Patent Grant
9181070
1. Field of the Invention
The present invention relates to a hydraulic driving apparatus provided in a working machine, such as a crane, to move a load, such as a suspended load.
2. Description of the Background Art
As a hydraulic driving apparatus provided in a working machine, there is known a type equipped with a hydraulic actuator, as described, for example, in JP 2000-310201 A, which will be called “Patent Document 1” below. In this type, the hydraulic actuator can be operated to move a load in the same direction as a self-weight falling direction which is a direction along which the load falls by its self-weight. Patent Document 1 discloses a lowering hydraulic circuit for operating a hydraulic motor serving as the hydraulic actuator, to move a suspended load in a lowering direction.
In the above working hydraulic driving apparatus, cavitation is likely to occur during a lowering drive mode in which the hydraulic motor is driven (operated) in a rotational direction corresponding to the lowering direction. Specifically, during the lowering drive mode, the self-weight of the suspended load increases the rotational speed of the hydraulic motor, which may cause a flow rate adsorbed by the hydraulic motor to be greater than a flow rate of hydraulic fluid supplied from a hydraulic pump to the hydraulic motor. This may lower a pressure of a meter-in fluid passage which is a fluid passage on a hydraulic fluid supply side of the hydraulic motor, namely a meter-in pressure, to generate cavitation in the meter-in fluid passage. The cavitation possibly steals a braking force from the hydraulic motor and possibly causes falling of the suspended load.
To suppress cavitation thus generated in a meter-in fluid passage, Patent Document 1 discloses an external pilot-operated counterbalance valve (hereinafter referred to simply as “counterbalance valve”) provided in a meter-out fluid passage, that is, a fluid passage on a hydraulic fluid discharge side of the hydraulic motor (counterbalance valve 11 in FIG. 1 of Patent Document 1). The counterbalance valve is applied with a meter-in pressure as a pilot pressure and applied with a set pressure P1 thereof by means of a spring or the like. The counterbalance valve has a variable valve opening degree, which is increased when the meter-in pressure becomes greater than the set pressure P1 while reduced when the meter-in pressure becomes lower than the set pressure P1. The counterbalance valve narrows down the meter-out fluid passage when the valve opening degree is reduced, thus producing a braking force in the hydraulic motor to decelerate the hydraulic motor and thereby suppress the flow rate adsorbed by the hydraulic motor. The counterbalance valve thus keeps the meter-in pressure to the set pressure P1 or below, thereby suppressing the cavitation in the meter-in fluid passage.
This unstable control system is likely to cause hunting in rotational speed of the hydraulic motor 13. For example, when a manipulation lever 16 shown in
As means for suppressing such hunting, it is conceivable to provide an orifice 786 shown in
The orifice 786, however, generates flow resistance due to the throttle of the meter-out fluid passage by the counterbalance valve 784, until the counterbalance valve 784 will have reached an adequate valve opening degree A1 as shown in
Patent Document 1 discloses a technique of providing a flow regulation valve in order to suppress the hunting. This flow regulation valve is operable to control a flow rate in the meter-in fluid passage so as to reduce the pressure difference between the meter-in fluid passage and the meter-out fluid passage. This however causes a problem that an operating speed (lowering speed) of the hydraulic motor is largely varied depending on a mass of the load. The reason is as follows.
When a hydraulic driving apparatus is operated in a direction to move a load downward, i.e., in a lowering direction, a holding pressure appropriate for a mass of the load is generally produced in a meter-out fluid passage. This holding pressure becomes higher when the load is relatively heavy, than when the load is relatively light. The flow regulation valve disclosed in the Patent Document 1 opens more largely as the holding pressure becomes higher. This increases a flow rate in the meter-in fluid passage, that is, a meter-in flow rate, and operating speed of the hydraulic motor. Hence, the lowering speed becomes higher in the case of a relatively heavy load than in the case of a relatively light load. In other words, even if a manipulation lever is not changed, the operating speed of the hydraulic motor can be varied depending on a level of weight of the load. This deteriorates operability.
JP 10-267007 A, which will be called Patent Document 2 below, discloses a regeneration circuit, for example, shown in FIG. 5 of Patent Document 2. This regeneration circuit comprises an orifice provided in a meter-out fluid passage and a regeneration fluid passage for communicating an upstream side of the orifice and a meter-in fluid passage. The regeneration circuit allows a part of hydraulic fluid flowing through the meter-out fluid passage to be returned to the meter-in fluid passage through the regeneration fluid passage, thereby increasing respective operating speeds of a hydraulic actuator and an attachment adapted to be driven by the hydraulic actuator.
If the regeneration circuit disclosed in Patent Document 2 were applied to a circuit where a hydraulic motor is used to lower a suspended load as disclosed in the Patent Document 1, a flow rate in the regeneration fluid passage (regeneration flow rate) would be increased along with an increase in weight of the suspended load. This makes the lowering speed become higher as the suspended load becomes heavier, resulting in a loss of safety and operability. Moreover, the technique disclosed in the Patent Document 2, which does not compensate for a minimum pressure of the meter-in fluid passage, has a possibility of cavitation in the meter-in fluid passage, which may cause the hydraulic motor to stall.
