Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B7/00—Piston machines or pumps characterised by having positively-driven valving
  • F04B7/02—Piston machines or pumps characterised by having positively-driven valving the valving being fluid-actuated
  • F04B7/0266—Piston machines or pumps characterised by having positively-driven valving the valving being fluid-actuated the inlet and discharge means being separate members
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B49/00—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
  • F04B49/06—Control using electricity
  • F04B49/065—Control using electricity and making use of computers
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
  • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
  • F04B7/00—Piston machines or pumps characterised by having positively-driven valving

Definitions

• the present invention relates to the technical field of hydraulic machines, such as hydraulic motors and hydraulic pumps. More specifically the invention relates to forced actuation of valves in hydraulic machines.
• Hydraulic machines is a common term used in this document to represent both hydraulic pumps and hydraulic motors. Hydraulic machines with electronically controlled distributor valve systems with individual valves for each cylinder or working chamber, are in the following called digital pumps and motors.
• Hydraulic machines such as hydraulic motors and hydraulic pumps are frequently used in industrial applications.
• hydraulic motors and hydraulic pumps can be interchangeable because they perform the opposite function, i.e.
• Hydraulic pumps and motors are often combined into hydraulic drive systems or hydraulic transmissions that have a large number of possible applications, such as transmission systems for entrepreneurial machines, farming equipment, mining equipment, conveyers, wind turbines, etc.
• the torque and rotational speed of the motor may be varied to provide a drive train with a variable gearing.
• the solenoids can then keep the valves in the open position once the open position has been reached, instead of letting the valves return passively to their initial position when the pressure difference across the valve decreases.
• Solenoids are well known for keeping valves open.
• the solenoids are weak compared to the pressures over closed valves, but strong enough to keep a valve open against the flow in case they are already open.
• Such solenoid activated valves may be used to improve the efficiency of the hydraulic machine by using an external control system to control the activation of the solenoids and thereby the activation or
• FIG. 1 A principal sketch of a balanced valve with solenoids for retaining a valve in open position is shown in Fig. 1.
• One cylinder with a cylinder chamber (4) and a piston (3) is shown.
• the valve (H) on the left hand side is connected to a high pressure source and the valve (L) to the left is connected to a high pressure line.
• the forces (FL, FH) that can act on the valves when the solenoids (s) are activated are indicated as arrows.
• One way of controlling torque and displacement is to utilize only a part of a stroke of a hydraulic machine by opening or closing valves in the middle of a stroke, or to temporarily disable a number of cylinders. Cylinders may be disabled by e.g. opening a valve of the cylinder over the full stroke. By appropriately controlling the valves, the operation may be varied between full-stroke and disabled.
• WO 2004025122 and later applications detailing this method focus on producing time averaged flow with minimum ripple, and the effective contribution of each cylinder (full stroke, part stroke or no stroke) is essentially decided cycle by cycle before the cylinder actually enters that cycle. The decision is based on history and prediction.
• Another problem is related to reverse pressure operation, i.e. interchanging high and low pressure sides of the hydraulic motors with solenoid activated valves according to prior art, since the valves are dedicated for high or low pressure, and reverse pressure operation is not possible.
• a main object of the present invention is to disclose a hydraulic machine valve arrangement, and a method for controlling the valve arrangement that overcomes the problems described above for hydraulic machines.
• the invention is therefore a method for controlling a positive displacement hydraulic machine with two or more working chambers, each in fluid contact with a valve arrangement comprising a controllable high pressure valve and a controllable low pressure valve, the method comprising the following steps;
• the valve arrangement according to the invention may be used in combination with different types of hydraulic pumps and motors, e.g. cylinder and piston based, vane based etc. in different topologies such as star, row etc.
• the working chamber is a fluid chamber with cyclically varying volume delimited in the case of a cylinder based motor, by the cylinder, piston and the cylinder top, at least partly constituted by the valve arrangement according to the invention, and in the case of a vane based motor by the vanes, the motor housing and the valve arrangement.
• a method of instant displacement of working chambers or cylinders of a hydraulic machine is possible with the new valve technology. This way, the sum of the effective displacements will be as close as possible to the instant displacement reference. This is of particular value when operating machines at low speed compared to the variation of reference. Also it means that it is possible to produce a low-ripple reduced displacement/torque from machines with as few as 5 cylinders, which elsewise is very difficult.
