Patent Grant
9963856
The present invention relates generally to hydraulic drive systems for construction machines such as hydraulic excavators and, more particularly, to a hydraulic drive system that performs load sensing control for controlling a delivery flow rate of a hydraulic pump such that a delivery pressure of the hydraulic pump is higher by a target differential pressure than a maximum load pressure of a plurality of actuators.
A known hydraulic drive system for a construction machine such as a hydraulic excavator controls a delivery flow rate of a hydraulic pump (one pump) such that a delivery pressure of the hydraulic pump is higher by a target differential pressure than a maximum load pressure of a plurality of actuators. This control is called load sensing control. The hydraulic drive system that performs the load sensing control includes a plurality of pressure compensating valves, each of the pressure compensating valves maintaining, as disclosed in Patent Document 1, a predetermined differential pressure across each of respective flow control valves. The hydraulic drive system is thereby be able, in a combined operation in which the actuators are driven simultaneously, to supply each of the actuators with a hydraulic fluid at a ratio corresponding to an opening area of each flow control valve regardless of the magnitude of a load pressure on each of the actuators.
Patent Document 1: JP-2009-14122-A
In the hydraulic drive system disclosed in Patent Document 1, the delivery pressure of the hydraulic pump is controlled so as to be higher by the target differential pressure than the maximum load pressure of the actuators whenever a combined operation in which the actuators are driven simultaneously is performed. Thus, in a combined operation of, for example, a horizontally leveling operation that involves a large load pressure difference and includes, for example, a boom raising fine operation (high load pressure) and an arm crowding operation (low load pressure) performed simultaneously, the delivery pressure of the hydraulic pump is controlled to be higher by a certain set pressure than the high load pressure on a boom cylinder. Further, the delivery pressure of the hydraulic pump restricts the pressure compensating valve for an actuator having a lower load pressure (an arm cylinder in the horizontally leveling operation) in order to prevent an excessive amount of hydraulic fluid from flowing to the actuator having the lower load pressure, thus consuming power drive (energy) due to this wasted restricting pressure loss.
Additionally, the hydraulic excavator may perform an operation called sweeping work in which the hydraulic excavator moves a bucket along the ground with a bucket claw end in contact with the ground and collects crushed waste including stone chips, concrete chips, and wooden chips, to thereby clean the ground. This sweeping work is performed through the combined operation of the boom raising fine operation (high load pressure) and the arm crowding operation (low load pressure), as in the horizontally leveling operation. It is, however, noted that, because the shape of the ground needs to be maintained in the sweeping work, the bucket claw end is required to be flexibly adjusted in a vertical position thereof so as to follow along bumps and dents, if any, on the ground.
To flexibly adjust the vertical position of the bucket claw end so as to follow along the ground, preferably, an extending/contracting speed of the boom cylinder changes flexibly corresponding to the load pressure on the boom cylinder when the load pressure on the boom cylinder varies with the magnitude of force with which the bucket claw end contacts bumps and dents on the ground.
In the hydraulic drive system disclosed in Patent Document 1, however, even when the boom operation is a fine operation, the load sensing control controls the delivery flow rate of the hydraulic pump that supplies the actuator (boom cylinder) with the hydraulic fluid and the pressure compensating valve maintains a predetermined differential pressure across the flow control valve. As a result, the flow rate of the hydraulic fluid supplied to the boom cylinder is less affected by the load pressure on the boom cylinder and depends only on an input of a lever in an operating unit. Thus, unfortunately, the hydraulic drive system disclosed in Patent Document 1 finds it difficult, when the ground has surface irregularities, to move the bucket claw end to follow along the bumps and dents on the ground, while keeping the bucket claw end in contact with the ground.
An object of the present invention is to provide a hydraulic drive system for a construction machine, capable of achieving favorable operability, in a combined operation that involves a specific actuator and involves a great difference in load pressure and when an operation of an operating unit for the specific actuator is a fine operation, by reducing energy consumption arising from wasted restricting pressure loss of a pressure compensating valve and by flexibly varying the flow rate of a hydraulic fluid supplied to the specific actuator depending on the load pressure.
(1) To achieve the foregoing object, an aspect of the present invention provides a hydraulic drive system for a construction machine. The hydraulic drive system includes: a variable displacement first pump device; a second pump device; a plurality of first actuators that are driven by hydraulic fluids delivered from the first pump device; a plurality of second actuators that are driven by hydraulic fluids delivered from the second pump device; a plurality of closed center type flow control valves that control flows of hydraulic fluids supplied from the first pump device to the first actuators; a plurality of open center type flow control valves that control flows of hydraulic fluids supplied from the second pump device to the second actuators; a plurality of pressure compensating valves that control differential pressures across the respective closed center type flow control valves; and a first pump control unit including a load sensing control section that controls capacity of the first pump device such that a delivery pressure of the first pump device is higher by a target differential pressure than a maximum load pressure of the first hydraulic actuators. The first and second actuators include at least one first specific actuator as a common actuator. The first actuators include a second specific actuator that is used at relatively high frequency in a combined operation with the first specific actuator. The open center type flow control valves include a first flow control valve that controls a flow of a hydraulic fluid supplied from the second pump device to the first specific actuator. The closed center type flow control valves include a second flow control valve that controls a flow of a hydraulic fluid supplied from the first pump device to the first specific actuator. The first and second flow control valves are set to have an opening area characteristic such that, when an operating unit for the first specific actuator is operated up to an intermediate zone of an operating range, only the first flow control valve opens to supply a hydraulic fluid from the second pump device to the first specific actuator and, when the operating unit is operated further from the intermediate zone, both the first and second flow control valves open to join and supply hydraulic fluids from the first and second pump devices to the first specific actuator.
In the aspect of the present invention, even in a combined operation (for example, a horizontally leveling operation and sweeping work) that involves the first specific actuator (that corresponds the “specific actuators” in the object of the present invention, for example, a boom cylinder) and the second specific actuator (for example, an arm cylinder) and involves a great difference in load pressure between the first specific actuator and the second specific actuator, the first and second specific actuators are driven by hydraulic fluids from the respective pump devices (the first specific actuator is driven by the hydraulic fluid delivered from the second pump device and the second specific actuator is driven by the hydraulic fluid delivered from the first pump device). Thus, restricting pressure loss in the pressure compensating valve does not occur, so that energy consumption arising from the wasted restricting pressure loss of the pressure compensating valve can be prevented.
The first flow control valve that controls the flow of the hydraulic fluid supplied to the first specific actuator from the second pump device is an open center type. Thus, use of the first specific actuator as a boom cylinder allows the flow rate of the hydraulic fluid supplied to the boom cylinder to be flexibly varied according to the load pressure on the boom cylinder when the operating unit for the boom cylinder involves a small operation amount, as in sweeping work, so that favorable operability can be obtained.
From the foregoing, in a combined operation that involves a specific actuator and involves a great difference in load pressure and when the operation of the operating unit for the specific actuator is a fine operation, favorable operability can be achieved by reducing energy consumption arising from the wasted restricting pressure loss of the pressure compensating valve and by flexibly varying the flow rate of the hydraulic fluid supplied to the specific actuator depending on the load pressure.
(2) In (1) above, preferably, the first flow control valve is set to have the opening area characteristic such that an opening area increases with increase in the spool stroke and reaches a maximum before a maximum spool stroke is reached, and the second flow control valve is set to have the opening area characteristic such that an opening area remains zero before a spool stroke reaches an intermediate stroke, opens at the intermediate stroke, and then increases with increase in the spool stroke and reaches a maximum opening area immediately before a maximum spool stroke is reached.
Thus, when the operating unit for the first specific actuator is operated up to the intermediate zone of the operating range, only the first flow control valve opens to supply the hydraulic fluid from the second pump device to the first specific actuator. When the operating unit is operated further from the intermediate zone, both the first and second flow control valves open to join and supply the hydraulic fluids from the first and second pump devices-to the first specific actuator.