An object of the present invention is to provide a hydraulic driving apparatus provided in a working machine to move a load in the same direction as a direction along which the load falls by its self-weight, capable of suppressing: cavitation in a meter-in fluid passage; hunting of a driving speed; deterioration in response and fuel economy which would otherwise be caused by suppressing the hunting; and a change in speed of a load depending on a level of weight of the load. The hydraulic driving apparatus provided by the present invention comprises a hydraulic pump, a hydraulic actuator adapted to be supplied with hydraulic fluid from the hydraulic pump to move the load, and a manipulation device having a manipulation member adapted to be operated to designate an operating speed of the hydraulic actuator. The hydraulic driving apparatus further comprises: a meter-in flow control device for controlling a meter-in flow rate which is a flow rate in a meter-in fluid passage for the hydraulic actuator; a meter-out flow control device for controlling a meter-out flow rate which is a flow rate in a meter-out fluid passage for the hydraulic actuator, the meter-out flow control device including a meter-out orifice provided in the meter-out fluid passage for the hydraulic actuator and has an opening degree variable depending on an operation amount of the manipulation member, and a meter-out flow regulation valve for changing the flow rate in the meter-out fluid passage so as to keep an inlet-outlet pressure difference of the meter-out orifice at a constant set pressure difference; a back pressure valve provided downstream of the meter-out orifice and downstream of the meter-out flow regulation valve, to produce a set back pressure on an upstream side thereof; a regeneration fluid passage branched from the meter-out fluid passage at a position upstream of the back pressure valve and merged with the meter-in fluid passage; and a check valve provided in the regeneration fluid passage to allow hydraulic fluid to pass therethrough only in a flow direction from the meter-out fluid passage to the meter-in fluid passage. The meter-in flow control device is operable to control the meter-in flow rate in a region of the meter-in fluid passage upstream of a merging point with the regeneration fluid passage. The meter-out flow control device is operable to control the meter-out flow rate in a region of the meter-out fluid passage upstream of a branching point of the regeneration fluid passage so as to make the meter-out flow rate in the region be greater than the meter-in flow rate in the region.
With reference to
As shown in
The engine 11, as shown in
The hydraulic motor 13 is driven by hydraulic fluid supplied from the hydraulic pump 12 to move the suspended load 15. Specifically, the hydraulic motor 13 is coupled to a winch drum 14, and the load 15 is suspended by a cable wound around the winch drum 14. The hydraulic motor 13 is operable to rotate the winch drum 14 to thereby move the load 15 suspended by the cable upward and downward.
The “hydraulic actuator” in the present invention may be a hydraulic cylinder. Besides, the “load” is not limited to the suspended load 15. For example, the hydraulic driving apparatus of the present invention may be a type comprising a hydraulic cylinder operable to drive an attachment serving as a load, such as a boom, in a lowering direction identical to a self-weight falling direction of the attachment, and drive the attachment in a raising direction opposite to the self-weight falling direction.
The manipulation lever 16 serves as a manipulation member to be manually operated by an operator to designate a rotational direction and a rotational speed of the hydraulic motor 13. The remote-control valve 17 has a pair of output ports and outputs a pilot pressure having a value corresponding to an amount of the operation (operation amount) of the manipulation lever 16 from one of the output ports corresponding to an operation direction, that is, a direction of the operation of the manipulation lever 16. The output ports are connected to a lowering-side pilot port 20a and a raising-side pilot port 20b of the direction selector valve 20 through a lowering-side pilot line 28 and a raising-side pilot line 27, respectively, so that the pilot pressures output from the remote-control valve 17 are supplied to respective ones of the lowering-side pilot port 20a and the raising-side pilot port 20b through the lowering-side pilot line 28 and the raising-side pilot line 27, respectively.
The direction selector valve 20, which is disposed between a region including the first and second ports 13a, 13b of the hydraulic motor 13 and a region including the hydraulic pump 12 and a tank T, is operable to change the direction of the flow of the hydraulic fluid supplied from the hydraulic pump 12 to the hydraulic motor 13 and vary the flow rate thereof. Specifically, the direction selector valve 20 comprises a main spool adapted to be moved in a direction corresponding to a direction of a pilot pressure input into the direction selector valve 20, by a stroke corresponding to a value of the pilot pressure, being operable to lead the hydraulic fluid discharged from the hydraulic pump 12 toward the hydraulic motor 13 in a direction corresponding to a position of the main spool and at a flow rate corresponding to the stroke of the main spool.
Among the hydraulic lines 31 to 33 forming the meter-in fluid passage 30, the hydraulic line 31 connects the hydraulic pump 12 to a pump port provided in the direction selector valve 20; the hydraulic line 32 connects a first motor port of the direction selector valve 20 to a merging point 52 which is an interconnection point of the meter-in fluid passage 30 and the regeneration fluid passage 50; the hydraulic line 33 connects the merging point 52 to the first port 13a of the hydraulic motor 13. Besides, among the hydraulic lines 41 to 43 making up the meter-out fluid passage 40, the hydraulic line 41 connects the second port 13b of the hydraulic motor 13 to a second motor port of the direction selector valve 20; the hydraulic line 42 connects a first tank port of the direction selector valve 20 to a branching point 51 which is an interconnection point of the meter-out fluid passage 40 and the regeneration fluid passage 50; the hydraulic line 43 connects the branching point 51 to the tank T.
The direction selector valve 20 has a neutral position 21, a raising position 22 and a lowering position 23.
