Electrical amplification unit

Abstract

An electrical amplification unit is provided that is capable of ensuring reliability. The electrical amplification unit comprises an input element designed to be moved forward or backward in response to the actuation of a brake pedal, a thrust transmission element designed to be movable relative to the input element, an electrical actuator designed to move the thrust transmission element forward or backward, and an output element connected to the thrust transmission element and designed to transmit a thrust force applied by the electrical actuator to the thrust transmission element to a piston of a master cylinder.The electric actuator comprises an electric motor, at least two threaded spindle elements designed to be rotated by the electric motor, and nut elements, each engaged with a threaded spindle element. Each nut element is connected to the thrust transmission element. The thrust transmission element is pivotally connected to the nut elements and / or the output element.

Description

TECHNICAL FIELD

[0001] The present invention relates to an electric booster unit that uses a thrust force generated by an electric actuator as a booster source. STATE OF THE ART

[0002] For example, JP 2007-191133 A discloses an electric booster unit that transmits a rotational force generated by an electric motor to a ball screw to convert it into a linear motion thrust of a thrust transmitting element (a booster piston). Such an electric booster unit includes a rotary motion-to-linear motion conversion mechanism formed by the ball screw and arranged coaxially with an input rod, making it difficult to downsize due to the constraints imposed by this arrangement.One approach to improve this situation is to use a rotary-to-linear motion conversion mechanism designed to operate on a different axis than the input rod, but this design poses a problem in that unnecessary moment and radial load are applied to a linear motion element, mainly due to an error in the assembly of components, thus affecting operational reliability. QUOTATION LISTPATENT LITERATURE

[0003] EP 2 918 462 A1 concerns the preamble of claim 1. SUMMARY OF THE INVENTION TECHNICAL PROBLEM

[0004] The present invention was made with the aim of providing an electrical amplifying unit that can ensure reliability. SOLUTION TO THE PROBLEM

[0005] According to one aspect of the present invention, an electric booster unit includes an input member configured to be moved forward or backward in response to an operation of a brake pedal, a thrust transmitting member provided for movement relative to the input member, an electric actuator configured to move the thrust transmitting member forward or backward, and an output member connected to the thrust transmitting member and configured to transmit a thrust applied by the electric actuator to the thrust transmitting member to a piston of a master cylinder. The electric actuator includes an electric motor, at least two lead screw members configured to be rotated by the electric motor, and nut members each engaging a lead screw member.Each of the nut elements is connected to the thrust transmission element. The thrust transmission element is pivotally connected to the nut elements and / or the output element.

[0006] Furthermore, according to another aspect of the present invention, an electric booster unit includes an input member configured to be moved forward or backward in response to an operation of a brake pedal, a thrust transmitting member provided to be movable with respect to the input member, an electric actuator configured to move the thrust transmitting member forward or backward, and an output member connected to the thrust transmitting member and configured to transmit a thrust applied by the electric actuator to the thrust transmitting member to a piston of a master cylinder. The electric actuator includes an electric motor, at least two lead screw members configured to be rotated by the electric motor, and nut members each engaging a lead screw member.Each of the nut elements is connected to the thrust transmission element. The thrust transmission element is connected to the nut elements and / or the output element via an elastic element.

[0007] Furthermore, according to another aspect of the present invention, an electric booster unit comprises a housing to which a master cylinder is attached, an electric motor mounted on the housing, a rotary-to-linear motion conversion mechanism configured to be rotated by the electric motor and having a rotation axis at a position different from a center axis of the master cylinder, an output member configured to move a piston of the master cylinder by receiving a linear motion thrust transmitted from the rotary-to-linear motion conversion mechanism, and a thrust transmitting member arranged to extend across the output member and the rotary-to-linear motion conversion mechanism.while engaging the output element and the rotary-to-linear motion conversion mechanism. The thrust transmission element is designed to transmit the linear motion thrust of the rotary-to-linear motion conversion mechanism to the output element. The output element or the rotary-to-linear motion conversion mechanism has a spherical shape at the mutual engagement portion.

[0008] According to the aspects of the present invention, the reliability of the electric amplifying unit can be ensured. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view of a master cylinder coupled to an electric booster unit according to a first embodiment. Fig. 2 is a side view of the master cylinder coupled to the electric booster unit according to the first embodiment. Fig. 3 is an enlarged view of a Fig. Section A shown in Figure 1. Fig. 4 is a front view illustrating a coupling structure between a thrust transmitting member and a nut member according to the first embodiment. Fig. 5 is a side view illustrating the coupling structure between the thrust transmitting member and the nut member according to the first embodiment. Fig. 6 is a cross-sectional view of a master cylinder coupled to an electric booster unit according to a second embodiment. DESCRIPTION OF THE EMBODIMENTS [First Embodiment]

[0009] In the following description, a first embodiment of the present invention will be described with reference to the accompanying drawings.

[0010] Fig. Fig. 1 is a cross-sectional view taken along an axial plane of an electric amplifying unit 1 according to the first embodiment. For convenience, the electric amplifying unit 1 will be described below based on the definition that a leftward direction and a rightward direction are Fig. 1 correspond to a direction forward (a front side) and a direction backward (a rear side) of the electric amplification unit 1, respectively, and an upward direction and a downward direction in Fig. 1 correspond to an upward or downward direction of the electrical amplification unit 1.

