Throttle valve control device

A throttle valve control device for controlling the amount of inlet air fed to an internal combustion engine has a throttle valve disposed in an air intake passage, a throttle shaft integrally connected with the throttle valve so as to rotate with the throttle valve in a body, a driving source for generating driving torque, and a driving torque transmitting mechanism disposed between the driving source and the throttle shaft for transmitting the driving torque to the throttle shaft. The driving torque transmitting mechanism includes a torque limiting mechanism for limiting the transmitted driving torque to a predetermined level.

This application is based on and claims priority under 35 U.S.C. .sctn. 119
 with respect to Japanese Application No. 10(1998)-137892 filed on May 20,
 1998, the entire content of which is incorporated herein by reference.
 FIELD OF THE INVENTION
 The present invention generally relates to a throttle valve. More
 particularly, the present invention pertains to a throttle valve control
 device for controlling the amount of inlet air fed to an internal
 combustion engine.
 BACKGROUND OF THE INVENTION
 A known throttle valve control device is disclosed, for example, in
 Japanese Laid-Open Publication No. Hei 07(1995)-97950. The throttle valve
 control device includes a throttle valve, a gear mechanism, a DC motor, an
 electronic control unit (ECU), a throttle valve position sensor and an
 accelerator pedal sensor. The throttle valve position sensor detects the
 actual throttle valve position and outputs a throttle valve position
 signal to the ECU. The accelerator pedal sensor detects the actual
 accelerator pedal position and outputs an accelerator pedal position
 signal to the ECU. The ECU determines a target throttle valve position in
 response to the actual accelerator pedal position and other parameters
 representing engine driving conditions, for example, the amount of fuel
 injection to the engine and the temperature of the engine. The gear
 mechanism is disposed between the DC motor and the throttle valve to
 transmit the rotating torque from the DC motor to the throttle valve. The
 DC motor is turned on electrically by the ECU to drive the throttle valve
 via the gear mechanism. That is, the throttle valve is opened and closed
 by the DC motor which is controlled by the ECU. The ECU performs a
 servo-control based on Proportional Integral Derivative control (PID
 control) such that the actual throttle valve position corresponds to the
 target throttle valve position.
 Generally speaking, for purposes of rotating the throttle valve within a
 predetermined range, the throttle valve control device has two stoppers.
 One stopper is a full opening stopper which is able to contact a part of
 the throttle valve when the throttle valve is positioned at the maximum
 opening position in the predetermined range. The other stopper is a
 closing stopper which is able to contact another part of the throttle
 valve when the throttle valve is positioned at the complete closing
 position or minimum opening position in the predetermined range.
 Therefore, if the throttle valve control device is in an abnormal state,
 for example when the throttle valve receives an excessive rotational
 torque, the position of the throttle valve is maintained in the
 predetermined range.
 However, when the throttle valve control device is in the abnormal state by
 virtue of changing conditions, for example a change in environmental
 temperature or a change in voltage of the power source, the stoppers
 receive excessive torque. Accordingly, the DC motor and the parts of the
 gear mechanism are susceptible to becoming broken.
 In an attempt to address this problem, it is of course possible to increase
 the strength of the parts. However, this increases the weight and the
 moment of inertia of the parts, thus decreasing the operating response.
 A need thus exists for a throttle value control device that is not
 excessively heavy and does not have an excessively large moment of
 inertia, but which nevertheless is not susceptible to damage and breakage
 of the DC motor and gear parts.
 SUMMARY OF THE INVENTION
 According to one aspect of the present invention, a throttle valve control
 device for controlling the amount of inlet air fed to an internal
 combustion engine has a throttle valve disposed in an air intake passage,
 a throttle shaft integrally connected with the throttle valve so as to
 rotate with the throttle valve in a body, a driving source for generating
 driving torque, and a driving torque transmitting mechanism disposed
 between the driving source and the throttle shaft for transmitting the
 driving torque to the throttle shaft. The driving torque transmitting
 mechanism includes a torque limiting mechanism for limiting the
 transmitted driving torque to a predetermined level.
