DE19603278A1 - Assembly method for anti-skid braking solenoid valve - Google Patents

Abstract

The solenoid valve assembly enables the piston part to be operated with a predetermined coil current without the necessity for precise machining or additional parts. The solenoid valve (50) consists of an armature piston (28) operable between two end positions, the first of which is maintained by means of spring pressure. EM power from the solenoid coil drives the piston to the second position against the spring pressure. A first solenoid current moves the armature at a lower speed to an intermediate position when the current is increased to complete the movement at a higher speed.

Description

The present invention relates to a method for Assemble a solenoid valve, and in detail one Method of assembling a solenoid valve, in which has an air gap between a valve piston and a Core is adjusted during the assembly process.

In a known solenoid valve, a valve piston is in a predetermined direction to maintain a Valve in a normally open or preloaded when closed. The valve piston (Plunger) is by means of an electromagnetic Coil including a core generated electro magnetic force driven. The electromagnetic Force acts against that exerted on the valve piston Preload. An air gap of a predetermined width is formed between the valve piston and the core, so that a predetermined magnetic force between the Valve piston and the core is generated when a magnetic field is formed by the core. Consequently the width of the air gap is a factor in highly the operating characteristics of the solenoid valve influenced.

Thus becomes a solenoid valve constructed in this way assembled, then it is necessary to adjust the width of the Adjust air gap very precisely. To control the  Width of the air gap are all parts related to the Formation of the air gap mechanically very precise manufactured so that a small tolerance of the air gap is achieved. However, this procedure requires high Manufacturing cost of the parts. In another case using a spacer to maintain the air gap a predetermined width during assembly of the Solenoid valve used. This procedure requires however, a variety of spacers between the respective parts. As a result, the process of Assembly very complex. An adjustment mechanism can be provided in the solenoid valve Setting the width of the air gap after assembly of the solenoid valve. This process also increases the Manufacturing cost of the solenoid valve and required complicated setting procedures.

From Japanese Patent Laid-Open No. 4-191,579 a method of assembling a solenoid valve known. In this procedure there is an elastic part between a core and a sleeve during the Assembling provided the width of the air gap using the elasticity of the elastic part very can be set precisely. In particular, the Valve piston arranged on the core, which in the sleeve with the elastic part between the sleeve and the core is used. The valve piston is then with the core against the elastic part to maintain the Valve piston together in a predetermined position pressed. After that, only the core will go against that elastic part pressed so that the core with one  predetermined distance from the valve piston is. This predetermined distance corresponds to the desired one Width of the air gap. The core is in this position fixed. This allows an adequate air gap with a predetermined width between the valve piston and the core.

The known one described above Recruitment process caused a problem that a additional part like the elastic part only for Setting the width of the air gap is required.

This increases the number of parts and the number of Sequences for the solenoid valve. Furthermore, the Adjustment process of the air gap between the valve piston and the core the complexes given above Operations.

The invention is therefore based on the object Method of assembling a solenoid valve of the type mentioned in such a way that the Solenoid valve during assembly with one predetermined one provided in the solenoid valve current supplied to the electromagnetic coil is operated, being a precise manufacture of the solenoid valve forming parts or the use of an additional Do not assemble part of solenoid valve required are.

It is another object of the present invention that Method of assembling the solenoid valve in such a way to design that the tolerance in the pressure force of the  Valve piston has no influence on the function and Effectiveness of the solenoid valve.

To solve the above problems is according to one Aspect of the present invention a method provided for assembling a solenoid valve with one between a first position and a second Position movable valve piston, the valve piston is pressed against the first position by means of a spring, and the valve piston by means of a electromagnetic coil generated electromagnetic Force in the direction of the second position against the medium the spring pressure force is moved, which Procedure includes the following steps:

• a) supplying a first current to the electro magnetic coil for generating the on the valve piston acting electromagnetic force,
• b) moving the valve piston in the direction of the second Low speed position, and
• c) determining the first position of the valve piston in Dependence on a third position of the valve piston, from which the valve piston towards the second Position is moved at a speed that is greater than the low speed due to the by the first current generated electromagnetic force.

According to the invention specified above, the Solenoid valve assembled during the first stream  actually determining the electromagnetic coil an initial position of the valve piston is supplied. The Starting position that corresponds to the first position determines if the valve piston actually occurs as a result the electromagnetic generated by the first current Power moves. Here, the valve piston by means of electromagnetic force generated by the first current moves, when the valve piston has reached the third position. Accordingly, the assembled solenoid valve clearly by supplying a current that is equal to or is greater than the first current. That is, the Solenoid valve can be operated clearly when on electro acting the valve piston in step a) magnetic force is set to be smaller than that generated in practical use is electromagnetic force.

According to one embodiment, the third position determined when a first pulsating voltage is applied to the Connections of the electromagnetic coil is detected. The first pulsating voltage is due to a movement of the Valve piston from the third position to the second position generated. The first pulsating voltage can be by means of one connected to the electromagnetic coil Voltage monitoring device can be detected.

In step b) the valve piston can be operated by means of a Compressive force are moved via a valve seat part is exercised. The valve seat part is in contact with the Valve piston in the first position when assembling of the solenoid valve has been completed. Of the  Valve piston is generated by means of the spring Compressed force pressed against the valve seat part, so that Solenoid valve is placed in a closed state. The voltage monitoring device gives a pressure End signal to end the movement of the Valve seat part when the first pulsating voltage is detected.

