cycle fractions may be selected depending on the rotational speed of the rotating shaft, for example the denominators may be selected such that the periods are higher than the minimum period. It is beneficial to have a short period to accommodate more frequent cycling of the active or inactive working chamber volumes and to remove low frequency content from the pattern of active and inactive cycles. Typically, the acceptable value of the denominator of the finite number of fractions varies depending on the rotational speed of the rotatable shaft. However, it is possible that the available active cycle fractions do not vary with the prime mover speed and are selected to remove low frequency content at the minimum prime mover speed. As a result, frequency content at higher speeds will also be acceptable.

[0053] The frequency with which the working chamber performs an active or inactive cycle is proportional to the rotational speed (in revolutions per second) of the rotatable shaft for a given active cycle fraction. The sequence of active and inactive cycles of the working chamber volume is independent of the shaft speed for a given active cycle fraction. However, the time between elements of the sequence does not vary with shaft speed. Thus, the frequency resulting from a particular sequence of active and inactive cycles is proportional to the rotational speed of the rotatable shaft.

[0054] Rather, it is the repeating pattern of active or inactive chambers that is important, regardless of whether the cylinders are active or inactive. For example, the sequence 0, 0, 0, 1, 0, 0, 0, 1 has the same fundamental frequency as the sequence 1, 1, 1, 0, 1, 1, 1, 0.

[0055] Thus, in accordance with the present invention, it is seen that the hydraulic machine generates vibrations which depend on the pattern of active and inactive cycles executed by the working chambers, and for a given sequence of active and inactive cycles, have intensity peaks at a frequency proportional to the rotational speed of the rotatable shaft.

[0056] The method may include selecting a minimum allowable frequency (e.g., 5 Hz, 10 Hz) and then creating a quantized list of a plurality of discrete active cycle fractions (e.g., values ​​of Fd and / or quantized demand signal, if applicable), the fractions being selected to generate one or more patterns of active and inactive cycles, the patterns having only frequency content that exceeds the minimum allowable frequency. The controller may be configured to determine a minimum allowable frequency (e.g., 5 Hz, 10 Hz) and then creating a quantized list of a plurality of discrete active cycle fractions (e.g., values ​​of Fd and / or quantized demand signal, if applicable), the values ​​being selected to generate one or more patterns of active and inactive cycles, the patterns having only frequency content that exceeds the minimum allowable frequency.

[0057] The discrete values ​​(in the quantized list) typically correspond to discrete fractions (of working chambers executing active cycles), but this is not required as the demand signal does not need to be expressed in terms of displacement fractions.

[0058] The discrete fractions (and / or values) may depend on the number of cylinders in the machine and / or the rotational operating speed of the rotatable shaft of the machine (as the rotational speed of the rotatable shaft and the number of cylinders affect the frequency that exists for a given demand value). For each active cycle fraction, a minimum frequency that exists can be calculated. While the machine is running, the (filtered) demand signal is sent to the hydraulic machine's controller. Note that the calculation of the continuous demand signal, and the quantization of the demand signal, and / or the selection of the discrete active cycle fractions can all be calculated within the controller itself.

[0059] The minimum allowable frequency may be less than 20 Hz or even less than 10 Hz. The present invention is particularly useful for avoiding these types of low frequencies.

[0060] The present invention extends in a fourth aspect to a solid-state memory device storing a plurality of discrete fractions calculated according to the method of the third aspect of the invention. The method of the first aspect may include reading the discrete fractions on the solid-state memory device of the fourth aspect. The apparatus of the second aspect may include the solid-state memory device of the fourth aspect in electronic communication with a controller.

[0061] The apparatus may be a vehicle, typically an industrial vehicle. The apparatus may be, for example, an excavator, a telehandler, or a backhoe loader. The apparatus may be a car, a bus, a truck, a forklift truck, and / or a wheel loader. The apparatus may be an injection molding machine or a water jet cutting unit. The apparatus may be a hydraulic power unit. The apparatus may include a hydraulic transmission. The apparatus may be a hydraulic hybrid vehicle transmission. The apparatus may be a renewable generator (such as a wind turbine generator or a wave or tidal generator). The apparatus may include a wireless transceiver. The apparatus may include a battery. The apparatus may include electrical terminals for charging. The apparatus may be a rail car. The apparatus may be a (non-industrial) passenger car. However, the apparatus may not be a vehicle.

[0062] The hydraulic machine may include more than 6 or 8 working chambers. The hydraulic machine may include more than 12 working chambers.

[0063] The apparatus may be configured to calculate a demand signal in response to a measured characteristic of the hydraulic circuit or one or more actuators. The apparatus typically includes a controller configured to calculate a demand signal in response to a measured characteristic of the hydraulic circuit or one or more of the hydraulic actuators.

[0064] The present invention also extends to a method of operating an apparatus comprising calculating a demand signal in response to one or more measured characteristics of the hydraulic circuit or actuator.

[0065] The method typically includes detecting a flow and / or pressure requirement of at least one of the one or more hydraulic actuators, or receiving a demand signal indicative of a requested pressure or flow based on the pressure and / or flow demand of one or more of the hydraulic actuators, and correspondingly controlling a flow rate of hydraulic fluid from or to each of a group of one or more actuation chambers fluidly connected to the one or more hydraulic actuators.

[0066] The method may include adjusting the displacement of a group of one or more working chambers in response to the measured pressure. Thus, the apparatus typically has a negative flow control loop. The apparatus may optionally include a feedforward controller configured to calculate a demand signal in response to a feedforward of a measured characteristic of the hydraulic circuit or one or more actuators (e.g., in addition to or instead of a feedback controller configured to calculate a demand signal in response to a feedback of a measured characteristic of the hydraulic circuit or one or more actuators).

[0067] For example, the demand signal may be determined in response to a pressure measurement and / or a flow measurement. The demand signal may include a pressure measurement, where the pressure measurement is measured at a throttle. The demand signal may indicate a fraction of the maximum displacement of hydraulic fluid for each group of one or more working chambers displaced per revolution of a rotatable shaft, referred to herein as Fd (fraction of maximum displacement per revolution). Fd is equal to the active cycle fraction where each working chamber displaces the maximum possible volume of working fluid.

[0068] Typically, the prime mover is in driving engagement with the hydraulic machine. The prime mover typically has a rotatable shaft that is coupled to (to which the prime mover can apply torque) a rotatable shaft of the ECM. The prime mover (e.g., engine) and the hydraulic machine may have a common shaft.

[0069] Where the apparatus is an excavator, the plurality of hydraulic actuators typically includes (e.g., at least) two actuators for moving the track (e.g., for moving the vehicle, typically the excavator), a rotation actuator (e.g., a motor) (e.g., for rotating the cab of the excavator relative to the base of the excavator, which typically includes the track), at least one ram actuator (e.g., for controlling the excavator arm, e.g., for the boom and / or stick), and at least two further actuators (e.g., for controlling movement of a tool such as a bucket).

