Abstract:
In a throttle body there are provided a throttle valve for controlling the flow of intake air in an internal combustion engine, and an electrically-driven actuator for actuating the throttle valve. A cover, which covers a receptacle portion, is attached to a side wall of the throttle body. The throttle assembly of the invention is provided with a potentiometer type sensor for detecting the degree of opening of the throttle valve, the sensor comprising a slider and a resistor, the slider being adapted to slide on the resistor and mounted to a peripheral surface of a driven gear so that a tip end thereof faces in a radial direction of a throttle valve shaft. The resistor is constituted by a curved resistor which confronts the slider in the said radial direction. A wall portion which holds the curved resistor is formed by molding integrally with the aforesaid cover.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a throttle assembly for controlling the flow(amount of the flow) of intake air in an internal combustion engine, as well as a throttle sensor for detecting the degree of opening of a throttle valve used in the throttle device. 
     2. Background Art 
     Heretofore, an electronically controlled throttle assembly has practically been used wherein the operation of a throttle valve in an engine is controlled by an electrically-driven actuator (e.g., a DC motor or a stepping motor). 
     The electronically controlled throttle assembly controls the throttle valve angle (throttle valve opening) to an optimum value according to the state of an engine and in accordance with a signal indicative of the degree of opening of an accelerator pedal or a traction control signal. To this end, a sensor for detecting the angle of the throttle valve, what is called a throttle sensor (also called an opening meter or a throttle position sensor) is attached to a throttle body. 
     As the throttle sensor there generally is adopted a potentiometer type sensor, wherein a brush (slider) adapted to rotate together with a throttle valve shaft slides on a resistor, thereby outputting a potential difference signal (sensor detection signal) corresponding to the degree of opening of a throttle valve. 
     As throttle sensors of this type so far used there are known, for example, such throttle sensors as are disclosed in Japanese Patent Laid Open Nos. 7-343878 and 9-32588, wherein a resistor and a wiring pattern of a potentiometer are formed on a substrate. The substrate is attached to a cover of a receptacle portion containing a reduction gear mechanism. A brush is attached to a flat surface of a driven gear (or a rotor) mounted on a throttle valve shaft. In this type of a throttle sensor, the brush slides on a resistor and a conductor both formed on the substrate (a flat surface). Since the driven gear is used also as a moving element to which the brush of the potentiometer is attached, the number of components used can be so much reduced. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a throttle device capable of contributing to reducing the number of components of a throttle sensor, capable of reducing the manufacturing cost and simplifying the assembling work, and further capable of ensuring high accuracy and reliability of the sensor. 
     DISCLOSURE OF INVENTION 
     For achieving the above-mentioned object the present invention basically proposes the following throttle assemblies: 
     (1) A throttle assembly comprising a throttle body having a throttle valve, an electrically-driven actuator for actuating the throttle valve, and a sensor for detecting the degree of opening of the throttle valve, 
     wherein the sensor is constituted by a potentiometer whose output varies according to the rotation of a throttle valve shaft and which comprises a slider (also called a brush) and a resistor, the slider being adapted to slide on the resistor and disposed on one end side of a throttle valve shaft so that a tip end thereof faces in a radial direction of the throttle valve shaft, the resistor being formed as an arcuately curved surface (what is called a curved resistor), and a wall portion which holds the curved resistor is formed by molding integrally with a cover which covers the one end side of the throttle valve shaft in the throttle body. 
     According to a preferred example of the above throttle device (1), the peripheral resistor holding portion (wall portion) is formed by molding integrally with the cover, as described above, and the slider is attached to a peripheral portion of a gear (a driven gear as a final-stage gear in a reduction gear mechanism) mounted on the throttle valve shaft. 
     (2) A throttle assembly comprising a throttle body and, as components mounted to the throttle body, a throttle valve for controlling the flow of intake air in an internal combustion engine, an electrically-driven actuator for actuating the throttle valve, a reduction gear mechanism for the actuator, and a sensor for detecting the degree of opening of the throttle valve, 
     wherein one end of a throttle valve shaft is projected outwards from a side wall of the throttle body, the reduction gear mechanism and the sensor are disposed on a side face of the throttle body on the projecting side of the throttle valve shaft, 
     a bearing which supports one end of the throttle valve shaft on the projecting side of the throttle valve shaft, out of bearings which support the throttle valve shaft, is a ball bearing, a bearing located on the opposite side of the throttle valve shaft is a cap-shaped plain bearing, and one bearing boss of the throttle valve shaft is covered with the plain bearing. 
