Initialization method for electro-mechanical brake

An initialization method for an EMB may include: opening an in-valve for controlling a flow path through which brake oil is introduced from a master cylinder, closing an out-valve for controlling a flow path through which the brake oil is transferred to an accumulator part, and driving a motor to move a master piston forward; when the master piston is moved by a preset distance after coming in contact with a slave piston which is brought in contact with an inner pad, closing the in-valve and driving the motor to move the master piston backward; when the contact between the master piston and the slave piston is released, determining whether a gap between the master piston and the slave piston is equal to or more than a preset gap; and when the gap is equal to or more than the preset gap, ending initialization of the EMB.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application claims priority to Korean application numbers 10-2014-0085961 and 10-2014-0117901, filed on Jul. 9, 2014 and Sep. 4, 2014, respectively, which are incorporated by reference in their entirety.

BACKGROUND

The present disclosure relates to an initialization method for an EMB (Electro-Mechanical Brake), and more particularly, to an initialization method for an EMB, which secures a gap between a master piston and a slave piston in a hydraulic EMB (hEMB), and maintains the effect of boosted hydraulic pressure in a braking section.

In general, a brake device refers to a device for decelerating or stopping a vehicle. Recently, an EMB has been developed to replace existing hydraulic brake systems. The EMB includes a smaller number of parts than the hydraulic brake systems, and can be reduced in weight. Furthermore, the EMB has excellent modularity and braking performance.

In the EMB, a hydraulic pipe and a hydraulic piping for guiding hydraulic pressure can be replaced with an electric wire Thus, the EMB can reduced the weight of the vehicle.

When the EMB is applied to both of the front and rear wheels of the vehicle, an ESC (Electronic Stability Control) function can be implemented without a separate ESC module. However, a system, which brakes the front wheels through an EMB and brakes the rear wheels through a general hydraulic pressure brake, includes an ESC module to implement the ESC function.

The related technology is disclosed in Korean Patent Laid-open Publication No. 10-2011-0065845 published on Jun. 16, 2011 and entitled “Brake System of Vehicle”.

SUMMARY

Embodiments of the present invention are directed to an initialization method for an EMB, which secures a gap between a master piston and a slave piston and a gap between a brake pad and a brake disk in an hEMB which brakes a vehicle by pressurizing the brake pad, or particularly the slave piston brought in contact with the brake pad, using the pressure of the master piston driven by a motor, thereby stably secure an effect of boosted hydraulic pressure in a braking section.

In one embodiment, an initialization method for an EMB may include: opening an in-valve for controlling a flow path through which brake oil is introduced from a master cylinder, closing an out-valve for controlling a flow path through which the brake oil is transferred to an accumulator part, and driving a motor to move a master piston forward; when the master piston is moved by a preset distance after coming in contact with a slave piston which is brought in contact with an inner pad for forming a braking force, closing the in-valve and driving the motor to move the master piston backward; when the contact between the master piston and the slave piston is released, determining whether a gap between the master piston and the slave piston is equal to or more than a preset gap; and when the gap is equal to or more than the preset gap, ending initialization of the EMB.

The determining of whether the gap between the master piston and the slave piston is equal to or more than the preset gap may include: when it is determined that the gap is less than the preset gap, opening the out-valve, and driving the motor to move the master piston forward until the master piston comes in contact with the slave piston; when the master piston comes in contact with the slave piston, opening the in-valve, closing the out-valve, and driving the motor to move the master piston forward by the preset distance; and when the master piston is moved by the preset distance after coming in contact with the slave piston, closing the in-valve, opening the out-valve, and driving the motor to move the master piston backward.

The slave piston may be moved by hydraulic pressure which is formed according to the movement of the master piston.

As the master piston has a smaller cross-sectional area than the slave piston, the master piston may have a larger displacement than the slave piston.

As the in-valve is opened, the brake oil may be introduced into the slave piston from the master cylinder.

As the out-valve is opened, the brake oil introduced into the slave piston may be transferred to the accumulator part.

When a current of the motor is equal to or more than a preset current while the master piston is moved forward, it may be determined that the master piston is brought in contact with the slave piston.

The determining of whether the gap between the master piston and the slave piston is equal to or more than the preset gap may include determining whether the gap between the master piston and the slave piston is equal to or more than the preset gap, by referring to the backward moving distance of the master piston and the displacement of the slave piston which is moved through hydraulic pressure formed by the brake oil introduced into the slave piston.

The EMB may include an hEMB which brakes a vehicle using the master piston which is moved by the motor and the slave piston which is moved through hydraulic pressure formed by the brake oil introduced into the slave piston according to the movement of the master piston.