 According to another aspect of the present invention, a throttle valve
 control device for controlling the amount of inlet air fed to an internal
 combustion engine includes a throttle valve disposed in an air intake
 passage, a throttle shaft integrally connected with the throttle valve so
 as to rotate with the throttle valve in a body, a driving source for
 generating driving torque, and a driving torque transmitting mechanism
 disposed between the driving source and the throttle shaft for
 transmitting the driving torque to the throttle shaft. The driving torque
 transmitting mechanism includes first and second gears urged apart from
 one another by an urging member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
 Referring initially to FIG. 1, the throttle valve control device of the
 prevent invention includes a throttle valve 10 and other components for
 driving the throttle valve. The throttle valve 10 is integrally fixed to a
 throttle shaft 12 by a known mechanism such as by a pair of bolts 11a, 11b
 as shown in FIG. 2. The throttle valve 10 is rotatably supported in an
 intake passage 14 which communicates with an intake port 16 of an internal
 combustion engine 18. A gear mechanism 20 is attached to one end of the
 throttle shaft 12 and a DC motor 22 causes the throttle shaft 12 to rotate
 via the gear mechanism 20 so that the amount of inlet air fed to the
 internal combustion engine 18 is controlled. The DC motor 22 is driven by
 a driver circuit 24 in response to the duty ratio signal which is
 calculated by a throttle controlling electronic control unit (ECU) 26.
 The throttle controlling ECU 26 receives an accelerator pedal position
 signal Ap from an accelerator pedal sensor 28 which detects the position
 of an accelerator pedal 30. The throttle controlling ECU 26 also receives
 other signals, for example signals indicating the amount of fuel injection
 to the internal combustion engine 18, the temperature of the internal
 combustion engine 18 and the like. The throttle controlling ECU 26
 receives these signals from an engine controlling ECU so that the throttle
 controlling ECU 26 is able to calculate a target position of the throttle
 valve 10. A throttle valve position sensor 32 is disposed at or
 operatively associated with the gear mechanism 20 to detect the position
 of the throttle valve 10 and output a throttle valve position signal 5a.
 The throttle controlling ECU 26 receives the throttle valve position
 signal 5a from the throttle valve position sensor 32. The throttle
 controlling ECU 26 calculates the difference between the throttle valve
 position signal 5a and the target position of the throttle valve 10. To
 decrease the calculated difference, the throttle controlling ECU 26
 carries out a PID control operation and calculates the duty ratio signal
 for supplying the driver circuit 24.
 As shown in FIGS. 2 and 3, the gear mechanism 20 includes a pinion gear 40,
 a first gear 42, a second gear 44 and a final gear 46. An intermediate
 shaft 48 is supported in a housing 50. A bearing 52 is rotatably fitted
 around the intermediate shaft 48 and a hub 54 is rotatably fitted around
 the bearing 52.
 As shown in FIG. 2, a flange portion 55 is integrally formed with the hub
 54 at the bottom end of the hub 54. The second gear 44, a plate spring 56
 and the first gear 42 are successively positioned in that order around the
 outer circumference of the hub 54 in a rotatable manner, and a nut or
 intermediate member 58 is fastened around the hub 54 adjacent the axial
 end of the hub.
 The plate spring 56 possesses a plurality of annular creases as shown in
 FIG. 2, and contacts the first gear 42 and the second gear 44 to push both
 the first gear 42 and the second gear 44 in the axial direction of the
 intermediate shaft 48. That is, the spring 56 urges the first gear 42 and
 the second gear axially away from one another. As a result, the first gear
 42 contacts the nut 58 to generate a first frictional force at a first
 contacting portion P1 between the first gear 42 and the nut 58. Further,
 the second gear 44 contacts the flange portion 55 of the hub 54 to
 generate a second frictional force at a second contacting portion P2
 between the second gear 44 and the flange portion 55. It is to be noted
 that the area of the first contacting particular P1 is greater than the
 area of the second contacting portion P2.
 The pinion gear 40 is fixed to an output shaft 23 of the DC motor 22 and
 engages the first gear 42. The final gear 46 is fixed to the throttle
 shaft 12 which integrally rotates with the throttle valve 10. The final
 gear 46 is a sector shaped gear as shown in FIG. 3 and engages the second
 gear 44. The driving torque of the DC motor 22 is transmitted to the first
 gear 42 via the output shaft 23, the pinion gear 40 and the engagement
 between the pinion gear 40 and the first gear 42. The driving torque which
 is transmitted to the first gear 42 is transmitted to the nut 58 which
 integrally rotates with the flange portion 55 of the hub 54 via the first
 frictional force between the first gear 42 and the nut 58 in the first
 contact portion P1. The driving torque which is transmitted to the flange
 portion 55 of the hub 54 is further transmitted to the second gear 44 via
 the second frictional force between the second gear 44 and the flange
 portion 55 in the second contacting portion P2. Finally, the driving
 torque which is transmitted to the second gear 44 is transmitted to the
 final gear 46 via the engagement between the second gear 44 and the final
 gear 46. Accordingly, the DC motor 22 rotates the throttle shaft 12 to
 drive or operationally move the throttle valve 10.