(3) In (1) above, preferably, the hydraulic drive system further includes a second pump control unit that controls capacity of the second pump device. The first pump device includes the load sensing control section and a first torque control section. The first torque control section receives the delivery pressure of the first pump device introduced thereto and controls to limit the capacity of the first hydraulic pump such that, when at least one of the delivery pressure and the capacity of the first hydraulic pump increases and absorption torque of the first pump device increases, the absorption torque of the first hydraulic pump does not exceed a first predetermined value. The second pump control unit includes a second torque control section that receives a delivery pressure of the second pump device introduced thereto and controls to limit the capacity of the second hydraulic pump such that, when the delivery pressure of the second hydraulic pump increases and absorption torque of the second pump device increases, the capacity of the second pump device is maintained at a maximum when the absorption torque of the second hydraulic pump is equal to or smaller than a second predetermined value and the absorption torque of the second hydraulic pump does not exceed the second predetermined value when the absorption torque of the second hydraulic pump increases up to the second predetermined value. The first pump control unit further includes: a reducing valve that receives the delivery pressure of the second pump device introduced thereto and, when the delivery pressure of the second pump device is equal to or lower than a capacity limiting control starting pressure of the second torque control section, outputs the delivery pressure of the second pump device without reduction and, when the delivery pressure of the second pump device increases beyond the capacity limiting control starting pressure of the second torque control section, reduces the delivery pressure of the second pump device to the capacity limiting control starting pressure of the second torque control section and outputs the reduced delivery pressure of the second pump device; and a reducing torque control actuator that receives the output pressure of the reducing valve and reduces the capacity of the first pump device such that the first predetermined value decreases as the output pressure of the reducing valve increases.
Through the foregoing, total torque control can be accurately performed not only when the absorption torque of the second pump device increases to the second predetermined value and operation is performed with the absorption torque limited to the second predetermined value by the control of the second torque control section, but also when the absorption torque of the second hydraulic pump is equal to or smaller than the second predetermined value and is free from limitation up to the second predetermined value, so that rated output torque of a prime mover can be effectively used.
(4) In any of (1) to (3) above, preferably, the first specific actuator is a boom cylinder that drives a boom of a hydraulic excavator and the second specific actuator is an arm cylinder that drives an arm of the hydraulic excavator.
Through the foregoing, in a horizontally leveling operation in which a boom raising fine operation (high load pressure) and an arm crowding operation (low load pressure) are performed simultaneously, wasteful energy consumption due to restricting pressure loss of the pressure compensating valve on the arm cylinder side on the low load side is reduced. In sweeping work through the boom raising fine operation (high load pressure) and the arm crowding operation (low load pressure), the flow rate of the hydraulic fluid supplied to the boom cylinder is flexibly varied by the load pressure, so that favorable operability can be achieved.
The present invention can achieve favorable operability by reducing energy consumption arising from the wasted restricting pressure loss of the pressure compensating valve and by flexibly varying the flow rate of the hydraulic fluid supplied to a specific actuator (first specific actuator) depending on the load pressure in a combined operation that involves the specific actuator and involves a great difference in load pressure and when the operation of an operating unit for the specific actuator is a fine operation.
Embodiments of the present invention will be described below with reference to the accompanying drawings.
—Structure—
In
Of the actuators 3a, 3b, 3c, 3d, 3e, 3f, 3g, and 3h, the actuators 3a, 3b, 3c, 3d, 3f, and 3g are each a first actuator driven by the hydraulic fluid delivered from the first and second delivery ports 102a and 102b of the main pump 102. Of the actuators 3a, 3b, 3c, 3d, 3e, 3f, 3g, and 3h, the actuators 3a, 3e, and 3h are each a second actuator driven by the hydraulic fluid delivered from the third delivery port 202a of the main pump 202. The actuator 3a is a common actuator that constitutes both the first and second actuators.
The control valve unit 4 includes a plurality of closed center type flow control valves 6b, 6c, 6d, 6f, 6g, 6i, and 6j, a plurality of pressure compensating valves 7b, 7c, 7d, 7f, 7g, 7i, and 7j, a plurality of operation detecting valves 8b, 8c, 8d, 8f, 8g, 8i, and 8j, a plurality of open center type flow control valves 6a, 6e, and 6h, a main relief valve 114, a main relief valve 214, a main relief valve 314, an unloading valve 115, and an unloading valve 215. More specifically, the flow control valves 6b, 6c, 6d, 6f, 6g, 6i, and 6j are connected to the first and second hydraulic fluid supply lines 105 and 205 and control flow rates of hydraulic fluids supplied from the first and second delivery ports 102a and 102b of the main pump 102 to the first actuators 3a, 3b, 3c, 3d, 3f, and 3g. The pressure compensating valves 7b, 7c, 7d, 7f, 7g, 7i, and 7j control differential pressures across the respective flow control valves 6b, 6c, 6d, 6f, 6g, 6i, and 6j such that the differential pressures across the respective flow control valves 6b, 6c, 6d, 6f, 6g, 6i, and 6j are equal to a target differential pressure. The operation detecting valves 8b, 8c, 8d, 8f, 8g, 8i, and 8j perform a stroke movement with spools of the respective flow control valves 6b, 6c, 6d, 6f, 6g, 6i, and 6j to thereby detect changeover of the respective flow control valves. The flow control valves 6a, 6e, and 6h are connected to the third hydraulic fluid supply line 305 and control flow rates of hydraulic fluids supplied from the third delivery port 202a of the main pump 202 to the second actuators 3a, 3e, and 3h. The main relief valve 114 is connected to the first hydraulic fluid supply line 105 and controls to keep the pressure in the first hydraulic fluid supply line 105 below a set pressure. The main relief valve 214 is connected to the second hydraulic fluid supply line 205 and controls to keep the pressure in the second hydraulic fluid supply line 205 below a set pressure. The main relief valve 314 is connected to the third hydraulic fluid supply line 305 and controls to keep the pressure in the third hydraulic fluid supply line 305 below a set pressure. The unloading valve 115 is connected to the first hydraulic fluid supply line 105 and opens to return the hydraulic fluid in the first hydraulic fluid supply line 105 back to a tank when the pressure in the first hydraulic fluid supply line 105 is higher than (an unloading valve set pressure that is) a maximum load pressure of the actuator driven by the hydraulic fluid delivered from the first delivery port 102a, to which a spring set pressure (predetermined pressure) is added. The unloading valve 215 is connected to the second hydraulic fluid supply line 205 and opens to return the hydraulic fluid in the second hydraulic fluid supply line 205 back to a tank when the pressure in the second hydraulic fluid supply line 205 is higher than (an unloading valve set pressure that is) a maximum load pressure of the actuator driven by the hydraulic fluid delivered from the second delivery port 102b, to which a spring set pressure (predetermined pressure) is added.
Further, the control valve unit 4 includes a first load pressure detecting circuit 131, a second load pressure detecting circuit 132, a differential pressure reducing valve 111, and a differential pressure reducing valve 211. More specifically, the first load pressure detecting circuit 131 includes shuttle valves 9d, 9f, 9i, and 9j that are connected to load ports of the flow control valves 6d, 6f, 6i, and 6j connected to the first hydraulic fluid supply line 105 and detect a maximum load pressure Plmax1 of the actuators 3a, 3b, 3d, and 3f. The second load pressure detecting circuit 132 includes shuttle valves 9b, 9c, and 9g that are connected to load ports of the flow control valves 6b, 6c, and 6g connected to the second hydraulic fluid supply line 205 and detect a maximum load pressure Plmax2 of the actuators 3b, 3c, and 3g. The differential pressure reducing valve 111 outputs, as an absolute pressure Pls1, a difference (LS differential pressure) between a pressure in the first hydraulic fluid supply line 105 (specifically, pressure at the first delivery port 102a) P1 and the maximum load pressure Plmax1 detected by the first load pressure detecting circuit 131 (maximum load pressure of the actuators 3a, 3b, 3d, and 3f connected to the first hydraulic fluid supply line 105). The differential pressure reducing valve 211 outputs, as an absolute pressure Pls2, a difference (LS differential pressure) between a pressure in the second hydraulic fluid supply line 205 (specifically, pressure at the second delivery port 102b) P2 and the maximum load pressure Plmax2 detected by the second load pressure detecting circuit 132 (maximum load pressure of the actuators 3b, 3c, and 3g connected to the second hydraulic fluid supply line 205). In the following, the absolute pressures Pls1 and Pls2 output by the differential pressure reducing valves 111 and 211 will be referred to as LS differential pressures Pls1 and Pls2 as appropriate.
