Vibration control method and vibration control system for fluid pressure control circuit

A first fluid channel for operating an actuator and a second fluid channel for operating an actuator are connected to a boom cylinder, including a boom rod side line, a boom head side line. A first and second supply line and a first and second discharge line of each of the first and second fluid channels, respectively, are connected to first and second meter-in control valve and first and second meter-out control valves, respectively. When the boom operating lever is returned an operating position to a neutral position, a pressure vibration generated in each fluid channel for operating the actuators is detected, and respective meter-in control valves and meter-out control valves are controlled to dampen the pressure vibration in each fluid channel.

TECHNICAL FIELD

This disclosure relates to a vibration control method and a vibration control system for a fluid pressure control circuit for damping pressure vibrations.

BACKGROUND

In general, work machines, such as a hydraulic excavator, are equipped with various fluid pressure actuators such as hydraulic cylinders. When the fluid pressure actuators are, for example, hydraulic cylinders for actuating a front work linkage mounted on a hydraulic excavator, returning an operating lever for the hydraulic cylinders abruptly from an operating position to a neutral position interrupts oil supply or discharge for the hydraulic cylinders. This causes kinetic energy remaining in the hydraulic cylinders to generate a pressure vibration whose natural frequency is determined by the compression of the oil in oil chambers of the hydraulic cylinder or in supply or discharge channels and the inertia of a weight load acting on the hydraulic cylinders. The pressure vibration lasts for a long time until the remaining kinetic energy disappears in the form of heat loss, giving an operator an unpleasant feeling and impairing operating efficiency.

There is thus a need for a technique for quickly dampening such pressure vibrations generated in fluid pressure actuators upon returning an operating lever from an operating position to a neutral position.

The control valve disclosed in Japanese Published Unexamined Patent Application No. 13-280305, which is controlled to dampen the pressure vibration, is arranged so that the supply and discharge control for a rod side oil chamber and a head side oil chamber of a hydraulic cylinder is carried out by a single spool valve. As a result, for example, when a pressure vibration is detected in the fluid channel for operating the actuators connected to the head side oil chamber and the control valve is displaced in a direction for damping the pressure vibration, the displacement of the valve can allow oil to be supplied to and discharged from not only the head side oil chamber, but also the rod side oil chamber. When this occurs the frequency of the generated pressure vibration is not only the same at both the rod and head sides of the hydraulic cylinder, but the phase is reversed between the two sides. Hence, the displacement of the control valve for damping the pressure vibration at the head side may not be effective in damping a pressure vibration also caused at the rod side.

In addition, a front work linkage mounted on a hydraulic excavator includes a plurality of members that are coupled together in a mutually swingable manner, such as a boom whose base end is pivoted on the machine body to allow the boom to move vertically, a stick pivoted on the front end of the boom to be swingable back and forth, and the like, and hydraulic cylinders for swinging these members. When a hydraulic cylinder for one member is brought to a sudden stop in such a machine, a shock caused by the stoppage is transmitted to the hydraulic circuit of a hydraulic cylinder for another member, generating a pressure vibration in the hydraulic cylinder for another member. This results in a vibration of the entire front work linkage.

This disclosure is aimed at providing solutions to these and other problems commonly known to those skilled in the art.

SUMMARY OF THE DISCLOSURE

In one aspect a vibration control method for a fluid pressure control circuit having a plurality of actuators is provided. Fluid channels for operating the actuators are provided with meter-in control valves for controlling fluid supply to the fluid pressure actuators and with meter-out control valves for controlling fluid discharge from the fluid pressure actuators. The method includes the step of, controlling the meter-in control valves and meter-out control valves on the basis of an operation command from an operating lever to operate the fluid pressure actuators, when the operating lever for the actuators is in a operating position. The method further includes the steps of detecting a pressure vibration generated in the respective fluid channels, and dampening the pressure vibration in the respective fluid channels when the operating lever is returned from the operation position to a neutral position.

