JP2004150533A - Ball screw for electric brake device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ball screw for an electric brake device capable of securing an excellent lubrication performance for a long time while maintaining required sealing performance. <P>SOLUTION: The ball screw for an electric brake device is equipped with a screw shaft 3 provided with a spiral screw groove 2 on an outer peripheral surface, a nut 6 provided with a spiral screw groove 4 corresponding to the screw groove 2 on an inner peripheral surface and fitted to the screw shaft 3, and a plurality of balls 5 rollably mounted between the screw grooves 2, 4. The ball screw is driven by the electric motor 19 to press a brake pad 13 against a brake disc 12 by the driving force, thereby generating a braking force. A labyrinth seal 30 made up of a lubricant-containing polymer member is fitted in the rear end inner peripheral surface of the nut 6 to be mounted between the rear end of the nut 6 and the screw shaft 3. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a ball screw for an electric brake device used for an electric brake device of an automobile or the like, for example.
[0002]
[Prior art]
Conventionally, a ball screw has a nut having a helical thread groove on an outer peripheral surface and a nut having a helical screw groove corresponding to the thread groove of the screw shaft on an inner peripheral surface of a screw shaft extending in the axial direction. The screw groove of the nut and the screw groove of the screw shaft face each other to form a spiral load track between them. A number of balls as rolling elements are rollably mounted on the load track, and the rotation of the screw shaft (or nut) causes the nut (or screw shaft) to move in the axial direction through the rolling of the ball. It is supposed to.
[0003]
By the way, in recent years, a ball screw driven by an electric motor may be used in place of a hydraulic cylinder as a drive mechanism of a brake device of an automobile or the like (for example, see Patent Document 1).
This ball screw is configured to generate a braking force by rotating a nut in the axial direction by, for example, driving a screw shaft by an electric motor, and pressing a brake pad against a brake disk or a brake shoe by the driving force of the nut. Things.
[0004]
In addition, a lubricant such as grease is usually applied between the thread groove of the nut and the ball and between the thread groove of the screw shaft and the ball. However, since the function of the lubricant as a lubricant deteriorates in a relatively short period of time due to the influence of foreign matter and the like, conventionally, a lip-type seal member is attached to the end of the nut. In this way, it is intended to prevent foreign matter and the like from entering the nut and to prevent grease and the like inside the nut from leaking to the outside, thereby ensuring good lubrication performance.
[0005]
[Patent Document 1]
Japanese Unexamined Patent Application Publication No. 2002-530597
[Problems to be solved by the invention]
However, in the ball screw for an electric brake device as described in Patent Document 1, since the screw groove does not form a closed circuit due to the spiral shape, it is difficult to completely seal the screw groove with a lip-type sealing member. There is a problem that it is impossible to completely prevent the intrusion of foreign matter and the like into the inside and the leakage of grease and the like in the nut to the outside, and it is difficult to secure good lubrication performance over a long period of time.
SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a ball screw for an electric brake device that can ensure good lubrication performance over a long period of time while maintaining necessary sealing performance.
[0007]
[Means for Solving the Problems]
The object of the present invention is to provide a screw shaft having a helical screw groove on the outer peripheral surface, and a helical screw groove corresponding to the screw groove of the screw shaft on the inner peripheral surface, which is fitted to the screw shaft. And a plurality of balls rotatably mounted between the two screw grooves, and is driven by an electric motor to generate a braking force by pressing a brake pad against a brake disc or a brake shoe by the driving force. In the ball screw for the electric brake device to be
This is achieved by a ball screw for an electric brake device, wherein a labyrinth seal made of a polymer material containing a lubricant is provided at at least one end in the axial direction of the nut.
[0008]
According to the above configuration, since the labyrinth seal made of the lubricant-containing polymer member is provided at the end of the nut in the axial direction, it is possible to prevent foreign matter such as large dust that adversely affects lubrication from entering the nut in a short period of time. In addition, a good lubricating performance can be ensured for a long time by oozing out the lubricant from the lubricant-containing polymer member, and a high-efficiency electric brake device with low rolling loss and low energy loss is realized. be able to.
[0009]
In addition, since the ball screw that generates a large thrust force and is exposed to the harshest environment in the electric brake device is almost maintenance-free, the maintenance only requires replacement of the brake pad like the conventional hydraulic brake device. Can be done.
