JP2009006756A - Electric booster - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric booster capable of keeping a good pedal feeling all the time by optionally adjusting a pedal reaction force according to operating conditions. <P>SOLUTION: This electric booster includes: an input piston 12 working with a brake pedal; a booster piston 11 which is arranged in a relative displaceable manner with the input piston 12 and driven by an electric actuator 13; and a balance spring 28 for retaining the input piston 12 and the booster piston 11 in the neutral position of the relative displacement when the brake is inoperative. Further, the electric booster generates desired brake hydraulic pressure in a master cylinder 30 by controlling the relative displacement amount of the both pistons 11 and 12. A hydraulic pressure chamber 18 is partitioned between the booster piston 11 and the input piston 12 so as to adjust reaction force (pedal reaction force) conducting to the brake pedal by supplying control pressure from a pressure control unit 40 to the hydraulic pressure chamber 18 in brake assist operations, regenerative coordination operations or the like. <P>COPYRIGHT: (C)2009,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, as this type of electric booster, there is one described in Patent Document 1. This includes an input piston interlocked with a brake pedal, a booster piston that is arranged so as to be relatively movable with respect to the input piston, and driven by an electric actuator, and the input piston and the booster piston are relatively arranged when the brake is not operated. And a biasing means for holding the neutral position of the movement, and a structure for generating a desired brake fluid pressure in the master cylinder by controlling a relative displacement amount between the input piston and the booster piston.

FIG. 7 is an explanatory diagram for explaining the pressure balance in the electric booster described in Patent Document 1, in which 1 is an input piston, 2 is a booster piston, and 3 and 4 are biasing means. The balance spring 5 is a master cylinder. Here, the displacement (input displacement) of the input piston 1 is Xi, its thrust (input thrust) is Fi, its pressure receiving area is Ai, the displacement (booster displacement) of the booster piston 2 is Xb, and its thrust (boost thrust) is Fb. The pressure receiving area is Ab, the brake fluid pressure in the master cylinder 5 is Pb, the spring constants of the balance springs 3 and 4 are K, and the relative displacement between the input piston 1 and the booster piston 2 is ΔX (= Xi−Xb). Then, the pressure balance equation is as shown in the following (1), and the boost ratio α is as shown in the following (2).
Pb = (Fi−K × ΔX) / Ai = (Fb + K × ΔX) / Ab (1)
α = Pb × (Ai + Ab) / Fi = (Fi−K × ΔX) / Ai × (Ai + Ab) / Fi = (1−K × ΔX / Fi) × (1 + Ab / Ai) (2)

  In this case, if the position of the booster displacement Xb is controlled so that the relative displacement amount ΔX is 0, that is, Xb = Xi, the boost ratio α becomes α = 1 + Ab / Ai, and the booster piston 21 of the booster piston 21 is similar to the vacuum booster. It is uniquely determined by the area ratio between the pressure receiving area Ab and the pressure receiving area Ai of the input piston 22. Further, if the booster displacement Xb is position-controlled so that the relative displacement amount ΔX is negative, that is, Xb> Xi is maintained, the boost ratio is increased (braking force increase), and the brake assist operation is realized. Conversely, the relative displacement amount ΔX Is positive, that is, if the booster displacement Xb is controlled so that Xb <Xi is maintained, the boost ratio is reduced (braking force is reduced), and the regenerative cooperative operation during regenerative braking is realized. Further, since the communication between the pressure chamber in the master cylinder 5 and the reservoir is blocked by the advance of the booster piston 2, automatic braking operations such as adaptive control (ACC) and hill start assist are also possible.

