Motor-operated flow control valve and exhaust gas recirculation control valve for internal combustion engine

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MOTOR-OPERATED FLOW CONTROL In the above motor-operated flow control valve, WALVE AND EXHAUST GAS preferably, the rotor unit comprises an integral magnet, a RECIRCULATION CONTROL VALVE FOR Single ball bearing and a resin-made magnet holder for INTERNAL COMBUSTION ENGINE Supporting the magnet and the ball bearing, the magnet, the

BACKGROUND OF THE INVENTION

ball bearing and the magnet holder being formed into an integral structure. With this feature, the weight of the rotor 1. Field of the Invention unit can be So reduced as to make the Specific frequency of The present invention relates to a motor-operated flow the rotor unit have a value not resonating with engine control valve Suitable for use in internal combustion vibration.

engines, and more particularly to an exhaust gas recircula Further, to Solve the above objects, according to the tion control valve for internal combustion engines. present invention, in a motor-operated flow control valve 2. Description of the Related Art comprising a rotor Shaft reciprocating with rotating motion Conventional motor-operated flow control valves have of a motor, and a valve head movable to open and close an Such a known Structure that a rotor unit of a motor for 15 orifice with the reciprocating motion of the rotor Shaft, a driving a valve is rotatably Supported by a pair of ball rotor unit of the motor comprises an integral magnet, a bearings disposed in upper and lower portions of the rotor Single ball bearing and a magnet holder for Supporting the unit. magnet and the ball bearing, the ball bearing having an outer Those conventional motor-operated flow control valves race heldoccurred fixed under a preload. With this feature, frictional are disclosed in, for example, U.S. Pat. Nos. 4,432,318, torque reduced and upon Starting the rotor unit to rotate is torque required for the motor to produce at the 4,381,747, 4,378,767, 4,378,768, 4.414,942, 4,397.275 and Start-up is made Smaller.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS In the conventional motor-operated flow control valves, 25 FIG. 1 is a vertical Sectional view of a push-opened, because the rotor unit of the motor is rotatably Supported by motor-operated flow control valve for internal combustion two ball bearings disposed in upper and lower portions of the engines according to one embodiment of the present inven rotor unit, there inevitably occurs relative wobbling between tion.

inner and outer races of each of the ball bearings. When used FIG. 2 is a Schematic view showing a construction of a in internal combustion engines, therefore, Such a motor device for measuring the resonance frequency of a rotor unit operated flow control valve tends to resonate with rotative of a motor in the motor-operated flow control valve accord Vibration of the internal combustion engine, resulting in a ing to one embodiment of the present invention. problem that the useful life of the valve itself and a device FIG. 3 is a graph showing a measured result of the including the valve is shortened. resonance frequency of the rotor unit of the motor in the To lessen the relative wobbling between the inner and 35 motor-operated flow control valve according to one embodi outer races, there is also known a structure that the rotor unit ment of the present invention. is Supported by two bearings under a State where a preload FIG. 4A is a view for explaining a preload applied to a ball is applied to press the rotor unit in one direction. bearing of the rotor unit of the motor in the motor-operated Specifically, for example, an outer race of one ball bearing flow control valve according to one embodiment of the is Supported by a rigid body Such as a housing, and an outer 40 present invention, and race of the other ball bearing is pressed by a Spring Such as a Spring washer or a coil Spring. With Such a structure, to FIG. a 4B is a similar view for explaining a preload applied ball bearing in the prior art.

however, because the preload generated by the Spring washer or the like is applied to balls of the ball bearing as FIG. 5 is an exploded perspective view of parts of the well, frictional torque occurred upon Starting the rotor unit 45 motor-operated flow control valve according to one embodi to rotate is increased. This results in another problem that the ment of the present invention. motor is required to produce a larger torque at the Start-up. DESCRIPTION OF THE PREFERRED An object of the present invention is to provide a motor EMBODIMENT operated flow control valve for internal combustion engines which is less affected by vibration and has a longer useful 50 A motor-operated flow control valve for internal combus life. tion engines according to an embodiment of the present Another object of the present invention is to provide a FIGS. 1 towill invention

be described hereunder with reference to motor-operated flow control valve for internal combustion engines which does not require a motor to produce a larger FIG. 1 is a vertical Sectional view of a push-opened, torque at the Start-up. 55 motor-operated flow control valve according to an embodi To achieve the above objects, according to the present ment of the present invention.

