Patent Publication Number: US-6339929-B1

Title: Swivel control apparatus

Description:
This application is a continuation of PCT Application No. PCT/JP99/06606 filed on Nov. 26, 1999. 
    
    
     This application is based upon Japanese Patent Application No. 337559 of Heisei 10, filed Nov. 27, 1998, and its contents are incorporated herein by reference. 
     TECHNICAL FIELD 
     The present invention relates to a swivel control apparatus for a construction machine such as a crane or the like. 
     BACKGROUND ART 
     In a control system for swiveling, in the past, there is a mode (termed the “neutral free mode”) in which the motor is rotated by the inertia of the swiveling body when the operating lever has been returned to neutral; and there is a mode (termed the “neutral brake mode”) in which the rotation of the motor is stopped when the operating lever has been returned to neutral. It is desirable for the use of these modes to be separated according to the nature of the job, and for example in Japanese Patent Publication Serial No. 2,549,420 there is disclosed an apparatus with which either of these modes can be selected with one machine. With the apparatus of this publication, respective relief valves are provided to conduits connected to the input and output ports of the hydraulic motor, and a relationship between the amount of actuation of the operating lever and the relief pressures of the relief valves are made into patterns and established in advance for each of the neutral free and neutral brake modes. It is possible to control the driving of the swiveling body in correspondence with each of the neutral free/neutral brake modes by controlling the relief valves in accordance with these characteristics (patterns) of relief pressure. 
     DISCLOSURE OF THE INVENTION 
     The above described characteristics of the relief valves of the apparatus described in the above publication are set so that the amounts of change of the relief pressure become greater in accompaniment with increase of the actuation amount of the operating lever, and since the relief valve is controlled in accordance with these characteristics, even in the case that the operating lever is actuated for deceleration by exactly the same amount, according to the position from which the operating lever was actuated, the amounts of change of the relief pressures vary. In other words, although the relief pressures vary greatly in positions in which the slopes of the characteristics are large, the relief pressures vary hardly at all in positions in which the slopes of the characteristics are small. As a result great differences occur in the deceleration of the motor due to the position of the operating lever, even if the operating lever is operated for deceleration by exactly the same amount, and operation becomes difficult from the point of view of the operator. 
     Further, with the apparatus described in the above publication, a plurality of different relief characteristics are set for the relief valves according to the direction of actuation of the operating lever, the direction of rotation of the motor, and whichever of the neutral free/neutral brake modes is established, and for this reason the control algorithm becomes complicated. In the above publication an apparatus is disclosed in which one relief valve is provided in order to simplify the control algorithm, but in this case the problem arises that, even in the neutral free mode, a large braking pressure is generated due to the actuation region of deceleration actuation of the operating lever. 
     The objective of this invention is to provide a swivel control apparatus which can most suitably realize the neutral free mode and the neutral brake mode by a simple construction. 
     In order to attain the above object, a swivel control apparatus according to the present invention , comprises: a hydraulic pump; a hydraulic motor for swiveling which is driven by hydraulic oil emitted from the hydraulic pump; a control valve which controls a flow of hydraulic oil which is supplied from the hydraulic pump to the hydraulic motor for swiveling, and at a neutral position of the control valve cuts off from one another a pair of ports which communicate to input and output ports of the hydraulic motor; a valve device which communicates and cuts off from one another a pair of conduits which are respectively connected to the input and output ports of the hydraulic motor for swiveling; a pressure detection device which detects respective pressures in the two conduits and outputs pressure signals; a rotational speed detection device which detects a physical quantity based upon a rotational speed of the hydraulic motor for swiveling and outputs a rotational speed signal; a mode selection device which selects a neutral brake mode and a neutral free mode; and a control device which controls driving of the valve device so as to cut off the two conduits from one another when the neutral brake mode is selected, and so as to communicate the two conduits based upon the pressure signals and the rotational speed signal when the neutral free mode is selected. 