In another embodiment, an initialization method for an EMB may include: a contact determination step of determining whether a master piston and a slave piston are brought in contact with each other before a brake pad and a brake disk are brought in contact with each other by the slave piston moved in connection with the master piston, when an in-valve for controlling entry and exit of brake oil to and from a master cylinder is closed, an out-valve for controlling entry and exit of brake oil to and from an accumulator part is closed, and a motor is rotated to move the master piston forward; a piston gap determination step of determining whether a moving distance required until the master piston comes in contact with the slave piston corresponds to a first section, when the master piston is moved forward in state where the out-valve is opened, in case where it is determined that the brake pad and the brake disk were brought in contact with each other before the master piston and the slave piston were brought in contact with each other; and a pad gap securing step of moving the master piston backward until a pad gap between the slave piston and the brake pad corresponds to a second section, when the moving distance of the master piston corresponds to the first section, and ending initialization of the EMB.

The piston gap determination step may include: an additional forward movement step of moving the master piston forward until the brake pad and the brake disk are brought in contact with each other in a state where the in-valve is opened, when it is determined that the brake pad and the brake disk were brought in contact with each other after the master piston and the slave piston were brought in contact with each other; and an oil injection step of moving the master cylinder backward by a distance corresponding to the first section by injecting brake oil through the in-valve, when the brake pad and the brake disk are brought in contact with each other through the additional forward movement step.

The slave piston may be moved by hydraulic pressure which is formed according to the movement of the master piston.

As the master piston has a smaller cross-sectional area than the slave piston, the master piston may have a larger displacement than the slave piston.

As the in-valve is opened, the brake oil may be introduced into the slave piston from the master cylinder.

As the out-valve is opened, the brake oil introduced into the slave piston may be transferred to the accumulator part.

The contact determination step may include determining that the brake pad and the brake disk were brought in contact with each other before the master piston came in contact with the slave piston, when a pressure measured through a pressure sensor connected to a hydraulic pressure chamber is equal to or more than a preset pressure while the master piston is moved forward.

The piston gap determination step may determine that the master piston is brought in contact with the slave piston, when a current of the motor is equal to or more than a preset current while the master piston is moved forward.

The EMB may include an hEMB which brakes a vehicle using the master piston which is moved by the motor and the slave piston which is moved through hydraulic pressure formed by the brake oil introduced into the slave piston according to the movement of the master piston.

DESCRIPTION OF EMBODIMENTS

Embodiments of the invention will hereinafter be described in detail with reference to the accompanying drawings. It should be noted that the drawings are not to precise scale and may be exaggerated in thickness of lines or sizes of components for descriptive convenience and clarity only.

Furthermore, the terms as used herein are defined by taking functions of the invention into account and can be changed according to the custom or intention of users or operators. Therefore, definition of the terms should be made according to the overall disclosures set forth herein.

In general, an ESC module is provided to perform ESC control and ABS control for rear wheels when the rear wheels are braked. Depending on cases, however, the ESC module may perform a parking brake function of the front-wheel EMB, a function of blocking a master piston pressure and an EMB wheel pressure during a braking operation, and an EMB initialization function.

In the case of a hydraulic EMB (hEMB) having an ESC module, a pressure generated by a motor is not directly transmitted to a slave piston, but transmitted to the slave piston through a hydraulic pressure formed by pressurizing a master piston. Thus, the hEMB may reduce the generation of noise and the damage of the device.

Furthermore, a boosted force is generated by a difference in cross-sectional area between the master piston and the slave piston. When the boosted force is used, a boosted force generated by a gear may be maximized or removed, which makes it possible to avoid noise and efficiency reduction which can occur when the gear is used. Furthermore, while the number of gear trains is minimized, the size of an actuator can be reduced. Thus, the entire size of the hEMB can be reduced.

The hEMB has a difference in cross-sectional area between the master piston which is driven by the rotational force of the motor and the slave piston which is brought in contact with a brake pad for forming a braking force. Thus, when the pistons are moved, the pistons have a difference in moving speed therebetween.

Thus, the two pistons gradually approach each other. When two pistons come in contact with each other in a braking section where a braking force needs to be generated, the effect of the boosted hydraulic pressure may disappear. In order to prevent the disappearance, an initialization operation for the hEMB may be performed as follows. The master piston and the slave piston may be forced to be spaced at a predetermined gap or more from each other such that the braking performance can be normally performed.

At this time, in order to space the master piston and the slave piston from each other, a solenoid valve may be operated in a state where the master piston and the slave piston are brought in contact with each other. Then, when only the master piston is moved backward in a state where the slave piston is stopped, a predetermined gap is formed between the master piston and the slave piston.