invention, in a motor-operated flow control valve compris The motor-operated flow control valve according to this ing a rotor shaft reciprocating with rotating motion of a embodiment is employed as an EGR (Exhaust Gas motor, and a valve head movable to open and close an orifice Recirculation) valve for internal combustion engines. A with the reciprocating motion of the rotor shaft, Specific 60 Valve body 1 defines an gas passage therein. Exhaust gas frequency of a rotor unit of the motor is Set to be higher than from an internal combustion engine flows into the valve the Secondary vibration frequency of rotation of a 4-cycle body 1 through an inlet 1a and then flows out through an internal combustion engine. With this feature, when applied outlet 1b for return to the intake pipe side of the internal to any of internal combustion engines having four, Six and combustion engine.

eight cylinders, the motor-operated flow control valve will 65 An orifice member 3 is Screwed into the gas passage not give rise to a resonance phenomenon and therefore has between the inlet 1a and the outlet 1b. A valve shaft 2 having a longer useful life. a valve head 2a provided at one end extends through a

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central opening (valve seat) formed in the orifice member 3 The construction of the motor 32 will be described below. So that an orifice is opened and closed by the valve head 2a. The stator unit of the motor 32 comprises a coil 19a housed A gas seal 6 is fixedly press-fitted in the valve body 1 and in a bobbin 22a and a coil 19b housed in a bobbin 22b. Serves to Seal off the exhaust gas flowing through the gas Magnetic fields are generated by Supplying electric currents passage against leakage. The valve shaft 2 is slidably to the coils 19a, 19b.

Supported by the gas Seal 6. A dust cover 31 is attached A yoke for forming a magnetic path has a C-shape in between the gas seal 6 and the valve body 1 to prevent Vertical Section, and is made up of a yoke 24 nearly in the foreign matters, Such as carbon and oil contained in the form of a hollow annulus cylinder and two disk-shaped exhaust gas, from adhering to a gap between an outer yokes 23a, 23b. The bobbin 22a including the coil 19a is circumferential Surface of the valve shaft 2 and the gas Seal 1O disposed in a Space defined by the yoke 24 and the yoke 23a, 6. while the bobbin 22b including the coil 9b is disposed in a A plate 7 is connected by caulking to an upper end of the space defined by the yoke 24 and the yoke 23b. Between valve shaft 2 through a joint 30. A spring 8 is interposed both the yokes 23a and 23b, a center plate 21 is disposed to between the plate 7 and the gas seal 6 to bias the plate 7 not only position the upper and lower yokes 23a, 23b, but upward. The valve shaft 2 joined to the plate 7 is thereby 15 also prevent magnetic interference possibly caused between urged upward, causing the valve head 2a to preSS against the the upper and lower coils 19a, 19b.

valve seat of the orifice member 3. The valve head 2a is of Disposed above the yoke 24 is a metallic upper plate 25 push-opened type that it opens the orifice when pushed which functions as a flat bearing for an upper portion of a downward. magnet holder 26. Terminals 17 are electrically connected to A body 11 and a motor 32 are both fixed to an upper the coils 19a, 19b for supplying electric currents to the coils portion of the valve body 1 by a set screw 16. A bushing 15 19a, 19b. A sealing rubber 18 is attached around the termi is inserted in a hole in which the set Screw 16 for the motor nals 17 to establish a watertight condition when connectors 32 is inserted. The motor 32 is mounted in coaxial relation are fitted into the terminals 17 for supply of electric currents. to the body 11. Between the motor 32 and the body 11, there housingThe stator unit thus constructed is covered and fixed by the is interposed an O-ring 13 to block off the intrusion of water, 25 The rotor resin 14.

