Patent Publication Number: US-7913612-B2

Title: Actuator control device

Description:
FIELD OF THE INVENTION 
     This invention relates to an actuator control device suitable for controlling a lowering operation of a lift cylinder in a forklift or the like. 
     BACKGROUND OF THE INVENTION 
     In a known conventional actuator control device that controls an operation of a lift cylinder in a forklift or the like, an operate check valve that allows working oil to flow into the cylinder is provided in a cylinder port, an orifice that communicates with a pilot chamber of the operate check valve is formed in a poppet of the operate check valve, and the pilot chamber is caused to communicate with a tank passage in accordance with the movement of a spool (see JP6-45682 Y2). 
     SUMMARY OF THE INVENTION 
     In this type of conventional actuator control device, the operate check valve opens when the pilot chamber of the operate check valve communicates with the tank passage. When the operate check valve opens, pressure acting on the operate check valve decreases rapidly. In this case, the operate check valve is closed again by the spring force action of a spring provided in the pilot chamber. When the operate check valve is closed, the pressure acting on the operate check valve rises such that the operate check valve reopens. This operation is performed repeatedly. 
     Hence, in a conventional device, the problem of so-called hunting, wherein the operate check valve opens and closes repeatedly, occurs. 
     This invention has been designed in consideration of this problem, and it is an object thereof to provide an actuator control device capable of suppressing the occurrence of hunting in an operate check valve. 
     In order to achieve above object, this invention provides an actuator control device that controls an expansion/contraction operation of a hydraulic cylinder. The actuator control device comprises an actuator port connected to the hydraulic cylinder, a main spool that switches the actuator port between communication with a working fluid supply passage and communication with a working fluid return passage, and an operate check valve interposed between the hydraulic cylinder and the main spool, which allows a working fluid to flow from the supply passage to the actuator port, and allows the working fluid to flow from the actuator port to the return passage in accordance with a pressure of a back pressure chamber, wherein, the actuator port communicates constantly with the back pressure chamber of the operate check valve via a connecting passage, the main spool comprises, a pilot spool housed slidably in the main spool, a pilot chamber delimited on one end side of the pilot spool, a spring chamber delimited on another end side of the pilot spool, a biasing member that is housed in the spring chamber and biases the pilot spool against a pressure of the pilot chamber, and a first port that connects the back pressure chamber to a tank passage downstream of the return passage and a second port that connects the return passage to the pilot chamber when the main spool is switched to a discharge position for discharging the working fluid in the hydraulic cylinder, the pilot spool comprises a control throttle that applies resistance to a flow of working fluid flowing out of the pilot chamber into the tank passage, and when the main spool is switched to the discharge position, the pilot spool is maintained in a balanced position by the pressure of the pilot chamber, which acts in accordance with a front-rear differential pressure of the control throttle, and a biasing force of the biasing member in the spring chamber, whereby an opening area of the first port is controlled to and maintained at a fixed level. 
     According to this invention, when a main spool is switched to a discharge position, a pilot spool is maintained in a balanced position by the pressure of a pilot chamber and the biasing force of a biasing member housed in a spring chamber, and therefore the opening of a first port is maintained at a fixed level. As a result, the pressure of a back pressure chamber delimited by the back surface of a valve body of an operate check valve is maintained at a fixed level, and therefore the occurrence of hunting in the operate check valve is suppressed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view showing an actuator control device according to a first embodiment of this invention, in a state where a main spool is in a neutral position. 
         FIG. 2  is a cross-sectional view showing the actuator control device in a state where the main spool is in a discharge position. 
         FIG. 3  is a cross-sectional view showing the actuator control device when the main spool is in the discharge position and a first port is in a controlled state. 
         FIG. 4  is a cross-sectional view showing an actuator control device according to a second embodiment of this invention, in a state where a main spool is in a neutral position. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of this invention will be described below with reference to the figures. 
     First Embodiment 
     First, referring to  FIGS. 1 to 3 , an actuator control device according to a first embodiment of this invention will be described. 
     The actuator control device according to this embodiment controls an expansion/contraction operation of a lift cylinder (not shown) of a forklift. The lift cylinder is a hydraulic cylinder driven by a working fluid such as oil. 
