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

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MOTOR-OPERATED FLOW CONTROL internal combustion engine. With this feature, when applied WALVE AND GAS RECIRCULATION to any of internal combustion engines having four, Six and CONTROL VALVE FOR INTERNAL eight cylinders, the motor-operated flow control valve will COMBUSTION ENGINE not give rise to a resonance phenomenon and therefore has a longer useful life.

This application is a continuation of application Ser. No. In the above motor-operated flow control valve, 08/897,307, filed Jul. 21, 1997, issued as U.S. Pat. No. preferably, the rotor unit comprises an integral magnet, a 6,089,536, Jul 18, 2000. Single ball bearing and a resin-made magnet holder for Supporting the magnet and the ball bearing, the magnet, the

BACKGROUND OF THE INVENTION ball bearing and the magnet holder being formed into an 1. Field of the Invention integral structure. With this feature, the weight of the rotor The present invention relates to a motor-operated flow unit can be So reduced as to make the Specific frequency of control valve Suitable for use in internal combustion the rotor unit have a value not resonating with engine engines, and more particularly to an exhaust gas recircula 15 vibration.

tion control valve for internal combustion engines. Further, to Solve the above objects, according to the 2. Description of the Related Art present invention, in a motor-operated flow control valve 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 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 held fixed under a preload. With this feature, frictional are disclosed in, for example, U.S. Pat. Nos. 4,432,318, torque occurred upon Starting the rotor unit to rotate is 4,381,747, 4,378,767, 4,378,768, 4.414,942, 4,397.275 and 25 reduced and torque required for the motor to produce at the 5,184,593, JP-A-7-190227 and 7-190226, etc. Start-up is made Smaller.

SUMMARY OF THE INVENTION BRIEF DESCRIPTION OF THE DRAWINGS

In the conventional motor-operated flow control valves, 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 35 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 40 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 45 present invention, and FIG. 4B is a similar view for explain race of the other ball bearing is pressed by a Spring Such as ing a preload applied to a ball bearing in the prior art. a Spring washer or a coil Spring. With Such a structure, FIG. 5 is an exploded perspective view of parts of the however, because the preload generated by the Spring motor-operated flow control valve according to one embodi washer or the like is applied to balls of the ball bearing as ment of the present invention.

well, frictional torque occurred upon Starting the rotor unit 50 to rotate is increased. This results in another problem that the DESCRIPTION OF THE PREFERRED motor is required to produce a larger torque at the Start-up. EMBODIMENT An object of the present invention is to provide a motor A motor-operated flow control valve for internal combus operated flow control valve for internal combustion engines tion engines according to an embodiment of the present which is less affected by vibration and has a longer useful 55 invention will be described hereunder with reference to life. FIGS. 1 to 5.

Another object of the present invention is to provide a FIG. 1 is a vertical Sectional view of a push-opened, motor-operated flow control valve for internal combustion motor-operated flow control valve according to an embodi engines which does not require a motor to produce a larger ment of the present invention.

torque at the Start-up. 60 The motor-operated flow control valve according to this To achieve the above objects, according to the present embodiment is employed as an EGR (Exhaust Gas invention, in a motor-operated flow control valve compris Recirculation) valve for internal combustion engines. A ing a rotor shaft reciprocating with rotating motion of a Valve body 1 defines an gas passage therein. Exhaust gas motor, and a valve head movable to open and close an orifice from an internal combustion engine flows into the valve with the reciprocating motion of the rotor shaft, Specific 65 body 1 through an inlet la and then flows out through an frequency of a rotor unit of the motor is Set to be higher than outlet 1b for return to the intake pipe side of the internal the Secondary vibration frequency of rotation of a 4-cycle combustion engine.

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An orifice member 3 is Screwed into the gas passage A hole 5a is bored in the valve body 1 to align with an between the inlet 1a and the outlet 1b. A valve shaft 2 having extension of the axis of the motor 32, allowing the valve a valve head 2a provided at one end extends through a shaft 2 to be inserted into the gas passage in the valve body central opening (valve seat) formed in the orifice member 3 1 for installation.