• One advantage of this invention is full control at low speed and under load, where valves can shift from an open to a closed position or vice-versa, even in a stand still situation. This is of particular interest in slow moving hydraulic motors (often referred to as “high torque low speed motors”), where start, stop and low speed rotation is of particular importance.
• valve arrangement can be implemented as an integrated solution in the hydraulic machine, the improved hydraulic machine may replace traditional hydraulic machines controlled by a hydrostatic pump and directional control valve without any adaptation and it can also be connected as self-controlling device to e.g . a constant pressure supply.
• a hydraulic machine with the valve arrangement according to the invention can easily freewheel by forcing all low pressure valves or all high pressure valves to open and to stay open.
• the invention allows a hydraulic motor to be designed symmetric, so that it can accept reversal of high- and low pressure.
• a further advantage of the invention is that a pressure relief function is inherent in the valve arrangement, where a closed valve will be forced to open when the pressure in the cylinder chamber provides a force on the valve element that overcomes an opposite force provided e.g. by the pilot pressure used to keep the valve closed.
• variable displacement function can be achieved by enabling and disabling cylinders.
• An advantage of the present invention is that flow capacity can easily be increased to increase power and speed.
• working chambers or cylinders of co- working hydraulic motors can be controlled by a common control system, resulting in less ripple and improved resolution, and also allowing for improved robustness against failures related to one cylinder.
• FIG. 1 illustrates in a simplified section view a valve arrangement for hydraulic machines according to prior art.
• FIG. 2 illustrates in a combined section view and diagram, a valve arrangement according to an embodiment of the invention.
• Fig. 4 illustrates in a diagram a valve arrangement according to the invention where pilot pressure is obtained via a select valve.
• Fig. 3 illustrates in a diagram a valve arrangement according to the invention where pilot pressure is directly obtained from high pressure source.
• FIG. 5 illustrates in a diagram a valve element comprising an anti-cavitation valve.
• Fig. 6a and 6b illustrate in a diagram a successive/continuous displacement control and torque control, respectively.
• Fig. 7 illustrates in a diagram an instant displacement control with pre-filter.
• Fig. 8a and 8b illustrates contribution from each working chamber in a hydraulic machine with instant displacement control.
• Fig. 9 illustrates in a diagram an instant torque control with pre-filter.
• Fig. 10 illustrates in a diagram an algorithm for initialization of the displacement control of a hydraulic machine.
• Fig. 11 illustrates common control of several motors driving a common load.
• valve arrangement (1) according to an embodiment of the invention is shown for one cylinder (2) with a piston (3) and a cylinder chamber (4) of a hydraulic motor. Although only one cylinder is shown here, the same valve arrangement may be used for the other cylinders of the hydraulic motor or for a hydraulic pump.
• First and second pressure valves (20h, 201) of poppet types are in connection with a motor cylinder (2), where the main ports (22) of the first and second pressure valves (20h, 201) are connected to respectively high- and low pressure sides (Ph, PI) of a hydraulic pump (6) as shown in Fig. 3.
• Fig. 3 shows a non-symmetric operated valve system.
• two pilot operated main valves (20h, 201) of poppet type connect each motor cylinder (2) with fluid supply lines, e.g. high- and low pressure sides (Ph, PI) of a pump (6).
• fluid supply lines e.g. high- and low pressure sides (Ph, PI) of a pump (6).
• the two main valves (20h, 201) are of similar configuration, with the cylinder chamber (4) connected to the working chamber port (23) of each main valve and one fluid supply line connected to the main port (22) of one valve (22h) and the other fluid supply line connected to the main port (22) of the other valve (221).
• a valve (201, 20h) is said to be closed when there is no connection between the working chamber port (23) and the respective fluid connection.
• Pilot means (30h, 301) operate the opening and closing of the valves (20h, 201) by controlling the pilot pressures in the pilot chambers of the valves (20h, 201) through the pilot port (21) of the valves (20h, 201), with the pressure working upon areas of third surface (A3) shown in Fig. 2.
• Pilot supply pressure is either established by the HP select valve (50) in Fig. 4 showing a symmetric valve system, where the HP select valve (50) connects the fluid connection line with the highest pressure to the pilot supply line or by using directly high pressure as shown in Fig. 3.
• a separate pilot pressure may be established, and separate (different) pilot pressures to each pilot valve offers extended opportunities.
