JP7212567B2 - electric booster - Google Patents

Description

The present invention relates to an electric booster.

2. Description of the Related Art In brake systems of automobiles such as passenger cars, electric boosters are used that generate a large output by boosting an input of a brake operation by a driver at a predetermined servo ratio. The electric booster receives the input of the brake operation by the driver at the input shaft, boosts the input with the output of the electric motor, and outputs it from the output shaft.

Japanese Patent Publication No. 2015-502886

The electric booster has a return spring for returning the output shaft to its initial position. The return spring is required to have at least a load necessary to return the output shaft to the initial position against the cogging torque of the electric motor. As a result, the outer shape of the return spring becomes relatively large, making it difficult to reduce the size of the electric booster.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and provides a negative pressure electric booster capable of reducing the load of the return spring.

In order to solve the above problems, according to one aspect of the present invention, there is provided an electric motor, an assist mechanism that converts rotary motion of the electric motor into linear motion and transmits it to an output shaft, and a return spring that retracts the output shaft. In the electric booster that boosts the input of the brake operation and outputs it from the output shaft, the assist mechanism includes a pinion gear provided on the motor shaft of the electric motor and the output torque of the electric motor via the pinion gear. A first gear that receives and moves in the axial direction, and a second gear that is provided coaxially with the first gear and is connectable with the first gear as the first gear moves in the axial direction, An electric booster in which the first gear and the second gear are connected when the output torque of the electric motor is equal to or higher than a predetermined value, and the connection is released when the output torque of the electric motor is less than the predetermined value. An electric booster is provided.

As described above, according to the present invention, the load of the return spring of the electric booster can be reduced.

1 is a schematic diagram showing an overall configuration example of an electric booster according to an embodiment of the present invention; FIG. It is a schematic diagram which shows the structural example of the assist mechanism of the electric booster which concerns on the same embodiment. It is a schematic diagram which shows the 1st gear and 2nd gear of an assist mechanism. FIG. 4 is an explanatory diagram showing the relationship between the amount of depression of a brake pedal and the output torque of an electric motor; FIG. 5 is an explanatory diagram showing the operation of the assist mechanism when the output torque of the electric motor is increased; FIG. 5 is an explanatory diagram showing the operation of the assist mechanism when the output torque of the electric motor is reduced; FIG. 5 is an explanatory diagram showing the operation of the assist mechanism just before the spindle returns to the non-operating position; FIG. 5 is an explanatory diagram showing the relationship between the force applied to the brake pedal and the brake pressure;

Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the present specification and drawings, constituent elements having substantially the same functional configuration are denoted by the same reference numerals, thereby omitting redundant description.

In this specification, "front" means the side on which the output shaft is arranged, that is, the side close to the master cylinder, and corresponds to the left side in each drawing. "Rear" means the side on which the input shaft is arranged, that is, the side closer to the brake pedal, and corresponds to the right side in each drawing.

<Overall Configuration of Electric Booster>
An overall configuration example of an electric booster (hereinafter also simply referred to as "booster") according to an embodiment of the present invention will be briefly described with reference to FIG. FIG. 1 is a partial cross-sectional view schematically showing an example of the electric booster 1. As shown in FIG. In FIG. 1, some members are shown in side view rather than in cross section.

The booster 1 includes a housing 5 , an input shaft 11 , an output shaft 13 , a valve body 15 , an electric motor 21 , an assist mechanism 50 and a return spring 17 .

The housing 5 has a front housing 5a and a rear housing 5b. The output shaft 13, the electric motor 21, the assist mechanism 50 and the return spring 17 are accommodated in the front housing 5a.

A mounting plate 7 is fixed to the rear of the rear housing 5b. Tie rods 9a and 9b pass through the mounting plate 7 for fixing the booster 1 to the vehicle body. However, the means for fixing the booster 1 to the vehicle body is not limited to the example using the tie rods 9a and 9b.

The input shaft 11 is connected to a brake pedal (not shown) and moves in the axial direction upon receipt of an input from the driver's pedal operation. The front end of the input shaft 11 is connected to the rear portion of the plunger 57 of the assist mechanism 50 via a ball joint.