     The actuator control device is formed by incorporating various members into a body  50 , and comprises an actuator port  1  connected to the lift cylinder, a main spool  52  which is interposed slidably in a spool hole  2  formed in the body  50  and switches the actuator port  1  between communication with a working fluid supply passage  3  and communication with a working fluid return passage  4 , and an operate check valve  51  interposed between the lift cylinder and the main spool  52 . 
     The operate check valve  51  is disposed in a confluence part of the supply passage  3  and return passage  4 , and opens and closes a seat portion  6  provided in the body  50  by means of a valve body  5 . More specifically, when the valve body  5  opens the seat portion  6 , the actuator port  1  communicates with the supply passage  3  and return passage  4 . When the valve body  5  is seated on the seat portion  6  such that the seat portion  6  is closed, communication between the actuator port  1  and the supply passage  3  and return passage  4  is blocked. 
     The valve body  5  comprises a poppet portion  5   a  that blocks passage of the working fluid when seated on the seat portion  6 , and a tubular tube portion  5   b  provided on a base end side of the poppet portion  5   a . An orifice  8  serving as a connecting passage for connecting the actuator port  1  to the interior of the tube portion  5   b  is formed in a fuselage portion of the tube portion  5   b . A back pressure chamber  7  into which the working fluid in the actuator port  1  is led via the orifice  8  is delimited by a back surface of the valve body  5 . Thus, the actuator port  1  communicates with the back pressure chamber  7  at all times through the orifice  8 . Further, a spring  9  serving as a biasing member that biases the valve body  5  in a closing direction is housed in the back pressure chamber  7 . 
     A pressure receiving portion  5   c  on which the pressure of the working fluid in the actuator port  1  acts is formed on an outer peripheral surface of the valve body  5  facing the actuator port  1 . The working fluid pressure acting on the pressure receiving portion  5   c  causes an opening direction force to act on the valve body  5 . Meanwhile, the pressure of the back pressure chamber  7  acts on the back surface of the valve body  5 , and this pressure causes a closing direction force to act on the valve body  5 . A closing direction pressure receiving area of the valve body  5  is larger than an opening direction pressure receiving area. Therefore, when the pressure acting on the pressure receiving portion  5   c  is equal to the pressure acting on the back surface of the valve body  5 , or in other words when the pressure of the actuator port  1  and the pressure of the back surface chamber  7  are equal, the operate check valve  51  is maintained in a closed state. 
     The main spool  52  is formed with a supply side ring-shaped groove  10  that is in constant communication with a pump passage  12  to which working fluid discharged by a pump (not shown) is led, and a return side ring-shaped groove  11  that is in constant communication with a tank passage  13  to which the working fluid in the return passage  4  is discharged. 
     When the main spool  52  moves from a neutral position shown in  FIG. 1  to a supply position (rightward in  FIG. 1 ) for supplying working fluid to the lift cylinder, the supply passage  3  communicates with the pump passage  12  via the supply side ring-shaped groove  10 . Further, when the main spool  52  moves from the neutral position to a discharge position (leftward in  FIG. 1 ) for discharging the working fluid in the lift cylinder, the return passage  4  communicates with the tank passage  13  via the return side ring-shaped groove  11 . 
     A load check valve  29  that allows the working fluid to flow only from the pump passage  12  to the actuator port  1  is interposed in the supply passage  3 . Further, a centering spring  28  that biases the main spool  52  to hold it in the neutral position is provided in an end portion of the main spool  52 . 
     A pilot spool  53  is interposed slidably in the interior of the main spool  52  coaxially with the main spool  52 . A pilot chamber  20  is delimited on one end side of the pilot spool  53 , and a spring chamber  21  is delineated on the other end side. 
     A spring  22  serving as a biasing member that biases the pilot spool  53  against the pressure of the pilot chamber  20  is housed in the spring chamber  21 . In a normal state, the pilot spool  53  is pressed against an end surface of the pilot chamber  20  by the biasing force of the spring  22 . 