     (3) A throttle sensor for detecting the degree of opening of a throttle valve which controls the flow of intake air in an internal combustion engine, 
     wherein the throttle sensor is constituted by a potentiometer whose output varies according to the rotation of the throttle valve, the potentiometer comprising a slider adapted to rotate integrally with a throttle valve shaft and a resistor on which the slider slides, the resistor being connected at one end thereof to a positive-side terminal of a power supply and at an opposite end thereof to a ground-side terminal, the position at which the resistor contacts the slider is an output point for taking out an output voltage, and an auxiliary resistor (or resistors) is connected either between one end of the resistor and the positive-side terminal of the power supply or between the opposite end of the resistor and the ground-side terminal, or both. In other words, an auxiliary resistor is provided at one end or at each of both ends of the resistor which is a component of the potentiometer. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a longitudinal sectional view of a throttle assembly according to an embodiment of the present invention and 
     FIG. 2 is a plan view showing a throttle body used in the embodiment, with a cover  16  removed from the throttle body to see the uncovered interior. A gear indicated at  12  in FIG. 2 is mounted to a throttle valve shaft on the throttle body side, but in the same figure, for understanding in what positional relation the gear  12  is inside the gear cover  16 , the gear  12  alone is removed from the throttle valve shaft  3  and is illustrated together with the gear cover. 
     FIG. 3 is a partial perspective view showing the state of FIG. 2 respectively, 
     FIGS. 4,  5  and  6  are exploded perspective views showing the throttle assembly of this embodiment as seen in different angles, 
     FIG. 7 is a perspective view showing, in a disassembled state, components of a throttle sensor which is attached to the cover, 
     FIG. 8 is a perspective view showing a driven gear with brush (slider) which is one of reduction gears used in the embodiment, 
     FIG. 9 is a side view of the cover, 
     FIG. 10 is a sectional view showing the driven gear as mounted to a throttle valve shaft, 
     FIGS. 11 and 12 are sectional views showing other examples of driven gears, 
     FIG. 13 is a developed view of a film with resistor used in the throttle sensor, 
     FIG. 14 is a circuit diagram of resistors and wiring patterns shown in FIG. 13, 
     FIG. 15 is an equivalent circuit diagram thereof, and 
     FIG. 16 is an operation characteristic diagram of the throttle sensor used in the embodiment. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of the present invention will be described hereinunder with reference to the accompanying drawings. 
     As shown in FIG. 1, an electronically controlled throttle assembly (throttle valve assembly) is composed principally of a throttle body  1 , which may be referred to simply as the body hereinafter, a throttle valve  4 , a motor (a throttle valve driving unit or an electrically-driven actuator)  22  for actuating the throttle valve  4 , a reduction gear mechanism  100 , a sensor (throttle sensor)  101  for detecting the angle (degree) of opening, which may be referred to simply as opening hereinafter, of the throttle valve  4 , and a cover  16  for protecting a throttle valve shaft  3 , motor  22  and reduction gear mechanism  100 . 
     The body  1  is formed by molding a receptacle portion (intake bore)  2  for the throttle valve  4  and a receptacle portion (motor housing)  1   c  for the motor  22  integrally with each other. The throttle valve  4  is mounted to the shaft  3  with screws  5 , and the shaft  3  is supported by bearings  6  and  26  which are installed in the body  1 . 
     Various bearings are mentioned as examples of the bearing  6 , among which a ball bearing has heretofore been used as a bearing usually adopted. In this embodiment, a ball bearing and a cap-shaped plain bearing are used as the bearings  6  and  26 , respectively. The reason therefor and their details will be described later. The ball bearing  6  is secured to a bearing boss  1   a  through a seal ring  8 . An inner ring  6   a  of the ball bearing  6  is press-fitted on an outer periphery of the throttle valve shaft  3 , while an outer ring  6   b  thereof is fitted in an inner periphery of the bearing boss  1   a  by transition fit (sliding fit). 