By the way, the discharge fluid amount Qb of the master cylinder can be obtained by the following equation (3). However, in the brake system of an automobile, the discharge fluid amount Qb is influenced by the rigidity of the wheel cylinder (disc brake) and the piping system. And the brake fluid pressure Pb have a non-linear relationship as shown in FIG. On the other hand, the driver's pedal feel is determined by the relationship between the input displacement Xi and the input thrust Fi as shown in FIG. In this case, when Pb = f (Qb) and its inverse function is Qb = f (Pb) and the relationship between the input displacement Xi and the input thrust Fi is arranged, the following equation (4) is obtained from the equation (1). .
Qb = Xi × Ai + Xb × Ab (3)
Fi = f (Xi * Ai + Xb * Ab) * Ai + K * (Xi-Xb) (4)

  From this, the booster displacement Xb that returns the desired input thrust Fi with respect to the input displacement Xi can be obtained by calculating back the equation (4). However, when the booster displacement Xb is determined, the brake fluid pressure Pb is also determined from the equation (1). When Ai and Ab are determined from the boost ratio, since the adjustment element is only the spring constant K of the balance springs 3 and 4 in the equation (4), the input thrust Fi and the brake fluid pressure Pb with respect to the input displacement Xi. Both cannot be changed freely. This will be explained with reference to FIG. 8 and FIG. 9. First, normally, when ΔX = 0 is controlled to perform a boost operation with a fixed boost ratio (α = 1 + Ab / Ai), Qb = Xi × (Ai + Ab), Since Pb = Fi / Ai, Equation (4) becomes Fi = f (Xi × (Ai + Ab)) × Ai, and the relationship between the input displacement Xi and the input thrust Fi in FIG. 9 is the discharge fluid amount of the master cylinder in FIG. This is similar to the relationship between Qb and brake fluid pressure Pb.

When the input displacement is Xia, the booster displacement Xb = Xia, the master cylinder discharge fluid amount is Qba = Xia × (Ai + Ab), and is at point A (brake fluid pressure Pba) in FIG. 8, and the input thrust Fi is Fi = Pba × Ai is at point S1 in FIG. At this time, when the brake assist operation is performed to increase the brake fluid pressure Pba to Pba ′ while maintaining the input thrust Fia, the master cylinder discharge fluid amount is Qba ′ = g ( Pba ′) is required, and the booster displacement is Xba ′ = (Qba′−Xia × Ai) / Ab. At this time,
Pba′−Pba = (Fia−K × ΔX) / Ai−Fi / Ai = −K × ΔX / Ai
Qba′−Qba = Xia × Ai + Xba ′ × Ab−Xia × (Ai + Ab) = − ΔX × Ab
Therefore, the spring constant K of the balance springs 3 and 4 is expressed by the following equation (6).
K = Ai × Ab × (Pba′−Pba) / (Qba′−Qba) (5)

  That is, the spring constant K of the balance springs 3 and 4 is proportional to the average gradient (Pba′−Pba) / (Qba′−Qba) between the curves AA ′ in FIG. Therefore, if the spring constant is adjusted to the above equation (6), the brake fluid pressure can be increased from Pba to Pba ′ while maintaining the input thrust Fia, but this requires replacement of the balance springs 3 and 4. Become.

  On the other hand, in an electric vehicle or a hybrid vehicle, as shown in FIG. 8, the brake fluid pressure is reduced by the amount of regenerative braking ΔP by the motor / generator from the brake fluid pressure Pba corresponding to the input displacement Xia. However, it is desirable that the input thrust Fi (pedal reaction force) does not change at this time as well. In order to cope with the specific input displacement Xia and the regenerative braking amount ΔP, it is possible to select a suitable spring constant K as in the above-described brake assist operation. However, the input displacement Xi varies depending on the driver's operation. In addition, the braking force of regenerative braking is limited by the state of the regenerative circuit and the vehicle speed, and fluctuates during braking. 8 and 9, braking is started at point A corresponding to the input displacement Xia, then regenerative braking corresponding to the regenerative braking amount ΔP is started and moved to A ″ and further reduced to the input displacement Xib. It is only necessary to move from the B point to the B ″ point reduced by ΔP and to hold the input thrust at the S2 point Fib in FIG.

