Patent Abstract:
A hydraulic circuit for a working machine includes hydraulic actuators which respectively drive a plurality of kinds of working devices and which are driven by a drive circuit having circuit states that correspond to the working devices, a directional control valve unit which, when one of the working devices is attached to the attachment, switches in response to a signal from a controller to select one of the circuit states, a detection sensor that detects the actual circuit state, and a display operated by the controller. The controller activates the display when the detected actual circuit state and the selected circuit state do not match.

Full Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a hydraulic circuit for a working machine, such as a crushing machine, that has an attachment to which working devices are selectively attached. 
   2. Description of the Related Art 
   A typical crushing machine includes a base machine and an attachment which is mounted on the base machine and to which working devices, such as a compression crusher and a breaker, are selectively attached at an end of the attachment depending on the kind of work to be performed. In the following description, work using the breaker is called breaking. 
   In this case, the compression crusher and the breaker use different hydraulic actuators, and the actuators must be provided with respective oil supply/discharge passages. Accordingly, a hydraulic circuit must be switched depending on the kind of the working device to be used. 
     FIGS. 6A and 6B  are diagrams illustrating a structure in which the circuit is switched manually.  FIG. 6A  shows a circuit state for compression crushing and  FIG. 6B  shows a circuit state for breaking. 
   Referring to  FIGS. 6A and 6B , the structure includes a hydraulic pilot-operated directional control valve  5  operated by a remote control valve  6 , a manual directional control valve (three-way valve)  7 , a hydraulic pump  8  that functions as a hydraulic power source for actuators, a tank T, and a primary hydraulic power source  11  for the remote control valve  6 . When the control valve  5  is operated, oil is supplied from the hydraulic pump  8  to a compression-crusher cylinder  9  or a breaker cylinder  10 , and the compression-crusher cylinder  9  or the breaker cylinder  10  is operated accordingly. 
   As shown in  FIG. 6A , when compression crushing is performed, similar to a double acting cylinder circuit, input and output ports of the compression-crusher cylinder  9  are connected to the hydraulic pump  8  and the tank T via the control valve  5 . 
   When breaking is performed, the power of the breaker is reduced if a back pressure is applied to a return line of the breaker cylinder  10  due to a throttle effect of the control valve  5 , and there is a risk that the breaker cannot be operated. In addition, pulsation occurs in an oil cooler (not shown) and there is risk that the oil cooler will be damaged. 
   Therefore, as shown in  FIG. 6B , when breaking is performed, the directional control valve  7  is operated so that the return line of the breaker cylinder  10  is directly connected to the tank T. 
   A technique for automatically switching the circuit state with a directional valve depending on the kind of the working device without using the manual directional control valve  7  shown in  FIGS. 6A and 6B  is disclosed in Japanese Unexamined Patent Application Publication No. 2002-294758. 
   Also in this case, there is a risk that a fail, such as a breakage of a line connecting a controller and a solenoid valve or a breakdown of the controller, will occur in an electrical or hydraulic control system of the directional control valve that functions as an automatic control device. Accordingly, there is a possibility that the circuit state expected by the operator and the actual circuit state do not match. 
   Therefore, the following problems occur: 
   (i) If the actual circuit state is set to the state for compression crushing even though breaking (circuit state for breaking) is selected by a mode switch operation performed by the operator and breaking is performed, the back pressure in the return line is increased as described above and there is a risk that the power of the breaker will be reduced or the breaker will stop. 
   (ii) If the actual circuit state is set to the state for breaking even though compression crushing (circuit state for compression crushing) is selected by the operator and compression crushing is performed, the compression-crusher cylinder cannot be reciprocated and operates in only one direction since one of the lines of the cylinder is directly connected to the tank. 
   SUMMARY OF THE INVENTION 
   Accordingly, an object of the present invention is to provide a hydraulic circuit for a working machine that performs a fail-safe function when actual and expected circuit states do not match. 
   According to the present invention, a hydraulic circuit for a working machine basically has the following structure. 
   That is, according to an aspect of the present invention, a hydraulic circuit for a working machine including a base machine and an attachment mounted on the base machine includes a controller that generates a signal depending on a selecting operation performed by an operator; hydraulic actuators for driving respective working devices, the hydraulic actuators being driven by a drive circuit having two kinds of circuit states that correspond to the working devices; a directional control valve unit which, when one of the working devices is attached to the attachment, switches in response to the signal from the controller to select one of the two kinds of circuit states; a detector for detecting the actual circuit state; and a display activated by the controller. The controller activates the display when the actual circuit state detected by the detector and the selected circuit state do not match. 