Furthermore, the method according to the invention can do the following Have steps:

• e) supplying a second current to the electro magnetic coil before performing step a) Holding the valve piston in the second position,
• f) gradually reducing the second stream,
• c) holding a value of the second current when the Valve piston starts moving from the second position in succession away from the pressure force exerted by the spring move, and
• d) setting the first current to a value which is in Depending on the value held in step c) determined is.

According to the invention, therefore, before feeding the first Stroms the second current of the electromagnetic coil fed so that the valve piston against the pressure force the spring is held at the second position. Of the second stream is then continuously reduced and the  The valve piston eventually moves due to the pressure force the spring away from the second position. The value of the second current (hereinafter referred to as return current), when the valve piston moves away from the second Position begins, depends on the strength of the Compressive force at the second position. The first stream is determined depending on the return current. So is that Compressive force of the spring is greater than a predetermined Design force, then the first current can be increased will. In contrast, the first current can be decreased be when the compressive force is weaker than the predetermined Interpretative power is. So the first position can always at the same distance from the second position can be set when the pressure force due to Tolerances of the spring is changeable. Therefore, each points solenoid valve assembled by this method the same distance between the first and the second Position on. Thus, the same path of movement of the Valve piston can be set for each solenoid valve.

The return current can be held if a second pulsating voltage across the terminals of the electro magnetic coil is detected. The second pulsating Voltage is caused by the valve piston moving away from the second position.

Advantageous refinements are in the subclaims characterized the invention.

The invention is described below with reference to the Drawing explained in more detail. Show it:  

Fig. 1 is a graphical representation of a solenoid valve and an assembly jig for illustrating an assembly method according to the first embodiment,

Fig. 2 is a graph of changes in the width of an air gap G, a magnetic flux Φ and an electromotive force V as a function of time,

Fig. 3 is a partially sectioned side view of an actuator of an anti-lock braking system in which an assembled according to the process solenoid valve is used,

Fig. 4 is a block diagram of a measuring apparatus for measuring a minimum operating current of the solenoid valve,

Fig. 5 is a graph showing a relationship between an electromagnetic force F _E and a width G of an air gap with respect to various settings of a coil supplied currents I,

Fig. 6 is a graphical representation of a solenoid valve and a device for assembling Ver anschaulichung an assembly method according to a second embodiment,

Fig. 7 is a block diagram of a measuring device shown in Fig. 6, and

Fig. 8 is a flowchart of a control program processed by means of a control device shown in Fig. 7.

A first embodiment will now be described with reference to FIG. 1. Fig. 1 illustrates a solenoid valve and an assembling device for explaining an assembling method according to the first embodiment. In Fig. 1, the assembly device for performing the assembly method according to the first embodiment includes a setting coil 10 , a voltage monitoring device 12 , a constant current source 14 , a servo motor control device 16 , a servo motor 18 , a ball screw 20 and a work table 22nd

The adjustment coil 10 includes a hollow coil around which a lead wire is wound. The wound around the coil conductor wire comprises N _O-turns. The lead wire is surrounded by a magnetic material. The adjustment coil has two terminals 10 a and 10 b, each of which is connected to the corresponding ends of the lead wire. The connections 10 a and 10 b are each connected to the positive and negative connections 12 a and 12 b of the voltage monitoring device 12 . The terminals 10 a and 10 b are also connected to the positive and negative terminals 14 a and 14 b of the constant current source 14 .

The voltage monitoring device 12 monitors the voltage across the connections 10 a and 10 b. The voltage monitoring device 12 outputs a pressure termination signal (described below) to the servo motor control device 16 when a pulsating voltage signal is detected at the terminals 10 a and 10 b.

The constant current source 14 supplies the setting coil 10 with a constant current via the connections 10 a and 10 b. An input impedance between the connections 14 a and 14 b of the constant current source 14 is set to a sufficient level for adaptation to a high-frequency input signal.

The servo motor controller 16 supplies the servo motor 18 with an appropriate drive signal when a start signal is input from a start switch (not shown in the figure). The drive signal is continuously supplied until the pressure termination signal is input from the voltage monitoring device 12 . The servo motor 18 is driven while the drive signal is supplied from the servo motor control device 16 , whereby the ball screw 20 is driven. If the ball screw 20 rotates, the end of the ball screw 20 moves downward according to FIG. 1. Thus, in the assembly device shown in FIG. 1, the ball screw 20 moves downward when the start switch is switched on and until the pressure end signal is emitted by the voltage monitoring device 12 , that is to say until the pulsating voltage signal is formed at the terminals 10 a and 10 b of the setting coil 10 becomes.

According to Fig. 1 22, the work table to a through hole 22 a. A tube 24 , which forms a basic component of the solenoid valve, is inserted into the through opening 22 a and a central opening of the adjustment coil 10 . The tube 24 forms a cylindrical part, one end of which is closed and the other end of which is open. The open end of the tube 24 is flared to form a conical part 24 a. A region of the through opening 22 a for receiving the conical part 24 a is correspondingly conical. Thus, the tube 24 is held in a predetermined position in the through hole 22 a when the tube 24 is inserted into the through hole 22 a.