So that an orifice is opened and closed by the valve head 2a. The construction of the motor 32 will be described below. A gas seal 6 is fixedly press-fitted in the valve body 1 and The stator unit of the motor 32 comprises a coil 19a housed Serves to Seal off the exhaust gas flowing through the gas in a bobbin 22a and a coil 19b housed in a bobbin 22b. passage against leakage. The valve shaft 2 is slidably Magnetic fields are generated by Supplying electric currents Supported by the gas Seal 6. A dust cover 31 is attached to the coils 19a, 19b.

between the gas seal 6 and the valve body 1 to prevent A yoke for forming a magnetic path has a C-shape in foreign matters, Such as carbon and oil contained in the Vertical Section, and is made up of a yoke 24 nearly in the exhaust gas, from adhering to a gap between an outer form of a hollow annulus cylinder and two disk-shaped circumferential Surface of the valve shaft 2 and the gas Seal yokes 23a, 23b. The bobbin 22a including the coil 19a is

disposed in a Space defined by the yoke 24 and the yoke 23a,

A plate 7 is connected by caulking to an upper end of the 15 while the bobbin 22b including the coil 19b is disposed in a valve shaft 2 through a joint 30. A spring 8 is interposed space defined by the yoke 24 and the yoke 23b. Between between the plate 7 and the gas seal 6 to bias the plate 7 both the yokes 23a and 23b, a center plate 21 is disposed to upward. The valve shaft 2 joined to the plate 7 is thereby not only position the upper and lower yokes 23a, 23b, but urged upward, causing the valve head 2a to preSS against the also prevent magnetic interference possibly caused between valve seat of the orifice member 3. The valve head 2a is of the upper and lower coils 19a, 19b. push-opened type that it opens the orifice when pushed Disposed above the yoke 24 is a metallic upper plate 25 downward. which functions as a flat bearing for an upper portion of a A body 11 and a motor 32 are both fixed to an upper magnet holder 26. Terminals 17 are electrically connected to portion of the valve body 1 by a set screw 16. A bushing 15 25 the coils 19a, 19b for supplying electric currents to the coils is inserted in a hole in which the set Screw 16 for the motor 19a, 19b. A sealing rubber 18 is attached around the termi 32 is inserted. The motor 32 is mounted in coaxial relation nals 17 to establish a watertight condition when connectors to the body 11. Between the motor 32 and the body 11, there are fitted into the terminals 17 for supply of electric currents. is interposed an O-ring 13 to block off the intrusion of water, The stator unit thus constructed is covered and fixed by the oil, etc. from the external. housing resin 14.

The body 11 serves as an intermediate member for joining The rotor unit 33 of the motor 32 comprises a magnet 25, the motor 32 and the valve body 1 to each other. Since the the ball bearing 27, and a resin-made magnet holder 26 exhaust gas at high temperature flows through the gas Supporting the former two members, which are integrally passage in the valve body 1, the body 11 has a cooling formed by insert molding. PPS (polyphenylene sulfide resin) Structure to prevent the heat of the exhaust gas from being 35 is used as a resin material of the magnet holder 26. Teflon is transmitted to the motor 32. Specifically, a cooling pipe 12 added to PPS to provide the resin material with higher is embedded inside the body 11 and cooling water is slidability. Note that, in addition to PPS, PBT (polybutylene Supplied from a cooling pipe inlet 12a to flow through the terephtalate resin), PA (polyamide resin), etc. are also usable cooling pipe 12. A cooling pipe outlet 12b is located, as as the resin material. The magnet holder 26 has female shown in FIG. 5, near the cooling pipe inlet 12a in side 40 threads 26.a formed in its inner circumferential Surface. A by-Side relation. The cooling water flows into the cooling Stopper 26b is integrally formed on the magnet holder 26 in pipe 12 through the inlet 12a, goes Substantially round the a position inside the magnet holder 26 and below the female interior of the body 11, and then flows out of the outlet 12b. threads 26a, thereby restricting the rotation of a rotor shaft The cooling water contributes to more than cooling the 7 when the rotor shaft 7 reaches a maximum pull-up motor 32 alone. The heat transmitted from the exhaust gas 45 position.

