CN1447038A - Rolling bearing esp. for dynamo - Google Patents

Abstract

A bearing arrangement 21 comprising an outer ring (24) to be adjusted in a cylindrical groove, a bearing raceway arranged on said outer ring, a series of rolling elements (26) arranged in contact with the bearing raceway, and at least one expansion compensating collar (35) fitted in an annular slit (33) formed by the outer cylindrical surface of the outer ring, said collar having a coefficient of expansion ratio to that of the material forming the outer ring The large material is formed and provides the collar with an outer diameter of between the outer ring outer diameter minus 50 μm and the outer ring outer diameter plus 20 μm.

Description

Especially for rolling bearings in electric motors

technical field

The invention relates to the field of rolling bearings, especially for use such as in electric motors.

Background technique

Electric machines generally include a housing in which a stator is fixed and a rotor mounted for rotation within the stator. The motor is mounted for rotation by means of two bearings, generally rigid ball bearings, positioned on each end of the rotor shaft.

Bearings of the "rigid ball" type generally have a bearing raceway of circular cross-section, which is symmetrical about a plane passing through the center of the ball, and which are capable of high radial loads and moderate axial loads. The two bearings are mounted on the shaft with a press fit by means of their inner rings.

The outer ring of the bearing fits in a cylindrical groove in the motor housing, which is generally constructed of a light aluminum alloy. The outer ring of one of the two bearings is axially secured in the motor housing by suitable means, such as circlips and/or shoulders, and optionally mounted in said housing by clamping.

The outer ring of the other bearing is mounted axially freely in the housing, that is, axial play is allowed. In fact, as the temperature of the electric machine increases, the axial distance separating the second bearing from the first bearing, which is axially fixed relative to the housing, changes slightly due to the different expansions of the various parts of the electric machine. The second bearing must therefore be able to move slightly axially relative to the housing without its outer ring turning at an inappropriate time relative to said housing.

FR-A-2585095 discloses a bearing equipped on its outer ring with a collar of synthetic resin double molded in an annular groove machined on the periphery of said outer ring. These collars protrude radially relative to the outer cylindrical surface of the bearing cup and prevent rotation of the cup relative to the grooves in the housing as the motor heats up.

The motor housing made of light alloy has an expansion coefficient approximately twice that of the steel material of the bearing rings. The temperature rise thus causes radial looseness between the outer ring of the bearing and the groove of the housing. This collar made of plastic material has a significantly higher coefficient of expansion compared to the housing light alloy, which prevents unintentional rotation of the outer ring relative to the groove due to the internal friction of the bearing. The collar has a very large outer diameter relative to the outer diameter of the bearing.

In this way, for example, for a bearing with an outer diameter of 32mm, for a bearing of the same nominal value, the tolerance of the outer diameter of the collar is from +20 to +50μm, that is, from +30 to +70μm, while the tolerance of the diameter of the outer ring of the bearing is from 0 to -10 μm. The result is that the collar protrudes radially and permanently relative to the outer ring surface of the bearing.

Although this device is very satisfactory for preventing unintentional rotation of the outer ring, it also has certain disadvantages.

Fitting the bearing into the groove requires shrinking it and therefore must be done under pressure. Since the collar is arranged on the outer ring and protrudes considerably radially with respect to the outer peripheral surface of the latter, this necessitates the risk of damage and removal of the collar during the shrink fitting process. Clamping the bearing in the groove does not allow the bearing to have sufficient freedom of axial movement during temperature changes. As a result, the bearing is subjected to abnormal axial loads, especially at low and moderate temperatures. The aforementioned abnormal axial loads are likely to detrimentally reduce the life of the bearing frame.

Contents of the invention

The present invention was made to solve the above-mentioned problems.

The present invention provides an improved bearing having a compensating collar.

According to one aspect of the invention, a bearing assembly comprises an outer ring intended to be adjusted in a cylindrical groove, a bearing raceway formed on said outer ring, a series of rolling elements arranged in contact with the raceway, and at least one An expansion compensating collar mounted in the annular throat formed by the outer cylindrical surface of the outer ring, the collar being formed of a material having a higher coefficient of expansion than the material constituting the outer ring. The outer diameter of the collar is between the outer diameter of the outer ring minus 50 μm and the outer diameter of the outer ring plus 20 μm.

Advantageously, the adjustment between the outer diameter of the bearing outer ring and the groove of the light alloy housing will be selected and properly slidable at ambient temperature.

