Piston operating device

Abstract

This invention relates to a piston actuation device (10), particularly for conveying pressure medium in the pressure medium circuit (23) of a motor vehicle braking device. A known piston actuation device (10) comprises a housing (14) and a piston (12) operable by a screw drive (24) for reciprocating translational motion along a piston guide axis (18). The screw drive (24) for this purpose has a screw nut (26) and a screw (28) acting in conjunction with the screw nut (26) via a threaded drive (30). The threaded drive (30) converts the rotational motion of the screw nut (26) into reciprocating translational motion of the screw (28) along a screw motion axis (36). To transmit the translational motion to the piston (12), the piston (12) is axially fixedly connected to the screw (28). It is proposed that the axially fixed connection between the piston (12) and the lead screw (28) includes a hinge connection (40) which allows for concentricity deviation between the piston guide axis (18) and the lead screw motion axis (36).

Description

Technical Field

[0001] The present invention relates to a piston actuation device, which is particularly used for actuating a piston to deliver pressure medium in a pressure medium circuit of an electrically slidingly adjustable braking device for motor vehicles. Background Technology

[0002] Such piston-operated devices are known from the background art, and in this regard, exemplary references are made to the disclosure of document DE 102014212409 A1. Summary of the Invention

[0003] The known piston actuation device thus includes a piston movably housed in an axial guide portion of a device housing, which can be actuated by a screw drive for reciprocating translational motion along a piston guide axis defined by the axial guide portion. The piston is implemented as a hollow piston with one open side and houses the screw drive within it. The latter has a rotatably driven, cylindrically constructed screw nut and a screw disposed within the screw nut, which is actuated by the screw nut. The rotational motion of the screw nut is converted by a transmission mechanism into translational motion of the screw along its axis of motion. To transmit this translational motion of the screw to the piston, the two components are axially fixedly connected to each other. In the cited background art, the piston and the screw are thus exemplary implemented in one piece, i.e., as a single component.

[0004] Coupled with the translational motion of the lead screw and the piston, this places high demands on the coaxiality between the piston guide axis in the device housing and the lead screw motion axis of the lead screw drive. However, because coaxiality deviations are almost unavoidable due to manufacturing tolerances, the resulting lateral forces can cause wear at the axial guide portion of the piston in the device housing. To counteract potential wear during the preparation stage, wear protection is provided in the piston guide area of ​​the device housing. This involves a coating on the housing wall.

[0005] The creation of this wear protection adversely increases the cost of manufacturing the device housing and thus its manufacturing cost.

[0006] The purpose of this invention is to improve the piston actuation device described in the prior art.

[0007] The above objective is achieved by a piston actuation device comprising a housing and a piston movably accommodated in a guide portion of the housing, the piston defining a working chamber of the housing, and the piston being actuated by a lead screw drive to reciprocate along a piston guide axis for changing the volume of the working chamber, wherein the lead screw drive has a lead screw nut and a lead screw that can be driven for rotational motion, and they interact with each other such that the rotational motion of the lead screw nut is converted into the reciprocating translational motion of the lead screw along the lead screw axis of motion, and wherein the piston and the lead screw are axially fixedly connected to transmit this translational motion. According to the present invention, the axially fixed connection between the piston and the lead screw includes a hinge connection that allows for concentricity deviation between the piston guide axis and the lead screw movement axis. The hinge connection includes a plug element and a socket, the plug element being pressed into the socket and held under radial preload. The plug element has at least a partially spherically bent plug, and the socket has a hollow cylindrical cross-section. The plug is held under radial preload, and the socket is widened by pressure on the spherically bent plug during manufacturing of the connection between the lead screw and the piston. By adapting the geometry and material elasticity of the plug element or the socket, the clamping force between the plug and the socket can be adjusted such that, under the expected driving force from the lead screw nut to the lead screw, no expected relative movement in the radial direction is anticipated between the plug and the socket, wherein the socket extends axially such that its free end terminates in the region of the rod of the plug element. This achieves coaxiality deviation between the piston guide axis and the lead screw movement axis without generating a lateral force that loads the axial guide portion of the piston in the device housing.

[0008] Compared with the prior art, the piston actuation device according to the present invention has the advantage that existing deviations in the coaxiality between the piston guide axis and the lead screw movement axis do not cause lateral forces leading to wear at the axial guide portion of the piston in the device housing. This reduces the tolerance and quality requirements of the lead screw drive and allows for the incorporation of a more cost-effective lead screw drive. Furthermore, the coating on the axial guide portion of the piston in the device housing can be omitted, thereby simplifying the manufacture of the device housing and further reducing costs.

[0009] According to the present invention, the advantages described above are achieved by replacing the rigid connection between the piston and the lead screw with a hinge connection that allows for concentricity deviations caused by tolerances between the piston guide axis and the lead screw movement axis, without generating lateral forces at the axial guide portion of the piston.

[0010] The present invention also relates to other advantages or advantageous modifications, as will be apparent from the following description.

