CN113119936A

CN113119936A - Electric brake booster with pedal behaviour simulator

Info

Publication number: CN113119936A
Application number: CN201911411598.2A
Authority: CN
Inventors: 陶垚
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2019-12-31
Filing date: 2019-12-31
Publication date: 2021-07-16
Anticipated expiration: 2039-12-31
Also published as: CN113119936B

Abstract

An electric brake booster for use in a vehicle comprising: braking the motor; an assist force transmission mechanism configured to be driven by the brake motor to move in the axial direction; a pedal behavior simulator configured to be driven by the brake pedal to move in an axial direction; a detection device configured to detect an axial movement of the pedal behavior simulator; and a control unit configured to control the brake motor to perform a motor braking operation mode based on the axial movement of the pedal behavior simulator detected by the detection means; wherein, in the motor braking operation mode, the braking assistance generated only by the motor constitutes the input force of the electric brake booster; and the pedal behaviour simulator is configured, on the one hand, to be actuated by the brake pedal to produce an axial movement detectable by the detection means and, on the other hand, to transmit to the driver's foot, via the brake pedal, a reaction force perceptible by the driver's foot reflecting the braking state of the vehicle.

Description

Electric brake booster with pedal behaviour simulator

Technical Field

The present application relates to a vehicle electric brake booster having a pedal behavior simulator that can be used to detect a driver's braking intention and to feed back a tactile sensation corresponding to a vehicle braking state to a driver's foot.

Background

Some vehicles have added to their hydraulic braking systems an electric brake booster that utilizes an electric motor as a source of brake boost. In the case of electric brake boosters of the prior art, the brake booster and the pedal force are usually coupled via a transmission line, i.e. transmitted to the master cylinder piston via common force transmission elements. In such an electric brake booster, when a driver performs a braking operation, the driver presses a brake pedal to apply a pedal force, a motor of the electric brake booster generates a brake assist force, and the pedal force and the brake assist force are transmitted to a master cylinder piston in combination. For vehicles having an automatic braking function (e.g., an automatic driving or active braking module, etc.), the electric motor of the electric brake booster actively generates a braking assistance without driver intervention (i.e., no pedal force input) when the vehicle automatically applies braking. However, when the brake assist force is transmitted to the master cylinder piston, the pedal force transmitting member, and even the brake pedal, is pulled. This affects the transmission efficiency of the brake assist force and may give a driver a bad feeling of putting his foot on the brake pedal.

Accordingly, it is desirable to provide a decoupling type electric brake booster in which a brake boosting transmission line of a brake motor of the electric brake booster is decoupled from a pedal force transmission line when a motor braking operation is performed. For such a decoupled electric brake booster, the controller needs to accurately detect the driver's true braking intention in order to control the brake motor to apply the brakes.

Disclosure of Invention

The present application aims to provide an improved decoupled electric brake booster with a pedal behaviour simulator enabling the controller to accurately detect the driver's true braking intention.

To this end, according to one aspect of the present application, there is provided a decoupled electric brake booster for use in a vehicle braking system, comprising: braking the motor; an assist force transmission mechanism configured to be driven by the brake motor to move in an axial direction so as to transmit a brake assist force generated by the brake motor to the piston of the master cylinder; a pedal behavior simulator configured to be driven by the brake pedal to move in an axial direction; a detection device configured to detect an axial movement of the pedal behavior simulator; and a control unit configured to control the brake motor to perform a motor braking operation mode based on the axial movement of the pedal behavior simulator detected by the detection means; wherein, in the motor braking operation mode, the braking assistance generated only by the motor constitutes the input force of the electric brake booster; and the pedal behaviour simulator is configured, on the one hand, to be actuated by the brake pedal to produce an axial movement detectable by the detection means and, on the other hand, to transmit to the driver's foot, via the brake pedal, a reaction force perceptible by the driver's foot reflecting the braking state of the vehicle.

According to the present application, when a motor braking operation is performed, a braking behavior of a driver is simulated using a pedal behavior simulator, and thus the braking intention of the driver can be accurately known so as to accurately control a brake motor to perform braking. On the other hand, the pedal behavior simulator can also give the driver's foot a realistic reaction feeling of the brake pedal, so that the driver can accurately step on the brake pedal based on the driving situation to brake the vehicle as the driver desires.