The maximum load pressure Plmax1 detected by the first load pressure detecting circuit 131 as the maximum load pressure of the actuators driven by the hydraulic fluid delivered from the first delivery port 102a is introduced to the unloading valve 115. The maximum load pressure Plmax2 detected by the second load pressure detecting circuit 132 as the maximum load pressure of the actuators driven by the hydraulic fluid delivered from the second delivery port 102b is introduced to the unloading valve 215.
The LS differential pressure Pls1 output by the differential pressure reducing valve 111 is introduced to the pressure compensating valves 7d, 7f, 7i, and 7j that are connected to the first hydraulic fluid supply line 105 and the regulator 112 of the main pump 102. The LS differential pressure Pls2 output by the differential pressure reducing valve 211 is introduced to the pressure compensating valves 7b, 7c, and 7g that are connected to the second hydraulic fluid supply line 205 and the regulator 112 of the main pump 102.
It is here noted that the actuator 3a is connected to the first delivery port 102a via the flow control valve 6i, the pressure compensating valve 7i, and the first hydraulic fluid supply line 105, and is further connected to the third delivery port 202a via the flow control valve 6a and the third hydraulic fluid supply line 305. The actuator 3a is, for example, a boom cylinder (first specific actuator) that drives a boom of the hydraulic excavator. The flow control valve 6a serves, for example, as a main drive (first flow control valve) for the boom cylinder 3a. The flow control valve 6i serves, for example, as an assist drive (second flow control valve) for the boom cylinder 3a. The actuator 3b is connected to the first delivery port 102a via the flow control valve 6j, the pressure compensating valve 7j, and the first hydraulic fluid supply line 105, and is further connected to the second delivery port 102b via the flow control valve 6b, the pressure compensating valve 7b, and the second hydraulic fluid supply line 205. The actuator 3b is, for example, an arm cylinder (second specific actuator) that drives an arm of the hydraulic excavator. The flow control valve 6b serves, for example, as a main drive for the arm cylinder 3b. The flow control valve 6j serves, for example, as an assist drive for the arm cylinder 3b.
The actuators 3d and 3f are connected to the first delivery port 102a via the flow control valves 6d and 6f and the pressure compensating valves 7d and 7f, respectively, and the first hydraulic fluid supply line 105. The actuators 3c and 3g are connected to the second delivery port 102b via the flow control valves 6c and 6g and the pressure compensating valves 7c and 7g, respectively, and the second hydraulic fluid supply line 205. The actuators 3d and 3f are, for example, a bucket cylinder that drives a bucket of the hydraulic excavator and a left track motor that drives a left crawler of a lower track structure of the hydraulic excavator, respectively. The actuators 3c and 3g are, for example, a swing motor that drives an upper swing structure of the hydraulic excavator and a right track motor that drives a right crawler of the lower track structure of the hydraulic excavator, respectively. The actuators 3e and 3h are connected to the third delivery port 202a via the flow control valves 6e and 6h, respectively, and the third hydraulic fluid supply line 305. The actuators 3e and 3h are, for example, a swing cylinder that drives a swing post of the hydraulic excavator and a blade cylinder that drives a blade of the hydraulic excavator, respectively.
The boom cylinder 3a and the arm cylinder 3b require a maximum demanded flow rate that is greater than maximum demanded flow rates of other actuators. Additionally, the arm cylinder 3b (second specific actuator) is used at relatively high frequency in a combined operation with the boom cylinder 3a (first actuator).
The flow control valve 6b for the main drive for the arm cylinder 3b is set to have an opening area characteristic in which the opening area of the meter-in passage increases with increase in the spool stroke after the dead zone of 0 to S1 and reaches a maximum opening area A1 at an intermediate stroke S2 and the maximum opening area A1 is thereafter maintained up to the maximum spool stroke S3.
The flow control valve 6j for the assist drive for the arm cylinder 3b is set to have an opening area characteristic in which the opening area of the meter-in passage remains zero until the spool stroke is the intermediate stroke S2, increases with increase in the spool stroke after the intermediate stroke S2, and reaches a maximum opening area A2 immediately before the maximum spool stroke S3 is reached.
The lower graph of
The meter-in passage of each of the flow control valves 6b and 6j of the arm cylinder 3b exhibits the opening area characteristic as described above, so that the combined opening area characteristic is such that the opening area increases with increase in the spool stroke after the dead zone of 0 to S1 and reaches a maximum opening area of A1+A2 immediately before the maximum spool stroke S3 is reached.
It is here noted that the maximum opening area A3 of the flow control valves 6c, 6d, 6e, 6f, 6g, and 6h of the actuators 3c to 3h shown in
The pressure compensating valves 7c to 7h and the pressure compensating valves 7b and 7j control differential pressures across the flow control valves 6c to 6h and the flow control valves 6b and 6j of the arm cylinder 3b, respectively. The flow rate through each of the flow control valves 6c to 6h and, 6b and 6j, thus increases in proportion to the opening area of a corresponding meter-in passage and the flow control valves 6c to 6h and, 6b and 6j, each exhibit a flow rate characteristic similar to the characteristics shown in
The flow control valve 6a for the main drive for the boom cylinder 3a is set such that the meter-in passage and the meter-out passage have an opening area characteristic in which the opening area increases with increase in the spool stroke after the dead zone of 0 to S1 and reaches a corresponding maximum opening area A4 or A5 before the maximum spool stroke S3 is reached. The opening area characteristic of the meter-in passage is, however, set such that the maximum opening area A4 is greater than the maximum opening area A5 of the opening area characteristic of the meter-out passage and, additionally, when the spool stroke increases beyond the intermediate stroke S2, the opening area increases at a rate higher than a rate at which the opening area increases before the intermediate stroke S2. The flow control valve 6a for the main drive for the boom cylinder 3a is set such that the bleed-off passage has an opening area characteristic in which the opening area is the maximum opening area A4 when the spool stroke is zero and decreases with increase in the spool stroke from zero and then becomes zero when the intermediate stroke S2 is reached. The opening area characteristic of the bleed-off passage is, however, set such, when the spool stroke increases beyond the dead zone of 0 to S1, the opening area decreases at a rate lower than a rate at which the opening area decreases in the dead zone.
The meter-in passage of the flow control valve 6i for the assist drive for the boom cylinder 3a is set to have an opening area characteristic in which the opening area remains zero until the spool stroke equals the intermediate stroke S2; the meter-in passage opens at the intermediate stroke S2 and increases its opening area with increase in the spool stroke and then becomes a maximum opening area A6 immediately before the maximum spool stroke S3 is reached.
As illustrated in the lower side of
As such, the flow control valves 6a and 6i (first and second flow control valves) are set to offer the following opening area characteristics. Specifically, when the operating unit 123 for the boom is operated up to the intermediate zone of the operating range, only the flow control valve 6a (first flow control valve) opens, so that the hydraulic fluid is supplied from the main pump 202 (second pump device) to the boom cylinder 3a (first specific actuator). When the operating unit 123 is operated further from the intermediate zone, both of the flow control valves 6a and 6i (first and second flow control valves) open, so that the hydraulic fluid from the main pumps 102 and 202 (first and second pump devices) are joined and supplied to the boom cylinder 3a (first specific actuator).