The electric motor 21 may be, for example, a DCDC motor including a stator as a fixed element and a rotor as a movable element. The electric motor 21 operates by being supplied with electric power (current) controlled by an electronic controller (not shown).

A motor shaft 23 of the electric motor 21 extending from or connected to the rotor is rotatably supported by the housing 5 via a bearing member (not shown). The motor shaft 23 is axially immovably supported by the housing 5 .

The assist mechanism 50 receives the operation of the electric motor 21 and moves the valve body 15 and the output shaft 13 toward the master cylinder 40 . Assist mechanism 50 includes pinion gear 25 , first gear 61 , second gear 65 , spindle nut 51 , spindle 53 and plunger 57 .

The pinion gear 25 is coaxially fixed to the motor shaft 23 of the electric motor 21 . The motor shaft 23 is supported by the housing 5 or the like so as to be rotatable and immovable in the axial direction. The pinion gear 25 is fixed to the motor shaft 23 so as not to move axially.

Both the first gear 61 and the second gear 65 are supported by the same rotary shaft member 69 . The rotary shaft member 69 is supported by the housing 5 or the like so as to be axially rotatable and axially immovable by a bearing member (not shown).

The first gear 61 is axially movably supported by a rotating shaft member 69 . The second gear 65 is fixedly supported by the rotating shaft member 69 so as not to move in the axial direction. The first gear 61 is connected to or disconnected from the second gear 65 by axial movement.

The first gear 61 meshes with the pinion gear 25 . The second gear 65 meshes with a hub gear 59 fixed to the outer circumference of the spindle nut 51 . A gear ratio between the pinion gear 25 and the first gear 61 is set to a predetermined speed reduction ratio. A gear ratio between the second gear 65 and the hub gear 59 is set to a predetermined speed reduction ratio. The rotation of the motor shaft 23 of the electric motor 21 is decelerated and transmitted to the spindle nut 51 .

A thread groove 51 a is formed in the inner peripheral hole of the spindle nut 51 . A spindle 53 is arranged in the inner peripheral hole of the spindle nut 51 . A thread 53 a is formed on the outer peripheral surface of the spindle 53 .

The thread groove 51 a of the spindle nut 51 and the thread ridge 53 a of the spindle 53 mesh with each other, and the rotation of the spindle nut 51 allows the spindle 53 to move relative to the spindle nut 51 in the axial direction.

The structure for moving the spindle 53 in the axial direction by rotating the spindle nut 51 is such that thread grooves are formed in the inner peripheral hole of the spindle nut 51 and the outer peripheral surface of the spindle 53, and a plurality of rolling elements are formed in the opposing thread grooves. It may be a ball screw mechanism in which the balls are arranged.

The spindle 53 is formed in a hollow shape having axial holes that are open at both ends in the axial direction. A plunger 57 is arranged in the axial hole of the spindle 53 so as to be slidable in the axial direction. The plunger 57 can be relatively displaced with respect to the spindle 53 by receiving an operation input of the brake pedal by the driver via the input shaft 11 .

The valve body 15 is supported by the support member 31 . The support member 31 is supported by a sliding support member 33 slidably attached to the tie rods 9a and 9b. This allows the valve body 15 to move in the axial direction. The support member 31 advances as the spindle 53 advances, and moves the valve body 15 in the advance direction.

An input receiving member 71 is fitted in the inner peripheral hole of the valve body 15 so as to be axially movable relative to the valve body 15 . A front end of the plunger 57 is connected to the input receiving member 71 so as to be relatively movable in the axial direction.

The rear end of the output shaft 13 is fitted in the inner peripheral hole of the front surface of the valve body 15 so as to be relatively movable in the axial direction. The output shaft 13 is held by a retainer 73 attached to the valve body 15 .

The output shaft 13 is advanced by the operation of the electric motor 21 to operate the primary piston 43 of the master cylinder 40 . Between the rear end of the output shaft 13 and the front surface of the valve body 15, a reaction disk 75 made of an elastic member such as rubber is arranged. The front surface of the input receiving member 71 faces the rear surface of the reaction disk 75 with a minute gap therebetween.