Drawings

FIG. 1 is a schematic cross-sectional view (through the booster central axis) of a decoupled electric brake booster according to one possible embodiment of the present application;

FIG. 2 is a schematic cross-sectional view of the electric brake booster in another direction (through the booster center axis in a direction perpendicular to FIG. 1);

FIG. 3 is a schematic view for explaining a pedal force transmission line in the electric brake booster;

FIG. 4 is a schematic diagram for explaining a brake assist transmission line in the electric brake booster;

FIGS. 5 and 6 are schematic views of a drive nut and a plunger, respectively, in the electric brake booster;

FIGS. 7 and 8 are schematic views of the components of one possible embodiment of a pedal spring retainer in an electric brake booster;

FIG. 9 is a schematic view of another possible embodiment of a pedal spring limit structure in an electric brake booster;

FIG. 10 is a graphical representation of the primary piston travel versus output force relationship for a conventional master cylinder;

FIG. 11 is a graphical illustration of a conventional brake pedal travel versus output force;

FIG. 12 is a graph of displacement versus spring force for the pedal spring of the present application;

FIG. 13 is a schematic view of one possible embodiment of the pedal spring of the present application;

fig. 14 is a schematic view of a variation of the pedal spring in fig. 13;

FIG. 15 is a schematic view of one form of the pedal spring of FIG. 13;

FIG. 16 is a schematic view of another possible embodiment of the pedal spring of the present application.

Detailed Description

Some possible embodiments of the present application are described below with reference to the drawings. It is to be noted that the drawings are designed solely to embody the principles of the present application and not to represent the actual configuration of the present application. Accordingly, the drawings are not to scale; also, some details are exaggerated and some details are omitted for clarity.

It is first of all pointed out that in the present application, "rear side" means the side which is kinematically close to the brake pedal of the vehicle, and "front side" means the side which is kinematically facing away from the brake pedal, i.e. close to the master cylinder.

As shown in fig. 1 and 2, a decoupling electric brake booster for use in a vehicle brake system according to one possible embodiment of the present application is used to transmit an output force to a piston 2 of a master cylinder 1 of a vehicle hydraulic brake system. Some structural details of the electric brake booster are shown in fig. 3-9. Fig. 1 and 2 show the home position (non-operating state) of the electric brake booster.

The piston 2 is axially movable relative to the cylinder body of the master cylinder 1. The master cylinder 1 and its piston 2 of a hydraulic vehicle brake system are common in the art and will not be described in detail. Note that the master cylinder 1 has a double piston, the piston 2 is shown as a master piston (rear chamber piston) of the master cylinder 1, and the master cylinder 1 further includes a second piston (front chamber piston) not shown.

The electric brake booster of the present application is associated with the brake pedal side presser 3, and includes a brake motor 4 for generating brake assist. The electric brake booster further includes a control unit 5 and a pedal stroke sensor 6. The pedal stroke sensor 6 is for detecting the stroke of the pushing member 3, that is, the stroke of the brake pedal. The control unit 5 is capable of receiving a brake pedal stroke signal detected by the pedal stroke sensor 6, and of controlling the operation of the brake motor 4. The control unit 5 activates the brake motor 4 to generate the brake assist pressure upon receiving the brake signal. The braking signal may be a brake pedal travel signal or a braking signal from an automatic vehicle braking function.

In the case of performing braking with the brake motor 4, only the brake assist force generated by the brake motor 4 is used as the input force of the electric brake booster, which does not include the pedal force from the brake pedal. In the case where braking is performed without using the brake motor 4, for example, the brake motor 4 is not supplied with electric power, or the brake motor 4 is disabled, the pedal force input by the driver through the brake pedal via the pushing member 3 may be used as the input force of the electric brake booster.

The electric brake booster further comprises a transmission sleeve 11 and a drive nut 12, both arranged coaxially with the piston 2 and thus defining a central axis of the electric brake booster. The transmission sleeve 11 is arranged in the drive nut 12 with a threaded transmission fit between the two. The drive nut 12 is rotatably arranged in a booster housing (not shown) by means of a bearing 13 (and possibly other bearings). The brake motor 4 rotates the drive nut 12 via a corresponding transmission mechanism (e.g., a gear train). According to a possible embodiment, in the case of an electrically charged brake motor 4 (motor rotor rotating or in the static state), the brake motor 4 can lock the axial position of the drive nut 12 by means of a transmission (in particular a gear train) between it and the drive nut 12, so that the drive nut 12 cannot move axially. Under the condition that the brake motor 4 is not electrified, as the motor rotor can rotate freely, the axial movement locking function of the brake motor 4 on the drive nut 12 is released, and the drive nut 12 can move axially.

Alternatively, a separate locking structure may be provided. In the case where the brake motor 4 is electrically charged, the locking structure locks the drive nut 12 axially, and thus the drive nut 12 does not have axial displacement capability. And in the case where the brake motor 4 is not charged, the locking structure unlocks the axial movement of the drive nut 12 so that the drive nut 12 can move axially.

In the case of an axially locked drive nut 12, rotation of the drive nut 12 may force the transmission sleeve 11 to move axially in the drive nut 12.