     In this swivel control, it is preferred that the control device calculates a direction of action of hydraulic oil upon the hydraulic motor based upon the pressure signals, calculates a rotational direction of the hydraulic motor based upon the rotational speed signal, and controls the driving of the valve device so as to communicate the two conduits when the neutral free mode is selected and the calculated direction of action of hydraulic oil upon the hydraulic motor and the rotational direction of the hydraulic motor are different. In this case, it is preferred that the control device calculates a target flow amount based upon the rotational speed signal and controls the driving of the valve device so that the target flow amount flows from one of the conduits to the other of the conduits. In addition, it is preferred that a deceleration ratio setting device which sets a deceleration ratio for the hydraulic motor for swiveling is further provided, and the control device calculates the target flow amount based upon a set value from the deceleration ratio setting device. Or it is preferred that the control device controls the driving of the valve device based upon a conversion table that is predetermined to obtain a value of a control signal for the valve device based upon the target flow amount. Or it is preferred that the target flow amount is assumed as a value for a flow amount passing through an orifice, a differential pressure between the two conduits detected by the pressure detection device is assumed as a value for a differential pressure of orifice, and the control device calculates an opening amount of orifice by substituting the assumed values into an equation based upon the orifice equation, and controls the driving of the valve device based upon a control signal corresponding to the calculated opening amount of orifice. 
     It is preferred that the valve device described above is an electromagnetic proportional valve and is controlled so as to be closed when the neutral brake mode is selected and so as to be opened with a predetermined opening area when the neutral free mode is selected. 
     A hydraulic swiveling type of crane according to the present invention comprises: a traveling body; a swiveling body that is mounted upon the traveling body to be able to swing; and the above described swivel control apparatus that controls swiveling of the swiveling body. 
     As described above, in the present invention, the valve apparatus which communicates together and cuts off from one another a pair of conduits which are respectively connected to the input and output ports of the hydraulic motor for swiveling is provided, in the neutral brake mode the two conduits are cut off from one another, and in the neutral free mode the two conduits are communicated based upon the pressure signals and the rotational speed signal, therefore it is possible to realize a suitable one of the neutral free/neutral brake states without any dependence upon the actuation position of the operating lever. The control algorithm becomes simplified compared with one in which each of the neutral free/neutral brake states is realized according to the predetermined patterns. In particular, since the target flow amount that is calculated based upon the rotational speed signal flows from one of the conduits to the other of the conduits, the speed control of the swiveling body can be performed accurately. Furthermore, since it is possible to set the deceleration ratio of the hydraulic motor for swiveling, therefore in the neutral free mode it is possible to alter the deceleration of the swiveling body to any value, and the convenience of use is enhanced. 
     Furthermore, since the conversion table that is predetermined to obtain a value of a control signal for the valve device based upon the target flow amount is used, the control can be implemented easily and the high speed of control can be achieved. And various types of empirical or experimental values can be used for the conversion table. On the other hand, in case that the equation based upon the orifice equation is used, the amount of memory where the conversion table is stored can be reduced. In addition, the target opening amount is calculated in consideration of not only the target flow amount but also the differential pressure, the target flow amount can be controlled with high accuracy. Also, the hydraulic swiveling type of crane can have above advantages. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a hydraulic circuit diagram of a hydraulic control apparatus according to an embodiment of this invention. 
     FIG. 2 shows the detailed construction of a control section of a swivel control apparatus according to a first embodiment. 
     FIG. 3 shows a general constructional view of a crane to which this invention is applied. 
     FIGS. 4A and 4B shows an example of swiveling speed versus operating lever input for each of the neutral free and the neutral brake modes. 
     FIG. 5 shows the detailed construction of a control section of a swivel control apparatus according to a second embodiment. 
     FIG. 6 shows the detailed construction of a control section of a swivel control apparatus according to a third embodiment. 
     FIGS. 7A and 7B show an example of swiveling speed versus swivel control apparatus operating lever input for the third embodiment. 
    
    
     BEST MODE FOR CARRYING OUT THE INVENTION 
     The embodiments of this invention will be described in the following with reference to the drawings. 
     The first embodiment 
     FIG. 1 is a hydraulic circuit diagram showing the construction of a hydraulic control apparatus (a swivel control apparatus) according to embodiments of this invention; FIG. 2 is a figure showing the detailed construction of a control section (a controller  12  which will be described hereinafter) of the hydraulic control apparatus according to the first embodiment; and FIG. 3 is a side view of the construction of a crane in which the hydraulic control apparatus according to this embodiment is used. The movable crane shown in FIG. 3 is made up of a travelling body  61 , a swiveling body  62  which is carried upon the travelling body  61  and can swivel, and a boom  63  which is supported upon the swivelling body  62  and can be raised and lowered; and a hanging load  66  is held up by a hook  65  which is connected to a wire rope, via a sheave  64  which is provided at the end of the boom  63 . 
