Electric parking brake

Disclosed herein an electric parking brake includes a pair of pressing portions provided in a caliper housing to convert rotational motion into linear motion to press a brake pad; an actuator configured to transmit power to the pair of pressing portions; and a load control portion provided rotatably between the pair of pressing portions and the actuator, the load control portion applying a uniform load to the pair of pressing portions by pressing any one of the pair of pressing portions that generates a less load during braking operation.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based on and claims priority under 35 U.S.C. § 119 to Korean Patent Application No. 10-2021-0034007, filed on Mar. 16, 2021 in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The disclosure relates to an electric parking brake, and more particularly, to an electric parking brake in which a caliper brake having two pistons applies a uniform load to the two pistons by operation of a motor and realizes a parking function.

BACKGROUND

In general, a brake device is a device that stops a vehicle from moving during braking or parking, and serves to hold wheels of the vehicle from rotating.

Recently, an Electric Parking Brake (EPB) system for electrically controlling operation of a parking brake has been widely used. The EPB is mounted on a conventional caliper brake to perform a function of the parking brake. Electric caliper brakes include a cable puller type, a motor-on-caliper (MOC) type, and a hydraulic parking brake type.

For example, Korean Patent Publication No. 10-2011-0072877 (Jun. 29, 2011) relates to a MOC-type EPB. The document discloses a structure that a motor generating power is connected to an actuator, and the power generated from the motor is decelerated while increasing torque using a plurality of gears to cause a piston to press against brake pads, thereby performing a braking operation.

On the other hand, vehicles, such as a large truck, requiring a large braking force are provided with a plurality of pistons (usually two pistons are applied) to perform a braking operation.

However, when a plurality of pistons are provided and a driving force thereof is transmitted from a single actuator, the load is non-uniformly transmitted to the plurality of pistons due to a non-uniform initial position of the pistons, so that several problems occurs for example, uneven wear of brake pads due to asymmetry, uneven wear of gears, and overload of the motor. As a result, parking performance is deteriorated.

To solve the problems, the same number of actuators as the pistons are provided to transmit power to each of the plurality of pistons, but weight and cost are increased and the application is difficult due to a narrow installation space.

SUMMARY

An aspect of the disclosure is to provide an electric parking brake that applies a uniform load to a plurality of pistons through one actuator and implements a parking function.

In accordance with an aspect of the disclosure, an electric parking brake includes a pair of pressing portions provided in a caliper housing to convert rotational motion into linear motion to press a brake pad; an actuator configured to transmit power to the pair of pressing portions; and a load control portion provided rotatably between the pair of pressing portions and the actuator, the load control portion applying a uniform load to the pair of pressing portions by pressing any one of the pair of pressing portions that generates a less load during braking operation.

The caliper housing may include a pair of coupling parts protruding from the rear thereof, and the load control portion is provided between the pair of coupling parts rotatably based on a pin coupled to a center thereof, and opposite ends of the load control portion is provided to face the pair of pressing portions based on the center thereof.

A thrust bearing configured to support a load according to axial force may be provided on a rear of the pair of pressing portions, respectively, and the load control portion and the thrust bearing may be in curved surface contact with each other by means of a curved surface contacting means.

The curved surface contacting means may include a curved surface contacting protrusion protruding from a center portion of an outer surface of the thrust bearing to form a curved surface, and a curved surface contacting groove formed to be in contact with the curved surface contacting protrusion on the load control portion facing the curved surface contacting protrusion.

The pair of pressing portions may include a piston slidably inserted into a cylinder part of the caliper housing, and a power transmission including a spindle rotating by receiving driving force from the actuator within the cylinder part, and a nut connected to the spindle and provided on the inside of the piston to press the piston or release the pressure of the piston while moving forward or backward by forward and reverse rotation of the spindle.

A through-hole may be provided respectively at the opposite ends of the load control portion so that a part of the spindle passes through and is connected to the actuator.

The actuator may include a motor; a power connecting portion connected to a rotation shaft of the motor; and a reduction device connected to the power connecting portion to transmit rotational force of the motor to the pair of pressing portions, respectively.