at high temperature may melt grease for a ball bearing 27 Here, Since the components of the rotor unit 33, i.e., the rotatably supporting a rotor unit 33 of the motor 32. If the magnet 25, the ball bearing 27 and the magnet holder 26, are Viscosity of grease is lowered, the rotor rotation would be So integrally formed by Simultaneous molding, it is possible to fast as to cause an overshoot in opening and closing opera omit steps of bonding the magnet and preSS-fitting the ball tion of the valve head 2a. 50 bearing, which have been essential in the prior art, and hence In this embodiment, the cooling water also cools the ball to reduce the number of Steps necessary for assembly. The bearing 27 So that the Viscosity of grease can be kept at a Simultaneous molding can also improve coaxiality among necessary level. Further, a wave washer 28 is interposed the magnet 25, the ball bearing 27 and the magnet holder 26, between the ball bearing 27 and a portion of the body 11 and therefore can reduce a variation in torque generated by Supporting it to prevent the heat from the exhaust gas from 55 the motor.

being directly transmitted to the ball bearing 27. On the The rotor unit 33 of the motor 32 is rotatably held within other hand, the cooling effected by the cooling water pro the Stator unit of the motor 32. Specifically, an upper end of motes heat dissipation from the circumference of an outer the rotor unit 33 is rotatably supported by the upper plate 20 race of the ball bearing 27. as part of the Stator unit. In other words, an upper end portion An outer race 27c of the ball bearing 27 is held by being 60 of the magnet holder 26 is rotatably Supported at its outer fitted astride between an inner peripheral wall of a Socket circumferential Surface by an inner circumferential Surface portion of the body 11 and an inner peripheral wall of a of the upper plate 20. Also, a lower end of the rotor unit 33 Socket portion of a housing resin 14 constituting a Stator unit is rotatably supported by the ball bearing 27. The ball of the motor 32. With this structure, the motor 32 and the bearing 27 as one component of the rotor unit 33 comprises body 11 are positioned to have their axes coaxial with the 65 an inner race 27a integrally fixed to the magnet holder 26, axis of the ball bearing 27 as if those two members are one balls 27b, and an outer race 27c. An upper end of the outer integral member. race 27.c is held against the inner peripheral wall of the

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S 6 housing resin 14 of the motor 32, as indicated by arrow A in wall of the socket portion of the housing resin 14 of the FIG. 1. Further, a lower end of the outer race 27.c is biased motor 32 and the inner peripheral wall of the Socket portion toward the side of the motor 32 under a preload applied by of the body 11. Therefore, the outer race 27c of the ball a wave washer 28. The wave washer 28 is interposed bearing 27 is movable through a distance corresponding to between the outer race 27c of the ball bearing 27 and the the gap g, in the thrust direction without undergoing resis body 11. tance by the tightening force produced when the Screw 16 is The rotor shaft 9 converts rotating motion of the motor 32 fastened to the body 11.

into reciprocating motion So that the valve shaft 2 recipro Whether the gap g, is to be left Somewhat or become Zero cates. The rotor shaft 9 has male threads 9a formed in after the Screw 16 has been fastened, is Set case by case complementary relation to the female threads 26.a formed in 1O depending the magnet holder 26. The rotor shaft 9 extends through the 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 15 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 of a valve attachment hole formed in the valve body 1. At D-shaped opening formed in the shaft bushing 10. The joint 30 connected by caulking to the upper end of the valve shaft this time, the dust cover 31 is held between the gas seal 6 and 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 25 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.

