JP2008162482A - Electric booster - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a required boosting ratio to input even if a brake assist by an electric motor is acted, and to ensure good pedal operability. <P>SOLUTION: An input piston 32 to which input thrust is added from an input rod 9 interlocking with a brake pedal B, and a booster piston 31 to which booster thrust is added from an electric motor 40 through a ball screw mechanism 50 are arranged so as to relatively move. Tip end portions of both pistons 31, 32 are made to face a pressure chamber 17 of a master cylinder 10, and both pistons 31, 32 are normally retained at neutral positions of relative movement. The electric motor 40 is controlled so as to make the relative displacement of both pistons 31, 32 become any predetermined value. At that time, reaction force of brake fluid pressure acted on the input piston 32 is canceled by energizing force, thereby obtaining a required boosting ratio. Both pistons 31, 32, the electric motor 40, and a ball screw mechanism 50 are concentrically polymerized/disposed to shorten axial dimensions. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a booster used for a brake mechanism of an automobile, and more particularly to an electric booster that uses an electric motor as a booster source.

  Conventionally, a vacuum booster that can generate an output boosted with respect to an input by using a negative pressure of an intake pipe of an engine is often used for a brake mechanism of an automobile. By the way, in recent years, the development of engines has progressed in terms of fuel efficiency improvement, exhaust gas purification, and the like, and accordingly, the intake pipe negative pressure tends to decrease. Therefore, in order to ensure the desired boosting performance or responsiveness as a vacuum booster, for example, measures such as increasing the size, increasing the negative pressure with an ejector, or providing an engine-driven vacuum pump are taken. It is necessary, and it is inevitable that the vehicle mountability deteriorates and the cost burden increases.

  Therefore, recently, an electric booster using an electric motor as a boost source has attracted attention. As this electric booster, for example, there are those described in Patent Documents 1 and 2, which can move relative to the main piston (shaft member) that moves forward and backward by operating a brake pedal. And a booster piston (cylindrical member) externally fitted to the motor and an electric motor for moving the booster piston forward and backward. The brake fluid pressure is generated in the master cylinder by the input thrust transmitted from the brake pedal to the main piston and the booster thrust transmitted from the electric motor to the booster piston.

Japanese Patent Laid-Open No. 10-138909 JP-A-10-138910

  However, according to the electric booster described in Patent Documents 1 and 2, a part of the reaction force due to the brake fluid pressure generated in the pressure chamber of the master cylinder is applied to the main piston (shaft member), Part of the torque is transmitted to the booster piston (cylindrical member), so if you try to increase the brake fluid pressure in the master cylinder by increasing the thrust of the booster piston to activate the brake assist, The pressure acts as a reaction force on the main piston, causing the main piston linked with the brake pedal to move backward. In other words, in order to secure a desired braking force, it is necessary to increase the input (pedal depression force) so that the main piston does not move backward, and as a result, the problem is that the boost ratio cannot be increased with respect to the input. there were. On the other hand, if the thrust of the booster piston is reduced to reduce the brake fluid pressure in the master cylinder, the reaction force transmitted to the main piston is reduced, so that the boost ratio cannot be reduced with respect to the input. there were.

  The present invention has been made in view of the above-described conventional problems, and the problem is that when the electric motor is used as a boost source, a desired boost ratio can be obtained with respect to the input. Thus, an object of the present invention is to provide an electric booster that contributes to an improvement in pedal operability.

  In order to solve the above-mentioned problem, a first invention is a first member that moves forward and backward by operating a brake pedal, a second member that is arranged to be relatively movable with respect to the first member, and the second member A rotation-linear motion conversion mechanism for moving the member forward and backward, and an electric motor for applying a rotational force to the rotation-linear motion conversion mechanism, and an input thrust applied to the first member from the brake pedal and the electric motor The brake fluid pressure is generated in the master cylinder by the booster thrust applied from the motor to the second member, a part of the reaction force due to the brake fluid pressure is applied to the first member, and the other part is In the electric booster respectively transmitting to the second member, the first member and the second member are relative to each other in at least one direction between the first member and the second member. When in a displaced state, the first member On the other hand, there is provided urging means for making the urging force of the second member in the displacement direction stronger than the state before the relative displacement of the two members, and the electric motor is connected to the first and second members and It is characterized by being superposed on the same axis as the rotation-linear motion conversion mechanism.

  The first aspect of the invention may be configured to include a return spring that biases the second member and the linear motion member of the rotation-linear motion conversion mechanism toward the brake pedal. In this case, the set load of the return spring may be set larger than the spring load of the urging means when the first member moves to a displacement corresponding to the brake fluid pressure during regenerative braking. it can.

