DESCRIPTION TITLE OF THE INVENTION CONTROL DEVICE FOR FLOW RATE CONTROL VALVE TECHNICAL FIELD [0001] The present invention relates to a control device for a flow rate control valve, and more particularly to a control device for a flow rate control valve that learns the neutral position of the flow rate control valve. BACKGROUND ART [0002] Vehicles in which the engagement of a clutch apparatus that transmits the engine torque to a mechanical automatic transmission is controlled by a clutch actuator have been developed and put to practical use. In such vehicles, the clutch apparatus is provided between the engine and the mechanical automatic transmission. The clutch apparatus is engaged and disengaged by the movement of the piston of a pneumatically or hydraulically operated clutch actuator. The operation of the clutch actuator is realized by the supply or discharge of a working fluid located inside the clutch actuator by a flow rate control valve provided with an electromagnetic solenoid. [0003] An intake passage that communicates with the clutch actuator, a pressure source passage that communicates with a working fluid pressure source such as an air tank, and an exhaust passage that discharges the working fluid from the clutch actuator are connected to such a flow rate control valve, and three ports, namely an intake port, a pressure source port, and an exhaust port, which are open to respective passages, are formed with a predetermined spacing in this flow rate control valve. A valve element is freely fitted into the hollow section of the flow rate control valve, and in this configuration, the aforementioned intake port, pressure source port, and exhaust port are communicated or blocked by the movement of the valve element. [0004] More specifically, when the clutch apparatus is disengaged, the valve element is moved to an intake position in which the intake port and the exhaust port are communicated with each other and the exhaust port is blocked, and the 1 working fluid is supplied into the clutch actuator. When the clutch apparatus is engaged, the valve element is moved to the exhaust portion in which he intake port and the exhaust port are communicated with each other and the pressure source port is blocked, and the working fluid is discharged from the clutch actuator. When the clutch apparatus is maintained in the disengagement position, the valve element is moved to the neutral position in which the intake port is blocked, and the working fluid is held inside the clutch actuator. [0005] For example, Patent Document 1 discloses a control device for a clutch that uses a flow rate control valve of this type. PRIOR ART DOCUMENTS PATENT DOCUMENTS [0006] Patent Document 1: Japanese Patent Publication No. 3417823 [0007] However, when the gear shifting is performed in the vehicle, it is preferred and the clutch apparatus be engaged and disengaged rapidly and so that the gear shift shock is small. For this purpose, it is necessary to move the piston of the clutch actuator rapidly in the engagement direction so that the ineffective region in which the engine torque is not transmitted be rapidly passed through, and also to increase the engagement amount gradually in order to avoid the gear shift shock in the so-called half-clutch region in which torque transmission is started. In order to realize such control rapidly, a flow rate characteristic representing the relationship between the energizing quantity supplied to the coil of the electromagnetic solenoid and the flow rate of the working fluid is stored in advance in the ECU that controls the flow rate control valve, and the flow rate control valve is controlled according to this flow rate characteristic. Further, this flow rate characteristic is also corrected according to the neutral position of the flow rate control valve in order to realize the accurate control of the flow rate control valve. [0008] However, in a flow rate control valve, a difference can occur between the intake-side neutral position assumed when the valve element moves from the intake position to the neutral position and the exhaust-side neutral position 2 assumed when the valve element moves from the exhaust portion to the neutral position. As a result, the flow rate control valve is difficult to control accurately. DISCLOSURE OF THE INVENTION PROBLEMS ADDRESSED BY THE INVENTION [0009] With the foregoing in view, it is an object of the present invention to provide a control device for a flow rate control valve that can accurately learn the neutral position of the flow rate control valve with a simple configuration. MEANS FOR RESOLVING THE PROBLEMS [0010] In order to attain the above-described problems, the present invention provides a control device for a flow control valve, including: an actuator that is actuated by a working fluid; a working fluid supply source that supplies the working fluid; a stroke sensor that detects a stroke amount of the actuator; a flow rate control valve that has a valve element movable in a hollow section and also has a supply section that is connected to the working fluid supply source, a discharge section that discharges the working fluid from the actuator, and a communication section communicating with the actuator; and a control unit that controls a movement amount of the valve element according to