JP2005325956A - Ball screw for motor-driven actuator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw for motor-driven actuator, absorbing bending force due to external force, reducing sliding resistance, improving wear resistance and facilitating manufacture. <P>SOLUTION: This ball screw for the motor-driven actuator is a ball screw 2 used in the form of rotating a nut 4 and sliding a screw shaft 3. The ball screw 2 is constructed by fitting an annular part 18, the surface of which is quenched and which is brought into sliding contact with a ball screw using device to the outer periphery of the screw shaft 3 in the press-fit state. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ball screw for an electric actuator that is used in an electric disc brake or the like of an automobile and requires a sliding surface on a screw shaft.

In recent years, in place of hydraulic actuators that have been used in automobiles, many electric actuators have been developed that substitute their functions with electric motors. As such an electric actuator, a ball screw is often used as a drive component that converts the rotational motion of the motor into linear motion at high speed and high efficiency.
As an example of such an electric actuator using a ball screw, as shown in FIG. 6, a connecting pin provided on an output shaft 34 that rotates a screw shaft 31 of a ball screw 30 with a motor and advances and retracts integrally with a nut 32. There has been proposed one in which the arm 36 and the like are operated via 35 (for example, Patent Document 1). The arm 36 transmits the operation to the transmission and the electric disc brake.

In the electric actuator having such a structure, a slight relative displacement occurs between the nut 32 and the screw shaft 31 due to the force in the bending direction acting on the portion of the ball screw 30 by the external force. It is said that the load balance of the ball 33 in the ball screw 30 is lost due to this relative displacement, so that the ball screw 30 is worn or damaged, and the durability is impaired. Therefore, as a countermeasure for solving this problem, in the electric actuator disclosed in Patent Document 1, a bushing 37 having a small elastic coefficient is provided between the screw shaft 31 and the nut 32 to absorb the bending force, and the ball screw 30 is reliable. To improve performance and durability. That is, the bush 37 is used as a means for preventing the ball screw 30 from directly receiving a load in the bending direction due to an external force.
JP 2003-194174 A

  However, in the ball screw 30 in the electric actuator having the above configuration, since the bush 37 is provided between the screw shaft 31 and the nut 32, the bush 37 is slid while being pressed against the screw groove 31a of the screw shaft 31 by the load in the bending direction. To do. In this case, the bush 37 is in contact with the outer periphery of the screw shaft 31 while receiving the force of the nut 32 that tends to tilt due to the bending load. For this reason, as shown in FIG. 7 showing an enlarged portion A of FIG. 6, when the bush 37 slides on the unevenness of the thread portion 31 b, the inner surface of the bush 37 is galled by the edge of the screw shaft 31. Occur. In particular, the above-mentioned galling occurs when the bush 37 slides beyond the range of the screw shaft 31. As a result, the wear on the bush 37 side progresses and the nut 32 is easily tilted, and the effect of absorbing the bending force by the bush 37 is reduced.

In the electric actuator having the above-described configuration, as shown in FIG. 8, the link portion (power point receiving the external force F _r1 ) 38 connected to the nut 32 of the ball screw 30 and the portion of the ball screw 30 provided with the bush 37 ( the distance L1 between the fulcrum) 39 of the external force F _r1 is short, the less the effect of the bending load the ball screw 30 is subjected by an external force F _r1. However, due to restrictions such as the need to avoid interference with the surrounding structure, as shown in FIG. 9, the link portion (power point that receives the external force F _r2 ) 38 is connected to the portion of the ball screw 30 provided with the bush 37 (external force F). _When separated from ( _r2 fulcrum) 39 (distance L2), the position where the external force is input and the fulcrum of the external force are greatly separated. For this reason, the influence of the bending load which the ball screw 30 receives will become large.

That is, the bending load received at the fulcrum 39 in the case of FIG. 8 and FIG.
F _r1 · L1 <F _r2 · L2
There is a large and small relationship.
Accordingly, as shown in FIG. 9, in the case where the link portion 38 and the portion 39 of the ball screw 30 are separated from each other, the bush 37 is extended to the position of the link portion 38, and the output shaft 34 as a connecting part is attached. A structure supported by the bush 37 is desirable.

