JP2016124355A - Electric booster - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric booster which can suppress generation of an allophone during operation thereof.SOLUTION: A housing 4 adopted in an electric booster 1 comprises a front housing 4A which accommodates a ball screw mechanism 41, and a rear cover 4B which covers an opening 7 at a rear end of the front housing 4A. In the rear cover 4B, a cover body 110 having an opening 105, and a cylindrical body 101 which extends concentrically with a master cylinder 2 from the opening 105 and so supports a screw shaft 47 of the ball screw mechanism 41 as to be axially movable in the interior thereof are independently configured. Thus, a process tolerance of an inner peripheral surface of a cylindrical main body part 125 of the cylindrical body 101 can be improved, and generation of an allophone during operation of the electric booster can be suppressed.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an electric booster that is incorporated in a brake device of a vehicle such as an automobile and generates a brake fluid pressure in a master cylinder using an electric motor.

  As a booster incorporated in a brake device, for example, as described in Patent Document 1, an electric booster using an electric motor as a boost source is known. An electric booster described in Patent Document 1 includes an input piston that moves forward and backward by operation of a brake pedal, a primary piston and a secondary piston that are arranged to be relatively movable with respect to the input piston, and a forward and backward movement of the primary piston and the secondary piston. A ball screw mechanism to be moved and an electric motor for applying a rotational force to the ball screw mechanism are provided.

  In the electric booster described in Patent Document 1, a ball screw mechanism is accommodated in a housing, and the housing includes a housing main body and a rear cover that closes an opening of the housing main body. And the said electric booster is attached to the partition which partitions off between an engine room and a vehicle interior using the some stud bolt provided in the attachment seat surface of the rear cover.

JP 2014-69678 A

  However, in the electric booster according to Patent Document 1, since the rear cover integrally forms the cylindrical portion, the finish processing of the inner peripheral surface of the cylindrical portion on which the screw shaft of the ball screw mechanism slides, that is, the cylinder Processing to finish the roughness of the inner peripheral surface of the portion within a predetermined range is difficult, and depending on the roughness after processing, there is a possibility that abnormal noise may be generated when the electric booster is operated.

  This invention is made | formed in view of the said point, and it aims at providing the electric booster which can suppress generation | occurrence | production of the noise at the time of an action | operation.

  In order to solve the above-described problems, the present invention provides an electric booster that is attached to a vehicle and moves a piston of a master cylinder through a rotation / linear motion conversion mechanism by rotation of an electric motor. The housing that houses the dynamic conversion mechanism includes a front housing and a rear cover that covers the rear end opening of the front housing, the rear cover being concentric with the master cylinder from the opening, and a cover body having the opening. And a cylindrical body that supports the linear motion member of the rotation / linear motion conversion mechanism so as to be movable in the axial direction is formed as a separate body.

  According to the electric booster according to the present invention, it is possible to suppress the generation of abnormal noise during operation.

It is sectional drawing of the electric booster which concerns on one Embodiment. The rear cover which concerns on 1st Embodiment is shown, (a) is the figure seen from back, (b) is sectional drawing which follows the AA line of (a). FIG. 3 is a perspective view of the cover main body of FIG. 2. It is a perspective view of the cylindrical body of FIG. The rear cover which concerns on 2nd Embodiment is shown, (a) is the figure seen from back, (b) is sectional drawing which follows the BB line of (a). It is a perspective view of the cover main body of FIG. It is a perspective view of the cylindrical body of FIG.

Hereinafter, an embodiment will be described in detail based on the drawings.
As shown in FIG. 1, the electric booster 1 according to the present embodiment includes a tandem master cylinder 2 and a housing 4 in which an actuator 3 is housed. A reservoir 5 is connected to the master cylinder 2. A controller C is attached to the upper part of the housing 4.

