Throttle valve control device

A throttle valve control device is composed of a stator core with a solenoid and a rotor carrying a throttle valve. The rotor has a pair of poles which is composed of one or a plurality of rare-earth-metal permanent magnets magnetized in the radial thickness direction. The stator core has an inner periphery sorounding the rotor, and the inner periphery is smooth with no slot so that uniform distribution of magnetic flux can be formed in the inner periphery, thereby reducing the detent torque.

CROSS REFERENCE TO RELATED APPLICATION 
The present application is based on and claims priority from Japanese 
Patent Applications Hei 9-28753 filed on Feb. 13, 1997, and Hei 10-2448 
filed on Jan. 8, 1998, the contents of which are incorporated herein by 
reference. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a throttle valve control device for 
controlling an air-intake passage. 
2. Related Art 
U.S. Pat. No. 5,287,835 discloses a throttle valve control device for 
controlling an air-intake passage in which the throttle valve is driven by 
a torque motor. In order to increase the response speed of the throttle 
valve, a return spring for biasing the throttle valve in one direction is 
omitted. 
A drawing of U.S. Pat. No. 5,287,835, shows a stator core of an actuator 
with no slot on the inner periphery surrounding a rotor. However, the 
drawing is only a diagrammatical view and there is no description on the 
inner periphery of the stator core in the specification. A stator core 
illustrated in another drawing has a separated N-pole stator section and 
an S-pole stator section, and slots or cut portions are formed between two 
sections. If the rotor is equipped with a permanent magnet made of 
rare-earth metal such as neodyum, samarium or cobalt, distribution of 
magnetic-flux density in the stator becomes more uneven than the 
distribution of magnet-flux density caused by the rotor equipped with a 
ferrite magnet. Accordingly, a large detent torque is applied to the rotor 
when the driving coil is turned off. 
In an actuator which has a return spring for returning the rotor to the 
fully closed position to prevent the throttle valve from opening if the 
current control device of the torque motor becomes out of order, a large 
spring force is necessary to return the rotor to the fully closed position 
against the detent torque if there is a slot on the inner periphery of the 
stator surrounding the rotor. That is, large electro-magnetic force and, 
accordingly, a large-sized torque motor are necessary to drive the 
throttle valve against the spring force. 
Although it is desired that the permanent magnet for magnetic poles on the 
rotor is magnetized in the radial directions, cracks may be formed during 
the step of cooling the permanent magnet if the magnetic poles of the 
permanent magnet are formed of a large number of sintered 
radially-magnetized particles. Thus, the yield rate decreases and the 
production cost increases. 
SUMMARY OF THE INVENTION 
A main object of the present invention is to provide a simple and compact 
throttle valve control device. 
Another object of the present invention is to provide a throttle valve 
control device which controls the throttle position accurately. 
Another object of the present invention is to provide a throttle valve 
control device which can be manufactured easily at low cost. 
According to the invention, a stator core of an electromagnetic driving 
unit is arranged to have a smooth inner periphery with no slot, so that 
unevenness in the distribution of the magnetic flux density in the stator 
core can be reduced. Accordingly, the detent torque applied to the rotor 
when the rotor is rotated without current supplied to the solenoid can be 
eliminated. Thus, the electro-magnetic force to drive the rotor can be 
reduced. Because the detent torque can be eliminated, the electromagnetic 
force of the throttle valve control device can be reduced. Therefore, the 
size of the electromagnetic drive unit and, finally, the throttle valve 
control device can be made small. 
In the throttle valve control device according to another aspect of the 
invention, a permanent magnet member disposed on the outer periphery of 
the rotor is magnetized in the radial directions from the center of the 
rotor. Accordingly, unevenness in the torque applied to the rotor can be 
reduced irrespective of the rotational position of the rotor. As a result, 
the throttle position can be controlled accurately irrespective of the 
rotational position of the rotor so that the intake air can be controlled 
accurately. 
In the throttle valve control device according to another aspect of the 
invention, a plurality of permanent magnets magnetized in the same 
direction are disposed on the outer periphery of the rotor to provide 
magnetic poles magnetized in the radial directions. Therefore, the 
permanent magnets can be manufactured easily without cracks at a high 
yield rate and low cost. 
