Patent Description:
In a hydraulic vehicle brake system, a piston pump is used for service braking, and/or slip adjustment. The piston pump generates brake pressure for delivering delivery brake fluid from a wheel brake to the wheel brake after the pressure drops, to increase the wheel brake pressure again, or for delivering the brake fluid in a direction of a main brake cylinder during slip adjustment. However, after the piston pump completes previous movement, a position at which a piston stops is difficult to determine. Therefore, when next braking is required, a braking operation is performed from a position at which the piston stops currently, which cannot ensure that the brake pressure generated by the piston pump reaches an expected effect, so that driving safety is affected.

Document <CIT> discloses a pressure generator for a hydraulic vehicle brake system including a piston-cylinder unit, a piston, a ball screw drive configured to move the piston, an electric hollow-shaft motor that surrounds and is configured to drive the ball screw drive, and a planetary gear set configured to transmit a rotational movement of the hollow-shaft motor to the ball screw drive. The generator also includes a flange part, a sleeve, and an axial needle-roller bearing. The flange part has a tubular collar configured to axially guide the piston in a movable fashion therein. The sleeve has a flange configured as a counterbearing which is attached to an interior of the tubular collar, and is further configured to support the bearing. The bearing is configured to rotatably mount and axially support the ball screw drive.

Document <CIT> discloses a hydraulics block having a piston-cylinder unit that can be driven by an electric motor via a gear in order to generate a brake pressure for a hydraulic non-muscular-energy vehicle brake system. An annular cavity is provided which encloses a piston of the piston-cylinder unit inside a cylinder, as a leakage chamber which communicates with a reservoir. Possible drag leakage is carried away in this manner. An end shield situated between the electric motor and the gear prevents lubricant or leakage from entering the electric motor.

Document <CIT> discloses a piston pump assembly for a hydraulic vehicle brake system having an electric motor and, coaxially to that, a planetary gear, a ball-screw drive and a piston-cylinder unit, in which a piston is connected in a rotatably and axially fixed manner to a spindle of the ball-screw drive and guiding the piston in a rotatably fixed manner in the cylinder, so that the spindle is retained in a rotatably fixed manner. Also, the planetary gear is mounted in a pot-shaped planetary-gear housing that is disposed on a ball bearing which is used for a rotational mounting of a spindle nut on a cylinder of the piston-cylinder unit.

This application aims to resolve at least one of the foregoing problems, and provides a piston pump group for a brake system and a control method thereof, which can better achieve an effect of pumping out high-pressure fluid, provide stable brake pressure for the brake system, and have good operating stability.

The technical solutions in this application are implemented as follows: a piston pump group for a brake system is provided, including: a piston, a pump body provided with an operating chamber, and a transmission mechanism used for driving the piston to move in the operating chamber, where the transmission mechanism includes a lead screw transmission assembly, a follower, and a planetary gear assembly used for transmitting power to the lead screw transmission assembly, the follower is fixedly connected to the piston, the lead screw transmission assembly is used for driving the follower to move relative to the operating chamber, and a limiting member used for limiting the movement of the follower is disposed between the lead screw transmission assembly and the follower.

Optionally, the planetary gear assembly includes a drive wheel, an inner gear ring, a planetary cover and a plurality of planetary gears, the plurality of planetary gears are respectively meshed with the inner gear ring, the planetary gears are located between the drive wheel and the inner gear ring, the drive wheel is meshed with the planetary gears respectively, and the planetary cover is connected to the inner gear ring through a positioning structure.

Optionally, the positioning structure includes a groove disposed in a circumferential direction of an inner ring of the planetary cover and a protrusion disposed in a circumferential direction of an outer ring of the inner gear ring and used for cooperating with the groove, or the positioning structure includes a protrusion disposed in the circumferential direction of the inner ring of the planetary cover and a groove disposed in the circumferential direction of the outer ring of the inner gear ring and used for cooperating with the protrusion.