[0010]
Further, the object of the present invention is to provide a screw shaft having a helical screw groove on the outer peripheral surface, and a helical screw groove corresponding to the screw groove of the screw shaft on the inner peripheral surface, and fitted to the screw shaft. A combined nut and a number of balls rollably mounted between the two screw grooves, and driven by an electric motor, the driving force of which presses a brake pad against a brake disc or a brake shoe, thereby providing a braking force. In a ball screw for an electric brake device that generates
A labyrinth seal is provided at at least one end in the axial direction of the nut, and a slide made of a lubricant-containing polymer member that is in sliding contact with at least one of the outer peripheral surface of the screw shaft and the inner peripheral surface of the nut. This is achieved by a ball screw for an electric brake device, characterized in that a contact member is provided.
[0011]
According to the above configuration, since the labyrinth seal is provided at the end in the axial direction of the nut, it is possible to prevent foreign matters such as large dusts that adversely affect lubrication from entering the nut in a short time, and Since the sliding contact member made of a lubricant-containing polymer member that slides on at least one of the outer peripheral surface of the screw shaft and the inner peripheral surface of the nut is provided, the lubricant oozes out from the sliding contact member. Good lubrication performance can be ensured for a long period of time, and a highly efficient electric brake device with low rolling resistance and low energy loss can be realized.
[0012]
In addition, since the ball screw that generates a large thrust force and is exposed to the harshest environment in the electric brake device is almost maintenance-free, the maintenance only requires replacement of the brake pad like the conventional hydraulic brake device. Can be done.
In this case, by forming the labyrinth seal with a lubricant-containing polymer member, lubrication performance can be further improved.
[0013]
In addition, since the electric brake device is exposed to a high temperature during use, the lubricant easily oozes out of the lubricant-containing polymer member and lubrication is effectively performed, but the polymer member that can withstand high temperatures does not ooze too much. The selection and combination of base oils is important.
Here, the lubricant-containing polymer member applied to the present invention includes a lubricant selected from a group of polyolefin resins having basically the same chemical structure, such as polyethylene, polypropylene, polybutylene, and polymethylpentene. In the form of any of single or mixed oils such as paraffinic hydrocarbon oils such as poly-α-olefin oils, naphthenic hydrocarbon oils, mineral oils, ether oils such as dialkyldiphenyl ether oils, and ester oils such as phthalic acid esters. The raw material prepared by mixing with the above is plasticized by heating at a temperature higher than the melting point of the resin, and then cooled to a solid state.An antioxidant, a rust inhibitor, an antiwear agent, a foam What added various additives, such as an eraser and an extreme pressure agent, may be used.
[0014]
The composition ratio of the above-mentioned lubricant-containing polymer member is 10 to 50% by weight of the polyolefin resin and 90 to 50% by weight of the lubricant based on the total weight. When the content of the polyolefin resin is less than 10% by weight, a certain level of hardness and strength cannot be obtained, and it becomes difficult to maintain the initial shape when a load is applied. When the polyolefin-based resin exceeds 50% by weight (that is, when the lubricant is less than 50% by weight), the supply of the lubricant is reduced, and the life of the ball screw is shortened.
[0015]
The synthetic resin group has the same basic structure but different average molecular weights, and ranges from 700 to 5 × 10 ⁶ . Waxes having an average molecular weight of 700 to 1 × 10 ⁴ (for example, polyethylene wax), those having a relatively low average molecular weight of 1 × 10 ⁴ to 1 × 10 ⁶ , and those having an average molecular weight of 1 × 10 ^{6 to} 5 An ultrahigh molecular weight of × 10 ⁶ is used alone or in combination as necessary.
[0016]
The combination of a relatively low molecular weight and a lubricant provides a lubricant-containing polymer with some mechanical strength, lubricant supply capacity, and oil retention. If some of the relatively low molecular weight compounds are replaced with those classified as wax, the difference in molecular weight between those classified as wax and lubricating oil will increase the affinity for lubricating oil. As a result, the oil retaining property of the lubricant-containing polymer member is improved, and the lubricant can be supplied for a long period of time. However, on the other hand, the mechanical strength decreases. As the wax, in addition to a polyolefin-based resin such as polyethylene wax, a hydrocarbon-based wax having a melting point in the range of 100 to 130 ° C. or more (for example, a paraffin-based synthetic wax) can be used.