In an embodiment of the invention, the outer diameter of the collar has a tolerance of between +10 and −50 μm relative to the nominal diameter, in particular this tolerance may be between +10 and −30 μm.

In one embodiment of the invention, the tolerance of the outer diameter of the outer ring relative to the nominal diameter is between 0 and -10 μm.

The bearing preferably comprises two compensating collars arranged in two slots on the outer ring, said slots being axially spaced apart. This bearing is preferably symmetrical with respect to a radial plane passing through the centers of the rolling elements.

The bearing may consist of a solid or sheet inner ring provided with an outer bearing raceway in contact with the rolling elements.

In one embodiment of the invention, the inner ring is made of synthetic material. In particular, the inner ring can be made of polyamide.

The bearing may be fixed in a groove provided with a cylindrical bore and forming part of a mechanical part, such as a stator part of an electric motor. The grooves can be made of light alloy.

The invention also provides an electric machine comprising a housing, a stator mounted in the housing, a rotor and at least one bearing as described above fixed between the housing and the rotor.

In one embodiment of the invention, the housing is made of a light alloy, in particular a metal alloy comprising aluminum and/or magnesium.

In one embodiment of the invention, the collar has a higher coefficient of thermal expansion than the material comprising the outer ring of the bearing and the material comprising the groove of said outer ring.

In other words, the outer peripheral surface of the collar may protrude radially by 10 μm relative to the cylindrical outer surface of the bearing outer ring, or may be set back by 25 μm relative to the former. Since the tolerance of the outer diameter of the bearing outer ring relative to its nominal side is from 0 to -10 μm, the tolerance of the groove of the light alloy relative to its nominal side is from 0 to +16 μm, where the nominal side of the groove is the same as the bearing The outer diameter of the outer ring has the same nominal side, and since the collar protrudes very little with respect to the maximum radial protrusion possible for the outer ring, the bearing can be easily fitted into its groove without risk of damaging the collar.

At low temperatures, especially below or close to 0°, there is a large interference between the outer steel ring of the bearing and the groove of the light alloy of the housing. This interference ensures alignment and ensures that the outer ring of the bearing will not rotate in its groove, while at the same time allowing the outer ring to move slightly axially in its groove under reasonable axial loads.

Conversely, when the temperature increases, for example up to 120°C, the interference between the collar and the groove more guarantees the centering and ensures that the outer ring of the bearing does not rotate relative to its groove. In fact, the expansion coefficient of the steel of the outer ring is about 1.5×10 ⁻⁵ , that of the light alloy of the housing is about 2.3×10 ⁻⁵ , and that of the compensation collar is about 13×10 ⁻⁵ . This collar expands much more than the outer ring, thereby ensuring good expansion compensation at normal and elevated temperatures.

In particular, the expansion of the collar in the radial direction is faster than the expansion of the housing groove, and is effectively bonded in the latter, avoiding any rotation of the bearing outer ring in the housing, and ensuring the bearing and the groove. between the centering, and thus ensure the centering between the motor rotor and stator. This last point is very important because the performance of an electric motor is especially dependent on the gap that exists between the stator and the rotor, and the reduction of the gap improves the performance of the motor. As is well known, the smaller this gap is, the higher the demands on the accuracy of the alignment between the rotor and the stator.

In certain applications, such as motors for assisted direction in automobiles, where these requirements are particularly stringent, the misalignment of the rotor relative to the stator must not exceed 50 μm. Thus, the present invention satisfies these demands.

In addition, in the high temperature range, the structure of the collar will temporarily improve, and the collar will become soft and more ductile, which is enough to realize a slight axial movement of the outer ring when it is under load.

By way of example, a PA11 type polyamide can be selected for the manufacture of a collar whose mechanical characteristics are as follows:

Young's modulus at -20°C is 2200MPa

- Poisson's coefficient is 0.4

- The coefficient of thermal expansion is 13×10 ^-5 .

Description of drawings

The invention will be made more comprehensible by the following detailed description of several non-limiting examples and the illustration of the accompanying drawings.

Fig. 1 is the view of the motor axial part in the prior art,

Figure 2 is a front view of a bearing according to one aspect of the invention,

Fig. 3 is a view of the axial part of the bearing in Fig. 2 installed on the motor,

Figures 4 and 5 are detailed views of Figure 3 at high and low temperatures, respectively, and

Figure 6 is a graph showing the axial force applied to a bearing as a function of temperature to translate the bearing within its groove.