     As shown in FIG. 1, a hydraulic circuit for swiveling of the swiveling body  62  of this movable crane consists of a hydraulic pump  3  which is driven by a motor  101 , a hydraulic motor for swiveling  2  which is driven by hydraulic oil ejected from the hydraulic pump  3 , a direction control valve for swiveling  1  which controls the flow of hydraulic oil supplied from the hydraulic pump  3  to the hydraulic motor for swiveling  2  and in neutral cuts off a pair of ports which connect to output and input ports of the hydraulic motor  2 , an operating lever  5  with which the operator inputs commands for swiveling, pilot valves  4 A and  4 B controlled by the operating lever  5 , two conduits  6 A and  6 B which are connected to the input and output ports of the hydraulic motor for swiveling  2 , a pilot hydraulic oil source  7  which supplies hydraulic oil to the pilot valves  4 A and  4 B, check valves  8 A and  8 B which are connected between a center port of the direction control valve for swiveling  1  and the conduits  6 A and  6 B, an electromagnetic proportional flow amount control valve  9  (hereinafter termed an electromagnetic proportional valve) which, via a throttle, communicates the two conduits  6 A and  6 B together or cuts them off from one another, pressure sensors  10 A and  10 B which output pressure signals P 1  and P 2  which measure the hydraulic oil pressures in the conduits  6 A and  6 B, a rotational speed sensor  11  which detects a rotational speed of the swiveling body  62  which is proportional to the speed of swiveling and outputs a signal Si which is positive in the case of forward rotation and minus in the case of reverse rotation, a mode selection switch  13  which selects either a neutral free mode or a neutral brake mode, and a controller  12  which controls the valve opening amount (the throttling cross section) of the electromagnetic proportional valve  9 . As described above, the direction control valve for swiveling  1  does not connect together the conduit  6 A and the conduit  6 B but cuts off them in the neutral position 
     Now the neutral free and the neutral brake modes will be explained. The neutral free mode is a mode in which driving torque is generated in the operating direction of the operating lever  5  and the hydraulic motor  2  is driven, and in this mode even if the operating lever  5  is returned to the neutral position braking force other than swiveling resistance does not act upon the hydraulic motor  2 , and the swiveling body  62  rotates by inertial force. This kind of mode is suitable when, for example, the swinging of a suspended load is to be reduced. Further, the neutral brake mode is a mode in which the hydraulic motor  2  is driven according to the amount of actuation of the operating lever  5 , and in this mode, when the operating lever  5  is returned to the neutral position, hydraulic braking force acts upon the hydraulic motor  2 , and rotation of the swiveling body  62  is prevented. This kind of mode is suitable when, for example, minute positional adjustment of the swiveling body is to be performed. It is to be noted that the neutral free/neutral brake actuation states are exemplarily shown in FIGS. 4A and 4B. FIG. 4A shows the input state of the operating lever  5  from the neutral position, while FIG. 4B shows the respective swivel speeds for each mode corresponding to this input state. In this embodiment, during the neutral brake mode braking force acts upon the hydraulic motor  2  by the electromagnetic proportional valve  9  closing and interrupting communication between the conduits  6 A and  6 B, while during the neutral free mode the hydraulic motor  2  rotates by inertial force by the electromagnetic proportional valve  9  opening and permitting communication between the conduits  6 A and  6 B. In the following this point will be explained in detail. 
     As shown in FIG. 2, the controller  12  comprises: a flow amount calculation device  21  which inputs a rotational speed signal S 1  from the rotational speed sensor  11  and multiplies it by a predetermined speed reduction ratio α (it is supposed in this embodiment that α=1) and a displacement amount q for one revolution of the hydraulic motor  2 , so as to calculate a flow amount QAB (=S 1 ×α×q : in the following, this will be termed the target flow amount) passing the electromagnetic proportional valve  9 ; a subtraction device  22  which inputs the pressure signals P 1  and P 2  and subtracts P 1  from the pressure signal P 2  so as to calculate a differential signal ΔP (=P 2 −P 1 ); a sign determination device  23  which determines the sign of the differential signal ΔP; conversion tables  24 A and  24 B which convert the target flow amount QAB into a control signal A′, using previously provided correspondence tables between target flow amounts QAB and control signals A′; and a mode determination device  25  which discriminates the signal from the mode changeover switch  13 , and when the neutral free mode is selected outputs the control signal A′ just as it is to the solenoid of the electromagnetic proportional valve  9 , while when the neutral brake mode is selected outputs a control signal A′ equal to 0. The valve characteristic of the electromagnetic proportional valve  9  is set so that the valve opening amount increases along with increase of the control signal A′ from the controller  12 , while it closes the valve with a control signal A′=0. Further, in the region of the conversion table  24 A in which the target flow amount QAB ≦0, and in the region of the conversion table  24 B in which the target flow amount QAB ≧ 0, processing is performed so as to bring the control signal A′ equal to 0 as a limit. 