[0011] A rear end portion of a tandem master cylinder 2 is coupled to the electric boost unit 1. The master cylinder 2 includes a cylinder main body 3 having a bottomed cylinder bore 4 formed therein. A front end portion of a primary piston 5 (a piston) formed in a cup-like shape is fitted into an opening side (a rear side) of the cylinder bore 4. The primary piston 5 is subjected to a thrust force by a driving force generated by the electric boost unit 1. A rear end portion of the primary piston 5 extends from an opening of the master cylinder 2 into a housing 41 of the electric boost unit 1. A cup-shaped secondary piston 6 is fitted into a bottom side (front side) of the cylinder bore 4. The secondary piston 6 is open at its front side.

[0012] The cylinder main body 3 has a primary chamber 7 and a secondary chamber 8. The primary chamber 7 is formed by the cylinder bore 4, the primary piston 5, and the secondary piston 6. The secondary chamber 8 is formed between the bottom of the cylinder bore 4 and the secondary piston 6. The primary chamber 7 and the secondary chamber 8 are connected to two systems of hydraulic circuits, which output a working fluid pressure (simply referred to as "hydraulic pressure") to a wheel cylinder of each of the wheels of a vehicle via ports (not shown) provided on the cylinder main body 3. The cylinder main body 3 has a passage 10 and a passage 11. The passage 10 connects the primary chamber 7 to a reservoir 9. The passage 11 connects the secondary chamber 8 to the reservoir 9.

[0013] Annular seal grooves 12 and 13 are formed on an inner peripheral surface of the cylinder bore 4. The seal grooves 12 and 13 are provided so that they are spaced from each other by a predetermined distance in the front-to-rear direction. A seal ring 14 and 15 is provided in the seal grooves 12 and 13, respectively. The seal rings 14 and 15 seal between the cylinder bore 4 and the primary piston 5. Annular seal grooves 16 and 17 are formed on the inner peripheral surface of the cylinder bore 4. The seal grooves 16 and 17 are provided so that they are spaced from each other by a predetermined distance in the front-to-rear direction. A seal ring 18 and 19 is provided in the seal grooves 16 and 17, respectively. The seal rings 18 and 19 seal between the cylinder bore 4 and the secondary piston 6. In a non-braking condition (see Fig. 1) the passage 10 opens between the sealing rings 14 and 15, and the passage 11 opens between the sealing rings 18 and 19.

[0014] So when the primary piston 5 is in its non-braking position (see Fig. 1), the primary chamber 7 is in communication with the reservoir 9 via a passage 20 provided on a side wall of the primary piston 5 at its front side and the passage 10 of the cylinder main body 3. When the primary piston 5 is moved forward from the non-braking position and the passage 20 reaches the seal ring 15, the communication between the primary chamber 7 and the passage 10, and consequently the communication between the primary chamber 7 and the reservoir 9, is blocked. As a result, a hydraulic pressure in the primary chamber 7 increases. A movement amount of the primary piston 5 from the non-braking position of the primary piston 5 to a position where the communication between the primary chamber 7 and the passage 10 (the reservoir 9) is blocked corresponds to a stroke, which is called an idle stroke.

[0015] When the secondary piston 6 is in its non-braking position (see Fig. 1), the secondary chamber 8 communicates with the reservoir 9 via a passage 21 provided on a side wall of the secondary piston 6 at the front thereof and the passage 11 of the cylinder main body 3. When the secondary piston 6 is moved forward from the non-braking position and the passage 21 reaches the seal ring 19, the communication between the secondary chamber 8 and the passage 11, and consequently the communication between the secondary chamber 8 and the reservoir 9, is blocked. As a result, a hydraulic pressure in the secondary chamber 8 increases.

[0016] A primary spring assembly 22 is provided between the primary piston 5 and the secondary piston 6. The primary spring assembly 22 determines a distance (a gap) between these pistons 5 and 6 in the non-braking state (see Fig. 1). The primary spring assembly 22 includes a compression coil spring 23, an engaging member 24, an engaging member 25, and a shaft member 26. The compression coil spring 23 acts as a return spring. The engaging member 24 is provided in a recessed portion of the secondary piston 6 at the rear end thereof. The engaging member 25 is provided in a recessed portion of the primary piston 5 at the front end thereof. One end of the shaft member 26 is fixed to the engaging member 24, and its other end is prevented from moving forward and backward with respect to the engaging member 25. The compression coil spring 23 is sandwiched between the engaging members 24 and 25, and the primary spring assembly 22 can be compressed against a spring force of the compression coil spring 23.

[0017] A secondary spring assembly 27 is provided between the secondary piston 6 and the cylinder main body 3. The secondary spring assembly 27 determines a distance (a clearance) between the secondary piston 7 and the bottom of the cylinder bore 4 in the non-braking state (see Fig. 1). The secondary spring assembly 27 includes a compression coil spring 28, an engaging member 29, an engaging member 30, and a shaft member 31. The compression coil spring 28 acts as a return spring. The engaging member 29 is provided at the bottom of the cylinder bore 4. The engaging member 30 is provided in a recessed portion of the secondary piston 6 at the front thereof. One end of the shaft member 31 is fixed to the engaging member 30, and its other end is prevented from moving forward and backward with respect to the engaging member 29. The compression coil spring 28 is sandwiched between the engaging members 29 and 30, and the secondary spring assembly 27 can be compressed against a spring force of the compression coil spring 28.