In the flow control valve 6a for the main drive (first flow control valve), both the meter-in passage and the bleed-off passage are open until the spool stroke reaches the intermediate stroke S2, during which period a supply flow rate increases with increase in the spool stroke after the dead zone of 0 to S1 and the supply flow rate decreases with increase in load pressure. When the spool stroke reaches the intermediate stroke S2, the opening area of the bleed-off passage is zero and a total amount Q1 of the fluid delivered from the main pump 202 is supplied to the boom cylinder 3a.
The pressure compensating valve 7b controls the differential pressure across the flow control valve 6i for the assist drive (second flow rate control valve). The flow rate through the flow control valves 6i thus increases in proportion to the opening area of the meter-in passage and the flow control valve 6i exhibits a flow rate characteristic similar to the characteristic shown in
The lower graph of
The flow control valves 6a and 6i of the boom cylinder 3a are set to have the flow rate characteristics as described above. As a result, before the spool stroke reaches the intermediate stroke S2, the supply flow rate increases with increase in the spool stroke after the dead zone of 0 to S1 and the supply flow rate decreases with increase in load pressure. After the spool stroke reaches the intermediate stroke S2, the supply flow rate increases with increase in the spool stroke and then becomes a maximum supply flow rate of Q1+Q2 immediately before the maximum spool stroke S3 is reached.
Reference is made back to
The track combined operation detecting hydraulic line 53 operates as follows. Specifically, during a time not involving a track combined operation in which the actuator 3f as the left track motor (hereinafter referred to as a left track motor 3f as appropriate) and/or the actuator 3g as the right track motor (hereinafter referred to as a right track motor 3g as appropriate), and at least one of the actuators 3a, 3b, 3c, and 3d other than the left and right track motors that are connected to the first hydraulic fluid supply line 105 and the second hydraulic fluid supply line 205 are simultaneously driven, the track combined operation detecting hydraulic line 53 communicates with the tank via at least any of the operation detecting valves 8a, 8b, 8c, 8d, 8f, 8g, 8i, and 8j, to thereby develop a tank pressure in the hydraulic line 53. During the track combined operation, the operation detecting valves 8f and 8g and any of the operation detecting valves 8a, 8b, 8c, 8d, 8i, and 8j perform a stroke movement with the respective flow control valves to thereby interrupt the communication with the tank, so that the operation detecting pressure (operation detecting signal) is generated in the hydraulic line 53.
During a time not involving the track combined operation, the first selector valve 40 is placed in a first position (interruption position) on the lower side in
During a time not involving the track combined operation, the second selector valve 146 is placed in a first position on the lower side in
During a time not involving the track combined operation, the third selector valve 246 is placed in a first position on the lower side in
By changing the positions of the first selector valve 40, the second selector valve 146, and the third selector valve 246 on the basis of the operation detecting pressure generated by the track combined operation detecting hydraulic line 53, during a time not involving the track combined operation (during a track individual operation), the left track motor 3f is driven by the hydraulic fluid delivered from the first delivery port 102a of the split-flow-type main pump 102 and the right track motor 3g is driven by the hydraulic fluid delivered from the second delivery port 102b of the split-flow-type main pump 102. During the track combined operation, the first selector valve 40 is placed in the second position to establish communication between the first hydraulic fluid supply line 105 and the second hydraulic fluid supply line 205. The first and second delivery ports 102a 102b then function as a single pump, so that the hydraulic fluid delivered from the first delivery port 102a of the main pump 102 is joined with the hydraulic fluid delivered from the second delivery port 102b of the main pump 102 and the the left track motor 3f and the right track motor 3g are driven with the joined hydraulic fluids.
In addition, in
The prime mover speed detecting valve 13 includes a flow detecting valve 50 and a differential pressure reducing valve 51. Specifically, the flow detecting valve 50 is connected between the hydraulic fluid supply line 31a of the pilot pump 30 and the pilot hydraulic fluid supply line 31b. The differential pressure reducing valve 51 outputs a differential pressure across the flow detecting valve 50 as the absolute pressure Pgr.
The flow detecting valve 50 includes a variable restrictor 50a that increases an opening area with increase in the flow rate passing therethrough (delivery flow rate of the pilot pump 30). The hydraulic fluid delivered from the pilot pump 30 passes through the variable restrictor 50a to flow to the side of the pilot hydraulic line 31b. During this time, a differential pressure that increases with increase in the flow rate through the variable restrictor 50a develops across the variable restrictor 50a of the flow detecting valve 50. The differential pressure reducing valve 51 outputs this differential pressure as the absolute pressure Pgr. Because the delivery flow rate of the pilot pump 30 varies with the speed of the prime mover 1, detecting the differential pressure across the variable restrictor 50a allows the delivery flow rate of the pilot pump 30 to be detected, so that the speed of the prime mover 1 can be detected. The absolute pressure Pgr output by the prime mover speed detecting valve 13 (differential pressure reducing valve 51) is introduced to the regulator 112 as a target LS differential pressure. In the following, the absolute pressure Pgr output by the differential pressure reducing valve 51 will be referred to as an output pressure Pgr or a target LS differential pressure Pgr as appropriate.
The regulator 112 (first pump control unit) includes a low pressure selection valve 112a, an LS control valve 112b, an LS control piston 112c, torque control (horsepower control) pistons 112e and 112d (first torque control actuators), and a spring 112u. Specifically, the low pressure selection valve 112a selects a low pressure side of the LS differential pressure Pls1 output by the differential pressure reducing valve 111 and the LS differential pressure Pls2 output by the differential pressure reducing valve 211. The LS control valve 112b receives an LS differential pressure Pls12 selected as the low pressure side and the output pressure Pgr of the prime mover speed detecting valve 13 as the target LS differential pressure introduced thereto. The LS control valve 112b thereby varies a load sensing drive pressure (hereinafter referred to as an LS drive pressure) such that the LS differential pressure Pls12 lowers as the LS differential pressure Pls12 is smaller than the target LS differential pressure Pgr. The LS control piston 112c receives the LS drive pressure introduced thereto and controls a tilting angle (capacity) of the main pump 102 such that the tilting angle of the main pump 102 increases with a decreasing LS drive pressure to thereby increase the delivery flow rate. The torque control pistons 112e and 112d receive pressures at the first and second delivery ports 102b and 102a introduced thereto, respectively, and control the tilting angle of a swash plate of the main pump 102 such that the tilting angle of the main pump 102 is reduced to reduce absorption torque when the pressures increase. The spring 112u serves as a first urging means that sets maximum torque T12max (see
Further, the regulator 112 (first pump control unit) includes a reducing valve 112g and a reducing torque control piston 112f. Specifically, the reducing valve 112g receives the delivery pressure from the third delivery port 202a of the main pump 202 (pressure in the third hydraulic fluid supply line 305) introduced thereto. When this pressure is equal to or lower than a set pressure of a spring 112t (capacity limiting control starting pressure), the reducing valve 112g outputs the delivery pressure from the third delivery port 202a of the main pump 202 without reduction; when the delivery pressure from the third delivery port 202a of the main pump 202 is higher than the set pressure of the spring 112t (capacity limiting control starting pressure), the reducing valve 112g reduces the delivery pressure from the third delivery port 202a of the main pump 202 to the set pressure of the spring 112t (capacity limiting control starting pressure) and outputs the reduced pressure. The reducing torque control piston 112f receives the output pressure from the reducing valve 112g introduced thereto and reduces the capacity of the main pump 2 such that maximum torque (first predetermined value) of the main pump 102 decreases with increase in the output pressure of the reducing valve 112g.
The low pressure selection valve 112a, the LS control valve 112b, and the LS control piston 112c constitute a first load sensing control section that controls the capacity of the main pump 102 such that the delivery pressure of the main pump 102 (delivery pressure on the high pressure of the first and second delivery ports 102a and 102b) is higher by the target differential pressure (target LS differential pressure Pgr) than the maximum load pressure of the actuators driven by the hydraulic fluid delivered from the main pump 102 (pressure on the high pressure side of the maximum load pressure Plmax1 and the maximum load pressure Plmax2).