A core 26 formed of magnetic material is inserted into the tube 24 . The core 26 is fastened in the tube 24, for example by caulking. The core 26 comprises a spring 25 . One end of the spring 25 protrudes from the core 26 for pressing the valve piston 28 arranged on the core 26 . The valve piston comprises a slider 28 a and a rod 28 b attached to the slider 28 a. The slider 28 a has a diameter that is slightly smaller than the inner diameter of the tube 24 , so that the slider 28 a can move within the tube 24 . If the valve piston 28 is inserted into the tube 24 , the valve piston 28 is pressed by the spring 25 , whereby an air gap with a width G _{O is formed} between the valve piston 28 and the core 26 .

A guide piece 30 is loosely placed on the rod 28 b for guiding the rod 28 b in the longitudinal direction of the tube 24 . The guide piece 30 is inserted into the tube 24 through the open end by means of a press fit. The guide piece 30 comprises a cylindrical part 30 c with lateral holes 30 a and 30 b. A valve seat part 32 is arranged by means of a press fit in the cylindrical region 30 c. The valve seat member 32 has a fluid passage 32 a at its center, and a valve seat surface is formed on the lower surface of the valve seat member 32 . One end of the rod 28 b of the valve piston 28 is adapted to the valve seat surface of the valve seat part 32 for opening or closing the fluid passage 32 a. Thus, the rod 28 b forms a valve body of the solenoid valve.

If the valve piston 28 is pressed in the direction of the valve seat part 32 by means of the spring 25 , then the end of the rod 28 b closes the fluid passage 32 a. As a result, a connection between the fluid passage 32 a and each of the side holes 30 a and 30 b is broken. This corresponds to a closed state of the solenoid valve. In contrast, if a magnetic field is generated in the coil 26 and the valve piston 28 , the valve piston 28 is attracted by the core 26 as a result of a magnetic force. If the magnetic force is greater than the compressive force of the spring 25 , the valve piston 28 is moved in the direction of the core 26 . Therefore, the end of the rod 28 b is lifted off the valve seat surface of the valve seat part 32 . This opens the fluid passage 32 a, so that the fluid passage 32 a is connected to each of the side holes 30 a and 30 b. This corresponds to an open state of the solenoid valve. Thus, the structure in tube 24 results in a solenoid valve when a coil for generating a predetermined magnetic field through core 26 and valve piston 28 is disposed around tube 24 .

With a solenoid valve constructed in this way, reliable operation is achieved by generating a stable magnetic force between the core 26 and the valve piston 28 . To achieve the stable magnetic force, it is necessary to determine and check the width G _{O of} the air gap very precisely. The appropriate width G _O is determined by a position of the valve piston 28 in the tube 24 . This means that the position of the valve piston 28 with respect to the core 26 is determined by the depth of the press fit of the valve seat part 32 . Thus, if the pressing-in process of the valve seat part 32 is ended exactly in a position with which the predetermined width G _{O is formed} between the valve piston 28 and the core 26 , then a solenoid valve with desired and reliable properties can be manufactured.

In the assembly device according to FIG. 1, the ball screw 20 is used to press the valve seat part 32 into the guide piece 30 . The ball screw 20 is driven by the servo motor 18 , which in turn is controlled by the servo motor control device 16 . If the operation of the servo motor 18 is thus ended when the pulsating voltage signal is determined at the connections 10 a and 10 b of the setting coil 10 , then an appropriate width of the air gap can be achieved.

If the setting coil 10 is supplied with a constant current I _O , then a magnetic field corresponding to a magnetomotive force N _O · I _{O is} generated in the setting coil 10 . In this case, since the magnetic gap Rm is formed from the sum of the magnetic resistance of the core 26 , the valve piston 28, and the air gap, a magnetic resistance Rm of the magnetic field formed by the adjustment coil 10 is decreased as the width of the air gap becomes smaller. Thus, the magnetic resistance Rm is reduced to the extent that the valve seat part 32 is pressed into the guide piece 30 .

In a corresponding manner, the magnetic flux Φ = _NO · I _O / Rm passing through the core 26 and the valve piston 28 is increased to the extent that the valve seat part 32 is pressed further into the guide piece 30 . Since the electromagnetic force acting on the valve piston 28 is proportional to the magnetic flux Φ, the electromagnetic force acting on the valve piston 28 is increased when the valve seat part 32 is pressed further into the guide piece 30 . Thus, the air gap between the core 26 and the valve piston 28 is formed at the beginning of the press-in process of the valve seat part 32 , even if the constant current I _O flows in the setting coil 10 . This is due to the fact that the pressure force of the spring 25 is greater than the electromagnetic attraction force generated by the setting coil 10 . With the progress of the press-in process and with the sufficient reduction in the width of the air gap, the electromagnetic attraction force becomes greater than the pressure force of the spring 25 . As a result, the valve piston 28 is tightened toward the core 26 so that the valve piston 28 contacts the core 26 .

According to the present embodiment, the number of turns N _{O of} the adjustment coil 10 , the constant current I _O , which is supplied from the constant current source 14 , and a spring constant of the spring 25 are determined such that the valve piston 28 its movement towards the core 26 due to the Electromagnetic attraction begins when the width of the air gap is equal to a predetermined width G _O. At this time, the relationship between the pressing force and the electromagnetic attraction force generated by the adjustment coil 10 described above is reversed after the width of the air gap has reached G _O. Thus, if the valve seat 32 is pressed in when the valve piston 28 moves rapidly toward the core 26 against the urging force of the spring 25 and contacts the core 26 while the constant current I _{O is being} supplied to the adjustment coil 10 , then solenoid valves having the this method were assembled, can be achieved, which can be activated at the same constant current I _O.