  In order to solve the above-mentioned problem, the second invention is a shaft member that moves forward and backward by operation of a brake pedal, a cylindrical member that is externally mounted on the shaft member so as to be relatively movable, and moves the cylindrical member forward and backward. A rotation-to-linear motion conversion mechanism, an electric motor for applying a rotational force to the rotation-to-linear motion conversion mechanism, a displacement detection means for detecting a relative displacement amount between the shaft member and the cylindrical member, and the displacement detection means. And a control device for controlling the electric motor based on the detection signal of the shaft, the shaft member and the cylindrical member as pistons of the master cylinder, the front ends thereof facing the pressure chambers of the master cylinder, and the brake In the electric booster that generates the brake hydraulic pressure in the pressure chamber by the input thrust applied from the pedal to the shaft member and the booster thrust applied from the electric motor to the cylindrical member, A force is generated between the shaft member and the tubular member that cancels the increase / decrease of the hydraulic reaction force transmitted from the pressure chamber of the master cylinder to the shaft member in accordance with the relative displacement of both members. A biasing means is provided, and the electric motor is superposed coaxially with the shaft member, the cylindrical member, and the rotation-linear motion conversion mechanism.

  The second aspect of the invention may be configured to include a return spring that biases the cylindrical member and the linear motion member of the rotation-linear motion conversion mechanism toward the brake pedal.

  In the first and second inventions configured as described above, in order to use the electric motor as a boosting source, for example, the second member or the cylindrical member is relatively displaced in the direction of increasing or decreasing the brake hydraulic pressure. Then, the urging force in the same direction from the urging means acts more strongly on the first member or the shaft member interlocked with the brake pedal, and due to the brake hydraulic pressure acting on the first member or the shaft member by this urging force. The reaction force is canceled by the amount of the urging force, and as a result, a desired boost ratio can be obtained with respect to the input. Further, the axial dimension can be shortened by coaxially arranging the electric motor, the first member or shaft member, the second member or cylindrical member, and the rotation-linear motion conversion mechanism.

  In the first and second inventions, a return spring is provided to bias the second member or the cylindrical member and the linear motion member of the rotation-linear motion conversion mechanism toward the brake pedal. In this case, when the motor fails, the brake fluid pressure can be reduced by moving each member in the return direction by the biasing force of the return spring.

  In the first invention, the set load of the return spring is set to be larger than the spring load of the urging means when the displacement of the first member reaches a hydraulic pressure corresponding to the regenerative braking force. In this case, it is possible to prevent the hydraulic pressure due to pedal input from being generated during regenerative braking.

  According to the electric booster according to the present invention, a desired boost ratio is obtained with respect to the input by the urging means provided between the member interlocked with the brake pedal and the member driven by the electric motor. As a result, good pedal operability can be secured. In addition, since the electric motor, the both members, and the rotation-linear motion conversion mechanism are arranged coaxially, the axial dimension can be shortened, and the mountability to the vehicle is improved. Further, since the rotation-linear motion conversion mechanism is directly driven by the electric motor, it is excellent in quietness and reliability.

  Further, when a return spring for biasing the second member or the cylindrical member and the linear motion member of the rotation-linear motion conversion mechanism to the brake pedal side is provided, the brake is applied by the biasing force of the return spring when the motor fails. Since the hydraulic pressure can be reduced, the brake can be automatically released and the reliability is improved.

  Further, when the set load of the return spring is set to be larger than the spring load of the urging means when the displacement of the first member reaches the hydraulic pressure corresponding to the regenerative braking force, Since pressure can be prevented from being generated, the brake feeling during regenerative braking is improved.

The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.
1-3 show one embodiment of the electric booster according to the present invention. The electric booster 1 includes a housing 2 in which a piston assembly 30 described later is used as a primary piston of a tandem master cylinder 10 described later. The housing 2 has a bottomed cylindrical housing main body 3 and an annular boss portion 4a fitted into an opening 3b formed in the bottom plate portion 3a of the housing main body 3 and is positioned in the radial direction, and a bolt not shown in the figure. (Not shown) A front cover 4 that is fixed over the bottom plate portion 3a and a cup-shaped rear cover that is fitted to the rear end opening of the housing 2 and fixed to the end surface of the housing body 3 with bolts 5. It consists of six. The housing 2 is fixed to a partition wall W that partitions the engine room and the passenger compartment by using stud bolts S planted on the rear cover 6. On the other hand, the housing 2 has studs planted on the front cover 4. Master cylinder 10 is connected using bolt S '.

  The front cover 4 constituting the housing 2 is provided with a stepped cylindrical guide portion 7 extending into the housing body 3 at the center thereof, and the piston assembly 30 is accommodated in the cylindrical guide portion 7. It is inserted. On the other hand, the rear cover 6 constituting the housing 2 is provided with a cylindrical guide portion 8 that extends through the partition wall W and extends into the vehicle interior, and the cylindrical guide portion 8 is interlocked with the brake pedal B. An input rod 9 is inserted. The two cylindrical guide portions 7 and 8 are arranged so as to be coaxial with the master cylinder 10 and the housing body 3.