However, when the reverse speed of the master piston is relatively high, the speed at which brake oil is introduced may be lowered to form low hydraulic pressure. Thus, the slave piston is moved backward together, thereby making it difficult to maintain the desired gap between the master piston and the slave piston.

Thus, the reverse speed of the master piston may be lowered to secure a gap. In this case, however, stability may be degraded, and a considerable amount of time may be required for initialization. Thus, there is a demand for an improved structure.

FIG. 1is a diagram schematically illustrating a brake device for a vehicle in accordance with an embodiment of the present invention. Referring toFIG. 1, the brake device1for a vehicle in accordance with the embodiment of the present invention may include a master cylinder10, a pedal20, a diverging line part30, a front wheel line part40, a hydraulic electro-mechanical brake (hEMB)50, a rear wheel line part60, a hydraulic brake70, an accumulator part80, a motor pump90, and a pedal simulator100.

The master cylinder10may be mounted on a vehicle body, and the pedal20may pressurize the master cylinder10. For example, the pedal20may be positioned at the bottom of a driver's seat such that a driver can step on the pedal20. When the pedal20pressurizes the master cylinder10, hydraulic pressure in the master cylinder10may be amplified.

The diverging line part30may be connected to the master cylinder10, and transfer hydraulic pressure generated through the master cylinder10. For example, the master cylinder10may have two chambers formed therein, and a pair of diverging line parts30may be connected to the respective chambers so as to transfer hydraulic pressure.

The diverging line part30may include a diverging supply part31, a diverging connection part32, a normal open valve33, a diverging storage part34, and a normal closed valve35.

The pair of diverging supply parts31may be connected to the master cylinder10so as to transfer hydraulic pressure. In the present embodiment, the pedal simulator100may be connected to the diverging supply part31.

The diverging connection part32may have one end connected to the diverging supply part31and the other end connected to the front wheel line part40. The normal open valve33may be mounted on the diverging connection part32, and open the diverging connection part32in a state where no electrical signal is received. When receiving an electrical signal, the normal open valve33may close the diverging connection part32.

The diverging storage part34may have one end connected to the diverging supply part31and the other end connected to the accumulator part80. The normal closed valve35may be mounted on the diverging storage part34, and close the diverging storage part34in a state where no electrical signal is received. When receiving an electrical signal, the normal closed valve35may open the diverging storage part34.

The front wheel line part40may be connected to the diverging line part30so as to guide hydraulic pressure, and the hEMB50may be connected to the front wheel line part40. The hEMB50may mechanically brake a front wheel150according to a received electrical signal.

The hEMB50may be connected to the front wheel line part40, and supply hydraulic pressure to the front wheel line part40while braking the front wheel150according to the electrical signal. In the present embodiment, the hEMB50may brake the front wheel150using the hydraulic pressure provided through the front wheel line part40.

At this time, the front wheel line part40may include a front wheel guide part41, an in-valve42, and an out-valve43. The front wheel guide part41may connect the diverging connection part32and the hEMB50. The in-valve42may be mounted on the front wheel guide part41and open/close the front wheel guide part41according to control, such that the brake oil of the master cylinder10is introduced.

In the present embodiment, one end of the front wheel guide part41may be connected to the normal open valve33formed at an end of the diverging connection part32, and the other end of the front wheel guide part41may be connected to the hEMB50.

The out-valve43may transfer the brake oil introduced from the master cylinder10to the accumulator part80according to control.

At this time, since the brake oil transferred to the accumulator part80has pressure formed therein, the brake oil is free from the surface tension between the master piston P1and the slave piston P2, unlike the brake oil which is directly introduced from the master cylinder10.

The front wheel guide part41may have a hydraulic pressure sensor mounted therein, the hydraulic pressure sensor measuring hydraulic pressure. During four-wheel independent active control, fluid pressure may leak when the hydraulic pressure between the in-valve42and the hEMB50becomes higher than the previous hydraulic pressure of the in-valve42. In order to prevent the leakage, a check valve may be removed from the in-valve42.

The rear wheel line part60may connected to the front wheel line part40so as to guide hydraulic pressure, and the hydraulic brake70may be connected to the rear wheel line part60. The hydraulic brake70may brake a rear wheel170using hydraulic pressure. In the present embodiment, the rear wheel line part60may include a rear wheel guide part61, a rear wheel valve62, a rear wheel bypass part63, and a check valve64.

The rear wheel guide part61may connect the front wheel guide part41and the hydraulic brake70, and the rear wheel valve62may be mounted on the rear wheel guide part61so as to open/close the rear wheel guide part61. For example, one end of the rear wheel guide part61may be connected to the front wheel guide part41between the normal open valve33and the in-valve42. The rear wheel bypass part63may have both ends connected to the rear wheel guide part61, and induce hydraulic pressure to bypass the rear wheel valve62. The check valve64may be mounted on the rear wheel bypass part63and allow hydraulic pressure to flow only in one direction.