  Therefore, as an improved product of the ball screw 30 having the above configuration, the present inventors have a structure in which the nut is a rotating member, the screw shaft is a slide member provided with a connecting part, and the screw shaft is received by a bush. A ball screw using a screw shaft with a thread groove machined by rolling, which is superior to grinding, was manufactured as a screw shaft. Moreover, in this prototype, in order to reduce sliding resistance and improve wear resistance, the sliding surface of the screw shaft was made harder by increasing the surface hardness.

However, the following problems arise in this prototype structure.
・ The hardened range when induction hardening the screw shaft is widened, and the heat treatment time is extended.
· Coaxial accuracy does not appear between the sliding surface part of the screw shaft and the screw part. In other words, on the sliding surface with the above structure, the diameter and surface roughness are controlled on both the male and female sides, and smooth sliding is possible by making the gap between the sliding parts appropriate, and abnormal wear due to inappropriate gaps. And noise generation can be prevented. Therefore, in order to achieve this problem, also in the case of the above-mentioned prototype, after the heat treatment of the screw shaft, a finishing process such as grinding is required. However, the rolling process of the thread groove on the screw shaft is a processing method in which the material round bar is sandwiched between two pairs of roll dies and plastically deformed, whereas the center holes provided at both ends of the screw shaft material are used. The finishing process of the sliding surface to be ground is not related to the center hole of the shaft end and the material outer diameter. From this, especially when the material round bar is manufactured centerless, the outer diameter of the sliding surface ground by using the center hole with respect to the thread portion rolled based on the outer diameter is Misalignment occurs.

  An object of the present invention is to provide a ball screw for an electric actuator that can absorb bending force due to external force, can reduce sliding resistance, and can improve wear resistance, and is easy to manufacture.

The ball screw for an electric actuator according to the present invention is the ball screw for an electric actuator used in a form in which a nut is rotated and a screw shaft is slid. The screw shaft is attached in a press-fit state to the outer periphery of the screw shaft.
According to this configuration, when an external force is applied to the tip end side of the screw shaft, a bending force acts on the threaded portion of the screw shaft, but an annular part that is slidably contacted with a ball screw using device is attached to the outer periphery of the screw shaft. Therefore, the bending load applied to the threaded portion of the screw shaft can be absorbed. In addition, the annular part is assumed to have a surface hardness increased by quenching, and the annular part is attached to the outer periphery of the screw shaft in a press-fit state. For example, the screw shaft is formed by rolling, and the screw shaft material before rolling Even if the center is manufactured without a center, it is not necessary to post-process the center hole to finish the sliding surface. This not only facilitates the manufacture, but also improves the accuracy of coaxiality between the sliding surface of the screw shaft (the outer peripheral surface of the annular part in this invention) and the thread groove, and reduces sliding resistance and wear resistance. Can be improved. In addition, in the heat treatment of the screw shaft, surface hardening by quenching of the sliding surface can be completed with an annular part which is a separate part, so the moving quenching time by induction quenching can be shortened, and manufacturing is also easy in this respect It becomes.

  In the present invention, a plurality of the annular parts may be provided side by side in the axial direction. If the axial direction sliding range of the screw shaft is wide, the annular part becomes longer if the sliding surface of the screw shaft is configured with one annular part. However, it is not easy to press-fit the annular part into the screw shaft. In this case, the work can be easily performed by press-fitting the annular part into a plurality of parts.

  In the present invention, the annular part may be of the same standard as the inner ring in the needle bearing with the inner ring. According to this configuration, since the inner ring of the standard needle bearing can be used as the annular part, it is not necessary to manufacture a special product as the annular part, and the annular part can be procured at low cost.

  When the annular part is of the same standard as the inner ring in a needle bearing with an inner ring, the screw shaft is formed by rolling a thread groove, and the shaft part into which the annular part of the screw shaft is press-fitted The outer diameter of the screw shaft may be the outer diameter of the screw shaft material before the rolling process. In the case where the outer diameter of such a screw shaft material is set, the inner ring of a standard needle bearing can be used as the annular part without separately performing grinding or the like to adjust the diameter, and the cost can be reduced.