In the throttle valve control device according to another aspect of the 
invention, the inner periphery surrounding the rotor is formed in an area 
other than the area extending from the width of portions of the solenoid 
in engagement with the portions of the stator core. Therefore, stress of 
the engagement portions does not affect the inner periphery of the stator 
core, and the air gap between the inner periphery of the stator core and 
the rotor can be kept uniform. As a result, the torque applied to the 
rotor can be regulated accurately to ensure smooth rotation of the rotor, 
high accuracy of the throttle valve position and accurate control of the 
intake air.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
(First Embodiment) 
A throttle valve control device according to a first embodiment of the 
present invention is described with reference to FIGS. 1, 2 and 3. The 
throttle valve control device 10 is composed of throttle body 11, throttle 
valve 13, a valve shaft 12, rotation position sensor 30 and 
electromagnetic torque motor 40 which controls position of throttle valve 
13 according to position of an accelerator of a vehicle. 
Throttle body 11 rotatably supports valve shaft 12 via bearings 15 and 16. 
Throttle valve 13 has a circular plate and is fixed to valve shaft 12 by 
screws 14. When throttle valve 13 turns about valve shaft 12, passage area 
of air intake passage 11a defined by the inner periphery of throttle body 
11 changes, so that an amount of the intake air can be controlled. 
Throttle lever 21 is press-fitted to an end of valve shaft 12 so that 
throttle lever 21 can rotate with valve shaft 12. Stopper screw 22 fixes 
the full-close position of throttle valve 13 by engaging therewith. The 
full-close position of throttle valve 13 can be adjusted by turning screw 
22. 
Rotation position sensor 30 is disposed at the side of throttle body 11 on 
the same end of the valve shaft 12. Rotation position sensor 30 is 
composed of contact member 31, resistance board 32 with the resistor 
member coated thereon and housing 33. Contact member 31 is press-fitted to 
valve shaft 12 to rotate together therewith. Resistance board 32 is fixed 
to housing 33 so that contact member 31 can slide on the resistor member 
of resistance board 32. Five volts-constant voltage is applied across the 
resistor member of resistance board 32. When the relative position between 
the resistor member and contact member 31 changes, the output voltage of 
rotation position sensor 30 changes. The output voltage is applied to an 
engine control unit (ECU, not shown) from rotation position sensor 30 to 
detect the position of throttle valve 13. 
Electro-magnetic torque motor 40 is composed of rotor 41, stator core 45 
and a pair of solenoid 50 and 55 and is disposed at the side of throttle 
body 11 on the other end of valve shaft 12. 
Rotor 41 is composed of cylindrical rotor core 42 into which valve shaft 12 
is press-fitted and permanent magnets 43 and 44. Rotor 41 is surrounded by 
inner periphery 45a of stator core 45. Rotor core 42 is made of magnetic 
material and is press-fitted to the other end of valve shaft 12. A pair of 
permanent magnets 43 and 44 is arc-shaped and bonded to the outer 
periphery of rotor core 42 at equal intervals. Throttle valve 13 can 
rotate within an angle of 90.degree.. Accordingly, the arc length of the 
permanent magnets 43 and 44 is arranged enough to rotate rotor 41 within 
the rotation angle. Permanent magnets 43 and 44 are made of rare-earth 
metal such as a high neodymium or samarium-cobalt alloy. 
Stator core 45 is made of a plurality of thin magnetic sheets laminated in 
the axial direction of valve shaft 12 and has inner periphery 45a which 
surrounds rotor 41. The inner periphery 45a of stator core 45 that 
surrounds rotor 41 is even and has no slot thereon. Solenoids 50 and 55 
have coils 52 and 57 which are wound around cores 51 and 56 respectively 
and have projections 55a fitted into grooves 45c of stator core 45. Coils 
52 and 57 are supplied with control current from pins of connector 60. 
Stator core 45 and solenoids 50 and 55 are shown in FIG. 3 in more detail. 
Each of solenoids 50 and 55 is inserted to one of the rectangular concave 
portions 45b of stator core 45 in the direction from this side of FIG. 3 
to the far side of it or from the far side thereof to this side thereof. 