The accumulator part80may store hydraulic pressure to perform a buffer function. The accumulator part80may be connected to the diverging line part30, the front wheel line part40, and the rear wheel line part60, and adjust hydraulic pressure passing through the diverging line part30, the front wheel line part40, and the rear wheel line part60.

In the present embodiment, the accumulator part80may include an accumulator81, a pump connection part82, a diverging connection part83, a front wheel connection part84, and a rear wheel connection part85. The pump connection part82may connect the motor pump90and the accumulator81, the diverging connection part83may connect the diverging storage part34and the accumulator81, the front wheel connection part84may connect the front wheel guide part41and the accumulator81, and the rear wheel connection part85may connect the rear wheel guide part61and the accumulator81.

The diverging connection part83may include a connection check valve831which allows hydraulic pressure to flow only in one direction. The front wheel connection part84may include a front wheel opening/closing part841which opens/closes the front wheel connection part84, and the rear wheel connection part85may include a rear wheel opening/closing part851which opens/closes the rear wheel connection part85.

In the present embodiment, the pump connection part82may have one end connected to the motor pump90and the other end connected to the accumulator81. One end of the diverging connection part83may be connected to the normal closed valve35formed at the end of the diverging storage part34, and the other end of the diverging connection part83may be connected to the pump connection part82formed between the motor pump90and the connection check valve831.

One end of the front wheel connection part84may be connected to the front wheel guide part41formed between the in-valve42and the hEMB50, and the other end of the front wheel connection part84may be connected to the pump connection part82formed between the connection check valve831and the accumulator81.

One end of the rear wheel connection part85may be connected to the rear wheel guide part61formed between the rear wheel bypass part63and the hydraulic brake70, and the other end of the rear wheel connection part85may be connected to the front wheel connection part84formed between the front wheel opening/closing part841and the accumulator81.

The motor pump90may be connected to the front wheel line part40so as to supply hydraulic pressure. In the present embodiment, the motor pump90may be driven according to an electric signal, and provide hydraulic pressure to the hydraulic brake70.

In the present embodiment, the motor pump90may be connected to each of the front wheel guide parts41. For example, the motor pump90may be connected to the front wheel guide part41formed between the normal open valve33and the in-valve42.

The pedal simulator100may be connected to the diverging line part30, and provide a pedal force to the pedal20. Through the pedal simulator100, a driver may recognize a pedal feel when stepping on the pedal20.

FIG. 2is a cross-sectional view schematically illustrating the hEMB for a vehicle in accordance with the embodiment of the present invention.FIG. 3is a cross-sectional view schematically illustrating the operation of the hEMB in accordance with the embodiment of the present invention.

Referring toFIGS. 2 and 3, the hEMB50in accordance with the embodiment of the present invention may include a housing510, a motor530, a spindle540, a master piston P1, and a slave piston P2.

The housing510may have a hydraulic pressure chamber formed therein. At one side of the hydraulic pressure chamber, a pair of brake pads600may be installed. Between the brake pads600, a brake disk700may be installed. The hydraulic pressure chamber may contain incompressible brake oil serving as working fluid.

The motor530may be coupled to the housing510through a bolting system or the like, and include an electric motor and a gear. As power is applied, the motor530may be driven.

The spindle540may be axially coupled to the motor530and formed in a cylindrical rod shape. The spindle540may be coupled to the master piston P1through a screw thread formed on the outer circumferential surface thereof.

The master piston P1may be movably coupled to the spindle540. In the present embodiment, the master piston P1may be positioned so as to be spaced from the slave piston P2. When the master piston P1is reciprocated forward and backward by the rotation of the spindle540, the master piston P1may pressurize the brake oil between the master piston P1and the slave piston P2so as to pressurize the slave piston P2.

The slave piston P2may be movably coupled to the hydraulic pressure chamber, and contain brake oil therein. The slave piston P2may be connected to the brake pad600. As the slave piston P2is moved to one side, the brake pad600may be brought in contact with the brake disk700to form a braking force.

Since the slave piston P2is pressurized through the brake oil serving as a medium, the master piston P1and the slave piston P2may be prevented from coming in contact with each other, which makes it possible to prevent noise and damage of the device.

Furthermore, since the slave piston P2is pressurized and moved by the pressure of the brake oil, which is formed through the movement of the master piston P1, the pressure of the working fluid may be uniformly applied to the slave piston P2.

Thus, since the slave piston P2uniformly pressurizes the entire brake pad600, the substantial friction area between the brake pad600and the brake disk700can be increased.