The torque control pistons 112d and 112e, the spring 112u, the reducing valve 112g, and the reducing torque control piston 112f constitute a first torque control section. The first torque control section controls to limit the capacity of the main pump 102 such that, when at least one of the delivery pressure of the first and second delivery ports 102a and 102b of the main pump 102 (delivery pressure of the main pump 102) and the capacity of the main pump 102 increases and the absorption torque of the main pump 102 increases, the absorption torque of the main pump 102 does not exceed the maximum torque (first predetermined value). It is noted that the maximum torque (first predetermined value) of the main pump 102 is variable over a range of T12max to T12max−T3max (to be described later).
The first load sensing control section (low pressure selection valve 112a, LS control valve 112b, and LS control piston 112c) functions to control the capacity of the main pump 102 through the load sensing control when the main pump 102 is not subject to torque control limiting by the first torque control section.
The regulator 212 (second pump control unit) includes a torque control (horsepower control) piston 212d (second torque control actuator) and a spring 212e. The torque control piston 212d receives delivery pressure P3 of the main pump 202 introduced thereto and controls the tilting angle of a swash plate of the main pump 202 such that the tilting angle of the main pump 202 is reduced to reduce the absorption torque when the pressures increase. The spring 212e serves as a second urging means that sets maximum torque T3max (see
The torque control piston 212d and the spring 212e constitute a second torque control section. When the delivery pressure P3 of main pump 202 increases and the absorption torque of the main pump 202 increases and when the absorption torque of the main pump 202 is equal to or lower than the maximum torque T3max (second predetermined value), the second torque control section maintains the capacity of the main pump 202 at a maximum q3max. When the absorption torque of the main pump 202 increases up to the maximum torque T3max (second predetermined value), the second torque control section controls to limit the capacity of the main pump 202 such that the absorption torque of the main pump 202 does not exceed the maximum torque T3max (second predetermined value).
The set pressure of the spring 112t of the reducing valve 112g is set to be equal to the capacity limiting control starting pressure as the set pressure of the spring 212 (hereinafter referred to as torque control starting pressure) P3c (
In
In
When the absorption torque (tilting angle) of the main pump 202 is controlled as described above, the delivery pressure (pressure of the third delivery port 202a) of the main pump 202 is introduced to the reducing torque control piston 112f via the reducing valve 112g and the reducing torque control to reduce the maximum torque T12max (first predetermined value) that is the set pressure of the spring 212e is performed.
Specifically, when the delivery pressure of the third delivery port 202a of the main pump 202 is equal to or lower than the torque control starting pressure P3c (
In
Thus, even in a combined operation that simultaneously drives an actuator associated with the main pump 102 and an actuator associated with the main pump 202, or an operation that drives an actuator associated with both the main pump 102 and the main pump 202 (boom cylinder 3a), the total of the absorption torque of the main pump 102 and the absorption torque of the main pump 202 is controlled not to exceed the maximum torque T12max (total torque control or full horsepower control; hereinafter referred to as total torque control), so that the prime mover 1 can be prevented from stalling (engine stall). In addition, the reducing valve 112g outputs a pressure that simulates the absorption torque of the main pump 202 and this pressure is introduced to the reducing torque control piston 112f so as to reduce the maximum torque of the main pump 102. This arrangement enables the total torque control to be accurately performed not only when the main pump 202 operates at the maximum torque T3max as being limited by the second torque control section, but also when the main pump 202 is not subject to limitation by the second torque control section, so that the rated output torque Terate of the prime mover can be effectively used.
Hydraulic Excavator
In
A canopy type cabin 108 is mounted on the upper swing structure 109. The cabin 108 includes a driver's seat 121, the front/swing left and right operating units 122 and 123 (only the left operating unit is shown in
—Operation—
Operation in the present embodiment will be described below.
A hydraulic fluid delivered from the fixed displacement pilot pump 30 that is driven by the prime mover 1 is supplied to the hydraulic fluid supply line 31a. The prime mover speed detecting valve 13 is connected to the hydraulic fluid supply line 31a. The prime mover speed detecting valve 13 uses the flow detecting valve 50 and the differential pressure reducing valve 51 to output as the absolute pressure Pgr (target LS differential pressure) a differential pressure across the flow detecting valve 50 varying according to the delivery flow rate of the pilot pump 30. The pilot relief valve 32 is connected downstream of the prime mover speed detecting valve 13 and generates a constant pressure (pilot primary pressure Ppilot) in the pilot hydraulic fluid supply line 31b.
(a) When all Control Levers are in Neutral Positions
Because all control levers of the operating units are in their neutral positions, all of the flow control valves 6a to 6j are in their neutral positions. Because all of the flow control valves 6a to 6j are in their neutral positions, the first load pressure detecting circuit 13 and the second load pressure detecting circuit 132 associated with the flow control valves 8b to 8d, 8f, 8g, 8i, and 8j that are connected to the first and second hydraulic fluid supply lines 105 and 205 detect tank pressures as the maximum load pressures Plmax1 and Plmax2, respectively. The maximum load pressures Plmax1 and Plmax2 are introduced to the unloading valves 115 and 215, and the differential pressure reducing valves 111 and 211, respectively.
The maximum load pressures Plmax1 and Plmax2 being introduced to the unloading valves 115 and 215 cause the pressures P1 and P2 of the first and second delivery ports 102a and 102b to be maintained at minimum pressures that represent the maximum load pressures Plmax1 and Plmax2 to which the set pressures of the springs of the unloading valves 115 and 215 are added (unloading valve set pressures). Let Punsp be the spring set pressure for the unloading valves 115 and 215. Then, Punsp is normally set to be slightly higher than the output pressure Pgr of the prime mover speed detecting valve 13, specifically, the target LS differential pressure (Punsp>Pgr).
The differential pressure reducing valves 111 and 211 output differential pressures (LS differential pressures) between the pressures P1 and P2 of the first and second hydraulic fluid supply lines 105 and 205 and the maximum load pressures Plmax1 and Plmax2 (tank pressure) as the absolute pressures Pls1 and Pls2, respectively. The maximum load pressures Plmax1 and Plmax2 are each the tank pressure as described previously. Let Ptank be the tank pressure, then
Pls1=P1−Plmax1=(Ptank+Punsp)−Ptank=Punsp>Pgr
Pls2=P2−Plmax2=(Ptank+Punsp)−Ptank=Punsp>Pgr
The LS differential pressures Pls1 and Pls2 are introduced to the low pressure selection valve 112a of the regulator 112.
Of the LS differential pressures Pls1 and Pls2 introduced to the low pressure selection valve 112a, the low pressure side is selected in the regulator 112 and introduced as the LS differential pressure Pls12 to the LS control valve 112b. Because Pls12>Pgr regardless of whichever is selected, Pls1 or Pls2, the LS control valve 122b is pushed to the left in
Meanwhile, the hydraulic fluid delivered from the main pump 202 is introduced to the third hydraulic fluid supply line 305 and discharged into the tank by way of the bleed-off passage that is open with the open center type flow control valves 6a, 6e, and 6h in their neutral positions. As a result, the pressure in the third hydraulic fluid supply line 305 is an extremely low pressure that is slightly higher than the tank pressure by only an extremely small resistance produced when the hydraulic fluid delivered from the main pump 202 flows past the bleed-off passage of the flow control valves 6a, 6e, and 6h.
The pressure in the third hydraulic fluid supply line 305 (delivery pressure from the main pump 202) is introduced to the torque control (horsepower control) piston 212d disposed in the regulator 212 of the main pump 202. Because this pressure is low, the capacity (flow rate) of the main pump 202 is maintained at a maximum level.
In
Additionally, the delivery pressure of the main pump 202 is introduced to the reducing torque control piston 112f via the reducing valve 112g. At the reducing torque control piston 112f, force determined by a product of the delivery pressure of the main pump 202 and a pressure receiving surface area of the reducing torque control piston 112f acts in a direction in which the capacity (tilting angle) of the main pump 102 is reduced. However, the capacity (tilting angle) of the main pump 102 is maintained at the minimum level by the LS control piston 112c as described previously and this condition is maintained.
