Electromechanical brake booster

Abstract

To eliminate concerns about function of poor contact with a piston of a master cylinder due to shearing of a thread part of a screw member and wear of a contact surface in an electromechanical brake assistor which, when a brake pedal is stepped on, drives a motor part by operation of a control rod such that the control rod performs linear motion in an axial direction, converts rotary motion into linear motion of the screw member by a rotation / linear motion converter, and moves the piston of the master cylinder, in which a brake fluid for a hydraulic brake is filled, by linear motion of the screw member.SOLUTION: A tabular push plate 44, which contacts an apical surface 81a of a screw member 81 and a connection surface 130a of a piston 130 and is made of a rigid material, is interposed between the apical surface 81a of the screw member 81 and the connection surface 130a of the piston 130.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to an electromechanical brake booster for amplifying the force applied when the brake pedal is depressed in an automobile. [Background technology]

[0002] Conventionally, brake boosters that amplify the force applied when the brake pedal is depressed have been known to assist in braking operations in automobiles. For example, a vacuum brake booster that utilizes the negative pressure of the engine, such as the invention described in JP 54-90459 A (Patent Document 1), has been commonly used.

[0003] In recent years, the movement towards carbon neutrality has been gaining momentum in countries around the world, and in order to achieve the goal of moving away from fossil fuels, the transition to vehicles that do not have engines as their power source, such as electric vehicles and fuel cell vehicles, has become an important issue for the future of the automotive industry.

[0004] In that case, one of the differences between conventional engine-equipped vehicles and non-engine vehicles such as electric vehicles is that, since they do not have an engine, the engine negative pressure (intake pipe negative pressure) used in conventional systems is not generated, which creates the problem that various parts that use negative pressure cannot be used.

[0005] Therefore, there is a need for a brake booster that can provide a high braking force that can be used in automatic braking as an alternative to a vacuum brake booster. For example, electromechanical brake boosters equipped with a motor as a power source are known, such as the inventions described in JP 2018-199448 A (Patent Document 2) and JP 2018 / 097278 A (Patent Document 3).

[0006] These conventional electromechanical brake boosters make it possible to amplify the force applied when stepping on the brake pedal by using an electrically powered motor, even in vehicles that do not have an engine.

[0007] 5 and 6 show an example of a conventional electromechanical brake booster, which includes a control rod 40 connected to a brake pedal BP at its base end and moving linearly in the axial direction in response to operation of the brake pedal BP, a sensor section 50 including a position sensor for detecting the displacement of the control rod 40, a motor section 60 having a stator 61, a rotor 62 and a rotating shaft 63 which operate in response to the displacement of the control rod 40, a control section 70 for driving the motor section 60 using information obtained from the sensor section 50, and a rotating member 82 which is linked to the motor section 60 and has a cylindrical screw member 81 with a male thread on its outer periphery and a female thread on its inner periphery which screws into the male thread of the screw member 81, and the rotational movement of the rotating member 82 which is rotated by the motor section 60 is controlled by the screw member 81. The electromechanical brake booster 2 includes a rotary-to-linear motion conversion unit 80 that converts rotational motion into linear motion of a screw member 81, and a master cylinder 120 filled with brake fluid for hydraulic brakes, which is connected to the tip surface of the screw member 81 and has a piston 130 that operates by the linear motion of the screw member 81. When the brake pedal BP is depressed, the sensor unit 50 detects the operation of the control rod 40, which moves linearly in the axial direction, to drive the motor unit 60, and the rotary-to-linear motion conversion unit 80 converts the rotational motion into linear motion of the screw member 81, and the linear motion of the screw member 81 moves the piston 130 of the master cylinder 120 filled with brake fluid for hydraulic brakes, thereby generating electromechanical brake boosting. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Publication No. 54-90459 [Patent Document 2] JP 2018-199448 A [Patent Document 3] Re-tabled publication 2018 / 097278 Summary of the Invention [Problem to be solved by the invention]

[0009] In the conventional electromechanical brake booster 2 shown in Figures 5 and 6, the contact between the screw member 81 and the piston 130 of the master cylinder 120 is between the end face 81a of the threaded portion of the screw member 81 and the end face 130a of the piston 130.