Referring to fig. 5, the drive nut 12 is generally cylindrical with an axial section being a thread section 12a provided with inwardly facing threads for engagement with the external threads of the transmission sleeve 11 (the transmission sleeve 11 may be provided with external threads over its entire length). In addition, the thread section 12a divides the inner bore of the drive nut 12 into a front section 12b and a rear section 12 c. The axial length of the thread segments 12a is about 1/3 or less of the axial length of the drive nut 12. The forward section 12b preferably has a smaller axial length than the rearward section 12 c.

Returning to fig. 1, 2, between the transmission sleeve 11 and the piston 2, a plunger 14 is arranged. The driving force generated by the brake motor 4, i.e. the braking assistance force, can be transmitted to the transmission sleeve 11 via the drive nut 12 and then from the transmission sleeve 11 to the piston 3 via the plunger 14. The plunger 14 and the piston 2 can be directly pushed against each other, so that the plunger 14 can directly transmit the braking assistance to the piston 2. Alternatively, a force transmission element (e.g. a ram) may be arranged between the plunger 14 and the piston 2, such that the plunger 14 transmits the braking assistance force to the piston 2 via the force transmission element. The arrangement of such force transmitting elements may facilitate the distribution of the braking assistance over the piston 2, etc.

Referring to fig. 6, the plunger 14 has a generally cylindrical body 14a, the front end of the body 14a forming a pair of diametrically opposed projecting flanges 14b, and the rear section of the body 14a being reduced in diameter to form a reduced diameter section 14 c. Further, in the body 14a, a radial through hole (cavity) 14d penetrating the body 14a is formed in a radial direction perpendicular to a radial direction in which the flange 14b extends. The front end of the radial through hole 14d terminates near the front end face of the body 14a, and the rear end of the radial through hole 14d communicates with the rear end face of the body 14a through the axial through hole 14 e. A front end wall 14f is present between the front end of the radial through hole 14d and the front end face of the body 14 a.

Returning to fig. 1 and 2, the front end of the plunger 14 is configured and adapted to push against the piston 2 (directly or indirectly). The small diameter section 14c of the plunger 14 is inserted into the front section 12b of the drive nut 12 such that the plunger 14 is axially movable relative to the drive nut 12.

A push rod 15 is arranged in the axial through hole defined by the transmission sleeve 11. The front end of the pushing component 3 is connected with a push rod 15. The front portion of the push rod 15 protrudes from the front end of the transmission sleeve 11, and is inserted into the radial through hole 14d through the axial through hole 14e of the plunger 14. The front end of the push rod 15 is connected to a pedal spring 16 and a reaction plate 17 located in front of the pedal spring 16. The pedal spring 16 and the reaction plate 17 are exposed from both sides in the radial direction of the plunger 14 through the radial through hole 14d of the plunger 14. In the home position, the reaction plate 17 is located axially rearward of the front end wall 14f of the plunger 14 and is spaced an axial distance from the front end wall 14 f.

The pedal spring 16 may be a combination of a plate spring and a coil spring (described in detail later), wherein the coil spring is connected to each of both ends of the plate spring. The plate spring is formed by stacking spring pieces such that the spring stiffness of the pedal spring 16 in the axial direction gradually increases from the longitudinal (radial) outer end toward the radial center.

The coil springs at both radial (longitudinal) ends of the pedal spring 16 are connected to a stopper rod 18 at the central ends of the coil springs, respectively. The stopper rod 18 extends parallel to the booster center axis and is restrained by a stopper plate 19 arranged around the small diameter section 14c of the plunger 14, so that the stopper rod 18 can move back and forth over a limited axial distance with respect to the stopper plate 19. In the example shown in fig. 7, the front end of the stopper rod 18 is fixed to the center tip of the coil spring of the pedal spring 16, and the rear portion of the stopper rod 18 is formed with a thin rod portion 18a, which thin rod portion 18a is inserted into a through hole 19a in the corresponding radial end portion of the stopper plate 19 shown in fig. 8 and is axially movable in the through hole 19 a. The axial movement range of the stopper rod 18, that is, the axial movement range of both ends in the radial direction of the pedal spring 16, is limited by the abutment between the large diameter portions of both ends in the axial direction of the thin rod portion 18a and the end surfaces of both sides in the axial direction of the stopper plate 19. Therefore, the stopper rod 18 and the stopper plate 19 constitute a stopper structure of the pedal spring 16. In the example shown in fig. 7, when the pedal spring 16 is elastically deformed in the axial direction by the push rod 15, the two stopper rods 18 cannot swing with respect to the booster center axis, and therefore the radial distance between the leading ends of the two stopper rods 18 is kept substantially constant, and the longitudinal distance between the center points of the coil springs at both ends of the pedal spring 16 is also kept substantially constant.