oil, etc. from the external. unit 33 of the motor 32 comprises a magnet 25, The body 11 serves as an intermediate member for joining the ball bearing 27, and a resin-made magnet holder 26 Supporting the former two members, which are integrally the motor 32 and the valve body 1 to each other. Since the formed by insert molding. PPS (polyphenylene sulfide resin) exhaust gas at high temperature flows through the gas is used as a resin material of the magnet holder 26. Teflon is passage in the valve body 1, the body 11 has a cooling added to PPS to provide the resin material with higher Structure to prevent the heat of the exhaust gas from being slidability. Note that, in addition to PPS, PBT (polybutylene transmitted to the motor 32. Specifically, a cooling pipe 12 terephtalate resin), PA (polyamide resin), etc. are also usable is embedded inside the body 11 and cooling water is as the resin material. The magnet holder 26 has female Supplied from a cooling pipe inlet 12a to flow through the threads 26.a formed in its inner circumferential Surface. A cooling pipe 12. A cooling pipe outlet 12b is located, as 35 Stopper 26b is integrally formed on the magnet holder 26 in shown in FIG. 5, near the cooling pipe inlet 12a in side a position inside the magnet holder 26 and below the female by-Side relation. The cooling water flows into the cooling threads 26a, thereby restricting the rotation of a rotor shaft pipe 12 through the inlet 12a, goes Substantially round the 7 when the rotor shaft 7 reaches a maximum pull-up interior of the body 11, and then flows out of the outlet 12b. position.

The cooling water contributes to more than cooling the 40 Here, Since the components of the rotor unit 33, i.e., the motor 32 alone. The heat transmitted from the exhaust gas magnet 25, the ball bearing 27 and the magnet holder 26, are at high temperature may melt grease for a ball bearing 27 integrally formed by Simultaneous molding, it is possible to rotatably supporting a rotor unit 33 of the motor 32. If the omit steps of bonding the magnet and preSS-fitting the ball Viscosity of grease is lowered, the rotor rotation would be So bearing, which have been essential in the prior art, and hence fast as to cause an overshoot in opening and closing opera 45 to reduce the number of Steps necessary for assembly. The tion of the valve head 2a. Simultaneous molding can also improve coaxiality among In this embodiment, the cooling water also cools the ball the magnet 25, the ball bearing 27 and the magnet holder 26, bearing 27 So that the Viscosity of grease can be kept at a and therefore can reduce a variation in torque generated by necessary level. Further, a wave washer 28 is interposed the motor.

between the ball bearing 27 and a portion of the body 11 50 The rotor unit 33 of the motor 32 is rotatably held within Supporting it to prevent the heat from the exhaust gas from the Stator unit of the motor 32. Specifically, an upper end of being directly transmitted to the ball bearing 27. On the the rotor unit 33 is rotatably supported by the upper plate 20 other hand, the cooling effected by the cooling water pro as part of the Stator unit. In other words, an upper end portion motes heat dissipation from the circumference of an outer of the magnet holder 26 is rotatably Supported at its outer race of the ball bearing 27. 55 circumferential Surface by an inner circumferential Surface An outer race 27c of the ball bearing 27 is held by being of the upper plate 20. Also, a lower end of the rotor unit 33 fitted astride between an inner peripheral wall of a Socket is rotatably supported by the ball bearing 27. The ball portion of the body 11 and an inner peripheral wall of a bearing 27 as one component of the rotor unit 33 comprises Socket portion of a housing resin 14 constituting a Stator unit an inner race 27a integrally fixed to the magnet holder 26, of the motor 32. With this structure, the motor 32 and the 60 balls 27a, and an outer race 27c. An upper end of the outer body 11 are positioned to have their axes coaxial with the race 27.c is held against the inner peripheral wall of the axis of the ball bearing 27 as if those two members are one housing resin 14 of the motor 32, as indicated by arrow A in integral member. FIG. 1. Further, a lower end of the outer race 27.c is biased A hole 5a is bored in the valve body 1 to align with an toward the side of the motor 32 under a preload applied by extension of the axis of the motor 32, allowing the valve 65 a wave washer 28. The wave washer 28 is interposed shaft 2 to be inserted into the gas passage in the valve body between the outer race 27c of the ball bearing 27 and the 1 for installation. body 11.