a value detected by the stroke sensor, wherein the control unit has a neutral position learning unit that learns a movement amount corresponding to a neutral position of the valve element, from a movement amount of the valve element at a time when it is determined from the value detected by the stroke sensor that the valve element has moved from the discharge section side and assumed a neutral position in which the valve element cuts off the communication section and a movement amount of the valve element at a time when it is determined from the value detected by the stroke sensor that the valve element has moved from the supply section side and assumed a neutral position in which the valve element cuts off the communication section. [0011] The control unit may determine that the valve element is in the neutral position when a variation amount of the value detected by the stroke sensor is equal to or less than a predetermined value. 3 [0012] Further, the control unit may determine that the valve element is in the neutral position when the variation amount of the value detected by the stroke sensor is equal to or less than the predetermined value continuously for a predetermined time. [0013] Further the control unit may proportionally control the movement amount of the valve element. EFFECT OF THE INVENTION [0014] With the control device for a flow rate control valve in accordance with the present invention, the neutral position of the flow rate control valve can be accurately learned with a simple configuration. BRIEF DESCRIPTION OF THE DRAWINGS [0015] FIG. 1 is a block diagram illustrating the control device for a flow rate control valve and the drive system for a vehicle according to an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating in detail the flow rate control valve according to the embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating the actuated state of the flow rate control valve shown in FIG. 2. FIG. 4 is a cross-sectional view illustrating the neutral position of the flow rate control valve shown in FIG. 2. FIG. 5 illustrates a flow rate characteristic of the flow rate control valve according to the embodiment of the present invention. FIG. 6 illustrates how the stroke control is performed with the control device for the flow rate control valve according to the embodiment of the present invention. FIG. 7 is a flowchart illustrating the contents of control performed by the control device for the flow rate control valve according to the embodiment of the present invention. BEST MODE FOR CARRYING OUT THE INVENTION [0016] An embodiment of the present invention will be described below with reference to the drawings. 4 [0017] FIGS. I to 7 illustrate an embodiment of the present invention. In the drawings, like components are assigned with like reference numerals and the names and functions thereof are the same. Accordingly, the redundant explanation thereof is omitted. [0018] First, a drive system of a vehicle 1 that uses a control device 10 for a flow rate control valve of the embodiment of the present invention will be explained below with reference to FIG. 1. As shown in FIG. 1, the drive system of the vehicle 1 of the present embodiment has an engine 100, a clutch apparatus 200, and a mechanical automatic transmission 300. [0019] The engine 100 is combustion controlled with an engine ECU (not shown in the figure) to generate a torque corresponding to the running state of the vehicle 1. An output shaft 110 of the engine 100 is configured to be engageable with a transmission input shaft 310 of the mechanical automatic transmission 300 by the below-described clutch apparatus 200. [0020] As shown in FIG. 1, the clutch apparatus 200 is a dry single-plate clutch apparatus that has a flywheel 210, a clutch disk 220, and a return spring 230. [0021] The flywheel 210 is fixed to the output shaft 110 of the engine 100 with a bolt and a nut (not shown in the figure). The clutch disk 220 is provided with a friction plate (not shown in the figure) on the peripheral portion thereof and slidably spline-mated with the transmission input shaft 310 of the below described mechanical automatic transmission 300. Further, one end of the below-described release fork 13 is attached to the clutch disk 220. The return spring 230 is provided between one end of the clutch disk 220 and the mechanical automatic transmission 300 and attached to bias the clutch disk 220 in the direction of the engine 100 (direction shown by arrow X in FIG. 1). [0022] The mechanical automatic transmission 300 is configured to convert and adjust the torque of the engine 100 transmitted by the flywheel 210 and the clutch disk 220 into the desirable rotation speed by the engagement of the 5 flywheel 210 and the clutch disk 220, and then to transmit the torque to the propeller shaft (not shown in the figure). [0023] The control device 10 for a flow rate control valve of an embodiment of the present invention will be explained below with reference to FIGS. I to 7. [0024] As shown in FIGS. 1 and 2, the control device 10 for a flow rate control valve of the embodiment of the present invention has a pressure supply source (working fluid supply source) 11, a clutch actuator (actuator) 12, a release fork 13, a stroke sensor 14, a flow rate control valve 15, an intake passage 16, a