[0070] One or more low pressure manifolds may extend to the working chambers of the hydraulic machine. One or more high pressure manifolds may extend to the working chambers of the hydraulic machine. A hydraulic circuit typically includes a high pressure manifold extending between the group of one or more working chambers and the one or more actuators. The low pressure manifold may be part of one or more hydraulic circuits. Low pressure manifold 54 and high pressure manifold 58 refer to the relative pressures within the manifolds.

[0071] At least the low pressure valve (and optionally the high pressure valve, and optionally both the low pressure valve and the high pressure valve) may be electronically controlled valves, and the apparatus may include a controller that controls the (e.g. electronically controlled) valve in step-wise relation to the cycles of the actuation chamber volume, thereby determining the net displacement of hydraulic fluid per actuation chamber for each cycle of the actuation chamber volume. The method may include controlling the (e.g. electronically controlled) valve in step-wise relation to the cycles of the actuation chamber volume, thereby determining the net displacement of hydraulic fluid per actuation chamber for each cycle of the actuation chamber volume.

[0072] The flow rate and / or pressure requirements of the one or more groups of hydraulic actuators may be determined, for example, by measuring the flow rate of hydraulic fluid to or from the one or more groups of hydraulic actuators, or the pressure of hydraulic fluid in or at the outlet or inlet of the one or more groups of hydraulic actuators. The flow rate and / or pressure requirements may be determined from one or more measured flow rates and / or measured pressures decreasing or falling below an expected value. A decrease in the flow rate and / or measured pressure from an expected value indicates insufficient flow rate to or from the one or more groups of hydraulic actuators. For example, it may be determined that the flow rate of hydraulic fluid to the actuators is below an expected value (e.g., a target value), and in response, the flow rate of hydraulic fluid to the actuators may be increased. It may be determined that the flow rate of hydraulic fluid from the actuators is above an expected value (e.g., a target value) (e.g., as the arm or other load is lowered), and in response, the flow rate from the actuators may be decreased. An increase or decrease in pressure can be detected in the one or more hydraulic actuators, and one or more groups of working chambers connected to the one or more hydraulic actuators can be controlled to modify (e.g. increase or decrease) the flow of hydraulic fluid from the one or more groups of working chambers to the one or more hydraulic actuators, or vice versa.

[0073] A group of one or more working chambers can be dynamically assigned to a respective group of one or more hydraulic actuators, whereby the connection of one or more working chambers to the hydraulic actuators (e.g., the group) can be changed, for example, by opening and closing electronically controlled valves (e.g., high pressure and low pressure valves as described below), for example, under the control of a controller. A group of (e.g., one or more) working chambers can be dynamically assigned to a (respective) group of (e.g., one or more) actuators, whereby which working chambers of a machine are coupled to which hydraulic actuators can be changed, for example, by opening and / or closing (e.g., electronically controlled) valves, for example, under the control of a controller. The net displacement of hydraulic fluid through each working chamber (and / or each hydraulic actuator) can be adjusted by adjusting the net displacement of one or more working chambers connected to the one or more hydraulic actuators. The group of one or more working chambers is typically connected to the respective group of one or more hydraulic actuators via the manifold described above.

[0074] Typically, the apparatus includes a controller. The controller includes one or more processors in electronic communication with a memory and program code stored in the memory. The controller may be distributed and include two or more controller modules (e.g., two or more processors), for example, the controller may include a hydraulic machine controller (including one or more processors in electronic communication with a memory and program code stored in the memory) that controls a hydraulic machine, and an equipment controller (including one or more processors in electronic communication with a memory and program code stored in the memory) that controls other components of the equipment (e.g., valves for changing the flow path of hydraulic fluid).

[0075] The flow rate of hydraulic fluid received by or output by each working chamber may be independently controllable. The flow of hydraulic fluid received by or produced by each working chamber may be independently controlled by selecting the net displacement of hydraulic fluid per working chamber on each cycle of working chamber volume. This selection is typically made by a controller.

[0076] The flow and / or pressure demand may be sensed by measuring the pressure of hydraulic fluid at the inlet of the hydraulic actuator. If the hydraulic actuator is a hydraulic machine, the flow demand may be sensed, for example, by measuring the rotational speed of a rotating shaft, or the translational speed of a ram, or the angular velocity of a joint. The pressure sums of the measured flows may be summed, or the maximum of the measured pressures or flows may be found.

[0077] The demand signal indicating the pressure or flow rate requested based on the pressure and / or flow rate demand of the hydraulic actuator may be a signal representing the flow rate of hydraulic fluid, or the pressure of hydraulic fluid, or the torque on a shaft of a machine, or the torque on a shaft of a hydraulic actuator driven by the machine, or the output of the machine, or any other signal indicative of a demand related to the pressure or flow requirements of one or more hydraulic actuators.

[0078] A hydraulic machine is typically operable as a pump in a pumping mode or as a motor in a motoring mode, with the working chambers of the hydraulic machine potentially functioning as pumps (and thus some working chambers may output hydraulic fluid) or as motors (and thus some working chambers may input hydraulic fluid).

[0079] The values ​​of the discrete values ​​vary with the rotational speed of the rotatable shaft and may be selected to avoid the generation of undesirable and / or unacceptable frequencies when the hydraulic machine controls the net displacement of a group of one or more working chambers to execute the quantized demand.

[0080] Each individual working chamber can be selected, for example by a valve control module, to either displace a predetermined fixed volume of hydraulic fluid with each cycle of working chamber volume (an active cycle) or to undergo an inactive cycle with no net displacement of hydraulic fluid (also referred to as an idle cycle), thereby allowing the net fluid throughput of the machine to be dynamically matched to the demand indicated by the demand signal. The controller and / or valve control module may be operable to cause each individual working chamber to undergo an active or inactive cycle by executing an algorithm (e.g., for each cycle of working chamber volume). The method may include executing an algorithm to determine whether the individual working chamber will undergo an active or inactive cycle (e.g., for each cycle of working chamber volume). Typically, the algorithm processes a (e.g., quantized) demand signal.

[0081] Exemplary embodiments of the present invention will now be described with reference to the following drawings. [Brief description of the drawings]

