Abstract:
The present invention provides a starter, including a motor generating torque; a shaft rotating by the torque; a clutch fitting an outer periphery of the shaft; a pinion gear receiving the torque; a pinion control means configured to allow the pinion gear integrally with the clutch to be pushed out; a motor control means for controlling current supplied to the motor; and an inner tube that is arranged to be extended from the inner and in the direction opposite to the motor, supports the pinion gear so as to inhibit rotation thereof with respect to the periphery of the inner tube, and supports the pinion gear to be slidable; wherein a gear-side face and a tube-side face are formed in the pinion gear and the inner tube, respectively, in which the faces are facing each other, and a cushioning member is disposed between the gear-side face and the tube-side face.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based on and claims the benefit of priority from earlier Japanese Patent Application No. 2009-96104 filed Apr. 10, 2009, the description of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. (Technical Field of the Invention) 
     The present invention relates to a starter for starting an engine and, more particularly, the present invention relates to a starter having a structure that reduces operation noise thereof. 
     2. (Related Art) 
     Conventionally, automatic engine stop/restart systems (hereinafter referred to as “idle stop system(s)”) are known. Such an idle stop system is able to automatically control stop/restart of an engine. 
     Specifically, Japanese patent Laid-open Publication No. 2005-330813 discloses an idle stop system. The idle stop system includes a pinion control means for controlling the pinion gear to be pushed out towards a ring gear and a motor control means for controlling current to be supplied to the motor on/off. In the idle stop system, the pinion control means and the motor control means are configured such that the both means can be operated individually. With this configuration, even if an event requiring an engine-restart occurs during the engine rotation is decreasing until the engine completely stopped, the pinion gear is pushed out to the ring gear while being rotated whereby the pinion gear meshes with the ring gear. As a result, the engine-restart can be made by powering the motor after completion of the meshing, With this method applied to this configuration, compared to the engine-restart being made after the complete engine stop, the driver of the vehicle does not feel anything uncomfortable because of the smooth engine-restart. 
     According to the above-described prior art, even if the engine-restart request is not issued while the engine rotation is decreasing, the pinion gear can be meshed with the ring gear when the rotation speed of the ring gear reaches a predetermined value. Subsequently, the meshing between pinion gear and the ring gear can be maintained until the complete engine stop without powering the motor. Therefore, since the pinion gear and the ring gear remain meshed when next engine-restart request occurs, necessary period for the engine-restart can be reduced. 
     An increase in vehicles including an idle-stop system that automatically controls stop and restart of the engine is expected in the next few years. As the vehicles including the idle stop system increase, for instance, it is expected situations that vehicles become stuck in a local road due to a traffic jam. In this case, it is considered that the engines in the vehicles start at almost the same time. As a result, operation noise of the starter when the engine starts increases and such a noise may cause a noise pollution problem along the road side. 
     The dominant noise elements accounting for the operation noise of the starter includes a strike noise that occurs when the end face of the pinion gear strikes the end face of the ring gear, a strike noise caused by the teeth faces of the pinion gear and the ring gear when the pinion gear meshes with the ring gear, and an operation noise of the electromagnetic solenoid which is a part of the pinion control means (i.e., a strike noise that occurs when a plunger strikes a core). 
     However, as described above, when the pinion gear meshes with the ring gear while the engine rotation is decreasing without supplying power to the motor, the end face of the pinion gear strikes the end face of the ring gear and at almost the same time, the plunger of the electromagnetic solenoid strikes the core. As a result, two types of noises caused by both striking influence each other and generate an impact noise that accumulates the noises. Moreover, at the moment, since the motor is not powered so that no operation sound is generated by the motor. Hence, the above-described impact noise significantly stands out and makes the driver of the vehicle uncomfortable. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in consideration of the foregoing conventional situation, and an object of the present invention is to provide a starter in which an impact shock caused by striking between the pinion gear and the ring gear is reduced whereby noise caused by the impact shock when the engine starts can be reduced. 