The neutral position 21 is a position for stopping the driving of the hydraulic motor 13. The direction selector valve 20 is held in the neutral position 21, when the manipulation lever 16 is in a neutral position, i.e., when the operation amount of the manipulation lever 16 is zero and no pilot pressure is supplied from the remote-control valve 17, to block between the hydraulic line 31 and the hydraulic line 32 while returning hydraulic fluid discharged from the hydraulic pump 12 to the tank T through the a bleed-off flow passage 26.
The raising position 22 is a position for driving the hydraulic motor 13 to move the suspended load 15 in the raising direction. The direction selector valve 20 is shifted to the raising position 22, when the manipulation lever 16 is manually operated in a direction for a raising drive mode, i.e., when a pilot pressure is supplied from the remote-control valve 17 to the raising-side pilot port 20b through the raising-side pilot line 27, to interconnect the hydraulic lines 31 and 41 and interconnect the hydraulic lines 32 and 42. The hydraulic fluid discharged from the hydraulic pump 12 is thereby supplied to the second port 13b of the hydraulic motor 13 through the hydraulic lines 31, 41 to drive the hydraulic motor 13 in the rotational direction corresponding to the raising direction, and returned from the first port 13a of the hydraulic motor 13 to the tank T through the hydraulic lines 33, 32, 42, 43.
The lowering position 23 is a position for driving the hydraulic motor 13 to move the suspended load 15 in the lowering direction. The direction selector valve 20 is shifted to the lowering position 23, when the manipulation lever 16 is manually operated in a direction for the lowering drive mode, i.e., when a pilot pressure is supplied from the remote-control valve 17 to the lowering-side pilot port 20a through the lowering-side pilot line 28, to interconnect the hydraulic lines 31 and 32 and interconnect the hydraulic lines 41 and 42. The hydraulic fluid discharged from the hydraulic pump 12 is thereby supplied to the first port 13a of the hydraulic motor 13 through the hydraulic lines 31, 33 to drive the hydraulic motor 13 in the rotational direction corresponding to the lowering direction, and returned from the second port 13b of the hydraulic motor 13 to the tank T through the hydraulic lines 41, 42, 43.
The direction selector valve 20 also has a throttle function, that is, has a valve opening degree which can vary depending on the operation amount of the manipulation lever 16. Specifically, the direction selector valve 20 is configured such that, the stroke of the main spool, i.e., a distance from the neutral position 21, becomes larger, as operation amount of the manipulation lever 16 and value of the pilot pressure corresponding to the operation amount is increased, thereby increasing a flow rate of hydraulic fluid to be supplied from the hydraulic pump 12 to the hydraulic motor 13 through the hydraulic line 32 (during the lowering drive mode) or the hydraulic line 41 (during the raising drive mode) to increase the rotational speed of the hydraulic motor 13, while reducing a flow rate of hydraulic fluid to be returned to the tank T through the bleed-off flow passage 26, that is, a bleed-off flow rate.
The meter-in fluid passage 30, through which hydraulic fluid is supplied from the hydraulic pump 12 to the hydraulic motor 13 when the direction selector valve 20 is shifted to the lowering position 23, is formed of the hydraulic line 31, an fluid passage within the direction selector valve 20 in the lowering position 23, the hydraulic line 32 and the hydraulic line 33. The meter-out fluid passage 40, through which hydraulic fluid is returned from the hydraulic motor 13 to the tank T when the direction selector valve 20 is shifted to the lowering position 23, is formed of the hydraulic line 41, an fluid passage within the direction selector valve 20 in the lowering position 23, the hydraulic line 42 and the hydraulic line 43. The following description about the hydraulic circuit in the first embodiment will be made on the assumption that the direction selector valve 20 is in the lowering position 23;
As shown in
Concerning the aforementioned throttle function, the direction selector valve 20 includes the meter-in orifice 61, the meter-out orifice 71, and further bleed-off orifice 21a. The bleed-off orifice 21a is to restrict the bleed-off flow rate, i.e., a flow rate of hydraulic fluid returned to the tank T through the bleed-off flow passage 26 bypassing the hydraulic motor 13, out of the hydraulic fluid discharged from the hydraulic pump 12.
The meter-in orifice 61 is provided in the meter-in fluid passage 30 to constitute the meter-in flow control device in cooperation with the meter-in flow regulation valve 62. The meter-in orifice 61 has a variable opening area, which becomes larger as the operation amount of the manipulation lever 16 and the value of the pilot pressure are increased. The meter-in orifice 61 may be provided outside the direction selector valve 20 independently thereof.
As shown in
The meter-out orifice 71 is provided in the meter-out fluid passage 40 to constitute the meter-out flow control device in cooperation with the meter-out flow regulation valve 72. The meter-out orifice 71 has a variable opening area, which becomes larger as the operation amount of the manipulation lever 16 and value of the pilot pressure are increased. The meter-out orifice 71 also may be provided outside the direction selector valve 20 independently thereof.
As shown in
The back pressure valve 81 is provided downstream of the meter-out orifice 71 and downstream of the meter-out flow regulation valve 72, to produce a set back pressure Pbk on an upstream side of the back pressure valve 81. The set back pressure Pbk is set to a constant pressure substantially equal to the set pressure P1 of the conventional external pilot-operated counterbalance valve 784 as shown in
The structure of the back pressure valve 81 is not limited to that of a relief valve. The back pressure valve 81 may be, for example, an orifice having an opening area Abk which is increased as the operation amount of the manipulation lever 16 is increased. The opening area Abk may be set according to the following formula 1, wherein: Cv is a flow coefficient; ΔPbk is a pressure difference between the set back pressure Pbk and a pressure within the tank T (generally, atmospheric pressure); and Qbk is a flow rate of hydraulic fluid passing through the back pressure valve 81, being equal to the meter-in flow rate Qmi because of flow balance therebetween, if ignoring leakage of the hydraulic fluid from the hydraulic motor 13 and others.