   When the circuit state expected by the operator and the actual circuit state do not match, the display is activated to inform the operator of the discrepancy. Accordingly, a fail-safe function is provided when the operator informed of the discrepancy stops the operation. 
   In a hydraulic circuit for a working machine according to another aspect of the present invention, working devices driven by different hydraulic actuators are selectively attached to an attachment mounted on a base machine, the hydraulic actuators being driven by a drive circuit having two kinds of circuit states that correspond to the working devices. A directional control valve unit selects one of the circuit states by switching in response to a signal generated by a controller depending on a selecting operation performed by an operator. The hydraulic circuit has the following features: 
   (A) A hydraulic pilot-operated directional control valve that functions as a common control valve for controlling the operation of the hydraulic actuators for driving the working devices and that is operated by a remote control valve is provided. 
   (B) The directional control valve unit includes a hydraulic pilot-operated main directional control valve that switches depending on whether a pilot pressure is supplied or shut off to generate the two kinds of circuit states and first and second solenoid valves that are selectively operated on the basis of an electric signal from a control means. 
   (C) Each of the solenoid valves is connected to the pilot hydraulic power source and applies a pilot pressure from the pilot hydraulic power source to the main directional control valve when the solenoid valve is operated. 
   (D) The pilot pressure from the pilot hydraulic power source is supplied to the remote control valve that operates the common control valve as a primary pressure when the solenoid valves are operated. 
   In this structure, when the solenoid valves included in the directional control valve unit are activated, the pilot pressure from the pilot hydraulic power source is supplied to the remote control valve via the directional control valve unit as the primary pressure. Therefore, if an abnormality like a breakage of electric lines connecting the controller to the solenoid valves occurs and the solenoid valves cannot be operated, the supply of the primary pressure to the remote control valve stops. 
   Therefore, the common control valve cannot be operated even when the remote control valve is operated (or the common control valve returns to neutral if the common control valve is being operated). As a result, the operation of the hydraulic actuator is automatically stopped and thus the fail-safe function is provided. 
   In addition, since the solenoid valves included in the directional control valve unit are used to shut off the primary pressure of the remote control valve, the structure is simpler than that in the case in which, for example, an additional solenoid shutoff valve is provided at a primary side of the remote control valve and the shutoff valve is operated when a fail is detected. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a diagram illustrating a circuit structure according to a first embodiment of the present invention; 
       FIG. 2  is a diagram illustrating a circuit structure according to a second embodiment of the present invention; 
       FIG. 3  is a diagram illustrating a circuit structure according to a third embodiment of the present invention; 
       FIG. 4  is a schematic side view of a crushing machine in which an opening/closing compression crusher is attached to an attachment; 
       FIG. 5  is a schematic side view of the crushing machine in which a breaker is attached to the attachment; and 
       FIGS. 6A and 6B  are diagrams illustrating the structure of a circuit that is switched with a manual directional control valve, where  FIG. 6A  shows a circuit state for compression crushing and  FIG. 6B  shows a circuit state for breaking. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 4 and 5  illustrate a crushing machine including a hydraulic excavator as a base body and a hydraulic circuit for a working machine according to the present invention. 
   The crushing machine includes a crawler type base machine  1  and a bendable attachment  2  mounted on the base machine  1 . In the embodiments described below, an opening/closing compression crusher  3  (see  FIG. 4 ) called a nibbler and a vibrating breaker  4  (see  FIG. 5 ) are explained as examples of working devices. 
   The opening/closing compression crusher  3  called a nibbler or the vibrating breaker  4  is attached to an end of the attachment  2  as a working device depending on the kind of work to be performed. 
   In this case, the compression crusher  3  and the breaker  4  use different hydraulic actuators, and the actuators must be provided with respective oil supply/discharge passages. Accordingly, a hydraulic circuit must be switched depending on the attached working device. 
   Hydraulic circuits for working machines according to embodiments of the present invention that provide a fail-safe function will be described below with reference to the accompanying drawings. 
   First Embodiment (see FIG.  1 ) 
   Referring to  FIG. 1 , a directional control valve unit  18  includes a hydraulic pilot-operated main directional control valve  19  that switches between a compression-crushing position a and a breaking position b and a solenoid valve  20  that switches the main valve  19  on the basis of an electric signal from a controller  21  that functions as control means. The solenoid valve  20  switches between a position y for supplying a pilot pressure to the main valve  19  and a position x for shutting off the pilot pressure on the basis of the electric signal from the controller  21 . 