  The tandem master cylinder 10 includes a bottomed cylinder main body 11 and a reservoir 12, and a piston assembly as the primary piston is disposed on the inner side of the cylinder main body 11 as shown in FIG. A secondary piston 13 that is paired with the three-dimensional body 30 is disposed. In this embodiment, the piston assembly 30 and the secondary piston 13 are slidably guided by two ring guides 15 and 16 disposed on both ends of a sleeve 14 fitted in the cylinder body 11. In the cylinder body 11, two pressure chambers 17 and 18 are defined by the piston assembly 30 and the secondary piston 13, and the inside of the pressure chambers 17 and 18 is defined on the wall of the cylinder body 11. Discharge ports 19 and 20 are formed to communicate with corresponding wheel cylinders (not shown).

  The cylinder body 11, the sleeve 14, and the ring guides 15, 16 are formed with relief ports 21, 22 that communicate the interior of the pressure chambers 17, 18 with the reservoir 12. Are provided with a pair of seal members 23 and 24 for sealing between the piston assembly 30 and the secondary piston 13 with the relief ports 21 and 22 interposed therebetween. Each of the pressure chambers 17, 18 is brought into sliding contact with the outer peripheral surface of the corresponding piston 30, 13 by the pair of seal members 23, 24 in accordance with the advancement of the pistons 30, 13. Will be closed against. In each of the pressure chambers 17 and 18, return springs 25 and 26 for urging the piston assembly 30 as the primary piston and the secondary piston 13 in the backward direction are disposed. The configuration of the master cylinder 1 described above is the same as that of a conventional general-purpose tandem master cylinder except for the piston assembly 30 as a primary piston, and the pressure chambers 17, 18 according to the advance of the pistons 30, 13. The brake fluid contained inside is pumped from the discharge ports 19 and 20 to the corresponding wheel cylinder.

  As shown well in FIG. 2, the piston assembly 30 includes a cylindrical booster piston (second member, cylindrical member) 31 and an input disposed in the booster piston 31 so as to be relatively movable therewith. It consists of a piston (first member, shaft member) 32. The booster piston 31 is slidably fitted into the cylindrical guide portion 7 of the front cover 4 and the ring guide 15 in the master cylinder 10, and its front end portion is a pressure chamber (primary chamber) 17 of the master cylinder 10. It is extended in. On the other hand, the input piston 32 is slidably fitted into an annular wall 31 a formed on the inner periphery of the booster piston 31, and a front end portion of the input piston 32 extends into the pressure chamber 27. The front end of the booster piston 31 and the front end of the secondary piston 22 are provided with through holes 33 and 34 (FIG. 3) that can communicate with the relief ports 21 and 22 in the master cylinder 6, respectively. When the brake is not operated, the pressure chambers 17 and 18 and the reservoir tank 12 are in communication with each other through the through holes 33 and 34.

  Here, the booster piston 31 and the input piston 32 constituting the piston assembly 30 are sealed by a seal member 35 disposed on the front side of the annular wall 31a of the booster piston 31, and the seal member 35 and the input piston 32 are sealed. The leakage of the brake fluid from the pressure chamber 17 to the outside of the master cylinder 10 is prevented by the seal members 23 on both ends of the ring guide 15. The seal member 35 is housed in the booster piston 31 and is fixed in position by a cylindrical member 36 that receives one end of the return spring 25 in the pressure chamber 17. A seal member 37 is interposed between the inner peripheral surface of the cylindrical guide portion 7 of the front cover 4 of the housing 2 and the booster piston 31 to prevent foreign matter from entering between the two.

  On the other hand, the rear end portion of the input piston 32 is connected to the front end portion of the input rod 9 interlocked with the brake pedal B by caulking. The input piston 32 is boosted by the operation of the brake pedal B (pedal operation). The piston 31 moves forward and backward. Further, a flange portion 38 is integrally formed in the middle of the input rod 9, and the input rod 9 is an inward in which the flange portion 38 is integrally formed at the rear end of the cylindrical guide portion 8 of the rear cover 6. The rearward movement of the input rod 9 and the input piston 32 is regulated by bringing the projection 39 into contact with the projection 39. The input rod 9 is connected in a state in which the spherical portion 9a at the tip thereof is fitted in a spherical concave portion 32a formed at the rear end of the input piston 32 (FIG. 2). Oscillation is allowed.