The master piston P1may have a smaller cross-sectional area than the inner cross-sectional area of the slave piston P2. The moving distance of the slave piston P2may be determined according to the cross-sectional area and the moving distance of the master piston P1.

For example, when the master piston P1has a diameter of 30 mm and the slave piston P2has an inner diameter of 60 mm, the cross-sectional area of the slave piston P2may be four times larger than the cross-sectional area of the master piston P1.

At this time, when the master piston P1is moved by 4 mm, the slave piston P2is moved by 1 mm. As a result, the displacement of the master piston P1becomes larger than the displacement of the slave piston P2. As such, the ratio of the cross-sectional areas of the slave piston P2and the master piston P1may be considered to determine the moving distances of the slave piston P2and the master piston P1.

FIG. 4is a flowchart illustrating an initialization method for an EMB in accordance with a first embodiment of the present invention. Referring toFIG. 4, the initialization method S1for an EMB in accordance with the first embodiment of the present invention will be described as follows.

An aspect of the present invention relates to a method for initializing an hEMB50which brakes a vehicle using a master piston P1which drives and moves a motor (not illustrated) and a slave piston P2which is moved through hydraulic pressure formed by brake oil introduced into the slave piston P2according to the movement of the master piston P1. The initialization method for maintaining a gap between the master piston P1and the slave piston P2will be described in detail as follows.

FIGS. 5 to 9are reference diagrams for describing the transfer of brake oil and the movement of the master piston P1and the slave pistons P2when the in-valve42and the out-valve43are opened and closed. Since the hEMB has substantially the same structure as a general EMB, components such as a caliper body, a gear, a motor, a screw, a nut, a cylinder, and a seal member are not illustrated inFIGS. 5 to 9.

FIG. 5is a diagram illustrating a state in which the in-valve is opened and the out-valve is closed in the initialization method for an EMB in accordance with the first embodiment of the present invention. Referring toFIG. 5, the in-valve42for controlling a flow path through which brake oil is introduced from the master cylinder10may be opened, the out-valve43for controlling a flow path through which brake oil is transferred to the accumulator part80may be closed, and the motor may be driven to move the master piston P1forward within the housing510, at step S10. When the motor is driven, a rotational force may be generated to move the master piston P1.

At this time, as the in-valve42is opened and the out-valve43is closed, the brake oil from the master cylinder10may be introduced into the slave piston P2.

More specifically, since a seal member (not illustrated) for sealing the master piston P1, the housing510, the slave piston P2, and a caliper body (not illustrated) is formed, the brake oil introduced into the slave piston P2may not leak to outside. As the master piston P1is moved, hydraulic pressure may be formed in the slave piston P2.

Furthermore, when the motor is driven, the master piston P1may be moved forward or backward within a guide region formed in the housing510according to the rotation direction of the motor. The slave piston P2may be moved forward or backward by the hydraulic pressure which is formed through the movement of the master piston P1.

FIG. 6is a diagram illustrating that the master piston is moved backward in a state where the in-valve and the out-valve are closed in the initialization method for an EMB in accordance with the first embodiment of the present invention.

When the master piston P1is moved by a preset distance after coming in contact with the slave piston P2which is brought in contact with an inner pad for forming a braking force at step S20, the in-valve42may be closed and the motor may be driven to move the master piston P1backward as illustrated inFIG. 6, at step S30.

When the master piston P1is moved forward, a current change of the motor may be measured to determine whether the master piston P1was brought in contact with the slave piston P2. More specifically, when a current measured during operation of the motor is equal to or more than a preset current, a control unit may determine that the master piston P1was brought in contact with the slave piston P2.

Furthermore, the reason that the master piston P1is further moved by the preset distance after coming in contact with the slave piston P2may be described as follows. When the master piston P1is moved only until the master piston P1is brought in contact with the slave piston P2, the brake oil introduced into the slave piston P2may escape toward the master cylinder10, because the master piston P1has a smaller cross-sectional area than the slave piston P2. Thus, in order to prevent the escape of the brake oil, the master piston P1may be further moved by the preset distance after coming in contact with the slave piston P2.

Furthermore, since the master piston P1has a smaller cross-sectional area than the slave piston P2, the displacement of the master piston P1is larger than that of the slave piston P2.

Thus, the master piston P1may be moved forward and backward at higher speed than the slave piston P2.

That is, when the master piston P1is moved backward, the master piston P1may be moved backward at higher speed than the slave piston P2. Thus, a gap may be formed between the master piston P1and the slave piston P2.

When the contact between the master piston P1and the slave piston P2is released at step S40as the master piston P1is moved backward at step S30, the control unit may determine whether the gap between the master piston P1and the slave piston P2is equal to or more than a preset gap. When it is determined that the gap is equal to or more than the preset gap, the control unit may end the initialization for the hEMB50at step S50.