[0018] The electric booster unit 1 includes the housing 41, which contains a device portion of an electric actuator 61, which will be described below. The housing 41 is configured to be divided into a front housing 42 and a rear housing 43. A bore 44, which is coaxial with the cylinder bore 4 of the master cylinder 2, is provided in the center of the front housing 42. A front end portion of a cylinder portion 46 of a base member 45, which will be described below, is inserted into the bore 44.

[0019] A rear end portion 3A of the cylinder main body 3 of the master cylinder 2 is inserted (press-fitted) onto an inner surface of the front end portion of the cylinder portion 46 of the base member 45. In other words, the front housing 42 is coupled to the cylinder main body 3 of the master cylinder 2 via the cylinder portion 46 of the base member 45. The cylinder main body 3 of the master cylinder 2 is fixed to the front housing 42 by means of two stud bolts 47 and nuts 48 projecting from the front housing 42 (see Fig. 2). In addition, a sealing element 49 seals between the front housing 42 and the cylinder portion 46 of the base element 45.

[0020] A cylinder portion 50, which is coaxial with the cylinder bore 4 of the master cylinder 2, is provided in the center of the rear housing 43. A generally cylindrical output piston 62 (an output member) is slidably and snugly fitted into a cylinder 51 within the cylinder portion 50. An input piston 64 (an input member) is provided within the output piston 62. The input piston 64 is coaxial with the output piston 62. A spherical front end portion of an input rod 33 is fitted into a rear end portion of the input piston 64, and a rear end portion of the input rod 33 is connected to a brake pedal (not shown) via a tie hook 34.

[0021] The output piston 62 has an axial bore 63 having a small-diameter portion 63A, a medium-diameter portion 63B, and a large-diameter portion 63C formed in this order from the master cylinder 2 side (the front side). A spring support member 36 is fixed to an opening of the axial bore 63 on a rear end surface of the output piston 62, that is, an opening portion of the large-diameter portion 63C. The input rod 33 is biased rearward relative to the output piston 62 by a compression coil spring 35 interposed between a spring support portion 37 formed on the input rod 33 and the spring support member 36.

[0022] A flange 67 (rear end portion) of the input piston 64 is slidably fitted into the large-diameter portion 63C of the output piston 62, and a tappet portion 66 of the input piston 64 is passed through the intermediate portion 63B of the output piston 62. A piston portion 65 of the input piston 64 is slidably fitted into the small-diameter portion 63A of the output piston 62, that is, a front end portion of the axial bore 63. A stopper 68 is fixed to the tappet portion 66 of the input piston 64. The stopper 68 engages a stopper groove 69 formed on the output piston 62. This configuration allows the input piston 64 to move relative to the output piston 62 in the front-to-back direction by a distance corresponding to a clearance in the front-to-back direction between the stop 68 and the stop groove 69.In addition, the input piston 64 is prevented from moving rearward relative to the rear housing 43 due to the abutment of the stopper 68 against an opening peripheral edge portion 50A at a front side of the cylinder portion 50 of the rear housing 43 (see . Fig. 1).

[0023] The electric booster unit 1 has an output rod 70 that presses against (or applies a thrust force to) the primary piston 5 of the master cylinder 2. The output rod 70 includes a shaft portion 71 and a pressure receiving portion 72. A front end of the shaft portion 72 abuts against a conical bottom portion 32 of a recessed portion of the primary piston 5 at the rear thereof. The pressure receiving portion 72 is coupled to a rear end portion of the shaft portion 71. The pressure receiving portion 72 includes a bottomed, cylindrical base portion 73 and a support rod 74. The base portion 73 is open at its rear. The support rod 74 extends forward (toward the master cylinder 2 side) from the center of the base portion 73 to support the shaft portion 71. A front end portion 62A of the output piston 62 is slidably inserted into the base portion 73.The shaft portion 71 and the support rod 74 (the pressure receiving portion 72) of the output rod 70 are coupled to each other by a thread 75. In other words, a shaft length (total length) of the output rod 70 can be adjusted using the thread 75.

[0024] A reaction disc 76 made of elastic material is provided between the output piston 62 and the output rod 70. The reaction disc 76 is contained inside the base portion 73 of the pressure receiving portion 72 of the output rod 70 and is tightly enclosed by the base portion 73 and the front end portion 62A of the output piston 62. In the non-braking state (see Fig. 1) a space referred to as offset clearance is provided between an end face of the reaction disc 76 at its rear side and an upper part of the input piston 64 having a conically shaped front end portion.

[0025] A compression coil spring 77 is provided between a spring support member 78, which is provided to cover the base portion 73 of the pressure-receiving portion 72 of the output rod 70, and an annular spring support portion 79 formed on an inner peripheral surface of the cylinder portion 46 of the base member 45. The output piston 62 is urged rearward by the compression coil spring 77. Due to this urging, the output piston 62 is brought into contact with the thrust transmitting member 81, which will be described below. An annular seal member 80 seals off a space on the master cylinder 2 side (inside the cylinder portion 46) and a space opposite a plate 79 on the rear housing 43 side (inside the housing 4).