     Only one end of the throttle valve shaft  3  projects to the exterior of a side wall of the body  1 , and a spring  10 , a lever  9 , a spring  11 , and a final-stage gear (driven gear)  12  in the reduction gear mechanism  100 , which will be described later, are fitted on the projecting one end of the throttle valve shaft. The plain bearing  26  is mounted by press-fitting for example. 
     Throttle valve-related components (hereinafter referred to as the throttle valve mechanism) such as the throttle valve shaft  3 , reduction gear mechanism  100  and motor  22  are accommodated within a receptacle portion (case)  1   d  formed in a side wall of the body  1 , the receptacle portion  1   d  being covered with a synthetic resin cover  16 . 
     More specifically, the throttle valve mechanism is disposed so as to be protected by a single cover  16 , an opening (a motor mounting opening)  1   c ′ of the motor housing  1   c  is positioned so as to face the interior of the receptacle portion  1   d,  through which opening the motor  22  is received into the housing, and an end bracket  22   a  of the motor is fixed with screws  37  around the opening  1   c ′ (see FIGS. 4 to  6 ). 
     Motor terminals  23  formed on the end bracket  22   a  are positioned near a side wall of the receptacle portion  1   d  so as to face toward the cover  16  and are connected to relay terminals  24   a  through relay connectors  33 . The relay connectors  33  may be in any of various forms. In this embodiment, sleeves are used as the relay connectors  33 , slits  34  and  35  (see FIG. 5) are formed respectively in both ends of each of the slits in 90°-shifted directions, and each motor terminal  23  and relay terminal  24   a  are fitted in the slits  34  and  35 . The terminals  23  and  24   a  also face in 90°-shifted directions to match the extending directions of the slits  34  and  35 . 
     The motor  22  is driven in accordance with an accelerator signal related to the depression quantity of an accelerator pedal and a traction control signal, and the power of the motor  22  is transmitted to the throttle valve shaft  3  through the reduction gear mechanism  100  (a motor pinion  21 , an intermediate gear  20 , and the final-stage fear  12 ). The pinion  21  is mounted on a motor shaft  27  and the intermediate gear  20  is fitted free on a shaft  19  which is fixed to the throttle body  1 . The intermediate gear  20  comprises a gear  20   a  of a larger diameter meshing with the pinion  21  and a gear  20   b  of a smaller diameter meshing with the gear  12 . 
     The final-stage gear  12  is a sectorial gear and, as shown in FIGS. 2 to  6  and FIG. 8, a holder  12   c  for holding brushes (sliders)  13  of a potentiometer is integral with the gear  12 . The holder  12   c  is formed so as to be positioned on a peripheral surface of the gear  12  on the side opposite to a toothed area of the same gear. 
     Before describing features of the gear  12  in detail, reference will first be made to the relation between the gear  12  and the lever  9 . As shown in FIG. 8, the gear  12  has a hole  12   h  for passing one end  3   a ′ (having at least two flat surfaces) of the throttle valve shaft  3  therethrough. The hole  12   h  is formed in a shape engageable with the one end  3   a ′ of the throttle valve shaft, and through this engagement the gear  12  rotates integrally with the throttle valve shaft  3 . 
     The lever  9  is fitted free on the outer periphery (circumferential surface) of the throttle valve shaft  3  so that the lever  9  and the gear  12  are pulled toward each other through a spring  11 . For example, a lug indicated at  12   f  in FIGS. 2 to  4  comes into engagement with a lug  9   a  of the lever  9  shown in FIG.  6 . The lug  12   f  is formed inside the gear  12 . Further, a lug  12   g  formed on the gear  12  is for positioning in an assembling work relative to a lug  9   b  formed on the lever  9  side. 
     A spring  10  is a return spring for the throttle valve. One end of the spring  10  is anchored to a spring retaining portion (not shown) provided on the body  1  side and the opposite end thereof is anchored to the lever  9 . 
     The spring  10 , which imparts a return force to the throttle valve shaft through the gear  12 , constitutes a known default opening setting mechanism in cooperation with the spring  11  and the lever  9 . 