However, as described above, the spring constant satisfying this condition is proportional to the slope of FIG. 8, and therefore, between A and A ″, between K = Ai × Ab × ΔP / (Qba−Qba ″) and BB ″. In this case, K = Ai × Ab × ΔP / (Qbb−Qbb ″), and with a fixed spring constant, the input thrust cannot be maintained in both sections, and fluctuations in thrust at the start / end of regenerative braking, that is, The reaction force transmitted to the brake pedal (pedal reaction force) fluctuates. It is also difficult to achieve both expansion of the hydraulic pressure increase effect during brake assist operation and thrust fluctuation suppression during regeneration coordination.
Japanese Patent Laid-Open No. 2007-112426

  The present invention has been made in view of the above-described technical background, and the problem is that the pedal reaction force can be arbitrarily adjusted in accordance with the operation state, so that a good pedal feel can be constantly maintained. It is in providing the electric booster which can be performed.

  In order to solve the above-described problems, the present invention provides an input piston that works in conjunction with a brake pedal, a booster piston that is disposed so as to be relatively movable with the input piston and that is driven by an electric actuator, the input piston, and the booster piston. An electric booster that generates a desired brake fluid pressure in the master cylinder by controlling a relative displacement amount between the input piston and the booster piston, and a liquid between the booster piston and the input piston. A reaction chamber that defines a pressure chamber, communicates the fluid pressure chamber with an external fluid pressure control device, supplies control fluid pressure to the fluid pressure chamber from the fluid pressure control device, and is applied to the input piston. It is characterized by adjusting.

  In the electric booster configured as described above, it is possible to arbitrarily change the pedal reaction force by applying the control hydraulic pressure from the hydraulic pressure control device to the hydraulic pressure chamber facing the input piston, and the brake assist operation. Good pedal feel can be ensured even during regenerative cooperative operation.

  The present invention may be configured such that a normally closed electromagnetic on-off valve is provided in a flow path that communicates the hydraulic pressure chamber and the hydraulic pressure control device. When configured in this way, the electromagnetic on-off valve can be kept closed when the electric actuator fails, and the relative displacement between the input piston and the booster piston can be maintained at the initial value, and the stroke of the brake pedal can be maintained. It becomes possible to brake without increasing the.

  In this invention, the said pressure control apparatus can be set as the structure provided with the cylinder apparatus which incorporates a control piston, and the sub electric actuator which drives the said control piston. In this case, controllability is improved because the control hydraulic pressure is electrically controlled.

  The pressure control device may be configured to include a cylinder device having a built-in control piston and an operating rod that drives the control piston in conjunction with a brake pedal. In this case, since the control hydraulic pressure is mechanically controlled, the device structure is simplified.

  According to the electric booster according to the present invention, the pedal reaction force can be arbitrarily adjusted, so that a good pedal feel can be secured even during a brake assist operation, a regenerative cooperative operation, etc., and the reliability of the device is improved. improves.

  The best mode for carrying out the present invention will be described below with reference to the accompanying drawings.

  FIG. 1 shows a first embodiment of an electric booster according to the present invention. The electric booster 10 includes a booster piston 11 shared as a primary piston of a tandem master cylinder 30 described later, and a booster piston 11 in a bottomed cylinder portion 11 a formed on the rear side of the booster piston 11. And an input piston 12 disposed so as to be relatively movable, an electric actuator 13 for driving the booster piston 11, and a casing 14 in which the pistons 11, 12 and the electric actuator 13 are collectively stored. Yes. The casing 14 includes a case main body 14 a that is integral with the cylinder main body 31 of the master cylinder 30 and a rear cover 14 b on the rear side. The electric booster 10 is connected to the engine room and the vehicle via the rear cover 14 of the casing 14. It fixes to the partition 15 which partitions off a chamber.