A key member 87 is arranged between the rear surface of the valve body 15 and the front surface of the spindle nut 51 of the assist mechanism 50 . The key member 87 is fixed to the plunger 57 and moves axially together with the plunger 57 . The movement range of the plunger 57 and the input receiving member 71 with respect to the valve body 15 is defined by the key member 87 .

A return spring 17 is arranged in a compressed state between the front housing 5a and the valve body 15. As shown in FIG. The return spring 17 always biases the valve body 15 in the non-operating direction. When the valve body 15 retreats in the non-operating direction, both the output shaft 13 and the reaction disc 75 retreat.

A return spring 19 is arranged in a compressed state between the spindle 53 and the input shaft 11 . The return spring 19 always biases the input shaft 11 against the spindle 53 in the non-operating direction. The support member 31 that supports the valve body 15 contacts the front surface of the spindle nut 51 to define the non-operating positions of the valve body 15 and the output shaft 13 .

A tandem-type master cylinder 40 is connected to the front side of the front housing 5a. A reservoir (not shown) that supplies brake fluid to the master cylinder 40 is attached to the upper portion of the master cylinder 40 .

The master cylinder 40 includes a primary piston 43 and a secondary piston 44 that are axially movably arranged in a bottomed cylinder bore 41 . The primary piston 43 is arranged closer to the output shaft 13 and the secondary piston 44 is arranged farther from the output shaft 13 .

The primary piston 43 and the secondary piston 44 are each formed cylindrical. The secondary piston 44 is wholly disposed within the cylinder bore 41 and a portion of the primary piston 43 is disposed within the cylinder bore 41 .

A primary chamber 47 is formed between the primary piston 43 and the secondary piston 44 , and a secondary chamber 48 is formed between the secondary piston 44 and the bottom of the cylinder bore 41 .

Each of the primary chamber 47 and the secondary chamber 48 is formed with a reservoir port (not shown) communicating with a reservoir, and the primary chamber 47 and the secondary chamber 48 are supplied with brake fluid.

A first spring 45 is arranged between the primary piston 43 and the secondary piston 44 . A second spring 46 is arranged between the secondary piston 44 and the bottom of the cylinder bore 41 .

One end of the output shaft 13 that advances by the output of the electric motor 21 to move the primary piston 43 in the axial direction contacts the primary piston 43 . The axial movement of the primary piston 43 also causes the secondary piston 44 to move axially.

The booster 1 also includes a relative displacement detection sensor 80 . The relative displacement detection sensor 80 has a magnetic sensor 85 such as a Hall element provided integrally with the valve body 15 and a magnet 81 provided integrally with the key member 87 .

The magnetic sensor 85 detects the relative displacement of the key member 87, that is, the plunger 57 and the input receiving member 71 with respect to the valve body 15, and outputs a sensor signal to the electronic control device.

Specifically, the relative displacement of the plunger 57 and the input receiving member 71 with respect to the valve body 15 causes the magnet 81 provided on the key member 87 to move relative to the magnetic sensor 85 . outputs a current to the electronic control unit according to the variation of the magnetic field from the

The electronic control device determines relative displacement of the plunger 57 and the input receiving member 71 with respect to the valve body 15 based on the magnitude of the current input from the magnetic sensor 85 . When the booster 1 is in a non-operating state, the relative displacement of the plunger 57 and the input receiving member 71 with respect to the valve body 15 is defined as zero.

In the electronic control device, the current of the magnetic sensor 85 generated by the magnetic field of the magnet 81 when the booster 1 is not operating is set to zero as a reference value. At this time, the electronic control device does not supply power (current) to the stator of the electric motor 21 .

On the other hand, when the driver depresses the brake pedal, the return spring 19 bends and the input shaft 11 advances. Accordingly, the input receiving member 71 moves forward, and the plunger 57 and the input receiving member 71 are displaced relative to the valve body 15 .

As a result, the magnetic field of the magnet 81 with respect to the magnetic sensor 85 fluctuates, and the magnetic sensor 85 generates a current and outputs it to the electronic control device. The electronic controller supplies power (current) to the stator of the electric motor 21 .