In another aspect, the present disclosure provides a vibration control system for a fluid pressure control circuit. The system includes, a plurality of fluid pressure actuators, a plurality of fluid channels connecting to the fluid pressure actuators and a plurality of operating levers, each one corresponding with a fluid pressure actuator. Also provided is a plurality of meter-in control valves and a plurality of meter-out control valves, which are arranged in the fluid channels, wherein the meter-in control valves control fluid supply to the fluid pressure actuators while the meter-out control valves control fluid discharge from the actuators. The vibration control system further includes first and second operating circuits for controlling the meter-in control valves and meter-out control valves, respectively, to operate the fluid pressure actuators on the basis of an operation command from an operating lever when the corresponding operating lever is in an operating position. The system further includes first and second vibration control circuits for controlling the meter-in control valves and meter-out control valves, respectively, to detect a pressure vibration generated in the respective fluid channels, and dampen the pressure vibration in the respective fluid channels when the corresponding operating lever is returned from the operating position to a neutral position.

In still another aspect, the present disclosure provides a work machine that includes an operator input device, at least one fluid pressure actuator, and a fluid pressure control circuit connecting with the at least one fluid pressure actuator. The work machine further includes at least one of a meter-in and a meter-out control valve disposed within the fluid pressure circuit to control a hydraulic fluid flow between the fluid pressure control circuit and the at least one fluid pressure actuator. The work machine still further includes at least one operating circuit for controlling the at least one of a meter-in and a meter-out control valve based at least in part on a command from the operator input device when the operator input device is in a operating position. The work machine still further includes at least one vibration dampening control circuit for controlling the at least one of a meter-in and a meter-out control valve based at least in part on a value indicative of a fluid pressure vibration in the hydraulic control circuit when the operator input device is in a neutral position.

DETAILED DESCRIPTION

A hydraulic excavator is shown inFIG. 1. The shovel1has lower traveling bodies2of a crawler type, an upper revolving body3supported revolvably on the lower traveling bodies2, a front work linkage4mounted on the upper revolving body3, and other components. The front work linkage4includes a boom5, whose base end is supported on the upper revolving body3to allow the boom5to swing vertically, a stick6supported on the front end of the boom5to swing back and forth freely, and a bucket7fitted on the front end of the stick6.

FIG. 1also shows a boom cylinder8for swinging the boom5, and a stick cylinder9for swinging the stick6. A hydraulic control circuit for the boom cylinder8and the stick cylinder9is shown inFIG. 2, where10is a hydraulic pump that acts as a pressure oil supply source for the boom cylinder8and stick cylinder9. Numeral11is an oil tank,12is a boom valve unit that controls oil supply and discharge for the boom cylinder8, and13is a stick valve unit that controls oil supply and discharge for the stick cylinder9. The boom cylinder8actuates a weight load W1which is the whole of the front work linkage4, while the stick cylinder9actuates a weight load W2, which is from the stick6to the tip end side part of the inside of the front work linkage4.

The boom valve unit12includes a first supply line14, a second supply line15, a first discharge line16, and a second discharge line17, all of which are connected to form a rectangular annular shape. The lines14,15,16and17are provided with a first meter-in control valve18, a second meter-in control valve19, a first meter-out control valve20, and a second meter-out control valve21, respectively. The first meter-in control valve18and the first meter-out control valve20operate according to a control signal output from a boom first control section22, which will be described later, and the second meter-in control valve19and the second meter-out control valve21operate according to a control signal output from a boom second control section23.

The boom valve unit12also has a pump port12aconnected to the hydraulic pump10via a delivery line10a, a tank port12bconnected to the oil tank11via a tank line11a, a rod side output port12cthat is connected to a rod side port8c, which is an oil inlet-outlet on a rod side oil chamber8aof the boom cylinder8, via a boom rod side line24, and a head side output port12dthat is connected to a head side port8d, which is an oil inlet-outlet on a head side oil chamber8bof the boom cylinder8, via a boom head side line25. The pump port12acommunicates with a connection A between the first supply line14and the second supply line15. The tank port12bcommunicates with a connection B between the first discharge line16and the second discharge line17. The rod side output port12ccommunicates with a connection C between the first supply line14and the first discharge line16. The head side output port12dcommunicates with a connection D between the second supply line15and the second discharge line17.

The boom rod side line24, the first supply line14, and the first discharge line16correspond to the first fluid channel for operating the actuators according to the disclosure, while the boom head side line25, the second supply line15, and the second discharge line17correspond to the second fluid channel for operating the actuators according to the disclosure.