 As shown in FIG. 3, because of the sector shaped nature of the final gear
 46, the final gear 46 has two end surfaces 46a, 46b. A full opening
 stopper 60 and a full closing stopper 62 are disposed in the housing 50.
 One of the end surfaces 46a contacts the full opening stopper 60 when the
 position of the throttle valve 10(10a) is the maximum opening position
 that is shown in broken line in FIG. 3. The other end surface 46b contacts
 the complete or full closing stopper 62 when the position of the throttle
 valve 10(10b) is the completely or fully closed position that is shown in
 dot-dash line in FIG. 3. As a result, the final gear 46 is able to rotate
 within a predetermined range defined at one end by the engagement between
 the end surface 46a and the full opening stopper 60 and at the other end
 by the engagement between the end surface 46b and the fully closing
 stopper 62. The throttle valve 10 is thus rotated within this
 predetermined range.
 In accordance with the present invention, if an excessive torque is applied
 to the first gear 42, for example when the voltage of the DC motor is
 increased, the first gear 42 and the second gear 44 can rotate relative to
 one another against the frictional forces of the plate spring 56.
 Considered in a bit more detail, because the area of the second contacting
 portion P2 is smaller than the area of the first contacting portion P1 as
 shown in FIG. 2, the second gear 44 tends to rotate around the hub 54 more
 than the first gear 42. Accordingly, if excessive torque is applied to the
 first gear 42, the first gear 42 is integrally rotated with the nut 58 and
 the hub 54, but the second gear 44 is not rotated around the hub 54. As a
 result, the second frictional force at the second contacting portion P2
 performs as a torque limiting mechanism or carries out a torque limiting
 function in that the transmitting torque from the first gear 42 to the
 second gear 44 is always less than a predetermined level. Here, because
 the first and the second frictional forces produced by the plate spring 56
 are dependent upon the fastening torque or degree of fastening of the nut
 58, it is rather easy to change the predetermined level of the
 transmitting torque by controlling or changing the fastening torque or
 degree of fastening of the nut 58.
 FIG. 4 illustrates an alternative version of the gear mechanism involving
 the use of a different type of spring, namely a modified plate spring 64.
 In the embodiment shown in FIG. 4, the parts of the gear mechanism
 corresponding to those shown in the embodiment of FIG. 2 are identified
 with the same reference numerals used in FIG. 2. In this alternative
 version shown in FIG. 4, the plate spring 66, which is arranged between
 the first gear 42 and the second gear 44, possesses a conical shape.
 FIG. 5 illustrates another alternative version of the gear mechanism
 involving the use of a coil spring 66. In the embodiment shown in FIG. 5,
 the parts of the gear mechanism corresponding to those shown in the
 embodiment of FIG. 2 are identified with the same reference numerals used
 in FIG. 2. In this version shown in FIG. 5, the coil spring 66 is arranged
 between the first gear 42 and the second gear 44. For purposes of
 arranging and positioning the coil spring 66, both the first gear 42 and
 the second gear 44 are provided with axially extending housings defining
 hollow portions 42a, 44a. The hollow portion 42a of the first gear 42
 faces the hollow portion 44a of the second gear 44 to thereby support the
 end portions of the coil spring 66.
 FIG. 6 illustrates a still further alternative version of the gear
 mechanism involving the use of a wave washer 68. FIG. 6 is a
 cross-sectional view of the gear mechanism, with the wave washer 68 being
 shown in side view. In the embodiment shown in FIG. 6, the parts of the
 gear mechanism corresponding to those shown in FIG. 2 are identified with
 the same reference numerals. In this version shown in FIG. 6, the wave
 washer 68, which is arranged between the first gear 42 and the second gear
 44, has plurality of waves along its circumferential extent.
 By virtue of the present invention as embodied by way of example in the
 various embodiments described above, the throttle valve control device is
 not readily susceptible to damage and breakage of the motor and gear
 parts. However, the throttle value control device is not excessively heavy
 and does not possess an excessively large moment of inertia.
 The principles, preferred embodiments and modes of operation of the present
 invention have been described in the foregoing specification. However, the
 invention which is intended to be protected is not to be construed as
 limited to the particular embodiments described. Further, the embodiments
 described herein are to be regarded as illustrative rather than
 restrictive. Variations and changes may be made by others, and equivalents
 employed, without departing from the spirit of the present invention.
 Accordingly, it is expressly intended that all such variations, changes
 and equivalents which fall within the spirit and scope of the invention be
 embraced thereby.