<Assist Mechanism>
The assist mechanism 50 provided in the booster 1 according to this embodiment will be described in detail. 2 and 3 are schematic diagrams for explaining the assist mechanism 50. FIG. FIG. 2 is a schematic diagram showing a configuration example of the electric motor 21 and the assist mechanism 50, and FIG. 3 is a schematic diagram showing axial cross sections of the first gear 61 and the second gear 65. As shown in FIG.

The assist mechanism 50 resists the biasing force of the return spring 17 by transmitting the output of the electric motor 21 to the spindle nut 51 via the pinion gear 25, the first gear 61, the second gear 65 and the hub gear 59. The valve body 15 and the output shaft 13 are advanced by advancing the spindle 53 .

The pinion gear 25, the first gear 61, the second gear 65 and the hub gear 59 are each configured as a helical gear. In this embodiment, at least the pinion gear 25 and the first gear 61 should be helical gears, and the second gear 65 and hub gear 59 may not be helical gears.

The first gear 61 and the second gear 65 are supported by the same rotating shaft member 69 . The second gear 65 is supported through a bearing member 66 so as to be relatively rotatable and axially immovable with respect to the rotating shaft member 69 .

The first gear 61 is supported through a connecting member 62 so as to be non-rotatable and axially movable relative to the rotating shaft member 69 . For example, spline grooves are formed on the inner peripheral surface of the connecting member 62 and the outer peripheral surface of the rotary shaft member 69 respectively, and the first gear 61 is spline-coupled to the rotary shaft member 69 . The first gear 61 and the rotating shaft member 69 are not joined together, and the first gear 61 is axially displaceable relative to the rotating shaft member 69 .

The first gear 61 has an internal hole 61a that opens toward the second gear 65 side. The second gear 65 has an internal hole 65a that opens toward the first gear 61 side. The rotary shaft member 69 has a collar portion 69a on its outer peripheral portion. In the example shown in FIG. 3 , the rotating shaft member 69 has a collar portion 69 a positioned inside the internal hole 65 a of the second gear 65 .

A spring 68 is provided between the first gear 61 and the flange portion 69 a of the rotating shaft member 69 . A spring 68 always biases the first gear 61 away from the second gear 65 .

The pinion gear 25 and the first gear 61 are configured as helical gears. When the output torque of the electric motor 21 exceeds a predetermined reference value, the first gear 61 moves toward the second gear 65 against the urging force of the spring 68 . It is designed to move in the axial direction.

The first gear 61 has a first engaging portion 63 on the surface facing the second gear 65 side. The second gear 65 has a second engaging portion 67 engageable with the first engaging portion 63 on the surface facing the first gear 61 side.

When the output torque of the electric motor 21 is small and the first gear 61 and the second gear 65 are separated by a predetermined distance or more, the first engaging portion 63 and the second engaging portion 67 are not engaged. . In this case, the first gear 61 to which the rotation of the motor shaft 23 is transmitted via the pinion gear 25 idles on the rotating shaft member 69 .

When the output torque of the electric motor 21 increases, the first gear 61 rotates and moves in the axial direction, and the first engaging portion 63 and the second engaging portion 67 are engaged. In this case, the second gear 65 is rotated by the first gear 61 to which the rotation of the motor shaft 23 is transmitted via the pinion gear 25 , and the spindle nut 51 is rotated via the hub gear 59 .

<Operation of Assist Mechanism>
The operation of the assist mechanism 50 of the booster 1 according to this embodiment will be described with reference to FIGS. 4 to 7. FIG.

FIG. 4 shows changes in the rotation angle θ_mtr and output torque Tq_mtr of the electric motor 21 and the advance amount St_spd of the spindle 53 in accordance with changes in the amount of depression St_brk of the brake pedal. 5 to 7 show operating states of the assist mechanism 50 at times t3, t6 and t8 in FIG. 4, respectively.

At time t1, when the driver starts depressing the brake pedal, the output torque Tq_mtr of the electric motor 21 increases and the electric motor 21 starts rotating.