     In order to achieve the object, the present invention provides, as one aspect, a starter mounted on a vehicle for starting the engine, including: a motor that generates torque by being energized; an output shaft that rotates by receiving the torque from the motor; a clutch that fits an outer periphery of the output shaft; a pinion gear that receives the torque generated by the motor via the clutch; a pinion control means configured to allow the pinion gear integrally with the clutch to be pushed out in the axial direction; a motor control means for controlling current supplied to the motor on and off; and an inner tube that is arranged to be cylindrically extended from the inner and in the direction opposite to the motor, supports the pinion gear so as to inhibit rotation thereof with respect to the periphery of the inner tube, and supports the pinion gear to be slidable in the axial direction; wherein a gear-side pressure receiving face and a tube-side pressure receiving face are formed in the pinion gear and the inner tube, respectively, in which the both faces are facing each other with a predetermined distance in the axial direction, and a cushioning member is disposed between the gear-side pressure receiving face and the tube-side pressure receiving face. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a general view of a starter according to a first embodiment of the present invention; 
         FIG. 2  is a sectional view of a pinion movable body according to the first embodiment; 
         FIG. 3  is a sectional view of a solenoid for pushing out a pinion and a solenoid for supplying current to a motor; 
         FIG. 4  is an electric circuit diagram of the starter; 
         FIG. 5A  is a graph of sound pressure which is produced at the time the starter operates; 
         FIG. 5B  is a graph of engine speed; 
         FIG. 5C  is a graph of starter current; 
         FIG. 6  shows results of the measurement of sound pressure obtained while pinion preset is performed; 
         FIG. 7  is a sectional view of a pinion movable body according to a second embodiment; 
         FIG. 8  is a sectional view of a pinion movable body according to a third embodiment; and 
         FIG. 9  is a sectional view of a pinion movable body according to a fourth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Hereinafter, embodiments of the present invention will now be described in connection with the accompanying drawings. 
     (First Embodiment) 
     A starter  1  according to a first embodiment is applied to an idle stop system which automatically controls stop/restart of an engine. 
     As shown in  FIG. 1 , the starter  1  includes a motor  2 , an output shaft  3 , a pinion movable body (described later). The motor  2  generates torque. The output shaft  3  is rotated by the motor  2 . The pinion movable body is provided so as to be movable on the periphery of the output shaft  3  and in the axial direction thereof. The starter  1  further includes a solenoid  5  (hereinafter referred to as “pinion solenoid  5 ”) which pushes out the pinion movable body in the direction opposite to the motor (leftward in  FIG. 1 ) via a shift lever  4 , a solenoid  6  (hereinafter referred to as “motor solenoid  6 ”) which opens/closes a motor contact (described later), and the like. A reduction gear (e.g. planetary gear reducer) may be provided between an armature  2   a  of the motor  2  (see  FIG. 4 ) and the output shaft  3  so that the torque of the armature  2   a  is reduced and transmitted to the output shaft  3 . 
     The pinion movable body is configured with a clutch  7  and a pinion gear  8  as described below. 
     The clutch  7  includes a spline barrel  7   a , an outer  7   b , an inner  7   c , a roller  7   d , and the like. The spline barrel  7   a  fits the periphery of the output shaft  3  (helical spline fitting). The outer  7   b  is provided integrally with the spline barrel  7   a . The inner  7   c  is arranged at the inner side of the outer  7   b  so as to be rotatable with respect to the outer  7   b . The roller  7   d  interrupts the transmission of the torque between the outer  7   b  and the inner  7   c . That is, the pinion movable body acts as a known one-direction clutch, which transmits torque in only one direction from the outer  7   b  to the inner  7   c.    
     The clutch  7  has an inner tube  9  provided integrally with the inner  7   c . The inner tube  9  fits the periphery of the output shaft  3  via bearings  10  so as to be rotatable with respect to the output shaft  3 . 
     As shown in  FIG. 2 , the inner tube  9  cylindrically extends from the inner  7   c  and in the direction opposite to the motor (leftward in  FIG. 2 ). A straight spline  9   a  is formed on the periphery of the inner tube  9  and in the axial direction thereof. A flange  9   b  is provided at the inner side end portion of the inner tube  9 . The outer diameter of the flange  9   b  is larger than that of the straight spline  9   a . The end face of the flange  9   b , which is located at a position opposite to the inner in the axial direction of the flange  9   b  (left side in  FIG. 2 ), serves as a tube-side pressure receiving face  9   c.    