(b) When the Boom Control Lever is Operated (Fine Operation)
Consider a case in which an input of the control lever in a boom raising direction is small and the boom cylinder 3a is driven by only the open center type flow control valve 6a.
When the control lever of the boom operating unit (boom control lever) is operated in a direction in which the boom cylinder 3a is extended, specifically, in the boom raising direction, the remote control valve of the boom operating unit outputs a boom raising pilot pressure. The flow control valves 6a and 6i for driving the boom cylinder 3a are each then placed in an upper position in
When the operation on the boom control lever is a fine operation, the spool strokes of the flow control valves 6a and 6i are equal to or more than S1 and equal to or less than S2 in
Because the spool stroke of the flow control valve 6a is equal to or more than S1 and equal to or less than S2, the bleed-off passage is not fully closed. As shown in the section between S1 and S2 of
At this time, the pressure of the third hydraulic fluid supply line 305 (delivery pressure of the main pump 202) is introduced to the torque control (horsepower control) piston 212d disposed in the regulator 212 of the main pump 202. When the pressure of the third hydraulic fluid supply line 305 falls short of the torque control starting pressure P3c of the torque constant curve 602 set by the spring 212e, the capacity of the main pump 202 is maintained at the maximum qmax. When the pressure of the third hydraulic fluid supply line 305 is equal to or higher than the torque control starting pressure P3c, the capacity of the main pump 202 is reduced to a tilting position at which force of the piston 212d and force of the spring 212e balance each other.
For example, when the main pump 202 operates at point B indicated in
Additionally, the pressure of the third hydraulic fluid supply line 305 (delivery pressure of the main pump 202) is introduced to the reducing valve 112g disposed in the regulator 112 of the main pump 102. When the pressure of the third hydraulic fluid supply line 305 (delivery pressure of the main pump 202) is equal to or lower than the set pressure (torque control starting pressure) P3c of the reducing valve 112g, the pressure of the third hydraulic fluid supply line 305 is directly introduced to the reducing torque control piston 112f. When the pressure of the third hydraulic fluid supply line 305 is higher than P3c, a pressure limited to P3c is introduced to the reducing torque control piston 112f. At the reducing torque control piston 112f, force determined by the product of the delivery pressure of the main pump 202 and the pressure receiving surface area of the reducing torque control piston 112f acts in the direction in which the capacity (tilting angle) of the main pump 102 is reduced. However, the current operation on the boom control lever is a fine operation and the capacity of the main pump 102 is maintained at the minimum level as described previously, so that this condition is maintained.
(c) When the Boom Control Lever is Operated (Full Operation)
Consider a case in which an input of the control lever in the boom raising direction is large and the boom cylinder 3a is driven by both the open center type flow control valve 6a and the closed center type flow control valve 6i.
When the boom control lever is fully operated in a direction in which the boom cylinder 3a is extended, specifically, in the boom raising direction, the flow control valves 6a and 6i for driving the boom cylinder 3a change their positions upwardly in
Thus, in the flow control valve 6a, the hydraulic fluid is supplied from the main pump 202 to the boom cylinder 3a via the meter-in passage of the flow control valve 6a as in the case of (b) fine operation. Because the bleed-off passage is fully closed in this case, however, the total amount Q1 of the hydraulic fluid of the main pump 202 is introduced to the boom cylinder 3a as indicated by S3 in the upper graph of
The capacity of the main pump 202 is controlled by the PQ characteristic shown in
Meanwhile, the load pressure on the bottom side of the boom cylinder 3a is detected as the maximum load pressure Plmax1 by the first load pressure detecting circuit 131 via the load port of the flow control valve 6i and introduced to the unloading valve 115 and the differential pressure reducing valve 111. The maximum load pressure Plmax1 being introduced to the unloading valve 115 causes the set pressure of the unloading valve 115 to increase to a level that represents the maximum load pressure Plmax1 (load pressure on the bottom side of the boom cylinder 3a) to which the spring set pressure Punsp is added, and the hydraulic line through which the hydraulic fluid of the first hydraulic fluid supply line 105 is discharged to the tank is interrupted. Additionally, the maximum load pressure Plmax1 being introduced to the differential pressure reducing valve 111 causes the differential pressure reducing valve 111 to output as the absolute pressure Pls1 the differential pressure (LS differential pressure) between the pressure P1 of the first hydraulic fluid supply line 105 and the maximum load pressure Plmax1. The absolute pressure Pls1 is introduced to the low pressure selection valve 112a of the regulator 112 and the low pressure selection valve 112a selects the low pressure side of Pls1 and Pls2.
In a full operation for boom raising, Pls2 is maintained at a value greater than Pgr as when the control lever is in the neutral position (Pls2=P2−Plmax2=(Ptank+Punsp)−Ptank=Punsp>Pgr). At a motion start for boom raising, the LS differential pressure Pls1 is nearly equal to zero and a relation of Pls1<Pgr holds. Thus, Pls1 is selected as the low pressure side LS differential pressure Pls12 by the low pressure selection valve 112a and introduced to the LS control valve 112b. The LS control valve 112b compares the target LS differential pressure Pgr with the LS differential pressure Pls1. In this case, because Pls1<Pgr, the LS control valve 112b is placed in the right position in
Then, as shown by S3 in the lower graph of
At this time, the hydraulic fluid at the same flow rate as that of the hydraulic fluid supplied to the first hydraulic fluid supply line 105 is supplied to the second hydraulic fluid supply line 205; however, the hydraulic fluid is returned as an excess flow rate to the tank via the unloading valve 215. It is here noted that the second load pressure detecting circuit 132 detects the tank pressure as the maximum load pressure Plmax2. Thus, the set pressure of the unloading valve 215 equals the spring set pressure Punsp, so that the pressure P2 of the second hydraulic fluid supply line 205 is maintained at the low pressure Punsp. This reduces pressure loss of the unloading valve 215 when the excess flow rate returns to the tank, enabling operation involving less energy loss.
When the delivery fluid of the main pump 202 and the delivery fluid of the main pump 102 are joined and supplied to the boom cylinder, the bleed-off passage of the open center type flow control valve 6a on the main pump 202 side is fully closed, while on the main pump 102 side, the load sensing control controls the delivery flow rate of the main pump 102. Thus, in an operation involving a large operation amount of the boom control lever, such as loading following excavating by the hydraulic excavator, a characteristic less susceptible to the effect of load pressure can be obtained and powerful operating feeling can be obtained.
When the main pump 102 is subject to the torque control limitation by the first torque control section (torque control pistons 112d and 112e, spring 112u, reducing valve 112g, and reducing torque control piston 112f), the capacity of the main pump 102 is controlled by the PQ characteristic shown in
The pressure P3 of the third hydraulic fluid supply line 305 is introduced to the reducing valve 112g disposed in the regulator 112 of the main pump 102. When the pressure P3 of the third hydraulic fluid supply line 305 is equal to or lower than the set pressure (torque control starting pressure) P3c of the reducing valve 112g, the pressure P3 is directly introduced to the reducing torque control piston 112f. When the pressure P3 of the third hydraulic fluid supply line 305 is higher than P3c, a pressure limited to P3c is introduced to the reducing torque control piston 112f. The reducing torque control piston 112f performs the following reducing torque control as described previously. Specifically, when the pressure P3 of the third hydraulic fluid supply line 305 is equal to or lower than the set pressure P3c of the reducing valve 112g, the reducing torque control piston 112f reduces the maximum torque of the main pump 102 by the absorption torque of the main pump 202 (T3) as indicated by the torque constant curve 504 in
As described above, the reducing valve 112g outputs a pressure that simulates the absorption torque of the main pump 202 and this pressure is introduced to the reducing torque control piston 112f so as to reduce the maximum torque of the main pump 102. This arrangement enables the total torque control to be accurately performed not only when the main pump 202 operates at the maximum torque T3max as being limited by the second torque control section, but also when the main pump 202 is not subject to limitation by the second torque control section, so that the rated output torque Terate of the prime mover can be effectively used.