It will be appreciated that other forms of pedal spring limiting elements may be employed. For example, fig. 9 shows another stopper structure of the pedal spring 16, in which a front end of a stopper rod 18 is hinged to a longitudinally outer end of the pedal spring 16, and a rear end of the stopper rod 18 is provided with a hinge shaft inserted into a guide groove 19a extending parallel to an axial direction in a stopper plate 19 so that the hinge shaft can move back and forth in the guide groove 19 a. In situ, the radial distance between the front ends of the two restraint rods 18 and the radial distance between the rear ends of the two restraint rods 18 may be different or the same. When the push rod 15 pushes the pedal spring 16 forward, the rear hinge shaft of the stopper rod 18 slides forward in the guide groove 19 a. When the rear end hinge shaft of the stopper rod 18 reaches the front groove bottom of the guide groove 19a, the rear end of the stopper rod 18 is restrained from further advancing, and therefore, the both ends in the radial direction of the pedal spring 16 cannot further advance. As the push rod 15 pushes the middle portion of the pedal spring 16 forward, the pedal spring 16 starts to elastically deform in the axial direction. In the example shown in fig. 9, when the pedal spring 16 is deformed axially, the two stopper rods 18 can swing with respect to the booster central axis, so that the radial distance between the front ends of the two stopper rods 18 decreases, and the longitudinal distance between the center points of the coil springs at both ends of the pedal spring 16 also decreases accordingly. Therefore, the pedal spring stopper structure in fig. 9 allows a larger axial deformation of the pedal spring 16 than the pedal spring stopper structure shown in fig. 7.

The retainer plate 19 is non-rotatable and remains in a constant axial position with the drive nut 12. In other words, the limit plate 19 is axially movable with the drive nut 12, but is not rotatable. The above-described capability of the stopper plate 19 can be achieved by an appropriate holding structure. For example, in the illustrated example, the stopper plate 19 is fixed to the outer ring of the bearing 13.

Spring pressing pieces 20 for pressing first return springs 21 are installed on the front sides of both ends in the radial direction of the reaction plate 17. The first return spring 21 serves to urge the push rod 15 axially rearward via the spring pressure piece 20, the reaction plate 17, and the pedal spring 16. The first return spring 21 may be installed between the cylinder body of the master cylinder 1 and the spring pressure block 20.

Further, a second return spring 22 is interposed between the cylinder body of the brake master cylinder 1 and the flange 14b of the plunger 14 for urging the plunger 14 axially rearward. The second return spring 22 has a spring rate greater than that of the first return spring 21.

It is understood that the first return spring 21 and the second return spring 22 may be disposed at other positions according to the internal structure of the booster. In the illustrated example, both are in the form of helical compression springs, but other types of springs may be employed as long as the above-described pressing functions of both can be achieved. For example, in the example shown in fig. 9, the first return spring 21 is a 3D wire spring, one end of which is hooked to the longitudinally outer end of the pedal spring 16, and the other end of which is fixed to the stopper plate 19. It will be appreciated that the second return spring 22 may also take the form of a 3D wire spring.

Fig. 3 schematically depicts a pedal force transmission mechanism (line) in the electric brake booster, in which pedal force can be transmitted to the pedal spring 16, the reaction plate 17 via the push piece 3, the push rod 15, so that the pedal spring 16, the reaction plate 17 can move forward against the first return spring 21. A radially extending section 17a is mounted or formed at one end of the reaction plate 17 in the radial direction, the radially extending section 17a facing the pedal stroke sensor 6, so that the axial movement of the radially extending section 17a can be detected by the pedal stroke sensor 6 (e.g. by a varying magnetic field), whereby the control unit 5 can determine the pedal stroke, and thus the braking intention of the driver.

Fig. 4 schematically depicts a brake assist transmission mechanism (line) in the electric brake booster, in which the driving force (brake assist) of the brake motor 4 is transmitted to the plunger 14 through the drive nut 12, the transmission sleeve 11, so that the plunger 14 is moved forward against the urging force of the second return spring 22, and the plunger 14 transmits the brake assist generated by the brake motor 4 to the piston 2 as the output force of the electric brake booster.

It is to be noted that in the example shown, the braking assistance is transmitted mainly through the drive nut 12 and the transmission sleeve 11; however, it is understood that other mechanisms for converting rotational motion into linear motion, such as rack and pinion mechanisms and the like, may be used herein to transmit braking assistance.

Furthermore, it should be noted that the plunger 14, the push rod 15, the pedal spring 16, the reaction plate 17 are only allowed to move axially, but not to rotate, and their rotation prevention can be achieved by suitable constraint structures, for example by a limit plate 19 (non-rotatable) through the rotation prevention constraint of the pedal spring 16 by a limit rod 18.

The operation of the electric brake booster is described below.