[0017]
On the other hand, when replaced with ultra-high molecular weight ones, the difference in molecular weight between the ultra-high molecular weight ones and the lubricating oil is so large that the affinity with the lubricating oil is reduced, resulting in reduced oil retention. The bleeding of the lubricant from the lubricant-containing polymer member is accelerated. Thereby, the time required to reach the amount of lubricant that can be supplied from the lubricant-containing polymer member is shortened, and the life of the ball screw is shortened. However, the mechanical strength is improved.
[0018]
Taking into account the balance of moldability, mechanical strength, oil retention, and lubricant supply, the composition ratio of the lubricant-containing polymer member is 0 to 5% by weight classified into wax, and 8 to 5% in relatively low molecular weight. Preferred is 48% by weight, 2 to 10% by weight of ultrahigh molecular weight, and 10 to 50% by weight in total of three resin components (the remainder is 90 to 50% by weight of lubricant).
[0019]
In order to improve the mechanical strength of the lubricant-containing polymer member of the present invention, the following thermoplastic resin and thermosetting resin can be added to the above-mentioned polyolefin-based resin. As the thermoplastic resin, resins such as polyamide, polycarbonate, polybutylene terephthalate, polyphenylene sulfide, polyether sulfone, polyether ether ketone, polyamide imide, polystyrene, and ABS resin can be used.
[0020]
On the other hand, as the thermosetting resin, each resin such as an unsaturated polyester resin, a urea resin, a melanin resin, a phenol resin, a polyimide resin, and an epoxy resin can be used. These resins may be used alone or as a mixture.
[0021]
Further, in order to disperse the polyolefin resin and the other resin in a more uniform state, a suitable compatibilizer may be added as needed. Further, a filler may be added to improve the mechanical strength. For example, calcium carbonate, magnesium carbonate, inorganic whiskers such as potassium titanate whiskers and aluminum borate whiskers, or inorganic fibers such as glass fibers and metal fibers, and those obtained by braiding them in a cloth form, and in organic compounds, Carbon black, graphite powder, carbon fiber, aramid fiber, polyester fiber and the like may be added.
[0022]
Further, for the purpose of preventing deterioration of the polyolefin-based resin due to heat, an anti-aging agent such as N, N'-diphenyl-P-phenyldiamine, 2,2'-methylenebis (4-ethyl-6-t-butylphenol), For the purpose of preventing deterioration due to light, 2-hydroxy-4-n-octoxybenzophenone, 2- (2′-hydroxy-3′-t-butyl-5′-methyl-phenyl) -5-chlorobenzotriazole And the like may be added.
[0023]
The addition amount of all of the above additives (other than the polyolefin resin and the lubricant) is preferably 20% by weight or less of the total amount of the molding raw material as a whole of the additives in order to maintain the lubricant supply capacity. .
Unlike the grease and the lubricating oil, the above-mentioned lubricant-containing polymer member itself is in a solid state, so that water and dust are not mixed therein. Therefore, when a lubricant-containing polymer is provided in the space between the nut end and the screw shaft, intrusion of water and dust, which causes a reduction in the life of the ball screw, in addition to or instead of the sealing member, is greatly reduced. be able to.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a sectional view for explaining a ball screw for an electric brake device according to a first embodiment of the present invention.
As shown in FIG. 1, the ball screw for an electric brake device according to the first embodiment includes a screw shaft 3 having a spiral screw groove 2 on an outer peripheral surface and extending in an axial direction, and a screw on an inner peripheral surface. A nut 6 having a spiral screw groove 4 corresponding to the groove 2 is fitted.
[0025]
The screw groove 4 of the nut 6 and the screw groove 2 of the screw shaft 3 are opposed to each other to form a spiral load track between them, and a number of balls 5 as rolling elements are rolled on the load track. It is movably loaded.
A circulating top 8 having a substantially S-shaped ball circulating groove 8a as an example of a ball circulating member is fitted on the outer peripheral surface of the nut 6, and the circulating top 8 is attached to the outer peripheral surface of the nut 6 by a lid 9. Fixed. The ball 5 which rolls on the load track between the two screw grooves 2 and 4 by the circulating frame 8 passes over the land 3a of the screw shaft 3 by the scooping portion of the circulating frame 8 and the ball circulating groove 8a inside the circulating frame 8 is formed. And the ball 5 is circulated by returning to the load track between the adjacent screw grooves 2 and 4 via the ball circulation groove 8a.