[0026] As in Fig. As shown in Figure 1, the electric booster unit 1 includes the thrust transmitting member 81 that transmits a thrust generated by the electric actuator 61 to the output piston 62. The thrust transmitting member 81 engages the output piston 62 (an output member) and a rotary-to-linear motion conversion mechanism 60, which will be described below, and is arranged to extend beyond the rotary-to-linear motion conversion mechanism 60. The thrust transmitting member 81 includes a protrusion portion 82 and arms 83 and 84 that extend upward and downward from the protrusion portion 82, respectively.The thrust transmitting element 81 is biased rearward by a helical compression spring 85, which is seated between a spring bearing portion 86 formed within the projection portion 82 of the thrust transmitting element 81 and the annular plate 79, which is fixed to a rear end surface of the base member 45. Due to this bias, in the non-braking state (see . Fig. 1) a rear end face 87 (see Fig. 3) the projection portion 82 of the thrust transmitting member 81 is brought into abutment with the opening peripheral edge portion 50A on the front side of the cylinder portion 50 of the rear housing 43.

[0027] As in Fig. 3, a flange bearing portion 89, which receives a flange portion 88 of the output piston 62, is provided within the projection portion 82 of the thrust transmission element 81. The flange bearing portion 89 is provided between an axial bore 82A open on a rear end surface of the projection portion 82 and the spring bearing portion 86 and is formed by a funnel-shaped inclined surface that reduces in diameter towards the rear. A surface 90 on a rear side of the flange portion 88 of the output piston 62, i.e., a contact surface 90 of the output piston 62, which bears against the flange bearing portion 89 of the thrust transmission element 81, is formed by the spherical surface 90, i.e., has a circular arc-like protruding shape along an axial plane of the output piston 62 in cross section.In other words, the output piston 62 is supported on its spherical contact surface 90 on the flange bearing section 89 of the thrust transmission element 81 (the other element).

[0028] As in Fig. 1, the electric actuator 61 comprises an electrically driven motor 91 (see Fig. 2) as a motor and the rotary-to-linear motion conversion mechanism 60. The rotary-to-linear motion conversion mechanism 60 converts a driving force (a rotational force) of the electrically driven motor 91 into the thrust of the thrust transmitting member 81. The rotary-to-linear motion conversion mechanism 60 includes two lead screw members 92 and 93 and two nut members 94 and 95. The lead screw members 92 and 93 have rotation axes located at different positions from the center axis of the master cylinder 2. The nut members 94 and 95 are engaged with the lead screw members 92 and 93, respectively. The threaded spindle element 92 is arranged at the top with respect to the central axis of the master cylinder 2 and is also parallel to the central axis of the master cylinder 2. A rear end portion 97 of the threaded spindle element 92 is supported by the rear housing 43 via a radial bearing 98.The rear end portion 97 of the lead screw element 92 is supported by the rear housing 43 via a thrust bearing 99. In other words, the rear end portion 97 of the lead screw element 92 is rotatably supported by a combination of the radial bearing 98 and the thrust bearing 99 coaxial with the radial bearing 98.

[0029] A hub 101 is fixed to a front end portion 100 of the threaded spindle element 92. The hub 101 and thus the front end portion 100 of the threaded spindle element 92 are rotatably supported by the base member 45 via a radial bearing 102. In other words, the threaded spindle element 92 is rotatably supported about the rotational axis of the threaded spindle element 92 by the two radial bearings 98 and 102 and the one thrust bearing 99. An output disk 104 is non-rotatably attached to a front end portion 103 of the hub 101. In other words, the output disk 104 is attached to the front end portion 100 of the threaded spindle element 92 via the hub 101. The radial bearing 102 is contained in a bearing receiving portion 52 provided in the base member 45. The radial bearing 98 and the thrust bearing 99 are contained in a bearing receiving portion 56 provided in the rear housing 43.An upper end portion 53 and a lower end portion 54 of the base member 45 are fixed to the rear housing 43 by screws 55.

[0030] As in Fig. 4 and Fig. 5, the nut member 94 is shaped like a flanged hex nut with a flange portion 106 formed at its rear end. A side surface 107 (referred to simply as "thrust surface 107") of the flange portion 106 at its front side extends parallel to a plane perpendicular to an axis of the nut member 94 (coincident with the rotational axis of the lead screw member 92), and thus parallel to a plane perpendicular to the rotational axis of the lead screw member 92. As shown in Fig. As shown in Figure 4, two surfaces 109 and 110, which define a screw width of a hexagonal portion 108 of the nut member 94, are slidably fitted into a constant-width groove portion 111 formed at an upper end portion of the arm 83 of the thrust transmitting member 81. The groove portion 111 extends vertically and is open at its upper end. In other words, the nut member 94 is vertically movable relative to the thrust transmitting member 81.

[0031] As in Fig. 5, an abutment surface 112 of the thrust transmitting member 81, which abuts against the pressure surface 107 of the flange portion 106 of the nut member 94, that is, a surface 112 of the thrust transmitting member 81 at a rear side of an upper end portion of the arm 83, is formed into a protruding circular arc shape in cross section along an axial plane of the thrust transmitting member 81. In other words, the thrust transmitting member 81 abuts against the pressure surface 107 of the nut member 94 (the other member) in the region of its abutment surface 112, which is formed into the protruding circular arc shape in cross section along the axial plane. Therefore, the arm 83 of the thrust transmission element 81 is displaceable and pivotable relative to the nut element 94 when the contact surface 112 of the thrust transmission element 81 is in contact with the pressure surface 107 of the nut element 94.