A first pressure detector26for detecting pressure vibrations is connected to the first supply line14in the boom valve unit12. The pressure detector26is connected to the part of the supply line14that communicates with the boom rod side line24in the downstream side of the first meter-in control valve18, and detects a pressure vibration generated in the rod side oil chamber8aof the boom cylinder8and the boom rod side line24. Also, a second pressure detector27for detecting pressure vibrations is connected to the part of the second supply line15that communicates with the boom head side line25in the downstream side of the second meter-in control valve19. The second pressure detector27detects a pressure vibration generated in the head side oil chamber8bof the boom cylinder8and the boom head side line25. The first and second pressure detectors26and27send a detected pressure signal to the boom first and second control sections22and23, respectively.

The boom valve unit12is further provided with a check valve28between the pump port12aand the connection A. The check valve28prevents oil from flowing backward from the valve unit12to the delivery line10a.

The stick valve unit13has a similar structure as the boom valve unit12, and includes a first supply line29, a second supply line30, a first discharge line31, and a second discharge line32, all of which are connected to form a rectangular annular shape. The lines29,30,31, and32are provided with a first meter-in control valve33, a second meter-in control valve34, a first meter-out control valve35, and a second meter-out control valve36, respectively. The first meter-in control valve33and the first meter-out control valve35operate according to a control signal output from a stick first control section37, and the second meter-in control valve34and the second meter-out control valve36operate according to a control signal output from a stick second control section38. The stick valve unit13also has a pump port13aconnected to the hydraulic pump10via the delivery line10a, a tank port13bconnected to the oil tank11via a discharge line11a, a rod side output port13cthat is connected to a rod side port9c, which is an oil inlet-outlet on a rod side oil chamber9aof the stick cylinder9, via a stick rod side line39, and a head side output port12dthat is connected to a head side port9d, which is an oil inlet-outlet on a head side oil chamber9bof the stick cylinder9, via a stick head side line40. The stick valve unit13is further provided with a check valve41, which prevents oil from flowing backward from the valve unit13to the delivery line10a. A first pressure detector42is connected to the part of the first supply line29that communicates with the stick rod side line39in the downstream side of the first meter-in control valve33. The first pressure detector42detects a pressure vibration generated in the rod side oil chamber9aof the stick cylinder9and the stick rod side line39. Also, a second pressure detector43is connected to the part of the second supply line30that communicates with the stick head side line40in the downstream side of the second meter-in control valve34. The second pressure detector43detects a pressure vibration generated in the head side oil chamber9bof the stick cylinder9and the stick head side line40. The first and second pressure detectors42and43send a detected pressure signal to the stick first and second control sections37and38, respectively.

The delivery line10ais an oil channel through which the pressure oil delivered from the oil pump10is supplied to each valve unit12and13. In the middle of the delivery line10a, a by-pass line44branches out from the oil pump10to directly reach the oil tank11without connecting to the valve units12and13. The by-pass line44is provided with a by-pass control valve45, which controls a flow rate in the by-pass line44and operates according to a control signal from a by-pass control section46.

A trigger signal output section47generates a trigger signal according to an input signal from a boom operating lever48. At the trigger signal output section47, as shown inFIG. 3, a command signal value from the boom operating lever48(the command signal value is positive when the lever48is operated to the extension side and the boom5is lifted, and is negative when the lever48is operated to the contraction side and the boom5is lowered) is input in a differentiator49, and an output signal from the differentiator49and the command signal from boom operating lever48are integrated at a first integrator50. An integrated result from the first integrator50is then input in a first function51, which outputs a positive logic value ‘1’ when the output from the first integrator50is negative, that is the boom operating lever48is at the extension side or is being moved from the contraction side to the neutral side. Similarly, a negative logic value ‘0’ is output when the output from the first integrator50is positive, that is the boom operating lever48is being moved from the neutral side to the extension side or to the contraction side. Meanwhile, a second function52outputs the positive value ‘1’ when the boom operating lever48is in the neutral position or in a neutral dead zone R near the neutral position (in a neutral state), while outputting the negative logic value ‘0’ when the boom operating lever48is being operated to the outside of the neutral dead zone R (in an operating state). Outputs from the second functions52and the first fuction51are integrated at a second integrator53, which outputs the positive value ‘1’ when output from the first function51and the second function52are both the positive value ‘1’, otherwise the second integrator53outputs the negative value ‘0’. Accordingly, when an operator returns the boom operating lever48from the extension side or the contraction side to the neutral position and tries to stop the boom cylinder8, the second integrator53outputs the positive logic value ‘1’ in a short time and is received by a first delay element54momentarily. An output from the first delay element54is then input in a third fuction55which outputs the negative value ‘0’ by default, but outputs the positive logic value ‘1’ as a trigger signal when the output from the first delay element54exceeds a value a specified at the third function55. As a result, when the operator has returned the boom operating lever48from the operating position to the neutral position, the positive logic value ‘1’ is output as the trigger signal from the trigger signal output section47during a predetermined time T (the duration in which the output from the first delay element54exceeds the specified value α, goes up to the maximum, and finally drops below the value α) after the lever48is returned to the neutral position. The trigger signal is sent to the boom first and second control sections22and23, to the by-pass control section46, and to the stick first and second control section37and38as well as via a trigger signal cut section67, which will be described later.

