MASTER CYLINDER FOR A BRAKE SYSTEM

Abstract

A master cylinder for a brake system is disclosed. The master cylinder includes a cylinder body having a bore therein; at least one piston provided in the bore to be moved forward and backward; a fluid pressure chamber compressed by the piston; a brake fluid passage port connected to a reservoir and configured to supply brake fluid to the fluid pressure chamber; and a brake fluid drain port for draining the brake fluid in the fluid pressure chamber to a wheel brake of a wheel. A valve unit including a check valve for controlling orRegulating the unidirectional flow of the brake fluid introduced from the reservoir to the fluid chamber and having a fluid resistance hole opened in two directions and smaller than the size of the brake fluid drain hole is provided in the brake fluid passage hole.

Description

CROSS-REFERENCE TO A RELATED PATENT APPLICATION

[0001] This application claims priority to and the benefit under 35 USC §119(a) of Korean Patent Application No. 10-2014-0143899, filed on October 23, 2014, which is hereby incorporated by reference for all purposes as if fully set forth herein. BACKGROUND OF THE INVENTION 1. Field of the Invention

[0002] The present invention relates to a master cylinder for a brake system, and more particularly to a master cylinder for a brake system capable of improving a braking feel. 2. Description of the state of the art

[0003] In a vehicle's hydraulic braking system, a master cylinder is a device that generates hydraulic pressure according to the driver's pedal operation and sends the hydraulic pressure needed to the brakes installed on the vehicle's wheels to perform the braking operation.

[0004] Fig. Figure 1 illustrates a general tandem-type master cylinder. Referring to the drawing, the master cylinder includes a first piston 3 and a second piston 4 installed in series within a bore 2 of a cylinder body 1 for forward and backward movement. The interior of the bore 2 is divided into a first fluid pressure chamber 5 and a second fluid pressure chamber 6 by the first piston 3 and the second piston 4.

[0005] According to the master cylinder, the first piston compresses the brake fluid in the first fluid pressure chamber 5 while being moved forward in the direction of an arrow by the driver's pedal operation, the pressure of the brake fluid in the first fluid pressure chamber 5 pushes the second piston 4, and the second piston 4 compresses the brake fluid in the second fluid pressure chamber 6. The brake fluid in the first fluid pressure chamber 5 is supplied to one wheel brake for braking two wheels through the first brake fluid drain port 7, and the brake fluid in the second fluid pressure chamber 6 is supplied to one wheel brake for braking the other two wheels through the second brake fluid drain port 8.

[0006] The master cylinder has a brake fluid passage 9 connected to a reservoir R provided above the cylinder body 1, in which the brake fluid is stored to supply the brake fluid to the fluid pressure chambers 5 and 6. Since the brake fluid passage 9 simply serves as a channel for the brake fluid between the master cylinder and the reservoir, it cannot effectively control the flow of the brake fluid according to the pressure of the fluid pressure chambers, which is necessary when immediate braking is required.

[0007] The pressure of the fluid pressure chambers 5 and 6 should be increased, for example, by closing the brake fluid passage opening 9 while the piston is moved forward to perform a braking operation, and because the brake fluid in the fluid pressure chamber is substantially discharged to the reservoir so that the fluid pressure chamber is not sealed in the piston moving section from an initial standby position to a position where the brake fluid passage opening 9 can be closed, no braking operation is performed in the section.

[0008] The section where no braking can be performed is called free travel. Free travel is provided to prevent a phenomenon in which braking pressure is generated without consideration of the driver's intention when a brake caliper plate is moved backward or peripheral temperature rises. For example, resistance due to abnormal expansion of the fluid in the fluid pressure chamber. [Previous technical documents][Patent documents]

[0009] (Patent Document 1) Korean Patent Application Publication No. 2008-0088053 (October 2, 2008)

[0010] US 6,014,862 A describes a brake system with a pedal feel emulator and a master cylinder with a damping mechanism including a damping piston. When the emulator piston is moved from the rest position, fluid is displaced from the emulator through a compensating orifice and through a flow-restricting orifice in the damping piston to the reservoir. OVERVIEW OF THE INVENTION

[0011] A master cylinder for a braking system in accordance with an embodiment of the present invention reduces free travel to allow immediate braking.