There will be described a function of the hydraulic driving apparatus 1 according to the first embodiment.
The hydraulic driving apparatus 1 has a function of preventing cavitation in the meter-in fluid passage 30, as with the conventional external pilot-operated counterbalance valve 784 (see
Firstly, the meter-out flow rate Qmo is controlled so as to be greater than the meter-in flow rate Qmi. Specifically, the valve opening degree of the meter-out flow regulation valve 72 and the valve opening degree of the meter-in flow regulation valve 62 are changed so as to satisfy the relation Qmo>Qmi. This control enables a regeneration flow rate Qr, that is, a flow rate of hydraulic fluid passing through the regeneration fluid passage 50, to be secured. More specifically, since the flow rate adsorbed by the hydraulic motor 13 and the flow rate discharged from the hydraulic motor 13 are equal to each other except leaked fluid, the hydraulic fluid flows from the meter-out fluid passage 40 into the meter-in fluid passage 30 through the regeneration fluid passage 50 in the regeneration flow rate Qr equivalent to a difference between the meter-out flow rate Qmo and the meter-in flow rate Qmi (Qmo−Qmi). In short, the meter-in flow rate and the meter-out flow rate are automatically balanced. Besides, since the pressure on the upstream side of the back pressure valve 91 is kept at the set back pressure Pbk of the back pressure valve 81 and the hydraulic fluid flows from the branching point 51 on the upstream side of the back pressure valve 81 to the meter-in fluid passage 30 through the regeneration fluid passage 50 (the regeneration flow rate Qr is secured), the meter-in pressure Pmi becomes equal to the set back pressure Pbk of the back pressure 81. This makes it possible to effectively suppress the occurrence of cavitation in the meter-in fluid passage 30.
Next will be more specifically described below the control of the meter-in flow rate Qmi and the meter-out flow rate Qmo.
The meter-in flow rate Qmi are controlled to satisfy the following formula 2, while the meter-out flow rate Qmo controlled to satisfy the following formula 3.
Qmi=Cv×Ami×√{square root over (ΔPmi)} [Formula 2]
Qmo=Cv×Amo×√{square root over (ΔPmo)} [Formula 3]
Cv is a flow coefficient. ΔPmi is an inlet-outlet pressure difference of the meter-in orifice 61 and a set pressure difference of the meter-in flow regulation valve 62. ΔPmo is an inlet-outlet pressure difference of the meter-out orifice 71 and a set pressure difference of the meter-out flow regulation valve 72. Ami is an opening area of the meter-in orifice 61. Amo is an opening area of the meter-out orifice 71. As shown in
The opening area Ami of the meter-in orifice 61 and the opening area Amo of the meter-out orifice 71 are adjusted so as to satisfy the condition for the flow rate control (Qmo>Qmi). For example, in the case where the set pressure difference ΔPmi (see the formula 2) and the set pressure difference ΔPmo (see the formula 3) are substantially equal to each other, the opening area Ami of the meter-in orifice 61 is set so as to be smaller than the opening area Amo of the meter-out orifice 71, as shown in
The meter-in flow rate Qmi can be also controlled by an adjustment of a discharge flow rate of the variable displacement hydraulic pump 12 shown in
Alternatively, the meter-in flow rate Qmi may be controlled by changing an opening area Abo of the bleed-off orifice 21a shown in
In the above hydraulic driving apparatus 1, during the lowering drive mode for moving the suspended load 15 in the same direction as the self-weight falling direction, the hydraulic fluid flows from the branching point 51 on the upstream side of the back pressure valve 81 to the merging point 52 of the meter-in fluid passage 30 through the regeneration fluid passage 50 under the condition that a pressure in a region of the meter-out fluid passage 40 upstream of the back pressure valve 81 is kept at the set back pressure Pbk or more by the back pressure valve 81, so that the lowest value of the meter-in pressure Pmi which is a pressure of the meter-in fluid passage is guaranteed to be equal to or greater than the set back pressure Pbk of the back pressure 81. The cavitation in the meter-in fluid passage 30 is thus effectively suppressed. In addition, the meter-in flow control device and the meter-out flow control device control the meter-in flow rate Qmi and the meter-out flow rate Qmo so as to make the meter-out flow rate Qmo be greater than the meter-in flow rate Qmi, which allows the flow of hydraulic fluid from the meter-out fluid passage 40 to the meter-in fluid passage 30 through the regeneration fluid passage 50 to be reliably produced. In short, the regeneration flow rate Qr is secured.