  The booster piston 11 is slidably inserted into the cylinder body 31 of the master cylinder 30 via the seal member 16. On the other hand, the input piston 12 is slidably mounted in the cylinder portion 11a of the booster piston 11 via a seal member 17, and the bottom side in the cylinder portion 11a is defined as a sealed hydraulic chamber 18. . The rear end of the input piston 12 is connected to the tip of an input rod 19 extending from a brake pedal (not shown). The input piston 12 moves forward and backward in the booster piston 11 by operating the brake pedal (pedal operation). It is supposed to move.

  The electric actuator 13 includes an electric motor 20 and a ball screw mechanism (rotation linear motion conversion mechanism) 21 that converts the rotation of the electric motor 20 into a linear motion and transmits the linear motion to the booster piston 11. The electric motor 20 includes a stator 22 and a hollow rotor 23, and the stator 22 is fixedly disposed on the casing 14, and the rotor 23 is rotatably disposed on the casing 14 via a bearing 24. Has been. On the other hand, the ball screw mechanism 21 includes a nut portion 25 provided integrally with the rotor 23 of the electric motor 20 and a hollow screw shaft 27 meshed with the nut portion 25 via a ball 26. The screw shaft 27 is supported by the casing 14 so as not to rotate and to be movable in the axial direction. As a result, when the nut portion 25 rotates together with the rotor 23, the screw shaft 27 moves directly. An inner flange 27a is formed at the rear end portion of the screw shaft 27, and the rear end of the booster piston 11 is abutted against the inner peripheral edge portion of the inner flange 27a. Therefore, when the screw shaft 27 moves forward, the booster piston 11 moves forward. The screw shaft 27 has a retracted end at a position where the inner flange 27a abuts the rear cover 14b.

  A pair of balance springs (biasing means) 28 are arranged in the cylinder portion 11 of the booster piston 11. The pair of balance springs 28 are respectively interposed between the input piston 12 and the inner bottom of the cylinder portion 11a of the booster piston 11 and between the annular protrusions 29 protruding from the opening end of the cylinder portion 11a. Yes. The pair of balance springs 28 serves to hold the booster piston 11 and the input piston 12 in a neutral position relative to each other when the brake is not operated.

  Here, the tandem master cylinder 30 is schematically configured from the cylinder body 31 and the reservoir 32. The cylinder body 31 has a bottomed cylindrical shape, and a secondary piston 33 that is paired with the booster piston 11 as the primary piston is disposed on the inner bottom side thereof. In the cylinder body 31, two pressure chambers 34 and 34 ′ are defined by the booster piston 11 and the secondary piston 33, and the pressure chambers 34 and 34 ′ correspond to the wall of the cylinder body 11. Discharge ports 35 and 35 'are formed to communicate with a wheel cylinder (not shown).

  The cylinder body 31 is formed with relief ports 36 and 36 'for communicating the pressure chambers 34 and 34' with the reservoir 32, and the booster piston is sandwiched between the relief ports 36 and 36 '. 11 and a pair of seal members 37 and 37 ′ for sealing between the secondary piston 33. Each of the pressure chambers 34, 34 ′ comes into contact with the outer peripheral surface of the corresponding piston 11, 33 by the pair of seal members 37, 37 ′ as the pistons 11, 33 move forward. 36 'is closed. Also, return springs 38 and 38 'for urging the booster piston 11 and the secondary piston 33 as the primary pistons in the backward direction are disposed in the pressure chambers 34 and 34', respectively. If the booster piston 11 is regarded as a primary piston, the configuration of the master cylinder 30 described above is the same as that of a conventional general-purpose tandem master cylinder, and the pressure chambers 34 and 34 ′ move in accordance with the advancement of the pistons 11 and 33. The contained brake fluid is pumped from the discharge ports 35 and 35 'to the corresponding wheel cylinder, and a braking force is generated.