[0012] A master cylinder for a brake system in accordance with an embodiment of the present invention also prevents a brake pressure from being generated without taking the driver's intention into account.

[0013] In accordance with the present invention, there is provided a master cylinder for a braking system having the features defined in independent claim 1.

[0014] Advantageous further training results from the dependent subclaims.

[0015] According to a master cylinder for a brake system in accordance with an embodiment of the present invention, a free stroke can be reduced and a braking response can be improved by instantly increasing the initial amount of fluid during a braking operation of a first fluid pressure chamber and a second fluid pressure chamber by installing a valve unit having a fluid resistance hole in a brake fluid passage port.

[0016] Furthermore, according to a master cylinder for a brake system in accordance with an embodiment of the present invention, it can be effectively prevented from generating a brake pressure without considering the driver's intention by installing a valve unit having a fluid resistance hole in a brake fluid passage port, and thus preventing the brake fluid of the fluid pressure chamber from being abnormally expanded. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings, in which: Fig. 1 is a sectional view illustrating a master cylinder for a brake system in accordance with the prior art; Fig. 2 is a sectional view illustrating a master cylinder for a brake system having a valve unit in accordance with an embodiment of the present invention; Fig. 3 is an exploded perspective view illustrating a check valve of a master cylinder for a brake system in accordance with an embodiment of the present invention; Fig. 4 is a graph for explaining the diameters of a fluid resistance hole of the master cylinder for a brake system and an effect thereof in accordance with an embodiment of the present invention; and Fig. 5 is a graph for explaining the number of fluid resistance holes of the master cylinder for a brake system and an effect thereof in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0018] In the following, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. Before the description, it should be noted that the terms or words used in the specifications and claims should not be limited to being interpreted as a common or dictionary definition, but rather should be interpreted to be consistent with the technical ideas of the present invention, based on the principle that the inventors can appropriately define the terms used in the specification to best describe their invention.Accordingly, it should be understood that the embodiments described in the specification and the configurations disclosed in the drawings are merely examples and do not represent all technical ideas of the invention, and that various modifications and variations can be made to the invention and equivalents thereof at the time of invention.

[0019] Fig. 2 is a view illustrating a master cylinder for a brake system in accordance with an embodiment of the present invention

[0020] With reference to Fig. 2, the master cylinder for a brake system in accordance with an embodiment of the present invention includes a cylinder body 10 having a bore 11, and first and second pistons 20 and 30 installed in the bore 11 of the cylinder body 10 so as to be moved forward and backward.

[0021] The cylinder body 10 has a first fluid pressure chamber 12 formed between the first piston 20 and the second piston 30, and a second fluid pressure chamber 14 formed between the second piston 30 and an inner surface of a distal end of the bore 11.

[0022] First and second brake fluid passages 16 and 18, connected to a reservoir R, are provided at an upper portion of the cylinder body 10. The first and second brake fluid passages 16 and 18 communicate with the first and second fluid pressure chambers 12 and 14, and are formed between a seal member 17 and a packing member 19.

[0023] The sealing member 17 and the sleeve member 19 are provided to seal the interior of the cylinder body 10 and the exterior of the first and second pistons 20 and 30, to prevent brake fluid from leaking between the inner peripheral surface of the bore 11 and the first and second pistons 20 and 30, and to form a high fluid pressure. The sealing member 17 and the sleeve member 19 are installed in receiving grooves formed on the inner surface of the bore 11 so that they are not moved even when the first and second pistons 20 and 30 are moved forward and backward.

[0024] A first brake fluid drain hole 13 is formed at a portion of the inner side of the cylinder body 10 close to the first fluid chamber 12, and a second brake fluid drain port 15 is formed at a portion of the inner side of the cylinder body 10 close to the second fluid pressure chamber 14, so that the brake fluid in the first and second fluid pressure chambers 12 and 14 is drained when the first and second fluid pressure chambers 12 and 14 are pressurized by the first and second pistons 20 and 30. The brake fluid in the first and second fluid pressure chambers 12 and 14 is drained through the first and second brake fluid drain ports 13 and 15 and is supplied to the wheel brakes (not illustrated) of the wheels.