Fig. 2 shows a graphical representation of changes in the width of the air gap G, the magnetic flux Φ and an electromotive force V generated between the connections 10 a and 10 b as a function of time. In Fig. 2, the press-in process of the valve seat part 32 is started at time t _O and ended at time t 1. Decreases as shown in FIG. 2 (A), the width of the air gap G, then the magnetic resistance of the magnetic circuit to the magnetic flux Φ also begins to decrease. As a result, the magnetic flux Φ begins to decrease at time t _O according to FIG. 2- (B). Reaches the width G of the air gap at time t 1 the value G _O , then the width G of the air gap decreases very quickly, as shown in Fig. 2- (A). This is caused by a rapid increase in the magnetic flux Φ at the time t₁ shown in Fig. 2- (A). If there is a rapid change in the magnetic flux Φ in the magnetic circuit of the adjustment coil 10 , then an oppositely directed electromotive force V is formed in the adjustment coil 10 to limit the change in the magnetic flux Φ. Thus, a pulsating voltage signal at the time t 1 between the terminals 10 a and 10 b of the setting coil 10 is determined.

Thus, the pressing process of the valve seat part 32 is terminated at the time t 1, then an appropriate air gap with a width G _{O is formed} between the valve piston 28 and the core 26 when no current is supplied to the adjustment coil 10 . In this case, the width of the air gap G is controlled so that each solenoid valve assembled by the assembling device according to the present embodiment is activated when the same magnetic force N _O · I _{O is} applied, that is, the same current I _{O is} supplied to the solenoid valve coil becomes. This can be achieved in that the magnetic permeability of the core 26 and the valve piston 28 and the spring constant of the spring 25 can be varied within permitted tolerances. This is in contrast to the known method in which a width of the air gap is set to come as close as possible to a target width, and the solenoid valve thus constructed cannot be activated at the same current when the magnetic permeability or the Spring constant are changeable. Thus, the exemplary embodiment specified above has advantages over the known method.

In the present embodiment, the magnetomotive force N _O · I _O generated by the adjustment coil 10 is set to be half or one third of the magnetic force actually generated by the coil provided in the assembled solenoid valve. Thus, the solenoid valve assembled by the assembly device according to the present embodiment can be activated even when a relatively large load is applied to the valve piston 28 due to a liquid pressure in the practical application. In addition, the press-in process of the valve seat part 32 can be ended when the valve piston 28 is pressed in further from the position corresponding to the time t 1. Thus, in the absence of a magnetic force generated by the adjustment coil 10 , the position of the valve piston 28 may be closer by a predetermined distance than the position at which the valve piston 28 is attracted to the core 26 when a current I _{O is} supplied to the adjustment coil 10 .

The parts of the solenoid valve assembled in the tube 24 shown in FIG. 1 are applied to a solenoid valve of a hydraulic circuit of an anti-lock braking system (ABS) of a vehicle. The solenoid valve arranged in the tube is inserted into an aluminum housing 42 of an ABS actuator 40 according to FIG. 3. The ABS actuator 40 includes an ABS pump 44 , a hydraulic circuit unit 46, and a coil unit 48 . The ABS pump 40 is a known hydraulic pump. The hydraulic circuit unit 46 includes passages for brake fluid. The coil unit 48 includes a plurality of drive coils for corresponding solenoid valves that control the flow of the brake fluid in the hydraulic circuit unit 46 . It should be noted that Fig. 3 shows only one of the solenoid valves contained in the ABS actuator 40 . The solenoid valve shown in FIG. 3 is hereinafter referred to as solenoid valve 50 , and the spool for driving the solenoid valve 50 is referred to as drive spool 52 .

The tube 24 of the solenoid valve 50 is attached to the hydraulic circuit unit 46 . The conical part 24 a of the tube 24 is fastened in an opening arranged in the hydraulic circuit unit 46 by means of a support ring. The valve seat member 32 is inserted into the opening of the hydraulic circuit unit 46 such that the solenoid valve 50 opens a hydraulic circuit formed in the fluid passage unit 46 and closes.

The drive coil 52 comprises N₁ turns of the windings and is arranged around the tube 24 after the tube 24 is attached to the hydraulic circuit unit 46 . If the drive coil 52 is supplied with a current I 1, then a magnetic force corresponding to a magnetomotive force N 1 · I 1 is exerted on the valve piston 28 .

As part of the assembly process for a solenoid valve described above, the adjustment coil 10 is used in the assembly device of FIG. 1. However, since the drive coil 52 is last inserted into the tube 24 , the adjustment process of the air gap G can be carried out after the drive coil 52 is inserted into the tube 24 . Thus, when the solenoid valve 50 is assembled, the drive coil 52 is first inserted before the tube 24 is placed in the hydraulic circuit unit 46 . In this case, the solenoid valve 50 is assembled with an air gap not set. The width of the air gap is then adjusted using the same method while a current I₂ = I _O · N _O / N₁ is supplied to the drive coil 52 . In this method, the air gap is adjusted in place using the drive coil 52 , and further differences in the characteristic of the drive coil 52 can be eliminated. With these methods, reliable operation of the solenoid valve can be obtained since the solenoid valve 50 is operated by the drive coil 52 , which is normally used. Thus, the solenoid valve 50 is not necessarily subjected to a minimum actuation current test to measure a minimum actuation current to actuate the solenoid valve 50 .