pressure source passage 17, an exhaust passage 18, and a control ECU (control unit) 20. [0025] The pressure supply source 11 is a pneumatic tank or the like and, as shown in FIG. 1, supplies a working fluid to the flow rate control valve 15. Further, the pressure source passage 17 communicating with a pressure source port 17a of the below-described flow rate control valve 15 is connected to the pressure supply source 11. [0026] As shown in FIG. 1, the clutch actuator 12 has a cylinder body 12a provided with a cylinder chamber, and a piston 12b slidably inserted into the cylinder chamber. In this configuration, the exhaust passage 18 communicating with the exhaust port 18a of the flow rate control valve 15 is connected to the side surface of the cylinder body 12a and the working fluid locates inside the cylinder chamber is discharged through the flow rate control valve 15. Further, the intake passage 16 communicating with an intake port 16a of the flow rate control valve 15 is also connected to the side surface of the cylinder body 12a, and the piston 12b is moved in the direction shown by the arrow X in FIG. 1 by the fluid pressure of the working fluid that is fed from the pressure supply source 11 through the flow rate control valve 15. [0027] As shown in FIG. 1, the release fork 13 is supported at one end on the distal end of the piston 12b of the clutch actuator 12 and attached at the other end to the clutch disk 220. Further, the release fork 13 is rotatably supported in the central portion thereof by a support shaft 13a. Thus, where the working 6 fluid is supplied into the cylinder chamber of the clutch actuator 12 and the piston 12 moves in the forward direction of the vehicle 1 (direction shown by the arrow X in FIG. 1), the release fork 13 is biased in the forward direction of the vehicle 1 (direction shown by the arrow X in FIG. 1). Further, the release fork 13 is configured such that the engagement of the clutch apparatus 200 is released when the release fork rotates to the left (as shown in FIG. 1) about the support shaft 13a. Where the working fluid located inside the cylinder chamber of the clutch actuator 12 is discharged, the release fork 13 is rotated in the direction shown by an arrow Y in FIG. 1 by the biasing force of the return spring 230, and the engagement of the clutch apparatus 200 is maintained. [0028] As shown in FIG. 1, the stroke sensor 14 detects the stroke amount of the clutch actuator 12, and the detected value S is outpoured to the operation control unit 21 of the below-described control ECU 20. [0029] As shown in FIGS. 1 and 2, the intake passage 16 is connected at one end to the cylinder chamber of the clutch actuator 12 and at the other end to the intake port 16a of the below-described flow rate control valve 15. [0030] As shown in FIGS. 1 and 2, the pressure source passage 17 is connected at one end to the pressure supply source 11 and at the other end to the pressure source port 17a of the below-described flow rate control valve 15. [0031] As shown in FIGS. 1 and 2, the discharge passage 18 is connected at one end to the cylinder chamber of the clutch actuator 12 and at the other end to the exhaust port 18a of the below-described flow rate control valve 15. [0032] As shown in FIG. 2, the flow rate control valve 15 has a proportional valve body 15a provided with a hollow section inside thereof, a valve element 19 that is slidably inserted into the hollow section, an electromagnetic solenoid 15b, and a spring 15c. The intake port (communication section) 16a, the pressure source port (supply section) 17a, and the exhaust port (discharge section) 18a, which are connected to the intake passage 16, the pressure supply passage 17, and the discharge passage 18, are formed with a predetermined spacing in the side portion of the proportional valve body 15a. In the present embodiment, the 7 intake port 16a is positioned between the pressure source port 17a and the exhaust port 18a. [0033] In the valve element 19, three lands, namely, an intake blocking section 19a, a power source blocking section 19b, and a discharge blocking section 19c are provided with a predetermined spacing so as to block the aforementioned intake port 16a, pressure source port 17a, and exhaust port 18a, respectively. The valve element 19 is connected at one end to a movable yoke of the electromagnetic solenoid 15b and biased at the other end by the spring 15c in the direction shown by arrow X in FIG. 2. [0034] Thus, the valve element 19 is configured such that the position thereof is determined by a balance of the magnetic force acting upon the movable yoke of the electromagnetic solenoid 15b and the biasing force of the spring 15c. For example, when the energizing of the coil of the electromagnetic solenoid 15b is stopped (energizing quantity supplied is 0%), the valve element 19 is biased by the spring 15c and assumes the position (exhaust position) shown in FIG. 3(a). As a result, the intake port 16a and the exhaust port 18a communicate with each other and the working fluid located inside the cylinder chamber of the clutch actuator 12 is discharged, whereby the clutch apparatus 200 is engaged. Where the energizing quantity supplied to the coil of the solenoid 15b is maximized (100%), the valve element 19 compresses the spring 15c and assumes the position (intake position) shown in FIG. 3(b), and the intake port 16a and the pressure source port 17a communicate with each other. As a result, the working fluid of the pressure supply source 11 is fed from the intake port 16a into the cylinder chamber of the clutch actuator 12, and the clutch apparatus 200 is disengaged. Where the energizing quantity supplied to the coil of the electromagnetic solenoid 15b is made 50%, the valve element 19 assumes the position (neutral position) shown in FIG. 3(c), the intake port 16a is cut off from the pressure source port 17a and the exhaust port 18a, and the engagement amount of the clutch apparatus 200 is maintained at a predetermined amount. [0035] The control ECU (control unit) 20 is configured of the conventional CPU and ROM and provided with the operation control unit 21 and a neutral position learning unit 22 as functional elements. 8 [0036] In the present embodiment, those functional elements are provided in the control ECU 20, which is integrated hardware, but either of them can be also provided in separate hardware. [0037] The operation control unit 21 controls the flow rate of the working fluid passing through the flow rate control valve 15, and a flow rate characteristic (solid line in FIG. 5) representing the relationship between the energizing quantity supplied to the coil of the electromagnetic solenoid 15b and the flow rate of the working fluid is stored in advance in the operation control unit. Further, the operation control unit 21 is configured such that the energizing quantity supplied correspondingly to the target flow rate is outputted to the coil of the electromagnetic solenoid 15b on the basis of this flow rate characteristic. In the present embodiment, a target waveform shown by a broken line in FIG. 6(a) is set in advance such that the clutch stroke shown by a solid line in FIG. 6(a) is realized when the gear shifting is performed in the vehicle. Thus, in such a configuration, the clutch stroke is rapidly changed from a complete engagement position to a disengagement position 1 and then returned to the complete engagement position via a disengagement position 2 so as to prevent the gear shift shock during gear shifting as shown in FIG. 6(a). Further, the energizing quantity supplied to the coil of the electromagnetic solenoid 15b is P controlled (proportionally controlled) as shown by the graph in FIG. 6(b) so as to realize the target waveform shown in FIG. 6(a). Thus, when the gear shifting is performed in the vehicle 1, the position of the valve element 19 of the flow rate control valve 15 is controlled in a sequence of exhaust position - intake position neutral position and then controlled in a sequence of neutral position - exhaust position - neutral position - exhaust position so as to change the engagement of the clutch apparatus 200 in a sequence of engagement - disengagement engagement. [0038] The neutral position learning unit 22 learns the energizing quantity E supplied to the coil of the electromagnetic solenoid 15b in the neutral position in which the working fluid passing through the flow rate control valve 15 is blocked. More specifically, the neutral position learning unit determines that the flow rate control valve 15 is in the neutral position when the stroke variation 9 speed is substantially zero on the basis of the detection value S outputted from the stroke sensor 14, and learns the energizing quantity E corresponding to this neutral position. [0039] In the present embodiment, the stroke variation speed is determined on the basis of the differential value of the stroke amount. More specifically, a stroke Si and a stroke S 2 after a predetermined time t has elapsed since the stroke Si has been detected are detected, and where a differential value D (D = (Si - S 2 )/t), which is a stroke variation speed after the predetermined time t has elapsed, is equal to or less than a predetermined value, it is determined that the stroke variation speed is substantially zero. In order to perform the determination in a state with a more stable stroke variation speed, it is possible to provide a plurality of calculation periods of the differential value D in a continuous manner within a predetermined time interval t and determine that the stroke variation speed is substantially zero only when all of the differential values D are equal to or less than the predetermined value. [0040] The neutral position learning unit 22 reads an energizing quantity E i (referred to as "intake-side learned value") corresponding to the intake-side neutral position (see FIG. 4(a)) at the time when the valve element 19 of the flow rate control valve 15 moves in a sequence of exhaust position - intake position neutral position (the clutch apparatus 200 operates in a sequence of engagement - disengagement - maintained disengagement) and an energizing quantity E 2 (referred to as "exhaust-side learned value") corresponding to the exhaust-side neutral position (see FIG. 4(b)) at the time when the valve element 19 of the flow rate control valve 15 moves in a sequence of the exhaust position - neutral position during a gear shifting operation in the vehicle 1. In this case, the neutral position learning unit 22 reads both the intake-side learned value E i and the exhaust-side learned value E 2 because a difference L occurs between the intake-side neutral position and the exhaust-side neutral position as shown in FIG. 4(a) and FIG. 4(b). This difference L occurs because a diameter Li of the intake blocking portion 19a of the valve element 19 is made larger than an opening diameter L 2 of the intake port 16a (Li > L 2 ) in order to block completely the intake port 16a at the neutral position of the flow rate control valve 15. 