[0011] According to a preferred embodiment, the hinge connection between the piston and the lead screw includes a plug element and a socket that engage with each other under force-locking conditions. This force-locking can be easily achieved technically through the common insertion of the plug element and the socket.

[0012] Furthermore, it is advantageous that the plug element or socket of the hinge connection is integrally constructed at its respective component, as it can thus be presented at these components particularly cost-effectively and especially since the number of parts to be assembled does not increase. Preferably, the plug element and the socket, or the lead screw and piston respectively coupled, are manufactured from plastic in an injection molding process.

[0013] The arrangement of the hinge coupling within the piston, or rather the lead screw nut, reduces the tendency for contamination and, over the course of its service life, minimizes the associated increase in the friction ratio of the hinge connection.

[0014] The plug element configuration, with at least a partially spherically bent plug (i.e., spherical), enables the following: lateral forces acting on the axial guide portion of the piston due to coaxiality misalignment are largely avoided, regardless of the spatial direction in which the lateral forces act. Furthermore, it eliminates the need for mutual alignment of the piston and lead screw to create the connection between them.

[0015] Instead of the known ball screw drive mechanism that forms a connection between a lead screw nut and a lead screw, a more cost-effective threaded drive mechanism can be used. In the case of a threaded drive mechanism, the threads of the lead screw nut directly engage with the mating threads on the lead screw, while in the case of a ball screw drive mechanism, torque transmission is indirectly achieved through balls arranged in a ball bearing track. This ball bearing track is constructed with a first portion of its track cross-section at the lead screw nut and a second portion at the lead screw. The advantage of the relatively simpler construction of the threaded drive mechanism lies primarily in its high mechanical efficiency. Attached Figure Description

[0016] Embodiments of the present invention are shown in the accompanying drawings and described in detail in the following description. Wherein:

[0017] Figure 1 A piston-operated device constructed according to the present invention is shown in longitudinal section. Detailed Implementation

[0018] Figure 1 A piston-operated device 10 with a piston 12 is shown, the piston being torsionally and axially movable within a recess in a device housing 14. This piston 12 is configured as a hollow piston open on one side, having a plurality of radially projecting protrusions 16 at its open end. These protrusions 16 extend along a portion of the piston's outer periphery and are embedded in associated axial guides 17 within the device housing 14. The axial guides 17 define a piston guide axis 18 on one hand and, on the other hand, cooperate with the radial protrusions 16 as torque supports for the piston 12. The latter prevents rotational movement of the piston 12 within the device housing 14.

[0019] The piston 12, together with the enclosed piston bottom 20, defines a working chamber 22 constructed within the device housing 14 and filled with a pressure medium. The volume of this working chamber can be changed according to the operation of the piston 12. If the piston 12 is driven, for example to the left or in the forward direction (direction arrow V) in the figure, the volume of the working chamber 22 decreases and the existing pressure medium is expelled from the working chamber 22 into the pressure medium circuit 23 connected to the working chamber. The pressure medium circuit 23 is indicated by the symbol of a wheel brake in the figure. The pressure level in the pressure medium circuit thus increases. Conversely, if the piston 12 moves to the right or in the backward direction (direction arrow R), the volume of the working chamber 22 increases, the pressure medium flows back from the pressure medium circuit 23 into the working chamber 22, and the pressure level in the pressure medium circuit 23 decreases. There exists a non-linear functional relationship between the pressure change in the pressure medium circuit 23 and the volume change of the working chamber 22, which can be represented by a so-called pressure / volume characteristic curve.

[0020] To operate the piston 12 in one or the other direction of movement (direction arrows V, R), the piston operating device 10 is equipped with a lead screw drive 24. This lead screw drive 24 is housed within the hollow interior of the piston 12 and includes a hollow cylindrical lead screw nut 26 and a lead screw 28 housed within the lead screw nut 26. The lead screw nut 26 and the lead screw 28 interact with each other via a threaded drive 30. For this purpose, an internal thread 32 is constructed on the inner circumference of the lead screw nut 26, which directly engages with an external thread 34 constructed on the outer circumference of the lead screw 28.

[0021] Not shown, but alternatively feasible, is to replace the threaded drive 30 with a ball screw drive in which balls are arranged in the gap between the screw and the screw nut and run in a ball-circling track, wherein a first portion of the cross-section of the ball-circling track is formed at the screw and a second portion is formed at the screw nut. In this case, the screw nut and the screw indirectly mesh with each other through the balls.

[0022] The lead screw nut 26 is fixedly positioned and rotatably supported, and performs rotational movement. The drive device required for this purpose is shown by reference in the figure. The drive device is arranged in the region of the open end of the piston 12 and has an electrically driven motor M and preferably a transmission mechanism G connected between the motor M and the lead screw nut 26.

[0023] The rotational motion of the lead screw nut 26 is transmitted to the lead screw 28 via the threaded drive 30. The latter, as will be understood from the following description, is protected from rotating with the lead screw nut 26 and thus performs a reciprocating translational motion relative to the lead screw nut 26 along the lead screw motion axis 36. This translational motion is transmitted to the piston 12. For this purpose, the lead screw 28 and the piston 12 are connected to each other in a torsional and axially fixed manner. This connection is located in a region of the enclosed interior of the piston 12 and, according to the invention, includes a hinged connection 40 that allows for concentricity deviation between the piston guide axis 18 and the lead screw motion axis 36.