As described above, the assembly process can be performed using either the adjustment coil 10 or the drive coil 52 . Although the valve seat part 32 is pressed into the guide piece 30 provided in the tube 24 by means of the ball screw 20 , the guide piece 30 can also be pressed against the valve seat part 32 by means of the tube 24 .

When assembling a solenoid valve 50 using the assembly device of FIG. 1, a minimum actuation current should be measured to check whether the solenoid valve can be actuated after the drive coil 52 is inserted into the tube 24 . A method of measuring the minimum actuation current of the solenoid valve 50 will now be described.

FIG. 4 shows a block diagram of a measuring device 60 for measuring the minimum actuation current of the solenoid valve 50 . In FIG. 4, the simplified solenoid valve 50 comprises the same parts as shown in FIG. 3.

A positive terminal 52a of the solenoid valve 50 is connected to a power supply terminal 60 a of the measuring device 60th A negative terminal 52 b of the drive coil of the solenoid valve 50 is connected to a ground terminal 60 b of the measuring device 60 . In the measuring device 60 , a variable power source 64 gradually increases an output voltage when a command to start the measurement is issued from a controller 62 . The variable power source 64 is connected to the positive terminal 60 a via a current detection device 66 and a choke coil 68 . The choke coil 68 is provided for increasing an impedance measured between the supply voltage connection 60 a and the ground connection 60 b, in particular for a high-frequency input signal. Furthermore, a comparator 72 is connected to the supply voltage connection 60 a via a high-pass filter 70 . If the output voltage of the variable power source 64 is gradually increased, the choke coil 68 does not form a large load. Thus, the gradually increasing voltage is supplied to the terminal 52 a of the solenoid valve 50 . At this time, no sudden change in voltage is detected by comparator 72 . In contrast, if a rapid voltage change is supplied to the supply voltage connection 60 a, then a rapid voltage change is determined by the comparator 72 as a result of the choke coil 68 .

If a supply voltage provided by the variable power source 64 is gradually increased and the voltage at which the valve piston 28 is attracted by the core 26 is reached, then, as already stated above, a pulsating voltage is generated. In a corresponding manner, a rapid change in voltage is detected by means of the comparator 72 at the time when the solenoid valve 50 is activated or actuated. The comparator 72 supplies a detection signal to a display unit 74 when the sudden voltage change is detected. The display unit 74 is supplied with information relating to a current detected by the current detection device 66 . The display unit 74 holds the supplied current value and displays it when a signal from the comparator 72 is supplied to it. Thus, the minimum actuation current of the solenoid valve 50 can be measured in a simple and accurate manner by the measuring device 60 using a rapid voltage change, which is determined between the connections 52 a and 52 b of the solenoid valve 50 . The minimum actuation current of the solenoid valve 50 is displayed by means of the display unit 74 .

In known methods, the minimum actuation current of the solenoid valve 50 was measured by supplying a fluid to the fluid passage 32 a. In this state, a gradually increasing current is supplied to the drive coil 52 . It is determined that the solenoid valve 50 is actuated (opened) when the fluid flows from the side openings 30 a or 30 b. To carry out this method, it is necessary to provide a fluid supply device within the scope of the measuring device, by means of which the fluid can be supplied to the fluid passage of the solenoid valve 50 . This leads to a measuring device with large dimensions. Fluid outflow problems may also occur. Further, since the solenoid valve 50 needs to be brought into its own fluid connection state, it is necessary to provide a fluid connection device for each type of solenoid valve. Thus, a measuring device cannot process multiple types of solenoid valves. Furthermore, a high measuring accuracy due to a time delay of the fluid movement depending on the actuation of the solenoid valve cannot be achieved.

In contrast, in the measuring device 60 according to FIG. 4, no fluid is used to measure the minimum actuation current. Furthermore, the operation of the solenoid valve 50 is determined by an electrical signal with a quick response. Therefore, the measuring device 60 can avoid the above-mentioned problems of the known measuring methods.

A second embodiment will now be described described.

As stated above in connection with the first exemplary embodiment, solenoid valves can be produced which can be actuated with the same magnetomotive force N _O · I _O. If the magnetomotive force is formed in detail by the drive coil 52 , then a magnetic force F _{E is} generated which is greater than the pressure force F _S generated by the spring 25 . The magnetic force F _E is a function of the magnetomotive force N _O · I _O and the air gap of the width G _O. Since the magnetomotive force is constant, the magnetic force F _{E is represented} by a function of the width G _{O of} the air gap. According to the condition specified above, in which the relationship F _S <F _{E is} ensured, the width G _{O is determined} as a function of the pressure force F _{S of} the spring 25 . Thus the tolerance of the compressive force F _S causes a change in the width G _{O of} the air gap.