Assembling work of such a valve assembly will now be threads formed on its outer circumferential Surface and described in more detail. meshing female threads formed in the valve attachment hole The upper end of the magnet holder 26 is fitted to the formed in the valve body 1.

upper plate 20, Serving as a flat bearing, provided in the 35 The valve shaft 2 extends upward through the center motor 32 Such that the former's outer circumferential Sur opening of the orifice member 3, the center hole of the dust face is slidably Supported by the latters inner circumferen cover 31, and the center hole of the gas Seal 6. The Spring tial Surface. Simultaneously, a ring 26a projecting around 8 is mounted on the upper end side of the valve shaft 2 the magnet holder 26 is brought into Slidable pressure between the gas seal 6 and the plate 7 with one end of the contact with an end face 20a of the flat bearing 20 in the 40 Spring 8 held against the gas Seal 6. The plate 7 is fixedly thrust direction. This pressure contact force is given by a connected by caulking to the upper end of the valve shaft 2, preload applied to the outer race 27c of the ball bearing 27 and supports the joint 30 and the other end of the spring 8. to bias it axially, as shown in FIG. 4A. On this occasion, the Spring 8 is maintained in a compressed In a State of no preload being applied, there is a Small gap State under a preset load.

g between one or upper axial end 27d of the Outer race 27c 45 Therefore, the restoring force of the Spring 8 pushes up of the ball bearing 27 and an axial end face 14a of the Socket the valve shaft 2 in the axial direction, causing the valve portion of the housing resin 14 of the motor 32. This gap g, head 2a to be pressed against the valve Seat of the orifice is Set to be Substantially equal to an amount of relative member 3. A resulting valve assembly is then fastened by the movement occurred between the inner and outer races of the screws 16 to a motor assembly assembled as described ball bearing 27 in the thrust direction. above.

Accordingly, by applying the preload to the outer race 27c At this time, the joint 30 is connected or locked to the end of the ball bearing 27 in a state where the ring 26a of the of the lower portion 9b of the rotor shaft 9 by any suitable magnet holder 26 is held in pressure contact with the end method. In this embodiment, the end of the joint 30 is first face 20a of the flat bearing 20, the gap g, is eliminated and resiliently spread outward, while splitting to pieces, by the at the same time the relative movement between the inner 55 end of the rotor shaft lower portion 9b and then restored to and outer races of the ball bearing 27 in the thrust direction an original converged State after riding over a step formed is prevented. around the end of the rotor shaft lower portion 9b, thereby The preload is Set to an appropriate value because the establishing a lock between the joint 30 and the rotor shaft preload would develop resistance against the rotation of the 9.

balls 27b if its value is greater than necessary. 60 After the valve body 1 and the motor 32 have been In this embodiment, the wave washer 28 interposed assembled with the intermediate body 11 held between between an end of the socket portion of the body 11 in the them, work of adjusting a flow rate is carried out in a thrust direction and an opposite or lower end of the outer predetermined manner, and thereafter the orifice member 3 race 27c of the ball bearing 27 in the thrust direction serves is fixed in the valve body 1 by welding or like. to not only produce but also adjust the preload. 65 More specifically, prior to the adjusting work, a Sealer is The outer race 27c of the ball bearing 27 is loose-fitted at applied to the meshed portion between the orifice member its outer circumference astride between the inner peripheral and the valve body. The inlet passage 1a and a chamber 1C

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defined between the valve body 1 and the body 11 are inders and the maximum rotational Speed of the internal maintained under atmospheric preSSure, while the outlet combustion engine. ASSuming, for example, that a 4-cycle passage 1b is kept at constant pressure (e.g., -350 mmHg at internal combustion engine with six cylinderS has a maxi 20° C). mum rotational speed of 6000 rpm, the secondary vibration After power-on, the motor is excited in two phases to frequency of rotation of the internal combustion engine is rotate through predetermined Steps in the valve-closing 300 Hz. This frequency can be determined as follows. In a 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) 15 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 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 25 fully-closed position of the valve. The power is once turned off in the fully-closed position of the valve. Subsequently, the above-Stated initializing operation is executed again and where the motor is rotated Step by Step in the valve-opening m: degree (the number of explosions per rotation of direction for confirming that the gas Starts to flow at the crankshaft) fully-closed position of the valve. m=2, 3, 4 for engines with four, Six and eight cylinders, Thereafter, it is confirmed whether predetermined flow respectively rates are achieved at a plurality of points where the motor is f: frequency rotated through respective predetermined Steps from the end n: engine rotational Speed point of initialization in the valve-opening direction. If not 35 On the other hand, in this embodiment, the rotor unit 33 achieved, then the adjusting work is repeated by turning the of the motor 32 is formed by integrally insert-molding the orifice member.