Since both of the measurement point and the control point of the meter-out flow regulation valve 72 are located on the meter-out fluid passage 40, co-location is control-theoretically established, differently from the conventional counterbalance valve in which a measurement point is located on a meter-in fluid passage while a control point is located on a meter-out fluid passage. Hence, hunting in valve opening degree of the meter-out flow regulation valve 72 and in pressure as shown in
Besides, no requirement of using such a valve as is likely to cause hunting in valve opening degree and pressure also eliminates necessity of taking anti-hunting measures, for example, gradually opening a valve (a meter-out flow regulation valve and a back pressure valve) provided in the meter-out fluid passage 40, when a pressure of the meter-in fluid passage 30 is increase, so as to allow a response of the valve to become moderate, as shown in
Specifically, according to the conventional hydraulic driving apparatus 701 shown in
On contrary, the hydraulic driving apparatus 1 shown in
Besides, since the hydraulic motor 13 in the hydraulic driving apparatus 1 is supplied with the hydraulic fluid in a flow rate corresponding to the sum of the original meter-in flow rate Qmi and the regeneration flow rate Qr, the required discharge flow rate of the hydraulic pump 12 is reduced by an amount corresponding to the regeneration flow rate Qr, as compared with the case of lack of the regeneration fluid passage 50. Hence, the power required for driving the hydraulic pump 12 is reduced, and the fuel consumption of the engine 11 is reduced (see, particularly, a region after the time T1 in the graph shown in
In addition, the hydraulic driving apparatus 1, where the speed of the hydraulic motor 13 is not changed if the lever operation amount is in the same condition, regardless of the change in the weight of the suspended load 15 shown in
Furthermore, the meter-in flow regulation valve 62 of the hydraulic driving apparatus 1, which is adapted to adjust the flow rate Qmi of the meter-in fluid passage 30 so as to keep the inlet-outlet pressure difference of the meter-in orifice 61 at the constant set pressure difference ΔPmi, enables the meter-in flow rate Qmi to be reliably controlled.
Next will be described a second embodiment of the present invention, with reference to
The difference between the second embodiment and the first embodiment is more specifically described below.
The bypass fluid passage 255 for raising is to supply the hydraulic fluid from the hydraulic pump 12 to the hydraulic motor 13, bypassing the meter-out valve 271, the meter-out flow regulation valve 72 and the back pressure valve 81, during the raising drive mode in which the direction selector valve 20 is shifted to the raising position 22. The bypass fluid passage 255 for raising is branched from the hydraulic line 241 and merged with the hydraulic line 242, at a branching point 256 and at a merging point 257 on both sides of a group of the valves 271, 72, 81, respectively. The bypass fluid passage 255 for raising is provided with a check valve 258 permitting the hydraulic fluid to flow only in a direction from the branching point 256 to the merging point 257; between the branching point 256 and the back pressure valve 81 is provided a check valve 244 permitting the hydraulic fluid to flow only in a direction from the merging point 257 to the branching point 256.
When the manipulation lever 16 is manually operated in the direction for the lowering drive mode to shift the direction selector valve 20 to the lowering position 23, the check valves 244, 258 enable the hydraulic fluid to be supplied from the hydraulic pump 12 to the first port 13a of the hydraulic motor 13 through the hydraulic lines 31, 32 and 33 and the hydraulic fluid discharged from the second port 13b of the hydraulic motor 13 is returned to the tank T through the meter-out valve 271, the meter-out flow regulation valve 72 and the back pressure valve 81.
The following description will be made on the basis of the lowering drive mode. The meter-out valve 271, which is provided separately from the direction selector valve 20 and has the same function as that of the meter-out orifice 71 (
In the hydraulic driving apparatus 201, when the operation amount of the manipulation lever 16, i.e., the lever operation amount, is zero, the direction selector valve 20 is held in the neutral position 21, and the meter-out valve 271 is held in the non-lowering position 271b. When the manipulation lever 16 is manually operated from the neutral position in the direction for the lowering drive mode, the pilot pressure is generated in the lowering-side pilot line 28 and the pilot line 228 to shift the direction selector valve 20 to the lowering position 23 and shift the meter-out valve 271 to the lowering position 271a.
In the hydraulic driving apparatus 201, locating both of the meter-out valve 271 and the meter-out flow regulation valve 72 upstream of the direction selector valve 20 allows the distance between the hydraulic motor 13 and each of the meter-out valve 271 and the meter-out flow regulation valve 72 to be less than that between the hydraulic motor 13 and the direction selector valve 20. This means that the meter-out valve 271 and the meter-out flow regulation valve 72 dominating the control of the meter-out flow rate Qmo in the above manner can be disposed near the hydraulic motor 13. This makes it possible to suppress deterioration in response to manipulation of the operating speed of the hydraulic motor 13.
The detail of this point is as follows. There is provided a hydraulic piping between the hydraulic motor 13 and the direction selector valve 20, and the length of the piping is often set great for the arrangement of some devices. Accordingly, providing the meter-out orifice 71 and the meter-out flow regulation valve 72 inside or downstream of the direction selector valve 20 as the hydraulic driving apparatus 1 shown in
Next will be described a third embodiment of the present invention with reference to
While the set back pressure Pbk of the back pressure valve 81 in the working hydraulic driving apparatus 1 shown in
The working hydraulic driving apparatus 301 has a meter-in fluid passage 330 for raising, which is to supply hydraulic fluid from the hydraulic pump 12 to the hydraulic motor 13 therethrough when the direction selector valve 20 is shifted to the raising position 22. The raising meter-in fluid passage 330 is formed of the hydraulic line 31, the fluid passage within the direction selector valve 20 in the raising position 22, and the hydraulic line 41. The direction selector valve 20 includes a meter-in orifice 365 for raising, in the raising position 22. Similarly to the lowering meter-in orifice 61, the raising meter-in orifice 365 has a variable opening area which is changed according to the lever operation amount of the manipulation lever 16.