  In the housing 2 of the electric booster 1, there is also a ball screw mechanism (rotation) for converting the electric motor 40 and rotation of the electric motor 40 into a linear motion and transmitting it to the booster piston 31 constituting the piston assembly 30. -Linear motion conversion mechanism) 50 is disposed. The electric motor 40 includes a stator 41 and a hollow rotor 42. The stator 41 is disposed between the housing body 3 and the rear cover 6 in a fixed manner, and the rotor 42 includes the housing body 3 and The rear cover 6 is rotatably supported via bearings 43 and 44.

  As shown well in FIG. 2, the ball screw mechanism 50 includes a nut member 52 that is non-rotatably fitted to the rotor 43 of the electric motor 40 via a key 51, and a ball 53 attached to the nut member 52. It comprises a meshed hollow screw shaft (linear motion member) 54. A slit 55 extending in the axial direction is formed at the rear end of the screw shaft 54, and an inward projection 39 at the rear end of the rear cover 6 is inserted into the slit 55 (FIG. 1). That is, the screw shaft 54 is disposed in the housing 2 so as not to be rotatable and movable in the axial direction, so that when the nut member 52 rotates integrally with the rotor 42, the screw shaft 54 moves linearly. Become. On the other hand, the screw shaft 54 is provided with an inner flange 56 at the start end portion of the slit 55, and an outer flange portion 57 a formed on the inner flange portion 56 at the rear end of the extension cylinder portion 57 of the booster piston 31. Are in contact with each other.

  In the present embodiment, a return spring (biasing means) 58 is interposed between the outer flange portion 57 a at the rear end of the extension cylinder portion 57 of the booster piston 31 and the cylindrical guide portion 3 a of the front cover 3. Has been. When the brake is not operated, the screw shaft 54 is positioned by the return spring 58 at the retracted end where the end face of the inner flange portion 56 (starting end of the slit 55) abuts against the inner protrusion 39 of the rear cover 6, and accordingly. The booster piston 31 is also positioned at the original position shown in FIG. Therefore, when the screw shaft 54 advances from this state, the booster piston 31 also advances.

  A pair of springs (biasing means) 60 (60A, 60B) are disposed between the booster piston 31 and the input piston 32 constituting the piston assembly 30, as well shown in FIG. ing. Of the pair of springs 60, one spring 60 </ b> A is between a flange portion 61 projecting from the rear end portion of the input piston 32 and the vertical wall 62 in the booster piston 31, and the other spring 60 </ b> B is the flange 60 </ b> B. Between the part 61 and the annular protrusion 62 formed in the extension cylinder part 57 integral with the booster piston 31, respectively. The pair of springs 60 serve to hold the booster piston 31 and the input piston 32 in the neutral position when the brake is not operated. This will be described in detail later.

  In the present embodiment, a potentiometer (displacement detecting means) 65 that engages with the brake pedal B and detects the absolute displacement of the input piston 32 with respect to the vehicle body via the brake pedal B is disposed in the fixed portion in the vehicle interior. ing. On the other hand, a rotation sensor 66 for detecting the rotational displacement of the electric motor 40 is disposed in the housing 2. The rotation sensor 66 includes a resolver stator 67 fixed to the housing body 3 and a resolver rotor 68 fixed to the outer peripheral surface of the rotor 42. The detection signals of the potentiometer 65 and the rotation sensor 66 are sent to a controller 70 installed separately. The controller C is also connected to a pressure sensor 69 (FIG. 1) for detecting the brake fluid pressure in the pressure chambers 17 and 18 in the master cylinder 10. The controller C includes the potentiometer 65, the rotation sensor 66 and the pressure sensor 69. The rotation of the electric motor 40 (rotor 43) is controlled on the basis of the signal from.

  In order to assemble the electric booster 1, as shown in FIG. 4, the housing main body 3 in which the resolver stator 67 constituting the rotation sensor 66 is assembled, the stator 41 constituting the electric motor 40, and one for supporting the rotor. The rear cover 6 to which the bearing 44 and the stud bolt S are assembled, and the rotor 42 to which the other bearing 43 for supporting the rotor is assembled are prepared. Then, after inserting the rotor 42 into the rear cover 6, the housing body 3 is put on the rotor 42, and the housing body 3 and the rear cover 6 are fastened and fixed by the bolts 5, thereby the sub-assembly in which the electric motor 40 is assembled. The body 70 (FIG. 5) is completed.

  Next, as shown in FIG. 5, the input piston 32 and the booster piston 31 to which the input rod 9 is connected in advance are assembled via a pair of springs 60 (60 </ b> A, 60 </ b> B), and the return spring is returned to the outer periphery of the booster piston 31. A piston assembly 30 wound with 58 and a ball screw mechanism 50 in which a nut member 53 is assembled to a screw shaft 54 via a ball 53 are prepared. Then, the ball screw mechanism 50 is first inserted into the sub-assembly body 70 to which the electric motor 40 is assembled, and then the piston assembly 30 is inserted. Finally, the entire housing body 3 of the sub-assembly body 70 is inserted. The front cover 4 (FIG. 1) is bolted to the electric booster 1 to complete the electric booster 1.