     A pinion gear  8  has a hale which fits the periphery of the inner tube  9  (hereinafter, referred to as “fitting hole”). A straight spline  8   a  (see  FIG. 2 ) is formed on the inner periphery of the fitting hole. The straight spline  8   a  engages with the straight spline  9   a  of the inner tube  9  and rotates integrally with the inner tube  9 . The straight spline  8   a  is movable on the periphery of the inner tube  9  and in the axial direction thereof. As shown in  FIG. 2 , the movement of the pinion gear  8  in the direction opposite to the clutch is restricted by a pinion stopper  11  disposed at an end portion of the inner tube  9  positioned opposite to the inner side. 
     A large-diameter hole is formed at the inner side of the pinion gear  8 . The inner diameter of the large-diameter hole is larger than that of the fitting hole in which the straight spline  8   a  is formed. As shown in  FIG. 2 , the large-diameter hole is formed at the clutch side with respect to the fitting hole (right side in  FIG. 2 ) in the axial direction of the pinion gear  8 . A step is provided between the fitting hole and the large-diameter hole. The step serves as a gear-side pressure receiving face  8   b  which faces the tube-side pressure receiving face  9   c  with a predetermined distance in the axial direction of the inner tube  9 . The inner diameter of the large-diameter hale is determined so that the pinion gear  8  can slide on the periphery of the flange  9   b  of the inner tube  9 . The length of the pinion gear  8  in the axial direction thereof is slightly longer than the distance between the pinion-side end face of the pinion stopper  11  and the tube-side pressure receiving face  9   c  in the axial direction. That is, as shown in  FIG. 2 , the pinion gear  8  is located so that the rear end thereof is positioned so as to be slightly distanced from the tube-side pressure receiving face  9   c  to the clutch side in the axial direction when the front end thereof contacts the pinion-side end face of the pinion stopper  11 . 
     A cushioning member  12  is arranged on the inner side of the large-diameter hole formed in the pinion gear  8 . The cushioning member  12  is an elastic member made of rubber or elastomer which is a composite of rubber and resin. The cushioning member  12  is held between the tube-side pressure receiving face  9   c  and the gear-side pressure receiving face  8   b  in a state where an initial load is applied therebetween, that is, elastic force is accumulated therebetween. Due to the initial load applied to the cushioning member  12 , the pinion gear  8  is pressed against the pinion stopper  11 . The initial load applied to the cushioning member  12  preferably has the magnitude which can prevent the pinion gear  8  from moving in the direction opposite to the pinion stopper due to vibration acceleration effected to the starter  1  from the outside thereof. 
     Hereinafter, configurations of the pinion solenoid S and the motor solenoid  6  are described. The pinion solenoid  5  and the motor solenoid  6  share a fixed core  13 . The pinion solenoid  5  and the motor solenoid  6  are integral with each other in the axial direction so as to hold the fixed core  13 . As shown in  FIG. 1 , the pinion solenoid  5  and the motor solenoid  6  are fixed to a starter housing  14  so as to be parallel to the motor  2 . 
     As shown in  FIG. 3 , the pinion solenoid  5  includes a solenoid case  15 , an excitation coil  16 , a plunger  17 , and a joint  18 , in addition to the fixed core  13 . The excitation coil  16  is accommodated in the solenoid case  15 . The plunger  17  is movable in the axial direction in a state where the plunger  17  faces the fixed core  13 . The joint  18  transmits the movement of the plunger  17  to the shift lever  4 . 
     As shown in  FIG. 4 , the excitation coil  16  has one end portion which is connected to a connector terminal  19  and the other end portion which is connected to the surface of the fixed core  13 , for example, for grounding by welding or the like. The connector terminal  19  is connected with an electrical wiring which is connected to a starter relay  20 . 
     The starter relay  20  is subjected to on/off control of an electronic control unit  21  (hereinafter referred to as “ECU  21 ”) which controls the operation of the starter  1 . When the starter relay  20  is controlled and turned on by the ECU  21 , current is supplied to the excitation coil  16  from a battery  22  via the starter relay  20 . 