10 [0041] The neutral position learning unit 22 also stores the average value EAve of the intake-side learned value E 1 and the exhaust-side learned value E 2 as an energizing quantity corresponding to the neutral position of the flow rate control valve 15, that is, as a learned value. [0042] Where the gear shifting operation in the vehicle 1 is thereafter completed, for example, the flow rate characteristic shown in FIG. 5 that has been stored in advance in the operation control unit 21 is corrected to the flow rate characteristic, such as shown by a broken line, on the basis of the stored average value EAve. [0043] Since the control device 10 for a flow rate control valve of the embodiment of the present invention has the above-described configuration, for example, the following control is performed according to the flowchart shown in FIG. 7 during the gear shifting operation in the vehicle 1. [0044] Where an operator performs the gear shifting operation in the vehicle 1, first, in step 1, the operation control unit 21 of the control ECU 20 controls the valve element 19 of the flow rate control valve 15 so that the valve element moves in a sequence of exhaust position - intake position - neutral position (the clutch apparatus 200 operates in a sequence of engagement - disengagement maintained disengagement). [0045] In step 2, the neutral position learning unit 22 determines whether or not the differential value D, which is a stroke variation speed, is equal to or less than a predetermined value (the stroke variation speed is substantially zero) on the basis of a detected value S outputted from the stroke sensor 14. Where the differential value D is equal to or less than the predetermined value continuously for a predetermined time, the flow rate control valve 15 is determined to be at the intake-side neutral position, and the processing advances to step 3. Meanwhile, where the differential value D is not equal to or less than the predetermined value continuously for a predetermined time, the flow rate control valve 15 is determined not to be at the intake-side neutral position and the control is returned. 11 [0046] In step 3, the neutral position learning unit 22 reads the energizing quantity at the time when it has been determined in the aforementioned step 2 that the flow rate control valve is in the intake-side neutral position, that is, reads the intake-side learned value Ei. [0047] In step 4, the operation control unit 21 controls the valve element 19 of the flow rate control valve 15 so that valve element moves in a sequence of neutral position - exhaust position - neutral position. [0048] In step 5, the neutral position learning unit 22 determines whether or not the differential value D, which is a stroke variation speed, is equal to or less than a predetermined value (the stroke variation speed is substantially zero) on the basis of a detected value S outputted from the stroke sensor 14. Where the differential value D is equal to or less than the predetermined value continuously for a predetermined time, the flow rate control valve 15 is determined to be at the exhaust-side neutral position, and the processing advances to step 6. Meanwhile, where the flow rate control valve 15 is determined not to be at the exhaust-side neutral position, the control is returned. [0049] In step 6, the neutral position learning unit 22 reads the energizing quantity at the time when it has been determined in the aforementioned step 5 that the flow rate control valve is in the exhaust-side neutral position, that is, reads the exhaust-side learned value E 2 . [0050] In step 7, the average value EAve of the intake-side learned value Ei, which has been read in the aforementioned step 3, and the exhaust-side learned value E 2 , which has been read in the aforementioned step 6, is stored by the neutral position learning unit 22 as the neutral position learned value of the flow rate control valve 15. [0051] In step 8, the neutral position learning unit 22 compares the energizing quantity corresponding to the neutral position in the flow rate characteristic shown in FIG. 5, which has been stored in advance by the operation control unit 21, with the learned value (average value EAve), which has been stored in step 7, and where a difference is found therebetween, this flow 12 rate characteristic is corrected, for example, to the flow rate characteristic such as shown by a broken line in FIG. 5, and the present control returns. [0052] With the above-described control, the control device 10 for a flow rate control valve of the embodiment of the present invention demonstrates the following operation and effects. [0053] Thus, the neutral position learning unit 22 learns the neutral position of the flow rate control valve 15 when the stroke variation speed is determined to be substantially zero on the basis of the detection value S outputted from the stroke sensor 