  In the present embodiment, a pressure control device 40 to be described later is separately provided, and the control hydraulic pressure is supplied from the pressure control device 40 to the hydraulic pressure chamber 18 defined between the booster piston 11 and the input piston 12. It can be supplied. More specifically, the cylinder body 31 of the master cylinder 30 is connected to the hydraulic chamber 18 via an annular passage 41 formed between the booster piston 11 and a radial through hole 42 formed in the booster piston 11. 43 is provided. The port 43 and the pressure control device 40 are connected by a pipe 44, and a normally closed electromagnetic on-off valve 45 is interposed in the pipe 44. Therefore, the control hydraulic pressure is supplied from the pressure control device 40 to the hydraulic pressure chamber 18 by opening the electromagnetic on-off valve 45.

  Here, as shown in FIG. 2, the pressure control device 40 includes a cylinder device 47 having a built-in control piston 46 and an electric actuator (sub-electric actuator) 48 for driving the control piston 46. The sub electric actuator 48 incorporates an electric motor and a rotation / linear motion conversion mechanism, and the control piston 40 is connected to a linear motion member constituting the rotation / linear motion conversion mechanism in the sub electric actuator 48. The non-rod side chamber in the cylinder device 47 is defined as a hydraulic pressure chamber 49, and a port 50 connected to the pipe 44 is opened in the hydraulic pressure chamber 49. In the hydraulic pressure control device 40, the control pressure sent to the hydraulic pressure chamber 18 in the booster piston 11 can be arbitrarily controlled by controlling the displacement Xc of the control piston 46 by the sub electric actuator 48. In the cylinder device 47, a pair of balance springs 51 that normally hold the control piston 46 in the neutral position are housed.

  In the present embodiment, a displacement detector 52 that engages with the rear end of the input piston 12 and detects the displacement of the input piston 12 is disposed inside the rear end of the rear cover 14b that constitutes the casing 14. An angle detector 53 for detecting the rotational displacement of the rotor 23 is disposed between the casing 14 and the rotor 23 of the electric motor 20. A pressure sensor 54 is provided in the middle of the pipe 44 for supplying the control hydraulic pressure from the pressure control device 40 to the hydraulic pressure chamber 18. The detection signals of the displacement detector 52, the angle detector 53, and the pressure sensor 54 are sent to a controller (not shown), and the controller, based on these detection signals, outputs the electric motor 20 in the electric actuator 13. And the electric motor in the sub electric actuator 48 is controlled.

Hereinafter, the operation of the electric booster 1 configured as described above will be described.
When the brake pedal is depressed and the input piston 12 starts moving forward together with the input rod 19, the movement is detected by the position detector 52. Then, in response to the signal from the position detector 52, the controller outputs a start command to the electric motor 20, whereby the rotor 23 of the electric motor 20 rotates, and the rotation is transmitted to the ball screw mechanism 21, and the screw shaft 27 advances and the booster piston 11 follows the movement. That is, the input piston 12 and the booster piston 11 integrally move forward, and a brake corresponding to the input thrust Fi applied to the input piston 12 from the brake pedal and the booster thrust Fb applied to the booster piston 11 from the electric motor 20. A hydraulic pressure is generated in the pressure chambers 17 and 18 in the tandem master cylinder 10.

  At this time, when the normally closed electromagnetic on-off valve 45 in the pipe 44 connected to the pressure control device 40 is opened at the same time as the input piston 12 starts moving forward, the control hydraulic pressure is applied to the hydraulic chamber 18 at the tip of the input piston 12. Pc is supplied and a reaction force acts on the input piston 12. Therefore, if the control pressure Pc is changed according to the input displacement Xi, a desired pedal reaction force (input thrust Fi) can be obtained.