Detailed ways

As can be seen in FIG. 1, the motor 1 comprises a housing 2 made of light alloy, a stator 3 integral with the housing 2, a rotor 4 and a shaft 5 on which the rotor 4 is mounted. The housing 2 comprises a substantially cylindrical portion 6, a radial annular portion 7 positioned at one end of the cylindrical portion 6, and a radial portion 8 of annular shape positioned at the opposite end.

An axial portion 9 with a cylindrical bore 10 , a shoulder 11 adjacent to the bore 10 and a groove 12 arranged opposite the shoulder 11 along the bore 10 are integral with the radial annular portion 7 . An axial portion 13 with a cylindrical bore 14 is integral with the radial annular portion 8 and extends axially towards the inside of the electric machine 1 . A bearing 15 of conventional type is mounted by its outer ring in the bore 10 of the axial flange 9 and is axially secured by a shoulder 11 and a circlip 16 arranged in a groove 12 . The bearing 15 is mounted by its inner ring on the outer cylindrical surface of the shaft 5 and is axially secured by a shoulder 17 provided on the shaft 5 and a circlip 18 mounted in a groove machined on the shaft 5 .

The bearing 19 is press-fitted by means of its inner ring at one end of the shaft 5 until it abuts against a shoulder 20 of said shaft 5 . While this press fit ensures the integrity of the bearing 19 to the shaft 5, additional connecting means may be provided between the inner ring of the bearing and the shaft, such as a circlip mounted on the end of the shaft. The outer ring of the bearing 19 is mounted in the bore 14 of the axial part 13 with the option that its outer ring is relatively axially movable relative to the axial part 13 . The rings and the balls of the bearing are generally made of steel, while the housing 2 is made of a light alloy, for example an alloy based on aluminum.

Since light alloys exhibit a much higher coefficient of expansion than steel, especially the outer ring of bearing 19, it is understood that in the low temperature range considerable axial forces are required to make the outer ring of bearing 19 Translating within the housing, in fact, imposes an axial load on the bearing which may be detrimental to said bearing. Conversely, in the high temperature range, excessive spacing can be translated by the rotation of the outer ring relative to the housing by means of the internal drag distance of the bearing 19 .

In order to avoid this situation, the bearing 19 will be replaced by a bearing 21 as shown in FIG. 3 . The bearing 21 comprises a fixed inner ring 22 with an annular bearing race 23, a fixed outer ring 24 with an annular bearing race 25, a series of rolling elements 26, in this case balls, arranged in the bearing race 23 and 25, and maintain regular circumferential intervals by a cage 27 made of synthetic material.

The outer ring 24 includes two grooves 28 and 29 which are provided on either side of the bearing raceway 25 and serve to support sealing flanges 30 and 31 which are made of sheet metal and extend close to The cylindrical bore of the inner ring 22 forms a seal by narrowing the passage.

In addition, the outer ring 24 comprises an outer cylindrical surface 32 in which are machined two slits 33 and 34 which are annular and symmetrical with respect to a radial plane passing through the center of the rolling element 26 and capable of presenting in axial section U-shaped profile. Mounted in each slit 33 , 34 is respectively a collar 35 , 36 made of synthetic material, such as polyamide PA11, which makes the cylindrical outer surface 32 of the outer ring 24 substantially flush.

More specifically, each collar 35 and 36 has a cylindrical outer surface with an outer diameter between the outer diameter of the outer ring 24 minus 50 μm and the outer diameter of the outer ring 24 plus 20 μm. In order to achieve the above objectives, the tolerance of the outer diameter of the collars 35 and 36 relative to the nominal diameter of the outer surface of said collars 35, 36 is set between +10 μm and -50 μm, said tolerance is preferably between +10 μm and - Between 30μm.

It can also be provided that the tolerance of the outer diameter of the outer ring relative to its nominal diameter is between 0 and −10 μm. Therefore, at ambient temperature, the collars 35 and 36 do not protrude beyond the outer surface 32 of the outer diameter 24, or protrude very little, so that the bearing in the bore hole such as the bore hole 14 of the axial flange 13 of the housing 2 A press fit can be easily achieved without force or damage to the collars 35 , 36 .

The collars 35 , 36 are preferably injection molded in the grooves 34 and 33 . In this way, they can protrude slightly relative to the outer surface 32 after injection molding, as shown in FIG. 4 , or be slightly recessed, as shown in FIG. 5 .