   According to the present invention, detecting means detects the switch state of the main valve  19  as the actual circuit state. Preferably, the detecting means is structured such that the main valve  19  included in the directional control valve unit  18  has a pressure port connected to a hydraulic power source at one end of the main valve  19  and a pressure sensor is connected to the pressure port. The detecting means may include, for example, a pressure sensor  23  which will be described below. 
   In this case, since the state of the main valve  19  included in the directional control valve unit  18  is detected as the actual circuit state, the structure of the detecting means can be made simple. In particular, when the pressure sensor  23  is used, the pressure sensor  23  simply detects whether or not a pressure is applied to the pressure port of the main valve  19 . Therefore, the detecting means is small and inexpensive, and can easily be installed in the circuit. 
   The basic structure and operation (circuit-state-switching operation) performed by the directional control valve unit  18  will be described below. 
   The solenoid valve  20  switches between the compression-crushing position x at which the pilot pressure of a pilot hydraulic power source  16  is not supplied to a pilot port  19   a  of the main valve  19  (that is, for connecting the port  19   a  to a tank T) and the breaking position y at which the pilot pressure is supplied to the pilot port  19   a.  In this structure, when a mode switch  17  as a switch for changing modes is switched to compression-crushing, the controller  21  does not transmit the electric signal to the solenoid valve  20 . Therefore, the solenoid valve  20  and the main valve  19  are switched to the compression-crushing positions x and a, respectively, as shown in  FIG. 1 . 
   Accordingly, lines of the compression-crusher cylinder  9  are connected to a hydraulic pump  8  and the tank T via a control valve  5  (circuit state for compression crushing). 
   When the mode switch  17  is switched to breaking, the controller  21  transmits the electric signal to the solenoid valve  20  so that the solenoid valve  20  switches to the breaking position y. Therefore, the main valve  19  also switches to the breaking position b. 
   Accordingly, the return line of the breaker cylinder  10  is directly connected to the tank T without passing through the control valve  5  (circuit state of for breaking). 
   In the first embodiment, the main valve  19  included in the directional control valve unit  18  has a sub-spool  22  that moves together with a spool (main spool) of the main valve  19 . 
   The sub spool  22  has input and output ports  22   a  and  22   b  and a tank port  22   c.    
   The input port  22   a  is connected to the pilot hydraulic power source  16  and the tank port  22   c  is connected to the tank T. When the main valve  19  is switched from the compression-crushing position a shown in the figure to the breaking position b, the input and output ports  22   a  and  22   b  communicate with each other and the pressure of the pilot hydraulic power source  16  is supplied to the output port  22   b.    
   The output port  22   b  is connected to the pressure sensor  23  and the pressure sensor  23  outputs a signal to the controller  21 . 
   Accordingly, whether the main valve  19  is at the compression-crushing position a or the breaking position b, that is, the actual circuit state, can be detected on the basis of whether or not the pressure is applied to the output port  22   b.    
   In addition, the controller  21  is connected to a display (lamp, buzzer, etc.)  24  that functions as display means. As is clear from the fact that a buzzer is mentioned as an example of the display  24 , the display  24  is not limited to a visual display that can be presented on a screen or the like. For example, other means for attracting an attention, such as an alarm, may also be used as the display  24  as long as the operator can be informed of the actual circuit state by the activated display  24 . 
   The controller  21  compares the signal from the pressure sensor  23  that represents the actual circuit state with an operation signal of the mode switch  17  that represents the circuit state expected by the operator. If the two signals do not match, that is, when the circuit is set for breaking even through compression crushing is selected by the operator or when the circuit is set for compression crushing even through breaking is selected by the operator, the display  24  is activated. 
   Thus, when an abnormality like a line breakage occurs in a control system of the directional control valve unit  18 , the operator can be informed of the situation by the display. Accordingly, the operator can stop the operation of the control valve  5  so that various troubles caused by the discrepancy between the expected and actual circuit states can be avoided. 
   In the above-described structure, a pressure switch may be used instead of the pressure sensor  23 . 
   Second Embodiment (see FIG.  2 ) 
   In the first embodiment, the display is activated when the expected and actual circuit states do not match. In comparison, in a second embodiment, the operation of a compression-crusher cylinder  9  or a breaker cylinder  10  is stopped automatically when an abnormality occurs. 
   According to the second embodiment, a directional control valve unit  25  includes a hydraulic pilot-operated main directional control valve  19  and first and second solenoid valves  26  and  27  for breaking and compression crushing, respectively, that are selectively operated by an electric signal transmitted from a controller  28  in accordance with the operation of a mode switch  17 . 
