Patent Application
20230304262
The present invention relates to a work machine.
There are known work machines including a hydraulic pump, a hydraulic actuator driven by a hydraulic fluid delivered from the hydraulic pump, a control valve for controlling flow of the hydraulic fluid supplied from the hydraulic pump to the hydraulic actuator, and an operation device for operating the control valve (see Patent Document 1).
The work machine disclosed in Patent Document 1 has a hydraulic system including a center bypass cutoff valve provided downstream of the control valve that corresponds to a particular hydraulic cylinder in a center bypass line, and control means for controlling the center bypass cutoff valve to operate when operation means is operated to supply a hydraulic fluid to a load-bearing cylinder chamber of the particular hydraulic cylinder, for thereby making the discharged pressure from the hydraulic pump higher than the load pressure on the particular hydraulic cylinder.
Patent Document 2 discloses a lifting and lowering hydraulic circuit for directly drive controlling a boom cylinder to raise and lower a boom, the lifting and lowering hydraulic circuit having a bypass circuit as a fluid pressure impact prevention device that provides fluid communication between the bottom-side and rod-side chambers of a load cylinder through a solenoid on/off valve and a restriction valve. In the lifting and lowering hydraulic circuit disclosed in Patent Document 2, a controller transmits a command for opening the bypass circuit only for a predetermined period of time to the solenoid on/off valve when the cylinder starts or stops operating, resulting in a surge pressure.
The hydraulic system disclosed in Patent Document 1 is likely to produce a surge pressure due to a delay in the opening of the center bypass cutoff valve, compared with the returning operation of the control valve when an operation is performed to return the control valve corresponding to the particular hydraulic cylinder. The produced surge pressure leads to a reduction in work performing efficiency.
The technology disclosed in Patent Document 2 is aimed at preventing surge pressures from being generated. However, when the solenoid valve provided in the bypass circuit suffers a delay in its operation, compared with the operation of a hydraulic pilot three-position directional control valve, surge pressures may not be prevented from being generated.
It is an object of the present invention to prevent a surge pressure from being generated when a hydraulic actuator stops operating.
A work machine according to an aspect of the present invention includes a pump that delivers a hydraulic fluid sucked from a tank, a hydraulic actuator that is driven by the hydraulic fluid delivered from the pump, a flow control valve having a center bypass passage section that introduces the hydraulic fluid from the pump into the tank when the flow control valve is in a neutral position and controlling a flow rate of the hydraulic fluid supplied to the hydraulic actuator according to an amount of displacement thereof from the neutral position, a center bypass line that introduces the hydraulic fluid supplied from the pump through the center bypass passage section of the flow control valve into the tank, a bypass cutoff valve that is provided downstream of the flow control valve in the center bypass line and that controls an opening of the center bypass line, a solenoid proportional valve that generates a pilot pressure for controlling the bypass cutoff valve, an operation device that operates the hydraulic actuator, a pilot valve that generates a pilot pressure for controlling the flow control valve on the basis of an amount of operation of the operation device, an amount-of-operation sensor that senses the amount of operation of the operation device, and a controller that controls the solenoid proportional valve on the basis of the amount of operation sensed by the amount-of-operation sensor, in which the controller controls the solenoid proportional valve to reduce an opening area of the bypass cutoff valve to a minimum opening area according to an increase in the amount of operation in a case the amount of operation sensed by the amount-of-operation sensor is in a range from a minimum amount of operation to less than a predetermined amount of operation, and the controller controls the solenoid proportional valve to make the opening area of the bypass cutoff valve larger than the minimum opening area in a case the amount of operation sensed by the amount-of-operation sensor is a maximum amount of operation.
According to the present invention, a surge pressure is prevented from being generated when the hydraulic actuator stops operating.
Work machines according to embodiments of the present invention will be described below with reference to the drawings. According to the embodiments, work machines illustrated as crawler-type hydraulic excavators will be described by way of example. Work machines perform kinds of work including earth-moving work, construction work, demolishing work, dredging work, and the like.
The swing structure 103 includes a cabin 118 to be occupied by the operator and an engine room housing therein an engine and hydraulic devices including hydraulic pumps and the like, driven by the engine. The engine is a power source of the hydraulic excavator 100 and includes, for example, an internal combustion engine such as a diesel engine.
The work implement 104 includes a multiple-joint work implement mounted on the swing structure 103 and has a plurality of hydraulic actuators and a plurality of driven members (front members) driven by the plurality of hydraulic actuators. Specifically, the work implement 104 comprises three driven members (a boom 111, an arm 112, and a bucket 113) coupled in series with each other. The boom 111 has a proximal end portion angularly movably coupled to a front portion of the swing structure 103 by a boom pin. The arm 112 has a proximal end portion angularly movably coupled to a distal end portion of the boom 111 by an arm pin. The bucket 113 is angularly movably coupled to a distal end portion of the arm 112 by a bucket pin.