Optionally, the lead screw transmission assembly includes a bearing outer ring, a bearing inner ring, a bearing holder, and a lead screw, the bearing outer ring is sleeved outside the bearing inner ring, the bearing holder is disposed between the bearing outer ring and the bearing inner ring, the bearing holder is provided with a plurality of accommodation cavities used for accommodating ball bearings, the bearing inner ring is fixedly connected to one end of the lead screw, the follower is threadably connected to the lead screw, the planetary gears are disposed on a top surface of the bearing inner ring through a planetary pin, and the planetary cover is fixedly connected to the bearing outer ring.

Optionally, the lead screw and the bearing inner ring are of an integrally formed structure.

Optionally, the lead screw is of a hollow structure, and a through hole is disposed in an axial direction of the lead screw.

Optionally, the limiting member is a limiting pin, the limiting pin penetrates through the bearing inner ring to form a collision portion, and a collision structure used for performing contact limit with the collision portion is disposed on the follower.

This application further provides a control method, used for controlling the foregoing piston pump group for a brake system, and the control method includes zero point calibration of a piston, and includes the following steps:.

Optionally, the control method further includes: controlling the piston to automatically stop the axial movement in a lower stop point after step S11, where the lower stop point is a position at a preset distance from an inner wall of the bottom of a pump body.

Optionally, the step of controlling the piston to automatically stop the axial movement in a lower stop point includes:.

Compared with the related art, the piston pump group for a brake system and the control method thereof provided by this application have the following beneficial effects:.

Additional aspects and advantages of the invention described in this application will be given in the following description, some of which will become apparent from the following description or may be learned from practices of this application.

The foregoing and/or additional aspects and advantages of the invention according to this application will become apparent and comprehensible in the embodiment description made with reference to the following accompanying drawings, where:.

Embodiments of the invention according to this application are described in detail below, and examples of the embodiments are shown in accompanying drawings, where the same or similar elements or the elements having same or similar functions are denoted by the same or similar reference numerals throughout the description. The embodiments described below with reference to the accompanying drawings are exemplary, and are intended to explain the invention of this application and cannot be construed as a limitation to the invention of this application as defined in the appended claims.

As shown in <FIG>, a piston pump group for a brake system provided by the embodiments of this application includes a piston <NUM>, a transmission mechanism <NUM>, and a pump body <NUM> provided with an operating chamber. The transmission mechanism <NUM> is used for driving the piston <NUM> to reciprocate in the operating chamber to change an operating volume of the operating chamber, and inhale liquid or discharge the liquid with pressure. The transmission mechanism <NUM> includes a lead screw transmission assembly <NUM>, a follower <NUM> and a planetary gear assembly <NUM>. The planetary gear assembly <NUM> is used for transmitting power of a driving element to the lead screw transmission assembly <NUM>, so that the lead screw transmission assembly <NUM> drives the follower <NUM> to move relative to the operating chamber in the pump body <NUM>. The follower <NUM> is fixedly connected to the piston <NUM>, so that the piston <NUM> can move with the follower <NUM> (that is, the piston <NUM> and the follower <NUM> are used as a whole). A limiting member <NUM> used for limiting the movement of the follower <NUM> is disposed between the lead screw transmission assembly <NUM> and the follower <NUM>, which can prevent the follower <NUM> (the piston <NUM>) from colliding and interfering with another component when the follower <NUM> (the piston <NUM>) moves upward (the operating volume of the operating chamber becomes larger). In addition, zero point calibration of the piston <NUM> can also be realized by using the limiting member <NUM>. After the follower <NUM> is blocked by the limiting member <NUM> and stops moving, the operating volume of the operating chamber is the largest (that is, the piston <NUM> is at a zero point position in this case), to ensure that fluid discharged from the piston pump group has sufficient pressure to provide stable brake pressure for the brake system. During operation, the driving element operates to drive the planetary gear assembly <NUM> to rotate, to drive the lead screw transmission assembly <NUM> to rotate, so that the follower <NUM> (the piston <NUM>) moves close to the limiting member <NUM> or away from the limiting member <NUM> with the rotation of the lead screw transmission assembly <NUM>. The movement of the piston <NUM> changes the operating volume of the operating chamber.