[0010] Therefore, there is a concern that the screw member 81 may have a defective contact with the piston 130 of the master cylinder 120 due to shearing of the threads of the screw member 81 or wear of the contact surface.

[0011] The present invention has been made to solve such problems, and has as its object to provide an electromechanical brake booster device by increasing the contact surface area between the screw member 81 and the piston 130 of the master cylinder 120, thereby eliminating concerns about poor contact function with the piston 130 of the master cylinder 120 due to shearing of the threaded portion of the screw member 81 or wear of the contact surface. [Means for solving the problem]

[0012] The electromechanical brake booster achieved in order to solve the above-mentioned problems includes a control rod having a base end connected to a brake pedal and moving linearly in the axial direction in response to operation of the brake pedal, a sensor unit including a position sensor that detects displacement of the control rod, a motor unit that operates in response to displacement of the control rod, a control unit that drives the motor unit using information obtained from the sensor unit, a rotary-to-linear conversion unit that includes a cylindrical screw member having a thread on its outer periphery and a rotating member that is linked to the motor unit and has a threaded portion on its inner periphery that screws into the threaded portion of the screw member, and converts the rotational motion of the rotating member rotated by the motor unit into linear motion of the screw member, and a master cylinder filled with brake fluid for hydraulic brakes, the master cylinder having a piston connected to a tip surface of the screw member and operated by the linear motion of the screw member, and a push plate that is plate-shaped and made of a rigid material and that comes into contact with the connection surface between the tip surface of the screw member and the piston of the master cylinder is disposed between the tip surface of the screw member and the connection surface between the piston of the master cylinder.

[0013] According to the present invention, the tip surface of the screw member and the connection surface of the piston each become a pressure-receiving surface having rigidity, thereby preventing concerns about poor contact function with the piston of the master cylinder due to shearing of the threaded portion of the screw member or wear of the contact surface.

[0014] In addition, in the present invention, when the push plate is donut-shaped with the screw member as its axis, has an inner diameter that is the same as or smaller than the inner diameter of the hollow portion of the screw member, and has an outer diameter that is the same as or larger than the outer diameter of the piston, the entire area of ​​the tip surface of the screw member and the connection surface of the piston of the master cylinder can be made into a pressure-receiving surface, thereby reliably preventing malfunction of the contact with the piston of the master cylinder due to shearing of the threaded portion of the screw member or wear of the contact surface that occurs during use. Effect of the Invention

[0015] According to the present invention, the connection surface of the screw member and the connection surface of the piston each become a pressure-receiving surface having rigidity over their entire surface, thereby preventing concerns about poor contact function with the piston of the master cylinder due to shearing of the threaded portion of the screw member or wear of the contact surface, and ensuring reliable operation of the screw member and the piston of the master cylinder. [Brief description of the drawings]

[0016] [Figure 1] 1 is a cross-sectional view showing a preferred embodiment of an electromechanical brake booster according to the present invention; [Diagram 2] 2A-2C are cross-sectional views of the embodiment shown in FIG. 1 at different angles. [Diagram 3] FIG. 2 is an enlarged partial cross-sectional view of a main portion of the embodiment shown in FIG. [Figure 4] 1A is a partial cross-sectional view showing an enlarged view of a main portion of a different embodiment, in which (a) is a view showing a case where the outer diameter of the push plate is larger than the outer diameter of the piston, and (b) is a view showing a case where the outer diameter of the push plate is smaller than the outer diameter of the piston. [Diagram 5] FIG. [Figure 6] FIG. 6 is an enlarged partial cross-sectional view of a main part of the conventional example shown in FIG. 5. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the same reference numerals are used to designate the same components as those of the conventional electromechanical brake booster 2.

[0018] 1 to 3 show a preferred embodiment of the electromechanical brake booster of the present invention, and this electromechanical brake booster 1 has a casing 10, an input rod 20, a biasing member 30, a control rod 40, a sensor unit 50, a motor unit 60, a control unit 70, a rotary-linear motion conversion unit 80, a bracket 90, a support 100, a return spring 110, and a master cylinder 120.