  As shown in FIG. 1, the housing 4 is coupled to a substantially bottomed cylindrical front housing 4A and an opening 7 on the rear end side of the front housing 4A by a plurality of bolts 4C to cover the opening 7. The rear cover 4B according to the first embodiment is configured. As shown in FIG. 2, referring also to FIG. 1, the rear cover 4 </ b> B according to the first embodiment is concentric with the master cylinder 2 from the cover body 100 having an opening 105 and the opening 105 of the cover body 100. A cylindrical body 101 (cylindrical body) that extends along the axial direction and supports a screw shaft 47 (linear motion member) of a ball screw mechanism 41 (rotational linear motion conversion mechanism) that is a configuration of the actuator 3 so as to be movable in the axial direction. ) And the separate body.

  As shown in FIGS. 2 and 3, the cover main body 100 is disposed concentrically on the inner side of the cylindrical wall portion 104 and the cylindrical wall portion 104 fitted to the inner peripheral surface of the opening 7 of the front housing 4 </ b> A. And an annular wall portion 106 having an opening 105, and a cylindrical support portion 107 that connects the cylindrical wall portion 104 and the annular wall portion 106 and extends in the axial direction. An annular groove 108 for a sealing member is formed on the outer peripheral surface of the cylindrical wall portion 104. The cylindrical wall portion 104 is disposed on the front side, and the annular wall portion 106 is disposed on the rear side. At the rear end of the cylindrical wall portion 104, a flange portion 110 that protrudes radially outward and extends in an annular shape is formed.

  When the rear cover 4B is assembled to the front housing 4A, the flange portion 110 comes into contact with the front surface around the opening 7 of the front housing 4A. From the outer peripheral surface of the flange part 110, the some fixing | fixed part 111 protrudes radially outward. Most of each fixing portion 111 is formed in a semicircular shape except for one place. A plurality of the fixing portions 111 are formed at intervals along the circumferential direction. In the present embodiment, six fixing portions 111 are formed. Each fixing portion 111 is formed with an insertion hole 112 for a bolt 4C for fixing the cover body 100 to the opening 7 of the front housing 4A.

  An opening 105 is formed in the annular wall portion 106 concentrically with the master cylinder 2. The cylindrical main body 125 of the cylindrical body 101 is inserted through the opening 105. A positioning recess 113 is formed around the opening 105 on the front surface of the annular wall 106. A plurality of insertion holes 114 along the axial direction are formed in the annular wall portion 106 within the range of the positioning recess 113. A plurality of the insertion holes 114 are formed at intervals along the circumferential direction. In this embodiment, four insertion holes 114 are formed. A stud bolt 120 is caulked and fixed to each insertion hole 114. The stud bolt 120 is for attaching the electric booster 1 to a dash panel (not shown) that is a partition wall between a vehicle engine room and a vehicle compartment, and includes a shaft portion 120A and ends of the shaft portion 120A. The head portion 120B is provided integrally with the head portion. On the inner peripheral surface of the cylindrical support portion 107, a plurality of concave portions 109 are formed inwardly at positions corresponding to the respective fixing portions 135 of the cylindrical body 101.

  As shown in FIGS. 2 and 4, the cylindrical body 101 includes a cylindrical main body 125 that extends concentrically with the master cylinder 2 along the axial direction, and projects radially outward from the front outer peripheral surface of the cylindrical main body 125. And an annular fixing portion 126. A screw shaft 47 of the ball screw mechanism 41 is supported inside the cylindrical main body 125 so as to be movable in the axial direction. A pair of anti-rotation portions 127 and 127 projecting inward in the radial direction are formed on the rear inner peripheral surface of the cylindrical main body 125. An annular groove 128 for a retaining ring 84 for fixing the covering member 76 is formed on the rear outer peripheral surface of the cylindrical main body 125.

  A plurality of fixing portions 135 are projected from the outer peripheral surface of the annular fixing portion 126. Each fixing part 135 is formed in a semicircular shape. A plurality of each fixing portion 135 is formed at intervals in the circumferential direction so as to correspond to each insertion hole 114 provided in the annular wall portion 106 of the cover main body 100. In the present embodiment, each fixing portion 135 is formed at four locations. Each fixing portion 135 is formed with an insertion hole 136 through which the stud bolt 120 is inserted. An annular groove portion 137 is formed on the rear surface of the annular fixing portion 126 concentrically with the cylindrical main body portion 125. A ring-shaped seal member 138 as a seal member is disposed in the annular groove portion 137. As the seal member 138, various seal members such as an O-ring, a square seal material, and a liquid gasket are employed.