     The default opening setting mechanism is for holding an initial opening of the throttle valve larger than a fully closed position during OFF of an engine key (in other words, while the electrically-driven actuator  22  is de-energized). From a default opening position up to a fully open control position, a throttle valve opening is determined in accordance with the balance between the motor power and the spring (return spring)  10 . For controlling the throttle valve opening smaller than the default opening, the movement of the lever  9  is prevented by a default opening stopper (not shown) and only the gear  12  and the throttle valve shaft  3  are turned in fully closing direction against the force of the spring  11 . Numeral  25  denotes a fully closing stopper which defines a mechanical fully closed position of the throttle valve, which fully closed position is determined by abutment of a movable-side stopper  12   d  against the stopper  25 , the stopper  12   d  being formed on one side of the sectorial gear  12 . The stopper  12   d  is fixed with a nut  25   a.    
     As to the material of the gear  12  used in this embodiment, as is seen from a sectional view of FIG. 10, a central portion is constituted by a metallic plate  12   a,  and a teeth-forming portion  12   b,  the brush holder  12   c  and the remaining portion are formed integrally by molding a synthetic resin (a reinforced plastic). In this case, the metallic plate  12   a  is insert-molded into the resin portion of the gear. The movable-side stopper  12   d  is integral with the metallic plate  12   a.    
     The stopper  12   d  is formed of a metal for improving the accuracy of the stopper position. More particularly, the mechanical fully closed position of the throttle valve serves as a reference point in control and the stopper  12   d  strikes against the fixed-side fully closing stopper  25  once at every beginning or end of operation. Thus, a high accuracy is required for the stopper  12   d,  and for this reason the stopper  12   d  is formed of a metal which is high in rigidity. 
     The gear  12  is further provided with a movable-side stopper  12   e  for defining a fully open position of the throttle valve (FIGS.  2  and  8 ). The stopper  12   e  is formed by molding a synthetic resin integrally with the gear  12  and the brush holder  12   c.  It suffices for the movable-side fully opening stopper  12   e  to be formed of a synthetic resin because the stopper  12   e  generally does not strike against any other component during operation. Numeral  12   i  denotes a guide for engagement of the gear  12  with the lever  9 . 
     The holder  12   c  for holding the brushes  13  is formed on a peripheral surface of the gear  12 , and two brushes  13  are arranged on an outer surface of the holder  13   c  side by side in the axial direction of the gear  12 . A rotational radius from the throttle valve shaft  3  up to the tips of the brushes  13  is set larger than that of the driven gear  12 . The reason why two brushes  13  are used is that it is intended to use a dual system (two) of throttle sensors. The dual system is advantageous in that even in the event of failure of one throttle sensor, the other can be used as a substitute and that even in the event of occurrence of any trouble on one sensor side, the trouble can be detected by processing signals provided from both sensors. 
     For example, as shown in FIG. 8, the brushes  13  are fitted on lugs  12   j  formed on the holder  12 , which lugs  12   j  are then crushed with heat to fix the brushes onto the holder. Alternatively, the brushes  13  may be fixed using screws or an adhesive. 
     The gear  12  is fixed to one end  3 ′ of the throttle valve shaft  3  with use of a nut  17  and a washer  18 . 
     The gear  12  is not limited to the one described above. Such gears as illustrated in FIGS. 11 and 12 are also employable. 
     In the gear  12  illustrated in FIG. 11, the portion of the brush holder  12   c  is formed of a synthetic resin, while the teeth-forming area  12   b  and the remaining portion are formed using a sintered metal, and the brush holder  12   c  is outer-molded to the gear  12  with use of a resin. 
     In the gear  12  illustrated in FIG. 12, all the constituent portions of the gear  12 , including the brush holder  12   c,  are formed using a synthetic resin, which resin is insert-molded into one end  3   a  of the throttle valve shaft  3 , thus dispensing with the nut  17  and the washer  18 . 
     The following description is now provided about the cover  16 . 
     A great feature of the cover  16  used in this embodiment is that a stator (resistors and wiring patterns) which constitutes the throttle sensor (potentiometer)  101 , as well as a wall portion  15  which holds the stator are provided directly in the cover  16 . 
     Heretofore, for reducing the number of components of a throttle assembly, there has been made an attempt to secure a brush directly to a driven gear in a reduction gear mechanism, but if the member for holding resistors and wiring patterns (conductors) in a potentiometer can be formed by molding integrally with the cover  16 , there can be made a further contribution to the reduction in the number of components. 
     However, in case of forming resistors and wiring patterns directly on an inner surface of the cover  16 , since the cover  16  is formed of a synthetic resin, the resistors may be deteriorated in accuracy under the influence of thermal expansion, contraction and deformation of the cover. According to a conventional measure adopted for avoiding such an inconvenience, resistors and wiring patterns are formed on a substrate as a separate member from the cover and the substrate is then attached to the inner surface of the cover. 