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The rotor shaft 9 converts rotating motion of the motor 32 tance by the tightening force produced when the Screw 16 is into reciprocating motion So that the valve shaft 2 recipro fastened to the body 11.

cates. The rotor shaft 9 has male threads 9a formed in Whether the gap g, is to be left Somewhat or become Zero complementary relation to the female threads 26.a formed in after the Screw 16 has been fastened, is Set case by case the magnet holder 26. The rotor shaft 9 extends through the depending on how much preload should be applied to bias magnet holder 26 with the male threads 9a engaging the the magnet holder 26 in the axial direction. female threads 26a. A stopper pin 29 is press-fitted over the The shaft bushing 10 is fixed to the body 11 at the center rotor Shaft 9 and brought into abutment against the Stopper thereof. The lower end of the rotor shaft 9 of the rotor unit 26b after the valve shaft 2 has seated onto the valve seat of 33 assembled to the motor 32 is inserted through the shaft the orifice member 3, thereby preventing the rotor shaft 9 bushing 10, while the socket portion of the body 11 includ from reciprocating over a greater Stoke than determined by ing the wave washer 28 set in place is fitted to surround the the abutment between the pin 29 and the stopper 26b. Ashaft outer race 27c of the ball bearing 27. The motor 32 and the bushing 10 is fixed to the body 11 and serves to restrict the body 11 are thereby assembled together. rotation of the rotor shaft 9. A lower portion 9b of the rotor On the other hand, the gas Seal 6 is preSS-fitted to one side shaft 9 has a D-shape in cross section and is fitted to a 15 of a valve attachment hole formed in the valve body 1. At D-shaped opening formed in the shaft bushing 10. The joint this time, the dust cover 31 is held between the gas seal 6 and 30 connected by caulking to the upper end of the valve shaft a corresponding Socket portion of the valve body 1. The dust 2 is snap-fitted to the rotor shaft 9 for interconnection cover 31 prevents dust contained in exhaust gas from between the valve shaft 2 and the rotor shaft 9. depositing in a gap between a center hole of the dust Seal 6 The orifice member 3 is Screwed into the gas passage of and the valve shaft 2 inserted through the center hole. the valve body 1 so that a flow rate can be adjusted by The orifice member 3 having a valve seat (opening) removing a plug 5 and then turning the orifice member 3 to formed at the center is fitted into the valve attachment hole move up or down. After the adjustment of a flow rate, the formed in the valve body 1 from the other side 5a. plug 5 is fitted in place to enclose the gas passage and is The orifice member 3 is a tubular member and has male fastened with a rivet 4 so as not to drop off. 25 threads formed on its outer circumferential Surface and

Assembling work of such a valve assembly will now be meshing female threads formed in the valve attachment hole described in more detail. formed in the valve body 1.

The upper end of the magnet holder 26 is fitted to the The valve shaft 2 extends upward through the center upper plate 20, Serving as a flat bearing, provided in the opening of the orifice member 3, the center hole of the dust motor 32 Such that the former's outer circumferential Sur cover 31, and the center hole of the gas Seal 6. The Spring face is slidably Supported by the latters inner circumferen 8 is mounted on the upper end side of the valve shaft 2 tial Surface. Simultaneously, a ring 26a projecting around between the gas seal 6 and the plate 7 with one end of the the magnet holder 26 is brought into slidable pressure spring 8 held against the gas seal 6. The plate 7 is fixedly contact with an end face 20a of the flat bearing 20 in the 35 connected by caulking to the upper end of the valve shaft 2, thrust direction. This pressure contact force is given by a and supports the joint 30 and the other end of the spring 8. preload applied to the outer race 27c of the ball bearing 27 On this occasion, the Spring 8 is maintained in a compressed to bias it axially, as shown in FIG. 4A. State under a preset load.

In a State of no preload being applied, there is a Small gap Therefore, the restoring force of the Spring 8 pushes up g between one or upper axial end 27d of the Outer race 27c 40 the valve shaft 2 in the axial direction, causing the valve of the ball bearing 27 and an axial end face 14a of the Socket head 2a to be pressed against the valve Seat of the orifice portion of the housing resin 14 of the motor 32. This gap g, member 3. A resulting valve assembly is then fastened by the is Set to be Substantially equal to an amount of relative screws 16 to a motor assembly assembled as described movement occurred between the inner and outer races of the above.