• valve arrangement according to the invention and as described in the different embodiments may be used in combination with different types of hydraulic pumps and motors, e.g. cylinder and piston based, vane based etc.
• valve arrangement ( 1) in the hydraulic circuit shown in Fig. 3, where the valve arrangement ( 1) according to the invention is a central part, three pressure levels are shown. In addition to the high- and low pressure sides (Ph, PI), a tank pressure (Pt) is also present. The tank pressure (Pt) is usually lower than the low pressure (PI).
• the first and second pressure valves (20h, 201) are of similar configuration, and the working chamber port (23) on each of the valves are connected to the cylinder chamber (4).
• the first and second pressure valves (20h, 201) are to be closed when there is no fluid connection (F) between the working chamber port (23) at the motor cylinder chamber (4) side and the respective main port (22).
• valve housing (24) is considered part of the valve (20h, 201). In Fig. 2 the valve housing is common for the valves, but valves may also be implemented as separate devices with separate valve housings (24) for each valve.
• the main ports (22) performing the same function i.e. all main ports to be connected to the same low pressure port or the same high pressure port may be connected to a manifold applying well known technology as understood by a person skilled in the art.
• the valves may also be integrated into the housing of the motor.
• the main port (22) on the left hand side is connected to a high pressure source (Ph), and the main port (22) on the right hand side is connected to a low pressure line (PI), e.g. tank.
• the two valves comprise a working chamber port (23) and a valve element (25) inside the valve housing (24).
• the valve element (25) is arranged to move in a first direction (d), i.e. up and down in this case, inside the valve housing (24) to control a hydraulic flow (F) between the valve main port (22) and the working chamber port (23).
• Fig. 2 it can be seen that the left hand valve (20h), i.e. the high pressure valve in this case, is closed, and there is no flow between the main port (22) and the working chamber port (23).
• the low pressure valve (201) to the right is in an open position and a flow (F) is indicated between the working chamber port (23) and the main port (22).
• each of the valves (20h, 201) comprises a pilot port (21).
• the pilot port (21) is in fluid connection with a third surface (A3) of the valve element (25).
• the third surface (A3) constitutes a part of an inner wall of a first pilot chamber (28) limited by the valve housing (24) and the valve element (25).
• the volume of the first pilot chamber (28) depends on the position of the valve element (25) since the valve element can move up and down inside the valve housing (24). When the valve is moving from a closed to an open position the volume of the first pilot chamber (28) decreases and vice versa.
• the third surface (A3) remains the same, and any pressure inside the first pilot chamber (28) will act on the third surface (A3) in any position.
• Fig. 2 shows a similar pilot port (23) for the low pressure valve (201), to the right.
• the pilot port (21) on the left hand side is connected to a pilot main port (31) of a first pilot pressure control means (30h).
• the first pilot pressure control means (30h) also comprises a pilot control port (32), arranged to receive a control signal (32s).
• the control signal (32s) will be an electric signal from a control system, but it may also be optical, hydraulic etc.
• a control system (201) providing the control signals (32s) to the pilot control ports (32) is illustrated.
• the first pilot pressure control means (30h) is implemented as a hydraulic valve arranged to be connected to a high pressure line (Ph) and a tank line (Pt), and the output pilot pressure on the pilot main port (31) can be switched between high pressure (Ph) and tank pressure (Pt) by opening or closing the valve.
• the value of the control signal (32) determines the state of the valve and thereby the pilot hydraulic pressure (Pp).
• the valves of the pilot pressure control means (30h, 301) can be either spool valves or poppet valves.
• the first pilot pressure control means (30h) is implemented as a pressure control valve arranged to be connected to a high pressure line (Ph) and a tank line (Pt), and the output pilot pressure on the pilot main port (31) can be varied between high pressure (Ph) and tank pressure (Pt) by opening or closing the valve.
• the value of the control signal (32) determines the state of the valve and thereby the pilot hydraulic pressure (Pp).
• the hydraulic valve or pressure control valves are connected to the high pressure line (Ph) and a low pressure line (PI) of the systems shown in Fig. 3 and 4.
• at least one of the sources are independent of the pressure lines used by the hydraulic machine, e.g. a higher pressure line with a higher pressure than the high pressure line (Ph), and a lower pressure line with a lower pressure than the high pressure line (PI).