[0019] The casing 10 is composed of a cylindrical cover 11 and a donut-shaped bottom plate 12. In FIG. 1, reference numeral 13 denotes a fixing screw for fixing the cover 11 and the bottom plate 12, and reference numeral 14 denotes a fixing member for fixing the casing 10 to the body of an automobile.

[0020] The input rod 20 is rod-shaped overall, movable in the axial direction and swingable within a certain angular range, and has a connection hole 21 extending in the axial direction of the input rod 20 and a spring retaining hole 22 extending in the axial direction and having a smaller diameter than the connection hole 21 formed continuously on its end face at one end (the control rod 40 side), and a brake pedal connector 23 is attached to the other end, which is rotatable in the circumferential direction and is used to connect to the brake pedal BP.

[0021] The biasing member 30 is made up of a coil spring 31 that exerts a repulsive force, and a retainer 32. The retainer 32 is generally conical in shape and has a mortar-shaped receiving surface 33 on the inside.

[0022] Furthermore, the control rod 40 is rod-shaped overall and can move in the axial direction. One end (the input rod 20 side) has a ball stud 41 fixed thereto with a position detection magnet 42 mounted thereon by a flange 43 so that it cannot fall off. The other end has a step 45 for engaging with a push plate 44 and a small-diameter tip 47 for mounting a coil spring 46 thereon.

[0023] The sensor section 50 is composed of a sensor board 51 and a position sensor 52, and the amount of displacement of the magnet 42 detected by the position sensor 52 is output as a signal via the sensor board 51.

[0024] The motor section 60 is composed of a stator 61, a rotor 62, a rotating shaft 63 that rotates in synchronization with the rotor 62, and two bearings 64, 65 that support the rotating shaft 63 rotatably in the circumferential direction. Reference numerals 66, 67 denote detection gears for detecting the number of rotations, and in the drawings, reference numeral 68 denotes a motor cover that is attached so as to stand from the bottom plate 12 and covers the motor section 60.

[0025] The control unit 70 is a control board 71 having the function of a motor driver for controlling the power supplied from outside via a power cable (not shown) to drive the motor unit 60. The control board 71 is connected to the position sensor 52 and the rotation speed sensor 72 via cables 73, 74, and drives the motor unit 60 using signals from each sensor.

[0026] In this embodiment, two sets of the rotation speed sensor 72 and the corresponding detection gears 66, 67 are provided. For example, by using rotation speed sensors with different performance, it is possible to achieve both high precision and high speed motor control. However, it is also possible to provide only one set of the rotation speed sensor and the corresponding detection gears.

[0027] The rotary-linear motion conversion unit 80 is a mechanism for converting the rotary motion of the motor unit 60 into linear motion, and is configured by a feed screw mechanism including a cylindrical screw member 81 having a thread formed on its outer periphery, a nut-shaped rotating member 82 having a thread groove formed on its inner periphery and screw-fitted with the screw member 81, and a cylindrical connecting member 83 that connects the rotating member 82 to the rotating shaft 63 of the motor unit 60. In this embodiment, the rotating member 82 and the connecting member 83 are formed separately and then integrally joined, but they may also be integrally molded.

[0028] The bracket 90 is a generally equilateral triangle in plan view, with through holes 91, 92 formed at the center and near each apex. The screw member 81 is inserted and fixed into the through hole 91 at the center, and is attached to three posts 100 via flange bushes 93 attached to the through holes 92 near each apex, making the bracket 90 immovable in the axial direction but movable in the axial direction, restricting the axial rotation of the screw member 81 and allowing it to move in the axial direction in conjunction with the screw member 81.

[0029] Three pillars 100 are installed between the cover 11 and the bottom plate 12, and are positioned by inserting a small diameter portion 101 formed near one end into a mounting hole 16 formed in the bottom plate 12 and by bringing a large diameter portion 102 formed adjacent to the small diameter portion 101 into contact with the bottom plate 12. The pillars are fixed by attaching a nut 104 to a tip portion 103 of the pillar protruding from a mounting hole 17 formed in the cover 11.

[0030] The return springs 110 are used to urge the bracket 90 back to its original position after it has been moved, and are attached to three reinforcing pillars 100 suspended between the cover 11 and the bottom plate 12, with one end in contact with the bottom plate 12 and the other end in contact with the flange bush 93.