Concave portions 45b are formed at opposite portions of stator core 45 
radially outside of inner periphery 45a as shown in FIG. 3A. A pair of 
grooves 45c is formed on the opposite wall of each of concave portions 
45b. A pair of projections 50a and 55a is formed on the opposite sides of 
solenoids 50 and 55 as shown in FIGS. 3B and 3C. 
Distance a1 between opposite surfaces of each of concave portions 45b is 
longer than length c1 of solenoids 50 and 55, and depth a2 of grooves 45c 
is larger than height c2 of projection 50a and 55a. On the other hand, 
width b of grooves 45c is narrower than width d of projection 50a and 55a. 
When solenoids 50 and 55 are press-fitted into grooves 45c, projections 
50a and 55a are tightly held by grooves 45c. Solenoids 50 and 55 are not 
held by any member other than grooves 45c. Inner periphery 45a is 
positioned in an area other than the area located on the extension of 
projections 50a and 55a. 
Thus, when the projections 50a and 55a are press-fitted into grooves 45c, 
projections 50a and 55a do not expand or deform inner periphery 45a, so 
that a uniform air gap can be formed between the inner periphery 45a of 
stator core 45 and permanent magnets 43 and 44. Accordingly, the torque 
applied to rotor 41 is kept constant and rotor 41 can rotate smoothly. 
With solenoid 50 and 55 being press-fitted into stator core 45, stator 
core 45 is provided with a smooth inner surface surrounding rotor 41 
without any slot. As a result, the distribution of the magnetic flux 
density in stator core 45 becomes uniform so that the detent torque 
applied to rotor 41 during the rotation can be eliminated. 
Permanent magnets 43 and 44 are magnetized in the radial directions from 
the center. When coils 52 and 57 are energized, the torque generated by 
magnetic force of coils 52 and 57 and permanent magnets 43 and 44 are 
applied to rotor 41. The characteristic curve of the torque applied to 
rotor 41 is not a sine wave that reduces the torque on the extreme sides 
of the area of the rotation but a rectangular wave that equalizes the 
torque irrespective of the position of throttle valve 13. Thus, the 
position of throttle valve 13 can be controlled with high accuracy. 
An end of return spring 17 shown in FIGS. 1 and 2 is fixed to rotor core 42 
and the other end thereof is fixed to the axial end surface of stator core 
45 by screw 18, thereby biasing throttle valve 13 to close the passage. 
Return spring 17 has a main spiral coil portion disposed in cylindrical 
rotor core 42. Because rotor core 42 as well as return spring 17 is 
disposed in stator core 45, the size of torque motor 40 is decided by the 
size of stator core 45. That is, return spring 17 does not increase the 
size very much. 
Wave washer 19 biases valve shaft 12 in an axial direction to prevent the 
same from shifting in the axial direction due to vibration of an engine in 
operation. Accordingly, the position of contact member 31 relative to 
resistance board 32 does not change, so that the signal indicating 
position of throttle valve 13 may not change and ware of the resistor 
member or contact member 31 due to abnormal friction therebetween can be 
prevented. 
The operation of throttle valve control device 10 is described hereafter. 
(1) Normal Running Modes: 
The normal running mode includes running under ISC (idle speed control) and 
cruise control as well as ordinary running. The position of the throttle 
valve 13 is calculated by an ECU (not shown) according to engine 
conditions including the accelerator position and rotation speed of the 
engine so that control current is supplied to coils 52 and 57 according to 
the calculated result. 
Because the rotating torque applied to rotor 41 when coils 52 and 57 are 
energized is larger than the biasing force of return spring 17, rotor 41 
rotates against the biasing force of return spring 17. 
The position of throttle valve 13 rotated by rotor 41 is detected by 
rotation position sensor 30 and fed back to the ECU, which controls the 
current supplied to coils 52 and 55. Thus, variation in the torque applied 
to rotor 41 due to temperature change or the like can be regulated by 
detecting the throttle valve position, and the throttle valve position can 
be controlled with high accuracy. 
(2) Control in Failure: 
If the target value of the position of throttle valve 13 is different from 
an actual position of throttle valve 13 as detected by rotation position 
sensor 30, it is decided that the throttle valve control of the ECU fails. 