• the pressure lines used enable the first and second pilot pressure control means (30h, 301) to open and close the valves (20h, 201) as intended by the operation, the actual source is not critical for the invention.
• Variable pilot pressure allows torque control of the hydraulic machine.
• the torque of the motor is controlled by varying the pilot hydraulic pressure (Pp) on the pilot port (21) on the valve connected to the low pressure line (PI) during contraction of the cylinder.
• pilot hydraulic pressure (Pp) is acting on the third surface (A3) to provide a pilot force (Fphl) acting on the valve element (25) in the first direction (d), as shown in Figure 2.
• the pilot force (Fph l) is arranged to close the valve (20) for a pressure on the working chamber port (23) up to at least the hydraulic pressure (Ph).
• pilot force (Fph l) is arranged to close the valve (20) for a pressure on the working chamber port (23) higher than the hydraulic pressure (Ph).
• a number of forces are acting on the valve (201). Most notable are forces resulting from the pressure in the cylinder chamber (4) that will act directly on the first area (Al), which is the area facing the cylinder chamber (4). A high pressure in the cylinder chamber (4) will result in a force acting on the valve trying to open it.
• the valve can be closed if the pilot force (Fph l) overcomes the net forces, including the force from the pressure in the cylinder chamber (4) acting on the first area (Al).
• the valve can be opened if a low pressure is present in the cylinder chamber (4) the valve can be opened if the pilot force (Fphl) overcomes the net forces, including the force from the pressure in the cylinder chamber (4) acting on the first area (Al).
• the pilot hydraulic pressure (Pp) is decreased, possible down to tank level (Pt), resulting in a small pilot force (Fph l) acting on the valve.
• the pressure on the effective surface (A2) of the main port will result in an upward force, larger than the pilot force (Fph l) acting on the valve element (25) open the valve.
• the valves (20h, 201) comprises return means arranged to return the valve element (25) to an initial position.
• the return force is arranged to be much smaller than the pilot force (Fphl), so that the pilot force (Fphl) can overcome the return force at any time.
• the valve housing (24) comprises a second pilot port (27) in fluid connection with a fifth surface (A5) of the valve element (25), wherein a second pilot hydraulic pressure (Pp2) on the second pilot port (27) is acting on the fifth surface (A5) to provide a second pilot force (Fph2) acting on the valve element (25) in a direction opposite to the pilot force (Fph l).
• a second pilot hydraulic pressure (Pp2) on the second pilot port (27) is acting on the fifth surface (A5) to provide a second pilot force (Fph2) acting on the valve element (25) in a direction opposite to the pilot force (Fph l).
• Pp2 second pilot hydraulic pressure
• Fph2 second pilot force
• valve housing (20) comprises a return spring
• one or more anti-cavitation valves (26) are connected between the cylinder chamber (4) and the housing/tank or another low pressure line as shown in Fig. 3, to secure a minimum working chamber pressure above cavitation pressure.
• valve element (25) of the second valve (201) comprises an anti-cavitation valve (26) as illustrated in Fig. 5.
• the anti-cavitation valve (26) is integrated into the valve element (25).
• boost pressure from a separate boost supply line is connected to the anti-cavitation valve (26).
• the anti-cavitation valve may be supplied from a low pressure select valve, which connects it to the one of the two supply pressure lines with the lower pressure.
• the displacement reference setting is continuously integrated over the shaft angle, and the result being the total geometric volume of oil that should have been moved. This is illustrated in Fig. 6a.
• the volume error value is evaluated. If the value is above a specified threshold, the new cylinder is activated. If the value is below the threshold, the new cylinder is not activated but idled.
• a torque reference setting is integrated over the shaft angle, and rotational energy from cylinders is subtracted from the result of the integration and the resulting shaft energy error is used to determine activation/de- activation of the next cylinder as shown in Fig. 6b.
• This method has a number of parameters for adjustments, but basically it has been shown to produce the same results as predefined cylinder patterns that were based on a minimum variance selection criteria.
• the method above has a pre-filter of displacement reference to use only displacement reference settings with known, acceptable ripples.
• the accepted displacements may be e.g. : 100%, 50%, 0%.
• the pre-filter sends out one of these values, based on the actual displacement reference input.
• the invention is a method for controlling a positive
• the method comprises the steps of;
• valve arrangement is the valve arrangement (1) according to any of the embodiments described above.
