SERVICE VALVE CIRCUIT IN A HYDRAULIC EXCAVATOR

Abstract: The service valve circuit has a predetermined actuator operation valve and is connected for operating a special attachment. A confluence valve (17) which effects electromagnetic proportional flow-rate control is provided in a confluence circuit (16) that makes communication between the inflow circuits (3F,3R) of two variable pumps (2F,2R). There are further provided an electric switch (21) which turns on or off the confluence valve depending upon a required flow rate, and a volume (22) which adjusts the flow rate after passing the confluence valve over a range of a maximum of 1 to 2 pumps depending upon the required flow rate. The necessity of confluence for the flow rate required by the special attachment (e) or the confluent flow rate is set in advance to eliminate excess or lack of confluent flow rate. Therefore, there is no need of adjusting the flow rate depending on the number of revolutions of the engine.

Description: BACKGROUND OF THE INVENTION Field of the Invention: The present invention relates to a service valve circuit of a hydraulic excavator and, in particular, to a service valve circuit of a hydraulic excavator which has been connected beforehand for use in controlling a special attachment in addition to a prescribed actuator control valve. Such a service valve circuit is known for example from EP-A-104 613. Description of a Related Art : As shown in Fig. 3, a hydraulic excavator is generally equipped with a pivoting motor (a) in the upper chassis which is actuated by one or more units of variable capacity type hydraulic pumps (hereinafter referred to as a variable pump) driven by means of an engine, a boom cylinder (b), an arm cylinder (c) and a bucket cylinder (d) for the control of a work machine control, a hydraulic breaker (e) as a special attachment in place of the bucket, and a traveling motor (f) in the under traveling car. Most of the basic circuits of such a hydraulic excavator are as shown in Fig. 4. The following apparatuses are connected to two units of the variable pumps 2F and 2R driven by an engine 1 according to power distribution. That is, a left traveling control valve 4, a boom control valve 5, a bucket control valve 6, and a service valve 8F for controlling the hydraulic breaker (e) employed as a special attachment are connected to the inflow circuit 3F of the one variable pump 2F. To the inflow circuit 3R of the other variable pump 2R are connected a right traveling control valve 9, an arm control valve 10, a pivoting control valve 11, and a service valve 8R for controlling a special attachment. There often arises a case in which a required quantity of flow must be backed up from the other variable pump 2R in an actuator connected to the inflow circuit 3F of the variable pump 2F, for example, the boom cylinder b. As a confluence circuit in such a case, a control valve for confluence is required and this control valve is needed not only for the boom cylinder b but for each actuator. In the case of the service valves 8F and 8R, particularly, a great variety of special attachments are installed. Therefore, its required quantity of flow differs in each case, and it must be so arranged that the present invention can be used for from a small flow rate to a large flow rate. Hence, the service valves 8F and 8R should be connected to the inflow circuit 3F and 3R of both the variable pumps 2F and 2R. For example, where the hydraulic breaker (e) is installed in the service valve 8F of the inflow circuit 3F and a required quantity of flow must be backed up from the other variable pump 2R, a control valve 12 for confluence must be disposed beforehand as its confluence circuit. In such service valve circuits, the service valves 8F and 8R, whose frequency of use is relatively low, must be connected to the inflow circuits 3F and 3R of both variable pumps. In addition, the service valve circuit is uneconomical and complex owing to the fact that the control valve 12 for confluence must be disposed beforehand according to a required quantity of flow. The control valve 12 for confluence performs only on-off control with an opening and closing valve and control of the confluent flow rate cannot be exercised. Therefore, the flow rate is adjusted using the number of rotations of an engine. This method of control causes inconveniences such that when it is switched from a special attachment control to a pivoting or traveling control, the action is slowed down. The present invention has been devised in light of the above-mentioned circumstances. Accordingly, it is an object of the present invention to provide a service valve circuit of a hydraulic excavator, in which an excessive quantity of confluence is not needed, by setting in advance the requirement of confluence with respect to a required quantity of flow for a special attachment and the quantity of confluence, and which will not be slowed down even if switched from a special attachment control to a pivoting or traveling control without adjusting the quantity of flow using the number of rotations of an engine. According to the present invention, there is provided a service valve circuit of a hydraulic excavator in which a confluence valve for performing electromagnetic proportional flow rate control is disposed in a confluence circuit in communication with the section between two units of variable pumps, an electrical switch for switching the confluence valve on or off according to a required quantity of flow, and a volume for adjusting flow rate after passing through a confluence valve in a range for a maximum of one to two pumps. When it is determined that confluence is needed from the required quantity of flow for an installed special attachment, the electrical switch is turned on and the maximum quantity of flow after passing through the confluence valve