Hereinafter, the operation of the electric booster 1 configured as described above will be described.
When the brake pedal B is operated, the input piston 32 moves forward together with the input rod 9, and its movement is detected by the potentiometer 65. Then, in response to the signal from the potentiometer 65, the controller C outputs a start command to the electric motor 40, whereby the rotor 42 of the electric motor 40 rotates, and the rotation is transmitted to the ball screw mechanism 50, and the screw shaft 54 Advances and the booster piston 31 follows the movement. That is, the input piston 32 and the booster piston 31 are integrally moved forward, and the brake fluid according to the input thrust applied from the brake pedal B to the input piston 32 and the booster thrust applied from the electric motor 40 to the booster piston 31. A pressure is generated in the pressure chambers 17 and 18 in the tandem master cylinder 10.

  At this time, based on the detection signals of the potentiometer 65 and the rotation sensor 66, the relative displacement amount of both pistons can be determined from the difference between the absolute displacement of the input piston 32 and the absolute displacement of the booster piston 31. Therefore, when the rotation of the rotor 42 of the electric motor 40 is controlled so that no relative displacement occurs between the input piston 32 and the booster piston 31, a pair of springs 60 (60A) interposed between the pistons 32 and 31 are controlled. 60B) maintain the neutral position. The boost ratio at this time is uniquely determined by the area ratio between the pressure receiving area of the booster piston 31 and the pressure receiving area of the input piston 32 because the relative displacement amount of both pistons is zero, and is a general-purpose vacuum booster. It will be the same.

  On the other hand, when the booster piston 31 is relatively displaced from the neutral position in the direction in which the brake fluid pressure is increased (forward) by the booster thrust, the boost ratio is increased, and the electric motor 40 acts as a boost source, and the pedal depression force ( (Pedal input) can be greatly reduced. Further, in this case, the urging force of the rear spring 60B increases according to the relative displacement of the booster piston 31, and the reaction force of the brake hydraulic pressure transmitted to the input piston 32 is canceled by the amount of the urging force. Thus, the boost ratio can be sufficiently increased with respect to the pedal depression force (input). Conversely, when the booster piston 31 is relatively displaced from the neutral position in the direction (rearward) in which the brake fluid pressure is reduced by the booster thrust, the biasing force of the front spring 60A increases in accordance with the relative displacement of the booster piston 31. Then, the reaction force transmitted to the input piston 32 is strengthened by this urging force, and the boost ratio can be reduced with respect to the pedal depression force (input).

  The release of the brake, that is, the retraction of the booster piston 31 is performed by rotating the rotor 42 of the electric motor 40 in the reverse direction to retract the screw shaft 54 of the ball screw mechanism 50. The booster piston 31 includes a master cylinder. Since the reaction force due to the hydraulic pressure within 10 and the spring force of the return spring 58 are applied, the booster piston 31 moves backward following the movement of the screw shaft 54.

  Here, since the booster piston 31 and the screw shaft (linear motion member) 54 of the ball screw mechanism 50 are merely in contact with each other via the flange member 78, the electric motor 40 has failed (failed) by any chance. In this case, the booster piston 31 follows the movement of the input piston 32 that moves forward in response to the depression of the brake pedal B via the spring 60, whereby the input piston 32 and the booster piston 31 move forward in a unified manner. The braking force can be obtained. Further, even if a failure occurs in the electric motor 40 during braking, the screw shaft 54 moves backward together with the booster piston 31 by the spring force of the return spring 58, so that the brake is automatically released.

  Particularly in the present embodiment, the rotation of the electric motor 40 is converted into motion by the ball screw mechanism 50 and transmitted to the booster piston 31, so that the drive transmission from the electric motor 40 to the booster piston 31 is smooth, and the booster thrust is reduced. Grant is stable. Further, since the moment does not act on the electric motor 40 from the booster piston 31 by adopting the ball screw mechanism 50, the load on the electric motor 40 is also reduced accordingly. Further, since the ball screw mechanism 50 is directly driven by the electric motor 40, it is excellent in quietness and reliability.

  By the way, in this embodiment, since the potentiometer 65 and the rotation sensor 66 which detect the absolute displacement of the input piston 32 with respect to a vehicle and the absolute displacement of the booster piston 31 are provided, the stroke and stepping speed of the input piston 32 (brake pedal B). These detection results can be used effectively for brake assist control, regenerative cooperative control, vehicle follow-up (ACC) control, etc. according to the control.