The boom 111 is turnably driven by a boom cylinder 111A as a hydraulic actuator (hydraulic cylinder) when it is extended or contracted. The arm 112 is turnably driven by an arm cylinder 112A as a hydraulic actuator (hydraulic cylinder) when it is extended or contracted. The bucket 113 is turnably driven by a bucket cylinder 113A as a hydraulic actuator (hydraulic cylinder) when it is extended or contracted.
As illustrated in
The main pump 1 is a variable-displacement hydraulic pump whose displacement is variable, and the pilot pump 9 is a fixed-variable hydraulic pump whose displacement is fixed. Note that the main pump 1 may alternatively be a fixed-variable hydraulic pump.
The flow control valve (directional control valve) 130 controls the direction of flow and flow rate of the hydraulic fluid supplied from the main pump 1 to the boom cylinder 111A. When a tank pressure acts on the pilot bearing members 136 and 137, the flow control valve 130 is in a neutral position. The flow control valve 130 is an open-center control valve and includes the center bypass passage section 131 that introduces the hydraulic fluid supplied from the main pump 1 through the center bypass line 171 into the tank 4 in the neutral position, a meter-in passage section 132 for guiding the hydraulic fluid supplied from the main pump 1 to the boom cylinder 111A, and a meter-out passage section 133 for guiding the hydraulic fluid (returning fluid) supplied from the boom cylinder 111A to the tank 4.
The flow control valve 130 controls the rate of the hydraulic fluid supplied to the boom cylinder 111A according to the displacement (spool stroke) of the flow control valve 130 from the neutral position. The larger the displacement of the flow control valve 130 from the neutral position becomes, the higher the speed at which the boom cylinder 111A operates becomes. Also, when the flow control valve 130 is moved in one direction from the neutral position, the boom cylinder 111A is extended. When the flow control valve 130 is moved in the opposite direction from the neutral position, the boom cylinder 111A is contracted. In other words, the flow control valve 130 controls the direction in which and the speed at which the boom cylinder 111A is driven.
The operation device 180 is an operation device for operating the boom 111 (the boom cylinder 111A and the flow control valve 130) and has an operation lever 181 as an operation member and a boom raising pilot valve 182 and a boom lowering pilot valve 183 for generating pilot pressures (hereinafter also referred to as operation pressures) for controlling the flow control valve 130. The operation device 180 is a hydraulic-pilot-type operation device for directly supplying the flow control valve 130 with pilot pressures (operation pressures) generated by the pilot valves 182 and 183 according to the direction in which and the degree to which the operation lever 181 is operated. The operation lever 181 is provided on the right side of an operator’s seat in the cabin (see
The boom raising pilot valve 182 reduces a primary pilot pressure supplied from the pilot pump 9 to generate a pilot pressure (an operation pressure) according to the amount of operation (lever stroke) of the operation lever 181 in a boom raising direction. The operation pressure supplied from the boom raising pilot valve 182 is applied through a pilot line to the pilot bearing member 136 (on the right-hand end as shown) of the flow control valve 130, driving the flow control valve 130 to the left in
The boom lowering pilot valve 183 reduces the primary pilot pressure supplied from the pilot pump 9 to generate a pilot pressure (operation pressure) according to the amount of operation (lever stroke) of the operation lever 181 in a boom lowering direction. The operation pressure supplied from the boom lowering pilot valve 183 is applied through a pilot line to the pilot bearing member 137 (on the left-hand end as shown) of the flow control valve 130, driving the flow control valve 130 to the rightward direction in
As illustrated in
As the operation pressure Po acting on the pilot bearing member 136 increases, the stroke of the flow control valve 130 increases. The higher the operation pressure Po acting on the pilot bearing member 136 becomes, the larger the opening area A2 of the meter-in passage section 132 becomes, and the smaller the opening area A1 of the center bypass passage section A1 becomes. When the operation pressure Po becomes equal to or higher than a second operation pressure Po2 to be described later, the center bypass passage section 131 is fully closed (i.e., the opening area A1 thereof becomes 0). When the operation pressure Po becomes equal to or higher than a predetermined pressure higher than the second operation pressure Po2, the opening area A2 of the meter-in passage section 132 reaches a maximum opening area A2max (A2max = A1max). As described above, changes in the opening area A1 of the center bypass passage section 131 in response to the operation pressure Po are in inverse relation to changes in the opening area A2 of the meter-in passage section 132 in response to the operation pressure Po. Note that, although not illustrated, the opening characteristics of the meter-out passage sections 133 are generally the same as the opening characteristics A2c of the meter-in passage sections 132.