An operating circuit and a vibration control circuit are incorporated into the boom first and second control sections22and23, and the stick first and second control sections37and38, respectively. The operating circuit is for outputting an operation signal corresponding to the operation of the boom operating lever48and a stick operating lever56. The vibration control circuit is for outputting a vibration control signal for suppressing a pressure vibration, which is generated in the boom and stick cylinders8and9when the boom operating lever48is returned from the operating position to the neutral position. Both circuits are incorporated into each control section22,23,37and38identically. Therefore, the operating circuit incorporated in the boom first control section22is described first referring toFIG. 4.

The operating circuit to be incorporated in the boom first control section22consists of a meter-in operating circuit and a meter-out operating circuit. The meter-in operating circuit inputs the command signal from the boom operating lever48, to a meter-in operating signal output unit57. When the command signal is for an operation to the contractions side, the signal output unit57adjusts the command signal into the signal that corresponds to an operating amount of the lever and reflects an element of the neutral dead zone R, and outputs the adjusted signal. The adjusted signal from the signal output unit57is then sent to a gain amplifier G1and a first adder58, sequentially, to be finally input in the first meter-in control valve19as an operating signal. Upon receiving this operating signal, the first meter-in control valve18opens the first supply line14at the opening amount corresponding to the operating amount of the boom operating lever48.

Also, the meter-out operating circuit inputs a command signal from the boom operating lever48to a meter-out operating signal output unit59. When the command signal is for an operation to the extensions side E, the signal output unit59adjusts the command signal into the signal that corresponds to an operating amount of the lever and reflects an element of the neutral dead zone R, and outputs the adjusted signal. The adjusted signal from the signal output unit59is then sent to a gain amplifier G2and a second adder60, sequentially, to be finally input in the first meter-out control valve20as an operating signal. Upon receiving this operating signal, the first meter-out control valve20opens the first discharge line16at the opening amount corresponding to the operating amount of the boom operating lever48.

Likewise, the operating circuit in the boom second control section23consists of a meter-in operating circuit for outputting an operating signal to the second meter-in control valve19, and a meter-out operating circuit for outputting an operating signal to the second meter-out control valve21.

Accordingly, the boom cylinder8extends and contracts in response to the operation of the boom operating lever48on the basis of the operating signal output from each operating circuit which is incorporated in the boom first and second control sections22and23.

In other words, when the boom operating lever48is in the neutral position (the predetermined time T after the boom operating lever's returning from the operating position to the neutral position is excluded), no operating signal is output from the operating circuits in the boom first and second control sections22and23, thus the first and second meter-in control valves18and19and the first and second meter-out control valves20and21are all kept closed. Therefore, no oil supply or discharge for the boom cylinder8is carried out, which keeps the boom cylinder8still.

When the boom operating lever48is operated from the neutral position to the contraction side C, the meter-in operating circuit in the boom first control section22outputs an operating signal to the first meter-in control valve18so that the control valve18opens the first supply line14at the opening amount corresponding to an operating amount of the lever, while the meter-out operating circuit in the boom second control section23outputs an operating signal to the second meter-out control valve21as well so that the control valve21opens the second discharge line17at the opening amount corresponding to the operating amount of the lever. In response to the output signals, pressure oil delivered from the hydraulic pump10is supplied to the rod side oil chamber8aof the boom cylinder8via the delivery line10a, the first supply line14, and the boom rod side line24, while discharged oil from the head side oil chamber8bis made to flow in the oil tank11via the boom head side line25, the second discharge line17, and the tank line11a. Thus the boom cylinder8contracts.