At this time, the control unit may determine whether the gap between the master piston P1and the slave piston P2is equal to or more than the preset gap by referring to the moving distance of the master piston P1and the displacement of the slave piston P2which is moved through the hydraulic pressure formed by the brake oil introduced into the slave piston P2. Alternatively, the control unit may determine whether the gap between the master piston P1and the slave piston P2is equal to or more than the preset gap, through position sensors (not illustrated) installed on the master piston P1and the slave piston P2, respectively.

As such, the hEMB50may be initialized through the gap secured between the master piston P1and the slave piston P2.

Only through steps S10to S40, the gap can be secured to perform initialization for the hEMB50. However, when the displacement of the master piston P1which needs to be moved at step S10in order to secure a sufficient gap becomes excessive, the current consumption of the motor may be increased. Thus, in the initialization method for an EMB in accordance with the first embodiment of the present invention, when the gap between the master piston P1and the slave piston P2is less than the preset gap, the above-described process from step S10to step S40may be repeated until the gap becomes equal to or more than the preset gap. Therefore, current consumption can be reduced and a sufficient gap between the master piston P1and the slave piston P2can be secured to stably initialize the EMB.

FIG. 7is a diagram illustrating that the master piston is moved forward in a state where the out-valve is opened in the initialization method for an EMB in accordance with the first embodiment of the present invention.

When it is determined at step S50that the gap between the master piston P1and the slave piston P2is less than the preset gap, the out-valve43may be opened and the master piston P1may be moved forward until the master piston P1is brought in contact with the slave piston P2, as illustrated inFIG. 7.

That is, when it is determined at step S50that the gap is less than the preset gap, the out-valve43may be opened and the master piston P1may be moved forward until the master piston P1is brought in contact with the slave piston P2, as illustrated inFIG. 5.

Furthermore, as the out-valve43is opened, the brake oil introduced from the master cylinder10may be transferred to the accumulator part80.

FIG. 8is a diagram illustrating that the master piston is moved forward in a state where the in-valve is opened and the out-valve is closed, in the initialization method for an EMB in accordance with the first embodiment of the present invention.

When the master piston P1is moved forward to come in contact with the slave piston P2, the in-valve42may be opened, the out-valve43may be closed, and the motor may be driven to move the master piston P1forward by a preset distance, as illustrated inFIG. 8.

At this time, as the in-valve42is opened and the out-valve43is closed, brake oil may be additionally introduced from the master cylinder10.

FIG. 9is a diagram illustrating that the master piston is moved backward in a state where the in-valve is closed and the out-valve is opened, in the initialization method for an EMB in accordance with the first embodiment of the present invention.

When the master piston P1is moved by the preset distance after coming in contact with the slave piston P2, the in-valve42may be closed, the out-valve may be opened, and the motor may be driven to move the master piston P1backward, as illustrated inFIG. 9.

As the out-valve43is opened, brake oil which is additionally introduced from the master cylinder10may be transferred to the accumulator part80. Then, when the contact between the master piston P1and the slave piston P2is released as the master piston P1is moved backward, the control unit may determine whether the gap between the master piston P1and the slave piston P2is equal to or more than a preset gap. When the gap is equal to or more than the preset gap, the initialization may be ended.

At this time, since the brake oil transferred to the accumulator part80has pressure formed therein, the brake oil is free from the surface tension between the master piston P1and the slave piston P2, unlike the brake oil which is directly introduced from the master cylinder10.

Furthermore, in the initialization method for an EMB in accordance with the first embodiment of the present invention, the master piston P1and the slave piston P2may be forced to be moved even while brake oil is introduced from the master cylinder10. Thus, the EMB may be stably initialized because another behavior is unlikely to occur.

That is, as the gap between the master piston and the slave piston of the hEMB is secured through the initialization, the initialization method can sufficiently secure the degree of freedom for active control and the degree of freedom for pedal feel tuning as a BBW (Brake By Wire) system.

As described above, the initialization method for an EMB in accordance with the first embodiment of the present invention may secure a gap between the master piston and the slave piston in the hEMB which pressurizes the slave piston in contact with the inner pad using hydraulic pressure, using the pressure of the master piston which is driven by the motor, thereby maximizing the effect of the boosted hydraulic pressure in a braking section.

FIG. 10is a flowchart illustrating an initialization method for an EMB in accordance with a second embodiment of the present invention. Referring toFIG. 10, the initialization method for an EMB in accordance with the second embodiment of the present invention will be described as follows.

The initialization method S2for an EMB in accordance with the second embodiment of the present invention may include a contact determination step S110, a piston gap determination step S120, and a pad gap securing step S130.