[0082] [Figure 1] 1 is a schematic diagram of an apparatus according to the present invention including an electronically commutated hydraulic machine and actuator; [Diagram 2] FIG. 1 is a schematic diagram of an electronically commutated hydraulic machine. [Diagram 3] The procedure performed by the electronically commutated hydrolic machine of FIG. 2 to sequentially determine the net displacement for each cylinder is shown. [Figure 4] FIG. 2 is a schematic diagram of data processing for performing quantization. [Diagram 5] 4 is a graph of quantized power in response to a received demand signal as a function of time. [Figure 6] FIG. 1 is a flow diagram of a procedure for creating a quantization table (multiple discrete fractions). [Figure 7A]We show the change in fraction of active cylinders (Figure 7A), the change in partial stroke size as a fraction of maximum (Figure 7B), and the change in scale factor (Figure 7C) with displacement demand Fd. [Figure 7B] We show the change in fraction of active cylinders (Figure 7A), the change in partial stroke size as a fraction of maximum (Figure 7B), and the change in scale factor (Figure 7C) with displacement demand Fd. [Figure 7C] We show the change in fraction of active cylinders (Figure 7A), the change in partial stroke size as a fraction of maximum (Figure 7B), and the change in scale factor (Figure 7C) with displacement demand Fd. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0083] With reference to FIG. 1, an apparatus 1, for example a hydraulic excavator or other vehicle, includes an electronically commutated hydraulic machine 10 (hereinafter "ECM") including a first group 10A and a second group 10B of working chambers, each group being fluidly connected to a valve block 8 via a first fluid connection 21A and a second fluid connection 21B, respectively, and the groups of working chambers being separately connected to one or more of the high pressure manifolds 22A, 22B or 22C. Thus, as shown in this FIG. 1 embodiment, the ECM 10 includes two groups 10A and 10B, each group including one or more working chambers, although the number of working chambers is not shown in the figure. The ECM 10 functions as the hydraulic machine described above and will be further described below with reference to FIG. 2. The ECM may be a pump or a motor, and in this example is operable as a pump or a motor. The ECM is driven by a prime mover 2 via a rotating shaft 4. A low pressure manifold 6 extends from a tank to a low pressure side that is input to the ECM. On the high pressure side, the ECM has a valve block 8 operable to selectively connect different groups 10A, 10B of one or more working chambers of the electronically commutated machine to high pressure manifolds 22a, 22b and 22c, thereby changing which working chambers are connected to each high pressure manifold. All working chambers (whether group 10A, or group 10B, or both groups, or one or more further groups) connected to a high pressure manifold (to displace working fluid into or out of the same high pressure manifold) function together as a group of one or more working chambers connected to one or more hydraulic actuators via hydraulic circuits, with the net displacement of working fluid by one or more working chambers of the group connected to a particular one or more actuators being controlled together to control or respond to the actuators in response to a demand signal. The invention is equally applicable when there is no option to change the allocation of working chambers to actuators. Each of these high pressure manifolds extends to an actuator, such as a further hydraulic machine 11.The machine 11 may be of fixed displacement or of variable displacement with valves actuated and controlled electronically or mechanically (hydraulically) and drives a load 12, such as one or more wheels of a vehicle, through a further shaft 14, or another kind of hydraulic actuator 16, 18, for example the bucket, or ram, of an excavator. The actuators may function only as sinks or only as sources of hydraulic fluid, but some or all may function as either sinks or sources, depending on the actuator actuation direction. When an actuator is actuated, the working chambers of the ECM connected to the actuator perform a pumping cycle, and when driven by the actuator, the working chambers of the ECM connected to the actuator perform a motoring cycle.

[0084] The machine includes a machine controller 100 that receives control signals from an operator via one or more manual controls, and feedback signals such as actuator position signals or pressure signals from the individual hydraulic actuators 11, 16, 18 and / or the high pressure manifolds 22A, 22B, 22C and / or the fluid connections 21A, 21B. The machine controller 100 processes these signals and calculates and sends continuously variable demand signals for each group of working chambers to the ECM to control the machine. In the illustrated example, the machine controller may also periodically send control signals to the valve block 8 to reconfigure which working chambers are connected to which actuators, for example in response to current or future load changes, thereby changing which working chambers are in which group of one or more working chambers. However, the valves in the valve block may alternatively be actuated via pilot pressure via a hydraulic joystick.

[0085] FIG. 2 is a schematic diagram of a portion of the embodiment of the ECM shown in FIG. 1, showing a single group of working chambers currently connected to one or more actuators via a high pressure manifold 54. FIG. 2 shows details on a first group 10A, which includes multiple working chambers (eight shown) having cylinders 24 with working volumes 26 defined by the cylinder's inner surface and pistons 28 driven from a rotatable shaft 30 by an eccentric cam 32 and reciprocating within the cylinder to cyclically vary the cylinder's working volume. The rotatable shaft is rigidly connected to and rotates with the drive shaft. A shaft position and speed sensor 34 determines the shaft's instantaneous angular position and rotational speed and communicates it over signal lines 36 to an ECM controller 50, which can then determine the instantaneous phase of each cylinder's cycle.

[0086] Each of the working chambers is associated with a low pressure valve (LPV) in the form of an electronically actuated face seal poppet valve 52 having an associated working chamber and operable to selectively seal a channel extending from the working chamber to a low pressure hydraulic fluid manifold 54 which may connect one or more of the working chambers, or indeed all of the working chambers as shown herein, to a low pressure hydraulic fluid manifold of the ECM. The LPV is a normally open, electromagnetically actuated valve which passively opens when the pressure in the working chamber is equal to or less than the pressure in the low pressure hydraulic fluid manifold, i.e. during the intake stroke, so that the working chamber is in fluid communication with the low pressure hydraulic fluid manifold, but which may be selectively closed under active control of the ECM controller via an LPV control line 56 so that the working chamber is not in fluid communication with the low pressure hydraulic fluid manifold. The valve may alternatively be a normally closed valve.

[0087] Each actuation chamber is further associated with a respective high pressure valve (HPV) 64, each in the form of a pressure actuated discharge valve. The HPVs open outwardly from their respective actuation chambers and are each operable to seal a respective channel extending from the actuation chamber through the valve block 8 to the high pressure hydraulic fluid manifold 22, 58, and may connect one or more actuation chambers, or indeed all as shown in FIG. 2. The HPVs function as normally closed pressure relief check valves that passively open when pressure in the actuation chamber exceeds pressure in the high pressure hydraulic fluid manifold. The HPVs also function as normally closed electromagnetically actuated check valves that can be selectively held open by the ECM controller via the HPV control line 62 when pressure in the associated actuation chamber opens the HPV. The HPVs are not normally openable by the ECM controller against pressure in the high pressure hydraulic fluid manifold. The HPVs can also be open or partially open under the control of the ECM controller when pressure is present in the high pressure hydraulic fluid manifold but not in the actuation chamber.

[0088] In pumping mode, the ECM controller selects the net displacement rate of the hydraulic fluid manifold by the hydraulic motor from the working chamber to the high pressure hydraulic fluid manifold by actively closing one or more of the LPVs near the cycle of the associated working chamber, typically a point of maximum volume, to close the path to the low pressure hydraulic fluid manifold, thereby directing hydraulic fluid out through the associated HPV on the subsequent retraction stroke (but not actively holding the HPV open). The ECM controller selects the number and sequence of LPVs closed and HPVs open that generate flow or generate shaft torque or power to meet the selected net displacement rate.

[0089] In a motoring mode of operation, the ECM controller selects a net displacement rate of hydraulic fluid displaced by the ECM through the high pressure hydraulic fluid manifold and actively closes one or more of the LPVs just prior to the point of minimum volume of the cycle of the associated working chamber, closing a path to the low pressure hydraulic fluid manifold that causes hydraulic fluid in the working chamber to be compressed by the remainder of the retraction stroke. The associated HPV opens when pressure thereon is equalized and a small amount of hydraulic fluid is directed outward through the associated HPV, and is held open by the ECM controller. The ECM controller then typically actively holds the associated HPV open until the associated working chamber approaches maximum volume of the cycle, admitting hydraulic fluid from the high pressure hydraulic fluid manifold into the working chamber and applying torque to the rotatable shaft.