  That is, as shown in the schematic diagram of FIG. 6, the relationship between the pressure chambers 17 and 18 of the master cylinder 10 and the rigidity (fluid amount versus generated hydraulic pressure) of all load side elements such as piping and disk brakes communicating with the pressure chambers 17 and 18. Considering the displacement Xm of the piston 10B having a sectional area equal to the sectional area (Ai + Ab) of the master cylinder pressure chamber 17, and the spring constant km of the spring element 10C attached thereto. In this case, the displacements (strokes) of the input piston 32 and booster piston 31 are Xi and Xb, respectively, and the generated force (input thrust) of the input piston 32 and the booster at the part facing the master cylinder pressure chamber 17 finally. If the generated force (booster thrust) of the piston 31 is Fi and Fb, the relationship of the following formula (1) is obtained from the balance of forces.

Fi + Fb = (Ab × Xb + Ai × Xi) / (Ab + Ai) × km (1)
Here, since Fb = Ab / Ai × Fi, the equation (1) becomes the following equation (2).

Fi = (Ab × Xb + Ai × Xi) / (Ab + Ai) ² × Ai × km (2)
On the other hand, if the input from the brake pedal B (pedal input) is Fi _B and the spring constant of the spring 85 interposed between the input piston 32 and the booster piston 31 is ks, Fi _B is the following equation (3): Therefore, the following equation (4) is obtained from the relationship between the above equation (1) and this equation (2).
Fi _B = Fi−ks × (Xb−Xi) (3)
Fi _B = (Ab × Xb + Ai × Xi) / (Ab + Ai) ² × Ai × km−ks × (Xb−Xi) (4)

Here, if Xb = Xi (no relative displacement), the equation (4) becomes the following equation (5), and a pedal feeling (relation between pedal input and stroke) having a predetermined boost ratio is obtained.
Fi _B = Ai / (Ab + Ai) × Xi × km (5)
On the other hand, when the booster piston 31 is controlled so as to give a relative displacement (Xb-Xi) between the input piston 32 and the booster piston 31 in order to change the boost ratio, the spring constant km on the load side and the spring are calculated from the equation (5). It can be seen that the pedal feeling changes with a spring constant ks of 60.

FIG. 7 shows the change in thrust F when the pedal input Fi _B is increased at a constant speed and the brake assist by the electric motor 40 is activated in the middle, and FIG. 8 shows the stroke of the input piston 32 at that time (pedal Stroke) Each change in Xi is seen. Accordingly, when the spring constant ks of the spring 60 interposed between the input piston 32 and the booster piston 31 is large, the brake pedal B moves forward (FIG. 8A), and the conventional brake assist is activated. Pedal feeling can be achieved. On the other hand, when the spring constant ks is small, the brake pedal B is returned to the reverse (FIG. 8B), and the brake pedal B can be shortened while operating the brake assist in an emergency. On the other hand, when the spring constant ks is set to an appropriate magnitude, the input piston 32 continuously changes (FIG. 8C), and even if the brake assist is operated, the influence on the brake pedal B is almost eliminated. That is, even if the hydraulic reaction force applied from the pressure chamber 17 of the master cylinder 10 to the input piston 32 is increased by the operation of the brake assist (the forward movement of the booster piston 31), Due to the displacement, the spring force of the spring 60 urging the input piston 32 forward becomes substantially equal, and the increased hydraulic pressure reaction force is almost completely offset by the spring force, eliminating the influence on the brake pedal B. It becomes possible.

  Here, the spring constant ks of the spring 60 required to eliminate the influence on the brake pedal B is a size necessary to make the above equation (5) into the following equation (6), (7) It can be decided like the formula.

Fi _B = Ai / (Ab + Ai) × Xi × km (6)
ks = (Ab × Ai) / (Ab + Ai) ² × km (7)

On the other hand, the brake fluid pressure Pm and the fluid volume Vm in the pressure chamber 17 are expressed by the following equations (8) and (9).
Pm = (Ab × Xb + Ai × Xi) / (Ab + Ai) ² × km (8)
Vm = Ab × Xb + Ai × Xi (9)
Therefore, Pm and Vm have the relationship of the following equation (10), and when this is converted, the following equation (11) is obtained.
Pm = Vm / (Ab + Ai) ² × km (10)
km = Pm / Vm × (Ab + Ai) ² (11)
Therefore, if this km is substituted into the above equation (7), the following equation (12) is obtained.
ks = Ai × Ab × Pm / Vm (12)

  That is, the spring constant ks of the spring (biasing means) 60 interposed between the input piston 32 and the booster piston 31 is applied to the pressure receiving area Ai of the input piston 32 and the booster piston 31 facing the pressure chamber 17 of the master cylinder 10. , Ab, and the brake fluid pressure Pm and fluid amount Vm of the master cylinder 10 can be determined. That is, the pressure receiving areas Ai and Ab of the input piston 32 and the booster piston 31 are known, and the ratio of increase / decrease in brake fluid pressure Pm accompanying increase / decrease in fluid volume Vm of the master cylinder is determined by the applied vehicle. 8 and the spring constant ks coincide with each other, the relationship shown in FIG. 8C can be obtained. That is, it is input by the increase in the hydraulic reaction force applied to the input piston 32 from the master cylinder pressure chamber 17 by the brake assist operation (the forward movement of the booster piston 31) and the relative displacement between the booster piston 31 and the input piston 32. The spring force of the spring 60 that biases the piston 32 forward can be made substantially equal. When the spring constant ks is larger than the set value, the relationship shown in FIG. 8A is established. Conversely, when the spring constant ks is smaller than the set value, the relationship shown in FIG. Become.