     An outer peripheral surface of the pilot spool  53  is partially cut away into a ring shape, and a ring-shaped pressure chamber  24  is formed by the cut away part and an inner peripheral surface of the main spool  52 . The pressure chamber  24  is in constant communication with the pilot chamber  20  via a communication passage  27  formed in the pilot spool  53 . The pressure chamber  24  and the communication passage  27  are connected by a control throttle  25  that applies resistance to the flow of working fluid from the pilot chamber  20  to the pressure chamber  24 . It should be noted that the pilot chamber  20  and pressure chamber  24  may be connected by the communication passage  27 , and the control throttle  25  may be interposed in the communication passage  27 . 
     A first port  14 , a second port  15  and a third port  16 , each having opening portions in an outer peripheral surface and an inner peripheral surface around which the pilot spool  53  slides, are formed in the main spool  52 . 
     One end of the first port  14  communicates with the pressure chamber  24 , while the other end is closed by the body  50  when the main spool  52  is in the neutral position. When the main spool  52  moves from the neutral position to the discharge position (leftward in  FIG. 1 ), the other end of the first port  14  communicates with the back pressure chamber  7  via a passage  17  formed in the body  50 . 
     One end of the second port  15  communicates with the pilot chamber  20 , while the other end is closed by the body  50  when the main spool  52  is in the neutral position. When the main spool  52  moves from the neutral position to the discharge position, the other end of the second port  15  communicates with the return passage  4 . 
     One end of the third port  16  is closed by a land portion  26  formed in the pilot spool  53  when the pilot spool  53  is held in a normal position shown in  FIG. 1  by the action of the spring  22 . The other end communicates with the spring chamber  21  via a communication passage  23  formed in the main spool  52 . When the main spool  52  moves from the neutral position to the discharge position, the other end of the third port  16  communicates with the tank passage  13  via a ring-shaped groove  18  formed in an inner surface of the spool hole  2 . As a result, the spring chamber  21  also communicates with the tank passage  13 , via the third port  16  and the ring-shaped groove  18 . 
     When the main spool  52  moves from the neutral position to the discharge position, the first through third ports  14  to  16  described above form the following relative positional relationship: first, the third port  16  communicates with the ring-shaped groove  18 ; next, the first port  14  communicates with the back pressure chamber  7  via the passage  17 , and at the same time, the second port  15  communicates with the return passage  4 . As shown in  FIGS. 2 and 3 , the return passage  4  communicates with the tank passage  13  via a notch  19  formed in the main spool  52  after the second port  15  communicates with the return passage  4 . 
     Next, actions of the actuator control device according to this embodiment will be described. 
     When the main spool  52  is in the neutral position, communication between the supply passage  3  and the pump passage  12  is blocked and communication between the return passage  4  and the tank passage  13  is blocked. Furthermore, all of the first through third ports  14  to  16  are closed, and communication between the back pressure chamber  7  of the operate check valve  51  and the tank passage  13  is blocked. The working fluid in the actuator port  1  is led to the back pressure chamber  7  through the orifice  8 , and therefore a lift cylinder holding pressure acts on the back pressure chamber  7 . The closing direction pressure receiving area of the valve body  5  of the operate check valve  51  is larger than the opening direction pressure receiving area, and therefore the operate check valve  51  is maintained in a closed state. 
     When the main spool  52  moves from the neutral position to the supply position (rightward in  FIG. 1 ), the supply passage  3  communicates with the pump passage  12  via the supply side ring-shaped groove  10 . Hence, working fluid supplied to the supply passage  3  from the pump passage  12  passes through the load check valve  29 , pushes open the operate check valve  51 , and is supplied from the actuator port  1  to the lift cylinder. 
     When the main spool  52  moves from the neutral position to the discharge position (leftward in  FIG. 1 ), first the third port  16  communicates with the tank passage  13  via the ring-shaped groove  18 , as shown in  FIG. 2 . As a result, the spring chamber  21  communicates with the tank passage  13  via the third port  16  and the ring-shaped groove  18 . Then, when the main spool  52  moves further leftward, the first port  14  communicates with the back pressure chamber  7  via the passage  17 , and at the same time, the second port  15  communicates with the return passage  4 . 