• system indicator is a measured or simulated volume error, displacement error, speed change, direction change, load direction change, pressure change, reference change or speed.
• the invention is a method illustrated in Fig. 7, for controlling a positive displacement hydraulic machine with two or more working chambers, each in fluid contact with arrangement comprising a controllable high pressure valve and a controllable low pressure valve, the method comprising the following steps;
• - choose the combination that best meets a selection criteria e.g. minimum deviation from the reference setting, at least as high as the reference setting or other criteria
• the selection criteria is one or more of;
• the instant contribution value is an instant contributing displacement value
• the reference setting is a displacement reference setting
• the instant contribution value is an instant contributing torque value
• the reference setting is a torque reference setting
• Figure 8a shows displacement results of a five cylinder machine with one high pressure line and one low pressure line.
• the reference setting is 0.6 displacement with an algorithm allowing for negative contributions (i.e. cylinders working against the rotation) and selecting the combination of cylinders that creates the smallest absolute displacement error.
• Other criteria than absolute error can be used, for instance relative error.
• each working chamber contributes positively in the middle part of each stroke. Some overlap occurs with the next cylinder, and during this overlap, negative contribution from two other cylinders are included, keeping deviation from reference setting low.
• the instant control is based on displacement, and the instant contribution value is the instant contributing displacement value, i.e. the displacement in a specific cylinder at the instant the value is determined, and the reference setting is a displacement reference setting, i.e. a desired displacement for the hydraulic machine.
• both positive and negative contributions from cylinders are included.
• the sum of the instant displacement contributions from the cylinders should be as close as possible to the instant displacement reference setting.
• cylinders are selected so that the sum of the cylinder's instant
• cylinders are selected so that the sum of the cylinders instant displacements have the least relative deviation from the reference setting, e.g. if reference setting is 50%, displacements of 25% and 100% are weighted equal.
• the criteria is one or more of a minimum instant displacement, a maximum instant displacement, a maximum linear deviation from the setting, a maximum logarithmic deviation from the setting etc.
• the instant control is based on torque, and the instant contribution value is the instant contributing torque value, i.e. the torque provided by a specific cylinder at the instant the value is determined, and the reference setting is a torque reference setting, i.e. a desired torque on the main shaft of the hydraulic machine.
• the instant torque contribution from each working chamber is determined by taking into account one or more of supply pressures, housing pressure, internal friction, pressure losses through in- and/or outlet valves. Pressures may be estimated or measured. Housing pressure acts on the backside of the pistons and work against the working chamber pressure.
• the selection criteria varies with operating conditions, e.g. speed, load, pressures, temperature etc.
• control system comprises a pre-filter allowing only torque reference settings with acceptable performance.
• Performance may be torque ripples, flow ripples, efficiency, motor load etc.
• losses are estimated and used as part of an optimization criterion with the scope of reducing losses.
• One example of a simple such criteria may be to allow an error window for the torque and within that window seek a cylinder combination that generates the least possible losses. Other more complex methods may apply.
• the invention is a method comprising the following steps when the hydraulic machine is in motoring mode;
• the invention is a method comprising the following steps when the hydraulic machine is in pumping mode;
• Both methods may use input from a torque measurement to increase precision.
• the cylinders are of different sizes with different nominal displacements.
• the housing pressure is included in the calculations to improve precision of the torque calculation.
• valves are throttled to actively introduce a pressure loss.
• a way of initializing the motor is disclosed. This is shown in Fig. 10. Initialisation may be used at any time during operation where a major shift in displacement is needed or by start of motor operation.
• the invention is a method based on the steps of the next cylinder activation method described above, comprising the step of, in an initializing phase;
• a working period may be any possible period of the hydraulic machine, such as 2 revolutions, 5 revolutions 6.5 revolutions etc.
• the working period also may change dynamically during the operation of the hydraulic machine depending on its current status.
• the indicator is, but not limited to, a measured or simulated volume error, displacement error, speed change, direction change, load direction change, pressure change, reference change or speed, displacement reference rate of change, known future changes in displacement reference, motor speed, number of active cylinders, actual displacement, displaced volume error or any combination hereof.
• valve states are estimated in a current working situation characterized by e.g. shaft position, pressure, torque, reference setting, etc. similar to that of the real motor and these states are used to initialize the real motor valves, so that they are shifted into states similar to those of the simulated motor.