     When the fixed core  13  is magnetized upon supply of current to the excitation coil  16 , the plunger  17  is attracted to the fixed core  13  against the reaction force of a return spring  23  arranged between the plunger  17  and the fixed core  13 . The plunger  17  has a substantially cylindrical shape with a cylindrical bore axially formed in the radial center thereof. The cylindrical bore is formed in the plunger  17  so that the plunger  17  is opened at one axial end side (leftward end side in  FIG. 3 ) thereof and bottomed at the other axial end side. 
     The rod-shaped joint  18  is inserted into the cylindrical bore of the plunger  17  together with a drive spring  24 . The joint  18  has one end in which an engagement groove  18   a  is formed which engages with one end of the shift lever  4 , and the other end at which a flange  18   b  is formed. The one end of the joint  18  projects from the cylindrical bore of the plunger  17 . The flange  18   b  has an outer diameter corresponding to the inner diameter of the cylindrical bore so that the flange  18   b  can slidably move along the inner periphery of the cylindrical bore. Being loaded by the drive spring  24 , the flange  18   b  is pressed against the bottom face of the cylindrical bore. With the movement of the plunger  17 , the pinion gear  8  is pushed out in a direction opposite to the motor via the shift lever  4 . As a result, an end face of the pinion gear  8  comes into contact with an end face of a ring gear  25 . During the movement of the plunger  17  from this instance up until the plunger  17  is attracted to the fixed core  13 , the drive spring  24  is compressed arid stores reaction force for allowing the pinion gear  8  to engage with the ring gear  25  of the engine. 
     As shown in  FIG. 3 , the motor solenoid  6  includes a cylindrical yoke  26 , a excitation coil  27 , a plunger  28 , a contact cover  29 , two terminal bolts  30 ,  31 , a pair of fixed contacts  32 , and a movable contact  33 , in addition to the fixed core  13 . The yoke  26  is integrally with the solenoid case  15  by extending the portion of the yoke  26  positioned at the opening side of the solenoid case  15  in the axial direction. The excitation coil  27  is arranged inside the yoke  26 . The plunger  28  is movable in the axial direction in a state where the plunger  28  faces the fixed core  13 . The contact cover  29  is made of resin and attached to yoke  26  so that the contact cover  29  closes the opening of the yoke  26 . The two terminal bolts  30  and  31  are fixed to the contact cover  29 . The pair of fixed contacts  32  is connected to a motor circuit via the respective two terminal bolts  30  and  31 . The movable contact  33  establishes electrical connection between the pair of fixed contacts  32 . 
     As shown in  FIG. 4 , the excitation coil  27  has one end which is connected to an external terminal  34  and the other end which is connected to the surface of the fixed core  13 , for example, by welding or the like for grounding. The external terminal  34  projects outward from the end face of the contact cover  29  while being connected with an electrical wiring which is connected to the ECU  21 . 
     A magnetic plate  35  is arranged at a position opposite to the fixed core side of the excitation coil  27 . The magnetic plate  35  has an annular shape and forms a part of a magnetic circuit. The outer peripheral end face of the magnetic plate  35  positioned at the coil side (left side in  FIG. 3 ) comes into contact with a step provided at the inner periphery of the yoke  26 , thereby restricting the position of the magnetic plate  35  at the coil side. 
     When the fixed core  13  is magnetized upon supply of current to the excitation coil  27 , the plunger  28  is attracted to the fixed core  13  against the reaction force of a return spring  36  arranged between the plunger  28  and the fixed core  13 . 
     The contact cover  29  has a cylindrical leg portion  29   a . The contact cover  29  is arranged in a state where the leg portion  29   a  is inserted into the yoke  26  so that an end face of the leg portion  29   a  is brought into contact with the surface of the magnetic plate  35 , Thus, the contact cover  29  is caulked and fixed to the yoke  26 . Of the two terminal bolts  30  and  31 , the terminal bolt  30  is a B terminal bolt to which a battery cable  37  (see  FIG. 4 ) is connected, and the terminal bolt  31  is an M terminal bolt to which a motor lead wire  38  (see Fig,  1 ) is connected. 