  The ball screw for an electric actuator according to the present invention is the ball screw for an electric actuator used in a form in which the nut is rotated and the screw shaft is slid. Since it is attached to the outer periphery of the screw shaft in a press-fit state, it can absorb the bending force received by an external force, can reduce sliding resistance and improve wear resistance, and can be easily manufactured.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 shows a cross-sectional view of an electric actuator using a ball screw according to this embodiment. The electric actuator includes a motor 1 that is a drive source and a ball screw 2 that converts rotation of the motor 1 into a sliding motion. The ball screw 2 is installed in a housing 8. The housing 8 is composed of a rear member 9 having a hat-shaped cross section, an intermediate member 10 having an L-shaped cross section, and a cylindrical front member 11, and these members are connected in this order to form a whole. Is assembled into a substantially cylindrical shape. The rear member 9 and the intermediate member 10 of the housing 8 are connected so that the flange portions 9a and 10a at one end thereof are opposed to each other, and the outer diameter side from the housing cylindrical space portion 8a is formed inside the opposed portions of the flange portions 9a and 10a. A gear portion space 8b is formed to project over the surface. The motor 1 is installed on the outer periphery of the rear portion of the housing 8 so that the output shaft 1a thereof is parallel to the axial direction of the housing 8, and the motor output shaft 1a passes through the flange portion 9a of the rear member 9 and the gear portion space. It is made to enter into 8b.

  As shown in FIG. 2, the ball screw 2 includes a screw shaft 3, a nut 4, a ball 5 interposed between the screw shaft 3 and the screw grooves 6 and 7 of the nut 4, and the screw grooves 6 and 7. And a circulation path (not shown) for picking up the balls 5 and returning them between the thread grooves 6 and 7. The circulation path is a spiral ball rolling path formed between the thread grooves 6 and 7 and is connected to both ends to form a circuit path. Circulation of a piece, a return tube, etc. provided in the nut 4 It is comprised by the member for use (not shown). The screw shaft 3 is disposed in the housing 8 concentrically therewith. The nut 4 is rotatably provided on the inner periphery of the housing 8 via bearings 12 and 13.

  A gear 15 that is concentric with the nut 4 and is disposed in the gear portion space 8b of the housing 8 is integrally formed on the outer periphery of the nut 4. The gear 15 is engaged with a gear 14 provided on the motor output shaft 1a. ing. Both the gears 14 and 15 constitute a rotation transmission system that transmits the rotation of the motor 1 to the nut 4.

  A bush 16 is press-fitted and fixed to the inner periphery of the housing front member 11. A flange portion 16a is formed at the rear end of the bushing 16 so as to project to the outer diameter side. The flange portion 16a is sandwiched between the front end of the housing intermediate member 10 and the rear end of the housing front member 11 facing the housing intermediate member 10. Yes. Further, the front end of the bush 16 is received by an inward flange portion 11a formed at the front end of the housing front member 11, whereby the bush 16 is positioned in the axial direction.

  The screw shaft 3 of the ball screw 2 has a screw portion 3a formed with a screw groove 6 (FIG. 2) at its rear half, and the front end of the front half protrudes forward from the housing 8. A connection hole 17 into which a connection pin (not shown) is fitted is formed. An annular part 18 that is slidably contacted with the bush 16 is attached in a press-fit state to a portion corresponding to the installation range of the bush 16 on the outer periphery of the front half of the screw shaft 3.

  The screw shaft 3 is formed by rolling the thread groove 6 (FIG. 2) of the threaded portion 3a. That is, the screw groove 6 of the screw shaft 3 is plastically processed by a roll die with reference to the outer diameter of the screw shaft material before rolling. As shown in FIG. 3, the nominal outer diameter d1 of the mounting portion of the annular part 18 in the threaded shaft material before rolling is formed to a dimension that allows the annular part 18 to be press-fitted. Furthermore, the portion on the tip side from the mounting portion of the annular part 18 is formed to have an outer diameter d2 slightly smaller than the outer diameter d1, so that the annular part 18 can be press-fitted smoothly. The annular part 18 is press-fitted into the screw shaft 3 after heat treatment, bending correction, and scale reduction of the screw portion 3a are performed on the screw shaft 3 in which the thread groove 6 is processed by rolling. The annular part 18 is supposed to have a surface hardness increased by quenching in advance, but here, a dedicated part is not used, but the inner part of the needle bearing with the inner ring is of the same standard, that is, manufactured as the inner ring of the needle bearing. The product is diverted as an annular part 18. For this reason, the nominal outer diameter d1 of the attachment portion of the annular part 18 in the screw shaft material is an integer value to which the inner ring inner diameter of the needle bearing can be applied.