(d) When the Arm Control Lever is Operated (Fine Operation)
When, for example, the control lever of the arm operating unit (arm control lever) is operated in a direction in which the arm cylinder 3b is extended, specifically, in an arm crowding direction, the flow control valves 6b and 6j for driving the arm cylinder 3b change their positions downwardly in
When the operation on the arm control lever is a fine operation and the stroke of the flow control valves 6b and 6j is equal to or less than S2 in
When the flow selector valve 6b is placed in the downward position in
Immediately after the operation of the control lever during the arm crowding start, the load pressure on the arm cylinder 3b is transmitted to the second hydraulic fluid supply line 205 and there is substantially no difference between both, so that the LS differential pressure Pls2 is substantially equal to zero and a relation of Pls2<Pgr holds. At this time, Pls1 is maintained at a value greater than Pgr as when the control lever is in the neutral position (Pls1=P1−Plmax1=(Ptank+Punsp)−Ptank=Punsp>Pgr). Thus, the low pressure selection valve 112a selects Pls2 as the LS differential pressure Pls12 on the low pressure side and Pls2 is introduced to the LS control valve 112b. The LS control valve 112b compares the output pressure Pgr of the prime mover speed detecting valve 13 as the target LS differential pressure with Pls2. In this case, because the relation of Pls2<Pgr holds as mentioned above, the LS control valve 112b is placed in the right position in
At this time, the hydraulic fluid at the same flow rate as that of the hydraulic fluid supplied to the second hydraulic fluid supply line 205 is supplied to the first hydraulic fluid supply line 105; however, the hydraulic fluid is returned as an excess flow rate to the tank via the unloading valve 115. It is here noted that the first load pressure detecting circuit 131 detects the tank pressure as the maximum load pressure Plmax1. Thus, the set pressure of the unloading valve 115 equals the spring set pressure Punsp, so that the pressure P1 of the first hydraulic fluid supply line 105 is maintained at the low pressure Punsp. This reduces pressure loss of the unloading valve 115 when the excess flow rate returns to the tank, enabling operation involving less energy loss.
Because the actuators associated with the main pump 202 are not driven at this time, the delivery pressure of the main pump 202 is extremely low in a similar manner as when all control levers are in their neutral positions. This low pressure is introduced to the torque feedback piston 112f without being reduced by the reducing valve 112g. The maximum torque of the main pump 102 shown in
(e) When the Arm Control Lever is Operated (Full Operation)
When, for example, the arm control lever is fully operated in a direction in which the arm cylinder 3b is extended, specifically, in an arm crowding direction, the flow control valves 6b and 6j for driving the arm cylinder 3b are placed in downward positions in
As described previously in (d), the second load pressure detecting circuit 132 detects as the maximum load pressure Plmax2 the load pressure on the bottom side of the arm cylinder 3b via the load port of the flow control valve 6b and the unloading valve 215 interrupts the hydraulic line through which the hydraulic fluid of the second hydraulic fluid supply line 205 is discharged to the tank. Additionally, the maximum load pressure Plmax2 being introduced to the differential pressure reducing valve 211 causes the LS differential pressure Pls2 to be output and to be introduced to the low pressure selection valve 112a of the regulator 112.
Meanwhile, the load pressure on the bottom side of the arm cylinder 3b is detected as the maximum load pressure Plmax1 (=Plmax2) by the first load pressure detecting circuit 131 via the load port of the flow control valve 6j and introduced to the unloading valve 115 and the differential pressure reducing valve 111. The maximum load pressure Plmax1 being introduced to the unloading valve 115 causes the unloading valve 115 to interrupt the hydraulic line through which the hydraulic fluid of the first hydraulic fluid supply line 105 is discharged to the tank. The maximum load pressure Plmax1 being introduced to the differential pressure reducing valve 111 causes the LS differential pressure Pls1 (=Pls2) to be introduced to the low pressure selection valve 112a of the regulator 112.
Immediately after the operation of the control lever during the arm crowding start, the load pressure on the arm cylinder 3b is transmitted to the first and second hydraulic fluid supply lines 105 and 205 to thereby produce substantially no difference between the two pressures. Thus, both of the LS differential pressures Pls1 and Pls2 are substantially equal to zero and a relation of Pls1, Pls2<Pgr holds. Thus, the low pressure selection valve 112a selects either Pls1 or Pls2 as the LS differential pressure Pls12 on the low pressure side, so that Pls12 is introduced to the LS control valve 112b. In this case, because Pls12 (Pls1 or Pls2)<Pgr as mentioned above, the LS control valve 112b is placed in the right position in
Because the actuators associated with the main pump 202 are not driven at this time, too, the delivery pressure of the main pump 202 is extremely low in a similar manner as when all control levers are in their neutral positions. This low pressure is introduced to the torque feedback piston 112f without being reduced by the reducing valve 112g. The maximum torque of the main pump 102 shown in
Through the foregoing arrangements, the first torque control section controls the tilting angle of the main pump 102 such that the absorption torque of the main pump 102 does not exceed the maximum torque T12max, so that the prime mover 1 can be prevented from stalling (engine stall) when the load on the arm cylinder 3b increases.
(f) Horizontally Leveling Operation and Sweeping Work
In a horizontally leveling operation and sweeping work, typically the arm control lever is operated as an arm crowding full operation and the boom control lever is operated as a boom raising fine operation.
Because the boom raising is a fine operation, the boom cylinder 3a is driven by only the hydraulic fluid supplied from the main pump 202 via the open center type flow control valve 6a as described previously in (b). Additionally, the spool stroke of the flow control valve 6a is equal to or more than S1 and equal to or less than S2 and the bleed-off passage is not fully closed. As shown in the section between S1 and S2 of
In contrast, the operation of the arm control lever is a full operation and, as described previously in (e), the flow control valve 6b for the main drive and the flow control valve 6j for the assist drive for the arm cylinder 3b change their positions through a full stroke and the opening areas of the meter-in passages are Al and A2, respectively. The load pressure on the arm cylinder 3b is detected as the maximum load pressures Plmax1 and Plmax2 (Plmax1=Plmax2) by the first and second load pressure detecting circuits 131 and 132 via the load ports of the flow control valves 6b and 6j and the unloading valves 115 and 215 interrupt the hydraulic lines through which the hydraulic fluids of the first and second hydraulic fluid supply lines 105 and 205 are discharged to the tank, respectively. Additionally, the maximum load pressures Plmax1 and Plmax2 are fed back to the regulator 112 of the main pump 102. When the main pump 102 is not subject to the torque control limitation by the first torque control section (torque control pistons 112d and 112e, spring 112u, reducing valve 112g, and reducing torque control piston 112f), the capacity (flow rate) of the main pump 102 increases corresponding to the demanded flow rates of the flow control valves 6b and 6j, so that the hydraulic fluid at the flow rate corresponding to the operation on the arm control lever is supplied from the first and second delivery ports 102a and 102b of the main pump 102 to the bottom side of the arm cylinder 3b. Thus, the arm cylinder 3b is driven in the extending direction by the joined hydraulic fluids from the first and second delivery ports 102a and 102b.
The horizontally leveling operation very often involves a low load pressure on the arm cylinder 3b and a high load pressure on the boom cylinder 3a. In the horizontally leveling operation according to the present embodiment, a specific pump is assigned for driving a specific actuator having a specific load pressure; specifically, the hydraulic pump that drives the boom cylinder 3a is the main pump 202, while the hydraulic pump that drives the arm cylinder 3b is the main pump 102. In this respect, unlike the related-art one-pump load sensing system that includes a single pump for driving a plurality of actuators, each actuator having a specific load pressure, the present embodiment does not consume energy as a result of wasted restricting pressure loss at the pressure compensating valve 7b on the low load side.