ball bearing 27 in the thrust direction. 45 At this time, the joint 30 is connected or locked to the end Accordingly, by applying the preload to the outer race 27c of the lower portion 9b of the rotor shaft 9 by any suitable of the ball bearing 27 in a state where the ring 26a of the method. In this embodiment, the end of the joint 30 is first magnet holder 26 is held in pressure contact with the end resiliently spread outward, while splitting to pieces, by the face 20a of the flat bearing 20, the gap g, is eliminated and end of the rotor shaft lower portion 9b and then restored to at the same time the relative movement between the inner 50 an original converged State after riding over a step formed and outer races of the ball bearing 27 in the thrust direction around the end of the rotor shaft lower portion 9b, thereby is prevented. establishing a lock between the joint 30 and the rotor shaft The preload is Set to an appropriate value because the 9 preload would develop resistance against the rotation of the After the valve body 1 and the motor 32 have been balls 27a if its value is greater than necessary. 55 assembled with the intermediate body 11 held between In this embodiment, the wave washer 28 interposed them, work of adjusting a flow rate is carried out in a between an end of the socket portion of the body 11 in the predetermined manner, and thereafter the orifice member 3 thrust direction and an opposite or lower end of the outer is fixed in the valve body 1 by welding or like. race 27c of the ball bearing 27 in the thrust direction serves More specifically, prior to the adjusting work, a Sealer is to not only produce but also adjust the preload. 60 applied to the meshed portion between the orifice member The outer race 27c of the ball bearing 27 is loose-fitted at and the valve body. The inlet passage 1a and a chamber 1C its outer circumference astride between the inner peripheral defined between the valve body 1 and the body 11 are wall of the socket portion of the housing resin 14 of the maintained under atmospheric pressure, while the outlet motor 32 and the inner peripheral wall of the Socket portion passage 1b is kept at constant pressure (e.g., -350 mmHg at of the body 11. Therefore, the outer race 27c of the ball 65 20° C).

bearing 27 is movable through a distance corresponding to After power-on, the motor is excited in two phases to the gap g, in the thrust direction without undergoing resis rotate through predetermined Steps in the valve-closing

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direction. A resulting position is defined as an end point of 4-cycle internal combustion engine, there occurs one explo initialization. This position represents a position reached Sion for every two rotations per cylinder. Accordingly, the when the motor has been rotated through Several Steps engine having Six cylinders causes Six explosions for every further from the mechanical stop position of the valve in the two rotations, i.e., three explosions for each rotation. On the Valve-closing direction. other hand, the maximum rotational speed of 6000 rpm is Next, the orifice member 3 is rotated a predetermined equivalent to 100 rps. Because of 100 rpsx3=300 (Hz), the angle for adjustment So that a first predetermined flow rate Secondary vibration frequency of rotation of Such an internal is achieved at a position reached when the motor has been combustion engine is provided by 300 Hz. rotated through first predetermined Steps (e.g., 25 steps) Likewise, assuming that a 4-cycle internal combustion from the end position of initialization in the valve-opening engine with eight cylinderS has a maximum rotational Speed direction. of 6000 rpm, the secondary vibration frequency of rotation In this embodiment, Since one thread pitch of the orifice of the internal combustion engine is 400 Hz. Further, assum member 3 has a stroke of 1.5 mm and one step of the motor ing as another higher-speed engine that a 4-cycle internal has a stroke of 0.078 mm, turning the orifice member 3 about 15 combustion engine with eight cylinderS has a maximum 18 provides an adjustment in an amount corresponding to rotational speed of 8000 rpm, the secondary vibration fre one Step of the motor. quency of rotation of the internal combustion engine is After the first predetermined flow rate has been achieved, calculated as 533 Hz from the following formula: the motor is rotated in the valve-closing direction until the fully-closed position of the valve. The power is once turned where m: degree (the number of explosions per rotation of off in the fully-closed position of the valve. Subsequently, crankshaft) the above-Stated initializing operation is executed again and m=2, 3, 4 for engines with four, Six and eight cylinders, the motor is rotated Step by Step in the valve-opening respectively direction for confirming that the gas Starts to flow at the f frequency fully-closed position of the valve. 25 n: engine rotational Speed Thereafter, it is confirmed whether predetermined flow rates are achieved at a plurality of points where the motor is of On the other hand, in this embodiment, the rotor unit 33 rotated through respective predetermined Steps from the end magnetmotorthe

32 is formed by integrally insert-molding the the ball bearing 27, and the resin-made magnet point of initialization in the valve-opening direction. If not holder 26 supporting achieved, then the adjusting work is repeated by turning the magnet 25 is Supportedthe by former two members. Thus, the the resin-made magnet holder 26.

orifice member.