As illustrated in
The solenoid proportional valve 7 is provided to a pilot line interconnecting the pilot pump 9 driven by the engine (not shown) and the pilot bearing member 6a of the bypass cutoff valve 6. The solenoid proportional valve 7 reduces the pilot primary pressure supplied from the pilot pump 9 to generate a pilot pressure according to a control current from the controller 150. The solenoid proportional valve 7 is a pressure reducing valve in which the degree of pressure reduction decreases as the control current applied thereto increases. Therefore, when the control current applied to the solenoid proportional valve 7 increases, a secondary pressure (pilot pressure) generated thereby increases according to the control current.
As illustrated in
The controller 150 controls the solenoid proportional valve 7 on the basis of the operation pressure Po sensed by the pressure sensors 185A and 185B (corresponding to the amount of operation of the operation device 180). The controller 150 includes a computer including a processor 151 such as a CPU (Central Processing Unit), an MPU (Micro Processing Unit), or a DSP (Digital Signal Processor, a nonvolatile memory 152 such as a ROM (Read Only Memory), a flash memory, or a hard disk drive, a volatile memory 153 generally called a RAM (Random Access Memory), an input interface 154, an output interface 155, and other peripheral circuits. Note that the controller 150 may comprise a single computer or a plurality of computers.
The nonvolatile memory 152 stores programs for performing various computations. In other words, the nonvolatile memory 152 is a storage medium capable of reading programs for realizing the functions according to the present embodiment. The processor 151 is a processing device for loading the programs stored in the nonvolatile memory 152 into the volatile memory 153 and performing computations. The processor 151 performs predetermined computations on signals fetched from the input interface 154, the nonvolatile memory 152, and the volatile memory 153 according to the programs.
The input interface 154 converts input signals into data that can be processed by the processor 151. Also, the output interface 155 generates output signals according to the result of computations carried out by the processor 151, and outputs the generated output signals to devices including the solenoid proportional valve 7, and the like.
The opening area computing section 161 refers to target opening characteristics A3tc stored in advance in the nonvolatile memory 152 and computes a target opening area A3t as a target value for the opening area A3 of the bypass cutoff valve 6 on the basis of the operation pressure Po sensed by the pressure sensor 185A.
The relation between the operation pressure Po and the target opening area A3t according to the target opening characteristics A3tc is as follows: When the operation pressure Po is in a range from a minimum pressure (hereinafter also referred to as a minimum operation pressure) Pon to less than the second operation pressure Po2, the target opening area A3t for the bypass cutoff valve 6 decreases until it reaches the minimum opening area A3min as the operation pressure Po increases. Specifically, when the operation pressure Po is the minimum operation pressure Pon (that is, when the operation lever 181 is in a neutral position and the amount of operation thereof is 0), the target opening area A3t is the maximum opening area A3max. When the operation pressure Po is in a range from the minimum operation pressure Pon to a first operation pressure Po1, the target opening area A3t for the bypass cutoff valve 6 continuously decreases as the operation pressure Po increases. When the operation pressure Po is the first operation pressure Po1, the target opening area A3t for the bypass cutoff valve 6 reaches the minimum opening area A3min. In addition, when the operation pressure Po is in a range from the first operation pressure Po1 to less than the second operation pressure Po2, the target opening area A3t for the bypass cutoff valve 6 remains to be the minimum opening area A3min.
As the operation pressure Po increases to the second operation pressure Po2, the target opening area A3t for the bypass cutoff valve 6 rises from the minimum opening area A3min to a predetermined opening area A30. According to the first embodiment, when the operation pressure Po is in a range from the second operation pressure Po2 to a maximum operation pressure Pox, the target opening area A3t for the bypass cutoff valve 6 remains to be the predetermined opening area A30. The predetermined opening area A30 is of a value larger than the minimum opening area A3min and equal to or smaller than the maximum opening area A3max.
As illustrated in
The current computing section 163 refers to control current characteristics Ci stored in advance in the nonvolatile memory 152, computes a control current value Ic to be supplied to the solenoid of the solenoid proportional valve 7 on the basis of the target pilot pressure Ppt computed by the pilot pressure computing section 162, and outputs a control current according to the computed control current to the solenoid proportional valve 7. The control current characteristics Ci are characteristics indicating that the control current value Ic increases as the target pilot pressure Ppt increases.