Because the boom cylinder 3a is controlled by the open center type flow control valve 6a, the bleed-off passage is open in the fine operation zone thereof and, as indicated by the section between S1 and S2 in
When the main pump 102 is subject to the torque control limitation by the first torque control section (torque control pistons 112d and 112e, spring 112u, reducing valve 112g, and reducing torque control piston 112f), the capacity of the main pump 102 is controlled by the PQ characteristic shown in
Additionally, as described previously in (c), the pressure P3 of the third hydraulic fluid supply line 305 is introduced to the reducing valve 112g disposed in the regulator 112 of the main pump 102. When the pressure P3 of the third hydraulic fluid supply line 305 is equal to or lower than the set pressure P3c (torque control starting pressure) of the reducing valve 112g, the pressure P3 is directly introduced to the reducing torque control piston 112f. When the pressure P3 of the third hydraulic fluid supply line 305 is higher than P3c, a pressure limited to P3c is introduced to the reducing torque control piston 112f. The reducing torque control piston 112f performs the following reducing torque control as described previously. Specifically, when the pressure P3 of the third hydraulic fluid supply line 305 is equal to or lower than the set pressure P3c of the reducing valve 112g, the reducing torque control piston 112f reduces the maximum torque of the main pump 102 by the absorption torque of the main pump 202 (T3) as indicated by the torque constant curve 504 in
As described above, the reducing valve 112g outputs a pressure that simulates the absorption torque of the main pump 202 and this pressure is introduced to the reducing torque control piston 112f so as to reduce the maximum torque of the main pump 102. This arrangement enables the total torque control to be accurately performed not only when the main pump 202 operates at the maximum torque T3max as being limited by the second torque control section, but also when the main pump 202 is not subject to limitation by the second torque control section, so that the rated output torque Terate of the prime mover can be effectively used.
—Effects—
The present embodiment achieves the following effects.
1. Even in a combined operation that involves a considerable difference in load pressure between the boom cylinder 3a and the arm cylinder 3b, such as the horizontally leveling operation in which the load pressure on the boom cylinder 3a is high and the load pressure on the arm cylinder 3b is low, the boom cylinder 3a and the arm cylinder 3b are driven by the hydraulic fluids from the main pumps 202 and 102, respectively. This arrangement prevents occurrence of energy consumption that arises from wasted restricting pressure loss at the pressure compensating valve on the low pressure side, when such a problem occurs in the related-art one-pump load sensing system that includes a single pump for driving a plurality of actuators. The embodiment can thus provide a highly efficient hydraulic drive system.
2. The flow control valve 6a that controls the flow of the hydraulic fluid supplied from the main pump 202 to the boom cylinder 3a is an open center type. Thus, in a fine operation zone in which the lever operation amount of the operating unit for the boom cylinder 3a is small, the bleed-off passage is open and the load pressure on the boom cylinder 3a varies flexibly the flow rate of the hydraulic fluid supplied to the boom cylinder 3a. Thus, when reaction that is received from the bucket claw end when the bucket claw end is moved along the ground during, for example, the sweeping work, slightly changes, the flow rate of the hydraulic fluid supplied to the boom cylinder 3a changes according to the magnitude of the reaction, so that favorable operability can be obtained.
3. Increasing the lever operation amount of the boom cylinder 3a causes the bleed-off passage of the open center type flow control valve 6a on the main pump 202 side to be fully closed; while on the main pump 102 side, the increase causes the load sensing control to control the delivery flow rate of the main pump 102. Thus, in an operation involving a large operation amount of the boom control lever, such as loading following excavating by the hydraulic excavator, a characteristic less susceptible to the effect of load pressure can be obtained and powerful operating feeling can be obtained.
4. The regulator 212 of the main pump 202 does not include a load sensing control section, but includes only the second torque control section (torque control piston 212d and spring 212e). In addition, the set pressure of the reducing valve 112g (set pressure of the spring 112t) is set to be equal to the torque control starting pressure of the second torque control section (set pressure of the spring 212) P3c. Thus, the reducing valve 112g outputs a pressure that simulates the absorption torque of the main pump 202 and this pressure is introduced to the reducing torque control piston 112f. This arrangement enables the total torque control to be accurately performed not only when the main pump 202 operates at the maximum torque T3max as being limited by the second torque control section, but also when the main pump 202 is not subject to the limitation by the second torque control section, so that the rated output torque Terate of the prime mover can be effectively used.
5. The regulator 212 of the main pump 202, because including no load sensing control section, can be simply configured and allows the reducing valve 112g to output a pressure that simulates the absorption torque of the main pump 202 without the need to incorporate a complicated mechanism. Thus, configuration of the regulator 112 for performing the total torque control can be simplified, reduction in size of the entire pump including the main pumps 102 and 202 and the regulators 112 and 212 can be achieved, and increase in cost can be prevented.
—Structure—
The second embodiment differs from the first embodiment shown in
Operations of the present embodiment are basically the same as the operations of the first embodiment except for the differences relating to the main pump 202A of the fixed displacement type and the effects of 1 to 3 described above can be achieved as in the first embodiment.
The delivery pressure of the main pump 202A being introduced to a reducing torque control piston 112f causes the main pump 102 reduces the absorption torque thereof by the absorption torque of the main pump 202A. Total torque control is thus performed such that the total of the absorption torque values of the main pump 102 and the main pump 202A does not exceed a predetermined value (maximum torque T12max).
Additionally, the main pump 202A is a fixed displacement type including no regulator. Further reduction in size and cost can thus be achieved of an entire pump including the main pumps 102 and 202A and the regulator 112A.
[Others]
It should be understood that the foregoing description of the embodiments is intended as illustrative only and various changes may be made without departing from the spirit and scope of the invention.
For example, while the above embodiments have been described to include the first pump device that is the split-flow-type hydraulic pump 102 having the first and second delivery ports 102a and 102b, the first pump device may be a variable displacement hydraulic pump having a single delivery port.
The above embodiments have been described in the case in which the construction machine is a hydraulic excavator, the first specific actuator is the boom cylinder 3a, and the second specific actuator is the arm cylinder 3b. Nonetheless, the first and second specific actuators may be any cylinders other than the boom cylinder and the arm cylinder, if the second actuator is an actuator used at relatively high frequency in a combined operation with the first specific actuator.
Additionally, the present invention may be applied to another type of construction machine other than the hydraulic excavator, such as a hydraulic traveling crane, when the construction machine includes an actuator that satisfies the operating conditions of the first and second specific actuators.
Additionally, the load sensing system in the above-described embodiments is illustrative only and various changes may be made in the load sensing system. For example, the above-described embodiments each include a differential pressure reducing valve that outputs the pump delivery pressure and the maximum load pressure as an absolute pressure; and the output pressure is introduced to the pressure compensating valve to thereby set a target compensating differential pressure and is introduced to the LS control valve to thereby set the target differential pressure for the load sensing control. Nonetheless, the pump delivery pressure and the maximum load pressure may be introduced to the pressure control valve and the LS control valve through respective hydraulic lines.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-054196 | Mar 2014 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2014/081912 | 12/2/2014 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2015/141073 | 9/24/2015 | WO | A |
| Number | Name | Date | Kind |
|---|---|---|---|
| 6408622 | Tsuruga | Jun 2002 | B1 |
| 7251934 | Lech | Aug 2007 | B2 |
| 7350353 | Ioku | Apr 2008 | B2 |
| Number | Date | Country |
|---|---|---|
| 0913586 | May 1999 | EP |
| 7-317708 | Dec 1995 | JP |
| 10-037907 | Feb 1998 | JP |
| 2009-014122 | Jan 2009 | JP |
| Entry |
|---|
| International Preliminary Report on Patentability (PCT/IB/338 & PCT/IB/373) including English translation of Written Opinion (PCT/ISA/237) issued in PCT Application No. PCT/JP2014/081912 dated Sep. 29, 2016 (five pages). |
| Number | Date | Country | |
|---|---|---|---|
| 20170037601 A1 | Feb 2017 | US |