[0031] The master cylinder 120 comprises a cylinder bore 121 which is cylindrical with a bottom and has a first output port 122 and a second output port 123 formed on the side, a piston 130 arranged in the cylinder bore 121, and a sub-piston 140 arranged in the cylinder bore 121 closer to the bottom than the piston 130. The master cylinder 120 is arranged so as to close the opening of the cylinder bore 121 facing the opening at the bottom of the casing 10, and is fixed by a bolt 125 and a nut 126 which are inserted while communicating the mounting hole 124 of the cylinder bore 121 and the mounting hole 18 of the bottom plate 12.

[0032] Both ends of the piston 130 are formed in a cup shape, and are formed with an H-shaped cross section partitioned by a partition wall 131. An elastic body 133 is fitted into a recess 132 formed on the base end side (the control rod 40 side) of the partition wall 131, and the tip end 47 of the control rod 40 comes into contact with the elastic body 133.

[0033] In this embodiment, particularly, a push plate 44 is interposed between the tip surface 81a of the screw member 81 and the connection surface 130a of the piston 130 of the master cylinder 120. The push plate 44 is in plate form and made of a rigid material such as metal, and is in contact with the tip surface 81a of the screw member 81 and the connection surface 130a of the piston 130.

[0034] In addition, the push plate 44 is donut-shaped with the screw member 81 as its axis, and has an inner diameter d1 that is equal to or smaller than the inner diameter d3 of the hollow portion of the screw member 81, and an outer diameter d2 that is equal to or larger than the outer diameter d4 of the piston 130, so that the entire area of ​​the connection surface 130a between the tip surface 81a of the screw member 81 and the piston 130 of the master cylinder 120 can be made into a pressure-receiving surface.

[0035] To explain in more detail, as shown in FIG. 3, in this embodiment, the inner diameter d1 of the push plate 44 is smaller than the inner diameter d3 of the hollow portion of the screw member 81, and the outer diameter d2 is formed to be equal to the outer diameter d4 of the piston 130. However, as in the embodiment shown in FIG. 4(a), it is also possible to make the outer diameter d5 of the push plate 44 larger than the outer diameter d4 of the piston 130, or as in the embodiment shown in FIG. 4(b), it is also possible to make the outer diameter d6 of the push plate 44 smaller than the outer diameter d4 of the piston 130.

[0036] Regardless of whether the outer diameter of the push plate 44 is smaller, the same as, or larger than the outer diameter of the piston 130, a force that causes the screw member 81 to move axially relative to the piston 130 can be applied without direct contact between the screw member 81 and the piston 130 as in the conventional example, and over a pressure-receiving surface that is wider than if the screw member 81 and the piston 130 were in direct contact.

[0037] Both ends of the sub-piston 140 are formed in a cup shape, and are formed in an H-shaped cross section partitioned by a partition wall 141. A recess 142 is formed on the base end side (the piston 130 side) of the partition wall 141, and a retainer rod 148 described later comes into contact with the recess 142.

[0038] Within the cylinder bore 121 of the master cylinder 120, a primary chamber 127 is formed between the piston 130 and the sub-piston 140, and a secondary chamber 128 is formed between the bottom of the cylinder bore 121 and the sub-piston 140. The inside of the cylinder bore 121 including the primary chamber 127 and the secondary chamber 128 is filled with brake fluid, which is a working fluid, and the brake fluid is supplied from a reservoir (not shown).

[0039] At this time, sealing members 151, 152 installed between the outer periphery of the piston 130 and the inner periphery of the cylinder bore 121, and sealing members 161, 162 installed between the outer periphery of the auxiliary piston 140 and the inner periphery of the cylinder bore 121, prevent the brake fluid from leaking outside the designated compartment.

[0040] The primary chamber 127 and secondary chamber 128 of the master cylinder 120 are respectively connected to a first output port 122 and a second output port 123 formed on the side of the cylinder bore 121, and the hydraulic pressure of the brake fluid output from each output port via a separate system is supplied to the brakes (not shown) of each wheel to generate braking force.