Major operation of the first embodiment will be described below. A crane work (load suspending work) carried out by the hydraulic excavator 100 will be described below by way of example. In the crane work, the hydraulic excavator 100 suspends a load with a wire joined to the load and engaging a hook provided on the back of the bucket 113 of the hydraulic excavator 100. Also, in the crane work, the boom 111 is raised and lowered to move the load upwardly and downwardly. When the boom 111 is raised, the bottom-side fluid chamber 111b of the boom cylinder 111A acts as a load holding side.
When the operator operates the operation lever 181 in the boom raising direction, the boom cylinder 111A is extended to turn the boom 111 upwardly. Thereafter, when the operator operates the operation lever 181 back to the neutral position, the boom cylinder 111A is decelerated to a stop.
According to the first embodiment, in the region where the operation pressure Po ranges from the minimum operation pressure Pon to the second operation pressure Po2 at which the center bypass passage section 131 of the flow control valve 130 is fully closed, the opening area of the center bypass line 171 is represented by a composite opening area (effective area) provided by the opening area of the flow control valve 130 and the opening area of the bypass cutoff valve 6. The composite opening area is smaller than the opening area A1 of the center bypass passage section 131.
In this manner, it is possible to reduce the flow rate of the hydraulic fluid returning from the center bypass line 171 to the tank 4 while maintaining the pressure of the hydraulic fluid discharged from the main pump 1 at a level required to operate the boom cylinder 111A. As a result, the energy loss can be reduced for improved fuel economy. Moreover, satisfactory fine operability can be achieved.
The controller 150 according to the first embodiment controls the solenoid proportional valve 7 to cause the opening area A3 of the bypass cutoff valve 6 to reach the predetermined opening area A30 larger than the minimum opening area A3min when the operation pressure Po sensed by the pressure sensor 185A is the maximum operation pressure Pox.
This makes it possible to decelerate the boom cylinder 111A smoothly to a stop without causing shocks when the operator returns the operation lever 181 back to the neutral position after having operated the operation lever 181 to a maximum in the boom raising direction. According to the configuration of the first embodiment, the ability of the configuration to be able to stop the boom cylinder 111A without causing shocks when the operation lever 181 is returned will be described below in comparison with a comparative example of the first embodiment.
As illustrated in
The bypass cutoff valve 6 starts to open with a delay time Δt1 from point t11 of time when the center bypass passage section 131 of the flow control valve 130 starts to open. In this manner, reasons that there is a response difference between the flow control valve 130 and the bypass cutoff valve 6 will be described below. The flow control valve 130 starts to return due to a reduction in the pilot pressure (operation pressure) output from the pilot valve 182 upon the operation to return the operation lever 181.
By contrast, the bypass cutoff valve 6 starts to return due to a reduction in the pilot pressure output from the solenoid proportional valve 7. The solenoid proportional valve 7 is controlled by the control current output from the controller 150. The controller 150 outputs the control current according to the operation pressure Po to the solenoid proportional valve 7 after having sensed a reduction in the operation pressure Po sensed by the pressure sensor 185A.
As described above, the bypass cutoff valve 6 is controlled in operation by the controller 150. Therefore, the period of time required for the controller 150 to perform communication and computation after having acquired the sensed operation pressure Po until it outputs the control current to the solenoid proportional valve 7 is enumerated as one of the causes of the response delay. In addition, the period of time after the control current has been input to the solenoid proportional valve 7 until the pilot pressure acting on the pilot bearing member 6a of the bypass cutoff valve 6 varies is also enumerated as another one of the causes of the response delay. By contrast, the flow control valve 130 is not controlled by the controller 150, but controlled directly by the operation pressure output from the operation device 180 operated by the operator. Consequently, the bypass cutoff valve 6 lags in operation behind the flow control valve 130.
Because the bypass cutoff valve 6 lags in operation behind the flow control valve 130, even when the opening area A1 of the center bypass passage section 131 of the flow control valve 130 has increased, since the bypass cutoff valve 6 remains closed, the pump pressure Ppu increases. When the pump pressure Ppu increases, the bottom pressure Pb as the pressure of the hydraulic fluid in the bottom-side fluid chamber 111b of the boom cylinder 111A that is connected to the main pump 1 through the meter-in passage section 132 also goes higher. When the bottom pressure Pb rises, the braking force (the rod pressure Pr × the pressure bearing area of the rod-side fluid chamber 111r - the bottom pressure Pb × the pressure bearing area of the bottom-side fluid chamber 111b) for decelerating the boom cylinder 111A becomes weaker. According to the comparative example, therefore, the meter-in passage section 132 and the meter-out passage section 133 are closed while the boom cylinder 111A is moving fast, producing a surge pressure in the rod-side fluid chamber 111r (at point t12 of time).