The normal operation mode of the electric brake booster is first described. The so-called normal operation is that the electric brake booster is started based on the action of the driver depressing the brake pedal, and the brake assist is provided by the brake motor 4. After the driver depresses the brake pedal, the push element 3 pushes the pedal spring 16 and the reaction plate 17 axially forward by a free stroke via the push rod 15. The distance of the idle stroke depends on the limit of the limit plate 19 to the limit rod 18. For example, the idle stroke is about 5mm or less. The control unit 5 detects the stroke through the pedal stroke sensor 6, thereby confirming that the driver depresses the brake pedal, thereby activating the brake motor 4 to rotate in the forward direction to drive the plunger 14 to move forward by a determined distance. This section of the plunger 14 moves forward, causing the piston 2 to move forward into the cylinder of the master cylinder 1, thereby initially building up pressure in the cylinder of the master cylinder 1.

After the idle stroke is finished, if the driver further steps on the brake pedal, the limiting rod 18 is limited by the limiting plate 19 and cannot move continuously, the two ends of the pedal spring 16 are limited by the limiting rod 18 and cannot move forward further axially, the pedal spring 16 starts to deform axially, the pedal spring 16 generates gradually increased reaction force transmitted to the brake pedal, and meanwhile, the reaction plate 17 moves forward further. The control unit 5 detects the further forward movement by the pedal stroke sensor 6 and thus determines the driver's braking intention, thereby controlling the brake motor 4 to rotate in the forward direction to drive the plunger 14 to move further forward by a determined distance. This section of the plunger 14 moves forward, causing the piston 2 to move further forward into the cylinder of the master cylinder 1, so that the brake fluid pressure of the master cylinder 1 increases abruptly, i.e., the pressure jumps. The master cylinder 1 outputs brake fluid of increasing pressure to a braking element of a brake system, thereby braking the vehicle. Thereafter, a booster phase is entered, in which the pressure-force curve between the output pressure of the master cylinder 1 and the booster has a high slope to provide a rapid increase in the non-output pressure.

At the end of braking, the driver releases the brake pedal, the reaction plate 17 moves backwards under the hydraulic pressure in the brake master cylinder 1 and the urging of the first return spring 21, the control unit 5 thus judges the intention of the driver to end braking, and drives the brake motor 4 to rotate in reverse, so that the transmission sleeve 11 returns to the home position, the reaction plate 17, the pedal spring 16 and the push rod 15 return to the home position under the action of the first return spring 21, and the plunger 14 also returns to the home position under the action of the second return spring 22.

In the normal operation mode of the electric brake booster of the present application, on the one hand, the booster provides a booster curve similar to a conventional vacuum booster, and therefore, the vacuum booster can be replaced and a similar boosting function provided. On the other hand, the pedal reaction force and the stroke that the driver feels on the brake pedal by virtue of the deformation and the reaction force of the pedal spring 16 are similar to those in the conventional brake pedal operation.

The electric-only operating mode of the electric brake booster is described next. The so-called electric-only operating mode is when the driver does not depress the brake pedal, the control unit 5 activates the electric brake booster on the basis of the brake signal from the automatic vehicle braking function, or the automatic vehicle braking function takes over the electric brake booster directly. In this case, the push rod 15, the pedal spring 16, and the reaction plate 17 are kept stationary, and the brake motor 4 is rotated in the forward direction to drive the plunger 14 to move forward through the drive nut 12 and the transmission sleeve 11 to push the piston 2 forward, thereby achieving vehicle braking. When it is determined that braking is finished, the brake motor 4 is controlled to rotate reversely so that the transmission sleeve 11 is returned to the home position, and the plunger 14 is also returned to the home position by the second return spring 22.

The input force of the electric brake booster comes only from the brake motor 4 without any pedal force component, regardless of the normal operation mode or the electric-only operation mode. Thus, these two braking modes may be collectively referred to as motor braking operation. Also, a similar boost ratio and boost profile to a conventional vacuum booster can be provided, whether in the normal or pure electric mode of operation. Furthermore, the pedal stroke applied by the driver is used by the control unit 5 for determining the driver's braking intention only in the normal operation mode. In the normal operation mode, the driver's braking experience is similar to a conventional braking system, including a conventional brake system with a vacuum booster, due to the deformation of the pedal spring 16, resulting in a gradually increasing reaction force being fed back to the driver's foot via the brake pedal. The pedal spring 16 and its associated limit element (limit rod 18 pulls limit plate 19), push rod 15, etc. constitute a pedal behavior simulator.

Furthermore, the electric brake booster has a pure pedal operating mode. The pure pedal operation mode occurs when the brake motor 4 is not functioning properly, or is disabled, in which case the brake motor 4 is not being supplied with electrical energy. At this time, the axial movement locking function of the drive nut 12 is released, and thus the axial movement is enabled. When the driver depresses the brake pedal, the pushing element 3 pushes the pedal spring 16 axially forward via the push rod 15 until the reaction plate 17 pushes against the front end wall 14f of the plunger 14, and thus the plunger 14 is moved forward, thereby pushing the piston 2 forward to apply the vehicle brake. In the process, the pedal spring 16 pulls the limit plate 19 through the limit rod 18, and the limit plate 19 with the driving nut 12 and the transmission sleeve 11 also moves forwards axially. After braking is finished, the related elements return to the original positions under the action of the first return spring 21 and the second return spring 22.