  The rear cover 4B is configured by assembling the cover body 100 and the cylindrical body 101 integrally. As an assembling method, first, the seal member 138 is disposed in the annular groove portion 137 of the annular fixing portion 126 of the cylindrical body 101. Subsequently, the cylindrical main body 125 of the cylindrical body 101 is inserted from the front into the opening 105 of the annular wall 106 of the cover main body 100. Subsequently, the annular fixing portion 126 of the cylindrical body 101 is brought into contact with the positioning recess 113 of the annular wall portion 106 of the cover main body 100, and the insertion holes 136 of the fixing portions 135 of the cylindrical body 101 and the annular shape of the cover main body 100 are arranged. The insertion holes 114 of the wall 106 are aligned with each other.

  Subsequently, the stud bolts 120 are inserted from the front into the insertion holes 136 of the fixing portions 135 of the cylindrical body 101 and the insertion holes 114 of the annular wall portion 106 of the cover body 100 to be fixed by caulking. At this time, the front surface of the head portion 120B of the stud bolt 120 and the front surface of the annular fixing portion 126 of the cylindrical body 101 are positioned on substantially the same plane. The cover body 100, the cylindrical body 101, and the stud bolts 120 are integrally assembled, and the annular groove portion 137 of the annular fixing portion 126 of the cylindrical body 101 and the positioning recess 113 of the annular wall portion 106 of the cover body 100 are formed. The seal member 138 disposed therebetween seals between the annular fixing portion 126 of the cylindrical body 101 and the positioning recess 113 of the annular wall portion 106 of the cover main body 100, and consequently the opening 105 of the cover main body 100 is liquid. It is tightly sealed.

  The electric booster 1 is configured so that the cylindrical body portion 125 of the cylindrical body 101 of the rear cover 4B passes through a dash panel that is a partition wall between the engine room and the vehicle compartment of the vehicle and extends into the vehicle interior. It arrange | positions in a room and it fixes to the dash panel using each stud bolt 120. FIG.

  As shown in FIG. 1, the master cylinder 2 includes a cylinder body 2 </ b> A having a substantially bottomed cylindrical shape, and the opening side thereof is coupled to the opening at the bottom of the housing 4 by a stud bolt 6 </ b> A and a nut 6 </ b> B. In the cylinder body 2A of the master cylinder 2, a cylindrical primary piston 10 whose front end is formed in a cup shape is inserted on the opening side (rear side), and a cup-shaped secondary piston on the bottom side (front side). 11 is inserted. The rear end portion of the primary piston 10 protrudes from the opening of the master cylinder 2 into the housing 4 and extends to the cylindrical body 101 of the rear cover 4B. In the cylinder body 2 </ b> A, two pressure chambers of a primary chamber 16 and a secondary chamber 17 are formed by the primary piston 10 and the secondary piston 11. The primary chamber 16 and the secondary chamber 17 are each provided with a hydraulic pressure port (not shown). Two systems of hydraulic circuits (not shown) for supplying hydraulic pressure to the brake calipers of each wheel are connected to the hydraulic ports.

  Reservoir ports 20 and 21 for connecting the primary chamber 16 and the secondary chamber 17 to the reservoir 5 are provided on the upper side of the side wall of the cylinder body 2A. The cylinder bore 12 of the cylinder body 2A and the primary piston 10 and the secondary piston 11 are sealed by two seal members 22A, 22B and 23A, 23B, respectively.