Also, Since only one ball bearing 27 is employed in the rotor

When the adjusting work is completed and the orifice unit 33, no ball bearing is provided in the upper portion of member 3 is fixed in the valve body 1, the plug 5 is the rotor unit 33 and the weight of the rotor unit 33 is press-fitted into the valve attachment hole on the lower side reduced correspondingly. With Such a structure, the reso 5a for enclosing the hole, and is fastened with the rivet 4 by 35 nance frequency of the rotor unit can be increased over the caulking. Secondary vibration frequency of rotation of a 4-cycle The operation of this embodiment will be described internal combustion engine, e.g., 533 Hz. As a result, the below. In the motor 32 as a stepping motor, pulse signals rotor unit of the motor will never resonate with the rotation supplied from the terminals 17 are applied to the coils 19, of the internal combustion engine and the useful life of the whereupon the rotor unit 33 of the motor 32 is rotated 40 motor-operated flow control valve can be prolonged. stepwisely. Rotating motion of the rotor unit 33 is converted Further, the motor-operated flow control valve can be into reciprocating motion through meshing between the mounted on most of internal combustion engines without female threads 26a of the magnet holder 26 and the male changing the design of the rotor unit.

threads 9a of the rotor shaft 9, thus causing the rotor shaft A method of measuring the resonance frequency of the 9 to reciprocate. The reciprocating motion of the rotor shaft 45 rotor unit of the motor in the motor-operated flow control 9 is transmitted to the valve shaft 2 for reciprocating it. Since Valve according to an embodiment of the present invention a gap between the valve head 2a of the valve shaft 2 and the will be described below with reference to FIGS. 2 and 3. valve seat of the orifice member 3 is changed with the FIG. 2 is a Schematic view showing a construction of a reciprocating motion of the valve shaft 2, a flow rate of device for measuring the resonance frequency of the rotor exhaust gas flowing from the inlet 1a to the outlet 1b can be 50 unit of the motor in the motor-operated flow control valve changed. according to an embodiment of the present invention. The relationship between the resonance frequency of the A motor-operated flow control valve 50 according to this rotor unit of the motor in the motor-operated flow control embodiment and having the structure shown in FIG. 1 is Valve constructed as described above and the Secondary fixedly placed on a base 52 of a vibrating machine 51. A G Vibration frequency of rotation of a 4-cycle internal com 55 (gravity) sensor 55 is attached to the upper end of the magnet bustion engine will now be described. In this embodiment, holder 26 of the rotor unit 33 in the motor-operated flow the resonance frequency of the rotor unit of the motor is Set control valve 50. An output of the G sensor 55 is taken in by to be not lower than the Secondary vibration frequency of an FET analyzer 54 through an amplifier 53. rotation of a 4-cycle internal combustion engine. The resonance frequency of the rotor unit 33 can be The Secondary vibration frequency of rotation of a 4-cycle 60 measured by vibrating the motor-operated flow control valve internal combustion engine depends on the number of cyl 50 with the base G and analyzing a resulting output Signal inders and the maximum rotational Speed of the internal by the FET analyzer 54 with frequency plotted along the combustion engine. ASSuming, for example, that a 4-cycle horizontal axis.

internal combustion engine with six cylinderS has a maxi FIG. 3 is a graph showing a measured result of the mum rotational speed of 6000 rpm, the secondary vibration 65 resonance frequency of the rotor unit of the motor in the frequency of rotation of the internal combustion engine is motor-operated flow control valve according to an embodi 300 Hz. This frequency can be determined as follows. In a ment of the present invention.

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In the graph of FIG. 3, the horizontal axis represents of the ball bearing is small. It is therefore possible to reduce frequency and the Vertical axis represents acceleration. frictional torque occurred upon Starting the rotor unit to When the rotor unit is resonated with the engine vibration, rotate and hence to avoid a drop of the torque generated by the acceleration shows a peak value at certain frequency the motor at the Start-up.

which is the resonance frequency of the rotor unit, as A method of assembling the motor-operated flow control indicated by a one-dot-chain line in the graph. By contrast, valve according to this embodiment will now be described as indicated by a Solid line, the resonance frequency does not with reference to FIG. 5.