     The pair of fixed contacts  32  is provided separately from the two terminal bolts  30  and  31 , for example, and is fixed to the two terminal bolts  30  and  31  inside the contact cover  29 . 
     The movable contact  33  is provided on the side opposite to the plunger  28  (right side in  FIG. 3 ) and is located at a position more distanced from the plunger  28  than at the position where the pair of fixed contacts  32  is located. The movable contact  33  is pressed against an end face of a resinous rod  39  fixed to the plunger  28  while being loaded by a contact pressure spring  40 . In this regard, the initial load of the return spring  36  is set to a value larger than that of the initial load of the contact pressure spring  40 . Therefore, when current is not supplied to the excitation coil  27 , the movable contact  33  is allowed to sit on an inner seat surface of the contact cover  29  in a state of pressing and contracting the contact pressure spring  40 . 
     The motor contact mentioned hereinbefore is formed of the pair of fixed contacts  32  and the movable contact  33 . When the movable contact  33  comes into contact with the pair of fixed contacts  32  and is biased by the contact pressure spring  40 , current is applied across the fixed contacts  32 , whereby the motor contact is closed. On the other hand, when the movable contact  33  comes out of contact with the pair of fixed contacts  32 , the current application across the contacts  32  is shut off, whereby the motor contact is opened. 
     Next, an operation of the starter  1  is described. 
     a) In a case where the engine is started in a normal manner (that is, a case where the engine is started by the user&#39;s turn-on operation of an ignition switch (not shown) in a state where the engine is completely stopped): 
     The ECU  21  effects control to close the starter relay  20  upon reception of an engine start signal produced by the user&#39;s turn-on operation of the ignition switch. Thereby, the excitation coil  16  of the pinion solenoid  5  is supplied with current from the battery  22 , whereby the plunger  17  is moved by being attracted to the magnetized fixed core  13 . With the movement of the plunger  17 , the pinion gear  8  is pushed out integrally with the clutch  7  in the direction opposite to the motor via the shift lever  4  and stops in a state where the end face of the pinion gear  8  is in contact with the end face of the ring gear  25 . 
     After expiration of the predetermined time following the production of the engine start signal, the ECU  21  outputs a turn-on signal to the excitation coil  27  of the motor solenoid  6 . Thereby, current is supplied to the excitation coil  27 , whereby the plunger  28  is attracted to the fixed core  13 . Thereby, the movable contact  33  comes into contact with the pair of fixed contacts  32  and is biased by the contact pressure spring  40 , whereby the main contact is closed. As a result, current is supplied to the motor  2  to generate torque of the armature  2   a . The torque is then transmitted to the output shaft  3 . Furthermore, the rotation of the output shaft  3  is transmitted to the pinion gear  8  via the clutch  7 . When the pinion gear  8  has rotated up to a position enabling engagement with the ring gear  25 , the pinion gear  8  engages with the ring gear  25  by the reaction force stored in the drive spring  24 . Thereby, the torque is transmitted from the pinion gear  8  to the ring gear  25  to crank the engine. 
     When the engine starts, the ECU  21  outputs a turn-off signal, which stops the supply of current to the excitation coil  16  of the pinion solenoid  5  and the excitation coil  27  of the motor solenoid  6 . As a result, the attraction force of the pinion solenoid  5  is lost, whereby the plunger  17  is pushed back. Thereby, the pinion gear  8  is released from the ring gear  25 . Then, the pinion gear  8  moves on the periphery of the output shaft  3  to the rest position (shown in  FIG. 1 ) integrally with the clutch  7  and stops. In addition, the attraction force of the motor solenoid  6  is lost, whereby the plunger  28  is pushed back. Thereby, the motor contact is opened to stop the power feed from the battery  22  to the motor  2 . Then, the rotation of the armature  2   a  gradually decelerates and stops. 
     b) In a case where an idle stop is performed when the vehicle is in an idling state or a case where a user operates an ignition switch to the engine stop position: 
     The ECU  21  outputs an engine stop signal to stop the fuel injection and the supply of intake air to the engine. Thereby, the engine proceeds to a stop process in which, as shown in  FIG. 5B , the rotation of the ring gear  25  (shown as engine speed in  FIG. 5B ) starts to decelerate. When the rotation of the ring gear  25  decelerates up to the predetermined engine speed, the ECU  21  outputs a turn-on signal to the excitation coil  16  of the pinion solenoid  5 . As a result, the pinion gear  8  is pushed out integrally with the clutch  7  in the direction opposite to the motor. Thereby, the end face of the pinion gear  8  comes into contact with the end face of the ring gear  25 . Thereafter, when the ring gear  25  rotates up to the position at which the ring gear  25  can engage with the pinion gear  8 , the engagement between the pinion gear  8  and the ring gear  25  is established. 