Likewise, when the boom operating lever48is operated from the neutral position to the extension side, the meter-in operating circuit in the boom second control section23outputs an operating signal to the second meter-in control valve19so that the control valve19opens the second supply line15at the opening amount corresponding to an operating amount of the lever, while the meter-out operating circuit in the boom first control section22outputs an operating signal to the first meter-out control valve20as well so that the control valve20opens the first discharge line16at the opening amount corresponding to the operating amount of the lever. In response to the output signals, pressure oil delivered from the hydraulic pump10is supplied to the head side oil chamber8bof the boom cylinder8via the delivery line10a, the second supply line15, and the boom head side line25, while discharged oil from the rod side oil chamber8ais made to flow in the oil tank11via the boom rod side line24, the first discharge line16, and the tank line11a. In this manner, the boom cylinder8extends.

As in the case of the boom cylinder8, the stick cylinder9also extends and contracts in response to the operation of the stick operating lever56on the basis of the operating signal output from each operating circuit, which is incorporated into the stick first and second control sections37and38.

Next, the vibration control circuit incorporated into the boom first control section22is described referring toFIG. 4. In the vibration control circuit, a pressure signal detected by the first pressure detector26arranged in the first supply line14is filtered through a band-pass filter61. The band-pass filter61passes only the natural frequency of a pressure vibration generated upon stopping the operation of the boom cylinder8and vibratory components having frequencies around the natural frequency, while removing DC components representing a setting pressure. The symbol ωL in a transfer function represents the angular frequency of the vibratory component at the lower limit of vibratory components that have frequencies lower than the natural angular frequency and are allowed to pass the filter61. The symbol ωH represents the angular frequency of the vibratory component at the upper limit of vibratory components that have a frequency higher than the natural angular frequency and are allowed to pass the filter61.

A signal output from the band-pass filter61is then input to an integrator62via a gain amplifier G3. The integrator62integrates the output signal from the band-pass filter61and a trigger signal from the trigger signal output section47. When the trigger signal is the positive logic value ‘1’, that is during the given time T after the boom operating lever48is returned to the neutral position, the signal from the band-pass filter61itself becomes an output signal from the integrator62. When the trigger signal is the negative logic value ‘0’, that is in a time duration other than the given time T after the boom operating lever48is returned to the neutral position, the signal from the band-pass filter61is blocked by the integrator62.

The output signal from the integrator62is input in the second adder60without changing the sign of the signal, and is input in the first adder58as well after changing the signal sign to negative. As a result, the output signal from the band-pass filter61that represents a pressure vibration in an area of the chevron waveform (positive vibration waveform) is output to the first meter-out control valve20as a vibration control signal via the second adder60. Upon receiving the vibration control signal, the first meter-out control valve20opens the first discharge line16so as to release a pressure generated in the rod side oil chamber8aof the boom cylinder8and in the boom rod side line24to the tank line11avia the first discharge line16. On the other hand, the output signal that represents a pressure vibration in an area of the valley-shaped waveform (negative vibration waveform) is output to the first meter-in control valve18as a vibration control signal via the first adder58. Upon receiving the vibration control signal, the first meter-in control valve18opens the first supply line14so as to supply pressure oil from the delivery line10ato the boom rod side line24and the rod side oil chamber8avia the first supply line14.

The boom second control section23is provided with a similar vibration control circuit as the boom first control section22. As in the case of boom first control section22, while a trigger signal is output from the trigger signal output section47, that is, during the given time T after the boom operating lever48is returned to the neutral position, the second meter-out control valve21opens to release a pressure to the oil tank11side when a pressure vibration generated in the head side oil chamber8bof the boom cylinder8and in the boom head side line25becomes the chevron waveform (positive pressure), while the second meter-in control valve19opens to supply pressure oil when the pressure vibration becomes the valley waveform (negative pressure).