In this case, the pressure balance will be described with reference to FIG. 3. The expressions corresponding to the expressions (1), (3) and (4) in the above-described conventional electric booster are the following (1 ′) and (3 ′). And (4 ').
Pb = (Fb + Fi) / Ab
= (Fb + K × ΔX) / Ab + Pc × Ai / Ab (1 ′)
Qb = Xb × Ab (3 ′)
Fi = Pc × Ai + K × ΔX (4 ′)

  Here, if the control pressure Pc is controlled according to the expression Pc = (Fia−K × ΔX) / Ai with respect to the input displacement Xia shown in FIG. 9, a desired input thrust Fia, that is, a pedal reaction force can be obtained. Further, if the booster displacement Xb is controlled so as to satisfy the formula Xb = Qba / Ab = g (Pba) / Ab, a desired brake hydraulic pressure Pba can be obtained. From the above formulas (1 ′), (3 ′) and (4 ′), if the spring constant K of the balance spring 28 is negligibly small, the input thrust Fi becomes independent of the booster displacement Xb and the brake hydraulic pressure Pb. The operation is equivalent to a stroke simulator. Therefore, the reaction force (pedal reaction force) transmitted to the brake pedal can be optimized by appropriately controlling the control pressure Pc by the pressure control device 40 during the brake assist operation, the regeneration cooperative operation, or the like. However, in the pressure control device 40 (FIG. 2) in the present embodiment, the displacement Xc of the control piston 41 is directly connected to the piston displacement Xi in a relationship of Xc × Ac = Xi × Ai, where the area is Ac. Therefore, the motor rotation of the sub electric actuator 48 is transmitted to the input piston 12 as it is, and the pedal feel is somewhat rugged.

  In the electric booster 10, the normally closed electromagnetic switching valve 45 is provided in the pipe 44 connecting the hydraulic chamber 18 on the tip side of the input piston 12 and the pressure control device 40. When the electric motor 20 of the electric actuator 13 fails, the electromagnetic on-off valve 45 can be kept closed to keep the relative displacement between the input piston 12 and the booster piston 11 at the initial value, and the stroke of the brake pedal can be increased. It becomes possible to brake without increasing, and the reliability of the device is improved. Incidentally, in the conventional electric booster shown in FIG. 7, only Qb = Xi × Ai can be supplied until a part of the input piston 1 comes into contact with the booster piston 2, so that a braking delay occurs.

  Here, the pressure control device 40 may have the structure shown in FIG. 4 or 5 instead of the embodiment (FIG. 2). A pressure control device 40 ′ shown in FIG. 4 includes a free piston 55 slidably accommodated in a cylinder device 47 in the pressure control device 40, and a pneumatic chamber 56 (between the free piston 55 and the control piston 46. Air spring). In this pressure control device 40 ′, the pressure in the pneumatic chamber 56 increases due to the movement of the control piston 46 by Xc, but the interval Xd between the control piston 46 and the free piston 55 decreases, and the pressure increase is alleviated. The In addition, since the spring constant of the air spring is proportional to the gas pressure, the spring constant also increases. The control hydraulic pressure Pc is added to (−K × ΔX) as in the above equation (4 ′), and since the variable range of the pneumatic chamber 56 is wide, the spring constant K of the balance spring 28 should be made as small as possible. A small gradient such as between BB ″ in FIG. 8 can be sufficiently dealt with.

  The pressure control device 40 ″ shown in FIG. 5 is connected to a brake pedal in parallel with the input rod 19 (FIG. 1), omitting the electric actuator 48 in the pressure control device 40 ′ shown in FIG. The control piston 46 is driven by the operating rod 57. In this pressure control device 40 ″, the volume of the air spring decreases as the input displacement Xi increases, and the spring constant increases. This characteristic is advantageous in that a characteristic close to the curve in FIG. 8 can be obtained without complicated control.

  In the pressure control devices 40 ′ and 40 ″ described above, the air pressure chamber 56 is provided between the control piston 46 and the free piston 55. However, the air pressure chamber 56 may be replaced with a closed-cell rubber sponge or an accumulator. A similar effect can be obtained, and a throttle may be provided in the flow path from the hydraulic chamber 49 in the cylinder device 47 to the hydraulic chamber 18 on the front end side of the input piston 12, and in this case, damping is performed. The pedal feel is further improved by adding characteristics.