The power connecting portion may include a power transmission shaft having a predetermined length and provided between the motor and the reduction device; a first helical gear coupled to the rotation shaft of the motor; a second helical gear provided on one end of the power transmission shaft and meshed with the first helical gear; a pair of worm shaft gears provided on the power transmission shaft and connected to the reduction device; and a bearing portion provided on the power transmission shaft to rotatably support the power transmission shaft.

The reduction device may include a worm wheel gear meshed with the pair of worm shaft gears; a sun gear coupled to a center of the worm wheel gear and rotating together as the worm wheel gear rotates; a plurality of planetary gears meshed with an outer side of the sun gear; a ring gear provided as an internal gear to accommodate the plurality of planetary gears; and a carrier supporting rotatably the plurality of planetary gears and installed to rotate coaxially with the sun gear to output rotational power.

DETAILED DESCRIPTION

FIG.1is a perspective view illustrating an electric parking brake according to an embodiment of the disclosure,FIG.2is a rear perspective view illustrating an electric parking brake according to an embodiment of the disclosure,FIG.3is a side cross-sectional view illustrating an electric parking brake according to an embodiment of the disclosure,FIG.4is an exploded perspective view illustrating a state in which a pair of pressing portions and a load control portion provided in an electric parking brake according to an embodiment of the disclosure are assembled,FIG.5is an assembled perspective view ofFIG.4,FIG.6is an exploded perspective view illustrating an actuator provided in an electric parking brake according to an embodiment of the disclosure, andFIG.7is a partially-cut perspective view illustrating a state in which a deceleration device of an actuator and a pair of pressing portions provided in an electric parking brake according to an embodiment of the disclosure are assembled.

Referring toFIGS.1to7, an electric parking brake (EPB)1according to an embodiment of the disclosure may include a pair of pressing portions200, an actuator300, and a load control portion400. Furthermore, the EPB1may further include a carrier (not shown) on which a pair of brake pads are installed to press a disc (not shown) rotating together with wheels of a vehicle, a caliper housing100slidably installed on the carrier to operate the pair of brake pads, and an electronic control unit (ECU) (not shown) for controlling operation of the actuator300. Herein, the pair of pressing portions200, the actuator300, and the load control portion400may be installed in the caliper housing100to implement a parking braking force.

The caliper housing100includes a pair of finger parts110bent downward on a front side (left side with reference toFIG.3) to operate the pair of brake pads that constituted of an outer brake pad and an inner brake pad, and a cylinder part120in which the pair of pressing portions200. The caliper housing is slidably fastened to the carrier. The cylinder part120and the finger part110are integrally formed. The pair of brake pads is pressed through a piston210provided in the cylinder part120and the finger part110of the caliper housing100to rub against the disc, thereby performing a braking operation. Since the configuration of the caliper brake is a well-known technologies, a detailed description thereof will be omitted.

On the other hand, a coupling part140for coupling with the load control portion400to be described later is provided on a rear side (right side with reference toFIG.3) of the caliper housing100. The coupling part140is provided as a pair, and the pair of coupling parts140are formed to be spaced apart from each other at regular interval in a vertical direction. The structure of installing the load control portion400on the coupling parts140will be described again below.

The pair of pressing portions200may be installed in the caliper housing100to receive power from the actuator300to convert a rotational motion into a linear motion. In other words, the pair of pressing portions200are provided to press the brake pads (refer to10inFIG.8) that generates contact friction with the disk (not shown) of the vehicle. The pair of pressing portions200may be arranged in parallel in the cylinder parts120. For example, the pair of pressing portions200are symmetrically arranged on left and right sides relative to a center part of the brake pad10. Accordingly, the pair of pressing portions200receives power from the actuator300and presses the brake pads10with the same pressure load to generate a parking braking force using friction between the brake pads10and the disc.

The pair of pressing portions200includes the piston210and a power transmission220, respectively. The pair of pressing portions200are provided to have the same configuration as each other, description will be made based on any one pressing portion.

The pressing portion200may include the piston210slidably inserted into the cylinder part120of the caliper housing100, and the power transmission220that receives a driving force from the actuator300to convert rotational motion into linear motion to press the piston210or release the pressed pressure of the piston210.