  The seal members 22A and 22B are arranged so as to sandwich the reservoir port 20 along the axial direction. When the primary piston 10 is in the non-braking position shown in FIG. 1 due to the seal member 22A, the primary chamber 16 communicates with the reservoir port 20 via the port 24 provided on the side wall of the primary piston 10, and the primary piston 10 When the vehicle advances from the non-braking position, the primary chamber 16 is blocked from the reservoir port 20 by the seal member 22A. Further, the seal members 23A and 23B are arranged so as to sandwich the reservoir port 21 along the axial direction. Among these, when the secondary piston 11 is in the non-braking position shown in FIG. 1 due to the seal member 23A, the secondary chamber 17 communicates with the reservoir port 21 via the port 25 provided on the side wall of the secondary piston 11, and the secondary piston 11 When 11 is advanced from the non-braking position, the secondary chamber 17 is blocked from the reservoir port 21 by the seal member 23A.

  A spring assembly 26 is interposed between the primary piston 10 and the secondary piston 11 in the primary chamber 16. A return spring 27 that is a compression coil spring is interposed between the bottom of the master cylinder 2 in the secondary chamber 17 and the secondary piston 11. The spring assembly 26 holds the compression coil spring 28 in a predetermined compression state by a retractable retainer 29 and can be compressed against the urging force thereof. A cylindrical spacer 29 </ b> A is interposed between the retainer 29 and an intermediate wall 30 (described later) of the primary piston 10.

  The primary piston 10 is formed in a cylindrical shape as a whole and includes an intermediate wall 30 that partitions the inside in the axial direction. A guide bore 31 is passed through the intermediate wall 30 along the axial direction. A small-diameter front end of a stepped input piston 32 having a step 32A is slidably and liquid-tightly inserted into the guide bore 31. The gap between the guide bore 31 and the front end of the input piston 32 is sealed by two seal members 33A and 33B, and the intermediate wall 30 of the primary piston 10 has an opening between the seal members 33A and 33B of the guide bore 31. The passage 33 is penetrated along the radial direction. The passage 33 is opened inside the seal member 22B.

  An intermediate portion of the primary piston 10 extending into the housing 4 is inserted into a cylindrical spring receiving member 70 fitted into an opening at the bottom of the front housing 4A, and is guided so as to be slidable along the axial direction. The spring receiving member 70 is connected to the cylinder bore 12 of the master cylinder 2 with an outer flange portion 71 formed at one end thereof being fitted into and fixed to the opening at the bottom of the front housing 4A. The space between the primary piston 10 is sealed by a seal member 72 attached to the inner periphery of the rear end of the spring receiving member 70.

  The rear end portion of the input piston 32 is connected to the cylindrical body 101 of the rear cover 4 </ b> B and the front end portion of the input rod 34 inserted into the rear portion of the primary piston 10. The rear end side of the input rod 34 extends from the cylindrical body 101 to the outside. A threaded portion 34B is formed at the rear end portion of the input rod 34 extending from the cylindrical body 101 to the outside. A clevis 73 for connecting a brake pedal (not shown) and a lock nut 74 of the clevis 73 are screwed to the screw portion 34B. A flange-shaped spring receiver 35 is attached to the rear end portion of the primary piston 10, and the primary piston 10 is a return that is a compression coil spring interposed between the rear end portion of the spring receiving member 70 and the spring receiver 35. The spring 36 is biased in the backward direction. The input piston 32 is elastically moved to the neutral position shown in FIG. 1 by springs 37 and 38 which are compression coil springs interposed between the intermediate wall 30 of the primary piston 10 and the spring receiver 35, respectively. Is retained. The retracted position of the input rod 34 is defined by the contact of a large diameter contact portion 34A provided at the intermediate portion of the input rod 34 with a pair of detent portions 127 provided on the cylindrical body 101 of the rear cover 4B. .

  In the housing 4, there is provided an electric motor 40 and an actuator 3 including a ball screw mechanism 41 that is a rotation / linear motion conversion mechanism that converts a rotation of the electric motor 40 into a linear motion and applies a thrust to the primary piston 10. . The electric motor 40 is a permanent magnet embedded synchronous motor, and includes a stator 42 and a rotor 45. The stator 42 has a plurality of coils fixed to the rear step portion of the bottom portion of the front housing 4A. The rotor 45 has a plurality of permanent magnets that are formed in a cylindrical shape and are disposed along the circumferential direction so as to face the inner peripheral surface of the stator 21. The electric motor 40 may be a synchronous motor in which a permanent magnet is arranged inside the rotor 45, or another type of motor such as an induction motor.