The stick first and second control sections37and38are also provided with a similar vibration control circuit, respectively. A trigger signal to the stick first and second control sections37and38receive the trigger signal via a trigger signal cut section67. At the trigger signal cut section67, a trigger signal from the trigger signal output section47is input in an integrator68, while a command signal from the stick operating lever56is input in a function69, as shown inFIG. 5. The function69outputs the positive logic value ‘1’ when the stick operating lever56is in the neutral position or in the neutral dead zone R near the neutral position (in the neutral state), while outputting the negative value ‘0’ when the operating lever56is operated to the outside of the neutral dead zone R (in the operating state). The output from the function68is integrated with the trigger signal at the integrator68. When the output from the function68and the trigger signal is equally the positive logic value ‘1’, that is while the stick operating lever56is in the neutral state during the given time T after the boom operating lever48is returned from the operating state to the neutral state, the positive logic value ‘1’ is output from the integrator68, which outputs the negative value ‘0’ otherwise. The output from the integrator68is then input in the vibration control circuits in the stick first and second control sections37and38, respectively, as the trigger signal.

According to the vibration control circuits in the stick first and second control sections37and38when the trigger signal from the trigger signal cut section67is the positive logic value ‘1’, that is, while the stick operating lever56is in the neutral state during the given time T after the boom operating lever48is returned from the operating state to the neutral state, the first and second meter-out control valves35and36open to release a pressure to the oil tank11side when a pressure vibration generated in the rod or head side oil chambers9aand9bof the stick cylinder9and in the stick rod or head side lines39and40become the chevron waveform (positive pressure). On the other hand, the first and second meter-in control valves33and34open to supply pressure oil when the pressure vibration becomes the valley-shaped waveform (negative pressure).

The by-pass control section46is for outputting a control signal to the by-pass control valve45arranged in the by-pass line44as described above. At the by-pass control section46, a command signal from the boom operating lever48and the stick operating lever56are input in an adder63. The by-pass control section46controls the by-pass control valve45on the basis of the input command signals, so that the opening amount of the by-pass control valve45becomes maximum when both operating lever48and56are in the neutral state, and the opening amount gets smaller as the operating amount of the levers increase when at least either of the operating levers is in the operating state. According to the control of the by-pass control valve45, delivery oil from the hydraulic pump10is by-passed through the by-pass line44to the oil tank11to place the hydraulic pump10in an unloaded state when both operating levers48and56are in the neutral state, while the delivery pressure of the hydraulic pump10is increased by closing the by-pass line44when at least either of the operating levers48and56is operated. At this time, the circuit maximum pressure of the delivery line10ais set by a relief valve64for setting circuit pressure.

The by-pass control section46further includes a high-pressure signal output unit65and an integrator66. The high-pressure signal output unit65outputs a signal that controls the opening of the by-pass control valve45so that the delivery pressure of the hydraulic pump10becomes a high pressure that is slightly lower than the circuit maximum pressure set by the relief valve64. The output signal from the high-pressure signal output unit65is input into the integrator66, which integrates the output signal from the signal output unit65and a trigger signal from the trigger signal output section47, and outputs the integrated signal to the adder63. When the trigger signal is the positive logic value ‘1’, that is during the given time T after the boom operating lever48is returned to the neutral position, the input signal from the high-pressure signal output unit65itself becomes the output signal from the integrator66to the adder63. When the trigger signal is the negative logic value ‘0’, which occurs in a time duration other than the given time T after the boom operating lever48is returned to the neutral position, the input signal from the signal output unit65is blocked by the integrator66. During the given time T after the boom operating lever48is returned to the neutral position, therefore, the output signal from the high-pressure signal output unit65is output to the by-pass control valve45as a vibration control signal via the integrator66and the adder63. As a result, the hydraulic pump10is put under an open loop control to make its delivery pressure the high pressure slightly lower than the circuit maximum pressure. The hydraulic pump10supplies high-pressure oil to the boom cylinder rod side and head side oil chambers8aand8band the stick cylinder rod side and head side oil chambers9aand9b. There a generated pressure vibration becomes the valley-shaped waveform via the first and second meter-in control valves18,19,33and34, which are opened according to respective vibration control signal output.