There is connected a pilot line 364 to the back pressure valve 81. The pilot line 364 is equivalent to a back pressure valve operating section which increases an opening degree of the back pressure valve 81 under a given condition, as described in detail later. The pilot line 364 is branched from the meter-in fluid passage 30 at a position downstream of the meter-in orifice 61 within the direction selector valve 20 in the lowering position 23, and, during the lowering drive mode, leads the meter-in pressure Pmi to the back pressure valve 81 as a pilot pressure. The meter-in pressure Pmi′ during the raising drive mode is a pressure of a region of the raising meter-in fluid passage 330 downstream of the raising meter-in orifice 365 (a pressure at an inlet of the hydraulic motor 13 during the raising drive mode, a pressure of the hydraulic line 41 during the raising drive mode). The pilot line 364 is branched from the raising meter-in fluid passage 330 at a position downstream of the raising meter-in orifice 365 in the raising position 22 of the direction selector valve 20.
Next will be described an action of the hydraulic driving apparatus 301.
The increase in the meter-in pressure Pmi during the lowering drive mode reduces the set back pressure Pbk of the back pressure valve 81 to thereby increase the valve opening degree of the back pressure valve 81. During a normal lowering drive mode (the normal-load lowering drive mode), the meter-in pressure Pmi is maintained constant at the set back pressure Pbk of the back pressure valve 81 (=the pressure P1) and thus not raised, as mentioned above; however, when the hydraulic motor 13 is moved in a rotational direction corresponding to the lowering direction in a state of lack of the suspended load 15 (with empty hook), that is, when the no-load lowering is performed, there is a possibility of a rise in the meter-in pressure. In detail, during the no-load lowering drive mode, the self-weight of the suspended load 15 does not act on the hydraulic motor 13 and thus produces no holding pressure in the meter-out fluid passage 40. Besides, for driving the hydraulic motor 13, the meter-in pressure Pmi is greater than the meter-out pressure Pmo. Accordingly, the check valve 53 in the regeneration fluid passage 50 prevents hydraulic fluid from flowing through the regeneration fluid passage 50. The meter-in pressure Pmi is therefore equal to or greater than at least the maximum value (=the pressure P1) of the set back pressure Pbk of the back pressure valve 81. In other words, the meter-in pressure Pmi becomes equal to or greater than a pressure on an upstream side of the meter-out flow regulation valve 72 and a pressure on an upstream side of the meter-out orifice 71. The meter-in pressure Pmi is raised or reduced depending on a discharge pressure of the hydraulic motor 13 and an operation of the meter-in orifice 61.
In not only the case of lowering without the suspended load 15, but also the case of lowering a suspended load which is light enough to fail to produce a holding pressure in the meter-out fluid passage 40, there is a possibility of a rise in the meter-in pressure Pmi.
The rise in the meter-in pressure Pmi increases the valve opening degree of the back pressure valve 81. Specifically, the raised meter-in pressure Pmi is input into the back pressure valve 81 through the pilot line 364 as a pilot pressure, thereby pushing back the spring which determines the set back pressure Pbk of the back pressure valve 81, to reduce the set back pressure Pbk of the back pressure valve 81.
On the other hand, during the raising drive mode, i.e., when the hydraulic motor 13 is driven to move the suspended load 15 in a direction opposite to the self-weight falling direction, there is performed a control for increasing the valve opening degree of the back pressure valve 81. Specifically, corresponding to respective operations of the hydraulic pump 12 and the raising meter-in orifice 365, the pressure of the hydraulic line 41 of the raising meter-in fluid passage 330 (the meter-in pressure Pmi′ during the raising drive mode) is raised, and the thus raised meter-in pressure Pmi′ is input into the back pressure valve 81 through the pilot line 364 as a pilot pressure, thereby increasing the valve opening degree of the back pressure valve 81 similarly to the no-load lowering drive mode. The relationship between the set back pressure Pbk and the meter-in pressure Pmi′ during the raising drive mode may be, for example, the same as the relationship between the set back pressure Pbk and the meter-in pressure Pmi during the lowering drive mode (see
In the hydraulic driving apparatus 301, respective upstream and downstream pressures of the hydraulic motor 13 are kept so high, in both of the cases (a) where the pressure of the meter-in fluid passage 30 is raised during the lowering drive mode and a situation and (b) where the hydraulic motor 13 is driven to move the suspended load 15 in a direction opposite to the self-weight falling direction, that cavitation can be prevented. Furthermore, in both of the cases (a) and (b), the valve opening degree of the back pressure valve 81 is increased to thereby reduce the pressures at respective positions upstream and downstream of the hydraulic motor 13. This makes it possible to suppress the rise in the pressures at the upstream and downstream positions of the hydraulic motor 13 due to the pressure loss in the back pressure 81 and suppress deterioration in fuel economy of the engine 11 due to an increase in driving power for the hydraulic pump 12.