Specifically, the operating chamber of the pump body <NUM> may be connected to an inhalation valve port and a discharge valve port, and change of the volume of the operating chamber generates a pressure difference, so that liquid (hydraulic oil) is inhaled into the operating chamber through the inhalation valve port, or the liquid (the hydraulic oil) is discharged from the operating chamber through the discharge valve port.

Specifically, the piston pump group for a brake system further includes the driving element used for providing the power. In this embodiment, the driving element is a motor, and the motor is connected to a motor controller and a rotation number sensor. The motor controller is used for controlling stop and operation of the motor. The operation of the motor includes clockwise rotation and counterclockwise rotation of the motor. The rotation sensor is used for obtaining a rotation number of an output shaft.

Optionally, the follower <NUM> may be connected and fixed to the piston <NUM> through a threaded structure, that is, the follower <NUM> is fixed to the piston <NUM> in a manner of threaded connection, where the threaded structure includes an external thread <NUM> disposed in a circumferential direction of an outer side of the follower <NUM> and an internal thread disposed in a circumferential direction of an inner side of the piston <NUM> (namely, an inner wall of the piston <NUM>), and the external thread <NUM> of the follower <NUM> cooperates with the internal thread of the piston <NUM>, to realize connection and fixation of the follower <NUM> and the piston <NUM>.

When the piston pump group is applied to the field of vehicle brake, it must be ensured that an effect of each brake is predictable. If the piston is deformed, first, the movement of the piston in the operating chamber of the pump body is unsmooth, which may cause that the brake of the piston pump group cannot keep up with a driver's action in time, that is, the brake is slow; second, there is a problem of poor coaxiality between the deformation of the piston and the operating chamber, which causes that the piston and an operating chamber wall are prone to be damaged by friction during operation, so that a service life of the piston is affected; and finally, the deformation of the piston may cause a certain gap disposed between the piston and the operating chamber wall, so that air tightness in the operating chamber is poor, an effect of inhaling liquid into the operating chamber or discharging the liquid out of the operating chamber cannot be ensured when the volume of the operating chamber changes, and brake reliability is thus affected. These problems may affect the brake reliability during driving, and endanger driving safety.

In this application, the follower <NUM> is fixed to the piston <NUM> by using the threaded connection, which can ensure that the follower <NUM>, the piston <NUM>, and the operating chamber have good coaxiality, and can also ensure the air tightness of the operating chamber, to provide the stable brake pressure for the brake system, and ensure the driving safety. In another aspect, the follower <NUM> is threadly connected to the piston <NUM>, which increases a force bearing area of the two, so that a problem of stress concentration can be well avoided, thereby improving a service life of the piston pump group.

Optionally, as shown in <FIG>, the planetary gear assembly <NUM> includes a drive wheel (not shown in the figure), an inner gear ring <NUM>, a planetary cover <NUM>, and a plurality of planetary gears <NUM> with the same structure. The planetary gears <NUM> are meshed with the inner gear ring <NUM> respectively, the planetary gears <NUM> are located between the drive wheel and the inner gear ring <NUM>, and the planetary gears <NUM> are also meshed with the drive wheel respectively. In this embodiment, the drive wheel is used as a sun wheel and is connected to the output shaft of the motor, to transmit the power of the motor to the planetary gears <NUM>, to drive the planetary gears <NUM> to rotate. The planetary cover <NUM> is sleeved on the inner gear ring <NUM>, and is connected to the inner gear ring <NUM> through a positioning structure, to fix the inner gear ring <NUM>. The planetary gear assembly <NUM> has advantages of a small size, large bearing capability, and stable operation.