INDUSTRIAL APPLICABILITY

In the above embodiment, oil supply and discharge control for the boom cylinder8and stick cylinder9is executed by respective first and second meter-in control valve and first and second meter-out control valve18to21and33to36, which are incorporated in the boom valve unit12and the stick valve unit13, respectively. Respective boom first and second control sections22and23, and stick first and second control sections37and38, output each control command to those control valves18to21and33to36, and are provided with operating circuits and vibration circuits.

When each boom or stick operating lever48and56is operated, an operation signal is sent from the operating circuit of each control section22,23,37and38to each control valve18to21and33to36. Receiving the operation signal, each control valve opens the supply or discharge lines14to17and33to36, respectively, so as to supply or discharge oil at the valve opening amount corresponding to the operation of the operating levers48and56. Thus the boom cylinder8and the stick cylinder9contract and extend in correspondence to the operation of the operating levers48and56.

In such an arrangement, when the boom operating lever48is returned abruptly from the operating position to the neutral position to stop the boom5, the output of the operating signal stops, which closes the first and second meter-in control valves18and19and the first and second meter-out control valves20and21. This results in a sudden interruption of oil supply to and discharge from the boom cylinder8, causing kinetic energy remaining in the boom cylinder8to generate a pressure vibration, which has a natural value determined by the compression of oil in the rod and head side oil chambers8aand8b, and the boom rod and head side lines24and25, and by the inertia of the weight load W1of the front work linkage4that acts on the boom cylinder8. Meanwhile, the impact caused by the sudden halt of the boom cylinder8also generates a pressure vibration in the hydraulic circuit of the stick cylinder9. Those pressure vibrations generated in the hydraulic circuits of the boom and stick cylinders8and9are detected by the first and second pressure detectors26,27,42and43, respectively, and pressure signals are sent to the boom first and second control sections22and23, and the stick first and second control sections37and38, respectively.

During the given time T after the boom operating lever48is returned from the operating position to the neutral position, the trigger signal output section47outputs a trigger signal of the positive logic ‘1’ to the boom first and second control sections22and23, and the by-pass control section46. Meanwhile, the trigger signal of the positive logic ‘1’ is also output to the stick first and second control sections37and38, during the given time T after the boom operating lever48is returned from the operating position to the neutral position, at which the stick operating lever56is in the neutral position.

Upon receiving the trigger signals of positive logic value ‘1’ from the trigger signal output section47and the pressure signals from the first and second pressure detectors26,27,42and43, the vibration control circuits of the boom first and second control sections22and23, and of the stick first and second control sections37and38, send vibration control signals to the first and second meter-in control valves18,19,33and34, and to the first and second meter-out control valves20,21,35and36, respectively. According to the vibration control signals, when the pressure vibration generated in the rod and head side oil chamber8aand8bof the boom cylinder8, the boom rod and head side lines24and25, the rod and head side oil chambers9aand9bof the stick cylinder9, and the stick rod and head side lines39and40become the chevron waveform (positive pressure), the first and second meter-out control valves20,21,35and36open to release a generated pressure to the oil tank11side to absorb the positive pressure of the pressure vibration to smooth it out. On the other hand, when the pressure vibration becomes the valley-shaped waveform (negative pressure), the first and second meter-in control valves18,19,33and34open to supply pressure oil to absorb the negative pressure of the pressure vibration to smooth it out.

Meanwhile, the by-pass control section46outputs a vibration control signal to the by-pass control valve45on the basis of an incoming trigger signal of the positive logic value ‘1’ so as to make the delivery pressure of the hydraulic pump10the high-pressure slightly lower than the circuit maximum pressure. Then the hydraulic pump10supplies high-pressure oil to the boom cylinder rod and head side oil chambers8aand8b, the boom rod and head side lines24and25, the stick cylinder rod and head side oil chambers9aand9b, and the stick rod and head side lines39and40, where the generated pressure vibration becomes the valley-shaped waveform, via the first and second meter-in control valves18,19,33and34, which are opened according to respective vibration control signal output.