     As a result of the communication between the first port  14  and the back pressure chamber  7 , the holding pressure in the back pressure chamber  7  is led to the pilot chamber  20  through the pressure chamber  24  and the control throttle  25 . At this time, the spool chamber  21  is held at a tank pressure, and therefore the pilot spool  53  moves in a direction (leftward in  FIG. 1 ) for increasing the volume of the pilot chamber  20  against the spring force of the spring  22 . 
     When the pilot spool  53  moves in this manner, one end of the third port  16  communicates with the pressure chamber  24  on the outer periphery of the pilot spool  53 , as shown in  FIG. 2 . As a result, the first port  14  and third port  16  communicate via the pressure chamber  24 , and therefore the back pressure chamber  7  communicates with the tank passage  13  through the passage  17 , the first port  14 , the pressure chamber  24 , the third port  16 , and the ring-shaped groove  18 , in that order. 
     When the back pressure chamber  7  communicates with the tank passage  13 , the pressure of the back pressure chamber  7  decreases. Accordingly, the poppet portion  5   a  of the valve body  5  is separated from the seat portion  6  by the pressure that acts on the pressure receiving portion  5   c  of the operate check valve  51 , thereby opening the operate check valve  51 . As a result, the working fluid in the lift cylinder flows to the return passage  4  side from the actuator port  1 . 
     Here, the second port  15  communicates with the return passage  4 , and therefore the fluid in the return passage  4  flows into the pilot chamber  20  via the second port  15 . As shown in  FIG. 3 , the working fluid that flows into the pilot chamber  20  passes through the control throttle  25 , the pressure chamber  24 , the third port  16 , and the ring-shaped groove  18  in that order, and then flows into the tank passage  13 . Hence, by generating a flow in the control throttle  25 , a differential pressure is generated to the front and rear of the control throttle  25 , and the upstream side pressure thereof acts on the pilot chamber  20 . 
     As a result, the pilot spool  53  compresses the spring  22  and moves further leftward in the figure. As a result of the movement of the pilot spool  53 , the outer peripheral surface of the pilot spool  53  impinges on the opening portion at one end of the first port  14 , thereby varying the opening area of the first port  14  relative to the pressure chamber  24 , or in other words the opening of the first port  14 . 
     The internal pressure of the pilot chamber  20  varies in accordance with the opening of the first port  14 , and therefore the pilot spool  53  is maintained in a balanced position by the internal pressure of the pilot chamber  20  and the biasing force of the spring  22 . 
     More specifically, the pilot spool  53  is maintained in a balanced position in the following manner. 
     When the pilot spool  53  moves to the left side of the figure, the opening of the first port  14  decreases. As a result, the pressure of the back pressure chamber  7  increases such that the operate check valve  51  moves in the closing direction and the flow rate of the working fluid that flows to the return passage  4  side from the actuator port  1  decreases. Hence, the flow rate of the working fluid that flows into the pilot chamber  20  also decreases, whereby the internal pressure of the pilot chamber  20  decreases and the pilot spool  53  is moved in a direction (rightward in the figure) for reducing the volume of the pilot chamber  20  by the biasing force of the spring  22 . When the pilot spool  53  moves rightward in the figure, the opening of the first port  14  increases, and therefore the pressure of the back pressure chamber  7  decreases. As a result, the operate check valve  51  moves in the opening direction, causing the pilot spool  53  to move in a direction (leftward in the figure) for increasing the volume of the pilot chamber  20  against the biasing force of the spring  22 . 
     When the main spool  52  is switched to the supply position in the manner described above, the pressure in the supply passage  3  becomes larger than the pressure in the actuator port  1 , and a differential pressure therebetween reaches or exceeds a predetermined value. Hence, the operate check valve  51  opens against the biasing force of the spring  9  such that working fluid is allowed to flow from the supply passage  3  to the actuator port  1 . Further, when the main spool  52  is switched to the discharge position, the pressure in the back pressure chamber  7  decreases, and as a result, the operate check valve  51  opens, thereby allowing working fluid to flow from the actuator port  1  to the return passage  4 . 
     Furthermore, the pilot spool  53  controls the opening of the first port  14  at a fixed level by maintaining in a balanced position using the internal pressure of the pilot chamber  20  and the biasing force of the spring  22 . When the opening of the first port  14  is controlled to a fixed level, the internal pressure of the back pressure chamber  7  is held at a fixed level in accordance therewith, and as a result, hunting in the operate check valve  51  is prevented. 