[0025] Meanwhile, the first and second pistons 20 and 30 are installed in the bore 11 to be moved forward and backward to generate brake hydraulic pressure in the first and second fluid pressure chambers 12 and 14. Although the first piston 20 and the second piston 30 are arranged in series in the embodiment of the present invention, they can also be arranged in parallel through appropriate modifications and corrections by those skilled in the art.

[0026] The first and second pistons 20 and 30 are moved forward and backward in the bore 11 of the cylinder body 10. For example, the first and second pistons 20 and 30 are moved forward (toward the left side of the drawing) in the bore 11 of the cylinder body 10 to increase the pressures of the first and second fluid pressure chambers 12 and 14 and to generate brake hydraulic pressure during braking, and they are moved backward (toward the right side of the drawing) in the bore 11 of the cylinder body 10 when the braking is released.

[0027] A plurality of communication channels 22 and 32 connecting the inner and outer surfaces of the first and second pistons 20 and 30 are formed in the first and second pistons 20 and 30 so that the brake fluid in the reservoir can be introduced into the first and second fluid pressure chambers 12 and 14 through the first and second brake fluid passages 16 and 18. The communication channels 22 and 32 are opened when the first and second pistons 20 and 30 are moved backward so that the brake fluid in the first and second fluid pressure chambers 12 and 14 can be replenished, and they are closed when the first and second pistons 20 and 30 are moved forward so that the first and second fluid pressure chambers 12 and 14 can be compressed by the first and second pistons 20 and 30.

[0028] First and second return springs 23 and 33, which return the first and second pistons 20 and 30 to the original positions in the first fluid pressure chamber 12 and the second fluid pressure chamber 14 after completion of the braking operation, are provided on the front side of the first and second pistons 20 and 30. The first and second pistons 20 and 30 each have spring receiving recesses 24 and 34 for receiving the first and second return springs 23 and 33 therein to reduce the overall length of the master cylinder.

[0029] First and second supports 26 and 36 protrude from the spring receiving recesses 23 and 34 of the first and second pistons 20 and 30 such that first and second retainers 25 and 35, which support the first and second return springs 23 and 33, can be installed. The first and second retainers 25 and 35, which respectively support the first and second return springs 23 and 33, are attached to the first and second supports 26 and 36 so that they can be moved forward and backward. Reference numerals 27 and 37 denote step rings for preventing the retainers 25 and 36 from being separated from the first and second supports 26 and 36. Due to the step rings 27 and 37, the ends of the first and second return springs 23 and 33 are supported by the inner sides of the spring receiving recesses 24 and 34, and the opposite ends thereof are supported by the flange-type ends of the retainers 25 and 35.

[0030] In the meantime, in the brake fluid passage opening 16, which is in Fig. 2 is illustrated in an enlargement, the reference numeral 28 denotes a seal for preventing the brake fluid from leaking between the reservoir (not illustrated) and the master cylinder, which are coupled to each other through the brake fluid passage opening 16.

[0031] In accordance with an embodiment of the present invention, the first brake fluid passage port 16 (the same applies to the second brake fluid passage port 18) is provided with a valve unit 40 having a check valve 41 and a fluid resistance hole 48 to effectively control the bidirectional flows of the brake fluid during a braking operation or when the braking operation is released.

[0032] The check valve 41 is closed in an initial phase of braking, and it opens when the pistons 21 and 22 return to their original positions after the braking is released. The check valve 41 is closed in an initial phase of braking because an amount of brake fluid transferred to a wheel brake (not illustrated) can be instantly increased by discharging the brake fluid in the first and second fluid pressure chambers 12 and 14 through the first and second brake fluid discharge ports 13 and 15 in an initial phase of braking. By increasing the amount of brake fluid in an initial phase of braking, a braking response speed and a braking feel can be improved.

[0033] The check valve 41 is described with reference to the enlarged views of Fig. 2 and Fig. 3 will be described in more detail. Furthermore, since the valve units 40 are installed in the first brake fluid passage 16 and the second brake fluid passage 18 in the same manner, the first brake fluid passage 16 will be described below as an example.