[0090] The ECM controller is operable not only to decide whether to close the LPV or hold it open every cycle, but also to vary the exact phasing of HPV closing relative to the changing actuation chamber volume, thereby selecting the net displacement rate of hydraulic fluid from the high pressure hydraulic fluid manifold to the low pressure hydraulic fluid manifold, or vice versa.

[0091] The arrows at low pressure fluid connection 6 and high pressure fluid connection 21A indicate the flow of hydraulic fluid in motoring mode, and the flow is reversed in pumping mode. A pressure relief valve 66 can protect the group in the ECM from damage.

[0092] The ECM, in normal operation, intersperses active and inactive cycles of the working chamber volume to meet the demand indicated by the received demand signal.

[0093] FIG. 3 illustrates the procedure executed by the ECM controller 50 to sequentially determine the net displacement per cylinder. The procedure begins at 200 after which a number of stored variable algorithmic accumulators are set to zero at 202. Variable algorithmic accumulators are maintained in groups of one or more cylinders independently controlled (functioning as groups of one or more working chambers) so that each group can respond to an independent demand signal. An "algorithmic accumulator" is more commonly known in computer science as an "accumulator," but a different term is used here to distinguish it from the hydraulic accumulator, which is an entirely different concept. The variable algorithmic accumulator stores the difference between the amount of hydraulic fluid displacement represented by the displacement demand and the amount actually displaced.

[0094] Then, at 204, the rotatable shaft of the ECM rotates until a decision point for an individual cylinder is reached. In the example shown in FIG. 1, there are eight cylinders that are equally phased apart without any redundancy, so each decision point is separated by 45 degrees of rotation of the rotatable shaft. Thus, the actual time period occurring between decision points is the time period required for the rotatable shaft to rotate 45 degrees, which is inversely proportional to the rotational speed of the rotatable shaft. However, in some embodiments, there may be different phases between decision points of actuation chamber activation, and there may be multiple actuation chambers that may be independently controlled but always have the same phase.

[0095] At each decision point, the ECM controller reads 206 a demand signal in the form of a displacement fraction Fd received from another controller (e.g., a machine controller) or calculated internally using a signal from the hydraulic circuit for each group of working chambers of the ECM. Then, at 208, for each group of working chambers, the ECM controller calculates a variable algorithmic sum equivalent to the associated algorithmic accumulator plus the displacement demanded for the group. This sum takes into account the time since the previous decision point and may be variable to account for variations in the rotational speed of the rotatable shaft and possible variations in the phase between decision points of the working chambers.

[0096] Next, at 210, the status of the cylinder being considered is checked by reference to a database of actuation chamber statuses 220. For each cylinder 24, if the cylinder is found to be damaged or is part of a different cylinder group that is not connected to an actuator or actuators, no further action is taken on that cylinder at this point. Once each cylinder (if any) that requires further consideration at the decision point has been considered, the method repeats from step 204 when the next decision point is reached.

[0097] For each cylinder to which a decision point is associated, the algorithmic sum of the associated working chamber group is compared at 212 to a threshold value. This value may simply be the maximum volume of hydraulic fluid that can be displaced by a cylinder if the only options being considered are an inactive cycle with no net displacement, or a full displacement active cycle with maximum displacement of hydraulic fluid by the cylinder selected. However, the threshold value may be higher or lower. For example, it may be less than the maximum displacement per cylinder if it is desired to perform a partial cycle in which only a portion of the cylinder's maximum displacement is displaced.

[0098] If the algorithmic sum is greater than or equal to the threshold, the cylinder 24 is determined to be undergoing an active cycle 214. Alternatively, if the algorithmic sum is not greater than or equal to the threshold, the cylinder 24 is determined to be inactive at 216 at the working volume of the cylinder 24 for the next cycle, resulting in a net displacement of zero. An accumulator value is calculated (218) by subtracting the displacement from the algorithmic sum.

[0099] Control signals are then sent to the low pressure valve 52 and high pressure valve 64 of the cylinder 24 under consideration to cause the cylinder to undergo an active or inactive cycle, as determined. (In the case of a pump, the high pressure valve may not be electronically controlled and the control signal may involve only the low pressure valve.) The control signals are sent over the respective control lines 56 (low pressure) and 62 (high pressure) for the particular valve associated with the cylinder under consideration.

[0100] This step effectively considers, for each group of working chambers (cylinders), the displacement demand represented by the displacement demand signal and the difference between the previous displacement represented by the displacement demand signal and the previous net displacement determined by the ECM controller (in this case in the form of a stored error), and then, if the algorithmic sum is greater than or equal to a threshold, matches the time-averaged net displacement of hydraulic fluid per cylinder to the time-averaged displacement represented by the displacement demand signal by subjecting the cylinder to an active cycle which produces a net displacement of hydraulic fluid. The error value is then set to the sum minus the displacement due to the active cylinder. Alternatively, if the algorithmic sum is not greater than or equal to the threshold, the cylinder is inactive and the algorithmic sum is not modified.

[0101] The procedure restarts at step 204 when the next decision point is reached for one or more cylinders.

[0102] Thus, it can be seen that for each group of actuating chambers, the algorithmic accumulator keeps a record of the difference between the requested displacement and the displacement actually produced. At each cycle, the requested displacement is added to a displacement error value and the actual selected displacement is subtracted. The algorithmic accumulator effectively records the difference between the requested displacement and the delivered displacement and an active cycle occurs whenever this accumulated difference exceeds a threshold. Because separate algorithmic accumulators are maintained for different groups of one or more cylinders connected together on the same high pressure manifold, the pressure in or flow through each high pressure manifold connected to the respective actuator may be independently controlled.

[0103] Those skilled in the art will appreciate that the effectiveness of this displacement determination algorithm can be accomplished in a number of ways. For example, rather than subtracting a selected displacement from the algorithm accumulator variable, the displacement of each individual cylinder could be selected to sum the requested displacement and the supplied displacement over a period of time and evenly match the two.

[0104] It can be seen that when the demand signal is low, the algorithm results in a very pulsating pressure ripple, as periodic active cycles are periodically interspersed between inactive cycles. If the demand signal is a constant fraction of 1 / n of the maximum demand, then in every n cycles of working chamber volume there will be one active cycle and the rest inactive cycles, resulting in a pulsating flow with a frequency equal to the frequency of the working chamber activation decision point 204 divided by n. A similar effect occurs when the demand signal is near or below, for example, 100% of the maximum demand, as occasional inactive cycles occur periodically between otherwise consecutive active cycles.

[0105] Typically, such vibrations begin at a relatively low amplitude, but the amplitude of the vibrations may increase over time, especially if the frequency of the vibrations is at (or close to) a resonant frequency of the vehicle (or a portion of the vehicle). Such vibrations may cause damage if the amplitude increases beyond a predetermined maximum amplitude.

[0106] In accordance with the present invention, the demand signal passed to the ECM controller and used as an input to the above algorithm is quantized to have only one of a predetermined group of discrete values ​​selected to avoid generating repetitive patterns of cylinder actuation that exceed a predetermined length, as described below, and a frequency component below a cutoff frequency.