In order to enable the pedal behaviour simulator of the present application to accurately simulate the pedal behaviour of a conventional brake booster, in particular a vacuum booster, the present application investigates some performance indicators in a vehicle brake system with a conventional brake booster. First, a graph showing the relationship between the master piston stroke and the output force of a master cylinder in a conventional braking operation of a brake system with a conventional brake booster is shown in fig. 10, in which the horizontal axis represents the master piston stroke (in mm) of the master cylinder and the vertical axis represents the input force (i.e., the output force of the booster, in N) of the master cylinder. As will be readily understood by those skilled in the art, the sharp point at the upper right corner of the curve in the figure divides the curve into a brake progress portion and a brake return portion.

Based on the graph of master piston stroke versus output force in fig. 10, a graph of brake pedal stroke versus output force in a conventional braking operation is obtained for the brake system with the conventional brake booster of fig. 11, wherein the horizontal axis represents brake pedal stroke (in mm) and the vertical axis represents brake pedal force (i.e., the force applied by the driver to the brake pedal, which is also equal to the force reacted by the brake pedal to the driver's foot, in N). As will be readily understood by those skilled in the art, the top right corner cusp of the curve divides the curve into a brake progress portion and a brake return portion.

In order for the pedal behavior simulator of the present application to accurately simulate the pedal behavior of a conventional brake booster in a normal braking operation, it is necessary to make the relationship curve between the spring axial movement distance of the pedal spring 16 and the spring force conform as closely as possible to the brake pedal stroke and output force relationship curve in fig. 11. To this end, the pedal spring 16 of the present application is configured such that it has the relationship between the axial movement distance and the spring force exemplarily illustrated in fig. 12. The axial moving distance and the spring force of the pedal spring 16 as referred to herein are measured at the longitudinal center point of the pedal spring 16 (i.e., the location where the push rod 15 is pushed).

The graph in fig. 12 is a pedal spring 16 graph produced when the brake booster of the present application is applied to a brake system of a specific vehicle type, in which the horizontal axis represents the spring axial movement distance, i.e., stroke (in mm), and the vertical axis represents the spring force (in N). In addition, when the brake system executes the brake operation, corresponding spring force is marked when various decelerations are generated for the vehicle, wherein the deceleration of 0.2 g-0.3 g is suitable for 90% of vehicle brake conditions, the deceleration of 0.3 g-0.5 g is suitable for 8% of vehicle brake conditions, 0.5g and above is suitable for vehicle emergency braking, 0.5g triggers ABS and ESP pressure building, and 1g triggers anti-lock function and ESP pressure building.

The pedal spring 16 of the present application needs to be configured to satisfy the conditions of the following stages.

Below 0.3g, the spring force is initially held substantially linear, e.g., substantially constant, with respect to the axial travel distance of the spring, and the spring force increases slightly more as it approaches 0.3 g.

From 0.3g to 0.5g, the brake pedal is highly compatible with the conventional relationship between the stroke of the brake pedal and the output force, and is stable over the entire service life (e.g., about six million operations).

Above 0.7g, a rapid increase in spring force is required that remains substantially linear with respect to the axial spring travel distance. Above 1g, a rapid increase of the spring force is required which remains approximately linear with respect to the axial spring travel distance, the spring force being required to be able to increase maximally to a maximum spring force corresponding to the maximum pedal force (taking into account factors of the pedal ratio), which should reach about 2000N, for example, at a pedal ratio of 3.3.

Several characteristic intervals are set according to the force-stroke characteristic curve of the pedal spring 16.

The interval from the spring force being substantially constant to the point where the increase in the spring force exceeds a set value (approximately 0.3 g) corresponds to the interval of the idle stroke (Cut in) of the booster. The idle stroke state starts at a spring zero stroke and ends before a spring stroke corresponding to a vehicle deceleration of 0.3 g. The region of 0 to 8mm in spring travel, for example, is referred to as an idle travel state (mainly depending on the free travel of the pedal spring 16 at both longitudinal ends thereof allowed by the stopper structure of the pedal spring 16). And starting from the idle stroke state end point, the brake main pump starts to output brake hydraulic oil.

Next, from the end of the idle stroke state, to the spring stroke corresponding to the 0.5g deceleration of the vehicle, the booster braking state of the booster is corresponded. In this stage, the pressure of the brake hydraulic oil output by the brake main pump is rapidly increased, and the pressure increase rate is gradually increased.

The spring travel corresponding to a deceleration of the vehicle of 0.5g or more corresponds to an emergency braking state of the booster. In this stage, the pressure of the brake hydraulic oil output from the brake main pump increases linearly and rapidly.