[0032] As in Fig. 1, the lead screw member 93 is arranged downward with respect to the center axis of the master cylinder 2 and is also parallel to the lead screw member 92. A rear end portion 117 of the lead screw member 93 is supported by the rear housing 43 via a radial bearing 118. Furthermore, the rear end portion 117 of the lead screw member 93 is supported by the rear housing 43 via a thrust bearing 119. In other words, the rear end portion 117 of the lead screw member 93 is rotatably supported by a combination of the radial bearing 118 and the thrust bearing 119 coaxial with the radial bearing 118.

[0033] A hub 121 is fixed to a front end portion 120 of the lead screw element 93. The hub 121 and thus the front end portion 120 of the lead screw element 93 are supported by the base member 45 via a radial bearing 122. In other words, the lead screw element 93 is rotatably supported about the rotational axis of the lead screw element 93 by the two radial bearings 118 and 122 and the one thrust bearing 119. A driven disk 124 is non-rotatably attached to a front end portion 123 of the hub 121. In other words, the driven disk 124 is attached to the front end portion 120 of the lead screw element 93 via the hub 121. The radial bearing 122 is contained in a bearing receiving portion 57 provided in the base member 45. The radial bearing 118 and the thrust bearing 119 are contained in a bearing receiving portion 58 provided in the rear housing 43.

[0034] The nut element 95 is identical in shape to the nut element 94 described above. Thus, a coupling structure between the nut element 95 and the arm 84 of the thrust transmission element 81 is also the same structure as the previously described coupling structure between the nut element 94 and the arm 83 of the thrust transmission element 81. Therefore, with the aim of simplifying the explanation of the present description, the explanations of the nut element 95 and the coupling structure between the nut element 95 and the arm 84 of the thrust transmission element 81 are omitted, and a corresponding configuration can be understood using the same designation and the same reference numeral.

[0035] As in Fig. 1, the electric actuator 61 comprises a drive pulley (not shown), the driven pulley 104, the driven pulley 124 and an endless belt 126. The drive pulley is mounted on a rotating shaft of the electric driven motor 21 (see Fig. 2). The driven pulley 104 is fixed to the lead screw member 92. The driven pulley 124 is fixed to the lead screw member 93. The endless belt 126 is guided over and suspended in a tension pulley (not shown). With this configuration, the driving force of the electrically driven motor 91 is transmitted to the lead screw members 92 and 93, respectively, via the endless belt 126. The nut members 94 and 95 are each prevented from rotating relative to the lead screw members 92 and 93, respectively, and are moved forward (or backward) along the lead screw members 92 and 93 depending on the rotation of the lead screw members 92 and 93 (for convenience, referred to as "advanced (or retracted)"). In other words, the driving force (the rotational force) of the electrically driven motor 91 is converted into a thrust force of the respective nut elements 94 and 95.

[0036] Thus, the thrust surfaces 107 of the nut members 94 and 95 press against the abutment surfaces 112 of the arms 83 and 84, respectively, of the thrust transmitting member 81, thereby applying a thrust force (or advancing) to the thrust transmitting member 81 against the spring force of the helical compression spring 95. In other words, the thrust force of each of the nut members 94 and 95 is transmitted to the thrust transmitting member 81. Furthermore, the flange bearing portion 89 of the thrust transmitting member 81 presses against the abutment surface 90 of the flange portion 88 of the output piston 62, thereby applying a thrust force (advancing) to the output piston 62 against the spring force of the helical compression spring 77. In other words, the thrust force of the thrust transmitting member 81 is transmitted to the output piston 62. Then, the thrust of the output piston 62 is transmitted to the output rod 70 via the reaction disc 76.

[0037] In the first embodiment, a thread formed on each of the threaded spindle elements 92 and 93 is a trapezoidal thread. Furthermore, as shown in Fig. 2, the electric booster unit 1 includes an electronic control unit 114 (referred to simply as “ECU 114”) for controlling the electrically driven motor 91.

[0038] In the electric booster unit 1 according to the first embodiment, when the brake pedal is depressed, the input rod 33 is advanced against the biasing force of the compression coil spring 35. An operation amount on the brake pedal at this time, that is, a displacement of the input rod 33, is detected by a stroke sensor or the like. Then, the ECU 114 controls the electrically driven motor 91 (the electric motor) of the electric actuator 61 based on the displacement of the input rod 33, thereby applying a thrust force (advancing) to each of the nut members 94 and 95 and, consequently, the thrust transmitting member 81. The thrust force of the thrust transmitting member 81 is transmitted to the primary piston 5 via the output piston 62 (the output member), the reaction disc 76, and the output rod 70.

[0039] Due to this configuration, when the primary piston 5 advances, the ECU 114 controls the electrically driven motor 91 such that the amount of movement of the primary piston 5 follows the displacement of the input rod 33, that is, the amount of brake pedal operation. The advance of the primary piston 5 causes an increase in the hydraulic pressure in the primary chamber 7, and this hydraulic pressure is transmitted to the secondary chamber 8 via the secondary piston 6. Then, the hydraulic pressure generated in the master cylinder 2 is supplied to the wheel cylinder of each of the vehicle's wheels via the two hydraulic circuit systems, thereby generating braking force through friction braking. A reaction force derived from the hydraulic pressure in the master cylinder 2, which is generated at the time of this braking operation, is transmitted to the input piston 64 (an input element) and output piston 62 via the primary piston 5, the output rod 70, and the reaction disc 76.Thus, a desired braking force can be generated with a boost ratio (a ratio between the hydraulic output and the operation input at the brake pedal) obtained based on a ratio between a pressure receiving area of ​​the front end surface of the output piston 62 and a pressure receiving area of ​​the piston portion 65 of the input piston 64.