In this embodiment, as shown in <FIG>, there are three planetary gears <NUM>, which are distributed in a form of a circumferential array with respect to a center of the drive wheel. The planetary gears <NUM>, the drive wheel, and the inner gear ring <NUM> may be of a helical tooth structure, which has characteristics of good meshing, stable transmission, and low noise. In addition, coincidence of helical gears is great, which reduces payloads of each pair of gears and improves bearing capability of the gears. It can be understood that, the drive wheel, the planetary gears <NUM>, and the inner gear ring <NUM> may also be of a straight tooth structure.

Optionally, as shown in <FIG>, the positioning structure includes a groove <NUM> disposed in a circumferential direction of an inner ring of the planetary cover <NUM> and a protrusion <NUM> disposed in a circumferential direction of an outer ring of the inner gear ring <NUM> and used for cooperating with the groove <NUM>, or the positioning structure includes a protrusion disposed in the circumferential direction of the inner ring of the planetary cover <NUM> and a groove disposed in the circumferential direction of the outer ring of the inner gear ring <NUM> and used for cooperating with the protrusion. The protrusion <NUM> and the groove <NUM> use an interference fit, and positioning connection is performed through the protrusion <NUM> and the groove <NUM>, so that assembly connection of the planetary cover <NUM> and the inner gear ring <NUM> is easy to realize.

Specifically, there may be a plurality of protrusions <NUM>, and the protrusions <NUM> are distributed on the inner gear ring <NUM> in the form of the circumferential array. Viewed from an axial direction of the inner gear ring <NUM>, cross-sections of the protrusions <NUM> may be of a structure of a rectangle, a triangle, a trapezoid, an arc, or the like. A quantity of grooves <NUM> and cross-sections thereof correspond to the protrusions <NUM>.

Optionally, as shown in <FIG> and <FIG>, the lead screw transmission assembly <NUM> includes a bearing outer ring <NUM>, a bearing inner ring <NUM>, a bearing holder <NUM> and a lead screw <NUM>. The bearing outer ring <NUM> is sleeved outside the bearing inner ring <NUM>, and the bearing holder <NUM> is disposed between the bearing outer ring <NUM> and the bearing inner ring <NUM>. The bearing holder <NUM> is provided with a plurality of accommodation cavities <NUM> for accommodating ball bearings <NUM>, and the bearing inner ring <NUM> is rollingly connected to the bearing outer ring <NUM> through the ball bearings <NUM>. The bearing inner ring <NUM> is fixedly connected to one end of the lead screw <NUM>, and the planetary gears <NUM> are respectively disposed on a top surface of the bearing inner ring <NUM> through a planetary pin <NUM>. The planetary gears <NUM> may rotate relative to the bearing inner ring <NUM> around the planetary pin <NUM>, and the planetary gears <NUM> may also rotate relative to the inner gear ring <NUM> simultaneously, to drive the bearing inner ring <NUM> (the lead screw <NUM>) to rotate. The follower <NUM> is threadedly connected to the lead screw <NUM>, so that the follower <NUM> can axially move (close to or away from the limiting member <NUM>) relative to the lead screw <NUM> with the rotation of the lead screw <NUM>. The planetary cover <NUM> is connected and fixed to the bearing outer ring <NUM> by welding, and the inner gear ring <NUM> is clamped in the planetary cover <NUM> by the bearing outer ring <NUM>. It can be understood that, the planetary cover <NUM> may also be connected and fixed to the bearing outer ring <NUM> by using screws.

Optionally, as shown in <FIG> and <FIG>, the lead screw <NUM> and the bearing inner ring <NUM> are of an integrally formed structure, cross-sections of the lead screw <NUM> and the bearing inner ring <NUM> may be T-shaped, and a center of the bearing inner ring <NUM> coincides with a central axis of the lead screw <NUM>. By using the design of the integrally formed structure, the structure has high strength, and can also prevent the bearing inner ring <NUM> from easily deforming when the lead screw <NUM> and the bearing inner ring <NUM> are press-fitted by interference, so that the bearing inner ring <NUM> rolls smoothly, and reliability of the overall operation of the piston pump group is ensured.