The slots 33 and 34 are axially spaced apart in the sense that the cylindrical outer surface 32 of the outer ring 24 is divided into three parts, one part between one of the radially front faces of the bearing and the slot 33 and the second part in the slot. between the openings 33 and 34, while the third portion is located between the slit 34 and the radially front surface opposite the first portion.

In order to facilitate the mounting of the bearing 21 into the bore 14 of the axial flange 13 , said bore may have a tolerance of between 0 and +16 μm relative to its nominal flank. This means that the bearings can be mounted easily.

By way of example, for a bearing with an outer diameter less than or equal to 50 mm, it can be assumed that the tolerance of the outer diameter is between 0 and -10 μm, while for a bearing with an outer diameter of 50 to 80 mm, it can be assumed that the tolerance of the outer diameter is The tolerance is between 0 and -50 μm.

The inner ring 22 can be mounted on the shaft 5 .

Figure 6 shows the variation of the force applied to the bearing to move it in the bore of the axial flange, on which the bearing groove is formed, at different temperatures. The bearing has a nominal outside diameter of 32 mm and the outside diameter tolerance provides maximum interference between the groove and the bearing with the collar. The curve is thus an envelope curve that delimits an area on the abscissa and said curve and within this area is an interference curve with respect to other, smaller diameters.

For temperatures below 0°C, the light alloy of the housing/steel of the bearing outer ring predominates, and for temperatures above 0°C, the light alloy of the housing/compensating collar contacts. It is to be noted that the axial load is less than 500 N for temperatures above 0°C, and between 400 and 500 N for ambient temperatures between 0 and 30°C.

Based on a temperature of 20°C, the load decreases as a function of temperature until the load is less than 200N around a temperature of 80°C. At temperatures below 0° C., the load also decreases consistently with a more pronounced slope as a function of temperature.

It will be understood that, thanks to the invention, it is possible to obtain a bearing suitable for various applications, in particular in the field of electrical machines, which has a compensating collar which does not stand against the outer ring of the bearing at low temperatures. The outer surface protrudes so that it can be easily press-fitted without risk, while at high temperatures said press-fit can be maintained thanks to the considerable expansion of the compensating collar, preventing the expansion of the groove from being translated between the two elements by separation Between rotations, the expansion of the groove is much larger than the expansion of the outer ring of the bearing.

As a result, the electric machine can be constructed with reduced radial play and thus improve performance. Excessive axial loads on the bearings, which would be detrimental to the life of the bearing frame, and a rotation of the outer ring relative to the groove, which is also detrimental to the life of the motor, can also be avoided.

Claims (11)

1. a bearing means (21), comprise the outer ring (24) that in cylinder shape groove, to regulate, be arranged on the bearing race on the described outer ring, the a scrolling series element (26) that contacts and arrange with bearing race, with at least one expansion compensation axle collar (35), this axle collar is arranged in the annular narrow orifice (33) that the exterior cylindrical surfaces by the outer ring forms, the described axle collar is formed by the expansion coefficient material bigger than the expansion coefficient of the material that forms the outer ring, it is characterized in that the external diameter of the described axle collar deducts 50 μ m and the outer ring external diameter adds between the 20 μ m between the outer ring external diameter.

2. the device described in claim 1 is characterized in that, the external diameter of the axle collar with respect to the tolerance of nominal diameter between+10 and-50 μ m.

3. device as claimed in claim 1 or 2 is characterized in that, the external diameter of the axle collar with respect to the tolerance of nominal diameter between+10 and-30 μ m.

4. each described device as in the above-mentioned claim is characterized in that, the external diameter of outer ring with respect to the tolerance of nominal diameter between 0 and-10 μ m.

5. as each described device in the above-mentioned claim, it is characterized in that this device comprises two compensating collars (35,36), they are installed in two narrow orifices (33,34) of outer ring, and described narrow orifice is axially separated.

6. as each described device in the above-mentioned claim, it is characterized in that the outer ring is formed from steel.

7. as each described device in the above-mentioned claim, it is characterized in that the axle collar is made by composite.

8. mechanical component, comprise a groove that is provided with cylindrical bore and as above-mentioned claim in each described device, this device is installed in the described groove.

9. element as claimed in claim 8 is characterized in that this groove is made by light alloy.

10. element as claimed in claim 9 is characterized in that, this groove is by making based on the alloy of aluminium or magnesium.

11., it is characterized in that the thermal expansion coefficient of the axle collar is than the material coefficient of thermal expansion coefficient that constitutes bearing outer ring and to constitute the material coefficient of thermal expansion coefficient of groove of described outer ring big as each described element in the claim 8 to 10.

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