  The ball screw mechanism 41 includes a nut member 46, a hollow screw shaft 47 that is a linear motion member, and a plurality of balls 48 that are loaded between screw grooves formed on the opposing surfaces. The nut member 46 extends in the axial direction from the vicinity of the bottom of the front housing 4A to the vicinity of the rear cover 4B, and both ends thereof are rotatably supported by the front housing 4A and the rear cover 4B by bearings 43 and 44. In particular, the bearing 44 is fixed inside the cylindrical support portion 107 of the cover body 100 of the rear cover 4B. The inner peripheral portion of the rotor 45 is fixed to the outer peripheral portion on the front side of the nut member 46. The screw shaft 47 is inserted into the nut member 46 and the cylindrical body 101 of the housing 4, is movable along the axial direction, and is supported so as not to rotate about the axis. Specifically, at the rear end portion of the screw shaft 47 protruding from the cylindrical body 101, guide grooves 47A extending to the end portion along the axial direction are formed at two locations in the diameter direction. A pair of detents 127 provided on the cylindrical body 101 of the rear cover 4B of the housing 4 are engaged with the guide grooves 47A, respectively, so that the screw shaft 47 can move in the axial direction and does not rotate about the axis. I support it.

  In the ball screw mechanism 41, the screw shaft 47 moves in the axial direction when the ball 48 rolls along the screw groove by the rotation of the nut member 46 accompanying the rotation of the rotor 45 of the electric motor 40. ing. Further, the ball screw mechanism 41 can mutually convert rotation and linear motion between the nut member 46 and the screw shaft 47. Although not provided in the present embodiment, a known speed reduction mechanism such as a planetary gear mechanism or a differential speed reduction mechanism is interposed between the electric motor 40 and the ball screw mechanism 41, and the electric motor 40 is provided. The rotation of the motor may be decelerated and transmitted to the ball screw mechanism 41.

  The screw shaft 47 of the ball screw mechanism 41 is urged in the backward direction by a return spring 49 which is a compression taper coil spring interposed between the outer flange portion 71 of the spring receiving member 70. The rear end position of the screw shaft 47 is restricted by abutting against a rotation stopper 127 provided on the cylindrical body 101 of the rear cover 4B. The rear end portion of the primary piston 10 is inserted into the screw shaft 47, and the retracted position of the primary piston 10 is regulated by the spring receiver 35 coming into contact with the step portion 50 formed on the inner peripheral portion of the screw shaft 47. ing. As a result, the primary piston 10 is pushed forward by the stepped portion 50 by the advancement of the screw shaft 47, and can move forward separately from the stepped portion 50. As shown in FIG. 1, the non-braking position of the primary piston 10 is defined by the screw shaft 47 that is in contact with the anti-rotation portion 127, and the secondary piston 10 and the maximum length of the spring assembly 26 in the non-braking position are A retracted position of the piston 11, that is, a non-braking position is defined.

  A resolver 60 as a rotational position sensor that detects the rotational position of the rotor 43 of the electric motor 40 is provided in the housing 4. The resolver 60 includes a sensor rotor 60A fixed to the outer peripheral portion on the rear side of the nut member 46, and a sensor stator 60B attached to the rear cover 4B so as to face the sensor rotor 60A.