The above effects will be more specifically described below. During the normal-load lowering drive mode, the self-weight of the suspended load 15 rotates the hydraulic motor 13 to thus reduce the meter-in pressure Pmi, which generates the possibility of the cavitation problem; however, in the case (b), driving the hydraulic motor 13 by supplying the hydraulic fluid thereto ensures the pressures at the upstream and downstream position of the hydraulic motor to be kept high enough to prevent the above cavitation from occurring. Similarly, in the case (a) of the no-load lowering, the cavitation problem in the meter-in fluid passage 30 fails to occur, as mentioned above. In the cases (a) and (b) where the cavitation problem thus fails to occurs, keeping the valve opening degree of the back pressure valve 81 a relatively small value would unnecessarily raise a circuit pressure. Specifically, the small valve opening degree raises respective pressures of the meter-in fluid passage 30 and the meter-out fluid passage 40 during the lowering drive mode, while raising respective pressures of the hydraulic lines 31, 41, 33, 32, 42, 43 during the raising drive mode. These result in an increased driving power for the hydraulic pump 12 and deteriorated fuel economy of the engine 11. The hydraulic driving apparatus 301, however, allows the valve opening degree of the back pressure valve 81 to be increased in a situation where the cavitation problem never occurs, thereby making it possible to suppress deterioration in fuel economy.
Next will be described a fourth embodiment of the present invention, with reference to
The hydraulic driving apparatus 401 shown in
In the hydraulic driving apparatus 401, when the rotational speed of the engine 11 as a driving power source for the hydraulic pump 12 or the rotational speed of the hydraulic pump 12 is reduced, the controller 491 operates the solenoid-operated pressure reducing valve 493 so as to reduce the valve opening degree of the meter-out orifice 71 (proportional to the opening area Amo in the formula 3), thereby reducing the meter-out flow rate Qmo (see the formula 3) and the rotational speed of the hydraulic motor 13. Specifically, the controller 491 inputs an electric control signal so as to make an outlet pressure of the solenoid-operated pressure reducing valve 493 (a pressure on the side of a direction selector valve 20) be lower than the pilot pressure for lowering detected by the pilot pressure sensor 494. The pilot pressure to be input into the direction selector valve 20 is thereby reduced, which makes the direction selector valve 20 be closer to the neutral position 21, reducing the valve opening degree of the meter-out orifice 71 and further the valve opening degree of the meter-in orifice 61 each included in the direction selector valve 20. In other words, the hydraulic driving apparatus 401 operates as if the manipulation lever 16 is manually operated in a direction toward the neutral position, i.e., the lever operation amount is reduced to reduce the rotational speed of the hydraulic motor 13. Conversely, when the rotational speed of the engine 11 is increased, the valve opening degree of the meter-out orifice 71 is increased to thereby increase the rotational speed of the hydraulic motor 13.
In the hydraulic driving apparatus 401, as mentioned above, the controller 491 reduces the valve opening degree of the meter-out orifice 71 (proportional to the opening area Amo in the formula 3), when the rotational speed of the engine 11 as a driving power source for the hydraulic pump 12 or the rotational speed of the hydraulic pump 12 is reduced, thereby reducing the flow rate Qmo in the meter-out fluid passage 40 (see the formula 3) and the rotational speed of the hydraulic motor 13. This control reduces the rotational speed of the engine 11 or the hydraulic pump 12, thus facilitating the operation of driving the hydraulic motor 13 at low speeds.
For example, for finely manipulating the suspended load 15, the conventional hydraulic driving apparatus permits an operation for reducing the rotation speed of the engine 11 to reduce a lowering speed of the hydraulic motor 13 to be performed, while the hydraulic driving apparatus 1 shown in
With reference to
The solenoid-operated pressure reducing valve 593 is designed to control the set pressure difference ΔPmo of the meter-out flow regulation valve 72. Specifically, the solenoid-operated pressure reducing valve 593 is operable to reduce an fluid pressure output from the pilot fluid pressure source 595 and thereafter apply the reduced fluid pressure, for example, to a spring chamber of the meter-out flow regulation valve 72. In other words, input into the meter-out flow regulation valve 72 as a pilot pressure is an outlet pressure of the solenoid-operated pressure reducing valve 593. The controller 491 inputs an electric control signal into the solenoid-operated pressure reducing valve 593 to change the outlet pressure thereof, thereby controlling the set pressure difference ΔPmo of the meter-out flow regulation valve 72.
In the hydraulic driving apparatus 501, when the rotational speed of the engine 11 as a driving power source for the hydraulic pump 12 or the rotational speed of the hydraulic pump 12 is reduced, the controller 491 performs the control for reducing the set pressure difference ΔPmo (see the formula 3) of the meter-out flow regulation valve 72, thereby reducing the flow rate Qmo (see the formula 3) in the meter-out fluid passage 40 and the rotational speed of the hydraulic motor 13. This reduces the rotational speed of the engine 11 or the hydraulic pump 12, thus facilitating the operation of driving the hydraulic motor 13 at low speeds.