     Moreover, inching control, in which a small amount of working fluid is discharged at a time using the notch  19 , can be performed with the pressure in the return passage  4  maintained in a stable state, and therefore the inching control can be performed smoothly. In other words, by holding the main spool  52  in a position where the notch  19  communicates with the return passage  4 , a small flow commensurate with the opening of the notch  19  can be returned to the tank passage  13 , and as a result, the lift cylinder can be lowered slowly. 
     Second Embodiment 
     Next, referring to  FIG. 4 , an actuator control device according to a second embodiment of this invention will be described. It should be noted that identical reference numerals have been allocated to identical members to the first embodiment, and detailed description thereof has been omitted. 
     The second embodiment differs from the first embodiment in the constitution of the operate check valve  51 . The following description will focus on this difference. 
     A valve hole  30  is formed in an axial direction in the poppet portion  5   a  of the operate check valve  51 , and the valve hole  30  is in constant communication with the actuator port  1  via a port  31  serving as a connecting passage. A plug  32  serving as a guide member is fitted into the valve hole  30 . It should be noted that the port  31  corresponds to the orifice  8  of the first embodiment described above, but the opening area thereof is considerably larger than that of the orifice  8 . 
     A recessed portion  33  is formed in an end portion of the plug  32 , which is inserted into the valve hole  30 , and the recessed portion  33  communicates with the back pressure chamber  7  via a passage  34  formed in the plug  32 . An auxiliary valve body  35  serving as a second valve body is interposed slidably in the recessed portion  33 . Thus, the auxiliary valve body  35  is housed in the valve body  5  of the operate check valve  51  and connects the actuator port  1  and the back pressure chamber  7 . 
     A pilot chamber  41  delimited by contact between a tip end portion of the auxiliary valve body  35  and an end surface of the poppet portion  5   a , a first control orifice  37  that opens into the pilot chamber  41 , a second control orifice  38  that communicates with the first control orifice  37  and has a larger opening diameter than the first control orifice  37 , and a spring chamber  39  that communicates with the second control orifice  38 , communicates with the back pressure chamber  7  via the passage  34 , and is delimited by the back surface of the auxiliary valve body  35 , are respectively formed in the auxiliary valve body  35  in axial series. Thus, the pilot chamber  41  and the spring chamber  39  communicate with each other via the first control orifice  37  and second control orifice  38 . 
     A spring  40  serving as a biasing member is housed in the spring chamber  39 . The spring  40  biases the auxiliary valve body  35  in a retreating direction from the recessed portion  33  of the plug  32 . Hence, when no pressure acts on the pilot chamber  41 , the tip end portion of the auxiliary valve body  35  is pressed against the end surface of the poppet portion  5   a  by the biasing force of the spring  40  such that the flow of working fluid through the first control orifice  37  is blocked. 
     A ring-shaped introduction port  36  that has an opening portion in its outer peripheral surface and communicates with the second control orifice  38  is formed in a fuselage portion of the auxiliary valve body  35 . The opening area of an opening portion  36   a  in the outer peripheral surface of the introduction port  36  is determined according to the relative positions of the auxiliary valve body  35  and the plug  32 . When the auxiliary valve body  35  is brought into contact with the end surface of the poppet portion  5   a  by the biasing force of the spring  40 , the opening portion  36   a  of the introduction port  36  is not closed by the inner peripheral surface of the recessed portion  33  of the plug  32 . When the auxiliary valve body  35  advances into the recessed portion  33  of the plug  32  while compressing the spring  40 , on the other hand, the opening area of the opening portion  36   a  decreases accordingly. Then, when the auxiliary valve body  35  comes into contact with a bottom surface of the recessed portion  33 , the opening portion  36   a  is closed by the inner peripheral surface of the recessed portion  33  of the plug  32 . Thus, the opening area of the opening portion  36   a  varies as the auxiliary valve body  35  slides along the inner peripheral surface of the recessed portion  33  of the plug  32 . 
     Next, actions of the actuator control device according to this embodiment will be described. 