     Next, the operation of this first embodiment will be explained. Moreover, in the following explanation, it will be postulated that the direction in which the hydraulic motor  2  rotates due to hydraulic oil from the conduit  6 A is the forward rotational direction, while the direction in which the hydraulic motor  2  rotates due to hydraulic oil from the conduit  6 B is the reverse rotational direction. 
     (1) Neutral Brake Mode 
     When the neutral brake mode is selected by the mode changeover switch  13 , a control signal A′=0 is output to the solenoid of the electromagnetic proportional valve  9  by the previously described mode determination device  25 , and the electromagnetic proportional valve  9  is closed so as to prevent communication between the conduits  6 A and  6 B. Here, when an attempt is made to rotate the swiveling body  62  forward and the operating lever  5  is actuated to drive it towards the forward rotation side, the pilot valve  4 A is driven according to this amount of actuation, and the hydraulic oil from the pilot hydraulic oil source  7  (the pilot pressure) is supplied to the pilot port of the direction control valve  1  via the pilot valve  4 A. When this is done, the direction control valve  1  is changed over to its position (a), and hydraulic oil from the hydraulic pump  3  is supplied to the hydraulic motor  2  via the direction control valve  1  and the conduit  6 A. Due to this, the hydraulic motor  2  rotates in the forward rotational direction, and the swiveling body  62  is driven at a speed according to the amount of actuation of the operating lever  5 . 
     When the operating lever  5  is actuated to drive it to the neutral side so as to decelerate the swiveling body  62 , the pilot pressure is reduced in accordance with the amount of this operation, and the direction control valve  1  is driven towards the neutral side. Due to this, the throttling due to the direction control valve  1  (the meter-out throttling) is closed down, and the pressure in the conduit  6 B increases which generates braking pressure, so that the rotation of the swiveling body  62  is decelerated. When the operating lever  5  has completely returned to the neutral position, the conduits  6 A and  6 B are blocked off from the hydraulic pump  3  and the tank, and as shown by the dotted line in FIG. 4B the rotation of the swiveling body  62  is quickly stopped. Moreover, even if in this state any external force should act upon the swiveling body  62 , the swiveling body  62  does not rotate. The above operation is the same even if the swiveling body was driven in the reverse rotational direction. It is to be noted that a crossover load relief valve (not shown) that starts operation when the braking pressure described above exceeds the predetermined pressure value becomes is provided between the conduits  6 A and  6 B 
     (2) Neutral Free Mode 
     When the neutral free mode is selected by the mode changeover switch  13  and initial actuation is applied to the operating lever  5  towards the forward rotation side for forward rotation of the swiveling body, in the same manner as described above, the direction control valve  1  is changed over to its position (a), and the hydraulic motor  2  is rotated in the forward rotational direction. At this time the target flow amount QAB becomes &gt;0, since the signal S 1  output from the rotational speed sensor  11  is positive (&gt;0) , and further the differential signal ΔP becomes &lt;0 since P 1 &gt;P 2  (referring to the signals P 1  and P 2  output from the pressure sensors  10 A and  10 B) . As a result processing is performed using the conversion table  24 B so as to bring the control signal A′ equal to 0 as a limit, and this control signal A′=0 is output to the electromagnetic proportional valve  9  just as it is. On the other hand, if initially the operating lever  5  is actuated towards the reverse rotation side, the target flow amount QAB becomes &lt;0, since the signal S 1  output from the rotational speed sensor  11  is negative (&lt;0), and further the differential signal ΔP becomes &gt;0 since P 1 &lt;P 2  (referring to the signals P 1  and P 2  output from the pressure sensors  10 A and  10 B) As a result processing is performed using the conversion table  24 A so as to bring the control signal A′ equal to 0 as a limit, and this control signal A′=0 is output to the electromagnetic proportional valve  9 . In this manner a control signal A′=0 is output to the electromagnetic control valve  9  during initial starting, and communication between the conduits  6 A and  6 B is cut off in the same manner as the previously described neutral brake mode, and the swiveling body  62  is driven at a speed according to the amount of actuation of the operating lever  5 . Moreover, when the operating lever is kept at a fixed position to the forward rotation side or to the reverse rotation side, and also when the operating lever is operated to accelerate, in the same manner, a control signal A′=0 is output to the electromagnetic proportional valve  9 . 