In the solenoid valve shown in Fig. 1, the amount of movement of the valve piston 28 is equal to the width G _{O of} the air gap. Thus, a distance between the end of the rod 28 b (valve body) of the valve piston 28 and the valve seat surface of the valve seat part 32 when the solenoid valve is in an open state is equal to the width G _{O of} the air gap. This means that the degree of opening of the solenoid valve is determined by the width G _{O of} the air gap. Since a pressure loss of the fluid flowing through the solenoid valve is determined by the degree of opening, it is desirable that the same width G _{O be provided} for each solenoid valve so that each solenoid valve has the same properties.

According to the second embodiment, the same width G _{O of} the air gap for each solenoid valve is set by setting a current I _O supplied to the adjusting coil 10 to a value corresponding to the pressing force generated by the spring 25 . The current I _O fulfilling these requirements can be calculated from a minimum current I 1 (hereinafter referred to as return current) which is supplied to the adjusting coil 10 for holding the valve piston 28 at a position (attracted position) in which the valve piston 28 contacts the core 26 .

FIG. 5 is a graph showing the relationship between the electromagnetic force F _E and the width G of the air gap with respect to different currents I supplied to the adjustment coil 10. As shown in FIG. 5, that on the valve piston 28 acting electromagnetic force F _E decreases as the width G of the air gap increases, and is rapidly increased as the width G of the air gap decreases. Furthermore, the electromagnetic force F _{E changes in} proportion to the current I supplied to the adjustment coil 10. Accordingly, the relationship indicated by the graph in FIG. 5 can be specified by means of a function F _E = I · f (G), where f ( G) is a function of the electromagnetic force F _E and the width G of the air gap.

Assuming that an air gap with the width G 1 is formed between the valve piston 28 and the core 26 when the valve piston 28 is attracted by the core 26 , the electromagnetic force F _E1 is represented by the following expression according to the above relationship.

F _E1 = I₁f (G₁) (1)

The minimum current I flowing through the setting coil 10 for holding the valve piston 28 in the tightened position corresponds to the return current I 1. Now flows the return current I₁ through the setting coil 10 , then the electromagnetic force exerted on the valve piston 28 F _{E1 is} equal to the pressure force F _S1 applied by the spring 25 (F _E1 = F _S1 ). The compressive force F _S1 can be given by the relationship F _S1 = K · L₁, where K is a spring constant of the spring 25 and L₁ is a deformation amount of the spring 25 when the valve piston 28 is in the tightened position. Expression ( 1 ) can be rewritten as follows:

F _S1 = KL₁ = I₁f (G₁) (2)

If the current I _{O is} supplied to the adjustment coil 10 when the width G _{O of} the air gap between the valve piston 28 and the core 26 is maintained, then an electromagnetic force F _E O is exerted on the valve piston 28 .

F _EO = I _O · f (G _O) (3)

In the above-mentioned first embodiment, the valve piston 28 must be moved toward the core 26 to stop the press-in operation of the valve seat part 32 when the width G of the air gap has become G _O when the electromagnetic force F _E becomes equal to F _EO . To move the valve piston 28 in the direction of the core 26 , the electromagnetic force F _EO must also be equal to the pressure force F _{SO of} the spring 25 when the electromagnetic force F _{E reaches} the value F _EO (F _EO = F _SO ).

It is now assumed that the valve piston 28 moves a distance S when the valve piston 28 moves from a state in which an air gap of width G _{O is} maintained to a state in which the valve piston 28 is in the tightened position has taken. A deformation (ie a length) L _{O of} the spring 25 is represented by the expression L _O = L₁-S if the width G _{O is} maintained. Accordingly, the compressive force applied by the spring 25 while maintaining the width G _{O can be represented} by the expression F _SO = K · (L₁-S). The above expression ( 3 ) can be rewritten as follows.

F _SO = K · (L₁-S) = I _O · f (G _O ) (4)

The distance S used in equation (4) is negligibly small in relation to the deformation (length) L 1. It can thus be assumed that the compressive force F _S1 represented by equation (2) is equal to the compressive force F _SO indicated by equation (4). Thus, the following equation can be obtained from equations (2) and (4).

I _O = I₁ · {f (G₁) / f (G _O )} (5)

The width G₁ of the air gap is a value determined by the dimensions of the parts forming the solenoid valve 50 when the valve piston 28 is in the tightened position. The width G₁ can be controlled with high accuracy. The width G _O forms a target value when the solenoid valve 50 is assembled so that the width G _O does not vary. Thus, the functions f (G₁) and f (G _O ) can be treated as a constant. In equation (5), the expression {f (G₁) / f (G _O )} can therefore be replaced by a constant a.

In the first embodiment, the current I _O supplied to the adjustment coil 10 to make the width G of the air gap match the value G _{O can be given} by the following equation using the return current I 1 measured for the solenoid valve to be assembled and the predetermined constant a.

I _O = I₁a (6)

Thus, the width G of the air gap can be set exactly to the value G _O without being influenced by tolerances in the dimensioning of the spring 25 , by previously obtaining the return current I 1 and determining the current I _O on the basis of the return current I 1.

Fig. 6 illustrates a solenoid valve and an assembling device for illustrating the method of assembly according to a second embodiment. In Fig. 6, the parts which are already shown in a similar manner in Fig. 1 are denoted by the same reference numerals, so that a description of these parts is not necessary.