At time t2, when the output torque Tq_mtr of the electric motor 21 increases and reaches a predetermined reference value Tq_mtr_thre, part of the torque transmitted from the pinion gear 25 to the first gear 61 is converted into thrust in the axial direction. , the first gear 61 begins to move toward the second gear 65 against the biasing force of the spring 68 .

Schematically, when the value obtained by multiplying the torsion angle (inclination with respect to the axial direction) of the first gear 61, which is a helical gear, by the output torque Tq_mtr (Tq_mtr_thre) of the electric motor 21 exceeds the biasing force of the spring 68, the first 1 gear 61 moves axially. As a result, the first engaging portion 63 of the first gear 61 is engaged with the second engaging portion 67 of the second gear 65, as shown in FIG.

Therefore, the second gear 65 rotates, and rotational torque is transmitted to the hub gear 59 and the spindle nut 51 . Therefore, from time t2 to time t4 when the stepping operation of the brake pedal ends, the spindle 53 advances against the biasing force of the return spring 17 that biases the valve body and the output shaft rearward.

At time t5, when the driver starts releasing the brake pedal, the rotation angle θ_mtr of the electric motor 21 decreases and the output torque Tq_mtr of the electric motor 21 starts decreasing. As a result, the spindle 53 begins to retreat due to the biasing force of the return spring 17 that biases the valve body (not shown) and the output shaft rearward.

From time t5 to time t7 when the output torque Tq_mtr of the electric motor 21 exceeds the reference value Tq_mtr_thre, the engaged state of the first gear 61 and the second gear 65 is maintained. For this reason, as shown in FIG. 6, a forward thrust force acts on the spindle 53 due to the operation of the electric motor 21 .

When the spindle 53 is advanced, the degree of compression of the return spring 17 is relatively large, and the biasing force of the return spring 17 is large. Therefore, even when the output torque Tq_mtr of the electric motor 21 is acting on the spindle 53, the spindle 53 retreats relatively smoothly.

However, when the spindle 53 retreats and approaches the non-operating position, the degree of compression of the return spring 17 decreases and the biasing force of the return spring 17 decreases. In this case, the retraction speed immediately before the spindle 53 returns to the non-operating position may become slow.

For this reason, in order to smoothly retract the spindle 53 to the non-operating position, it is necessary to use the return spring 17 having a relatively large biasing force, which has been a factor in increasing the size of the booster 1 .

On the other hand, in the assist mechanism 50 of the booster 1 according to the present embodiment, after the time t7 when the output torque Tq_mtr of the electric motor 21 further decreases to the reference value Tq_mtr_thre, the axial direction of the first gear 61 increases. The thrust force to is reduced, and the biasing force of the spring 68 moves the first gear 61 away from the second gear 65 .

Therefore, as shown in FIG. 7, the engagement between the first engaging portion 63 of the first gear 61 and the second engaging portion 67 of the second gear 65 is released, and the first gear 61 becomes idle. As a result, the output torque Tq_mtr of the electric motor 21 does not act on the second gear 65 , hub gear 59 and spindle nut 51 .

Therefore, even when the degree of compression of the return spring 17 is reduced and the biasing force of the return spring 17 is reduced, the spindle 53 can be smoothly retracted.

<Action of Assist Mechanism>
A biasing force F_rs required for the return spring 17 immediately before the spindle 53 retreats to the non-operating position is given by the following equation (1).

F_rs > Eff_sn x (Friction_Torque_gr + Turning_Torque_mtr)
+ Axial_Friction_bp + Cutin_sp (1)
F_rs: Biasing force of return spring 17
Eff_sn: conversion efficiency for converting the force pushing back the spindle 53 into the rotational force of the spindle nut 51
Friction_Torque_gr: Resistance torque of assist mechanism 50
Turning_Torque_mtr: Rotation resistance torque (cogging torque) of the electric motor 27
Axial_Friction_bp: Axial resistance of bushing 33 and plunger 57
Cut_in_sp: Resistance torque by return spring 19

That is, when the first gear 61 and the second gear 65 are engaged, the rotational resistance torque Turning_Torque_mtr of the electric motor 27 acts as a force opposing the biasing force F_rs of the return spring 17 .