  A reaction force applying means 75 is provided at the rear end portion of the cylindrical body 101 of the rear cover 4B. The reaction force applying means 75 is generally composed of a cylindrical cover member 76, a movable spring receiver 78, and a reaction force spring 79. The cover member 76 is attached to the rear end portion of the cylindrical body 101 of the rear cover 4B and is provided so as to cover the outer periphery of the screw shaft 47. Specifically, the cover member 76 is attached to the rear end portion of the rear cover 4B via a retaining ring 84 provided in the annular groove portion 128 of the cylindrical body 101 of the rear cover 4B. The movable spring receiver 78 is provided so as to be movable along the axial direction in the screw shaft 47 and not rotatable relative to the screw shaft 47 and the cover member 76. The reaction force spring 79 is a compression coil spring interposed between the pair of rotation stoppers 127 and the movable spring receiver 78. The reaction force spring 79 is compressed in a free length or with a predetermined set load (in this embodiment, in a state slightly compressed from the free length in order to suppress rattling between components), It is interposed between the stopper 127 and the movable spring receiver 78. A washer 80 and a spring washer 82 are stacked on the rear side of the rotation stopper 127.

  When the input rod 34 moves forward by a predetermined distance with respect to the cylindrical body 101, that is, the housing 4, the lock nut 74 comes into contact with the movable spring receiver 78, and when the input rod 34 further moves forward, the reaction force spring 79. Is compressed and its urging force is applied as a reaction force against the advance of the input rod 34.

  The electric booster 1 includes a brake pedal, that is, a stroke sensor (not shown) that detects displacement of the input piston 32 and the input rod 34, a resolver 60 that detects the rotational position of the rotor 43 of the electric motor 40, Various sensors (not shown) such as a current sensor for detecting a current supplied to the electric motor 40 and a hydraulic pressure sensor for detecting a hydraulic pressure of the primary chamber 16 and the secondary chamber 17 are connected. The controller C as a control circuit is a microprocessor-based electronic control device including an ECU and a RAM. Based on detection signals from these various sensors, the input rod 34 and the screw shaft 47 (primary piston 10) of the ball screw mechanism 41 The operation of the electric motor 40 is controlled so that the brake fluid pressure is generated in the primary chamber 16 and the secondary chamber 17 in the master cylinder 2 with a desired boost ratio by adjusting the relative position of the motor.

Next, the operation of the electric booster 1 according to this embodiment will be described.
When the input piston 32 is moved forward via the input rod 34 by operating the brake pedal, the displacement of the input piston 32 is detected by the stroke sensor, and the operation of the electric motor 40 is controlled by the controller C based on the displacement of the input piston 32. Then, the primary piston 10 is advanced via the ball screw mechanism 41 to follow the displacement of the input piston 32. Thereby, a hydraulic pressure is generated in the primary chamber 16, and this hydraulic pressure is transmitted to the secondary chamber 17 via the secondary piston 11. Thus, the brake fluid pressure generated in the master cylinder 2 is supplied to the brake caliper of each wheel via the fluid pressure port, and a braking force is generated. When the operation of the brake pedal is released, the input piston 32, the primary piston 10 and the secondary piston 11 are moved backward to reduce the brake fluid pressure in the master cylinder 2, and the brake pad is moved backward to release the brake. Here, since the primary piston 10 and the secondary piston 11 operate in the same manner, only the primary piston 10 will be described below.

  At this time, a part of the hydraulic pressure in the primary chamber 16 is received by the input piston 32, and the reaction force is fed back to the brake pedal via the input rod 34. Thereby, a desired braking force can be generated with a predetermined boost ratio. Then, by adjusting the relative position between the input piston 32 and the primary piston 10 that follows the input piston 32, the spring force of the springs 37 and 38 is applied to the input piston 32, and the reaction force on the input rod 34 is adjusted. The boost ratio can be adjusted. The boost ratio is increased by adjusting the displacement of the primary piston 10 forward relative to the displacement of the input piston 32, and the boost ratio is decreased by adjusting backward. Accordingly, brake control such as boost control, brake assist control, inter-vehicle stability control, inter-vehicle control, and regenerative cooperative control can be executed. The input piston 32 is adjusted so that the primary piston 10 is rearward to reduce the boost ratio, and the hydraulic pressure in the primary chamber 16 is reduced, thereby suppressing the braking force due to the hydraulic pressure and regenerative coordination. The amount of time regeneration can be increased.