[0107] FIG. 4 is a schematic diagram of the data processing performed by the equipment controller 100 and ECM controller 50 which together implement the present invention. It will be apparent to one skilled in the art that the functions of the equipment controller and ECM controller may be combined or even distributed. The equipment control program module 300 (represented by computer code executed by the equipment controller) processes feedback signals 310, 312, 314 received by the equipment controller from the actuators and the high pressure manifold. These signals may include pressure measurements, actuator position or velocity measurements, etc. The equipment controller also receives operator command signals 316 which may be input via a user interface such as a touch screen or keyboard, or manual controls such as a joystick or lever used to control the actuators (e.g., to control the operation of the hydraulic actuators of an excavator and / or drive the vehicle). This data is used to calculate current displacement demand signals 301A, 301B, 301C for each group of working chambers. In this example, the displacement demand signal is represented as Fd (a fraction of the maximum displacement per revolution of the rotatable shaft). These signals are then digitally processed by the machine controller to implement hysteresis using hysteresis logic 302A, 302B, 302C which outputs partially processed displacement demand signals 303A, 303B, 303C.

[0108] Hysteresis is useful to prevent chattering between adjacent quantization steps and is used in all quantization methods. The level of hysteresis in a system without an integral term, such as a negative flow control system, is inherent to the system's compatibility and pressure vs. displacement relationship (and possibly proportional gain). Hysteresis is not effective in a system with an integral term when using a quantized active cycle fraction and only pumping strokes are fully available, but only functions to change the frequency of the displacement cycle. When designing a hysteresis system, it is preferable to take into account that a human operator effectively compensates for slight errors between the produced displacement of the hydraulic fluid and the demanded displacement, for example by adjusting the joystick position to achieve the actuator position. In some embodiments, hysteresis is only provided when the displacement demand is decreasing and not when it is increasing. This is particularly useful in the variable stroke volume embodiment described below. Thus, the continuous demand signal that is fed to the ECM controller 50 and processed using the algorithm described with reference to FIG. 3 is quantized and typically also processed to introduce hysteresis.

[0109] The partially processed displacement demand is then quantized (304A, 304B, 304C). Referring to FIG. 5, instead of passing the originally calculated displacement demand signal 400 to the ECM controller 50, the demand signal is quantized, i.e., corresponds to one of a number of different displacement fractions 402A, 402B, 402C, 402D, 402E, etc. This is performed with reference to a solid-state memory that stores a data structure 306 that sets out a number of discrete fractions. The active cycle fraction can also be calculated during run-time without having a stored table. The quantized demand signal 305A, 305B, 305C is then passed to the ECM controller 50. The active cycle fraction can also be calculated during run-time without having a stored table.

[0110] The discrete fractions are selected to avoid the generation of patterns of active or inactive cycles of the cylinder volumes having a frequency content below the determined cutoff frequency, assuming a predetermined minimum rotational speed of the rotatable shaft. The pressure pulsations in the hydraulic lines arise from and have the same frequency content as those found in the active patterns including active and inactive cycles of the cylinder working volumes. This vibration is transmitted to the components. The objective of the quantized control method is to prevent the mechanical components of the system / vehicle from being excited at their natural frequency (either directly or indirectly, e.g., via operator activation). This can occur if the cylinders are activated at the same frequency as the natural frequency of the mechanical components where there is some path (e.g., mechanical coupling path) for the vibration to be transmitted from the pump (or connected hoses / pipes) to the mechanical components.

[0111] Quantization is used to remove frequencies from the effective pattern of the cylinders, preventing a specific displacement level from being commanded by the ECM controller. The displacement level may be defined in terms of volume of fluid per shaft revolution, or a fraction of the maximum displacement of fluid per shaft revolution. If the continuous displacement level demand is not equal to one of the discrete displacement levels, the closest discrete displacement level is selected, and there is a resulting error between the continuous displacement demand and the discrete displacement level. Thus, in this case, an error occurs between the demand volume and the delivered volume of the pump. This does not occur in a system where an error between the exact volume of fluid produced and the delivered volume is allowed.

[0112] Moreover, the human operator effectively compensates for slight errors between oil demand and production by adjusting the joystick position to achieve the desired actuator position.

[0113] The importance of the "minimum frequency" is that when quantization is used, there are no frequencies below which there are no valid patterns for the cylinder. If the selected "minimum frequency" is above the natural frequency of the component, then the mechanical component will not resonate at its natural frequency.

[0114] For this purpose, the group of discrete fractions may consist of fractions with denominators up to an integer n, where n is selected such that at the expected speed of shaft rotation, the frequency of selection of active cycles of the cylinder volume at displacement fraction 1 / n is above the cut-off frequency.

[0115] For example, if a machine has 12 evenly spaced cylinders and rotates at 1000 rpm, then a cylinder selection decision is reached every (60 / 1000) / 12=5 ms. With a maximum denominator of 5, a cylinder will perform an active cycle every 25 ms, the active cycle fraction is 1 / 5, and therefore the minimum frequency that exists is 40 Hz. This can be seen in the following example cylinder firing pattern:

[0116] [Table 1]

[0117] The table above shows that for Fd=1 / n (here 5), a pattern is generated with a repetition every n cylinders. For m / n, where m and n are both integers, expressed as an irreducible fraction (i.e. m and n have no common divisors other than 1), a pattern with sequence length n (m cylinders undergoing an active cycle) is again generated.

[0118] For example, the group of allowable parts may be each fraction m / n that is an irreducible fraction, where n ranges from 1 to a predefined maximum integer (5 in this example) and m is less than n (for each value of n). An example table for n=5 is shown below:

[0119] [Table 2]

[0120] More generally, for x cylinders evenly distributed around an axis and with a minimum operating rotational speed r (in revolutions per second), a pattern that repeats every n cylinders will produce vibrations of frequency xr / n.

[0121] Tables with larger maximum sequence length n can be generated by including every m up to n-1, and every irreducible fraction m / n for every n up to a determined maximum value.

[0122] A larger repeat pattern length (determined by n) leads to a proportionally lower frequency, but also to a larger table length.

[0123] For example, if n=12, the corresponding table is shown below.

[0124] [Table 3]

[0125] In practice, the fraction may be stored in a binary format that requires some rounding depending on the number of significant bits stored. Alternatively, the displacement fraction may be calculated without the use of a stored table.

[0126] In the table above, it is noted that the smallest non-zero fractions implemented by the ECM, and therefore the smallest Fd values, are 1 / n, 1 / (n-1), 1 / (n-1)… (until the next number in the array is 2 / n or greater). The largest fractions less than 1 are (n-1) / n, (n-2) / (n-1), (n-3) / (n-2).

[0127] The maximum displacement band gives the maximum displacement gap value shown in the table, which is usually 1 / n. This indicates how coarse the displacement steps are after quantization, and therefore how tolerant the quantization table is. Very coarse steps in displacement can prevent accurate control of the actuator, which may be of particular concern in vehicle applications.