The assembly device shown in FIG. 6 comprises a measuring device 70 which is connected to the connections 10 a and 10 b of the setting coil 10 . The measuring device 70 supplies the setting coil 10 with a gradually increasing voltage. The measuring device 70 also detects a pulsating voltage that is formed between the terminals 10 a and 10 b. The measuring device 70 is connected to a sequencer 80 , which controls the servo motor control device 16 and an operation of the assembly device. Signals indicating the operating state of the assembly device are transmitted between the measuring device 70 and the sequence control device 80 . In the same way as in the voltage monitoring device 12 according to FIG. 1, the measuring device 70 emits a pressure termination signal to the servo motor control device 16 when the pulsating voltage is determined between the connections 10 a and 10 b of the setting coil 10 .

Fig. 7 shows a block diagram of the measuring device 70th In Fig. 7, the parts which are already shown in the same way in Fig. 4 are designated by the same reference numerals, so that a description of these parts is not necessary. As shown in FIG. 7, the parts of the measuring device 70 are the same parts that are already shown in connection with the measuring device 60 in FIG. 4, with the exception of a control device 74 . The control device 74 is connected to the variable power source 64 , the current detection device 66 and the comparator 72 . The servo motor control device 16 and the sequence control device 80 are also connected to the control device 74 . The control device 74 controls the variable power source as a function of the signals which are supplied by the current detection device 66 , the comparator 72 and the sequence control device 80 . The controller 74 outputs a print completion signal to the servo motor controller 16 and the sequencer 80 .

Fig. 8 shows a flow diagram of means of the control means 74 to process control program. The control program shown in FIG. 8 begins when a start signal is transmitted from the sequence control device 80 to the control device 74 after the start of an assembly process.

After the control program shown in FIG. 8 is started, a sequence for supplying an initial current I _{ST is} carried out in step 100. The initial current I _{ST is set} to a value which is sufficient to attract the valve piston 28 through the core 26 under the condition that the valve seat part 32 is not fully pressed into the guide piece 30 , ie a large air gap between the valve piston 28 and the Core 26 is present. Thus, when the initial current I _{ST is} supplied to the setting coil 10 , the valve piston 28 is held in an appropriate position.

In step 102, the initial current I _{ST is} slightly reduced. In step 104, it is determined whether or not a predetermined pulsating voltage is detected by the measuring device 70 . If it is determined that the predetermined pulsating voltage has not yet been determined, the program goes back to step 102 and repeats steps 102 and 104.

During the above steps, the valve piston 28 is held at a predetermined position immediately after the initial current I _{ST is} supplied to the adjustment coil 10 . Thereafter, the initial current I _{ST is} repeatedly reduced, whereupon the electromagnetic force acting on the valve piston 28 gradually decreases. Finally, the electromagnetic force F _E becomes equal to the pressing force F _{S of} the spring 25 , and the pressing force F _S becomes larger than the electromagnetic force F _E. At this point, the valve piston 28 moves away from the core 26 . Here, since the movement of the valve piston 28 is fast, a large change in the magnetic flux through the adjustment coil 10 occurs. As a result, an electromotive force is generated in the adjustment coil 10 . Then the measuring device 70 detects the pulsating voltage which is generated (generated) between the connections 10 a and 10 b of the setting coil 10 as a result of the electromotive force.

Correspondingly, steps 102 and 104 are carried out repeatedly as part of the program, while the valve piston 28 is in the position attracted by the core 26 . Step 104 denotes a determination process as to whether or not the valve piston 28 has moved away from the core 26 due to the pressing force of the spring 25 .

If it is determined in step 104 that the predetermined pulsating voltage is detected, then the program flow goes to step 106. In step 106, a value of the current I currently being fed to the setting coil 10 is stored as a return current I 1. Then in step 108 the current I _O is calculated by multiplying the return current I 1 by the constant a. The current I _O is supplied to the adjustment coil 10 when the valve seat part 32 is pressed into the guide piece 30 (see equation (6)).

After the calculation of the current I _O , a sequence for supplying the current I _O to the setting coil 10 is carried out in step 110. In step 112, a command to start the press-in process of the valve seat part 32 to the sequence control device 80 is issued. The sequence control device 80 then sends a start command to the servo motor control device 16 . As a result, the servo motor 18 is operated to press the valve seat part 32 into the guide piece 30 .

In the measuring device 70 , it is determined in step 104 after the start command for the press-in process has been issued by the sequence control device 80 whether the pulsating voltage is determined or not. If, as described above, the valve piston 28 is suddenly moved to the attracted position, then a pulsating voltage due to an electromotive force between the terminals 10 a and 10 b of the adjusting coil 10 is determined. Thus, step 114 is repeated until the valve piston 28 suddenly moves in the direction of the core 26 .

If the valve piston 28 moves in the direction of the core 26 , the pulsating voltage is determined by the measuring device 70 and the determination in step 114 becomes positive. The program flow thus goes to step 116 for outputting the print completion signal to the servo motor control device 16 . Then, in step 118, a process for switching off the current I flowing through the setting coil 10 is carried out and the program is ended.

As described above, the appropriate width G _{O of} the air gap is set by the press-in operation of the valve seat member 32 depending on the current I _O calculated from the return current I 1. The width of the air gap of each solenoid valve assembled by the assembling method according to the second embodiment is always set to the predetermined width G _O without being affected by the tolerances of the spring 25 . It should be noted that the value of the constant a can be set such that the magnetomotive force N _O · I _{O is} approximately half or one third of the electromagnetic force generated in actual operation.