When the electric booster 1 is incorporated in the regenerative cooperative brake system, the relationship between the pedal input Fi _B and the brake hydraulic pressure Pm is as shown in FIG. In FIG. 9, Pre is a brake fluid pressure generated by regenerative braking, and when the regenerative braking is activated when the pedal input Fi _B is Fa, the electric booster 1 corresponds to the booster piston 31 in the rear direction. It is only necessary to displace by the amount. In this case, if the spring constant ks is in the relationship of the above expression (12), the brake fluid pressure Pm decreases by the amount corresponding to Pre, but the spring force of the spring 60 that is substantially equal to the decreased amount corresponding to Pre decreases. As a whole, the reaction force corresponding to the braking force corresponding to the pedal stroke Xi is maintained in the brake pedal B (input piston 32). At this time, the pedal input Fi _B is maintained at a value determined by Xi and km according to the equation (6). As a result, the braking force (hydraulic pressure) generated in the master cylinder 10 is changed without changing the reaction force applied to the brake pedal B (input piston 32) from the master cylinder 10 by the sum of the hydraulic pressure and the spring force of the spring 60. You can increase or decrease.

  In this embodiment, the return spring 58 that applies a biasing force in the return direction to the booster piston 31 and the screw shaft (linear motion member) 54 of the ball screw mechanism 50 is a deceleration (for example, 0.3 G) during the regenerative braking. The set load is set so as not to generate the brake fluid pressure by the input piston (first member, shaft member) 32 until the brake fluid pressure corresponding to is reached. That is, the set load Fre of the return spring 58 is set to be larger than the value obtained by multiplying the spring constant ks of the spring 60 by the stroke Xmax of the input piston 32 corresponding to the upper limit of the brake hydraulic pressure for regenerative braking. (Fre> ks · Xmax). As a result, no excessive brake fluid pressure is generated during regenerative braking, and good brake feeling is ensured.

  When the electric booster 50 is incorporated in the preceding vehicle following system (ACC), the relationship between the displacement Xb of the booster piston 31 and the master cylinder hydraulic pressure Pm is as shown in FIG. In this case, if deceleration is started following the preceding vehicle from a certain time ta, the booster piston 31 is displaced forward in response to a necessary deceleration command from an ECU (not shown) to generate the brake fluid pressure Pm. . Then, the vehicle starts to decelerate according to the generation of the brake fluid pressure Pm. In this case as well, the spring force of the spring 60 that biases the input piston 32 forward by the relative displacement between the booster piston 31 and the input piston 32, and the master The brake pedal B does not move because the increased amount of the hydraulic reaction force applied from the cylinder pressure chamber 17 to the input piston 32 is balanced (Xi is at the position of displacement 0 in FIG. 10). Here, in the input piston 32, the position where the flange portion 38 of the input rod 9 abuts against the inward projection 39 of the rear cover 6 is the retracted end, so that the spring constant ks of the spring 60 is made slightly smaller than the set value. By setting, the increase in the hydraulic reaction force applied to the input piston 32 may be made slightly larger than the spring force of the spring 60 that biases the input piston 32 forward. By doing so, even if the spring constant km of the master cylinder 10 becomes small due to variations in the brake pad thickness (for example, uneven wear of the brake pad) (in this case, the spring 60 is determined from the relationship of the expression (7)). However, since the spring constant ks is set slightly smaller than the above set value, the system in which the brake pedal B does not advance can be realized.

In the above description, for the sake of convenience, the spring constant km of the master cylinder 10 has been described as having a linear characteristic. However, in practice, the spring constant km is, for example, as shown in FIG. In general, the displacement and the resulting hydraulic pressure have nonlinear characteristics. For this reason, a preferable pedal feeling can be obtained by setting the spring constant ks of the spring 60 in accordance with the regenerative braking region where the pedal feeling is particularly affected (for example, the hydraulic pressure region where the deceleration is 0.3 G or less). Obtainable. In this case, instead of Pm / Vm in the above formula (12), based on the following formula (13) using the change rate of the increase / decrease in the minute brake fluid pressure ΔPm accompanying the increase / decrease in the minute fluid amount ΔVm in the regenerative braking region. The spring constant ks of the spring 60 may be obtained.
ks = Ai × Ab × ΔPm / ΔVm (13)
In FIG. 11, the invalid stroke of the master cylinder 10 is not considered because it is based on the schematic diagram of FIG.