is set using the volume. Then a service valve control lever is moved from the normal state "N" to an operating state. The confluence valve is not open until the discharge flow rate of the variable pump at the side on which the service valve is connected becomes full. When the discharge flow rate becomes full because the control lever is moved further, the bleed off valve at the confluence side is closed and the confluence valve opens so that the required flow quantity flows together. With the above-mentioned construction, even if maximum quantities of flow of various kinds of special attachments differ, excessive confluence will not be made. Therefore, the quantity of flow need not to be adjusted using the number of rotations of an engine and even if switched from a special attachment control to a pivoting or traveling control, the action will not be slowed down. These and other objects, features and advantages of the present invention will become clear when reference is made to the following description of the preferred embodiments of the present invention, together with reference to the accompanying drawings. Fig. 1 is a service valve circuit diagram showing a first embodiment of the present invention; Fig. 2 is a service valve circuit diagram showing a second embodiment of the present invention; Fig. 3 is a schematic side view in which a hydraulic breaker is installed in place of the bucket of a hydraulic excavator; and Fig. 4 shows one example of a conventional service valve circuit diagram. Fig. 1 is a service valve circuit diagram showing one embodiment of the present invention. Two units of variable pumps 2F and 2R are driven by a common engine 1. The control of discharge of these pumps is performed by means of regulators 7F and 7R. A control valve group 13 consisting of a left traveling control valve 4, a boom control valve 5, and a bucket control valve 6 is connected to the inflow circuit 3F of one variable pump 2F. A control valve group 14 consisting of a right traveling control valve 9, an arm control valve 10, and a pivoting control valve 11 is connected to the inflow circuit 3R of the other variable pump 2R. A service valve 15 for controlling a special attachment is connected to the inflow circuit 3F of one variable pump 2F. As this special attachment, a hydraulic. breaker e employed as a rock crushing work machine is installed in this embodiment. To ensure a required flow rate for the hydraulic breaker e, a confluence circuit 16 for backing up a discharge flow rate from the other variable pump 2R is disposed between the inflow circuits 3F and 3R of both the variable pumps, and a confluence valve 17 consisting of a piloting valve 19 in communication with the section between a poppet valve 18 and the upper stream, and lower stream of this poppet valve 18 is disposed in the confluence circuit 16. The confluence valve 17 is adapted to make the poppet valve 18 open at a valve opening corresponding to the operation of the pilot valve 19 by an electrical signal from a controller 24 to be described later. Bleed off valves 20F and 20R for regulating operating speed are disposed in the section between the confluence valve 17 and both control valves 13 and 14. Next, the control of the service valve 15 in a circuit constructed as shown above will be explained. The control is completely electronic. First, whether or not confluence should be made is checked from a required flow rate of the hydraulic breaker e. When it is sufficient merely from the flow rate from the variable pump 2F at the side on which the service valve 15 is connected, namely, when confluence is not needed, a confluence switching electrical switch 21 is left unchanged in the state of "off". In contrast to this, when confluence is needed, the confluence switching electrical switch 21 is switched to "on" and the confluence flow rate is set by using a volume 22 for regulating confluence flow rate. Next, when a service valve control lever 23 is moved from the normal state "N" to a required direction, the port of the service valve 15 is switched and pressure oil is supplied to the hydraulic breaker e, causing this breaker to operate. This pressure oil is first supplied from the variable pump 2F at the service valve side, and the confluence valve 17 is left closed until the discharge flow rate becomes full. When the control lever 23 is further moved and the discharge flow rate becomes full, the confluence valve 17 gradually opens. As the discharge flow rate from the variable pump 2R at the confluence side increases, a bleed off valve 20R is closed and the discharge flow rate joins together to the inflow circuit 3F at the service valve side. In this way, since the valve opening of the confluence valve 17 is proportional to the control amount of the service valve control lever 23, the confluence flow rate can be controlled freely. Therefore, the striking capability of the hydraulic breaker e can be used properly depending upon a hard rock or a soft rock. A second service valve may be connected to the service valve 15 so that another special attachment may be used too. In that case, it is easy to install an additional second service valve control lever. The control of the service valve confluence flow rate in this embodiment is performed under electronic control, as shown in the figure. An electrical signal circuit is formed in such a way that when input signals for the confluence switching electrical switch 21, the service valve control lever 23, and the volume 22 are input to an input interface 25 in the controller 24, these signals pass through an output interface 28 for outputting values obtained from a calculation and control via a control circuit 26 for performing a required calculation and control and a storage circuit 27 for storing a processing procedure, constants and so forth on the basis of the signals, and