[0024] For this purpose, the hinge connection 40 includes a plug element 42 disposed at the end of the lead screw 28 and a socket 44 disposed on the inner side of the piston bottom 20. The plug element 42 and the socket 44 are exemplary integrally constructed with the lead screw 28 and each with the piston 12.

[0025] The plug element 42 extends coaxially along the longitudinal axis of the lead screw 28 and has a plug 46 that is at least partially spherically bent. The latter is constructed at the end of the lead screw 28 by a rod 48 whose outer diameter is reduced relative to the outer diameter of this plug 46, the end being located inside the lead screw nut 26.

[0026] The socket 44 and the plug element 46 are concentrically constructed on the inner side of the piston bottom 20. The socket has a hollow cylindrical cross-section into which the plug element 42 is pressed and held under radial preload.

[0027] During the manufacturing of the connection between the lead screw 28 and the piston 12, the socket 44 is widened by pressure on the spherically bent plug 46 until the plug 46 is finally able to enter the interior of the socket 44 in a substantial manner, until the plug, as shown in the figure, still has only a small gap relative to the inside of the piston bottom 20.

[0028] As the plug 46 is introduced into the socket 44, the two participating elements come into contact along a line (which runs along the outer periphery of the plug 46). Through the fit of the geometry of the plug element 42 or the socket 44 and the elasticity of the materials, the clamping force between the plug 46 and the socket 44 can be adjusted so specifically for the application that, under the desired driving force from the lead screw nut 26 to the lead screw 28, no radial relative movement, i.e., no radial slippage, is expected between the plug 46 and the socket 44.

[0029] The socket 44 extends so far in the axial direction that its free end terminates in the region of the rod 48 of the plug element 42. This allows for restricted mutual deflection transverse to the piston guide axis 18, or transverse to the lead screw motion axis 36, and thus allows for coaxiality deviation between the piston guide axis 18 and the lead screw motion axis 36 without generating a lateral force that loads the axial guide portion of the piston 12 in the device housing 14.

[0030] As a result, the guide region of the piston 12 in the device housing 14 is less subjected to mechanical loads due to the provided hinge connection 40, and does not require additional wear protection. This saves on the cost of manufacturing the device housing 14 and thus reduces manufacturing costs.

[0031] Of course, improvements or additions to the illustrated embodiments are possible without departing from the subject matter of the invention.

Claims

1. Piston control device (10). The piston actuation device includes: Device housing (14). A piston (12) is movably housed in a guide portion (17) of the device housing (14), defining a working chamber (22) of the device housing (14), and the piston can be manipulated by a lead screw drive (24) to reciprocate along a piston guide axis (18) to change the volume of the working chamber (22). The lead screw drive (24) includes a lead screw nut (26) and a lead screw (28) that can be driven for rotary motion. They work together in such a way that the rotary motion of the lead screw nut (26) is converted into the reciprocating translational motion of the lead screw (28) along the lead screw motion axis (36). Furthermore, the piston (12) and the lead screw (28) are axially fixedly connected to transmit this translational motion. Its features are, The axially fixed connection between the piston (12) and the lead screw (28) includes a hinge connection (40), which allows for concentricity deviation between the piston guide axis (18) and the lead screw motion axis (36). The hinge connection (40) includes a plug element (42) and a socket (44), wherein the plug element (42) is pressed into the socket and held under radial preload. The plug element (42) has a plug (46) that is at least partially spherically bent, and the socket (44) has a hollow cylindrical cross-section, wherein the plug (46) is held under radial preload. In the process of manufacturing the connection between the lead screw (28) and the piston (12), the socket (44) is widened by the pressure on the spherically bent plug (46). Specifically, by adjusting the geometry and material elasticity of the plug element (42) or the socket (44), the clamping force between the plug (46) and the socket (44) can be adjusted such that, under the condition of the expected driving force from the lead screw nut (26) to the lead screw (28), no expected relative movement in the radial direction between the plug (46) and the socket (44) is anticipated. The socket (44) extends so far in the axial direction that the free end of the socket terminates in the region of the rod (48) of the plug element (42), thereby enabling coaxiality deviation between the piston guide axis (18) and the lead screw motion axis (36) without generating a lateral force that loads the axial guide portion of the piston (12) in the device housing (14).

2. The piston actuation device according to claim 1, Its features are, The plug element (42) or the socket (44) is integrally constructed at the end of the lead screw (28) facing the piston (12), and the socket (44) or the plug element (42) is integrally constructed on the inside of the piston bottom (20) of the piston (12).

3. The piston actuation device according to claim 1 or 2, Its features are, The lead screw nut (26) and the lead screw (28) work together through a threaded transmission device (30), wherein the thread (32) constructed at the lead screw nut (26) directly engages with the mating thread (34) constructed at the lead screw (28).

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