     This embodiment intends to make it possible to mold the holding member (wall portion)  15  for the potentiometer (especially resistors and wiring patterns) integrally with the cover  16  while minimizing the influence of such thermal expansion, contraction and deformation of the cover as just referred to above, and to this end the following means is adopted in the embodiment. 
     As a basic structure, the wall portion  15  is formed by bending a thin plate in a curvilinearly projecting shape so as to minimize the area thereof occupied on the cover  16  and by raising, like erection, the thus-curved thin plate from the inner surface of the cover. According to such an arcuately curved shape of the wall portion  15 , not only the thermal expansion and contraction of the wall portion can be kept to a minimum, but also the wall portion can be enhanced in its rigidity and is difficult to be thermally deformed. In this embodiment, moreover, a reinforcing rib  15   d  is formed on the back of the wall portion  15  to enhance the strength of the wall portion. 
     As to the brushes  13 , they are mounted on the peripheral surface through the holder  12   c  so that their tips face in the radial direction of the throttle valve shaft  3 . The brushes  13  may be mounted to a component other than the gear  12 . For example, a rotor used exclusively for the brush holder may be attached to one end  3   a ′ of the throttle valve shaft  3 . 
     Resistors R 1  and R 2  (see FIG. 13) on which the brushes  13  slide are formed on one side of a film  14  by printing together with auxiliary resistors R 3 , R 4 , conductors  150 ,  151 ,  151 ′ which constitute wiring patterns, conductors  141 ,  142  for taking out signals, and terminals  161 ˜ 164 . As shown in FIGS. 2,  3  and  4 , these registers and conductors are arcuately curved together with the film  14 . Thus, the resistors R 1  and R 2  are formed as curved resistors. 
     The reason why two resistors R 1  and R 2  are used in the potentiometer and so are the brushes  13  is because it is intended to form two throttle sensors. As to operational characteristics of the potentiometer used in this embodiment, reference will be made thereto later. 
     In the other figures than FIG. 13, for example in FIGS. 2,  3 ,  4  to  6  and  7 , the curved resistors R 1  and R 2  are omitted their illustration for the convenience of drawing. For convenience sake, the film  14  may hereinafter be referred to as the curved resistor or film with resistors. 
     As noted earlier, the wall portion  15  which holds the curved resistor  14  (i.e., film with resistors R 1  and R 2 ) is formed by molding integrally with the cover  16  which covers one end side of the throttle valve shaft of the throttle body  1 . 
     As shown in FIG. 2, the wall portion  15  is formed in conformity with the direction of the bushes  13  and is positioned on the inner surface of the cover  16  and near the corner located on the side opposite to the teeth portion of the gear  12 . The wall portion  15  is in a curvilinearly erected shape which draws an arc about the axis of the throttle valve shaft  3 . 
     Now, with reference to FIGS. 13 to  15 , a description will be given below about the circuit configuration of the potentiometer and related wiring layout used in this embodiment. 
     As shown in FIG. 13, the conductor  141  for taking out an output signal and the resistor R 1 , as well as the conductor  142  for taking out an output signal and the resistor R 2 , are arranged in parallel on one side of the synthetic resin film (sheet)  14 , with auxiliary resistors R 3  and R 4  being further added. 
     The conductors  141  and  142  are formed using a material of a low resistivity, e.g., silver paste, while the resistors R 3  and R 4  are formed using a material of a relatively high resistivity, e.g. carbon, provided no limitation is made thereto. 
     Actually, the surfaces of the conductors  141 ,  142 ,  150 ,  150 ′,  151  and  151 ′ formed of silver paste for example are also coated with carbon. One of the two brushes  13  slides while straddling both resistor R 1  and conductor  141 , while the other brush  13  slides while straddling both resistor R 2  and conductor  142 . The conductors  141 ,  142  and the brushes  13  turn conductive with each other in the thickness direction of the carbon film at the brush contact positions (the resistance is low because the film thickness is small), so the carbon film formed on the conductors causes no obstacle. Rather, by coating the conductors (silver paste) with a hard carbon, it is possible to improve the abrasion resistance when the brushes  13  slide on the conductors  141  and  142 . 