appear in a frequency range up to 600 Hz in the motor FIG. 5 is an exploded perspective view of parts of the operated flow control valve of this embodiment because the motor-operated flow control valve according to an embodi rotor unit of the motor is constructed to have resonance ment of the present invention.

frequency higher than the Secondary vibration frequency of Referring to FIG. 5, steps of assembling the motor rotation of a 4-cycle internal combustion engine. operated flow control valve according to this embodiment Further, in this embodiment, the rotor unit 33 of the motor are as follows. After attaching the Stopper pin 29 to the rotor 32 comprises the magnet 25, the ball bearing 27, and the shaft 9, the rotor shaft 9 with the stopper pin 29 is screwed resin-made magnet holder 26 Supporting the former two 15 into the rotor unit 33. Because the male threads 9a are members, which are integrally formed by insert molding. formed on the upper portion of the rotor shaft 9 and the Additionally, the rotor unit 33 includes only one ball bearing female threads are formed in the magnet holder 26, the rotor 27 and the outer race of the ball bearing is fixedly held at its shaft 9 is screwed in and attached to the rotor unit 33 through upper and lower ends by a structure exerting no preload meshing between the male threads 9a and the female upon the balls of the ball bearings. This means that frictional threads. The rotor unit 33 is formed by molding the magnet torque occurred upon Starting the rotor unit to rotate is 25 and the ball bearing 27 integrally with the magnet holder reduced and hence a drop of the torque generated by the 26. The rotor unit 33 is placed in the housing resin 14 of the motor can be avoided at the Start-up. motor 32. The stator unit is previously mounted in the The above point will be described in detail with reference housing resin 14 with the bushings 15 and the sealing rubber to FIG. 4. 25 18 inserted in place.

FIG. 4 is a view for explaining a preload applied to a ball The shaft bushing 10 is fitted to the center of the body 11. bearing of a rotor unit of a motor in motor-operated flow The O-ring 13 is inserted in a groove formed in an upper control valves. surface of the body 11, and the wave washer 28 is placed in FIG. 4A Schematically shows the Structure of applying a a recess at the upper end side of the body 11. After that, the preload to the rotor unit of the motor in this embodiment. motor 32 is tentatively placed on the body 11. At this time, The rotor unit 33 of the motor 32 is formed by integrally the D-shaped lower portion 9b of the rotor shaft 9 is inserted insert-molding the magnet 25, the ball bearing 27, and the through the shaft bushing 10 in alignment with the D-shaped resin-made magnet holder 26 Supporting the former two opening formed in the shaft bushing 10. Further, two sets of members. Here, only one ball bearing 27 is employed in the three holes defined in the housing resin 14 of the motor 32 rotor unit 33. The upper end of the outer race 27c of the ball 35 and the body 11 for attachment of set screws 16, 16', 16" are bearing 27 is held against the housing resin 14 of the motor aligned with each other.

32, and the lower end of the outer race 27.c is biased toward Then, into a central opening of the valve body 1 on the the side of the motor 32 under a preload applied by the wave upper end Side is inserted the dust cover 31 and then washer 28. In other words, the outer race of the single ball preSS-fitted the gas Seal 6. Also, the orifice member 3 is bearing is held at the upper and lower ends thereof to be 40 screwed into the valve body 1 from the lower end side. The fixed in place with the Structure exerting no preload on the valve shaft 2 is inserted from below through the center balls of the ball bearing. Accordingly, frictional torque opening of the orifice member 3, the center hole of the dust occurred upon Starting the rotor unit to rotate can be reduced cover 31, and the center hole of the gas Seal 6. The Spring and hence a drop of the torque generated by the motor can 8 and the plate 7 are set in place from the upper end side of be avoided at the Start-up. 45 the valve shaft 2. The joint 30 is then connected by caulking FIG. 4B schematically shows a conventional structure of to the upper end of the valve shaft 2 while the spring 8 is Supporting a rotor unit by two ball bearings. In Such a held in a compressed State.

conventional Structure, for example, a magnet 101 is fixed to The valve body 1 thus assembled is combined with the a magnet holder 100 and two ball bearings 102,103 are fixed body 11 and the motor 32 which have been tentatively one to each of both ends of the magnet holder 100. An outer 50 positioned in place as mentioned above. The end of the joint race 102c of one upper ball bearing 102 is held at its upper 30 is then Snap-fitted over the end of the rotor shaft 9. After end against a Stationary portion 104. Then, a preload is positioning the valve body 1 relative to the motor 32 and the applied by a spring or the like to an outer race 103c of the body 11, these three members are joined together by using other lower ball bearing 103. In this structure, since the the set Screws 16, 16', 16".