     The difference between the neutral free mode and the neutral brake mode is when as described below the operating lever  5  is operated to decelerate or to stop. When during forward rotation the operating lever  5  is actuated to the neutral position so as to stop the movement of the swiveling body  62 , the pilot pressure to the direction control valve  1  drops and the direction control valve  1  is driven to the neutral position, and the pressure in the conduit  6 B increases. At this time, although the target flow amount QAB is &gt;0 since the signal output from the rotational speed sensor  11  is positive, the differential signal ΔP&gt;0 since P 1 &lt;P 2  (referring to the signals P 1  and P 2  output from the pressure sensors  10 A and  10 B), and a control signal A′&gt;0 is calculated by the control table  24 A, and this control signal A′ is output to the electromagnetic proportional valve  9 . As a result, the electromagnetic proportional valve  9  is opened to a specified amount, and a flow amount corresponding to the target flow amount QAB flows from the conduit  6 B to the conduit  6 A via the electromagnetic proportional valve  9 . Due to this the hydraulic pressure in the conduit  6 B is reduced, and braking force does not act upon the hydraulic motor  2  so that the swiveling body  62  continues rotating by inertial force. It is to be noted that since in practice swiveling resistance as well acts upon the swiveling body  62  rotating in this manner, as shown by the solid line in FIG. 4B the driving of the swiveling body  62  stops in due course. If the driving of the swiveling body  62  is to be forcibly stopped, it is acceptable to actuate the operating lever  5  to the reverse side (so called “reverse lever”), so as to increase the hydraulic pressure in the conduit  6 B. 
     In this manner according to the first embodiment it is always possible to realize a suitable one of the neutral free/neutral brake states without any dependence upon the actuation position of the operating lever  5 , since the electromagnetic proportional valve  9  is provided which communicates together the input and output ports of the hydraulic motor  2  and cuts them off from one another, and it is arranged that the valve opening amount of the electromagnetic proportional valve  9  is controlled based upon the rotational speed of the swiveling body  62  and the forward and reverse differential pressure of the hydraulic motor  2 , and based upon the neutral brake/neutral free mode. Furthermore the control algorithm becomes simple, since the target flow amount QAB is calculated by the controller  12  and it is arranged that the control signal A′ is output according to this target flow amount QAB. Yet further, since in the neutral free mode it is arranged that the flow amount passing through the electromagnetic proportional valve  9 , i.e. the flow amount supplied to the hydraulic motor  2 , is directly controlled, the accuracy of speed control of the swiveling body is improved, as compared with indirect control of the flow amount supplied to the hydraulic motor by pressure control of the relief valve. 
     The second embodiment 
     FIG. 5 is a hydraulic circuit diagram showing the construction of a hydraulic control apparatus according to a second embodiment of this invention. It should be understood that to elements which are identical to ones shown in FIGS. 1 and 2 identical reference symbols are attixed, and in the following principally the points of difference will be explained. As shown in FIG. 5, the second embodiment differs from the first embodiment by the method for calculation of the control signal to A′. That is, by contrast to the first embodiment in which the control signal A′ was derived from the target flow amount QAB using the conversion tables  24 A and  24 B, in the second embodiment the control signal A is calculated from the pressure signal ΔP and the target flow amount QAB using an equation for calculation (I), as will be explained below. 
     Referring to FIG. 5, the calculation shown in Equation (I) is performed in a opening amount calculation device  26 , based upon the target flow amount QAB calculated by a flow amount calculation device  21  and the differential signal ΔP calculated by a subtraction device  22 , and the valve opening amount A (in the following this will be termed the “target opening amount”) for the electromagnetic proportional valve  9  is calculated which is necessary for the flow of this target flow amount QAB. A=Cl×QAB/{square root over ( )}|ΔP| . . . (I), where Cl is a constant. 