  The electric actuator having this configuration is connected to, for example, an automobile transmission or an electric disc brake via a connection pin or an arm (both not shown) fitted in the connection hole 17 at the tip of the screw shaft 3, and the motor The rotation of 1 is converted into a sliding motion via the ball screw 2 and transmitted to the transmission and the electric disc brake. That is, the rotation output of the motor 1 is transmitted to the nut 4 via the gears 14 and 15, and the rotation of the nut 4 is converted into the sliding motion of the screw shaft 3 via the ball 5, and the sliding motion is converted to the connecting pin or arm. Is transmitted to the transmission and the electric disc brake.

  In this electric actuator, when an external force is applied to the tip end side of the screw shaft 3, a bending force acts on the screw portion 3 a of the second half portion of the screw shaft 3 in the ball screw 2, but the front half portion of the screw shaft 3 has an annular part 18. Therefore, the bending load applied to the screw portion 3a of the screw shaft 3 can be absorbed.

  The ball screw 2 in this electric actuator has an annular part 18 slidably brought into contact with the bush 16 of the electric actuator, which is a ball screw using device, with a surface hardness increased by quenching, and this annular part 18 is placed on the outer periphery of the screw shaft 3. Since it is installed in the press-fit state, the following advantages are obtained. That is, even if the screw shaft 3 is formed by rolling and the screw shaft material before rolling is manufactured centerless, there is no need to post-process the center hole and finish grinding of the sliding surface with respect to the bush 16. Manufacturing becomes easy. Further, the accuracy of coaxiality between the sliding surface of the screw shaft 3, that is, the outer peripheral surface of the annular component 18 and the screw groove 6 in this embodiment can be improved, and the sliding resistance is reduced and the wear resistance is improved. Is possible. Furthermore, in the heat treatment of the screw shaft 3, since the surface hardening by quenching of the sliding surface can be completed by the annular part 18 which is a separate part, the moving quenching time by induction hardening can be shortened, and this point is also produced. Becomes easy.

  Furthermore, in the ball screw 2 of this embodiment, the outer diameter d1 of the mounting portion of the annular part 18 in the screw shaft 3 is an integer value of the same standard as the inner diameter of the inner ring in the needle bearing with the inner ring. The inner ring of the needle bearing can be diverted, and the annular part 18 can be procured at a low cost.

  FIG. 4 shows another embodiment of the present invention. In the electric actuator of this embodiment, in the first embodiment shown in FIG. 1, a plurality (two in this case) of annular parts 18 attached in a press-fit state on the outer periphery of the screw shaft 3 are arranged in the axial direction. It is. Other configurations are the same as those of the first embodiment shown in FIG.

  When the sliding range of the screw shaft 3 with respect to the bush 16 is wide, if the sliding surface of the screw shaft 3 is configured by one annular component 18, the annular component 18 becomes long. Although the press-fitting work of the part 18 is not easy, in this case, the work can be easily performed by dividing the annular part 18 into a plurality of parts and press-fitting as described above.

It is sectional drawing of the electric actuator using the ball screw concerning 1st Embodiment of this invention. It is a fragmentary sectional view of the ball screw in the electric actuator. It is a partially broken front view of the screw shaft in the ball screw. It is sectional drawing of the electric actuator using the ball screw concerning other embodiment of this invention. It is a partially broken front view of the screw shaft in the same electric actuator. It is a fragmentary sectional view of the electric actuator using the ball screw of the prior art example. It is an expanded sectional view of the A section in FIG. It is explanatory drawing of the bending-force effect | action to the ball screw in a prior art example. It is other explanatory drawing of the bending-force effect | action to the ball screw in a prior art example.

Explanation of symbols

2 ... Ball screw 3 ... Screw shaft 4 ... Nut 16 ... Bush 18 ... Ring component

Claims (4)

  In the ball screw for an electric actuator used in the form of rotating the nut and sliding the screw shaft, an annular part that is hardened on the surface and is brought into sliding contact with the device using the ball screw is attached to the outer periphery of the screw shaft in a press-fitted state. A ball screw for an electric actuator.   The ball screw for an electric actuator according to claim 1, wherein a plurality of the annular parts are arranged in the axial direction.   The ball screw for an electric actuator according to claim 1 or 2, wherein the annular component is of the same standard as an inner ring in a needle bearing with an inner ring.   4. The threaded shaft according to claim 3, wherein the threaded shaft is formed by rolling a thread groove, and an outer diameter of a shaft portion into which the annular part of the threaded shaft is press-fitted is set to an outer diameter of the threaded shaft material before the rolling process. Ball screw for electric actuator with a diameter.

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