[0041] A coil spring 134 is interposed between the piston 130 and the sub-piston 140, and biases the piston 130 and the sub-piston 140 in a direction separating them from each other. Inside the coil spring 134, an expandable member 135 consisting of a retainer guide 136 and a retainer rod 138 for maintaining a predetermined distance between the piston 130 and the sub-piston 140 is arranged.

[0042] The retainer guide 136 is cylindrical and has a stopper portion 137 that protrudes inward at its tip. The retainer rod 138 is rod-shaped and has a flange portion 139 that protrudes radially outward at its base end. By inserting the retainer rod 138 into the retainer guide 136, the two can move relative to each other in the axial direction, and when the stopper portion 137 of the retainer guide 136 and the flange portion 139 of the retainer rod 138 interfere with each other, the expandable member 135 is expanded to a predetermined extent.

[0043] A coil spring 144 is interposed between the secondary piston 140 and the bottom of the cylinder bore 121, and biases the secondary piston 140 and the bottom of the cylinder bore 121 in a direction separating them from each other. An expandable member 145 consisting of a retainer guide 146 and a retainer rod 148 is disposed inside the coil spring 144 to maintain a predetermined distance between the secondary piston 140 and the bottom of the cylinder bore 121.

[0044] The retainer guide 146 is cylindrical and has a stopper portion 147 that protrudes inward at its tip. The retainer rod 148 is hollow rod-shaped and has a flange portion 149 that protrudes radially outward at its base end. By inserting the retainer rod 148 into the retainer guide 146, the two become capable of moving relative to each other in the axial direction, and when the stopper portion 147 of the retainer guide 146 and the flange portion 149 of the retainer rod 148 interfere with each other, the expandable member 145 is expanded to a predetermined extent.

[0045] The operation of the electromechanical brake booster 1 according to this embodiment will now be described.

[0046] With the electromechanical brake booster 1 installed in an automobile, when the driver depresses the brake pedal BP, the input rod 20 connected to the brake pedal BP moves axially, and the control rod 40 moves linearly in synchronization with the input rod 20.

[0047] At this time, the control rod 40 and the screw member 81 are not synchronized and can move axially separately, so that only the control rod 40 moves without changing the position of the screw member 81.

[0048] Then, the control rod 40 advances the piston 130 and the sub-piston 140 against the biasing forces of the coil springs 46 , 134 , 144 .

[0049] In addition, when the control rod 40 moves, the control unit 70 uses a signal sent from the position sensor 52 that detects the displacement to control the supply of power and an operating signal to the motor unit 60, causing the motor unit 60 to operate and rotate.

[0050] In addition, a separate rotation speed sensor 72 is provided which detects the motor rotation speed by detecting the rotation speed of detection gears 66, 67 attached to the rotating shaft 63. When the control unit 70 controls the supply of power and an operating signal to the motor unit 60, the signal sent from the rotation speed sensor 72 to the control unit 70 via a cable 74 can be utilized.

[0051] When the motor unit 60 rotates, the rotating member 82 rotates in synchronization with the rotating shaft 63 via the connecting member 83, but since the axial rotation of the screw member 81 is restricted by the bracket 90, the rotational movement of the rotating member 82 which is screw-engaged with the screw member 81 is converted into linear movement, and the piston 130 and sub-piston 140 on the axis move forward in the direction.

[0052] At this time, the bracket 90 also moves in synchronization with the screw member 81 in a direction that advances the piston 130 and sub-piston 140 on the axis while compressing the return spring 110, but since the bracket 90 slides while being guided by the support 100 via the flange bush 93, smooth operation is possible.

[0053] Then, the screw member 81 advances the piston 130 and the sub-piston 140 against the biasing forces of the coil springs 134 and 144 via the push plate 44 .

[0054] In this way, the force exerted when the driver depresses the brake pedal BP is applied directly to the piston 130 and the sub-piston 140 of the master cylinder 120 via the input rod 20 and the control rod 40, and in addition, the pressing force obtained by converting the rotational movement of the motor section 60 into the linear movement of the screw member 81 is applied to the piston 130 and the sub-piston 140 of the master cylinder via the screw member 81. As a result, by using a motor driven by electricity, the force exerted when the brake pedal BP is depressed can be amplified.