At the contact determination step S110, the control unit may determine whether the master piston P1and the slave piston P2come in contact with each other before the brake pad600and the brake disk700come in contact with each other, when the master piston P1is moved forward.

FIG. 11is a conceptual view for describing the operation of the hEMB in the initialization method for an EMB in accordance with the second embodiment of the present invention.FIG. 12is a conceptual view illustrating that the master piston and the slave piston of the hEMB are moved forward in the initialization method for an EMB in accordance with the second embodiment of the present invention.

Referring toFIGS. 11 and 12, the motor530may be rotated to move the master piston P1forward, in a state where the in-valve42for controlling entry and exit of brake oil to and from the master cylinder10is closed and the out-valve43for controlling entry and exit of brake oil to and from the accumulator part80is closed, at steps S111and S112.

Since the master piston P1is moved forward in a state where the entry and exit of brake oil through the in-valve42and the out-valve43is not performed, the slave piston P2may be moved forward by the increase in pressure of the brake oil housed between the master piston P1and the slave piston P2.

Since the master piston P1has a smaller cross-sectional area than the slave piston P2, the moving distance of the master piston P1is larger than the moving distance of the slave piston P2.

FIG. 13is a diagram illustrating a state in which the brake pad and the brake disk are brought in contact with each other by the slave piston of the hEMB, in the initialization method for an EMB in accordance with the second embodiment of the present invention.

Referring toFIG. 13, when a gap between the master piston P1and the slave piston P2is secured, the movement of the master piston P1may be stopped as the brake pad600moving with the slave piston P2comes in contact with the brake disk700, before the master piston P1comes in contact with the slave piston P2.

FIG. 14is a conceptual view illustrating a state in which the master piston and the slave piston of the hEMB are brought in contact with each other while being moved forward, in the initialization method for an EMB in accordance with the second embodiment of the present invention.

Referring toFIG. 14, when a sufficient gap between the master piston P1and the slave piston P2is not secured, the master piston P1may come in contact with the slave piston P2before the brake pad600comes in contact with the brake disk700.

In the second embodiment of the present invention, when the pressure of a pressure sensor PS connected to the hydraulic pressure chamber corresponds to a preset pressure or more, the control unit may determine that the brake pad600and the brake disk700are brought in contact with each other, before the master piston P1is brought in contact with the slave piston P2.

That is, when the brake pad600attached to the slave piston P2comes in contact with the brake disk700as the master piston P1is moved forward, the movement of the slave piston P2may be limited.

When the master piston P1is moved forward in a state where the slave piston P2is not moved forward, the pressure of the brake oil as incompressible fluid may be increased. Thus, the control unit may determine whether the pressure measured through the pressure sensor PS is equal to or more than the preset pressure, and determine whether the brake pad600is brought in contact with the brake disk700as the master piston P1is moved forward, at step S113.

On the other hand, when the master piston P1and the slave piston P2are brought in contact with each other before the brake pad600comes in contact with the brake disk700, the pressure may not reach the preset pressure.

When the master piston P1and the slave piston P2are first brought in contact with each other while the slave piston P2is moved as the master piston P1is moved forward, the master piston P1and the slave piston P2may be moved at the same speed.

When the master piston P1having a smaller cross-sectional area than the inner cross-sectional area of the slave piston P2is moved at the same speed as the slave piston P2, the pressure may be reduced while the internal volume of the hydraulic pressure chamber containing brake oil expands.

Thus, depending on whether the value measured through the pressure sensor PS reached the preset value, the control unit may determine whether the master piston P1and the slave piston P2are brought in contact with each other as the master piston P1is moved forward.

In the second embodiment of the present invention, as a sufficient gap is secured between the master piston P1and the slave piston P2, the brake pad600may be brought in contact with the brake disk700so as to form a braking force, before the master piston P1comes in contact with the slave piston P2when being moved forward.

At the piston gap determination step S120, the control unit may determine whether a piston gap between the master piston P1and the slave piston P2corresponds to a first section.

When it is determined at the contact determination step S110that the brake pad600and the brake disk700were brought in contact with each other before the master piston P1and the slave piston P2were brought in contact with each other, the master piston P1may be moved forward in a state where the out-valve43is opened at step S121. In this state, the control unit may determine whether a moving distance required until the master piston P1comes in contact with the slave piston P2corresponds to the first section, at steps S122and S123.

FIG. 15is a conceptual view illustrating a state in which the master piston and the slave piston of the hEMB are brought in contact with each other, in the initialization method for an EMB in accordance with the second embodiment of the present invention.

Referring toFIG. 15, the master piston P1be moved forward in a state where the out-valve43is opened and the forward movement of the slave piston P2is limited by the brake pad600. Thus, as the master piston P1is moved forward, the brake oil may be transferred to the accumulator part80through the out-valve43.