[0128] In one experiment, using an excavator with an operator cab that can be vibrated at low frequencies (approximately 3-15 Hz), with an ECM driven hydraulic actuator fluidly connected to the ECM, the quantization table in Table 2 (maximum array length of 12, i.e., n=12) did not excite the cab but provided displacement steps that were coarse enough to provide an unacceptable user experience. Increasing the array length to 24, i.e., n=24, provided displacement steps that did not excite the cab but provided an acceptable user experience. Further increasing the array length to 36, i.e., n=36, provided acceptable step sizes but frequency content that excited the cab.

[0129] Thus, there is a trade-off between the coarseness of the quantized displacement level and the minimum frequency. In some applications, a gap of up to 5-10% is acceptable. The gap can be reduced by choosing an ECM with more working chambers at different phases, or by choosing a prime mover with a higher minimum shaft speed (or limiting the minimum shaft speed) and choosing a larger maximum denominator.

[0130] While in the case of hydraulic excavators the main concern is resonance of the cab itself, other vehicle body excitations and resonances are also of concern. For example, movement of the vehicle cab can set off resonances in the individual operator which can result in unintended movement of the joystick, thus exacerbating the situation. The present invention is particularly useful for avoiding low frequency resonance effects.

[0131] Furthermore, some displacement fractions may be deemed unacceptable, for example due to the risk of exciting further resonances, and displacement fractions that are deemed unacceptable may be excluded from the table of displacement fractions.

[0132] In the example of Table 1, the cylinders are equally spaced and in phase with no redundancy (n cylinders are configured such that their volume cycles are 360 / n° phase apart). However, ECMs in which the working chambers are not equally spaced in phase and / or are redundant are known, thereby referring to multiple working chambers having in-phase with each other. The latter is common where the cylinders are driven by multi-lobe cams, meaning, for example, that one or more working chamber cycles occur within one revolution of a rotatable shaft. Unevenly phased working chambers can result from the design of the ECM or from allocating working chambers to different groups of working chambers during operation.

[0133] For example, an ECM has 24 cylinders that are equally spaced and in phase (360 / 24=15° apart). Groups of 3 cylinders spaced 120° apart have a common high pressure output, and there are 8 independent outputs. Three of these independent outputs are connected to a first high pressure manifold, four of these independent outputs are connected to a second high pressure manifold, and one independent output is connected to a third high pressure manifold.

[0134] The phasing of the nine cylinders connected to the first high pressure manifold can be as shown in the table below.

[0135] [Table 4]

[0136] Table 4 shows that in this embodiment, the phase between successive cylinders is sometimes 30° and sometimes 60°, so the phase between cylinders is not constant.

[0137] In the example of Table 4, the length of the repeating cylinder phase pattern is 3. This number indicates the number of cylinders needed to repeat the cylinder phase. The phase difference between cylinder 1 and cylinder 2 is 30. The phase difference between cylinder 2 and cylinder 3 is 30. The phase difference between cylinder 3 and cylinder 4 is 60. This pattern is then repeated. It takes 3 cylinders to repeat this pattern, so the length of the repeating cylinder phase pattern is 3.

[0138] Machines can also be designed with cylinders that have duplicate phases (redundancy). The table below shows a 6-cylinder machine with redundancy 2.

[0139] [Table 5]

[0140] The quantization tables for such machines must be written with consideration of the requirement to ensure that a particular maximum sequence length bounds the lowest frequency in the expected manner.

[0141] If all working chambers have a redundancy greater than 1, the denominator of the fraction may be chosen to be a multiple of the redundancy. Thus, if the redundancy is 3, the table might contain fractions 1 / 3, 1 / 6, 1 / 9, 1 / 12, 1 / 15, etc.

[0142] One option when a machine has unequally spaced working chambers is to choose all denominators that are multiples of the repeating cylinder phase pattern length. This will give the same minimum frequency as an equally spaced machine with the same number of cylinders.

[0143] Therefore, the allowable deviation level of machines or services with inconsistent phase or redundancy is reduced to limit the lowest frequency, which creates additional coarseness in the quantization table.

[0144] The table below shows the effect of working chamber redundancy in a machine having 12 cylinders. The table shows which cylinders perform an active cycle at 1 / 3 displacement fraction.

[0145] [Table 6]

[0146] Table 6 shows that for a redundancy of 1, there is a repeating pattern every 90° (i.e., the pattern repeats four times per revolution of the rotatable shaft, which is four times the number of revolutions of the rotatable shaft). For a redundancy of 3, there is a repeating pattern every 90° (i.e., the pattern repeats four times per revolution of the rotatable shaft, which is four times the number of revolutions of the rotatable shaft). However, for a redundancy of 2, the phase difference between the active cylinders may be 120° and the phase difference between the active cylinders may be 60°. This causes a repeating pattern every 180° (i.e., the pattern repeats every half revolution of the rotatable shaft, which is twice the number of revolutions of the rotatable shaft). For the example with redundancy of 1 and the example with redundancy of 3, when the effective fraction is 1 / 3, there is a frequency four times the number of revolutions of the shaft. When the effective fraction is 1 / 3, there is a lower frequency at twice the number of revolutions of the shaft.

[0147] From this example it is clear that lower frequencies will exist if a denominator that is not an integer multiple of the redundancy is used in the quantization table. If it is desired to eliminate frequencies less than twice the shaft speed, then a cylinder phase with a redundancy of 2 cannot use a significant fraction of 1 / 3.

[0148] In such cases, the quantization tables for embodiments with redundancy > 1 consist of fractions with denominators that are multiples of the redundancy. For example, if n is up to 18, the following fractions are calculated, then sorted and duplicates removed: 1 / 3, 2 / 3, 3 / 3, 1 / 6, 2 / 6, 3 / 6, 4 / 6, 5 / 6, 6 / 6, 1 / 9, 2 / 9, 3 / 9, 4 / 9, 5 / 9, 6 / 9, 7 / 9, 8 / 9, 9 / 9, 1 / 12, 2 / 12, 3 / 12, 4 / 12, 5 / 12, 6 / 12, 7 / 12, 8 / 12, 9 / 12, 10 / 12, 11 / 12, 12 / 12, 1 / 15, 2 / 15, 3 / 15, 4 / 15, 5 / 15, 6 / 15, 7 / 15, 8 / 15, 9 / 15, 10 / 15, 11 / 15, 12 / 15, 13 / 15, 14 / 15, 15 / 15, 1 / 18 2 / 18 / 18 3 / 18 4 / 18 5 / 18 6 / 18 7 / 18 8 / 18 9 / 18 10 / 18 11 / 18 12 / 18 13 / 18 14 / 18 15 / 18 16 / 18 17 / 18 18 / 18.