  The electric motor 40 has a predetermined maximum output. The maximum output of the electric motor 40 may be an output that can be maximized by supplying power, or an output at the time of supplying a predetermined maximum power in order to prevent damage to the electric motor 40 due to excessive supply of power. When the output of the electric motor 40 controlled by the controller C reaches the maximum output and the hydraulic pressure in the primary chamber 16 and the thrust of the primary piston 10 are balanced, the primary piston 10 can no longer move forward and stops. When the brake pedal is further depressed in such a full load state, only the input piston 32 moves forward while the primary piston 10 remains stopped with respect to the forward movement of the input rod 34. Since the operation is stopped, the ratio of the reaction force increase amount fed back to the brake pedal via the input piston 32 and the input rod 34 is reduced by the increase of the hydraulic pressure in the primary chamber 16 with respect to the advance amount of the input piston 32. However, when the movement distance of the input piston 32 relative to the housing 4 by the operation of the brake pedal reaches a predetermined distance, the lock nut 74 comes into contact with the movable spring receiver 78 of the reaction force applying means 75 and the reaction force spring 79 is compressed. Thus, the biasing force is applied to the brake pedal as a reaction force.

  When the brake pedal is further depressed, the step 32A of the input piston 32 comes into contact with the intermediate wall 30 of the primary piston 10, the primary piston 10 moves forward together with the input piston 32, and the reaction force due to the increase of the hydraulic pressure in the primary chamber 16 is generated. Increase. At this time, an appropriate reaction force is applied to the operation of the brake pedal by the reaction force applying means 75, so that the uncomfortable feeling due to a sudden increase in the amount of increase in the reaction force can be alleviated.

  Next, the rear cover 4B 'according to the second embodiment will be described with reference to FIGS. For the rear cover 4B 'according to the second embodiment, only differences from the rear cover 4B according to the first embodiment will be described.

  In the rear cover 4B ′ according to the second embodiment, as shown in FIGS. 5 and 6, an annular recess 150 is formed around the opening 105 on the rear surface of the annular wall portion 106 of the cover body 100. On the other hand, as shown in FIGS. 5 and 7, the cylindrical body 101 protrudes in the radial direction from the outer peripheral surface on the front side of the cylindrical main body 125 and is positioned in the annular recess 150 of the annular wall 106 of the cover main body 100. An annular wall 151 is formed. As shown in FIG. 5B, a ring-shaped seal member 138 is disposed between the annular recess 150 of the cover main body 100 and the annular wall 151 of the cylindrical body 101. Further, as shown in FIG. 5, a fixing plate 155 that integrally fixes the cover main body 100, the cylindrical body 101, and each stud bolt 120 is provided. The fixed plate 155 is formed in a substantially rectangular shape, and an opening 156 through which the cylindrical main body 125 of the cylindrical body 101 is inserted is formed in a substantially central portion. The fixing plate 155 is formed with insertion holes 157 through which the stud bolts 120 are inserted at the four corners.

  First, the seal member 138 is disposed in the annular recess 150 of the cover body 100. Subsequently, the cylindrical main body portion 125 of the cylindrical body 101 is inserted into the opening portion 105 of the annular wall portion 106 of the cover main body 100 from the rear, and the annular wall portion 151 of the cylindrical main body portion 125 of the cylindrical body 101 is inserted into the cover main body 100. The annular recess 150 is disposed on the seal member 138. Subsequently, the cylindrical body 125 of the cylindrical body 101 is inserted into the opening 156 of the fixed plate 155, and the fixed plate 155 is brought into contact with the annular wall part 106 of the cover body 100 from the annular wall part 151 of the cylindrical body 101. Thus, the insertion holes 114 of the annular wall portion 106 of the cover main body 100 and the insertion holes 157 of the fixing plate 155 are made to coincide with each other.

  Subsequently, the stud bolts 120 are inserted from the front into the insertion holes 114 of the annular wall portion 106 of the cover body 100 and the insertion holes 157 of the fixing plate 155 to be fixed by caulking. As a result, the cover body 100, the cylindrical body 101, the fixing plate 155, and each stud bolt 120 are assembled together, and the annular recess 150 of the annular wall portion 106 of the cover body 100 and the annular wall portion 151 of the cylindrical body 101 are formed. The seal member 138 disposed therebetween seals between the annular recess 150 of the annular wall portion 106 of the cover body 100 and the annular wall portion 151 of the cylindrical body 101, and as a result, the opening portion 105 of the cover body 100 is liquid. It is tightly sealed.