[0034] The check valve 41 is installed in the first brake fluid passage 16 and is selectively opened and closed from the reservoir (not illustrated) to the fluid pressure chambers 16 and 18 to control the flow of the brake fluid.

[0035] The check valve 41 includes a valve housing 42 having a communication hole 42a in the center thereof, a valve body 43 having a dome shape for opening and closing the communication hole 42a on a lower side thereof, a valve spring 44 for supporting the valve body 43 to press the valve body 43 toward the communication hole 42a so as to close a channel, and a valve seat 45 coupled to the valve housing 42 while supporting the valve spring 44.

[0036] The check valve 41 having the above-mentioned configuration can be assembled as a single product, and accordingly, the finally assembled check valve 41 can be easily installed in the brake fluid passageway while interposing an elastic member 46 between the check valve 41 and the brake fluid passageway. That is, a circumferential groove is formed on the outer peripheral surface of the valve body, and an annular elastic member can be coupled to the groove and installed in the brake fluid passageway.

[0037] Meanwhile, the valve housing 42 has one or more fluid resistance holes 48 provided around the communication hole 42a. The fluid resistance holes 48 prevent brake pressure from being generated due to the brake pressure being generated without considering the driver's intention in accordance with a backward movement of a brake caliper plate and / or a rise in peripheral temperature, for example, without considering the driver's braking intention as a result of abnormal expansion of the brake fluid in the fluid pressure chamber.

[0038] The fluid resistance holes 48 have a polygonal or circular cross section and are smaller than the brake fluid drain port 13 provided in the fluid pressure chamber 12. Since the amount of brake fluid drained through the brake fluid drain port 13 to generate braking pressure is reduced due to the brake fluid being drained from the fluid pressure chamber 12 to the reservoir through the fluid resistance holes 48, when the size of the fluid resistance holes 48 is equal to or larger than the size of the brake fluid drain port 13, a free travel is not reduced, but rather a time in which a suitable pressure necessary for braking can be achieved is lengthened.In contrast, a necessary appropriate pressure can be reached more quickly because the amount of brake fluid discharged to the brake fluid discharge port 13 in a unit area increases due to a reduction in the amount of brake fluid discharged through the fluid resistance holes 48 when the size of the fluid resistance holes 48 is smaller than the size of the brake fluid discharge port 13.

[0039] Here, although it has been exemplified in the embodiment of the present invention that the size of the fluid resistance holes 48 is smaller than the size of the brake fluid drain port 13 so that a larger amount of the brake fluid can be drained through the brake fluid drain port 13 of the brake fluid drain port 13 and the fluid resistance holes 48 through which the brake fluid is drained from the fluid pressure chamber, the present invention is not limited to this, but the same effect can be achieved, for example, by installing porous filters in the fluid resistance holes 48 even if the size of the fluid resistance holes 48 becomes larger to make the speed of the brake fluid traveling through the fluid resistance holes lower than the speed of the brake fluid drained through the brake fluid drain port.

[0040] The diameter of the fluid resistance holes 48 is 0.1 mm to 0.7 mm, and a plurality of fluid resistance holes 48 are properly arranged with respect to the communication hole 42a of the valve body 43.

[0041] Fig. Figure 3 is a graph illustrating an input distance (a movement distance of a brake pedal) required to achieve a predetermined braking pressure corresponding to the diameter of the fluid resistance holes. The line in the graph represents that the brake pedal is moved by approximately 1 mm to achieve a braking pressure of 1 kgf / cm. 2 and it is assumed in the embodiment of the present invention that the above condition corresponds to an ideal brake pressure response.

[0042] L1 corresponds to a case where the diameter of the fluid resistance holes 48 is 0.1 mm, and the brake pedal is moved by 1.05 mm to achieve a braking pressure of 1 kgf / cm2 L2 corresponds to a case where the diameter of the fluid resistance holes 48 is 0.5 mm, and the brake pedal is moved by 1.55 mm to produce a braking pressure of 1 kgf / cm 2 L3 corresponds to a case where the diameter of the fluid resistance holes 48 is 0.7 mm, and the brake pedal is moved by 2.95 mm to produce a brake pressure of 1 kgf / cm 2 L4 corresponds to a φ25.4-M / CYL master cylinder that does not have a fluid resistance hole 48 in the brake passage 16 and is currently mass-produced and mounted in a vehicle, and the brake pedal is moved by 3.7 mm or more to produce a braking pressure of 1 kgf / cm 2 to spend.

