Control device for multiple hydraulic apparatus

Abstract: A control device for multiple hydraulic actuators which is capable of rapidly increasing a discharge pressure of a variable pump (1) to prevent a decrease in discharge quantity of the variable pump even when one of the actuators is required to be fed with hydraulic fluid in a micro-amount under a low pressure. An operating valve (42) of a spin motor (39) is connected on a downstream side thereof through a converging passage (44) to a feed side of a boom cylinder (37) and the converging passage is provided with a change-over valve (67) which is changed over to an open position when an operating valve (40) for operating the above-described boom cylinder is changed over.

Description: This invention relates to a control device for multiple hydraulic actuators, and more particularly to a control device which is adapted to control multiple hydraulic actuators by means of one variable pump, thereby to be suitably used for an industrial vehicle. It is an object of the present invention to provide a control device for multiple hydraulic actuators which is capable of permitting a discharge pressure of a variable pump to be rapidly increased effectively to prevent the amount of fluid discharged from the variable pump from being decreased even when a specific one of the actuators requires that fluid is fed thereto at a micro flow rate under a low pressure. In accordance with the present invention, there is provided a control device for multiple hydraulic actuators which comprises a plurality of actuators provided with operating valves, respectively, a single variable pump for feeding hydraulic fluid to the actuators, a variable orifice which is connected to a feed passage and each of the actuators communicating with the feed passage and of which a degree of opening is controlled depending on the amount of changing-over of each of the operating valves, a pressure compensating valve arranged on a downstream side of each of the variable orifices to keep a pressure difference between a load pressure and a pressure on the downstream side of the variable orifice constant, and a control mechanism for causing the load pressure and a discharge pressure of the variable pump to act as a pilot pressure and the discharge pressure of the variable pump to be kept increased by a predetermined level as compared with the load pressure. The control device of the present invention generally constructed as described above is characterised in that the operating valve of one of the actuators is connected on a downstream side thereof to a feed side of at least one of the other actuators through a converging passage and the converging passage is provided with a change-over valve which is changed over to an open position when the operating valve of at least one of the other actuators is changed over. In the control device of the present invention constructed as described above, when a load pressure of the specific actuator is increased, the pilot change-over valve is changed over to permit a part of hydraulic fluid fed to an operation system of the specific actuator to be fed to the other actuators, resulting in an excessive increase in circuit pressure of the operation system being effectively prevented. The present invention is now described by way of example with reference to the accompanying drawings, in which like reference characters designate like or corresponding parts throughout, wherein:- FIGURE 1 is a circuit diagram showing a first embodiment of a control device for multiple hydraulic actuators according to the present invention; FIGURE 2 is a circuit diagram showing a second embodiment of a control device for multiple hydraulic actuators according to the present invention; and FIGURE 3 is a circuit diagram showing a conventional or prior art control device for multiple hydraulic actuators. A conventional control device will first be described with reference to Figure 3, which is a circuit diagram showing a power shovel which has been conventionally known in the art. A variable pump 1 is connected on a discharge side thereof to a high pressure flow passage 2. The high pressure passage 2 is connected to an input port 5 of a first operating valve 40 connected to a boom cylinder 37, an input port 5 of a second operating valve 41 connected to a bucket cylinder 38, and an input port 5 of a third operating valve 42 connected to a spin motor 39. When the first, second and third operating valves 40, 41 and 42 are each at a neutral position shown in Figure 3, the input ports 5 are kept closed. When the operating valves 40, 41 and 42 are shifted or changed over to either lateral position, variable orifices 6 are rendered open. The degree of opening of the variable orifices 6 is determined depending on the amount of changing-over of the operating valves 40, 41 and 42, respectively. On a downstream side of the variable orifices 6 relay ports 61 are provided respectively. The relay ports 61 are arranged so as to communicate with pressure compensating valves 8, respectively. The pressure compensating valves 8 are arranged so as to communicate on a downstream side thereof with feed ports 9 of the first, second and third operating valves 40, 41 and 42, respectively. The feed ports 9 are adapted to be kept closed when the operating valves 40, 41 and 42 are each at the neutral position and communicate with either actuator port 10 or 11, when the operating valves 40, 41 and 42 are changed over the their respective lateral positions. At this time, the remaining actuator ports which do not communicate with the feed ports are kept communicating with tank passages 