[0026]
The nut 6 of the ball screw thus configured is fitted inside the caliper 10 via the bush 11 so as to be slidable in the axial direction. The front end (left end in the figure) of the nut 6 presses the rear brake pad 13 of a pair of front and rear brake pads 13 that sandwich the brake disc 12 (or brake shoe) to press the brake pad 13. A plunger 15 for pressing the disc against the brake disc 12 (or the brake shoe) is attached by a pin 16 or the like.
[0027]
At the center of the front end face of the plunger 15, a rod cell 17 as a braking force measuring means is attached, and the rod cell 17 is covered with a cap 18.
A motor shaft 20 of an electric motor 19 is connected substantially concentrically to a rear end (right end in the figure) of the screw shaft 3 via a key or the like. And is fixed to the caliper 10. The rear end of the screw shaft 3 is rotatably supported by a rolling bearing such as a cross ball bearing 23, and the cross ball bearing 23 is preloaded by a preload spring 24.
[0028]
Then, by driving the electric motor 19 to rotate the screw shaft 3, the nut 6 moves axially forward through the rolling of the ball 5 and the rear brake pad of the pair of front and rear brake pads 13. 13 is pressed by the plunger 15, whereby the brake pad 13 presses the brake disc 12 (or brake shoe) to generate a braking force.
[0029]
Here, in the present embodiment, a labyrinth seal 30 made of a polymer material containing a lubricant is fitted between the rear end of the nut 6 and the screw shaft 3 by being fitted to the inner peripheral surface of the rear end of the nut 6. Thereby, it is possible to prevent foreign matters such as large dusts which adversely affect the lubrication from entering the nut 6 in a short term, and to obtain a good lubricating performance for a long time by exuding the lubricant from the lubricant-containing polymer member. As a result, it is possible to realize a high-efficiency electric brake device with low rolling resistance and low energy loss.
[0030]
In addition, since the ball screw which generates a large thrust force and is exposed to the most severe environment in the electric brake device becomes almost maintenance-free, only the replacement of the brake pad 13 is performed similarly to the conventional hydraulic brake device. Maintenance can be completed.
[0031]
In the first embodiment, the labyrinth seal 30 made of a lubricant-containing polymer member is arranged only between the rear end of the nut 6 and the screw shaft 3, but the present invention is not limited to this. Instead, as shown in FIG. 2, a labyrinth seal 30 made of a polymer member containing a lubricant is provided between the rear end of the nut 6 and the screw shaft 3 and between the front end of the nut 6 and the screw shaft 3. They may be arranged to further improve sealing performance and lubrication performance.
[0032]
Further, in the first embodiment, the plunger 15 is attached to the front end of the nut 6 via the pin 16, but instead, the plunger 15 is attached to the front end of the nut 6 as shown in FIGS. The plunger 15 may be attached by serration fitting.
[0033]
Next, a ball screw for an electric brake device according to a second embodiment of the present invention will be described with reference to FIG. The basic configuration of the electric brake device is the same as that described with reference to FIG. 1, and therefore, the same parts are denoted by the same reference numerals in the drawing, and detailed description will be omitted. As shown in FIG. 3, the ball screw for an electric brake device according to the second embodiment has a labyrinth including a normal sealing member between the rear end (the right end in the figure) of the nut 6 and the screw shaft 3. The seal 40 is fitted on the inner peripheral surface of the rear end of the nut 6 and attached, and the sliding contact member 50 made of a lubricant-containing polymer member slidingly contacting the outer peripheral surface (land portion 3 a) of the screw shaft 3 is moved in the axial direction of the labyrinth seal 40. The nut 6 is fitted and attached to the inner peripheral surface of the rear end of the nut 6 at a position adjacent to the inside.
[0034]
The sliding contact member 50 is radially pressed toward the outer peripheral surface of the screw shaft 3 at a constant pressure by a garter spring 51 fitted on the outer peripheral surface. Even if it wears over time, appropriate contact with the screw shaft 3 is always maintained and good lubrication is ensured.
[0035]
As described above, in the second embodiment, since the labyrinth seal 40 made of a normal sealing member is provided between the rear end (the right end in the figure) of the nut 6 and the screw shaft 3, the lubrication is adversely affected in a short time. It is possible to prevent foreign matter such as large dust from entering the nut 6.