  According to the electric booster 1 according to the present embodiment described above, the rear covers 4B and 4B ′ according to the first and second embodiments include the cover body 100 having the opening 105 and the opening of the cover body 100. A cylindrical body 101 that extends along the axial direction concentrically with the master cylinder 2 from the portion 105 and supports the screw shaft 47 of the ball screw mechanism 41 so as to be movable in the axial direction is formed separately. As a result, chucking and handling for processing becomes easier and the cylindrical main body portion 125 of the cylindrical body 101 is easier than processing the rear cover in which the cover main body and the cylindrical body are integrally molded as in the prior art. The processing accuracy of the inner peripheral surface of the electric booster 1 can be improved, and the generation of abnormal noise during operation of the electric booster 1 can be suppressed.

  Further, in the rear cover 4B according to the first embodiment, the gap between the annular fixing portion 126 of the cylindrical body 101 and the positioning recess 113 of the annular wall portion 106 of the cover main body 100 that communicates with the opening 105 of the cover main body 100 is a seal. On the other hand, in the rear cover 4B ′ according to the second embodiment, the annular recess 150 and the cylindrical body of the annular wall portion 106 of the cover body 100 that communicate with the opening 105 of the cover body 100 are sealed in a liquid-tight manner by the member 138. Since the space between the annular wall portion 101 and 101 is liquid-tightly sealed by the seal member 138, a waterproof function can be provided. Also, the seal member 138 can absorb the assembly play between the cylindrical body 101 and the cover main body 100, and further, between the screw shaft 47 of the ball screw mechanism 41 and the cylindrical main body 125 of the cylindrical body 101. Propagation of the sliding sound to the cover main body 100 can also be suppressed.

  Furthermore, according to the electric booster 1 according to the present embodiment, the rear covers 4B and 4B ′ according to the first and second embodiments constitute the cover main body 100 and the cylindrical body 101 separately, The material and surface treatment of the cover main body 100 and the cylindrical body 101 can be made different. For example, with respect to the cover body 100 that receives the thrust of the electric motor 40 and the depression force of the brake pedal, the cylindrical body 101 returns the screw shaft 47 of the ball screw mechanism 41, the primary piston 10, the input rod 34, and the like to the retracted position. Since it only needs to have a strength enough to withstand the urging force of the springs 36, 49, etc., the cover main body 100 is made of an iron material, and the cylindrical body 101 is made of a different material such as an aluminum material having a lower strength than the iron material. Is possible. Further, even when both the cover body 100 and the cylinder body 101 are made of iron, the cover body 100 having a tight fitting tolerance is subjected to a surface treatment by electroless plating for easy film thickness control, and the cylinder body 101 is a surface by inexpensive galvanization. Different surface treatments can be applied.

  DESCRIPTION OF SYMBOLS 1 Electric booster, 2 Master cylinder, 4 Housing, 4A Front housing, 4B, 4B 'Rear cover, 7 Opening part, 10 Primary piston, 11 Secondary piston, 40 Electric motor, 41 Ball screw mechanism (rotation linear motion conversion mechanism), 47 Screw shaft (linear motion member), 100 cover body, 101 cylinder (cylinder), 105 opening, 138 seal member

Claims (1)

An electric booster that is attached to a vehicle and moves a piston of a master cylinder via a rotation / linear motion conversion mechanism by rotation of an electric motor,
The housing that accommodates the rotation / linear motion conversion mechanism includes a front housing and a rear cover that covers a rear end opening of the front housing,
The rear cover includes a cover body having an opening, a cylindrical body that extends concentrically with the master cylinder from the opening, and supports a linear motion member of the rotation / linear motion conversion mechanism in an axial direction therein. An electric booster characterized in that is configured as a separate body.

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