Although the adjustment coil 10 has been used for the assembly process in the above-described embodiments, a drive coil that is inserted into the solenoid valve when assembled can be used in place of the adjustment coil 10 .

Thus, the solenoid valve 50 can be operated with a predetermined current supplied to an electromagnetic coil 52 without the parts forming the solenoid valve having to be manufactured precisely or without additional parts being required for assembly. The solenoid valve 50 includes a valve piston 28 that is movable between first and second positions. The valve piston 28 is pressed against the first position by means of a spring. The valve piston 28 is moved in the direction of the second position against an urging force of the spring by an electromagnetic force generated by means of an electromagnetic coil 52 . A first current is supplied to the electromagnetic coil 52 to generate an electromagnetic force acting on the valve piston 28 . The valve piston 28 is then moved towards the second position at low speed. The first position of the valve piston 28 is determined in dependence on a third position of the valve piston 28 , from which the valve piston 28 moves in the direction of the second position at a speed which is greater than the low speed, as a result of the electromagnetic force generated by the first current emotional.

Claims (11)

1. A method of assembling a solenoid valve ( 50 ) with a valve piston ( 28 ) which is movable between a first and a second position, the valve piston ( 28 ) being pressed against the first position by means of a spring ( 25 ), and the valve piston ( 28 ) is moved in the direction of the second position counter to the compressive force generated by the spring ( 25 ) by an electromagnetic force generated by means of an electromagnetic coil ( 10 ; 52 ),
the method being characterized by the steps:

• a) supplying a first current to the electromagnetic coil ( 10 ; 52 ) to generate the electromagnetic force acting on the valve piston ( 28 ),
• b) moving the valve piston ( 28 ) in the direction of the second position by means of a first speed, and
• c) determining the first position of the valve piston ( 28 ) as a function of a third position of the valve piston ( 28 ), the valve piston ( 28 ) moving from the third position towards the second position as a result of the electromagnetic force generated by the first current Speed moves that is greater than the first speed.

2. The method according to claim 1, characterized by determining the third position when a first pulsating voltage is determined at the connections ( 10 a, 10 b; 52 a, 52 b) of the electromagnetic coil ( 10 ; 52 ), the first pulsating voltage is generated by the movement of the valve piston ( 28 ) from the third position to the second position. 3. The method according to claim 2, characterized by the detection of the first pulsating voltage by means of a voltage monitoring device ( 12 ) connected to the electromagnetic coil ( 10 ; 52 ). 4. The method according to claim 3, characterized in that the valve piston ( 28 ) is moved in step b) by a force acting on a valve seat part ( 32 ) touching the valve piston ( 28 ) in the first position when the assembly of the solenoid valve ( 50 ) is completed, the valve piston ( 28 ) being pressed against the valve seat part ( 32 ) by a pressure force generated by the spring ( 25 ), so that the solenoid valve ( 50 ) is brought into a closed state, and wherein the voltage monitoring device ( 12 ) outputs a pressure termination signal to terminate the movement of the valve seat part ( 32 ) when the first pulsating voltage is detected. 5. The method according to claim 1, characterized in that during the assembly of the solenoid valve ( 50 ), the electromagnetic force generated in step a) is smaller than the electromagnetic force generated after assembly. 6. The method of claim 1, further characterized by the steps:

• d) supplying a second current to the electromagnetic coil ( 10 ; 52 ) before carrying out step a) for holding the valve piston ( 28 ) in the second position against the compressive force of the spring ( 25 ),
• e) gradually reducing the second stream,
• f) maintaining a value of the second current when the valve piston ( 28 ) begins to move away from the second position due to the compressive force generated by the spring ( 25 ), and
• g) setting the first current to a value which is determined as a function of the value held in step f).

7. The method according to claim 6, characterized in that the value of the second current is maintained when a second pulsating voltage is detected at the terminals of the electromagnetic coil ( 10 ; 52 ), the second pulsating voltage due to the movement of the valve piston ( 28 ) is generated from the second position. 8. The method according to claim 7, characterized by detecting the second pulsating voltage by means of a voltage monitoring device ( 12 ) connected to the electromagnetic coil ( 10 ; 52 ). 9. The method according to claim 7, characterized in that the third position is determined when a first pulsating voltage at the terminals ( 10 a, 10 b; 52 a, 52 b) of the electromagnetic coil ( 10 ; 52 ) is detected, wherein the first pulsating voltage is generated as a result of movement of the valve piston ( 28 ) from the third to the second position. 10. The method according to claim 9, characterized in that the valve piston ( 28 ) in step b) is moved by a pressure force acting on a valve seat part ( 32 ) touching the valve piston ( 28 ) at the first position when the assembly of the solenoid valve ( 50 ) is completed, the valve piston ( 28 ) being pressed against the valve seat part ( 32 ) by a pressure force generated by the spring ( 25 ), so that the solenoid valve ( 50 ) is brought into a closed state, and the movement of the valve seat part ( 32 ) is terminated when the first pulsating voltage is detected. 11. The method according to claim 6, characterized in that during the assembly of the solenoid valve ( 50 ), the electromagnetic force generated in step a) is smaller than the electromagnetic force generated after the assembly.