  Thus, according to the electric booster 1 of the present embodiment, even if the brake operation by the electric motor 40 is performed, the brake pedal B is not affected, so that a good pedal feeling is maintained and the brake is maintained. In addition to the assist system, the reliability of the apparatus is improved in application to a regenerative cooperative brake system, a preceding vehicle following system, and the like. Further, since only the spring 60 having a predetermined spring constant is interposed between the input piston 32 and the booster piston 31, the structure does not become complicated and large, and there are advantages in terms of cost and vehicle mountability. large.

It is sectional drawing which shows the whole structure of the electric booster as one Embodiment of this invention. It is sectional drawing which shows the principal part structure of this electric booster. It is sectional drawing which shows the structure of the master cylinder combined with this electric booster. It is sectional drawing which shows the initial stage of the assembly procedure of this electric booster. It is sectional drawing which shows the last step of the assembly procedure of this electric booster. It is a schematic diagram which shows the basic concept of this electric booster. It is a graph which shows the time-dependent change of the input and output characteristics at the time of the brake assist operation | movement in this electric booster. It is a graph which shows the time-dependent change of the pedal stroke at the time of the brake assist operation | movement in this electric booster. It is a graph which shows a time-dependent change of pedal input and brake fluid pressure when this electric booster is built in a regenerative cooperation brake system. It is a graph which shows a time-dependent change of a booster piston displacement and brake fluid pressure when this electric booster is integrated in a preceding vehicle following system. It is a graph which shows the actual correlation of piston displacement and hydraulic pressure in the master cylinder combined with this electric booster.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Electric booster 2 Housing 9 Input rod 10 Tandem master cylinder 17, 18 Pressure chamber of master cylinder 21 Booster piston (tubular member, second member)
22 Input piston (shaft member, first member)
30 (30A, 30B) Spring (biasing means)
40 Electric motor 42 Electric motor rotor 50 Ball screw mechanism (rotation-linear motion conversion mechanism)
54 Screw shaft of ball screw mechanism (linear motion member)
58 Return spring 65 Potentiometer 66 Rotation sensor B Brake pedal C Controller

Claims (5)

  A first member that moves forward and backward by the operation of the brake pedal, a second member that is arranged to be relatively movable with respect to the first member, a rotation-linear motion conversion mechanism that moves the second member forward and backward, An electric motor for applying a rotational force to the rotation-linear motion conversion mechanism, an input thrust applied from the brake pedal to the first member, and a booster thrust applied from the electric motor to the second member To generate a brake fluid pressure in the master cylinder and transmit a part of the reaction force due to the brake fluid pressure to the first member and the other part to the second member. And when the first member and the second member are relatively displaced in at least one direction between the first member and the second member, , In the displacement direction of the second member The urging means for making the force stronger than the state before the relative displacement of the both members is provided, and the electric motor is arranged coaxially with the first and second members and the rotation-linear motion conversion mechanism. Electric booster characterized by.   The electric booster according to claim 1, further comprising a return spring that biases the second member and the linear motion member of the rotation-linear motion conversion mechanism toward the brake pedal.   The set load of the return spring is set larger than the spring load of the urging means when the first member moves to a displacement corresponding to the brake fluid pressure during regenerative braking. The electric booster described in 1.   A shaft member that moves forward and backward by operating a brake pedal, a cylindrical member that is externally mounted on the shaft member, a rotation-linear motion conversion mechanism that moves the cylindrical member forward and backward, and the rotation-linear motion conversion An electric motor for applying a rotational force to the mechanism, a displacement detection means for detecting a relative displacement amount between the shaft member and the cylindrical member, and a control device for controlling the electric motor based on a detection signal of the displacement detection means; The shaft member and the cylindrical member are used as pistons of the master cylinder, the front ends thereof face the pressure chambers of the master cylinder, and the input thrust applied from the brake pedal to the shaft member and the electric motor In the electric booster that generates the brake fluid pressure in the pressure chamber by the booster thrust applied to the cylindrical member from between the shaft member and the cylindrical member, There is provided urging means for generating a force that cancels the increase / decrease of the hydraulic reaction force transmitted from the pressure chamber of the master cylinder to the shaft member according to the displacement, and the electric motor is connected to the shaft member, the cylinder. An electric booster characterized by being arranged in a coaxial manner with the cylindrical member and the rotation-linear motion conversion mechanism.   5. The electric booster according to claim 4, further comprising a return spring that urges the cylindrical member and the linear motion member of the rotation-linear motion conversion mechanism to a brake pedal side.

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