[0040] When the brake pedal is released, the ECU 114 controls the electrically driven motor 91 based on the displacement of the input rod 33, causing the nut members 94 and 95 and, consequently, the thrust transmitting member 81 to retract, respectively. Accordingly, the primary piston 5 and the secondary piston 6 are retracted via the output piston 62, the reaction disc 76, and the output rod 70, so that the hydraulic pressure in the master cylinder 2 decreases and the braking force decreases.

[0041] If a ball screw is used for the rotary-to-linear motion conversion mechanism 60, as explained in the previously described JP 2007-191133 A, this makes the device (the electric actuator) expensive. One attempt to address this situation is to use a rotary-to-linear motion conversion mechanism 60 designed to operate on a different axis than the input rod instead of the ball screw. However, this approach raises the problem of reduced operational reliability. One of the reasons for this is that unnecessary torque and radial load are applied to the linear motion element, mainly due to faulty component assembly.

[0042] To solve this problem, the first embodiment enables an offset load applied to the output piston 62 due to an error in assembling the electric actuator 61 to be absorbed by the flange bearing portion 89 of the thrust transmitting member 81 pivoting relative to the abutment surface 90 of the output piston 62, thereby successfully preventing or reducing the generation of unnecessary torque and radial load on the lead screw members 94 and 95 when transmitting the driving force of the electrically driven motor 91. As a result, the first embodiment can prevent the transmission efficiency from being reduced and the nut members 94 and 95 from locking on the lead screw members 92 and 93, respectively, thereby providing an electric booster unit 1 that is highly reliable in operation.

[0043] Having explained the first embodiment in detail, advantageous effects of the first embodiment will now be described.

[0044] The first embodiment is an electric booster unit comprising an input member configured to be moved forward or backward in response to an operation of a brake pedal, a thrust transmitting member provided for movement relative to the input member, an electric actuator configured to move the thrust transmitting member forward or backward, and an output member connected to the thrust transmitting member and configured to transmit a thrust applied by the electric actuator to the thrust transmitting member to a piston of a master cylinder. The electric actuator includes an electric motor, at least two lead screw members configured to be rotated by the electric motor, and nut members each engaging a lead screw member.Each of the nut members is connected to the thrust transmission member. The thrust transmission member is pivotally connected to the nut members and / or the output member. Therefore, the first embodiment makes it possible to absorb a displaced load applied to the output member due to a positional difference between the nut members in a front-to-rear direction, which may be caused by an error in the assembly of the electric actuator. Due to this effect, the first embodiment can prevent a decrease in transmission efficiency and the locking of the nut members on the lead screw members because unnecessary torque and radial load are not generated on the lead screw members when the drive force of the electric motor is transmitted.As a result, the first embodiment can provide an electric amplifying unit that is extremely reliable in operation.

[0045] The first embodiment employs a rotary-to-linear motion conversion mechanism in which the rotary axis is located at a different position from the center axis of the master cylinder. This improves design flexibility compared to the conventional technique using a ball screw for the rotary-to-linear motion conversion mechanism, thereby reducing the size of the electric actuator and thus the size of the electric amplification unit. In addition, the first embodiment enables the electric amplification unit 1 to use a lead screw member with an inexpensive trapezoidal screw instead of an expensive ball screw, thereby reducing the manufacturing cost of the electric actuator and consequently the manufacturing cost of the electric amplification unit.

[0046] The first embodiment causes the output member to pivotally engage the thrust transmitting member on the abutment surface having the circular arc-like protruding shape in cross section, thereby making it possible to absorb a displaced load applied to the output member due to a positional difference in the front-rear direction between the nut members caused by an error in the assembly of the electric actuator, the displaced load being absorbed by allowing the thrust transmitting member to pivot relative to the abutment surface of the output member.Due to this effect, the first embodiment can prevent or reduce the generation of unnecessary torque and radial load on the lead screw elements, thereby preventing a reduction in transmission efficiency and jamming of the nut elements on the lead screw elements when transmitting the driving force of the electric motor. As a result, the first embodiment can provide an electric booster unit that is highly reliable in operation.

[0047] In the first embodiment, each of the nut members is connected so as to be vertically movable relative to the thrust transmitting member. The abutting surface of the thrust transmitting member, which abuts against the respective nut members, is formed into a protruding circular arc-like shape in cross-section along the axial plane of the thrust transmitting member. Each of the protruding abutting surfaces of the thrust transmitting member is brought into pivotal contact with the thrust surface of each of the nut members.Therefore, the first embodiment makes it possible to absorb the above-described offset load applied to the output member due to the positional difference between the nut members in the forward and backward directions caused by an error in the assembly of the electric actuator, and absorb the offset load by having each of the corresponding abutment surfaces of the thrust transmitting member pivot relative to the thrust surface of each of the nut members. Through this action, the first embodiment can prevent or reduce the generation of unnecessary torque and radial load on the lead screw members when transmitting the driving force of the electric motor.