62, respectively. Also, the first to third operating valves 40, 41 and 42 are formed with load detecting ports 13, respectively. the load detecting ports 13 are adapted to communicate with the tank passages 62, respectively, when the first to third operating valves 40, 41 and 42 are each at the neutral position. When the first to third operating valves 40, 41 and 42 are each changed over to either lateral position, the load detecting ports 13 are caused to communicate with the actuator ports positioned on a high pressure side. The above-described pressure compensating valves 8 are adapted to introduce a pressure on an upstream side of the pressure compensating valves 8 to one of the pilot chambers 8a of the respective valve 8 and a pressure on a side of the load detecting ports 13 to the other pilot chamber 8b of the respective valve 8. Such introduction of the pressure is selected by a plurality of shuttle valves 14 so that a maximum load pressure in each of circuit systems is introduced into each of the other pilot chambers 8b. Thus, the pressure compensating valves 8 carry out controlling in a manner to permit a pressure on the downstream side of the variable orifices 6 to be kept increased by a predetermined level as compared with the maximum load pressure. The maximum load pressure selected by the shuttle valves 14 is introduced to one pilot chamber 63a of a control valve 63 for controlling the variable pump 1. The other pilot chamber 63b of the control valve 63 is fed with a pressure in the high pressure flow passage 2 or a discharge pressure of the variable pump 1. Thus, the control valve 63 is caused to operate depending on a relative difference between the discharge pressure of the variable pump 1 and the maximum load pressure. Such operation of the control valve 63 causes a control cylinder 64 to operate so that the discharge pressure of the variable pump 1 may be kept constantly increased by a predetermined level as compared with the maximum load pressure. In Figure 3, reference numeral 65 designates a main relief valve, which functions to set a maximum pressure of the circuit system of each of the boom cylinder 37, bucket cylinder 38 and spin motor 39. Co-operation between the amount of discharge of the variable pump 1 and the amount of control of the pressure compensating valves 8 permits fluid to be fed to the actuators in an amount proportional to the amount of changing-over of the first to third operating valves 40, 41 and 42. The conventional control system constructed as described above is of the load-sensing type, wherein the variable pump 1 discharges a pressure slightly higher than the maximum load pressure and the pressure compensating valves 8 of the circuit system control the variable orifices 6 of the first to third operating valves 40, 41 and 42 depending on the maximum load pressure. This causes a pressure difference between both sides of each of the variable orifices 6 to be kept constant, thereby to permit fluid to be fed to the actuators in an amount proportional to the amount of changing-over of the operating valves. Such circuit construction results in the maximum discharge pressure of the variable pump 1 being controlled to a set pressure of the main relief valve 65. Thus, in the conventional control device constructed as described above, the maximum load pressure established in any of the multiple hydraulic actuators causes the discharge pressure of the variable pump 1 to be controlled, thereby to increase energy loss in the following cases. For example, when the conventional control circuit is used for a power shovel and an inertia body is used as a load as in spin motion, a load pressure is rapidly increased for accelerating the inertia body at a moment of changing-over of the operating valves, resulting in a pressure in the circuit being increased to a set pressure of the main relief valve 65. The circuit pressure thus increased, as described above, constitutes a control signal for each of the first to third operating valves 40, 41 and 42 and variable pump 1. Therefore, if a large amount of hydraulic fluid is flowed under a low pressure in a circuit system other than a spin circuit system, the variable pump 1 is obliged to discharge hydraulic fluid at an increased flow rate under a high pressure. Thus, it is required to feed hydraulic fluid at a large flow rate under a high pressure to the circuit system which requires that hydraulic fluid is fed thereto at a large flow rate under a high pressure for the sake of the spin circuit system which requires to feed hydraulic fluid at a micro flow rate and under a high pressure, so that energy loss is extensively increased. In particular, when the discharge pressure of the variable pump 1 is increased during controlling which is carried out so as to keep an output of the variable pump 1 constant, a discharge capability of the variable pump is decreased along a pump output control curve. This causes restriction of a flow rate of hydraulic fluid fed to the circuit system which requires that hydraulic fluid is fed at a large flow rate under a low pressure. For example, when a power shovel is pivotally moved for the purpose of charging a truck with a material in the power shovel, a swinging-up speed of a boom is caused to be decreased during pivotal movement of the power shovel. Unfortunately, this leads to striking of a bucket of the shovel against the truck before the bucket is lifted to a desired height. The present invention has been made in view of the foregoing disadvantage of the prior art. Referring now to Figure 1, a first embodiment of a control device for multiple hydraulic actuators according to the present