[0043] A line close to an ideal line can be obtained when the diameter of the fluid resistance holes 48 is less than 0.1 mm, but a resistance phenomenon in which braking force is generated without considering the driver's intention may occur, as in the case without a fluid resistance hole. In contrast, when the diameter of the fluid resistance holes exceeds 0.7 mm, there is almost no difference from L4 corresponding to a mass-produced product, but rather at a time required for generating braking pressure; that is, a free travel portion is increased due to the brake fluid being discharged to the reservoir through the fluid resistance holes during a free travel.

[0044] Fig. 5 is a graph illustrating an input distance (a moving distance of a brake pedal) necessary to achieve a predetermined braking pressure according to the number of fluid resistance holes.

[0045] In the graph, an ideal line for a predetermined brake pressure response is not indicated, where H1 corresponds to a case where the number of fluid resistance holes 48 is one, H2 corresponds to a case where the number of fluid resistance holes 48 is two, H3 corresponds to a case where the number of fluid resistance holes 48 is three, and H4 corresponds to a mass-production type master cylinder having no fluid resistance hole.

[0046] As illustrated, when one to three fluid resistance holes 48 having a diameter of 0.1 mm to 0.7 mm are provided in the brake fluid passage opening, resistance can be prevented and a free travel portion can be effectively reduced. Meanwhile, because a single fluid resistance hole 48 may be blocked by foreign matter contained in the brake fluid, two or three fluid resistance holes 48 are preferable. In contrast, there is almost no difference from H4 corresponding to a mass-produced product when the number of fluid resistance holes 48 exceeds three, but rather at a time necessary for forming a brake pressure; that is, a free travel portion increases due to the brake fluid being discharged to the reservoir through the fluid resistance holes during a free travel, as in the case of Fig. 4.

[0047] The following describes an operation of the master cylinder for a brake system having the valve unit described above.

[0048] Generally, braking is not generated immediately after pedal power is applied to a brake pedal (not illustrated), but rather, this braking is initiated only after the brake pedal has been advanced a certain amount. That is, a section from the point where the brake pedal is started to the point where braking starts is called a lost travel section (hereinafter referred to as an LT (Lost Travel) section), and the driver experiences a much better braking feel as the LT section becomes shorter.In the embodiment of the present invention, the LT portion can be reduced and the braking feel can be improved by preventing resistance irrelevant to the driver's intention by using the fluid resistance holes 48 of the valve unit and by improving the initial amount of brake fluid discharged through the brake fluid discharge port 13.

[0049] Specifically, in the braking operation, first, the first piston 20 is pushed and advanced by an initial braking operation to compress the first fluid pressure chamber 12, and the second fluid pressure chamber 14 is compressed, while the second piston 30 is pushed and advanced by the pressure with which the first fluid pressure chamber 12 is compressed. Then, the brake fluid in the first fluid pressure chamber 12 is supplied to the front and rear wheel brakes through the first brake fluid discharge port 13 by the pressure with which the first piston 20 is pushed, and the brake fluid in the second fluid pressure chamber 14 is supplied to the front and rear wheel brakes through the second brake fluid discharge port 15 by the pressure with which the second piston 20 is pushed.

[0050] In the meantime, because the brake fluid (about 0.3 cm 3 up to 0.5 cm 3), which increases through the fluid resistance holes 48 in accordance with the embodiment of the present invention, is added to the brake fluid discharged from the first and second fluid pressure chambers 12 and 14 and to the brake fluid discharge ports 13 and 15 in the initial stage of braking and supplied to the wheel brakes, the brake hydraulic pressure in the initial stage of braking increases to reduce the LT portion.