When the surge pressure is generated at the time of stopping the boom cylinder 111A, the work implement 104 tends to suffer impacts and vibrations, which makes it difficult to position the work implement 104. In addition, when the work implement 104 suffers impacts and vibrations, the operator is liable to experience increased fatigue. Consequently, the surge pressure thus produced is likely to invite a reduction in the work performing efficiency of the hydraulic excavator 100.
In contrast, according to the first embodiment, as described above, the controller 150 controls the solenoid proportional valve 7 such that the opening area A3 of the bypass cutoff valve 6 reaches the predetermined opening area A30 when the operation pressure becomes equal to or higher than the second operation pressure Po2. Thus, according to the first embodiment, as illustrated in
When the operator then operates the operation lever 181 to return (at point t21 of time), since the bypass cutoff valve 6 has already been open, the hydraulic fluid discharged from the main pump 1 can be relieved into the tank 4. The pump pressure Ppu and the bottom pressure Pb can thus be prevented from rising. As the braking force is appropriately applied to the boom cylinder 111A, the boom cylinder 111A is smoothly decelerated to a stop.
According to the first embodiment, a delay time Δt2 thus occurs from point t21 of time when the flow control valve 130 starts to return until the bypass cutoff valve 6 starts to open (until the opening area A3 of the bypass cutoff valve 6 starts to increase). However, a surge pressure can be prevented from being generated in the rod-side fluid chamber 111r by opening the bypass cutoff valve 6. According to the first embodiment, in other words, since the work implement 104 can be prevented from suffering impacts and vibrations, the work implement 104 can easily be positioned. According to the first embodiment, moreover, since the work implement 104 can be prevented from suffering impacts and vibrations, the operator can experience reduced fatigue. As a consequence, the work performing efficiency of the hydraulic excavator 100 can be increased.
The above embodiment offers the following advantages:
(1) The hydraulic excavator (work machine) 100 has the main pump (pump) 1 for discharging the hydraulic fluid sucked from the tank 4, the boom cylinder (hydraulic actuator) 111A driven by the hydraulic fluid discharged from the main pump 1, and the center bypass passage section 131 for guiding the hydraulic fluid from the main pump 1 to the tank 4 when in the neutral position. The hydraulic excavator 100 also includes the flow control valve 130 for controlling the flow rate of the hydraulic fluid supplied to the boom cylinder 111A according to the amount of displacement from the neutral position, the center bypass line 171 for guiding the hydraulic fluid supplied from the main pump 1 via the center bypass passage section 131 of the fluid control valve 130 to the tank 4, the bypass cutoff valve 6 provided downstream of the flow control valve 130 in the center bypass line 171, for controlling the opening of the center bypass line 171, the solenoid proportional valve 7 for generating the pilot pressure for controlling the bypass cutoff valve 6, the operation device 180 for operating the boom cylinder 111A, the pilot valve 182 for generating the operation pressure (pilot pressure) for controlling the flow control valve 130 on the basis of the amount of operation of the operation device 180, the pressure sensor (amount-of-operation sensor) 185A for sensing the operation pressure (the amount of operation) of the operation device 180, and the controller (controller) 150 for controlling the solenoid proportional valve 7 on the basis of the operation pressure Po sensed by the pressure sensor 185A.
The controller 150 controls the solenoid proportional valve 7 such that in a case the operation pressure Po sensed by the pressure sensor 185A is in a range from the minimum operation pressure Pon to less than the second operation pressure Po2, the opening area A3 of the bypass cutoff valve 6 decreases until it reaches the minimum opening area A3min according to the increase in the operation pressure Po. Accordingly, the energy loss of the main pump 1 is reduced for improved fuel economy. Moreover, satisfactory fine operability can be achieved.
The controller 150 controls the solenoid proportional valve 7 such that the opening area A3 of the bypass cutoff valve 6 becomes an opening area (predetermined opening area A30) larger than the minimum opening area A3min in a case the operation pressure Po sensed by the pressure sensor 185A is the maximum operation pressure Pox. A surge pressure can thus be prevented from being generated when the boom cylinder (hydraulic actuator) 111A stops operating. As a result, the work performing efficiency of the hydraulic excavator 100 can be increased.