Next will be described an explanation about the safety-ensuring pressure control valve 682 shown in
The safety-ensuring pressure control valve 682 is adapted to be closed in emergency situations, for example, in the event of breakage of the meter-in fluid passage 30, to thereby decelerate the hydraulic motor 13. The safety-ensuring pressure control valve 682, provided in the meter-out fluid passage 40 at a position upstream of the branching point 51, is configured to be closed when the meter-in pressure Pmi is lower than a set pressure P3 of the safety-ensuring pressure control valve 682. The meter-in pressure Pmi is input into the safety-ensuring pressure control valve 682, through a pilot line 683, as a pilot pressure. Hence, with a focus on only the safety-ensuring pressure control valve 682 itself, the safety-ensuring pressure control valve 682 has the same structure as that of the conventional external pilot-operated counterbalance valve 784 (see
The set pressure P3 (cracking set pressure) of the safety-ensuring pressure control valve 682 is slightly lower than the set back pressure Pbk (=the pressure P1, etc.) of the back pressure 81. In the case where the set back pressure Pbk is variable (see
To the meter-out fluid passage 40 is connected a bypass fluid passage 655 for raising in parallel with the safety-ensuring pressure control valve 682. The bypass fluid passage 655 for raising is one for supplying the hydraulic fluid from the hydraulic pump 12 to the hydraulic motor 13, during the raising drive mode, bypassing the safety-ensuring pressure control valve 682. The bypass fluid passage 655 for raising is provided with a check valve 658 adapted to permit hydraulic fluid to flow only in a direction from the hydraulic pump 12 to the second port 13b of the hydraulic motor 13.
The safety-ensuring pressure control valve 682 is normally opened. Specifically, upon manually operating the manipulation lever 16 in the direction for the lowering drive mode, the meter-in pressure Pmi immediately reaches the set back pressure Pbk of the back pressure valve 81, which keeps the safety-ensuring pressure control valve 682 fully opened, because the set back pressure Pbk is greater than the set pressure P3. In other words, during a normal lowering drive mode, the safety-ensuring pressure control valve 682 does not perform an opening-closing action, differently from the conventional external pilot-operated counterbalance valve 784 as shown in
On the other hand, in an emergency situation where the meter-in Pmi becomes equal to or lower than the set back pressure Pbk of the back pressure valve 81, for example, due to breakage of the meter-in fluid passage 30, the safety-ensuring pressure control valve 682 is closed or its valve opening degree is significantly reduced, at a time when the meter-in Pmi becomes equal to or lower than the set pressure P3 of the safety-ensuring pressure control valve 682, which reduces the meter-out flow rate Qmo to zero or a value close to zero. This enables the hydraulic motor 13 to be effectively decelerated and make an emergency stop.
In summary, the safety-ensuring pressure control valve 682 is moved in a valve closing direction to significantly reduce the flow rate of the meter-out fluid passage 40 in an emergency or failure situation, for example, in the event of breakage of the meter-in fluid passage 30, at a time when the pressure of the meter-in fluid passage 30 (meter-in pressure Pmi) becomes lower than the set pressure P3 of the safety-ensuring pressure control valve 682, thereby effectively decelerating or stopping the hydraulic motor 13. This enhances safety in the emergency or failure situation. Besides, the safety-ensuring pressure control valve 682, which is provided upstream of the branching point 51, can prevent hydraulic fluid from flowing through the regeneration fluid passage 50 when closed. Thus, the hydraulic motor 13 is reliably decelerated.
The present invention permits the arrangement of the components and the connection of the hydraulic lines in the circuit shown in
For example, the pilot lines 64, 73 shown in
While, in the above embodiments, the hydraulic fluid supplied from the hydraulic pump 12 to the hydraulic motor 13 is returned directly to the tank T, the hydraulic fluid discharged from the hydraulic motor 13 may be further supplied to another hydraulic actuator (not shown) or the like. For example, there may be configured a circuit in which hydraulic fluid supplied from the hydraulic pump 12 to a main raising/lowering motor (hydraulic motor 13) is further supplied to an auxiliary raising/lowering motor (not shown) and then returned to the tank T, namely, a series circuit.
This application is based on Japanese Patent applications No. 2011-108293 and No. 2011-209678 filed in Japan Patent Office on May 13, 2011 and Sep. 26, 2011, the contents of which are hereby incorporated by reference.
Although the present invention has been fully described by way of example with reference to the accompanying drawings, it is to be understood that various changes and modifications will be apparent to those skilled in the art. Therefore, unless otherwise such changes and modifications depart from the scope of the present invention hereinafter defined, they should be construed as being included therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-108293 | May 2011 | JP | national |
| 2011-209678 | Sep 2011 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3895564 | Pinson | Jul 1975 | A |
| 5884984 | Arai et al. | Mar 1999 | A |
| 6378303 | Higuchi et al. | Apr 2002 | B1 |
| 6393838 | Moriya et al. | May 2002 | B1 |
| 20050011190 | Bitter | Jan 2005 | A1 |
| 20060048508 | Nakamura et al. | Mar 2006 | A1 |
| 20070151238 | Kraft | Jul 2007 | A1 |
| 20090308068 | Yoshino | Dec 2009 | A1 |
| Number | Date | Country |
|---|---|---|
| 1174596 | Feb 1998 | CN |
| 1697933 | Nov 2005 | CN |
| 1914384 | Feb 2007 | CN |
| 27 19 585 | Apr 1982 | DE |
| 199 13 277 | Nov 2007 | DE |
| 10-267007 | Oct 1998 | JP |
| 2000-310201 | Nov 2000 | JP |
| WO 2008147303 | Dec 2008 | WO |
| Entry |
|---|
| U.S. Appl. No. 13/467,453, filed May 9, 2012, Sugano, et al. |
| Office Action issued Mar. 18, 2013, in German Patent Application No. 10 2012 207 880.0 with English translation. |
| U.S. Appl. No. 13/713,680, filed Dec. 13, 2012, Kondo, et al. |
| Number | Date | Country | |
|---|---|---|---|
| 20120285159 A1 | Nov 2012 | US |