The power transmission220may include a spindle221that rotates by receiving a driving force within the cylinder part120, and a nut223that is connected to the spindle221and moves forward or backward by forward and reverse rotation of the spindle221, and a plurality of balls (not shown) interposed between the spindle221and the nut223. In this case, the nut223may be provided to limit rotation thereof inside the piston210. The power transmission220may be provided as a ball-screw type converter for converting a rotational motion of the spindle221into a linear motion.

The spindle221has a certain length, and a thread may be formed on an outer circumferential surface for coupling with the nut223. The nut223is coupled to one side (front side which is the left side based onFIG.3) of the spindle221, and the other side (rear side which is the right side based onFIG.3) thereof is connected to the actuator300to receive a driving force. For example, the other side of the spindle221may be coupled to a carrier335from which a driving force is output from an actuator300to be described later in a spline manner. Furthermore, the other side of the spindle221may be connected to the actuator300passing through the load control portion400to be described later.

The nut223may have a thread formed therein so as to mesh with the thread of the spindle221via a ball (not shown). The nut223may be provided inside the piston210in a state in which rotation thereof is restricted. Accordingly, the nut223moves linearly according to the forward and reverse rotation directions of the spindle221to press the piston or release the pressure of the piston210.

The actuator300may include a motor310, a reduction device330that is connected to the pair of pressing portions200to transmit rotational force of the motor310, and a power connecting portion320that connects a rotation shaft of the motor310and the reduction device330. Meanwhile, although not shown, the actuator300may be accommodated in an actuator housing and installed outside the rear of the caliper housing100or in the vehicle.

The motor310receives power by operating a switch (not shown) provided on a driver seat of the vehicle and converts electrical energy into mechanical rotational kinetic energy. The control of braking operation according to an operation signal of the switch may be performed by the ECU (not shown) of the vehicle.

The power connecting portion320directly connects the motor310and the reduction device330to transmit the rotational force of the motor310to the reduction device330. To this end, the power connecting portion320includes a power transmission shaft325which has a certain length and is provided between the motor310and the reduction device330, a first helical gear321coupled to a rotation shaft (not shown) of the motor310, a second helical gear322which is installed at one end of the power transmission shaft325and meshes with the first helical gear321, a worm shaft gear323which is installed on the power transmission shaft325to connect to the reduction device330, and a bearing portion324which is provided on the power transmission shaft325to rotatably support the power transmission shaft325. Herein, the bearing portion324is illustrated as being installed only at the other end of the power transmission shaft325, it is not limited thereto. In other words, the bearing portion324may be installed in a suitable position in a longitudinal direction of the power transmission shaft325so that the power transmission shaft325may rotate stably. Meanwhile, because a pair of reduction devices330to be described later is provided as a pair in order to connect to the pair of pressing portions200, respectively, the worm shaft gear323may also be provided as a pair. Accordingly, the pair of worm shaft gears323are provided to be spaced apart from each other by a certain interval so as not to interfere with the pair of reduction gears330when connected thereto.

The first helical gear321has a center coupled to the rotation shaft of the motor310to rotate, and the second helical gear322meshed with the first helical gear321rotates while changing the rotation direction thereof to a direction perpendicular to the rotation shaft of the motor310. Changing of the rotation direction using a helical gear may reduce noise considerably because meshing rate is better than that of a spur gear, and when gear ratio is adjusted, it may also be used as a deceleration function.

The reduction device330is connected to the power connecting portion320to transmit power to the pair of pressing portions200. Accordingly, the reduction device330may be provided as a pair in order to connect to the pair of pressing portions200, respectively. Since the pair of reduction devices330are provided to have substantially the same structure, the following description will be based on any one reduction device.

The reduction device330may include a worm wheel gear331meshed with the worm shaft gear323, a sun gear332rotating together with the worm wheel gear331, a plurality of planetary gears333meshed with an outer side of the sun gear332, a ring gear334formed as internal gears to accommodate the plurality of planetary gears333, and a carrier335that rotatably supports the plurality of planetary gears333and is installed to rotate coaxially with the sun gear332and outputs rotational power.

The worm wheel gear331is meshed with the worm shaft gear323to receive rotational force to rotate. The sun gear332is coupled to a center of the worm wheel gear331so that the sun gear332rotates together with the rotation of the worm wheel gear331.