14. [0054] Therefore, the neutral position of the flow rate control valve 15 is learned in a state in which the stroke does not change and the behavior of the clutch apparatus 200 is stable. Therefore, the spread in the learned values can be reduced. Since the clutch control is performed on the basis of the flow rate characteristic corrected according to the learned values after the learning, the occurrence of a gear shifting shock during gear shifting can be effectively inhibited. [0055] Further, the neutral position learning unit 22 reads the intake-side learned value Ei at the time when the valve element 19 of the flow rate control valve 15 moves in a sequence of intake position - neutral position and the exhaust-side learned value E 2 at the time when the valve element 19 of the flow rate control valve 15 moves in a sequence of exhaust position - neutral position, and saves the average value EAve of the intake-side learned value E 1 and the exhaust-side learned value E 2 as a learned value corresponding to the neutral position of the flow rate control valve 15. [0056] Therefore, even when a difference L appears between the exhaust-side neutral position and the intake-side neutral position, the neutral position of the flow rate control valve 15 can be accurately learned, and the occurrence of a gear shifting shock during gear shifting, naturally, can be effectively inhibited by executing the clutch control on the basis of the flow rate characteristic corrected according to the learned value. 13 [0057] Further, the control of the movement amount (energizing quantity supplied to the coil) of the valve element 19 of the flow rate control valve 15, that is, the flow rate control of the working fluid flowing through the flow rate control valve 15, by the operation control unit 21 is performed by a P control (proportional control). [0058] Therefore, since abrupt output variations in the flow rate control valve 15 are inhibited, the stroke variation speed can be made more stable and the neutral position of the flow rate control valve 15 can be learned more accurately than in the case where a PD control or PID control is used. [0059] Further, it is determined whether or not the stroke variation speed is substantially zero continuously for a predetermined time, and the neutral position is learned in a state in which the stroke variation rate is stable. Therefore, the learned value of neutral position can be obtained with an accuracy higher than that in the case where the learning is performed in a state with abrupt variations in stroke, such as take place immediately after the clutch apparatus 200 is engaged. [0060] The present invention is not limited to the above-described embodiment and can be changed, as appropriate, without departing from the essence of the present invention. [0061] For example, in the above-described embodiment, the control device 10 for a flow rate control valve in accordance with the present invention is applied to the clutch apparatus 200, but this control device can be also generally applied to control systems in which control is performed by constant-rate proportional valves. [0062] Further, in the present embodiment, the configuration is explained in which the flow rate control valve 15 is provided with the intake port 16a, the pressure source port 17a, and the exhaust port 18a, and the intake passage 16, the pressure source passage 17, and the exhaust passage 18 are connected to the respective ports, but a configuration may be also used in which the flow rate 14 control valve 15, the working fluid supply source 11, and the clutch actuator 12 are disposed adjacently to each other, and the intake passage 16, the pressure source passage 17, and the exhaust passage 18 are omitted. [0063] Further, in the present embodiment, the configuration is explained in which the intake port 16a is disposed between the pressure source port 17a, and the exhaust port 18a, but such positional relationship of the ports is not limiting, and for example the pressure source port 17a may be positioned between the intake port 16a and the exhaust port 18a. [0064] Further, either of a pneumatic pressure and a hydraulic pressure can be used as the fluid pressure of the working fluid actuating the clutch actuator 12 in the control device 10 for a flow rate control valve in accordance with the present invention. [0065] In the present embodiment, the flow rate control valve 15 is explained that is controlled by the energizing quantity supplied to the coil of the electromagnetic solenoid, but for example a configuration in which the control is performed by using a pulse motor and changing the number of pulses can be also used. [0066] Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps. [0067] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that the prior art forms part of the common general knowledge in Australia. EXPLANATION OF REFERENCE NUMERALS [0068] 1 vehicle 10 control device for flow control valve 11 pressure supply source (working fluid supply source) 15 12 clutch actuator (actuator) 14 stroke sensor 15 flow rate control valve 16a intake port (communication section) 17a pressure source port (supply section) 18a exhaust port (discharge section) 19 valve element 20 control ECU (control unit) 21 operation control unit 22 neutral position learning unit 16