     When the main spool  52  is in the neutral position, communication between the back pressure chamber  7  and the tank passage  13  is blocked, and therefore the pressure of the actuator port  1  and the pressure of the back pressure chamber  7  are equal. At this time, the spring chamber  39  and the pilot chamber  41  delimited on either end of the auxiliary valve body  35  are also at equal pressure, and therefore the auxiliary valve body  35  is held in a normal position, shown in  FIG. 4 , by the biasing force of the spring  40 . In this state, the tip end portion of the auxiliary valve body  35  is held in contact with the end surface of the poppet portion  5   a  by the biasing force of the spring  40 , and therefore no flow is generated through the first control orifice  37 . On the other hand, the introduction port  36  is open, and therefore the port  31  communicates with the second control orifice  38  via the introduction port  36 . Hence, when no pressure acts on the pilot chamber  41 , the introduction port  36  communicates with the port  31  and the second control orifice  38  while bypassing the first control orifice  37 . In other words, when the auxiliary valve body  35  is in the normal position, the actuator port  1  communicates with the back pressure chamber  7  via the port  31 , the introduction port  36 , and the second control orifice  38 . 
     Next, a case in which the main spool  52  is moved to the supply position to open the valve body  5  of the operate check valve  51  and then switched to the discharge position in a single stroke, passing straight through the neutral position, will be described. In this case, when the return passage  4  and tank passage  13  are connected while the opening of the valve body  5  is large, the returning fluid from the lift cylinder flows directly into a lap part between the return passage  4  and the return side ring-shaped groove  11 . As a result, pressure loss in the lap part increases rapidly, generating shock. 
     Hence, in this embodiment, measures are taken to ensure that the valve body  5  returns smoothly to a controlled state, thereby reducing shock even when the lift cylinder is lowered in a single stroke after being raised. 
     When the main spool  52  is switched from the supply position to the discharge position, the back pressure chamber  7  communicates with the tank passage  13 , as illustrated above in the first embodiment. As a result, the actuator port  1  communicates with the tank passage  13  via the port  31 , the introduction port  36 , the second control orifice  38 , and the back pressure chamber  7 . Accordingly, a flow is generated through the second control orifice  38 . 
     Here, the opening area of the second control orifice  38  is large, and therefore the working fluid from the lift cylinder flows easily into the back pressure chamber  7  through the second control orifice  38 . Hence, the pressure of the back pressure chamber  7  increases, and therefore the valve body  5  moves smoothly in the closing direction to return to a controlled state. 
     When the valve body  5  returns to the controlled state such that the opening of the seat portion  6  decreases to a certain extent, the pressure of the pilot chamber  41  is increased by the action of pressure loss in the fluid passing through the second control orifice  38 . Then, when the differential pressure between the pilot chamber  41  and the spring chamber  39  reaches or exceeds a predetermined value, the auxiliary valve body  35  moves against the biasing force of the spring  40  such that the opening portion  36   a  of the introduction port  36  is closed by the inner peripheral surface of the recessed portion  33  of the plug  32 . At the same time, the tip end portion of the auxiliary valve body  35  separates from the end surface of the poppet portion  5   a , and therefore the first control orifice  37  communicates with the port  31  such that the working fluid passes through the first control orifice  37 . Thereafter, normal control is performed in an identical manner to the first embodiment. 
     It should be noted that the auxiliary valve body  35  is set to switch to the first control orifice  37  when the lift cylinder is raised but not to switch when the valve body  5  is reseated. When the auxiliary valve body  35  does not switch, the working fluid bypasses the first control orifice  37 , and therefore the auxiliary valve body  35  returns at a higher speed. 
     According to the embodiments described above, the valve body  5  is returned to a controlled state smoothly even when a rapid switch is performed from a supply mode, in which the working fluid is supplied to the actuator port  1  from the supply passage  3 , to a return mode, in which the working fluid is returned to the return passage  4  from the actuator port  1 , in a similar manner to the prior art. As a result, shock is alleviated to a greater extent than the prior art. 
     This invention is not limited to the embodiments described above, and may of course be subjected to various modifications within the scope of the technical spirit thereof. 
     INDUSTRIAL APPLICABILITY 
     This invention may be applied to an actuator control device used to control an expansion/contraction operation of a lift cylinder in a forklift.