The sun gear332may be coupled passing through the center of the worm wheel gear331. The sun gear332may have a body portion coupled to the worm wheel gear331, and a portion thereof where gear teeth are formed is exposed from the worm wheel gear331to be meshed with the plurality of planetary gears333. Preferably, when the sun gear332is coupled to the worm wheel gear331, the portion of the sun gear332where the gear teeth are formed may be provided to be positioned inside the ring gear334.

The plurality of planetary gears333are provided as three in consideration of efficiency and economic feasibility, and three planetary gears are respectively rotatably provided on branch shafts335ain three directions branched from the carrier335.

The ring gear334penetrates vertically, accommodates the plurality of planetary gears333thereinside, and having an internal gear is provided to mesh with the plurality of planetary gears333. The ring gear334may have a protrusion334aprotruding from an outer surface thereof to be fixed to the actuator housing (not shown). Accordingly, as the sun gear332rotates, the plurality of planetary gears333may rotate and revolve within the ring gear.

The carrier335may be made in the form of a disk, on one surface thereof are provided the plurality of planetary gear branch shafts335aspaced apart from each other by a certain interval along a circumferential direction, and the center thereof may be an output hole335bcoupled to the spindle221of the pressing portion200. In this case, the output hole335bis formed coaxially with the sun gear332.

Meanwhile, the output hole335bmay be splined with the spindle221in order to transmit rotational force to the spindle221, or may be coupled to mesh with the spindle221through gear teeth. Accordingly, as the carrier335rotates, the spindle221may rotate together therewith.

The load control portion400is rotatably installed between the pair of pressing portions200and the actuator300and is provided to apply a uniform load to the pistons210respectively provided in the pair of pressing portions200by pressing the pressing portion200on the side that generates a less load during braking operation. More specifically, the load control portion400has a predetermined length and may be rotatably coupled to the caliper housing100. As shown in drawings, at the rear of the caliper housing100, the pair of coupling parts140spaced apart from each other in the vertical direction and protruded are provided. The load control portion400is provided between the pair of coupling parts140rotatably based on a pin410coupled to a center of the load control portion. The pin410passes through the pair of coupling parts140. Furthermore, opposite ends of the load control portion400coupled to the caliper housing100are provided to face the pair of pressing portions200.

Meanwhile, because the load control portion400is provided between the pair of pressing portions200and the actuator300, through-holes420may be formed on opposite sides of the load control portion400so that the driving force generated from the actuator300is transmitted to the pair of pressing portions200. In other words, a part of the spindle221passes through the through-hole420and is connected to the actuator300to receive a rotational force.

According to the disclosure, a thrust bearing500may be provided between the rear of the pair of pressing portions200and the load control portion400in order to apply a uniform load to the pistons210of the pair of pressing portions200. Herein, the thrust bearing500serves to support an axial force generated during the braking operation. The thrust bearing500may be provided to be in curved contact with the load control portion400by means of a curved surface contacting means. As shown in drawings, a washer510provided on one side of the thrust bearing500opposite to the load control portion400and the load control portion400are shown to be in curved contact with each other as the curved surface contacting means, but are not limited thereto. Also, they may be provided to be in directly curved contact with the thrust bearing500.

The curved surface contacting means includes a curved surface contacting protrusion530protruding from a center portion of one side surface of the washer510of the thrust bearing500to form a curved surface, and a curved surface contacting groove430formed to be in contact with the curved surface contacting protrusion530on the load control portion400facing the curved surface contacting protrusion530. As shown in drawings, the curved surface contacting protrusion530is formed on a perimeter of a central hole through which the spindle221, and the curved surface contacting groove430is formed on an inlet side of the through-hole420of the load control portion400. Accordingly, when rotating around the pin410, the load control portion400may be rotated at a predetermined angle while in smooth contact with the curved surface contacting means, and the piston of the pressing portion200on the side pressed by the load control portion400may be rapidly moved.

Hereinafter, an operation of the EPB1according to an embodiment of the disclosure will be described.

FIG.8is a schematic view illustrating a state in which a uniform load is generated in the pair of pressing portions when the EPB according to an embodiment of the disclosure is operated.

Referring toFIGS.1to8, when a driver operates the parking brake after stopping the vehicle, the motor310is driven so that the first helical gear321coupled to the rotation shaft of the motor310rotates together, and thus the second helical gear322meshed with the first helical gear321is rotated.