Consequently, the ECU provides a signal to close throttle valve 13. Then 
throttle valve 13 is returned by return spring 17 to the full-close 
position, thereby preventing throttle valve 13 from moving to an abnormal 
position. 
The ECU has a sub-ECU which always watches abnormal conditions of the ECU. 
When the ECU fails, the sub-ECU stops the control current supplied to 
coils 52 and 57. Thus, throttle valve 13 is returned to the full-close 
position by return spring 17 whenever the ECU fails. 
(Second Embodiment) 
A second embodiment of the present invention is described with reference to 
FIG. 4. Portions which are substantially the same as those of the first 
embodiment are denoted by the same reference numerals. 
A pair of poles 46 and 47 is composed of four flat permanent magnets 46a 
and 47a, which are bonded to the outer periphery of rotor core 42. 
Permanent magnets 46a and 47a are made of rare-earth metal and disposed on 
the circumference of rotor core 42 as shown in FIG. 4 so that permanent 
magnets 46 and 47 are magnetized in the radial directions from the center 
of rotor 48. 
The second embodiment having a plurality of permanent magnets 46a and 47a 
is arranged to have substantially the same construction as the first 
embodiment having a pair of permanent magnets magnetized in the radial 
directions. The flat magnets can be produced and magnetized easily. 
If a large number of magnetized particles are sintered to form permanent 
magnets 43 and 44 used in the first embodiment that have arc-shaped outer 
surfaces, the thermal expansion thereof in the magnetized direction is 
different from the thermal expansion in the direction perpendicular to the 
magnetized direction. This may cause cracks in the permanent magnets when 
they are cooled after the step of sintering. Flat permanent magnets 46a 
and 47a used in this embodiment do not have the above stated problem. 
Accordingly, the yield rate of the permanent magnets becomes higher and 
the production cost thereof can be reduced. 
(Third Embodiment) 
A divided stator core used in a third embodiment of the present invention 
is shown in FIG. 5. In the third embodiment, there are gaps 71 of about 
0.1 mm caused by the production step between two pieces of stator core 70. 
However, it is negligibly small to generate the detent torque. Thus, the 
electromagnetic force torque necessary for driving the rotor can be 
reduced. 
(Fourth Embodiment) 
A fourth embodiment of the present invention is described with reference to 
FIG. 6. Portions which are substantially the same as those of the first 
and second embodiments are denoted by the same reference numerals. 
Magnetic poles 80 and 81 are respectively composed of four permanent 
magnets 80a and 81a. Each of permanent magnets 80a and 81a has flat 
surface at the side of rotor core 42 and a semi-cylindrical surface facing 
stator core 45, and is bonded to the outer periphery of rotor core 42. 
Permanent magnets 80a and 81a are made of rare-earth metal material, 
magnetized in the radial thickness direction and disposed to form the 
semi-cylindrical surfaces into an arc as shown in FIG. 6. As a result, two 
magnetic poles 80 and 81 are magnetized in the radial directions from the 
center of rotor 82. 
The semi-cylindrical surfaces of permanent magnets used in the fourth 
embodiment render the air gap between permanent magnet 80a and 81a and the 
inner periphery of stator core 45 uniform, and the flat surfaces thereof 
render the machine works and assembling works such as bonding to be 
simple. 
The outer surface of the permanent magnets used in the fourth embodiment 
can be shaped cylindrical by machining after trapezoidal or flat permanent 
magnets are bonded to the outer periphery of rotor core 42. In this case, 
the air gap between the permanent magnets and inner periphery of stator 
core 45 can be more uniform. 
(Fifth Embodiment) 
A fifth embodiment of the present invention is described with reference to 
FIG. 7. The portions of the fifth embodiment which are substantially the 
same as those of the fourth embodiment are denoted by the same reference 
numerals. 