• the invention is also in an embodiment a method for controlling torque in a positive displacement hydraulic machine with a valve arrangement (1) connected to a cylinder or working chamber, comprising;
• a first valve (20h) comprising;
• valve element (25) arranged to move inside the valve housing (24) to control a hydraulic flow (F) between the valve main port (22) and the working chamber port (23), wherein the method comprises the step of
• valve element (25) of the first or second valve (20h, 201) between a closed position and an open position, during contraction or expansion, to throttle the hydraulic flow (F) and thereby altering a pressure inside the working chamber and accordingly the torque of the hydraulic machine.
• Throttling will limit the hydraulic flow through the valve. Instead of closing and opening the valve as indicated in prior art, a smoother operation can be obtained by throttling the valve in the intermediate positions.
• a pre-defined number of intermediate positions are defined, and throttling positions are limited to a final number.
• valve element (25) can be set in any intermediate position.
• valve main port (22) of the a first valve (20h) is connected to a hydraulic fluid source with a first hydraulic pressure (Ph) and the second valve (201) is connected to a hydraulic fluid source with a second hydraulic pressure (PI) lower than the first hydraulic pressure (Ph)
• the method comprises one or more of the steps of;
• valve main port (22) of the a first valve (20h) is connected to a hydraulic fluid source with a first hydraulic pressure (Ph) and the second valve (201) is connected to a hydraulic fluid source with a second hydraulic pressure (PI) lower than the first hydraulic pressure (Ph)
• first valve (20h) or the second valve (201) comprises a pilot port (21), the valve arrangement (1) further comprising a first pilot pressure control means (30h), wherein the first pilot pressure control means (30) is arranged to provide a pilot hydraulic pressure (Pp) on the pilot main port (31) as a function of a control signal (32s) on the pilot control port (32), wherein the method comprises the step of;
• the position of the valve element (25) may in one embodiment in addition be a function of the pressure inside the working chamber, and vary with this pressure even when the control signal remains the same.
• pilot port (21) is in fluid connection with a third surface (A3) of the valve element (25), the valve arrangement (1) further comprises a first pilot pressure control means (30h) comprising;
• pilot hydraulic pressure (Pp) is acting on the third surface (A3) to provide a pilot force (Fph l) acting on the valve element (25) in the first direction (d), and wherein the pilot force (Fph l) is arranged to close the valve (20) for a pressure on the working chamber port (23) up to the hydraulic pressure (Ph).
• Throttling may be achieved in a number of ways, and one solution according to the invention is to control the position of the first valve (20h) and/or the second valve (201) according to speed and pressures and position of the hydraulic machine.
• it can be achieved by controlling the pressure on third surface A3 during outlet from a compression stroke if area four (A4) ⁇ area one (Al), it can be controlled by controlling pressure on third surface A3 during an inlet stroke if area four (A4) > area one (Al).
• two or more hydraulic motors are coupled in parallel and are driving the same load. This is illustrated in Fig. 11, where hydraulic motors (200) with cylinders (2) and valve arrangements (1), where the valve arrangements (1) are controlled from a control system (201). The interconnection of the motor shafts and the transmission for driving the load is not shown.
• One such application area is formed by large winches for fishery and off-shore. If for instance three 5 cylinder motors are driving one load, they may be controlled as if they are one 15 cylinder motor, thereby achieving control of displacement, torque, flow or speed with less ripple and improved resolution, and also allowing for improved robustness against failures related to one cylinder.
• One such example is wheel motors driving each one wheel on a vehicle, the wheels having different diameters and the vehicle being steerable.
• Another example is two or more motors driving in parallel a marine winch through each a transmission.
• speed may vary between motors, phasing of motors may vary, cylinder sizes may vary, etc.
• the invention is therefore a method for controlling two or more positive displacement hydraulic machines each with two or more working chambers, each in fluid contact with a valve arrangement (1) comprising a controllable high pressure valve (20h) and a controllable low pressure valve (201) and each of the machines connected to a same load, wherein the method comprises the step of activating or deactivating each of the controllable high pressure valves (20h) and the controllable low pressure valves (201) of the working chambers of the hydraulic machines based on a method according to any of the methods for controlling a hydraulic machine above.

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• 2015
  • 2015-01-27 EP EP15704396.9A patent/EP3099933A1/de not_active Withdrawn
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