     The resistor R 1  is formed between ends  151   a  and  151   b  of a wiring conductor, using only a resistive material. Also as to the resistors R 2 , R 3  and R 4 , they are formed in the same way. 
     In FIG. 13, the portions corresponding to the resistors R 1 , R 2 , R 3  and R 4  are hatched. The resistors and wiring layout in FIG. 13 coincide with the circuit diagram of FIG.  14 . 
     At one end  14   a  of the film  14  are disposed a first sensor output terminal (TPS 1 )  161 , a positive terminal (Vcc)  162  of a power supply, a second sensor output terminal (TPS 2 )  163 , and a ground terminal (GND)  164 . 
     The first sensor output terminal  161  serves as a terminal of the output taking-out conductor  141 . The conductor  141  is wider at its portion where the associated brush  13  slides. 
     The power supply terminal  162  is connected to one end of the auxiliary resistor R 3  through the conductor  150 , while the opposite end of the auxiliary resistor R 3  is connected to one end of the resistor R 1  through the conductor end  151   a  and is also connected to one end of the resistor R 2  through the conductor end  151   a  and the conductor  151 . The opposite end of the resistor R 1  is connected to one end of the auxiliary resistor R 4  through the conductors  151   b,    151 ′ and  151   a ′. The opposite end of the auxiliary resistor R 4  is connected to the ground terminal  164  through conductors  150   a ′ and  150 ′. 
     The second sensor output terminal  163  serves as a terminal of the output taking-out conductor  142 . The conductor  142  is wider at its portion where the associated brush  13  slides. 
     FIG. 14 schematically illustrates a state in which one brush  13  slides while straddling the resistor R 1  and the conductor  141  and the other brush  13  slides while straddling the resistor R 2  and the conductor  142 . According to the wiring illustrated in FIGS. 13 and 14, if the brushes  13  move, for example, in an opening direction from a closed state, the brush  13  which slides on the resistor R 1  moves from a low potential side (ground side) to a high potential side (positive side of the power supply), while the brush  13  which slides on the resistor R 2  moves from the high to the low potential side. An equivalent circuit thereof is illustrated in FIG.  15 . The sensor output terminals  161  and  162  take out potentials at the brush contact points of the resistors R 1  and R 2 . 
     According to the above wiring patterns, the resistors R 1  and R 2  are connected at one ends thereof to the positive terminal  162  of the power supply and at the opposite ends to the ground terminal  164 . Further, the contact positions of the brushes  13  serve as output points for taking out output voltages, the auxiliary resistor R 3  is connected between one ends of the resistors R 1 , R 2  and the positive terminal  162  of the power supply, and the auxiliary resistors R 3  and R 4  are connected between the opposite ends of the resistors R 1 , R 2  and the ground terminal  164 . In other words, the auxiliary resistors R 3  and R 4  are provided at both ends of the resistors R 1  and R 2 . The resistors R 1  and R 2  are each several kilo-ohms and the resistors R 3  and R 4  are each several hundred ohms. 
     FIG. 16 illustrates operational characteristics of sensor output voltages relative to movement quantities (throttle valve openings) of the brushes  13 . In the same figure, the movement quantity  0  corresponds to a fully closed position in control of the throttle valve opening and the movement quantity  40  corresponds to a fully open position in control. The numeral {circle around ( 1 )} represents an operational characteristic at the brush contact point potential in resistor R 1  and numeral {circle around ( 2 )} represents an operational characteristic at the brush contact point potential in resistor R 2 . A mean value of both operational characteristics {circle around ( 1 )} and {circle around ( 2 )} lies at an intermediate level of potential. If there should occur any trouble in one of the sensor outputs, the mean value of the operational characteristics {circle around ( 1 )} and {circle around ( 2 )} is biased to either the upper or the lower side of the above intermediate level. From this bias it is possible to judge which sensor is out of order. 
     By using the auxiliary resistors  33  and  34  it is possible to make gentle the gradient of the sensor output characteristics (operational characteristics {circle around ( 1 )} and {circle around ( 2 )}) relative to the movement quantity of the brushes (throttle valve opening) and hence possible to diminish output variation characteristics induced by changes in temperature of the resistors for example. 