Optionally, as shown in <FIG>, the lead screw <NUM> is of a hollow structure, and a through hole <NUM> is disposed in an axial direction of the lead screw <NUM>. The through hole <NUM> and the lead screw <NUM> are coaxially disposed, that is, a central axis of the through hole <NUM> coincides with the central axis of the lead screw <NUM>, to ensure that a center of mass of the lead screw <NUM> is on the central axis during rotation. The lead screw <NUM> is designed to the hollow structure.

Specifically, a diameter of the through hole <NUM> is <NUM>/<NUM> to <NUM>/<NUM> of a diameter of the lead screw <NUM>.

Optionally, as shown in <FIG>, the bearing outer ring <NUM> is connected to the pump body <NUM> through a connecting member <NUM>, and the planetary gear assembly <NUM> and the lead screw transmission assembly <NUM> are installed and fixed on the pump body <NUM>. In this embodiment, the bearing outer ring <NUM> is integrated with the pump body <NUM> through the connecting member <NUM> in a manner of press fitting by interference. When the piston pump group operates, the planetary cover <NUM>, the inner gear ring <NUM>, and the bearing outer ring <NUM> are all fixed and do not move, to support the planetary gears <NUM>, the bearing inner ring <NUM>, and the lead screw.

Optionally, as shown in <FIG>, the limiting member <NUM> is a limiting pin, the limiting pin penetrates through the bearing inner ring <NUM>, a collision portion <NUM> is formed on one side of the limiting pin toward the follower <NUM>, and a collision structure used for performing contact limit with the collision portion <NUM> is disposed on the follower <NUM>. When the follower <NUM> moves toward the bearing inner ring <NUM> (a direction of the planetary gear assembly <NUM>), the collision structure disposed on the follower <NUM> and the collision portion <NUM> on the bearing inner ring <NUM> gradually approach and finally contact to generate a collision signal, and the motor stops rotating immediately after receiving the collision signal, and the lead screw <NUM> stops rotating simultaneously, so that the piston <NUM> stops moving and stops at a current position. The movement of the follower <NUM> is limited by setting the limiting member <NUM>, to prevent the follower <NUM> from colliding and interfering with the bearing inner ring <NUM> when the piston <NUM> returns. In actual applications, the zero point calibration of the piston <NUM> may also be performed by using the limiting member <NUM>, to ensure that the piston <NUM> is at the zero point position each time the piston <NUM> operates (definition: the zero point position is a position of the piston <NUM> when the operating chamber is at a maximum operating volume).

Specifically, the limiting member <NUM> is threadedly connected to the bearing inner ring <NUM>, and a length of the collision portion <NUM> may be controlled by adjusting a length of the limiting member <NUM> penetrating through the bearing inner ring <NUM>, to limit a movement stroke of the piston <NUM> to the limiting member <NUM>, and adjust the maximum volume of the operating chamber. In addition, the limiting member <NUM> is easy to replace after being damaged by collision.

In this embodiment, as shown in <FIG>, the follower <NUM> may be a nut, the external thread <NUM> is disposed at a lower end of an outer circumferential direction of the nut, and the collision structure may be integrally formed on a boss <NUM> at a top end of the nut. After the boss <NUM> is in contact with the collision portion <NUM>, the nut (the piston <NUM>) stops moving immediately, and a current position of the piston <NUM> is the zero point position. A total length of the nut is <NUM> (which includes the boss <NUM> of <NUM>), and a length of the external thread <NUM> is <NUM>. It can be understood that, the collision structure is mainly used for positioning the collision portion <NUM>. Therefore, the collision structure may also be a groove disposed in a top surface of the nut.

This application further provides a control method, used for controlling the foregoing piston pump group for a brake system, and the control method includes zero point calibration of a piston <NUM>, that is, the piston <NUM> needs to be first moved to a zero point position before operation, to ensure that pressure of liquid initially discharged by the piston pump group is an expected value, and a brake effect is stable. For ease of understanding, this embodiment describes with reference to a motor, and specific steps are as follows:.