(2) The center bypass passage section 131 of the flow control valve 131 has such an opening characteristics A1c that the opening area A1 thereof decreases as the operation pressure Po increases and the center bypass passage section 131 is fully closed at the second operation pressure Po2 in a case the operation pressure Po is in a range less than the second operation pressure Po2. The controller 150 controls the solenoid proportional valve 7 such that the opening area A3 of the bypass cutoff valve 6 increases from the minimum opening area A3min in a case the operation pressure Po sensed by the pressure sensor 185A is in a range of equal to or larger than the second operation pressure Po2 and equal to or less than the maximum operation pressure Pox. The energy loss can thus be made smaller than that if the opening area A3 of the bypass cutoff valve 6 increases from the minimum opening area A3min when the operation pressure Po is less than the second operation pressure Po2. Note that a delay in opening the bypass cutoff valve 6 can effectively be prevented by setting the target opening area A3t for the bypass cutoff valve 6 at a time at which the operation pressure Po is the second operation pressure Po2 to the predetermined opening area A30.
A hydraulic excavator 200 according to a second embodiment of the present invention will be described below with reference to
According to the second embodiment, the temperature sensor 286 senses the temperature of the hydraulic fluid in the tank 4 that stores the hydraulic fluid to be drawn by the main pump 1. Note that the temperature sensor 286 may not necessarily be located in the tank 4.
The second opening area computing section 261B refers to second target opening characteristics A3bc different from the first target opening characteristics A3ac and computes a target opening area A3t for the bypass cutoff valve 6 on the basis of the operation pressure Po sensed by the pressure sensor 185A.
The relation between the operation pressure Po and the target opening area A3t according to the second target opening characteristics A3bc is as follows: When the operation pressure Po is the minimum operation pressure Pon, the target opening area A3t is the maximum opening area A3max. When the operation pressure Po is in a range from the minimum operation pressure Pon to less than the second operation pressure Po2, the target opening area A3t for the bypass cutoff valve 6 continuously decreases until it reaches a minimum opening area A3min2 as the operation pressure Po increases. Note that the minimum opening area A3min2 according to the second target opening characteristics A3bc is larger than the minimum opening area A3min according to the first target opening characteristics A3ac.
When the operation pressure Po is equal to or higher than the second operation pressure Po2, the target opening area A3t for the bypass cutoff valve 6 becomes the predetermined opening area A30 that is larger than the minimum opening area A3min2. The rate of change (gradient) of the target opening area A3t with respect to the operation pressure Po in the range from the minimum operation pressure Pon to less than a third operation pressure Po3 and the rate of change (gradient) of the target opening area A3t with respect to the operation pressure Po in the range from the third operation pressure Po3 to less than the second operation pressure Po2 are different from each other. Note that the magnitudes of the operation pressures are related as follows: Pon < Po3 < Po1 < Po2 < Pox.
When the operation pressure Po is in the range from the third operation pressure Po3 to less than the second operation pressure Po2, the target opening area A3t determined according to the second target opening characteristics A3bc is larger than the target opening area A3t determined according to the first target opening characteristics A3ac.
As illustrated in
The pilot pressure computing section 162 computes a target pilot pressure Ppt on the basis of the target opening area A3t selected by the selector 264. The current computing section 163 computes a control current value Ic on the basis of the target pilot pressure Ppt computed by the pilot pressure computing section 162, and outputs a control current according to the computed control current value Ic to the solenoid proportional valve 7.
Major operation of the second embodiment will be described below. A crane work (load suspending work) carried out by the hydraulic excavator 200 will be described below by way of example. When the operator operates the operation lever 181 in the boom raising direction, the boom cylinder 111A is extended to turn the boom 111 upwardly. When the operator gradually increases the amount of operation of the operation lever 181 (finely operates the operation lever 181), the load is smoothly lifted by the work implement 104.
Here, the hydraulic excavator 100 according to the first embodiment may possibly be unable to operate the boom cylinder 111A smoothly owing to an increased pressure loss of the hydraulic fluid passing through the center bypass passage section 131 of the flow control valve 130 and the bypass cutoff valve 6 if the temperature T of the hydraulic fluid is low.
In contrast, according to the second embodiment, in a case the temperature T of the hydraulic fluid sensed by the temperature sensor 286 is lower (T < T0), the controller 150 controls the solenoid proportional valve 7 to make the opening area A3 of the bypass cutoff valve 6 larger than in a case the temperature T of the hydraulic fluid sensed by the temperature sensor 286 is higher (T ≥ T0).
When the operator operates the operation lever 181 in the boom raising direction, for example, the boom cylinder 111A can thus be operated smoothly without causing shocks. The ability of the configuration according to the second embodiment to be able to operate the boom cylinder 111A without causing shocks when the operation lever 181 is operated to raise the boom 111 will be described below in comparison with the first embodiment.