Magnetic poles 83 and 84 are respectively composed of four permanent 
magnets 83a and 84a which are bonded to the outer periphery of rotor core 
42. Each of permanent magnets 83a and 84a has a semi-cylindrical inner 
surface on the side of rotor core 42 and a semi-cylindrical outer surface 
facing the inner periphery of stator core 45, forming a semi-circular 
member. Permanent magnets 83a and 84a are made of rare earth metal and 
magnetized in the radial thickness direction. They are disposed to form an 
arc along the circumference of rotor core 42 as shown in FIG. 7. Thus, 
magnetic poles 83 and 84 are magnetized in the radial directions from the 
center of rotor 85. 
The outer surface facing stator core 45 of permanent magnets 83a and 84a 
used in the fifth embodiment is semi-cylindrical, the air gap between 
permanent magnets 83a or 84a and the inner periphery of stator core 45 
becomes uniform. Because the inner surface on the side of rotor core 42 is 
also semi-cylindrical, the volume of the permanent magnets can be reduced. 
This reduces magnetic material and the production cost. 
(Sixth Embodiment) 
A sixth embodiment of the present invention is described with reference to 
FIG. 8. The portions which are substantially the same as those of the 
second embodiment are denoted by the same reference numerals. 
A pair of stator cores 90 and 91 is disposed to surround the outer 
periphery of rotor 88 which has two magnetic poles. Slots 92 and 93 are 
disposed at 180.degree. apart, on opposite sides of rotor 88, thereby 
demarcating the magnetic paths of the stator core. 
In the sixth embodiment, rotor 88 has two magnetic poles 86 and 87 which 
are composed of one-way-magnetized flat permanent magnets 86a and 87a 
respectively. Because it is easy to magnetize the flat magnets in one way, 
magnetic poles 86 and 87 can be provided easily at low production cost. 
In the sixth embodiment, each of the permanent magnets has a trapezoidal 
cross-section as viewed from axially outside of rotor 88 so that permanent 
magnets 86a and 87a are lined up circumferentially in close contact with 
another in the respective magnetic poles of rotor 88. Accordingly, 
variation in the detent torque applied to rotor 88 is smaller than that of 
the second embodiment in which there are spaces between the permanent 
magnets on the rotor surface facing the inner periphery of the stator core 
as shown in FIG. 4. 
(Seventh Embodiment) 
A seventh embodiment of the present invention is described with reference 
to FIG. 9. A single solenoid 58 is used instead of a pair of solenoids 50 
and 55 used in the first to sixth embodiments, which are provided to 
improve the response time. Therefore, the device can be made smaller at 
lower cost. 
The seventh embodiment has a pair of stator cores 94 and 95 forming two 
poled-cores separated by two slots 96 and 97 when solenoid 58 is 
energized. Two slots 96 and 97 are disposed respectively at portions on 
opposite sides of rotor 42 with an angle shifted about a half pitch of one 
of permanent magnets 86a and 87a from 180.degree.. A plurality of flat 
permanent magnets are disposed on the circumference of the rotor and the 
air gap increases at the middle surface of the flat permanent magnets, 
causing cyclic torque change related to the rotation position. In this 
embodiment, the maximum torque is applied to the rotor near the pair of 
slots. In order to cancel the maximum torque, the slots are positioned at 
an angle on opposite sides of the rotor about a half pitch of one of 
permanent magnets 86a and 87a shifted from 180.degree.. Thus, the rotor 
can have uniform torque in the rotation area. The variations in the torque 
can be eliminated in this way even if the rotor has a plurality of 
permanent magnets disposed on the circumference of the rotor at a space 
between each of the permanent magnets. 
In the above embodiments of the invention, return spring 17 returns the 
rotor to the full-close position if the operation fails. However, it is 
possible to omit return spring 17 and allow the rotor to rotate in both 
directions. 
A cylindrical retainer cover can be provided to retain the permanent 
magnets on the rotor. If this cover is made of magnetic material, the 
cover is magnetized by the permanent magnets so that the air gap between 
the poles of the rotor and the inner periphery of the stator core can be 
made uniform. 
In the foregoing description of the present invention, the invention has 
been disclosed with reference to specific embodiments thereof. It will, 
however, be evident that various modifications and changes may be made to 
the specific embodiments of the present invention without departing from 
the broader spirit and scope of the invention as set forth in the appended 
claims. Accordingly, the description of the present invention in this 
document is to be regarded in an illustrative, rather than restrictive, 
sense.