The pedal spring 16 of the present application is designed for these different phases. To this end, according to one possible embodiment of the present application, as shown in fig. 13, the pedal spring 16 includes a plate spring 16a and coil springs 16b respectively connected to longitudinal ends of the plate spring 16 a. The plate spring 16a is formed by stacking a plurality of spring pieces such that the spring stiffness of the pedal spring 16 in the axial direction increases stepwise (stepwise) from the longitudinal outer end toward the radial center. The outer end of each coil spring 16b is smoothly engaged with the end of the plate spring 16a, and the inner end of each coil spring 16b is connected to the stopper bar 18. In this regard, it should be noted that the inner end of the coil spring 16b may be fixed to the stopper rod 18 or may be pivotally connected to the stopper rod 18. The push rod 15, not shown in this figure, acts on the middle of the leaf spring 16a and applies an axial pushing force F to the middle of the leaf spring 16 a. Under the action of the axial thrust force F, the pedal spring 16 is deformed as schematically shown in fig. 14, in which the middle portion of the leaf spring 16a is elastically deformed forward (in the direction toward the master cylinder), and the two coil springs 16b are also elastically deformed accordingly.

As shown in fig. 15, with the pedal spring 16 in fig. 13, two coil springs 16b may be integrally formed at both longitudinal ends of one spring piece. Then, another spring piece is laminated on this spring piece with the coil spring 16b to constitute a plate spring 16a, thereby forming the pedal spring 16. The spring pieces can be connected by means of adhesive, welding, riveting and the like.

According to another possible embodiment of the present application, as shown in fig. 16, the pedal spring 16 includes a plate spring 16a and coil springs 16b respectively attached to longitudinal ends of the plate spring 16 a. The plate spring 16a is configured such that the thickness thereof in the axial direction becomes larger in a continuous manner from the longitudinal outer end toward the radial center, so that the spring rate of the pedal spring 16 in the axial direction continuously increases from the longitudinal outer end toward the radial center.

It should be noted that the plate spring 16a can be formed by stacking several spring plates or can be integrally formed by a single piece of spring material.

Further, the spring rates of the respective portions of the pedal spring 16 are set so that the spring force-stroke curve of the idle stroke state is mainly achieved by the two disc springs 16b, the spring force-stroke curve of the power-assisted braking state is mainly achieved by the plate spring 16a, and the spring force-stroke curve of the emergency braking state is mainly achieved by the two disc springs 16 b. It will be appreciated that the above requirements for each portion of the pedal spring 16 can be achieved by designing the size, shape, material stiffness, etc. of each portion of the pedal spring 16. Specifically, the force-travel curve of the pedal spring 16 is substantially linear in both the lost motion state and the hard braking state, but the slope of the force-travel curve of the pedal spring 16 in the hard braking state is greater than the slope of the force-travel curve of the pedal spring 16 in the lost motion state. In the power-assisted braking state, the force-stroke curve of the pedal spring 16 is curved, and the slope of the force-stroke curve becomes larger as the moving distance increases.

Specifically, considering that the force-stroke curve of the coil spring 16b may be configured to be substantially linear, while the force-stroke curve of the plate spring 16a may be configured to be substantially curved, when the spring force (load) of the pedal spring 16 is below 60N (substantially corresponding to the idle stroke state), the spring characteristic (force-stroke curve) of the pedal spring 16 is mainly determined by the two coil springs 16 b; when the spring force (load) of the pedal spring 16 is between 60N and 250N, approximately corresponding to (power-assisted braking state), the spring characteristic (force-stroke curve) of the pedal spring 16 is mainly determined by the plate spring 16 a; when the spring force (load) of the pedal spring 16 is above 250N (roughly corresponding to the emergency braking state), the spring characteristic (force-stroke curve) of the pedal spring 16 mainly depends on the two disc springs 16 b.

It will be appreciated that a pedal behaviour simulator consisting of a pedal spring and its associated stop element, push rod or the like may be constructed in a variety of suitable forms under the principles of the present application.

According to the present application, the brake boosting transmission line of the brake motor of the electric brake booster is decoupled from the pedal force transmission line when the motor braking operation is performed. The action of the brake boosting force transmission element does not drag the pedal force transmission element and the brake pedal, so that the transmission of the brake boosting force can be prevented from being blocked, and the driver can be prevented from having poor feeling from the brake pedal. Further, when the brake motor is operated, the input force of the electric brake booster is derived only from the brake motor without combining the pedal force. In the case where the brake motor is normal, the pedal behavior simulator, which is mainly based on the brake pedal, is used to provide the driver's foot with a tactile sensation for feedback of the braking state and to judge the driver's braking intention, the pedal force is not converted into a part of the output force of the brake booster. When the motor braking operation is executed, the braking action of the driver is simulated by the pedal action simulator, so that the braking intention of the driver can be accurately known, and the braking motor can be accurately controlled to brake. On the other hand, the pedal behavior simulator can also give the driver's foot a realistic reaction feeling of the brake pedal, so that the driver can accurately step on the brake pedal based on the driving situation to brake the vehicle as the driver desires. The decoupling electric brake booster can completely replace the traditional vacuum booster and can provide the brake boosting performance similar to the vacuum booster.