[0036]
Further, since the sliding member 50 made of a lubricant-containing polymer member that is in sliding contact with the outer peripheral surface (land portion 3 a) of the screw shaft 3 is disposed adjacent to the inside of the labyrinth seal 40 in the axial direction, the sliding member 50 is A good lubricating performance can be ensured for a long period of time by oozing out of the lubricant, and a highly efficient electric brake device with low energy loss and low rolling resistance can be realized.
[0037]
Further, since a ball screw that generates a large thrust force and is exposed to the most severe environment in the electric brake device becomes almost maintenance-free, only the replacement of the brake pad 13 is required as in the case of the conventional hydraulic brake device. Maintenance can be completed.
Here, by forming the labyrinth seal 40 from a polymer material containing a lubricant, it is possible to further improve the sealing performance and the lubrication performance.
[0038]
In the second embodiment, the labyrinth seal 40 and the sliding contact member 50 are arranged on the rear end side of the nut 6 as an example. Instead, as shown in FIG. Are disposed between the rear end of the nut 6 and the screw shaft 3 and between the front end of the nut 6 and the screw shaft 3 and slidably contact the outer peripheral surface (land portion 3a) of the screw shaft 3. The slide contact member 50 made of a polymer member may be disposed adjacent to the front end side of the labyrinth seal 40 in the axial direction. In this case, the sealing performance and the lubrication performance can be further improved, and the rear end side can be effectively lubricated.
[0039]
It should be noted that the ball screw for an electric brake device according to the present invention is not limited to the above embodiments, and it goes without saying that various forms can be adopted based on the spirit of the present invention.
For example, in each of the above embodiments, the case where the nut 6 is moved in the axial direction by rotating the screw shaft 3 is taken as an example. However, the present invention is not limited to this, and the screw shaft 3 is rotated in the axial direction by rotating the nut 6. The present invention may be applied to a moving type ball screw for an electric brake device.
[0040]
【The invention's effect】
As described above, according to the ball screw for an electric brake device of the present invention, good lubrication performance can be ensured for a long period of time while maintaining the required sealing performance, so that rolling resistance is reduced and energy loss is reduced. A small and highly efficient electric brake device can be realized.
In addition, since the ball screw that generates a large thrust force and is exposed to the harshest environment in the electric brake device is almost maintenance-free, just like the conventional hydraulic brake device, the maintenance only requires replacement of the brake pad. Can be done.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view for explaining a ball screw for an electric brake device according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view illustrating a modified example of the ball screw for an electric brake device shown in FIG.
FIG. 3 is a cross-sectional view illustrating a ball screw for an electric brake device according to a second embodiment of the present invention.
FIG. 4 is a cross-sectional view for explaining a modified example of the ball screw for an electric brake device shown in FIG.
[Explanation of symbols]
2 Screw groove (screw shaft side)
3 Screw shaft 4 Screw groove (nut side)
5 Ball 6 Nut 12 Brake Disc 13 Brake Pad 19 Electric Motor 30 Labyrinth Seal

Claims (3)

A screw shaft having a spiral screw groove on the outer peripheral surface, a nut fitted on the screw shaft having a spiral screw groove on the inner peripheral surface corresponding to the screw groove of the screw shaft, and the two screws A ball screw for an electric brake device, comprising: a plurality of balls rotatably mounted between grooves, driven by an electric motor, and generating a braking force by pressing a brake pad against a brake disk or a brake shoe by the driving force. At
A ball screw for an electric brake device, wherein a labyrinth seal made of a lubricant-containing polymer member is provided on at least one end of the nut in the axial direction. A screw shaft having a spiral screw groove on the outer peripheral surface, a nut fitted on the screw shaft having a spiral screw groove on the inner peripheral surface corresponding to the screw groove of the screw shaft, and the two screws A ball screw for an electric brake device, comprising: a plurality of balls rotatably mounted between grooves, driven by an electric motor, and generating a braking force by pressing a brake pad against a brake disk or a brake shoe by the driving force. At
A labyrinth seal is provided at at least one end in the axial direction of the nut, and a slide made of a lubricant-containing polymer member that slides on at least one of the outer peripheral surface of the screw shaft and the inner peripheral surface of the nut. A ball screw for an electric brake device, comprising a contact member. 3. The ball screw according to claim 2, wherein the labyrinth seal is made of a lubricant-containing polymer member.

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