  FIG. 6 shows a second embodiment of the electric booster according to the present invention. The electric booster 10 ′ according to the second embodiment is except that the tip of the input piston 12 is inserted into the pressure chamber 34 of the master cylinder 30 through the booster piston 11 in a liquid-tight manner. Since it is exactly the same as that of the first embodiment, the same parts as those shown in FIG. 1 are denoted by the same reference numerals, and redundant description is omitted. Further, the electric booster 10 ′ is provided with a hydraulic pressure chamber 18 between the booster piston 11 and the input piston 12 so that the control hydraulic pressure Pc can be supplied from the pressure control device 40 to the hydraulic pressure chamber 18. Except for the above points, the configuration and the basic operation thereof are substantially the same as those described in Patent Document 1 (FIG. 7), and therefore, a duplicate description is omitted here.

In the second embodiment, the pressure balance equation corresponding to the equation (1) in the above-described conventional electric booster is changed to the following equation (1 ″), but the equations (3) and (4) remain as they are. It becomes.
Pb = (Fi−Pc × Ac−K × ΔX) / Ai
= (Fb + Pc × Ac + K × ΔX) / Ab (1 ″)

  Therefore, also in the second embodiment, the reaction force (pedal reaction force) transmitted to the brake pedal is optimal if the control pressure Pc is appropriately controlled by the pressure control device 40 during the brake assist operation, the regeneration cooperative operation, or the like. The same effects as those of the first embodiment can be obtained.

It is sectional drawing which shows the whole structure of the electric booster as the 1st Embodiment of this invention. It is sectional drawing which shows an example of the structure of the pressure control apparatus with which this electric booster is equipped. It is explanatory drawing for demonstrating the pressure balance in this electric booster. It is sectional drawing which shows the other example of the structure of the pressure control apparatus with which this electric booster is equipped. It is sectional drawing which shows the further another example of the structure of the pressure control apparatus with which this electric booster is equipped. It is sectional drawing which shows the whole structure of the electric booster as the 2nd Embodiment of this invention. It is explanatory drawing for demonstrating the pressure balance in the conventional electric booster. It is a graph which shows the relationship between the master cylinder discharge fluid quantity and brake fluid pressure in an electric booster. It is a graph which shows the relationship between the displacement of an input piston in an electric booster, and input thrust.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10,10 'Electric booster 11 Booster piston 12 Input piston 13 Electric actuator 18 Hydraulic chamber 20 Electric motor 21 Ball screw mechanism (rotation linear motion conversion mechanism)
28 Balance spring 30 Tandem master cylinder 32 Reservoir 40, 40 ', 40 "Pressure control device 45 Normally closed solenoid valve 46 Control piston 47 Cylinder device 48 Sub electric actuator 57 Actuating rod

Claims (4)

  An input piston interlocked with the brake pedal, and a booster piston that is arranged to be movable relative to the input piston and driven by an electric actuator, and controls a relative displacement amount between the input piston and the booster piston. In the electric booster that generates a desired brake fluid pressure in the master cylinder, a fluid pressure chamber is defined between the booster piston and the input piston, and the fluid pressure chamber is used as an external fluid pressure control device. An electric booster characterized in that a control hydraulic pressure is supplied from the hydraulic pressure control device to the hydraulic pressure chamber to adjust a reaction force applied to the input piston.   2. The electric booster according to claim 1, wherein a normally closed electromagnetic on-off valve is provided in a flow path that communicates the hydraulic pressure chamber and the hydraulic pressure control device.   3. The electric booster according to claim 1, wherein the pressure control device includes a cylinder device having a built-in control piston and a sub electric actuator that drives the control piston. 4.   3. The electric booster according to claim 1, wherein the pressure control device includes a cylinder device having a built-in control piston and an operating rod that drives the control piston in conjunction with a brake pedal. apparatus.

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