As illustrated in
If the temperature T of the hydraulic fluid is equal to or higher than the predetermined temperature T0, then the pump pressure Ppu gradually rises from point t31 of time. The pump pressure Ppu exceeds the bottom pressure Pb immediately prior to point t32 of time when the meter-in passage section 132 starts to open. By thus matching the pump pressure Ppu to the bottom pressure Pb at a time at which the meter-in passage section 132 starts to open, it is possible to start to operate the boom cylinder 111A smoothly. Consequently, the boom 111 is operated slowly to lift the load.
However, as illustrated in
In contrast, according to the second embodiment, as described above, if the temperature T of the hydraulic fluid is less than the threshold value T0, the controller 250 controls the solenoid proportional valve 7 to make the opening area A3 of the bypass cutoff valve 6 larger than if the temperature T of the hydraulic fluid is equal to or higher than the threshold value T0. According to the second embodiment, consequently, as illustrated in
According to the second embodiment, as described above, as the work implement 104 is prevented from starting to operate abruptly if the temperature of the hydraulic fluid is lower, it is possible to position the work implement 104 easily. According to the second embodiment, moreover, since the work implement 104 can be prevented from starting to operate abruptly if the temperature of the hydraulic fluid is lower, it is possible to reduce the fatigue of the operator. As a result, the work performing efficiency of the hydraulic excavator 200 can be increased.
A hydraulic excavator 300 according to a third embodiment of the present invention will be described below with reference to
As illustrated in
The hydraulic excavator 300 includes an operation device 380 for operating the arm cylinder 112A and pressure sensors 385A and 385B for sensing pilot pressures acting on respective pilot bearing members 136 and 137 of the flow control valve 130B.
The operation device 380 is an operation device for operating the arm 112 (the arm cylinder 112A and the flow control valve 130B) and has an operation lever 381 as an operation member and an arm-crowding pilot valve 382 and an arm-dumping pilot valve 383 for generating pilot pressures (operation pressures) for controlling the flow control valve 130B on the basis of the degree to which the operation lever 381 is operated. The operation device 380 is a hydraulic-pilot-type operation device for directly supplying the flow control valve 130B with pilot pressures (operation pressures) generated by the pilot valves 382 and 383 according to the direction in which and the degree to which the operation lever 381 is operated. The operation lever 381 is provided on the left side of the operator’s seat in the cabin 118 (see
The pressure sensor 385A senses the operation pressure Po output from the arm-crowding pilot valve 382 when an arm crowding operation is carried out by the operation lever 381, and outputs the sensed pressure to a controller 350. The pressure sensor 385B senses the operation pressure Po output from the arm-dumping pilot valve 383 when an arm dumping operation is carried out by the operation lever 381, and outputs the sensed pressure to the controller 350.
When the operation lever 181 and the operation lever 381 perform a combined operation on the flow control valves 130A and 130B, the opening area (composite opening area) of the center bypass line 171 is made smaller than if the operation lever 181 or the operation lever 381 performs an individual operation on the flow control valve 130A or 130B. Therefore, the fluid pressure of the boom cylinder 111A that is supplied with the hydraulic fluid from the flow control valve 130A that is disposed upstream in the center bypass line 171, of the flow control valve 130A and the flow control valve 130B that are connected in tandem, becomes unnecessarily high. Consequently, as with the situation described in the second embodiment in which the temperature of the hydraulic fluid is in a low-temperature state, shocks are likely to occur when the boom cylinder 111A starts to operate.
According to the third embodiment, the controller 350 controls the solenoid proportional valve 7 to make the opening area A3 of the bypass cutoff valve 6 larger than in a case an individual operation is performed on the flow control valve 130A or 130B, in a case a combined operation is performed on the flow control valves 130A and 130B.
The selector 364 determines the combined operation state, if either one of the operation pressures Po sensed by the pressure sensors 185A and 185B is equal to or higher than a threshold value Po0 and either one of the operation pressures sensed by the pressure sensors 385A and 385B is equal to or higher than the threshold value Po0. Otherwise, the selector 364 determines no combined operation state. The threshold value Po0 is a threshold value used in determining whether the operation devices 180 and 380 are operated or not. The threshold value Po0 is stored in advance in the nonvolatile memory 152. The selector 364 selects the target opening area A3t computed by the first opening area computing section 261A, if the selector 364 determines no combined operation state (i.e., an individual operation state), and outputs the selected target opening area A3t to the pilot pressure computing section 162. The selector 364 selects the target opening area A3t computed by the second opening area computing section 261B, if the selector 364 determines the combined operation state, and outputs the selected target opening area A3t to the pilot pressure computing section 162. Note that the present invention is not limited to the selector 364, but a target opening area A3t may be selected from a three-dimensional table in response to an operation pressure output from the operation device 180 and input thereto and an operation pressure output from the operation device 380 and input thereto, for example.