   The solenoid valves  26  and  27  are both connected to a pilot hydraulic power source  16 . When the first solenoid valve  26  is operated, a pilot pressure of the pilot hydraulic power source  16  is supplied to a pilot port  19   a  of the main valve  19  so that the main valve  19  is switched from a compression-crushing position a to a breaking position b. 
   In addition, when the solenoid valves  26  and  27  are operated, the pilot pressure is output from output ports thereof and is supplied to a remote control valve  6  for controlling a control valve  5  via a shuttle valve  29  as a primary pressure. 
   In this structure, when the solenoid valves  26  and  27  are operated normally, the primary pressure is supplied to the remote control valve  6  via the operated solenoid valve  26  or  27 . Accordingly, the control valve  5  is switched in accordance with the operation of the remote control valve  6  and the compression-crusher cylinder  9  or the breaker cylinder  10  is operated. 
   However, if an abnormality like a breakage of electric lines connecting the controller  28  to the solenoid valves  26  and  27  occurs and the solenoid valves  26  and  27  cannot be operated, the supply of the primary pressure to the remote control valve  6  stops. 
   More specifically, if an abnormality occurs while breaking is selected, the first solenoid valve  26  cannot be operated and the pilot pressure is not output from the solenoid valve  26 . Therefore, the primary pressure of the remote control valve  6  is shut off. 
   Similarly, if an abnormality occurs while compression crushing is selected by the mode switch  17 , the second solenoid valve  27  cannot be operated. Therefore, also in this case, the primary pressure of the remote control valve  6  is shut off. 
   Accordingly, the control valve  5  cannot be operated even when the remote control valve  6  is operated (or the control valve  5  returns to neutral if the control valve  5  is being operated). As a result, the compression-crusher cylinder  9  or the breaker cylinder  10  is automatically stopped, and thus the fail-safe function is provided. 
   According to the present embodiment, the solenoid valves  26  and  27  included in the directional control valve unit  25  are used to shut off the primary pressure of the remote control valve  6 . Therefore, the structure is simpler than that in the case in which, for example, an additional solenoid shutoff valve is provided at a primary side of the remote control valve  6  and the shutoff valve is operated when a fail is detected. 
   Thus, according to the present embodiment, operation-stopping means for stopping the operation of the compression-crusher cylinder  9  or the breaker cylinder  10 , which functions as a hydraulic actuator, is provided. The controller  28  that functions as control means causes the operation-stopping means to stop the operation of the compression-crusher cylinder  9  or the breaker cylinder  10  when the actual circuit state and the selected circuit state do not match. 
   Thus, when the actual and selected circuit states do not match, the operation of the compression-crusher cylinder  9  or the breaker cylinder  10  can be automatically stopped by the operation-stopping means in addition to activating a display. Accordingly, the reliability of the fail-safe function can be increased. In addition, when the display and automatic stopping are performed simultaneously, the operator can reliably recognize the discrepancy between the expected and actual circuit states (occurrence of a fail). Therefore, recognition of the cause and repair can be facilitated. 
   Third Embodiment (see FIG.  3 ) 
   In the third embodiment, the display function described in the first embodiment and the automatic stopping function described in the second embodiment are both performed when an abnormality occurs. 
   More specifically, the circuit structure according to the first embodiment is basically applied, and an additional solenoid shutoff valve  30  is provided at a primary side of a remote control valve  6 . In this case, when the actual and expected circuit states do not match, in addition to activating a display  24 , the shutoff valve  30  is activated by a signal from a controller  21  so that the primary pressure of the remote control valve  6  is shut off. 
   Accordingly, since the display  24  is activated and the operation of a hydraulic actuator (a compression-crusher cylinder  9  or a breaker cylinder  10 ) is automatically stopped simultaneously, the reliability of the fail-safe function can be increased. In addition, since the automatic stopping and display are simultaneously performed, the operator can reliably recognize the discrepancy between the expected and actual circuit states (occurrence of a fail). Therefore, recognition of the cause and repair can be facilitated. 
   In the above-described embodiments, the compression crusher and the breaker are explained as examples of working devices that can be selectively attached. However, other various combinations of devices can be applied as long as the devices are driven by different hydraulic actuators and it is necessary to switch the circuit state depending on the actuator to be used. 
   Although the invention has been described with reference to the preferred embodiments in the attached figures, it is noted that equivalents may be employed and substitutions made herein without departing from the scope of the invention as recited in the claims.

Technology Classification (CPC): 5