[0048] Now that the first embodiment has been described, in the first embodiment, the funnel-shaped inclined surface (see Fig. 3) is formed on the flange bearing portion 89 of the thrust transmitting element 81, and the spherical abutment surface 90 (which has a circular arc-like protruding shape in cross-section) is formed on the flange portion 88 of the output piston 62. On the other hand, the electric amplification unit 1 can also be designed such that the funnel-shaped inclined surface is formed on the flange portion 88 of the output piston 62 and the spherical abutment surface 90 is formed on the flange bearing portion 89 of the thrust transmitting element 81, whereby with this configuration, the spherical abutment surface 90 of the thrust transmitting element 81 slidably abuts the funnel-shaped flange portion 88 of the output piston 62.

[0049] Furthermore, in the first embodiment, the abutment surface 112 of the thrust transmitting member 81, which abuts the thrust surface 107 of the flange portion 106 of each of the nut members 94 and 95, is formed in a protruding circular arc-like shape in cross-section along the axial plane of the thrust transmitting member 81. However, the electric amplifying unit 1 may also be configured such that the thrust surface 107 of each of the nut members 94 and 95 is spherical, whereby this configuration achieves that the spherical thrust surface 107 of each of the nut members 94 and 95 pivotally abuts the flat abutment surface 112 of the respective corresponding arm 83 or 84 of the thrust transmitting member 81.

[0050] In other words, at the engagement portions of the output member and the rotary-to-linear motion conversion mechanism in the thrust transmitting member, the abutment surface 90 of the flange portion 88 of the output piston 62 and the thrust surface 107 of the flange portion 106 of each of the nut members 94 and 95 may be spherically shaped. [Second embodiment]

[0051] Next, with reference to Fig. 6 describes a second embodiment, which mainly focuses on the differences from the first embodiment. Fig. 6 is a cross-sectional view of engaging portions of the output member and the rotary-to-linear motion conversion mechanism with the thrust transmitting member according to the second embodiment. The portions used in the first embodiment are denoted by the same notations and reference numerals.

[0052] As in Fig. 6, in the second embodiment, the output piston 62 (the output member) and the thrust transmitting member 81 are connected to each other via an elastic member 131, and the nut members 94 and 95 (the rotary-to-linear conversion mechanism 60) and the thrust transmitting member 81 are connected to each other via an elastic member 132. The other portions are the same as in the first embodiment. Furthermore, the nut member 94 and the nut member 95 are identical components, so the illustration of the nut member 95 is omitted here.

[0053] The axial bore 82A of the protrusion portion 82 of the thrust transmitting member 81 according to the second embodiment is a stepped bore with a diameter that gradually increases from the rear end surface 87 toward the front side. A hole of the stepped bore at the front side thereof is used as a groove portion 133 containing the elastic member 131, which is rectangular in cross section along the axial plane. Specifically, the groove portion 133 includes an annular receiving surface 134 that receives a rear end surface of the elastic member 131 and an annular receiving surface 135 that receives an outer peripheral surface of the elastic member 131.

[0054] The output piston 62 has a groove portion 136 formed at a corner region on a rear side of an outer peripheral edge portion of the flange portion 88. A contact surface 137 is formed on the groove portion 136. The contact surface 137 abuts against a front end surface of the elastic member 131 mounted in the groove portion 133, i.e., it faces the receiving surface 134 of the groove portion 133 with a predetermined distance therebetween. A clearance surface 138 is formed on the groove portion 136. The clearance surface 138 has a predetermined distance from an inner peripheral surface of the elastic member 131, and the contact surface 137 abuts against the front end surface of the elastic member 131 (see Fig. 6). Specifically, a predetermined space 139 is formed between the flank surface 138 of the groove portion 136 and the inner peripheral surface of the elastic member 131. A height (a length in the front-to-rear direction) of the flank surface 138 is set to be slightly shorter than the thickness of the elastic member 131 (a height of the receiving surface 135).

[0055] The flange portion 106 of the nut member 94 according to the second embodiment is formed in a step shape, with a projection portion 140 provided at the front thereof. An annular groove portion 142 is provided at an inner peripheral portion of a front end surface 141 of the flange portion 106 so as to surround the projection portion 140. The annular elastic member 132 is attached to the groove portion 142. The elastic member 132 is formed in a rectangular shape in cross section, and a front end surface 132A is located in the front-to-rear direction (in the axial direction) between a front end surface 140A of the projection portion 140 and the front end surface 141 of the flange portion 106. In other words, the front end surface 132A of the elastic member 132 is located further forward with respect to the front end surface 141 of the flange portion 106.

[0056] Instead of the groove section 111 (see Fig. 4) A hexagonal hole 144 is formed in the arm 83 of the thrust transmitting member 81 according to the second embodiment, and the hexagonal portion 108 of the nut member 94 is inserted into the hexagonal hole 144. The fitting engagement between the hexagonal hole 144 and the hexagonal portion 108 is set to allow some compensation movement caused by the positional difference between the nut members 94 and 95 in the front-to-rear direction due to an error in the assembly of the electric actuator 61. An annular protruding portion 146, provided around the hexagonal hole 144, is formed on the rear surface 145 of the arm 83 of the thrust transmitting member 81.

[0057] As in Fig.6, an inner peripheral surface of the annular protruding portion 146 faces an outer peripheral surface of the protruding portion 140 of the nut member 94, forming a predetermined space therebetween. An annular abutment surface 147 is formed on the annular protruding portion 146. The abutment surface 147 is brought into contact with the front end surface 132A of the elastic member 132. A space for allowing a balancing movement between the lead screw member 92 and the nut member 94, with the abutment surface 147 in contact with the front end surface 132A of the elastic member 132, is formed between the rear surface 145 of the arm 83 of the thrust transmitting member 81 and the front end surface of the protruding portion 140 of the nut member 94.