preload applied to the outer race 103c of the lower ball 55 Finally, the orifice member 3 is turned from the lower side bearing 103 is transmitted to the stationary portion 104 of the valve body 1 for adjustment of a flow rate, and the through balls 103b, 102b of both the ball bearings 103,102. plug 5 is inserted into the valve body 1 and fastened with the Stated otherwise, pressure is exerted on the balls 103b, 102b rivet 4. The assembly of the motor-operated flow control in the conventional Structure. As a result, frictional torque Valve is thus completed.

occurred upon Starting the rotor unit to rotate is increased 60 With this embodiment, as described above, since the and hence the torque generated by the motor is reduced Specific frequency of the rotor unit is Set to be higher than correspondingly at the Start-up. the Secondary vibration frequency of rotation of a 4-cycle By contrast, with the Structure of this embodiment, Since internal combustion engine, the useful life of the motor the rotor unit 33 employs the single ball bearing 27 and the operated flow control valve can be prolonged. outer race of the Single ball bearing is held at the upper and 65 Also, Since the Specific frequency of the rotor unit is Set lower ends thereof to be fixed in place as described above to be higher than the Secondary vibration frequency of with reference to FIG. 4A, the pressure exerted on the balls rotation of a 4-cycle internal combustion engine, the useful

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life of the motor-operated flow control valve can be applied In addition, Since a flow rate is adjusted by turning the to most of internal combustion engines without changing the orifice member, an amount of gas can be adjusted in units of design of the rotor unit.

Further, Since the magnet holder constituting the rotor unit one Step of the motor by adjusting the orifice member is made of resin and the ball bearing for rotatably Supporting through a Small angle for each turn. the rotor unit is provided only one, the weight of the rotor It is to be noted that while the above embodiment has been unit can be reduced and the resonance frequency of the rotor described as using the motor-operated flow control valve for unit can be raised. EGR, the present invention is also applicable to, e.g., air Since the outer race of the single ball bearing is held fixed flow control for ISC (Idle Speed Control) and control of any Vertically under a preload, the inner race of the ball bearing other fluids.

is Subject to no preload and frictional torque occurred upon

Starting the rotor unit to rotate can be reduced remarkably. What is claimed is:

Therefore, a drop of the torque generated by the motor due 1. A motor-operated flow control valve comprising a rotor to the increased frictional torque of the rotor unit at the shaft reciprocating with rotating motion of a motor, and a Start-up can be made Smaller. valve head movable to open and close an orifice with the Since the components of the rotor unit, i.e., the magnet, 15 reciprocating motion of Said rotor Shaft, wherein: the ball bearing and the magnet holder, are integrally formed by Simultaneous molding, it is possible to omit Steps of means is provided for Setting Specific frequency of a rotor bonding the magnet and preSS-fitting the ball bearing, which unit of Said motor to be higher than the Secondary have been essential in the prior art, and hence to reduce the Vibration frequency of rotation of a 4-cycle internal number of Steps necessary for assembly. combustion engine according to a relationship defined Since the Simultaneous molding of components of the rotor unit also contributes to improving coaxiality among the by (n/60)xm, wherein m is the engine rotational speed magnet, the ball bearing and the magnet holder, a variation and m is the number of explosions per crankshaft in torque generated by the motor can be reduced. rotation.

Since the load imposed on the ball bearing can be 25 2. A motor-operated flow control valve according to claim reduced, it is possible to provide the ball bearing in the rotor 1, wherein Said rotor unit comprises an integral magnet, a unit only on one end Side the rotor Shaft and employ a flat Single ball bearing and a resin-made magnet holder for bearing for Supporting the other end Side of the rotor Shaft. Supporting Said magnet and Said ball bearing, Said magnet, Since the outer race of the ball bearing is disposed to position astride a joint plane between the motor and the Said ball bearing and Said magnet holder being formed into intermediate body, the axes of the motor and the interme an integral Structure.

diate body can be simply aligned with the axis of the ball bearing.