magnet 25, the ball bearing 27, and the resin-made magnet

When the adjusting work is completed and the orifice holder 26 supporting the former two members. Thus, the member 3 is fixed in the valve body 1, the plug 5 is magnet 25 is Supported by the resin-made magnet holder 26. press-fitted into the valve attachment hole on the lower side 40 Also, Since only one ball bearing 27 is employed in the rotor 5a for enclosing the hole, and is fastened with the rivet 4 by unit 33, no ball bearing is provided in the upper portion of caulking. the rotor unit 33 and the weight of the rotor unit 33 is The operation of this embodiment will be described reduced correspondingly. With Such a structure, the reso below. In the motor 32 as a stepping motor, pulse signals nance frequency of the rotor unit can be increased over the supplied from the terminals 17 are applied to the coils 19, 45 Secondary vibration frequency of rotation of a 4-cycle whereupon the rotor unit 33 of the motor 32 is rotated internal combustion engine, e.g., 533 Hz. As a result, the stepwisely. Rotating motion of the rotor unit 33 is converted rotor unit of the motor will never resonate with the rotation into reciprocating motion through meshing between the of the internal combustion engine and the useful life of the female threads 26a of the magnet holder 26 and the male motor-operated flow control valve can be prolonged. threads 9a of the rotor shaft 9, thus causing the rotor shaft 50 Further, the motor-operated flow control valve can be 9 to reciprocate. The reciprocating motion of the rotor shaft mounted on most of internal combustion engines without 9 is transmitted to the valve shaft 2 for reciprocating it. Since changing the design of the rotor unit. a gap between the valve head 2a of the valve shaft 2 and the A method of measuring the resonance frequency of the valve seat of the orifice member 3 is changed with the rotor unit of the motor in the motor-operated flow control reciprocating motion of the valve shaft 2, a flow rate of 55 Valve according to an embodiment of the present invention exhaust gas flowing from the inlet la to the outlet 1b can be will be described below with reference to FIGS. 2 and 3. changed. FIG. 2 is a Schematic view showing a construction of a The relationship between the resonance frequency of the device for measuring the resonance frequency of the rotor rotor unit of the motor in the motor-operated flow control unit of the motor in the motor-operated flow control valve Valve constructed as described above and the Secondary 60 according to an embodiment of the present invention. Vibration frequency of rotation of a 4-cycle internal com A motor-operated flow control valve 50 according to this bustion engine will now be described. In this embodiment, embodiment and having the structure shown in FIG. 1 is the resonance frequency of the rotor unit of the motor is Set fixedly placed on a base 52 of a vibrating machine 51. A G to be not lower than the Secondary vibration frequency of (gravity) sensor 55 is attached to the upper end of the magnet rotation of a 4-cycle internal combustion engine. 65 holder 26 of the rotor unit 33 in the motor-operated flow The Secondary vibration frequency of rotation of a 4-cycle control valve 50. An output of the G sensor 55 is taken in by internal combustion engine depends on the number of cyl an FET analyzer 54 through an amplifier 53.

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The resonance frequency of the rotor unit 33 can be in the conventional Structure. As a result, frictional torque measured by vibrating the motor-operated flow control valve occurred upon Starting the rotor unit to rotate is increased 50 with the base G and analyzing a resulting output Signal and hence the torque generated by the motor is reduced by the FET analyzer 54 with frequency plotted along the correspondingly at the Start-up. horizontal axis. By contrast, with the Structure of this embodiment, Since FIG. 3 is a graph showing a measured result of the the rotor unit 33 employs the single ball bearing 27 and the resonance frequency of the rotor unit of the motor in the outer race of the Single ball bearing is held at the upper and motor-operated flow control valve according to an embodi lower ends thereof to be fixed in place as described above ment of the present invention. with reference to FIG. 4A, the pressure exerted on the balls 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, the motor hence rotate and at the to avoid a drop of the torque generated by

the acceleration shows a peak value at certain frequency A method of assembling the motor-operated flow control which is the resonance frequency of the rotor unit, as valve according to this embodiment will now be described indicated by a one-dot-chain line in the graph. By contrast, 15 with reference to FIG. 5.

as indicated by a Solid line, the resonance frequency does not FIG. 5 is an exploded perspective view of parts of the appear in a frequency range up to 600 Hz in the motor motor-operated flow control valve according to an embodi operated flow control valve of this embodiment because the ment of the present invention.