invention is illustrated. In the illustrated embodiment, the relay port 61 of the third operating valve 42 and the pressure compensating valve 8 communicating with the relay port 61 are connected through a converging passage 44 to a side of an inlet port 68 of a change-over valve 67. An outlet port 69 of the change-over valve 67 is connected through a load check valve 72 to a side of a bottom of the boom cylinder 37. When the change-over valve 67 thus arranged is at a normal position shown in Figure 1, it interrupts communication between the inlet port 68 and the outlet port 69. Also, the change-over valve 67 is changed over to its upper open position (as shown in Figure 1) when a pilot pressure acts on a pilot chamber 70 of the change-over valve 67, thereby to cause both ports 68 and 69 to communicate with an orifice 71. Thus, when the boom cylinder 37 is extended, the change-over valve 67 is changed over to the open position. The remaining part of the illustrated embodiment is constructed in substantially the same manner as the prior art described above. When the first operating valve 40 is changed over to its left-side position as viewed in Figure 1 in order to extend the boom cylinder 37, a pilot pressure acting on the first operating valve 40 then acts on the pilot chamber 70 of the change-over valve 67, leading to changing-over of the change-over valve 67 to the open position. This results in a part of hydraulic fluid fed to a circuit system of a spin motor 39 being fed to the bottom side of the boom cylinder 37 through the change-over valve 67. Thus, a part of hydraulic fluid fed to the circuit system of the spin motor is fed to the boom cylinder 37. This effectively prevents a rapid increase in load pressure of the circuit system of the spin motor 39, even when the spin motor 39 is rapidly accelerated or a load pressure on the side of the spin motor 39 is increased. Thus, the illustrated embodiment effectively eliminates a problem that an excessive increase in pressure of the spin motor 39 causes the amount of hydraulic fluid to the boom cylinder 37 to be insufficient. Referring now to Figure 2, a second embodiment of a control device for multiple hydraulic actuators according to the present invention is illustrated, which is so constructed that a downstream side of a pressure compensating valve 8 and a feed port 9 of a third operating valve 42 are connected to an inlet port 68 of a change-over valve 67 through a converging passage 44. The remaining part of the second embodiment is constructed in substantially the same manner as the first embodiment described above. The control device for the multiple hydraulic actuators according to the present invention permits, when a load pressure of one of the actuators is increased, a part of hydraulic fluid fed to the one actuator to be fed to the other actuators. This effectively prevents the one actuator which is required to be fed with hydraulic fluid in a micro-amount under a high pressure from decreasing a discharge quantity of the variable pump, thereby to minimize energy loss. While preferred embodiments of the invention have been described with a certain degree of particularity with reference to the drawings, obvious modifications and variations are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practised otherwise than as specifically described.

Claims: A control device for multiple hydraulic actuators comprising a plurality of actuators provided with operating valves (40,41,42) respectively, a single variable pump (1) for feeding hydraulic fluid to the actuators, each of which has a variable orifice (6) which is connected to a feed passage (9) and each of the actuators communicating with the feed passage (9) and the degree of opening of the variable orifice (6) being controlled dependent on the amount of changing-over of each of the operating valves (40,41,42), a pressure compensating valve (8) arranged on a downstream side of each of the variable orifices (6) to keep a pressure difference between a load pressure and a pressure on the downstream side of the variable orifice (6) constant, and a control mechanism for causing the load pressure and a discharge pressure of the variable pump (1) to act as a pilot pressure and the discharge pressure of the variable pump (1) to be kept increased by a predetermined level as compared with the load pressure, characterised in that the operating valve (42) of one of the actuators is connected on a downstream side thereof to a feed side of at least one of the other actuators through a converging passage (44), and the converging passage (44) is provided with a change-over valve (67) which is changed over to an open position when the operating valve (40,41) of at least one of the other actuators is changed over. A control device for multiple hydraulic actuators as defined in claim 1, characterised in that the converging passage (44) is connected at one end thereof between the operating valve (42) for controlling the one actuator and the pressure compensating valve (8) connected thereto. A control device for multiple hydraulic actuators as defined in claim 1, characterised in that the converging passage (44) is connected at one end thereof to a downstream side of the pressure compensating valve (8) connected to the operating valve (42) for controlling the one actuator.

Inventors: HASEGAWA YOSHIMI, KOIWAI HIDESHI, NAITO HISATO, NISHIUMI KENICHI, YONEKUBO YOSHITAKE, HASEGAWA, YOSHIMI, KOIWAI, HIDESHI, NAITO, HISATO, NISHIUMI, KENICHI, YONEKUBO, YOSHITAKE
Applicants: KAYABA INDUSTRY CO LTD, KAYABA INDUSTRY CO., LTD.
Application year: 1992
Main classification: F15B11
IPC codes: F15B11, E02F9