S10: controlling a motor to enable and rotate in a first direction, to drive a planetary gear assembly <NUM> to rotate in the first direction, to drive a lead screw transmission assembly <NUM> to rotate in the first direction, so that a follower <NUM> moves close to a limiting member <NUM> with the rotation of the lead screw transmission assembly <NUM>, and the piston <NUM> moves close to the limiting member <NUM> with the follower <NUM>; and.

S11: generating a collision signal when a collision structure of the follower <NUM> is in contact with the limiting member <NUM>; feeding back, by a rotation sensor of the motor, the collision signal to a motor controller after receiving the collision signal; and generating, by the motor controller, an instruction of stopping operation, and executing the instruction of stopping operation, so that the motor stops rotating in the first direction, so that the planetary gear assembly <NUM> and the lead screw transmission assembly <NUM> stop rotating, and then the follower <NUM> and the piston <NUM> stop axial movement, and a current position of the piston <NUM> is a zero point position. The piston <NUM> may alternatively stop automatically at the zero point position by means of limiting, to prevent the piston <NUM> from colliding with another component.

Optionally, the method further includes: controlling the piston <NUM> to automatically stop the axial movement in a lower stop point after step S11, where the lower stop point is a position at a preset distance from an inner wall of the bottom of a pump body <NUM>, and specifically, to a position of the piston <NUM> when a distance between the piston <NUM> and the inner wall of the bottom of the pump body <NUM> (the bottom of an operating chamber) is equal to a preset distance.

Optionally, the step of controlling the piston <NUM> to automatically stop the axial movement in a lower stop point includes:.

S20: controlling the motor to rotate in a second direction after the piston <NUM> stops at the zero point position, to drive the planetary gear assembly <NUM> to rotate in the second direction, to drive the lead screw transmission assembly <NUM> to rotate in the second direction, so that the follower <NUM> moves away from the limiting member <NUM> with the rotation of the lead screw transmission assembly <NUM>, an operating volume of the operating chamber becomes smaller gradually with the movement of the piston <NUM>, the operating chamber is compressed to generate pressure to discharge liquid in the operating chamber from a discharge valve port, and the discharged liquid has certain pressure; and obtaining a current rotation number of the motor (where the motor controller may obtain a rotation number of an output shaft of the motor through the rotation number sensor) or a current rotation number of the lead screw transmission assembly <NUM> (that is, a rotation number of a lead screw <NUM>, which may be indirectly obtained by obtaining the rotation number of the motor) in real time;.

S21: determining whether the current rotation number exceeds a preset revolution threshold, to determine whether the piston <NUM> moves to the lower stop point, where the preset revolution threshold is the rotation number of the output shaft of the motor or the rotation number of the lead screw <NUM> when the piston <NUM> moves from the zero point position to the lower stop point; if the current rotation number of the motor or the current rotation number of the lead screw transmission assembly <NUM> does not exceed the preset revolution threshold, performing step S20; and if the current rotation number of the motor or the current rotation number of the lead screw transmission assembly <NUM> is equal to the preset revolution threshold, performing step S22; and.

S22: if the current rotation number of the motor or the current rotation number of the lead screw transmission assembly <NUM> is equal to the preset revolution threshold, generating, by the motor controller, an instruction of stopping operation, and executing the instruction of stopping operation, so that the motor stops rotating in the second direction, and the planetary gear assembly <NUM> and the lead screw transmission assembly <NUM> stop rotating in the second direction, to control the follower <NUM> (the piston <NUM>) to stop moving, and the piston <NUM> stops at the lower stop point, that is, the piston <NUM> automatically stops moving once the piston <NUM> reaches the lower stop point, to prevent the piston from colliding with a bottom surface of the operating chamber.