[0149] When reduced to an irreducible fraction, we get:

[0150] [Table 7]

[0151] Referring to FIG. 6, more generally, the procedure for determining the quantization table begins with calculating (500) the repeating cylinder pattern, which depends on the relative phase differences of the individual cylinders, and whether and how much redundancy there is between the cylinders. Broken cylinders may be taken into account before operation (such as in simulations or experiments as in FIG. 6) or during operation. In a simple example where there is no redundancy and each cylinder is equally spaced, then the repeating phase difference is simply the phase spacing between the cylinders. If the cylinders are not evenly spaced, then the repeating pattern must be calculated by identifying the number of cylinders required to generate a repeating phase difference pattern and then summing the phase differences between all the cylinders. This is used to determine the phase difference between the repeating arrangements of the working chambers. In the examples of Tables 4 and 5, this is 120°. For a machine with c cylinders evenly spaced and r redundancy, this is 360*r / c. The number of cylinders required to generate the repeating pattern is also determined. This is 3 in the examples of Tables 4 and 5.

[0152] In the next step, the allowable denominators of the displacement fraction are calculated (502). This is calculated using the minimum expected operating shaft rotation speed and using the number of cylinders and the phase difference between the repeating patterns of the cylinders calculated in the previous step, which also includes the minimum allowable frequency. This allows for the calculation of an allowable denominator that does not lead to repeating patterns with frequencies below the minimum frequency. In the example of Figure 6, with a redundancy of 3, a shaft speed of 1500 rpm, and a minimum frequency of 15 Hz, the allowable denominators are 3, 6, 9, 12, and 15.

[0153] These denominators are then used to calculate the allowable Fd values ​​(i.e., the displacement fraction that is selected as one of the available quantizers) 504. For each allowable denominator n, the quantization table typically contains a respective m / n, where m is an integer from 1 to n for each value of n.

[0154] The calculated fractions are then processed by removing duplicates and sorting by numerical order (506). Optionally, in a next step, some Fd values ​​may be filtered (removed) from the calculated list (508) because they may generate some other resonances, for example in other components of the device.

[0155] This is followed by a verification step 510 where the calculated acceptable Fd values ​​are analyzed to determine whether they provide sufficiently smooth operation for the user.

[0156] The final set of calculated FD values ​​are then stored 512 in memory and used during operation of the machine. As mentioned above, there may be different tables of allowable Fd for different shaft speeds, or operating modes of the machine, for example, when different working chamber groups are connected to individual high pressure manifolds.

[0157] In the above example, the machine controller 100 created a quantized demand signal and avoided the generation of repetitive patterns of cylinder actuation beyond a predetermined length without the need to modify the ECM controller 50 or change the algorithm used (the sigma-delta algorithm). Thus, the exact cylinders that actually undergo an active cycle to achieve the requested displacement are determined by the ECM controller. Typically they are not predetermined but will vary from use to use depending on the time history of shaft rotation and the displacement required.

[0158] As previously discussed, it is typically advantageous for electrically commutated hydraulic machines to intersperse active and inactive cycles of working chamber volume to meet fractional displacement requirements, with each active cycle typically having the same net displacement, which is the maximum net displacement of each working chamber. However, with reference to Figures 7A-7C, an embodiment is now described in which the stroke volume of the working chamber during an active cycle is reduced by modifying the valve timing. While this may be less efficient in some respects, it can be combined with the quantization approach described above to result in a more reliable machine that suppresses the generation of undesirable low frequencies, vibrations, etc., which can provide a wide (and in some embodiments) continuous range of displacement fractions.

[0159] In these embodiments, the net displacement during the active cycle is reduced to less than 100% of the maximum displacement by varying the timing of the active control of the low and high pressure valves. Methods for this are known from WO2004 / 025122. For example, during a pumping cycle, the timing of closing the low pressure valve may be delayed from the normal phase, which is just after the point of maximum cylinder volume (top dead center). A short delay will only reduce the displacement slightly. Delaying the closing of the low pressure valve until it is closer to the point of minimum cylinder volume (top dead center) will reduce the displacement to a fraction of the maximum displacement. For a motoring cycle, the low pressure valve is opened and the high pressure valve is closed earlier than during the expansion stroke (from top dead center to bottom dead center), reducing the volume of working fluid it receives from the high pressure manifold. This step usually occurs late in the expansion stroke, and a little forward advance will reduce the displacement slightly, but a forward advance just after the point of minimum cylinder volume will reduce the net displacement significantly.

[0160] In operation, for any value of received (e.g. calculated or input) displacement demand Fd (x-axis), Fd is multiplied by a scaling factor 406 intended to ensure that the selected quantized displacement fraction is always greater than the demand so that the actual demand displacement can still be achieved by reducing the volume delivered by each cylinder (by adjusting the valve timing). Figures 7A and 7B use a scaling factor. As seen in Figure 7A, the fraction of cylinders performing an active cycle is quantized as before, thereby suppressing the generation of unwanted frequency components. However, the valve timing is modified to more closely match the total net displacement to the demanded displacement. As seen in Figure 7C, since the scaling factor used to "round up" the displacement must itself be a function of Fd, it is desirable to keep the stroke size of each cylinder as close to 100% as possible. Using this type of function ensures that the quantized Fd is maintained at an approximately fixed level higher than the Fd demand, thus maximizing the stroke size.

[0161] As an example, 0.9 on the y-axis in FIG. 7B corresponds to a net displacement per cylinder that is 90% of the volume delivered when using a full stroke (maximum). Quantizing the displacement demand is useful for controlling the frequency content of the machine output as a result of the cylinder activation algorithm, and looking from the left side of FIGS. 7A-C, it can be seen that at low displacement demands the cylinder actuation frequency does not drop below a threshold (approximately 0.1), but instead the partial stroke volume is reduced. This allows for an output displacement that closely matches the input displacement demand while avoiding the generation of pulse patterns with very low frequency content. A similar effect is seen at high displacement demands, where this method avoids the generation of low frequency patterns of cylinder deactivation.

[0162] As can be seen above and as shown in Figure 7A, the quantized demand sent to the ECM controller 50 is always higher than the continuous displacement demand. The necessary condition is that the quantized active cycle fraction is higher than the continuous displacement demand so that the partial stroke size can be less than or equal to 1 to ensure the continuous displacement demand is achieved. If the quantized demand is lower than the continuous displacement demand, then the partial stroke size required to achieve the continuous displacement would need to be greater than 1, which is not possible.

[0163] It is possible to leave gaps for displacements that cannot be satisfied, but the gaps can be avoided if one is sure that the quantized demand signal is greater than the continuous displacement demand over the entire displacement range. In this example, this is achieved by multiplying the continuous displacement demand by a scale factor shown in Figure 7C, but this is not the only possible approach. For example, a bias could be applied to the continuous demand and could vary over the entire displacement range.

[0164] In other embodiments, the gap is addressed by selecting the discrete active cycle fraction closest to the continuous displacement demand, applying no upward hysteresis and only downward hysteresis. These methods prevent requests for partial stroke fractions greater than one of the effective cylinders. For the reasons previously mentioned, it is preferred that the partial stroke size be as close to the full stroke size as possible throughout the displacement range.