As the power transmission shaft325rotates together with the second helical gear322, the pair of worm shaft gears323provided on the power transmission shaft325rotate together. Next, as the worm wheel gear331meshed with the worm shaft gear323rotates, the rotational force is output to the spindle221through the carrier335of the reduction device330.

As the spindle221rotates by receiving the rotational force through the carrier335, the nut223moves in an axial direction, and the nut223presses the piston210, thereby performing parking braking operation.

After the parking braking operation, the motor310is stopped, and the rotation of the spindle221is prevented by the reduction device330and the power connecting portion320having a large reduction ratio. Accordingly, a braking state is maintained as long as the motor310is not driven again.

As such, because the pair of pressing portions200receive power through the actuator300and generate a parking braking force through the same driving, the same load is applied to the piston210as indicated by the arrow F1, thereby performing stable braking operation.

When releasing a parking braking force, the driver release the braking by manipulating a parking switch on the driver seat. At this time, because the motor310rotates in a reverse direction of the rotational direction when parking and the spindle221rotates in the reverse direction of the rotational direction when parking, the nut223releases the pressure of the piston210to release the braking.

On the other hand, when the pair of pressing portions200press the brake pads10through the piston210with the same force, but an initial position of the piston210may be non-uniform due to installation errors. As a result, the load is non-uniformly transmitted to the pair of pistons210, so uneven wear of the brake pads10, uneven wear of the gear, and overload of the motor310occur due to asymmetry. These problems may address by allowing a uniform load to be generated in the pair of pressing portions200by the load control portion400according to an embodiment of the disclosure.

FIG.9is a schematic view illustrating a state in which different loads are generated in the pair of pressing portions to cause a load control portion to be operated when the EPB according to an embodiment of the disclosure is operated.

Referring toFIG.9, It has been shown that a load is generated in any one of the pair of pressing portions200(right side based onFIG.9) in the direction of the arrow F1, and a load is generated in the other pressing portion200(left side based onFIG.9) in the direction of the arrow F2. At this time, the load of the arrow F1is provided to receive a greater load than that of the arrow F2. In other words, because the initial positions of the pistons210provided in the pair of pressing portions200are non-uniform, respectively, the pressing portion200on the right side presses the brake pad10first, thereby receiving a greater load than pressing portion200on the left side. In this case, the load control portion400is rotated toward the pressing portion200on the left side where a low load is generated.

More specifically, as the pressing portion200on the right side receives power, the nut223moves and presses the piston210, so that the load is first generated compared to the pressing portion200on the left side. Accordingly, an axial force is generated in the thrust bearing500by the load generated in the pressing portion200on the right side, and thus the load control portion400at the rear of the thrust bearing500is pressed in the axial force direction.

The load control portion400rotates around the pin410coupled to the center thereof and presses the thrust bearing500provided on the left side. At this time, the load control portion400may be in contact with the washer510of the thrust bearing500via the curved surface contacting means, thereby rotating smoothly with respect to the center thereof.

As a result, the pressing portion200on the left side may press the brake pad10by rapidly moving the piston210through pressing by the rotation of the load control portion400. Accordingly, even if a non-uniform load is generated in the pair of pressing portions200, a uniform load is applied through the load control portion400to solve the problems, such as uneven wear of the brake pad, uneven wear of the gear, and overload of the motor. Furthermore, it is possible to generate a stable parking braking force.

As is apparent from the above, the EPB according to an embodiment of the disclosure may transmit the pressed load that is biased to any one of the pair of pressing portions through the load control portions to the other pressing portion, thereby applying a uniform load to the pair of pressing portions and realizing the parking function.

Furthermore, the EPB according to an embodiment of the disclosure may apply the same load to the pair of pressing portions (pistons) through one actuator, thereby reducing manufacturing cost and weight compared to the conventional EPB and improving design freedom.

As described above, the exemplary embodiments of the disclosure have thus far been described with reference to accompanying drawings. It will be obvious to those of ordinary skill in the art that the disclosure may be practiced in other forms than the exemplary embodiments as described above without changing the technical idea or essential features of the disclosure. The above exemplary embodiments are only by way of example, and should not be interpreted in a limited sense.