If the current rotation number of the motor or the current rotation number of the lead screw transmission assembly <NUM> does not exceed the preset revolution threshold, the motor controller generates an instruction of continuing operation, and executes the instruction of continuing operation, to control the motor to continuously rotate in the second direction, until the current rotation number of the motor or the current rotation number of the lead screw transmission assembly <NUM> is equal to the preset revolution threshold (the piston <NUM> moves to the lower stop point), and control the motor to stop rotating in the second direction.

In this embodiment, the first direction and the second direction are determined according to a rotation direction of a thread of the lead screw <NUM>. For example, if the thread of the lead screw <NUM> is right-handed, the first direction is a counterclockwise direction, and the follower <NUM> moves upward relative to the lead screw <NUM>; and the second direction is a clockwise direction, and the follower <NUM> moves downward relative to the lead screw <NUM>. If the thread of the lead screw <NUM> is left-handed, the first direction is the clockwise direction, and the follower <NUM> moves upward relative to the lead screw <NUM>; and the second direction is the counterclockwise direction, and the follower <NUM> moves downward relative to the lead screw <NUM>.

An operating process of the piston pump group for a brake system of this application is as bellow: zero point calibration is first performed on the piston <NUM>, the piston <NUM> is then controlled to move downward to the lower stop point from the zero point position, to discharge the liquid in the operating chamber for braking, and the piston <NUM> is finally controlled to return, move upward from the lower stop point, and inhale liquid into the operating chamber. Specifically, according to usage requirements, the operation of the piston pump group may be a continuous process, that is, after the zero point calibration of the piston <NUM>, the piston <NUM> continuously reciprocates between the zero point position and the lower stop point.

The embodiments of this application provide the piston pump group for a brake system and the control method thereof, and compared with the related art, this application has the following beneficial effects:.

In the description of this application, it should be understood that orientation or position relationships indicated by the terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "on", "below", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "anticlockwise", "axial direction", "radial direction", and "circumferential direction" are based on orientation or position relationships shown in the accompanying drawings, and are used only for ease and brevity of illustration and description, rather than indicating or implying that the mentioned apparatus or component must have a particular orientation or must be constructed and operated in a particular orientation. Therefore, such terms should not be construed as limiting of this application.

In addition, the terms "first" and "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, a feature defined by "first" or "second" can explicitly or implicitly includes one or more features. In the descriptions of this application, "a plurality of" means two or more, unless otherwise definitely and specifically limited.

In this application, unless otherwise explicitly specified or defined, the terms such as "install", "connect", "connection", and "fix" should be understood in a broad sense. For example, the connection may be a fixed connection, a detachable connection, or an integral connection; or the connection may be a mechanical connection or an electrical connection; or the connection may be a direct connection, an indirect connection through an intermediate medium, internal communication between two components, or an interaction relationship between two components. A person of ordinary skill in the art may understand the specific meanings of the foregoing terms in this application according to specific situations.

In this application, unless otherwise explicitly specified or defined, the first feature being located "above" or "below" the second feature may be the first feature being in a direct contact with the second feature, or the first feature being in an indirect contact with the second feature through an intermediary. In addition, the first feature being located "above" the second feature may be the first feature being located directly above or obliquely above the second feature, or may simply indicate that the first feature is higher in level than the second feature. The first feature being located "below" the second feature may be the first feature being located directly below or obliquely below the second feature, or may simply indicate that the first feature is lower in level than the second feature.

Claim 1:
A piston pump group for a brake system, comprising a piston (<NUM>), a pump body (<NUM>) provided with an operating chamber, and a transmission mechanism (<NUM>) used for driving the piston to move in the operating chamber, wherein the transmission mechanism comprises a lead screw transmission assembly (<NUM>), a follower (<NUM>), and a planetary gear assembly (<NUM>) used for transmitting power to the lead screw transmission assembly, the follower is fixedly connected to the piston, the lead screw transmission assembly is used for driving the follower to move relative to the operating chamber, characterized by
a limiting member (<NUM>) used for limiting the movement of the follower is disposed between the lead screw transmission assembly and the follower.