[0055] At this time, in this embodiment, a push plate 44 is interposed between the tip surface 81a of the screw member 81 and the connection surface 130a of the piston 130 of the master cylinder 120. The push plate 44 is in the form of a plate that contacts the tip surface 81a of the screw member 81 and the connection surface 130a of the piston 130 and is formed of a rigid material such as a metal.

[0056] As a result, the contact surface area between the screw member 81 and the piston 130 of the master cylinder 120 is increased, not only ensuring that the driving force from the screw member 81 is transmitted to the piston 130 of the master cylinder 120, but also eliminating concerns about poor contact function with the piston 130 of the master cylinder 120 due to shearing of the threaded portion of the screw member 81 or wear on the contact surface. [Explanation of symbols]

[0057] 1,2 electromechanical brake booster, 10 casing, 11 cover, 12 bottom plate, 13 fixing screw, 14 fixing member, 16 mounting hole, 17 mounting hole, 18 mounting hole, 20 input rod, 21 connection hole, 22 spring retaining hole, 23 brake connection device, 30 biasing member, 31 coil spring, 32 retainer, 33 receiving surface, 35 conical spring, 36 fixing bracket, 40 control rod, 41 ball stud, 42 magnet, 43 flange, 44 push plate, 45 step portion, 46 coil spring, 47 tip portion, 50 sensor portion, 51 sensor board, 52 position sensor, 60 motor portion, 61 stator, 62 rotor, 63 rotating shaft, 64 bearing, 65 bearing, 66 detection gear, 67 detection gear, 68 motor cover, 70 Control unit, 71 control board, 72 RPM sensor, 73 cable, 74 cable, 80 rotary-linear conversion unit, 81 screw member, 81a tip surface, 82 rotating member, 83 connecting member, 90 bracket, 91 through hole, 92 through hole, 93 flange bush, 100 support, 101 small diameter portion, 102 large diameter portion, 103 tip portion, 104 nut, 110 return spring, 120 master cylinder, 121 cylinder bore, 122 first output port, 123 second output port, 124 mounting hole, 125 bolt, 126 nut, 127 primary chamber, 128 secondary chamber, 130 piston, 130a piston connection surface, 1131 bulkhead, 132 recess, 133 elastic body, 134 coil spring, 135 elastic member, 136 Retainer guide, 137 stopper portion, 138 retainer rod, 139 flange portion, 140 sub-piston, 141 partition wall, 142 recessed portion, 143, 144 coil spring, 145 expandable member, 146 retainer guide, 147 stopper portion, 148 retainer rod, 149 flange portion, 151 seal member, 152 seal member, 161 seal member, 162 seal member, BP brake pedal, d1 inner diameter of push plate, d2 outer diameter of push plate, d3 inner diameter of hollow portion of screw member, d4 outer diameter of piston

Claims

1. an electromechanical brake booster comprising: a control rod having a base end connected to a brake pedal and linearly moving in an axial direction in response to operation of the brake pedal; a sensor unit including a position sensor that detects displacement of the control rod; a motor unit that operates in response to displacement of the control rod; a control unit that drives the motor unit using information obtained from the sensor unit; a rotary-to-linear conversion unit that includes a cylindrical screw member having a thread on its outer periphery and a rotating member that is linked to the motor unit and has an inner circumferential surface that is provided with a thread that screws into the thread of the screw member, and that converts rotational motion of the rotating member rotated by the motor unit into linear motion of the screw member; and a master cylinder that is connected to a tip surface of the screw member and is filled with brake fluid for a hydraulic brake, the master cylinder having a piston that is operated by the linear motion of the screw member, the master cylinder being connected to a tip surface of the screw member and filled with brake fluid for a hydraulic brake, An electromechanical brake booster, characterized in that a push plate in the shape of a plate and made of a rigid material is interposed between the tip surface of the screw member and the connection surface with the piston of the master cylinder, the push plate contacting the tip surface of the screw member and the connection surface with the piston.

2. 2. The electromechanical brake booster according to claim 1, wherein the push plate is in the shape of a doughnut disk with the screw member as its axis, has an inner diameter equal to or smaller than the inner diameter of the hollow portion of the screw member, and has an outer diameter equal to or larger than the outer diameter of the piston.

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