Furthermore, the decoupled electric brake booster according to the invention is particularly suitable for vehicles with an automatic braking function, i.e. the control of the electric brake booster and the vehicle brake system is taken over by the automatic braking function without the driver having to press down the brake pedal.

It should be noted that although the present application has been described and illustrated herein with reference to particular embodiments, the scope of the present application is not limited to the details shown. Various modifications may be made to these details without departing from the underlying principles of the application.

Claims

1. An electric brake booster for use in a vehicle, comprising:

a brake motor (4);

an assist force transmission mechanism configured to be driven by the brake motor (4) to move in an axial direction so as to transmit a brake assist force generated by the brake motor to the piston (2) of the master cylinder (1);

a pedal behavior simulator configured to be driven by the brake pedal to move in an axial direction;

a detection device configured to detect an axial movement of the pedal behavior simulator; and

a control unit (5) configured to control the brake motor (4) to perform a motor braking operation mode based on the axial movement of the pedal behavior simulator detected by the detection means;

wherein, in the motor braking operation mode, the braking assistance generated only by the motor constitutes the input force of the electric brake booster; and is

The pedal behaviour simulator is configured, on the one hand, to be actuated by the brake pedal to produce an axial movement detectable by the detection means and, on the other hand, to transmit to the driver's foot, via the brake pedal, a reaction force perceptible by the driver's foot reflecting the braking state of the vehicle.

2. The electric brake booster of claim 1, wherein the pedal behavior simulator comprises:

a push rod (15) driven by the brake pedal; and

and the pedal spring (16) is connected with the push rod (15), and the pedal spring (16) has the capacity of elastic deformation along the axial direction under the axial pushing action of the push rod (15).

3. An electric brake booster according to claim 2, wherein the boost transfer mechanism comprises a drive nut (12) configured to be driven in rotation by the motor and a transmission sleeve (11) coupled to the drive nut to convert the rotational movement of the drive nut into an axial linear movement;

the power transmission mechanism further comprises a plunger (14) arranged axially between the piston (2) of the master cylinder (1) and the transmission sleeve (11), the plunger being configured and adapted to be urged axially forward by the transmission sleeve (11) towards the cylinder of the master cylinder (1).

4. An electric brake booster according to claim 3, wherein the body of the pedal spring (16) is disposed in the interior chamber of the plunger with longitudinal ends projecting in opposite radial directions from the interior chamber of the plunger.

5. The electric brake booster according to any one of claims 2 to 4, wherein the push rod is connected to a pedal spring middle portion;

the pedal behavior simulator also includes stop elements connected to longitudinal ends of the pedal spring, each stop element allowing a respective end of the pedal spring to move forward within a defined axial distance.

6. The electric brake booster of claim 5, wherein the stopper member is configured to keep a distance between both longitudinal ends of the pedal spring substantially constant when the pedal spring is elastically deformed in the axial direction; or

The stopper member is configured to allow a distance between both longitudinal ends of the pedal spring to become smaller when the pedal spring is elastically deformed in the axial direction.

7. The electric brake booster according to claim 5 or 6, wherein the pedal spring (16) includes a plate spring (16a) and coil springs (16b) respectively connected to ends of the plate spring (16 a); each coil spring has an outer end connected to an end of the leaf spring and an inner end connected to a respective stop member.

8. The electric brake booster according to claim 7, wherein the plate spring (16a) is gradually increased in spring rate from an outer end to a center in the axial direction; for example, the plate spring is configured such that its thickness in the axial direction becomes larger from the outer end toward the center;

optionally, the plate spring is a combined spring formed by overlapping spring sheets, or is an integrated spring made of the same spring material.

9. The electric brake booster of claim 7 or 8, wherein the electric brake booster is configured in a motor brake operating mode having a lost motion state, an assisted braking state, an emergency braking state;

wherein in the lost motion state and the emergency braking state, the spring characteristic of the pedal spring is provided mainly based on the coil spring; in the power-assisted braking state, the spring characteristic of the pedal spring is provided mainly on the basis of the leaf spring.

10. The electric brake booster of claim 9, wherein the force-travel curve of the pedal spring is substantially linear in both the lost motion state and the emergency braking state, and the slope of the force-travel curve of the pedal spring in the emergency braking state is greater than the slope of the force-travel curve of the pedal spring in the lost motion state;

in the power-assisted braking state, the force-stroke curve of the pedal spring is curved, and the slope of the force-stroke curve becomes larger as the moving distance increases.