     In this connection, reference will now be made, for example, to the case where the power supply voltage is 5V and the ground voltage is 0V. In this case, in the absence of resistors R 3  and R 4 , a voltage of 5V is applied to both ends of the resistors R 1  and R 2 , but in the presence of the auxiliary resistors R 3  and R 4  as in this embodiment, the voltage at one ends (the ground side) of the resistors R 1  and R 2  is raised to a higher level (say, 0.3V) than zero level because of the presence of resistor R 3 , while the voltage at the opposite ends (the positive side of the power supply) becomes somewhat lower (say, 4.7V) than 5V because of the presence of resistor R 4 . Thus, the potential difference at both ends of the resistors R 1  and R 2  becomes 4.4V, so that the gradient of output characteristics (operational characteristics {circle around ( 1 )} and {circle around ( 2 )}) relative to the movement quantity of the brushes becomes smaller than that at the both-end potential difference of 5V of the resistors R 1  and R 2  (in the absence of the auxiliary resistors R 3  and R 4 ). Therefore, even where the operational characteristics vary according to temperatures, the variation range is made narrow to prevent deterioration of the sensor accuracy. 
     Although in this embodiment the auxiliary resistors R 3  and R 4  are disposed at both ends of the resistors R 1  and R 2 , such an auxiliary resistor R 3  or R 4  as described above may be disposed at only one ends of the resistors R 1  and R 2 , and even in this case it is possible to narrow the variation range of the sensor operation characteristics. 
     As shown in FIG. 13, one end  14   a  of the film  14  is made small in width and the terminals  161 ˜ 164  are arranged on one side of the one end  14   a.    
     On the inner surface of the cover  16 , as shown in FIGS. 2 and 7, a terminal box  32  for insertion therein of one end  14   a  of the film is formed by the side of the wall portion  15  integrally with the cover  16 . 
     In the terminal box  32 , an upper portion  32   a  and a side portion  32   b  close to the wall portion  15  are open so that one end  14   a  of the film can be inserted therein. 
     At the position of the terminal box  32  the terminals  161 ˜ 164  formed at one end of the film  14  and relay terminals  40 - 1  to  40 - 4 , which communicate with connector terminals, are connected together electrically. 
     More specifically, as shown in FIG. 9, connector terminals  40  (four in this embodiment) for external connection of the throttle sensors and connector terminals  24  (two in this embodiment) for external connection of the motor power supply are disposed in a connector case  16   b  of the cover  16 . Conductors  40 ′ for connection between the connector terminals  40  and the throttle sensors and conductors  24 ′ for connection between the connector terminals  24  and the relay terminals  24   a  of the motor power supply are insert-molded into the cover  16  (this state is shown in FIG. 7 with the conductors partially omitted) and one ends of the conductors  40 ′, i.e., the terminals  40 - 1  to  40 - 4 , are erected so as to be positioned by the side of one end  15   b  of the wall portion which is for holding the curved resistors, in other words, they rise so as to project upward from the inner surface of the cover  16 , further, one ends  24   a  of the conductors  24 ′ of the motor power supply are erected from the inner surface of the cover  16 . 
     One end  14   a  of the film  14  is inserted into the terminal box  32  in such a manner that the terminals  161 ˜ 164  formed on the film  14  and the terminals  40 - 1 ˜ 40 - 4  conducted into the terminal box  32  confront each other, and a plate spring  36  serving as a film pressing member is inserted into the terminal box  32 , whereby the terminals can be connected positively without separation. The relay terminals  24   a  on the motor side and the motor terminals  23  are connected together through the relay connectors  33 . 
     Advantages of this embodiment are as follows. 
     {circle around ( 1 )} In the throttle sensor, the brushes  13  come into contact with the curved resistors  14  (R 1 , R 2 ) while facing in the radial direction of the throttle valve shaft  3 . This is advantageous in point of reliability. 
     More particularly, the brushes  13  are mounted on the throttle valve shaft through the holder, but an assembling error developed in the throttle valve shaft is generally larger in the thrust direction than in the radial direction. The reason is that variations in machining and variations in assembly accumulate to 1 mm or so in the radial direction, whereas in the thrust direction there occur only coaxiality deviation and variations among molded products, which can be suppressed to below several hundred micron meters. 