According to the third embodiment, as described above, the plurality of flow control valves 130A and 130B are provided to the center bypass line 171. The controller 350 controls the solenoid proportional valve 7 to make the opening area A3 of the bypass cutoff valve 6 larger than when the flow control valve 130A or the flow control valve 130B is individually operated in the individual operation state, when the plurality of flow control valves 130A and 130B are operated in the combined operation state.
According to the third embodiment, consequently, the work implement 104 can be prevented from starting to operate abruptly when the plurality of flow control valves 130A and 130B are operated in the combined operation state, and hence, the work implement 104 can easily be positioned. According to the third embodiment, furthermore, when the plurality of flow control valves 130A and 130B are operated in the combined operation state, since the work implement 104 can be prevented from starting to operate abruptly, it is possible to reduce the fatigue of the operator. As a result, the work performing efficiency of the hydraulic excavator 300 can be increased.
Modifications to be described below fall within the scope of the present invention. It is possible to combine the configurations according to the modifications and the configurations according to the above embodiments with each other, combine the configurations according to the above different embodiments with each other, and combine the configurations to be described in the following different modifications.
According to the first embodiment described above, when the operation pressure Po sensed by the pressure sensor 185A is the second operation pressure Po2, the controller 150 controls the solenoid proportional valve 7 to increase the opening area A3 of the bypass cutoff valve 6 from the minimum opening area A3min. However, the present invention is not limited such a feature.
The controller 150 may control the solenoid proportional valve 7 to increase the opening area A3 of the bypass cutoff valve 6 from the minimum opening area A3min when the operation pressure Po is higher than the second operation pressure Po2. As described above, the controller 150 can reduce the energy loss by controlling the solenoid proportional valve 7 to increase the opening area A3 of the bypass cutoff valve 6 from the minimum opening area A3min when the operation pressure Po is in the range from the second operation pressure Po2 to the maximum operation pressure Pox.
The controller 150 may control the solenoid proportional valve 7 to increase the opening area A3 of the bypass cutoff valve 6 from the minimum opening area A3min when the operation pressure Po is less than the second operation pressure Po2. Note that the lower the operation pressure Po is at a time at which the opening area A3 of the bypass cutoff valve 6 increases from the minimum opening area A3min, the more the energy loss is caused. Therefore, it is preferable for the operation pressure Po to be higher (i.e., closer to the second operation pressure Po2) at a time at which the opening area A3 of the bypass cutoff valve 6 increases from the minimum opening area A3min.
According to the first embodiment described above, the operation device 180 has been described as a hydraulic-pilot-type operation device by way of example. However, the present invention is not limited to such a feature. The operation device 180 may be an electric operation device. The amount of operation of the electric operation device is sensed by an amount-of-operation sensor such as a potentiometer for sensing a rotational angle of the operation lever. The controller 150 outputs a control current to a solenoid proportional valve (pilot valve) on the basis of the amount of operation sensed by the amount-of-operation sensor. The solenoid proportional valve (pilot valve) reduces the pilot primary pressure supplied from the pilot pump 9 to generate pilot pressures (operation pressures) and outputs the generated pilot pressures (operation pressures) to the pilot bearing members 136 and 137 of the flow control valve 130. With such a configuration, the solenoid proportional valve 7 that controls the bypass cutoff valve 6 and the solenoid proportional valve (pilot valve) that controls the flow control valve 130 are controlled by the controller 150, and their responses are less likely to differ from each other. However, the bypass cutoff valve 6 may lag in operation behind the flow control valve 130 due to the difference between the lengths of a pilot line interconnecting the pilot bearing member 136 of the flow control valve 130 and the solenoid proportional valve (pilot valve) and a pilot line interconnecting the bypass cutoff valve 6 and the solenoid proportional valve 7, valve characteristics differences, and the like. Therefore, a hydraulic excavator having an electric operation device can offer the same advantages as those described in the above embodiments.
According to the first embodiment described above, the configuration for preventing a surge pressure from being generated in the boom cylinder 111A has been described. However, the present invention is not limited to such a feature. According to the present invention, a surge pressure can similarly be prevented from being generated in the arm cylinder 112A and the bucket cylinder 113A.
According to the embodiment described above, the work machine has been described as the crawler-type hydraulic excavator 100. However, the present invention is not limited to such a feature. The present invention is also applicable to various work machines including a wheel-type hydraulic excavator, a wheel loader, and the like.
The embodiments of the present invention have been described above. The embodiments described above merely represent some of the applications of the present invention, and should not be construed as limiting the technical scope of the invention to the specific details of the embodiments.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-215521 | Dec 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/041600 | 11/11/2021 | WO |