However, in the assist mechanism 50 of the booster 1 according to this embodiment, the engaged state between the first gear 61 and the second gear 65 is released when the output torque Tq_mtr of the electric motor 21 falls below the reference value Tq_mtr_thre.

Therefore, when the biasing force F_rs of the return spring 17 is small, the rotational resistance torque Turning_Torque_mtr of the electric motor 27 can be reduced to zero. can be made

<Effect of booster>
As described above, according to the booster 1 according to this embodiment, the return spring 17 having a relatively small load can be used. Therefore, the outer shape of the booster 1 can be reduced.

In addition, since the return spring 17 having a relatively small load can be used, for example, when the electric motor 21 or the assist mechanism 50 fails, the required depressing force of the brake pedal by the driver can be reduced.

FIG. 8 shows the brake pressure P_brk with respect to the depression force F_pdl of the brake pedal when the electric motor 21 or the assist mechanism 50 fails. In FIG. 8, a dashed line 93 indicates an example using a return spring 17 with a large load, and a solid line 91 indicates an example using a return spring 17 with a small load.

When the load of the return spring 17 is small, braking force can be generated with a relatively small pedaling force compared to when the load of the return spring 17 is large. Also, even after the braking force is generated, the braking force can be efficiently increased with respect to the increase in the pedaling force.

As described above, according to the booster 1 according to the present embodiment, even when the electric motor 21 or the assist mechanism 50 fails, the driver can relatively easily operate the brake.

Although the preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, the present invention is not limited to such examples. It is clear that a person having ordinary knowledge in the technical field to which the present invention belongs can conceive of various modifications or modifications within the scope of the technical idea described in the claims. It is understood that these also belong to the technical scope of the present invention.

For example, the configuration of the first gear and the second gear that are connected or released by the output torque of the electric motor or the method of supporting the first gear and the second gear with respect to the rotating shaft member are not limited to the above examples.

DESCRIPTION OF SYMBOLS 1... Electric booster 13... Output shaft 17... Return spring 21... Electric motor 23... Motor shaft 25... Pinion gear 50... Assist mechanism , 51... spindle nut, 53... spindle, 59... hub gear, 61... first gear, 63... first engaging portion, 65... second gear, 67 ... second engaging portion, 68 ... spring (biasing member), 69 ... rotating shaft member,

Claims (6)

an electric motor (21), an assist mechanism (50) that converts the rotary motion of the electric motor (21) into linear motion and transmits it to an output shaft (13), and a return spring (17) that retracts the output shaft. In an electric booster (1) that boosts the input of brake operation and outputs it from the output shaft (13),
The assist mechanism (50)
a pinion gear (25) provided on a motor shaft (23) of the electric motor (21);
a first gear (61) that receives the output torque of the electric motor (21) through the pinion gear (25) and moves in the axial direction;
a second gear (65) provided coaxially with the first gear (61) and connectable with the first gear (61) as the first gear (61) moves in the axial direction; including
The first gear (61) and the second gear (65) are
wherein the electric motor (21) is connected when the output torque of the electric motor (21) is equal to or greater than a predetermined value, and the connection is released when the output torque of the electric motor (21) is less than the predetermined value. booster. The first gear (61) and the second gear (65) are
supported by the same rotating shaft member (69),
The first gear (61) is
The motor shaft (21) of the electric motor (21) is supported so as to be axially movable relative to the rotating shaft member (69), and is biased toward the side opposite to the second gear (65). 23) in mesh with a pinion gear (25) fixed to the booster according to claim 1. A biasing member (68) is provided between the first gear (61) and the rotating shaft member (69),
3. The electric multiplier according to claim 2, wherein the biasing member (68) biases the first gear (61) in a direction opposite to the second gear (65). power device. wherein said first gear (61) is a helical gear;
The electric booster according to any one of claims 1 to 3, characterized in that: The first gear (61) and the second gear (65) are
The electric booster according to any one of claims 1 to 4, wherein engagement portions (63, 67) are provided on axial end faces facing each other. The assist mechanism (50)
including a spindle (53) and a spindle nut (51);
The second gear (65) is
The electric booster according to any one of claims 1 to 5, which meshes with a hub gear (59) provided on the spindle nut (51).

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