     Thereafter, the ring gear  25  continues to rotate with deceleration and stops. The pinion gear  8  rotates together with the ring gear  25  while engaging with the ring gear  25 , and stops. In the meantime, as shown in  FIG. 5C , the excitation coil  16  of the pinion solenoid  5  is supplied with holding current by which the engagement between the pinion gear  8  and the ring gear  25  can be maintained. Hereinafter, the following operation is referred to as “pinion preset”, which is performed in the stop process of the engine. In this operation, the pinion solenoid  5  is actuated during rotation of the ring gear  25  to make the pinion gear  8  engage with the ring gear  25 . While the pinion preset is performed, current is not supplied to the excitation coil  27  of the motor solenoid  6 . 
     c) When the engine is restarted after the pinion preset: 
     Next, when the ECU  21  outputs a restart signal for the engine, current is supplied to the excitation coil  27  of the motor solenoid  6 , whereby the motor contact is dosed. As a result, current is supplied to the motor  2  to generate torque of the armature  2   a . At this time, since the pinion gear  8  has already engaged with the ring gear  25 , the torque of the motor  2 . is transmitted from the pinion gear  8  to the ring gear  25  to crank the engine. 
     (Advantages of the First Embodiment) 
     In the starter  1  of the present embodiment, the pinion solenoid  5  and the motor solenoid  6  are separately controlled by the ECU  21 . Hence, in a case where the engine is stopped when the vehicle is in an idling state, even after only the pinion solenoid  5  is actuated to engage the pinion gear  8  with the rotating ring gear  25  and then the rotating ring gear  25  stops, the engagement between the pinion gear  8  and the ring gear  25  can be maintained. Thereafter, when the engine is restarted, the pinion gear  8  has already engaged with the ring gear  25 . Therefore, only actuating the motor solenoid  6  is required, which closes the motor contact. That is, when the engine is restarted, the pinion movable body is not required to be pushed out, which shorten the time to make the pinion gear  8  engage with the ring gear  25 . Therefore, the engine can restart quickly. 
     While the pinion preset is performed, at the substantially same time when the end face of the pinion gear  8  strikes the end face of the rotating ring gear  25 , the plunger  17  of the pinion solenoid  5  strikes the fixed core  13 . Hence, impact noises due to the two impacts are produced and combined with each other. When sound pressure is measured which is produced at the time the starter  1  operates, as shown in  FIG. 5A , the sound pressure level of the impact noises is larger than that of the operation noise of the starter  1  produced at the time the engine normally starts. In addition, when the pinion preset is performed, current is not supplied to the motor  2 . Therefore, noises due to the operation of the motor  2  are not produced, which emphasizes only the above impact noises remarkably.  FIG. 5A  shows a waveform of sound pressure produced at the time the starter  1  operates.  FIG. 5B  shows a waveform of engine speed.  FIG. 5C  shows a waveform of starter current. The arrow “A” in  FIG. 5A  indicates the sound pressure produced at the time the pinion preset is performed (the time the pinion gear  8  is engaged with the ring gear  25  by actuating the pinion solenoid  5  while the rotation of the ring gear  25  decelerates). 
     To solve the above problems, in the starter  1  according to the embodiment, the cushioning member  12  is incorporated into the pinion movable body. Specifically, the cushioning member  12 , which is an elastic member made of rubber, elastomer, or the like, is arranged between the tube-side pressure receiving face  9   c  formed by the flange  9   b  of the inner tube  9  and the step provided between the fitting hole and the large-diameter hole of the pinion gear  8 . Hence, when the end face of the pinion gear  8  strikes the end face of the ring gear  25 , the member  12  is contracted between the tube-side pressure receiving face  9   c  and the gear-side pressure receiving face  8   b , which reduces the impact between the end face of the pinion gear  8  and the end face of the ring gear  25 . Therefore, the noise of the starter  1  can be reduced which is produced due to the impact propagated to the output shaft  3  and the like. 