The master piston P1may be moved forward to come in contact with the slave piston P2. The control unit may determine whether the master piston P1comes in contact with the slave piston P2, through a current sensor mounted on the motor530which moves the master piston P1.

When the pressure applied to the master piston P1is changed, the load applied to the motor530may be varied. Thus, the control unit may measure whether a current measured during operation of the motor530is equal to or more than a preset current, in order to determine whether the master piston P1came in contact with the slave piston P2.

Since the master piston P1is moved forward in a state where the slave piston P2is stopped, the moving distance of the master piston P1may correspond to the moving distance of the slave piston P2before the master piston P1is moved. The control unit may determine whether a value obtained by measuring the moving distance of the master piston P1corresponds to the first section.

The first section may indicate a gap required between the master piston P1and the slave piston P2in a state where the movement of the slave piston P2is limited by the contact between the brake pad600and the brake disk700, and correspond to a section which is previously set by considering brake oil, the device size, a braking force, abrasion of the brake pad600or the like.

FIG. 16is a conceptual view illustrating a state in which the master piston is moved backward in order to secure a gap between the master piston and the slave piston of the hEMB, in the initialization method for an EMB in accordance with the second embodiment of the present invention.

Referring toFIG. 16, when the master piston P1is moved backward in a state where the out-valve43is opened, the brake oil transferred to the accumulator part80may be introduced into the hydraulic pressure chamber.

In the second embodiment, the piston gap determination step S120may include an additional forward movement step and an oil injection step. At the additional forward movement step, when it is determined that the brake pad600and the brake disk700were brought in contact with each other after the master piston P1and the slave piston P2were brought in contact with each other, the master piston P1may be moved forward until the brake pad600and the brake disk700come in contact with each other in a state where the in-valve42is opened.

After the additional forward movement step, the state in which the master piston P1and the slave piston P2are brought in contact with each other may be switched to the state in which the brake pad600and the brake disk700are brought in contact with each other. Then, the brake oil may be injected to secure a gap between the master piston P1and the slave piston P2.

At the oil injection step, when the brake pad600and the brake disk700are brought in contact with each other through the additional forward movement step, the master piston P1may be moved backward by a distance corresponding to the first section while brake oil is injected through the in-valve42.

Specifically, at the oil injection step, the in-valve42and the normal closed valve35may be opened in a state where the out-valve43and the normal open valve33are closed, and the master piston P1may be moved forward while the motor pump90is operated to inject the brake oil of the master cylinder10into the hydraulic pressure chamber.

FIG. 17is a conceptual view illustrating a state in which the master piston and the slave piston of the hEMB are moved backward to secure a gap from the brake pad, in the initialization method for an EMB in accordance with the second embodiment of the present invention.

Referring toFIG. 17, when the moving distance of the master piston P1corresponds to the first section at the pad gap securing step S130, the master piston P1may be moved backward until the pad gap between the slave piston P2and the brake pad600corresponds to a second section. Then, the initialization of the hEMB50may be ended.

When the moving distance of the master piston P1corresponds to the first section, it may indicate that a sufficient gap is secured between the master piston P1and the slave piston P2. Thus, the master piston P1may be moved backward to introduce the brake oil leaking to the accumulator part80into the hydraulic pressure chamber in a state where the out-valve43is opened, at step S131.

When the brake oil is introduced into the hydraulic pressure chamber, the master piston P1may be moved backward after the out-valve43is closed. Since the master piston P1is moved backward in a state where the in-valve42and the out-valve43are closed, the slave piston P2may be moved backward in connection with the movement of the master piston P1, at step S132.

Based on the moving distance of the master piston P1and the ratio of the cross-sectional areas of the master piston P1and the slave piston P2, the moving distances of the slave piston P2and the brake pad600may be calculated. The master piston P1may be moved backward until the moving distance of the slave piston P2corresponds to less than the second section. Then, the initialization may be ended.

The initialization method for an EMB in accordance with the second embodiment of the present invention may secure a gap between the master piston P1and the slave piston P2in the hEMB50which pressurizes the slave piston P2brought in contact with the brake pad600using hydraulic pressure, using the pressure of the master piston P1driven by the motor530, thereby maximizing the effect of boosted hydraulic pressure in a braking section.

Furthermore, as the gap between the master piston and the slave piston of the hEMB is secured through the initialization, the initialization method can sufficiently secure the degree of freedom for active control and the degree of freedom for pedal feel tuning as a BBW (Brake By Wire) system.

Furthermore, the initialization method may complete the initialization operation for the EMB through one reciprocation of the master piston P1. Thus, the initialization process can be simply and rapidly performed.