Hence, according to this embodiment, the pressure vibration generated by the residual kinetic energy in the boom cylinder8is detected when the boom operating lever48is returned abruptly from the operating position to the neutral position. When the pressure vibration is positive, the resulted pressure is released via the first and second meter-out control valves20,21,35and36. When the pressure vibration is negative, pressure oil is supplied via the first and second meter-in control valves18,19,33and34. As a result, the pressure vibration is smoothed out, thus damped quickly as a whole. In this arrangement, the first and second pressure detectors26,27,42and43for detecting pressure vibrations, and the first and second meter-in control valves18,19,33and34and the first and second meter-out control valves20,21,35and36, for absorbing pressure vibrations, are arranged separately for the rod side and the head side of the boom cylinder8and of the stick cylinder9, respectively. Thus vibration control is executed separately for the rod side and the head side of each cylinder, respectively.

Accordingly, when the cycles or phases of respective pressure vibrations generated on the rod and head sides of the boom cylinder8and the stick cylinder9are different, vibration control is executed separately in response to each vibration at the rod side and head side to achieve effective vibration control for both sides. As shown inFIGS. 6 and 7, this enables quick damping of the pressure vibration and reduces spikes of pressure surges generated upon returning the boom operating lever48abruptly from the operating position to the neutral position. InFIGS. 6 and 7, the X axis represents time, whereas the Y axis represents pressure on the boom cylinder rod side and pressure on the boom cylinder head side, respectively, inFIGS. 6 and 7. Thus no unpleasant feeling due to the continuing pressure vibration is given to an operator, which contributes to better operability. InFIGS. 6 and 7, the solid line represents the damping state of a pressure vibration in a hydraulic control circuit in which the vibration control according to the disclosure is executed, while the dotted line represents the damping state of a pressure vibration in a hydraulic control circuit in which the vibration control is not executed.

In addition, according to the embodiment, the vibration control is executed in the hydraulic circuit of the stick cylinder9at the same time when the control is executed in the circuit of the boom cylinder8. This is because a pressure vibration generated in the hydraulic circuit of the boom cylinder8is transmitted to the circuit of the stick cylinder9from the boom5via the stick6when the boom operating lever48is returned abruptly from the operating position to the neutral position. The point at which the boom operating lever is returned abruptly from an extension side to a neutral position is denoted with P1and P2inFIGS. 6 and 7respectively. This simultaneous vibration control enables more effective damping of the pressure vibration, thus contributes further to the improvement of operability.

In this embodiment, the vibration control is executed when the boom operating lever48is returned to the neutral position. This is because the weight load W1acting on the boom cylinder8is heavier than the weight load W2acting on the stick cylinder9, and a pressure vibration caused by abrupt return of the boom operating lever48to the neutral position is larger than that caused by a similar return of the stick operating lever56. However, another application of the vibration control executed upon returning of the stick operating lever56, can be easily achieved by providing a trigger signal generating unit that generates a trigger signal in response to the operation of the stick operating lever56.

Also, according to the embodiment, the first and second meter-in control valves18,19,33and34open to supply pressure oil to the boom cylinder8and the stick cylinder9when the generated pressure vibration is negative. At this time, the delivery pressure of the hydraulic pump10is put under the open loop control to be the high-pressure slightly lower than the circuit maximum pressure according to the vibration control signal input in the by-pass control valve45. The open loop control enables quick supply of enough pressure to compensate the negative pressure, which cancels the negative pressure in an early stage. The controlled high delivery pressure also eliminates as effectively as possible such a problem that the boom5or the stick6lowers due to a shortage in the flow rate of the oil that is supplied to the weight load holding side oil chamber of the boom cylinder8and of the stick cylinder9(the head side oil chamber8bof the boom cylinder8and the rod side oil chamber9aof the stick cylinder9) when the vibration control is executed.

The vibration control is executed while the trigger signal of the positive logic value ‘1’ is output, that is, during the given time T after the boom operating lever48is returned from the operating position to the neutral position, and is not executed otherwise. Accordingly, if a pressure vibration is detected, for example, when the boom operating lever is held in the operating position or in the neutral position, no vibration control signal is output to the control valves18to21and33to36. This prevents such a problem that any of the control valves accidentally opens unnecessarily.

While the boom cylinder mounted on the hydraulic excavator as the fluid pressure actuator is described in this embodiment, the method and system of the disclosure can apply to a variety of hydraulic cylinders other than such a boom cylinder. The system and method is also applicable to a hydraulic motor, such as a revolving motor for revolving an upper revolving body, and is applicable not only to a hydraulic apparatus or machine, but also to one actuated by other pressurized fluids, such as air pressure.