[0058] Furthermore, similar to the first embodiment, the connecting structure between the nut member 95 and the arm 84 of the thrust transmitting member 81 according to the second embodiment is the same structure as the above-described connecting structure between the nut member 94 and the arm 83 of the thrust transmitting member 81, which is realized via the elastic member 132. Therefore, in order to simplify the explanation of the present description, the explanations of the nut member 95 and the connecting structure between the nut member 95 and the arm 84 of the thrust transmitting member 81 are omitted below, and a corresponding configuration can be understood by the same designation and the same reference numeral.

[0059] In this way, in the second embodiment, the output piston 62 (the output member) and the thrust transmitting member 81 are connected to each other via the elastic member 131. More specifically, the output piston 62 and the thrust transmitting member 81 are connected to each other, while at the same time, the abutment surface 137 of the output piston 62 abuts against the elastic member 131 disposed in the groove portion 133 of the thrust transmitting member 81. Thus, with the deformation of the elastic member 131 during operation of the electric actuator 61 in the second embodiment, it is possible to absorb an offset load acting on the output piston 62 due to a positional difference in the front-rear direction between the nut members 94 and 95 caused by an error in the assembly of the electric actuator 61.

[0060] Furthermore, in the second embodiment, each of the nut members 94 and 95 (rotational-to-linear motion conversion mechanism) and the thrust transmitting member 81 are connected to each other via the elastic member 132. More specifically, the nut members 94 and 95 and the thrust transmitting member 81 are connected to each other, while the abutment surface 147 of each of the arms 83 and 84 of the thrust transmitting member 81 abuts against the elastic member 132 attached to each of the nut members 94 and 95. Therefore, with deformation of the elastic member 132 during operation of the electric actuator 61 in the second embodiment, it is possible to absorb an offset load acting on the output piston 62 due to a positional difference in the front-rear direction between the nut members 94 and 95 caused by an error in the assembly of the electric actuator 61.

[0061] As a result, in the second embodiment, the transmission efficiency can be prevented from decreasing and the nut members 94 and 95 from jamming on the lead screw members 92 and 93, thereby providing an electric amplifying unit 1 that is highly reliable in operation.

[0062] In the second embodiment, the output piston 62 (the output member) and the thrust transmitting member 81 are connected to each other via the elastic member 131, while each of the nut members 94 and 95 (rotational-to-linear conversion mechanism) and the thrust transmitting member 81 are connected to each other via the elastic member 132. However, the thrust transmitting member 81 may be configured to be connected to the output member 62 and / or the nut members 94 and 95 via the elastic member 131 or the elastic member 132.

[0063] Furthermore, the elastic element 131 is attached to the thrust transmission element 81, but the electric booster unit 1 may also be configured such that the elastic element 131 is attached to the output piston 62. Similarly, the elastic element 132 is attached to the nut elements 94 and 95, respectively, and the electric booster unit 1 may also be configured such that the elastic element 132 is attached to the thrust transmission element 81. List of reference symbols 1 Electrical amplification unit 2 master cylinders 5 primary pistons (pistons) 61 Electric actuator 62 Output piston (output element) 64 Input piston (input element) 81 Thrust transmission element 91 Electrically driven motor (electric motor) 92, 93 Threaded spindle element 94, 95 Nut element

Claims

[1] Electrical amplification unit (1), comprising: an input member (64) adapted to be moved forward or rearward in accordance with an operation of a brake pedal; a thrust transmission element (81) provided to be movable with respect to the input element (64); an electric actuator (61) configured to move the thrust transmitting element (81) forward or backward; and an output element (62) connected to the thrust transmission element (81) and designed to transmit a thrust applied by the electric actuator (61) to the thrust transmission element (81) to a piston (5) of a master cylinder (2), wherein the electric actuator (61) an electric motor (91), at least two threaded spindle elements (92, 93) designed to be rotated by the electric motor (91), and nut elements (94, 95) each engaging a threaded spindle element (92, 93), each of the nut elements (94, 95) being connected to the thrust transmission element (81), characterized by that the thrust transmission element (81) is pivotally connected to the nut elements (94, 95) and / or the output element (62). [2] Electrical amplification unit (1) according to claim 1, wherein the thrust transmission element (81) abuts the output element (62) or the output element (62) abuts the thrust transmission element (81) on a surface portion which has a circular arc-like protruding shape in cross section along an axial plane. [3] Electrical amplification unit (1) according to claim 1 or 2, wherein the thrust transmission element (81) bears against the nut element (94, 95) or the nut element (94, 95) bears against the thrust transmission element (81) on a surface portion which has a circular arc-like protruding shape in cross section along an axial plane. [4] An electric amplifying unit (1) according to any one of claims 1 to 3, wherein a center line of each of the lead screw members (92, 93) extends parallel to a center line of the output member (62) and is disposed in the same plane as the center line of the output member (62). [5] Electric amplifying unit (1) according to claim 1, wherein the thrust transmitting element (81) is connected to the nut elements (94, 95) and / or the output element (62) via an elastic element. [6] An electric amplifying unit (1) according to claim 1, wherein the output member (62) or the nut members (94, 95) have a spherical shape at the mutual engagement portion.

Images