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

to FIG. 4. The shaft bushing 10 is fitted to the center of the body 11. FIG. 4 is a view for explaining a preload applied to a ball 35 The O-ring 13 is inserted in a groove formed in an upper bearing of a rotor unit of a motor in motor-operated flow surface of the body 11, and the wave washer 28 is placed in control valves. a recess at the upper end side of the body 11. After that, the FIG. 4A Schematically shows the Structure of applying a motor 32 is tentatively placed on the body 11. At this time, preload to the rotor unit of the motor in this embodiment. the D-shaped lower portion 9b of the rotor shaft 9 is inserted The rotor unit 33 of the motor 32 is formed by integrally 40 through the shaft bushing 10 in alignment with the D-shaped insert-molding the magnet 25, the ball bearing 27, and the opening formed in the shaft bushing 10. Further, two sets of resin-made magnet holder 26 Supporting the former two three holes defined in the housing resin 14 of the motor 32 members. Here, only one ball bearing 27 is employed in the and the body 11 for attachment of set screws 16, 16', 16" are rotor unit 33. The upper end of the outer race 27c of the ball aligned with each other.

bearing 27 is held against the housing resin 14 of the motor 45 Then, into a central opening of the valve body 1 on the 32, and the lower end of the outer race 27.c is biased toward upper end Side is inserted the dust cover 31 and then the side of the motor 32 under a preload applied by the wave preSS-fitted the gas Seal 6. Also, the orifice member 3 is washer 28. In other words, the outer race of the single ball screwed into the valve body 1 from the lower end side. The bearing is held at the upper and lower ends thereof to be valve shaft 2 is inserted from below through the center fixed in place with the Structure exerting no preload on the 50 opening of the orifice member 3, the center hole of the dust balls of the ball bearing. Accordingly, frictional torque cover 31, and the center hole of the gas Seal 6. The Spring occurred upon Starting the rotor unit to rotate can be reduced 8 and the plate 7 are set in place from the upper end side of and hence a drop of the torque generated by the motor can the valve shaft 2. The joint 30 is then connected by caulking be avoided at the Start-up. to the upper end of the valve shaft 2 while the spring 8 is FIG. 4B schematically shows a conventional structure of 55 held in a compressed State.

Supporting a rotor unit by two ball bearings. In Such a The valve body 1 thus assembled is combined with the conventional Structure, for example, a magnet 101 is fixed to body 11 and the motor 32 which have been tentatively a magnet holder 100 and two ball bearings 102,103 are fixed positioned in place as mentioned above. The end of the joint one to each of both ends of the magnet holder 100. An outer 30 is then Snap-fitted over the end of the rotor shaft 9. After race 102c of one upper ball bearing 102 is held at its upper 60 positioning the valve body 1 relative to the motor 32 and the end against a Stationary portion 104. Then, a preload is body 11, these three members are joined together by using applied by a spring or the like to an outer race 103c of the the set Screws 16, 16', 16".

other lower ball bearing 103. In this structure, since the Finally, the orifice member 3 is turned from the lower side preload applied to the outer race 103c of the lower ball of the valve body 1 for adjustment of a flow rate, and the bearing 103 is transmitted to the stationary portion 104 65 plug 5 is inserted into the valve body 1 and fastened with the through balls 103b, 102b of both the ball bearings 103,102. rivet 4. The assembly of the motor-operated flow control Stated otherwise, pressure is exerted on the balls 103b, 102b Valve is thus completed.