       FIG. 6  shows results of the measurement of sound pressure at point “A” shown in  FIG. 5A . The measurement is conducted by using the starter  1  in which the cushioning member  12  is incorporated into the pinion movable body, and the conventional starter which does not have the cushioning member  12 . In  FIG. 6 , the axis of abscissa indicates rotating speed in meshed state between the pinion gear  8  and the ring gear  25 , and the axis of ordinate indicates sound pressure. As shown in  FIG. 6 , the starter  1  according to the embodiment can reduce the sound pressure while the pinion preset is performed, compared with the conventional starter. 
     As described above, the starter  1  according to the embodiment can reduce the noise (the noise of the starter  1 ) produced when the engine is restarted after an idle stop. Hence, an idle stop system can be provided which is comfortable for a user, without harming the environment along roads. 
     In addition, in the pinion movable body according to the embodiment, the cushioning member  12  is disposed at the inner periphery of the large-diameter hole formed in the pinion gear  8 . Hence, an expansion preventing means can be provided at the outer periphery side of the cushioning member  12 . That is, as shown in  FIG. 2 , a boss  8   c  of the pinion gear  8 , which forms the large-diameter hole, is provided at the outer periphery side of the cushioning member  12 . Hence, the boss  8   c  can functions as the expansion preventing means, which prevents the cushioning member  12  from radially expanding to the outside by centrifugal force when the pinion movable body rotates. Thereby, the pinion movable body is pushed out to the ring gear  25  of the engine. Even when the end face of the pinion gear  8  strikes the end face of the ring gear  25 , the function of the cushioning member  12  is not degraded which reduces the impact between the end face of the pinion gear  8  and the end face of the ring gear  25 , thereby exerting the predetermined effects of the cushioning member  12 . 
     In addition, in the pinion movable body according to the embodiment, the maximum diameters of the gear-side pressure receiving face  8   b  and the tube-side pressure receiving face  9   c  are smaller than the root diameter of the pinion gear  8 , and the minimum diameters of the gear-side pressure receiving face  8   b  and the tube-side pressure receiving face  9   c  are larger than the outer diameter of the inner tube  9 . According to the configuration, a space for the cushioning member  12  can be provided between the root diameter of the pinion gear  8  and the outer diameter of the inner tube  9 . Furthermore, the cushioning member  12  can be disposed within the axial dimension of the pinion gear  8 . Hence, the pinion movable body is prevented from increasing in size, while the cushioning member  12  can be incorporated into the pinion movable body. 
     (Second Embodiment) 
     According to a second embodiment, as shown in  FIG. 7 , a helical compression spring  41  is employed as the cushioning member  12 . According to the configuration, since a general-purpose helical compression spring can be used as the helical compression spring  41 , manufacturing costs of the starter can be reduced. 
     (Third Embodiment) 
     According to a third embodiment, as shown in  FIG. 8 , the in combination of an elastic body such as rubber or elastomer and the helical compression spring  41  is used as the cushioning member  12 . 
     According to the configuration, the impact is absorbed by the helical compression spring  41  and is reduced by the elastic body, whereby the noise of the starter can be further reduced. 
     (Fourth Embodiment) 
     According to a fourth embodiment, axial length of the teeth of the pinion gear  8  is shortened with respect to that of the boss  8   c.    
     The axial length of the teeth of the pinion gear  8  is simply required so that the teeth of the pinion gear S can engage with the ring gear  25 . Hence, as shown in  FIG. 9 , the axial length of the teeth can be shortened with respect to that of the boss Sc. Meanwhile, lengthening the axial length of the boss  8   c  compared with that of the teeth can provide the expansion preventing means for the cushioning member  12  at the periphery of the large-diameter hole. 
     It will be appreciated that the present invention is not limited to the configurations described above, but any and all modifications, variations or equivalents, which may occur to those who are skilled in the art, should be considered to fall within the scope of the present invention.