[0165] Hysteresis can prevent jumps between quantized steps when the requested displacement is noisy. In the example shown in Figure 7A, if the Fd (linear continuous displacement demand) signal is smooth, hysteresis (or scaling) may be omitted and it is sufficient to round up to the nearest quantized step above Fd (linear continuous displacement demand). Unfortunately, in reality, the demand signal contains noise and therefore hysteresis is required, which refers to the difference in thresholds involved in deciding whether to change the step up or down. Applying hysteresis to the quantizer will prevent switching between steps in the presence of noise if the hysteresis is sufficient. If the noise level is greater than the steps themselves, then the amount of hysteresis alone will not help.

[0166] An alternative and potentially preferred approach is to use backlash. Backlash prevents the output signal from changing when the sign of the rate of change of the input signal changes. Usually this has a single parameter called the "deadband". The deadband is the amount of difference between the input and the output before the output starts again following the input. This type of signal processing often causes an offset between the input and the output signal. It is possible to correct the offset by using scaling as shown in the graph of Figure 7C. The scaling function is of the type y=n / x+1, where n is half the deadband width.

[0167] In the above example, the discrete values ​​in the quantization table correspond to discrete fractions of the working chamber performing an active cycle of the working chamber volume. This occurs because the units of the demand signal are fractions of displacement, although this is not required.

[0168] Further variations and modifications can be made within the scope of the invention disclosed herein.

Claims

1. 1. A method of operating an apparatus, the apparatus comprising: a prime mover and a plurality of hydraulic actuators, the hydraulic machine having a rotatable shaft in driving engagement with the prime mover and comprising a plurality of working chambers having volumes that vary periodically with rotation of the rotatable shaft; a hydraulic circuit extending between a group of one or more working chambers of the hydraulic machine and one or more of the hydraulic actuators; each working chamber of the hydraulic machine includes a low pressure valve for regulating the flow of hydraulic fluid between the working chamber and a low pressure manifold, and a high pressure valve for regulating the flow of hydraulic fluid between the working chamber and a high pressure manifold; the hydraulic machine is configured to actively control at least the low pressure valves of the one or more groups of working chambers to select a net displacement of hydraulic fluid per working chamber in each cycle of working chamber volume, thereby selecting a net displacement of hydraulic fluid per group of the one or more working chambers in response to a demand signal; The method includes controlling the valves to cause each working chamber to undergo either an active or inactive cycle of the working chamber volume during each cycle of the working chamber volume; the fraction of the working chambers that undergo an active cycle is variable and selected from a plurality of discrete fractions; The method of claim 1, wherein the plurality of discrete fractions are selected to avoid generating any repeating patterns of active and inactive cycles of working chamber volumes having a length that exceeds a predetermined maximum repeating pattern length.

2. The method of claim 1 , wherein the plurality of discrete fractions does not include any fraction having a denominator greater than a predetermined maximum denominator when expressed in irreducible fractions.

3. The method of claim 1 or claim 2, wherein the demand signal to which the hydraulic machine responds is quantized and has one of a plurality of discrete values.

4. 2. The method of claim 1, wherein the discrete fractions are expressed as irreducible fractions, with denominators ranging up to a maximum value selected to avoid generating repetitive patterns of actuation chamber actuation at frequencies below a predetermined minimum value.

5. 2. The method of claim 1, wherein the smallest non-zero fraction of the plurality of discrete fractions is 1 / n, and the second smallest fraction of the plurality of discrete fractions is typically 1 / (n-1), where n is an integer.

6. 2. The method of claim 1, wherein the smallest non-zero fraction of the plurality of discrete fractions is selected taking into account two or more working chambers having the same phase or having a non-uniform phase difference between two or more working chambers.

7. 2. The method of claim 1, wherein the discrete fractions are determined by simulation or experiment, and typically the discrete fractions are included in the plurality of discrete fractions in response to a simulation or experiment that indicates that the frequency content of the resulting high pressure manifold pressure, or valve actuation current, or other signal meets one or more acceptable frequency spectrum criteria, and / or that the frequency content below a cutoff frequency is below a threshold, or that the effect of the selection of active and inactive cycles is acceptable, or is excluded if they do not meet such criteria.

8. The method of claim 1 , wherein the discrete fractions and / or discrete values ​​of the quantized demand signal are calculated during run-time and / or in real time, taking into account predefined parameters and / or current measurement parameters.

9. 2. The method of claim 1 , wherein the plurality of discrete fractions varies in response to a rotational speed of the rotatable shaft or another operating parameter of the apparatus, and optionally the method includes switching from using a first plurality of discrete fractions to a second plurality of discrete fractions when the rotational speed of the rotatable shaft exceeds a threshold value.

10. 2. The method of claim 1, wherein the opening and closing timing of at least the low pressure valve is adjusted to vary the fraction of maximum stroke volume displaced per working chamber during each active cycle, the fraction of working chambers performing active cycles being limited to one of a plurality of discrete fractions, but optionally allowing for a continuous range of displacement per revolution of the rotatable shaft to be produced.

11. The method of claim 1, wherein to calculate the plurality of discrete fractions, the method includes inputting a minimum allowable frequency, a target rotational operating speed of a rotatable shaft, and data indicating the number and / or phase difference between working chambers of the machine and / or the phase difference between working chambers within a group, calculating an integer number n of working chamber decision points between active cycles that result in the occurrence of a frequency of cylinder operation only if it exceeds the minimum allowable frequency, and including 1 / n in the plurality of discrete fractions.

12. 12. The method of claim 11, further comprising including in the plurality of discrete fractions, after removing duplicate values, a plurality of fractions whose denominators are integers up to n and whose numerators are integers up to n-1.

13. 13. A method according to claim 11 or 12, comprising removing one or more discrete fractions from the plurality of discrete fractions to avoid generating repetitive cylinder actuation patterns having frequency content below a particular value.

14. 12. The method of claim 11, further comprising storing the plurality of discrete fractions in a solid-state memory device for retrieval during operation.

15. 15. A solid-state memory device storing a plurality of discrete fractions calculated according to the method of claim 14.

16. 1. An apparatus comprising a prime mover and a plurality of hydraulic actuators, the hydraulic machine having a rotatable shaft in driving engagement with the prime mover and comprising a plurality of working chambers having volumes that vary periodically with rotation of the rotatable shaft; a hydraulic circuit extending between a group of one or more working chambers of the hydraulic machine and one or more of the hydraulic actuators; each working chamber of the hydraulic machine includes a low pressure valve for regulating the flow of hydraulic fluid between the working chamber and a low pressure manifold, and a high pressure valve for regulating the flow of hydraulic fluid between the working chamber and a high pressure manifold; the hydraulic machine comprising a controller configured to actively control at least the low pressure valves of the one or more groups of working chambers to select a net displacement of hydraulic fluid per working chamber in each cycle of working chamber volume, thereby selecting the net displacement of hydraulic fluid per group of the one or more working chambers in response to a demand signal; the controller is configured to control the valves to cause each working chamber to undergo either an active cycle or an inactive cycle of the working chamber volume during each cycle of the working chamber volume; the apparatus is configured such that the fraction of the working chambers that undergo an active cycle is variable and selected from a plurality of discrete fractions; The apparatus, wherein the plurality of discrete fractions are selected to avoid generating any repeating patterns of active and inactive cycles of working chamber volumes having a length that exceeds a predetermined maximum repeating pattern length.

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