output signals are output to the confluence valve 17, the service valve 15, the regulators 7F and 7R of both the variable pumps, and the bleed off valves 20F and 20R, respectively. Fig. 2 is a service valve circuit diagram showing a second embodiment of the present invention. The same reference numerals are given to the same construction as that in Fig. 1 and the explanation thereof is omitted. In the second embodiment, electromagnetic proportional flow rate control is performed by using a meter-in valve and a meter-out valve as a confluence valve 217, and also a meter-in valve and a meter-out valve as a service valve 215. First, the confluence valve 217 will be described. A meter-in valve 29 and a meter-out valve 30 are disposed in the confluence circuit 16 in communication with the section between the inflow circuits 3F and 3R of both the variable pumps. An electrical signal circuit is formed in such a way that these valves are electronically controlled by an output signal from the controller 24 and at the same time this signal is output to a bleed off valve 220 disposed in the drain circuit 31 at the confluence side. Meter-in valves 32 and 33 and meter-out valves 34 and 35 are disposed as the service valve 215 in the inflow circuit 3F of the variable pump at the service valve side. An electrical signal circuit is formed in such a way that each of these valves is electronically controlled by an output signal from the controller 24. The service valve 215 in the above-mentioned circuit is controlled as follows. When confluence should be made from a required flow rate of the hydraulic breaker e, the confluence switching electrical switch 21 is switched to "on"; a confluence flow rate is set using the volume 22; and the service valve control lever 23 is turned from the normal state "N" to a required direction. For example, as shown in the figure, where pressure oil is supplied from an oil path 36 of the hydraulic breaker e and is drained from an oil path 37, when the control lever 23 is turned in the F direction shown in Fig. 2, a control signal is sent to the meter-in valve 29 and the meter-out valve 30 of the confluence valve 217 from the controller 24 via an electrical signal circuit 38 and both valves open gradually. At the same time, the control signal is also sent to the bleed off valve 220 via the electrical signal circuit 31 and this valve is closed. As a result, a flow rate determined from a valve opening proportional to the control amount of the service valve control lever 23 flows together to the inflow circuit 3F of the variable pump at the service valve side. Also, a control signal in response to the control amount of the service valve control lever 23 is also sent to the meter-in valves 32 and 33, and the meter-out valves 34 and 35 of the service valve 215 via the electrical signal circuits 39 and 40, respectively and each valve opens. As a result, a flow rate determined from the valve opening proportional to the control amount of the service valve control lever 23 is supplied from the oil path 36 of the hydraulic breaker e and is drained from the oil path 37. When this control lever is completely turned, a required flow rate joins together and the hydraulic breaker e operates fully by the required flow rate. The service valve circuit of the present invention is suitable for use in a service valve circuit of a hydraulic excavator which is connected beforehand for use in controlling a special attachment such as a hydraulic breaker or the like in addition to a prescribed actuator control valve.

Claims: A service valve circuit in a hydraulic circuit of a hydraulic excavator which is provided with two units of variable capacity type hydraulic pumps (2F, 2R) (hereinafter referred to as a variable pump) and which is connected with a control valve group (13, 14) having a plurality of control valves in the inflow circuits (3F, 3R) of both variable pumps (2F, 2R), and these respective control valves being connected to respective actuators, a service valve (15)(215) for controlling a special attachment (e) connected to the inflow circuit (3F) of one of the variable pumps (2F); and a confluence valve (17)(217) for performing electromagnetic proportional flow rate control in the confluence circuit (16) in communication with the section between the inflow circuits (3F, 3R) of both variable pumps (2F, 2R), characterized in an electrical switch (21) for switching between confluence and non-confluence by means of said confluence valve (17)(217), the section between this confluence valve (17)(217) and the electrical switch (21) being connected by an electrical signal circuit (25-28). A service valve circuit of a hyudraulic excavator as claimed in claim 1, comprising a volume (22) for regulating a flow rate after confluence by means of said confluence valve (17) in a range of flow rate for a maximum of one or two pumps (2F, 2R), the section between this confluence valve (17) and the volume (22) being connected by an electrical signal circuit. A service valve circuit of a hydraulic excavator as claimed in claim 1, wherein said confluence valve (17) consists of a poppet valve (18) and an electromagnetic proportional pilot valve (19) for controlling a poppet valve. A service valve circuit of a hydraulic excavator as claimed in claim 1, wherein said confluence valve (217) consists of electromagnetic proportional meter-in and meter-out valves (29)(30) and said service valve (215) consists of a plurality of electromagnetic proportional meter-in and meter-out valves (32-35).

Inventors: MORIYA YUKIO KOMATSU OSAKA PLA, ONODA TAKUMI, TAKAMURA FUJITOSHI, YOKOYAMA TOSHIO, MORIYA, YUKIO KOMATSU OSAKA PLANT, ONODA, TAKUMI, TAKAMURA, FUJITOSHI, YOKOYAMA, TOSHIO
Applicants: KOMATSU MFG CO LTD, KABUSHIKI KAISHA KOMATSU SEISAKUSHO
Application year: 1989
Main classification: E02F3
IPC codes: F15B11, E02F9