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With this embodiment, as described above, since the What is claimed is:

Specific frequency of the rotor unit is set to be higher than 1. A motor-operated exhaust gas recirculation control the Secondary vibration frequency of rotation of a 4-cycle comprising a rotor Shaft reciprocating with rotating motion internal combustion engine, the useful life of the motor of a motor, and a valve head movable to open and close an operated flow control valve can be prolonged. 5 orifice with the reciprocating motion of Said rotor Shaft, Also, Since the Specific frequency of the rotor unit is Set wherein Said valve comprises a motor, a valve body for to be higher than the Secondary vibration frequency of Supporting Said valve head, and a body joining Said rotation of a 4-cycle internal combustion engine, the useful motor and Said valve body together and having a life of the motor-operated flow control valve can be applied cooling water passage formed therein, and to most of internal combustion engines without changing the the outer race of Said ball bearing is held in place by Said design of the rotor unit. body,

Further, Since the magnet holder constituting the rotor unit wherein an end face of an outer race of a ball bearing is is made of resin and the ball bearing for rotatably Supporting held in place through a washer in the axial direction of the rotor unit is provided only one, the weight of the rotor 15 Said rotor Shaft, unit can be reduced and the resonance frequency of the rotor wherein the washer is a wave washer arranged to form a unit can be raised. heat insulating space between the outer race of the Since the outer race of the single ball bearing is held fixed bearing and the body joining Said motor and Said valve Vertically under a preload, the inner race of the ball bearing body together.

is Subject to no preload and frictional torque occurred upon 2. A motor-operated exhaust gas recirculation control Starting the rotor unit to rotate can be reduced remarkably. Valve according to claim 1, wherein a cooling water passing Therefore, a drop of the torque generated by the motor due through Said cooling water passage is a cooling water for an to the increased frictional torque of the rotor unit at the internal combustion engine.

Start-up can be made Smaller. 3. A motor-operated flow control valve comprising a rotor Since the components of the rotor unit, i.e., the magnet, 25 shaft reciprocating with rotating motion of a motor, and a the ball bearing and the magnet holder, are integrally formed valve head movable to open and close an orifice with the by Simultaneous molding, it is possible to omit Steps of reciprocating motion of Said rotor Shaft, wherein bonding the magnet and preSS-fitting the ball bearing, which a rotor unit of Said motor comprises a magnet, a Single ball have been essential in the prior art, and hence to reduce the bearing and a magnet holder for Supporting Said magnet number of Steps necessary for assembly. and an inner race of Said ball bearing, Said ball bearing Since the Simultaneous molding of components of the having an outer race held fixed under a preload, rotor unit also contributes to improving coaxiality among the between a case of Said motor and a body holding Said magnet, the ball bearing and the magnet holder, a variation motor, a Small gap existing between an upper axial end in torque generated by the motor can be reduced. of Said motor case and Said Single ball bearing and a Since the load imposed on the ball bearing can be 35 axial end face of a Socket portion being equal to or reduced, it is possible to provide the ball bearing in the rotor Smaller than an amount of relative movement between unit only on one end Side the rotor Shaft and employ a flat Said inner and outer races of Said Single ball bearing in bearing for Supporting the other end Side of the rotor Shaft. a thrust direction.

Since the outer race of the ball bearing is disposed to 4. A motor-operated flow control valve according to claim position astride a joint plane between the motor and the 40 3, wherein Said magnet holder is formed by insert molding, intermediate body, the axes of the motor and the interme and Said magnet and inner race of Said Single ball bearing are diate body can be simply aligned with the axis of the ball inserted in Said magnet holder.

bearing. 5. A motor-operated flow control valve according to claim In addition, Since a flow rate is adjusted by turning the 4, wherein an end face of Said race of Said Single ball bearing orifice member, an amount of gas can be adjusted in units of 45 is held in place through a washer in the axial direction of Said one Step of the motor by adjusting the orifice member rotor shaft.

through a Small angle for each turn. 6. A motor-operated flow control according to claim 3, It is to be noted that while the above embodiment has been wherein an end face of Said race of Said Single ball bearing described as using the motor-operated flow control valve for is held in place through a washer in the axial direction of Said EGR, the present invention is also applicable to, e.g., air 50 rotor shaft.

flow control for ISC (Idle Speed Control) and control of any other fluids.