     Consequently, the separating force of each brush from the associated resistor induced by wobbling of the throttle valve shaft is larger in the case where the brush is brought into contact (sliding contact) with the resistor in the thrust direction of the throttle valve shaft (the contact in this case is a plane contact) than in the case where the brush is brought into contact with the resistor in the radial direction of the throttle valve shaft (the contact in this case is a curved contact). Therefore, in the former (plane contact) case, it is necessary that the contact pressure of the brush against the resistor be set larger than in the latter (curved contact) to prevent the brush and the resistor from coming out of contact with each other. So increasing the contact pressure will accelerate the wear of the brush and that of the resistor. 
     This embodiment adopts the latter method, whereby it is possible to prevent the brush-resistor separation without so much increasing the contact pressure. Consequently, it is possible to enhance the reliability of the throttle sensor and also enhance the abrasion resistance and durability of the sensor components. 
     {circle around ( 2 )} Even in case of adopting such a curved contact (curved resistor) type throttle sensor (potentiometer) as described above, this embodiment makes it possible to reduce the number of components and reduce the product cost. More particularly, for mounting a curved resistor type sensor into the cover  16  of the throttle body  1 , there may be adopted a different method wherein the throttle sensor is beforehand unitized separately from the cover and is then installed into the cover. In this case, however, it is necessary that sensor components (e.g., resistor, rotor with brush, and resistor holding member) be accommodated together into a dedicated unit case (sensor housing). On the other hand, this embodiment dispenses with such a sensor unit as mentioned above and permits the gear  12  to serve also as the rotor with brush. In this embodiment, moreover, since the curved resistor holding member (wall portion  15 ) is integral with the cover  16 , it is possible to reduce the number of throttle sensor components and hence reduce the product cost and simplify the assembling work. 
     Further, although the curved resistor holding portion is provided in the cover, it is possible to ensure a high sensor accuracy because there is adopted a structure which is difficult to be influenced by thermal expansion, contraction and deformation of the cover. 
     {circle around ( 3 )} By providing at least one of the auxiliary resistors R 3  and R 4  in each throttle sensor it is possible to obtain operational characteristics of the sensor with suppressed thermal variation. 
     {circle around ( 4 )} It is possible to simplify the bearing structure of the throttle valve shaft having the throttle sensors; besides, it is possible to reduce the number of components used and thereby realize a compact bearing protecting structure. 
     In more particular terms, according to this embodiment, only one end  3   a ′ of the throttle valve shaft  3  is projected to the exterior of a side wall of the throttle body and the reduction gear mechanism and the throttle sensors are disposed on the throttle body side face on the projecting side of the throttle valve shaft. 
     Thus, where the reduction gear mechanism and the throttle sensors are arranged together on one side face of the throttle body, a highly accurate bearing such as the ball bearing  6  or any other rolling bearing of reduced wobbling may be used as the bearing for the throttle valve shaft on the side where the above components are arranged, while a bearing, e.g., plain bearing, which is less expensive but somewhat inferior in accuracy than the ball bearing, may be used as the other bearing. 
     Further, since the plain bearing  26  is cap-shaped and covers one bearing boss  1   b  on the throttle valve shaft, it is possible to omit the use of a dedicated cap or cover for the bearing boss  1   b.    
     {circle around ( 5 )} Additionally, according to this embodiment, at least one end  15   a  of the wall portion  15  which holds the curved resistor  14  is rounded at  41 , so at the time of positioning the brushes  13  on the curved resistor after installation of the gear  12  and the cover, the brushes  13  can be mounted easily by allowing them to slide on the rounded surface  41 . The numeral  15   c  in FIGS. 2 and 3 denotes a stepped portion to be used for positioning the film  14 , the stepped portion  15   c  being formed at one end of the wall portion  15 . Also for mounting the film  14  to the wall portion  15 , for connecting the sensor terminals and for mounting the brushes, this embodiment adopts a structure which takes the easiness of those works into account, thus permitting the reduction of the working cost. 
     Although in the above embodiment the film  14  with curved resistors is affixed to the wall portion  15 , the resistors and wiring patterns may be printed directly onto the surface of the wall portion  15 . 
     INDUSTRIAL APPLICABILITY 
     According to the present invention, as set forth above, it is possible to provide a throttle assembly and a throttle sensor, capable of contributing to the reduction in the number of components of the throttle sensor, capable of reducing the manufacturing cost and simplifying the assembling work and further capable of ensuring high sensor accuracy and reliability.