[0051] Thereafter, for example, when the communication channels 22 and 32 pass the seal member 17 after the LT section in which the first and second pistons 20 and 20 are further moved by a predetermined distance, the master cylinder performs its original function. That is, when the first and second pistons 20 and 30 are moved forward (moved to the left side) and the communication channels 22 and 32 of the first and second pistons 20 and 30 pass the seal member 17, the first and second fluid pressure chambers 12 and 14 are sealed, and the internal pressure of the fluid pressure chambers 12 and 14 increases.Then, because the first and second pistons 20 and 30 are continuously moved forward, the brake fluid in the first and second fluid pressure chambers 12 and 14 is moved to the reservoir through the fluid resistance holes 48 of the first and second brake fluid passage ports 16 and 18 to release the pressure of the reservoir, and is supplied to the wheel brakes of the wheels through the first and second brake fluid discharge ports 13 and 15 to perform a braking operation.

[0052] When the braking operation is released, the first and second pistons 20 and 30 are pushed backward by the elastic forces of the first return spring 23 and the second return spring 33 and return to the original state.

[0053] Specifically, upon actuation of the check valve 41, the valve body 43 is opened with respect to the valve housing 41, while the interiors of the first and second fluid pressure chambers 12 and 14 are placed under vacuum when the braking operation is released, so that the brake fluid in the reservoir is supplied to the fluid pressure chambers 12 and 14 through the first and second brake fluid passage holes 16 and 18. It is impossible to fill the fluid pressure chamber 12 with a sufficient amount of brake fluid required for a secondary braking operation for a short time with only the fluid resistance holes 48 without the check valve 41. After the braking operation is released, the remaining brake fluid of the brake fluid that has been replenished into the fluid pressure chambers 12 and 14 can return to the reservoir through the fluid resistance hole 48.When the brake fluid in the fluid pressure chambers 12 and 14 is fully replenished, the first and second pistons 20 and 30 normally return to the original positions and the check valve 41 is closed.

Claims

[1] Master cylinder for a braking system, comprising: a cylinder body (10) having a bore (11) therein; at least one piston (20, 30) provided in the bore (11) to be moved forward and backward; a fluid pressure chamber (12,14) compressed by the piston (20,30); a brake fluid passage opening (16, 18) connected to a reservoir (R) and configured to supply a brake fluid to the fluid pressure chamber (12, 14); and a brake fluid drain opening (13, 15) for draining the brake fluid in the fluid pressure chamber (12, 14) to a wheel brake of a wheel, wherein a valve unit (40) having a check valve (41) for controlling one-way flows of the brake fluid introduced from the reservoir (R) to the fluid chamber, and a fluid resistance hole (48) open in two directions and having a size which is smaller than the size of the brake fluid drain opening (13, 15) is provided in the brake fluid passage opening (16, 18); wherein two or three fluid resistance holes (48) are provided. [2] A master cylinder according to claim 1, wherein the cross-sectional shape of the fluid resistance hole (48) is polygonal. [3] A master cylinder according to claim 1, wherein the cross-sectional shape of the fluid resistance hole (48) is circular and the diameter thereof is 0.1 mm to 0.7 mm. [4] Master cylinder according to claim 1, wherein the check valve (41) comprises: a valve housing (42) having a communication hole (42a) in the center thereof; a valve body (43) raised on a lower side of the communication hole (42a) and configured to open and close the communication hole (42a); a valve spring (44) supporting the valve body (43) and configured to close the communication hole (42a) by pressing the valve body (43) toward the communication hole (42a); and a valve seat (45) coupled to the valve housing (42) while supporting the valve spring (44), and wherein the fluid resistance hole (48) is provided around the communication hole (42a) of the valve housing (42). [5] A master cylinder according to claim 4, wherein a circumferential groove is formed on the outer peripheral surface of the valve housing (42) and an annular elastic member is coupled to the groove. [6] A master cylinder according to claim 4, wherein two or three fluid resistance holes (48) are provided so as to be circumferentially spaced from each other around the communication hole (42a) of the valve housing (42). [7] A master cylinder according to claim 1, wherein the fluid resistance hole (48) is smaller than the brake fluid drain hole (13, 15). [8] A master cylinder according to claim 1, wherein the fluid resistance hole (48) comprises a porous filter for reducing the fluid velocity of the brake fluid discharged through the brake fluid discharge port (13, 15) during a braking operation.

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