     The above equation (I) is a variant of a following equation (II) which is a general type of equation regarding orifice, in which the flow amount Q passing through the orifice corresponds to the target flow amount QAB, and the differential pressure of orifice Δp corresponds to the differential signal ΔP. Q=C 2 ×A{square root over ( )}(2×Δp/ρ) . . . (II), where C 2  is a constant and ρ is the density. 
     The target opening amount A calculated in this manner is converted into a control signal A′ which corresponds to the target opening amount A by a limit processor  27 A or  27 B. At this time, limit processing for the control signal A′=0 is performed in the region of the limit processor  27 A where the target opening amount A≦0, and in the region of the limit processor  27 B where the target opening amount A≧0. 
     The operation of the second embodiment constituted in this manner is basically identical to that of the first embodiment. However, since with the second embodiment the target opening amount A is calculated while considering not only the target flow amount QAB but also the differential pressure signal ΔP, therefore it is possible to cause the target flow amount QAB to flow in the electromagnetic proportional valve  9  with high accuracy. 
     The third embodiment 
     FIG. 6 is a hydraulic circuit diagram showing the construction of a hydraulic control apparatus according to a third embodiment of this invention. It should be understood that to elements which are identical to ones shown in FIG. 5 identical reference symbols are attixed, and in the following principally the points of difference will be explained. As shown in FIG. 6, the third embodiment differs from the second embodiment in the points that a gain setting device  29  on which the operator can adjust a gain to any value, and a multiplication device  28  which inputs a signal from the gain setting device  29  and calculates a gain flow amount QAB′ (=K×QAB) by multiplying the target flow amount QAB by the gain K are provided; and in the third embodiment the control signal A′ is calculated based not upon the flow amount QAB but upon the gain flow amount QAB′. Moreover, in this case, the gain K is set to within the region 0≦K≦1, and accordingly the gain flow amount QAB′ satisfies the condition 0≦QAB′ &lt;QAB. 
     With the third embodiment structured in this manner, the deceleration of the swivel speed may be varied during the neutral free mode by adjusting the gain K, as shown for example in FIGS. 7A and 7B. Referring to FIG. 7B, when the gain K is set to 0, the gain flow amount QAB′ becomes 0, and in this situation, in the same manner as during the neutral brake mode, the electromagnetic proportional valve  9  is closed and the swiveling body  62  quickly decelerates in response to the input state of the operating lever  5 . Further, when the gain K is set to 1, the gain flow amount QAB′ becomes equal to the target flow amount QAB, and in this situation the valve opening of the electromagnetic proportional valve  9  becomes equal to the target opening amount A of the second embodiment, and the swiveling body  62  rotates by inertial force, even if the operating lever  5  is actuated for deceleration. 
     Since in this manner, according to this third embodiment, it is so arranged that the gain flow amount QAB′ is calculated by multiplying the target flow amount QAB by any value of the gain K, and the control signal A′ is calculated based upon this gain flow amount QAB′, therefore it is possible freely to alter the deceleration during the neutral free mode, and due to this it is possible easily to satisfy the demands of an operator who wishes to alter the deceleration feeling, so that the convenience of use is enhanced. 
     It should be understood that, although the swivel control apparatus according to the above described embodiments may be applied to a crane, it can also be applied in an identical manner to a hydraulic shovel. Further, although in the above described embodiments it was so arranged that, during the neutral free mode, hydraulic oil flowed from the conduit  6 A ( 6 B) to the conduit  6 B ( 6 A) using the electromagnetic proportional valve  9  in correspondence to the target flow amount QAB or the gain flow amount QAB′, it is also possible to realize the neutral free mode simply without calculating any target flow amount QAB or gain flow amount QAB′, just by permitting flow from the conduit  6 A ( 6 B) to the conduit  6 B ( 6 A). 
     Further, although in the above described embodiments it was so arranged that the pressures in the conduits  6 A and  6 B are controlled by using the electromagnetic proportional valve  9 , any structures that enable the pressures in the conduits  6 A and  6 B increase or decrease may be adopted. Furthermore, although in the above described embodiments the rotational speed sensor  11  was used to calculate the target flow amount QAB, the speed sensor may be used. Also, although in the above described embodiments the control algorithm of the controller  12  was explained in the example of hardware by using the block diagram, this is for convenience in explanation. The control algorithm is actually executed in the software manner.