Method of fixing a first component in a second component and unit, in particular actuator, manufactured thereby

Abstract

The invention relates to a method for fixing a first component in a second component. At least a portion of the inner side of the second component is covered with a plastic bushing, and the first component is positioned and fixed in the plastic bushing of the second component by means of a press fit. In this way, a reliable fixing of the first component in the second component is achieved. The invention also relates to a unit formed by this method.

Description

TECHNICAL FIELD

[0001] The invention relates to a method for fixing a first component in a second component, wherein the first component is centered and fixed in the second component by means of a press fit. BACKGROUND

[0002] Such a method is known and is used, for example, for fixing an electric motor, in particular a direct current motor, in a housing of an actuator. Such an actuator can be used, for example, for controlling certain components, wherein the electric motor is connected to a transmission which provides a corresponding movement variable.

[0003] The first component, which is, for example, a direct current motor, is fixed in the second component, which is, for example, an actuator housing, by means of a press fit, and this press fit must be suitable for both components, since the tolerance ranges in the respective components must be taken into account. Furthermore, the problem exists that the press fit must be suitable for all temperatures in the respective operating temperature range, for example between -40°C and +200°C. However, since the first component and the second component are usually made of different materials having different coefficients of thermal expansion, and since both materials have a certain size tolerance range and there are some size differences at different temperatures, it can happen that the press fit between the first component and the second component becomes too large and in this way generates corresponding stresses in the components, or that the press fit between the first component and the second component becomes too small so that there is no longer any contact between the components and a gap is formed between the components. SUMMARY

[0004] The invention is based on the object of providing a method of the type mentioned at the outset with which a particularly reliable fixing of the components to one another can be achieved.

[0005] According to the invention, this object is achieved by a method of the type specified, which comprises the following steps:

[0006] • coating at least a portion of the inside of the second component to form a plastic bushing; and

[0007] • centering and fixing the first component in the plastic bushing of the second component by means of a press fit.

[0008] Without affecting the respective tolerance ranges of the components, the invention proposes arranging an additional element in the system, which additional element is produced by coating the inside of the second component. The first component is then centered and fixed in the plastic bushing which is coated on the second component.

[0009] By providing an intermediate element between the two components, the transition between the first component and the second component can be compensated or balanced, so that corresponding differences in the press-fit force can be greatly reduced or normalized. Thus, despite different materials, different coefficients of thermal expansion, different temperatures, etc., the occurrence of excessively high press-fit forces and excessively low press-fit forces, which can lead to the above-mentioned disadvantages, is avoided.

[0010] In the method according to the application, it is preferred to coat with a plastic bushing whose coefficient of thermal expansion is coordinated / matched to the coefficient of thermal expansion of the first component and / or the second component in such a way that, in the operating temperature range, no more than the critical stress is reached in the components during / after the press-fitting, and there is no contact wear between the components. In particular, it is preferred to coat with a plastic bushing whose coefficient of thermal expansion satisfies the above-mentioned conditions in the operating temperature range of -40°C to 200°C.

[0011] The material of the thus-coated plastic bushing is therefore selected in such a way that the coefficient of thermal expansion of the plastic bushing, in combination with the respective coefficients of thermal expansion of the first component and the second component, does not cause damage to the system in the temperature range, and furthermore does not cause a gap between the components that would lead to a loosening of the press fit.

[0012] The method according to the application is preferably used in the case of an application in which a DC motor is used as the first component and an actuator housing is used as the second component. The actuator housing is substantially cylindrical. As described above, it is at least partially coated on its inner side with a plastic bushing. As a result, both the base of the actuator housing and the cylindrical inner wall can be coated with the plastic bushing. It is also possible to coat only the portion of the cylindrical inner wall that is used to provide the press fit.

[0013] In a particularly preferred embodiment, a first component is used that has a central boss on the base side, which engages in a recess of the second component, and the inner side of the recess is coated to form a plastic bushing or a portion thereof at this location. For example, a bearing bushing (bronze bushing) for the rotor of a DC motor can be arranged in the manner described above. The boss of the first component is then arranged in the recess of the second component, which is coated with the plastic bushing, by press fitting.

[0014] In particular, in the method according to the application, the base region of the second component is coated with a plastic bushing that has an H-shaped cross section, in which the boss of the first component engages. The centering of the first component is always achieved in one of the two functional phases, namely the internal press fit between the first component and the coated plastic bushing, and the external press fit between the first component and the coated plastic bushing, since the coated plastic bushing contacts the second component both internally and externally.

[0015] In any case, the application is not limited to the above-mentioned application cases. The application can be used in any case where an assembly by means of a press fit is required and in particular where the corresponding system has to be operated over a large temperature range.

[0016] In any case, in the method according to the application, the axial force of the press fit is also of such a size that during the assembly process the corresponding components, for example the DC motor and the actuator housing, are not damaged.

[0017] According to the application, the different coefficients of thermal expansion of the materials used for the motor housing, the overmoulded plastic bushing and the actuator housing are matched to one another, so that the stresses produced in the system by the press fit are reduced below the critical limit. In particular, the contact between the components does not disappear for any temperature in the corresponding temperature range required for the function of the system, for example -40°C to 200°C, since the centring process is always in one of the following two phases:

[0018] Phase 1 : Press fit of the inside between the second component (actuator housing) and the overmoulded plastic bushing;

[0019] Phase 2: Press fit of the outside between the second component (actuator housing) and the overmoulded plastic bushing.

[0020] Depending on the actual size values and the actual temperature, the centring is switched between phase 1 and phase 2 and vice versa, so that there is always a press fit force during this transition.

[0021] The application also relates to a unit formed by the method of the above-mentioned type. The unit is preferably an actuator, in the housing of which a motor, in particular a DC motor, is fixed by means of a press fit. BRIEF DESCRIPTION OF DRAWINGS

[0022] The application is explained in detail below by means of an embodiment with reference to the drawings. The drawings show:

[0023] Figure 1 A first component embodied as a DC motor is shown as being fixed in a second component embodied as an actuator housing by means of a press fit in the prior art;

[0024] Figure 2 is a similar view in which the press fit region is identified; and Figure 1

[0025] Figure 3 A fixing of the first component in the second component in the application is shown. DETAILED DESCRIPTION

[0026] In Figure 1 ​In the method shown, an approximately cylindrical first part 2, which here is a DC motor with a corresponding housing, is fixed in a second part 1, which here is an actuator housing. Here, the approximately cylindrical first part 2 is inserted in an approximately cylindrical inner space of the second part 1, i.e. is positioned centrally, and is fixed by a press fit.

[0027] The first part 2 has a boss 3 on its bottom side, which can contain, for example, a bronze bushing, which serves to support the rotor 10 of the DC motor.

[0028] Figure 2 The press fit region 5 between the two parts is shown, which ensures the fixing of the DC motor in the actuator housing.

[0029] Since the first part 2, i.e. the motor housing, and the second part 1, i.e. the actuator housing, are each made of different materials with different coefficients of thermal expansion, and both the first part and the second part have a given dimensional tolerance range and a certain dimensional deviation at different temperatures, the press fit force between the first part and the second part can become too large or too small. The problems resulting therefrom have already been mentioned at the outset.

[0030] These problems are overcome by the method according to the invention. Here, at least a portion of the inner side of the second part 1 is first coated to form a plastic bushing 8. The profile of this H-shaped plastic bushing is designated by reference numeral 8. In this embodiment, the bottom of the inner space of the second part 1 has a central recess for receiving the support boss 3 of the motor housing, and is coated in this recess region, so that Figure 3 The plastic bushing 8 shown has an H-shaped profile. The coating described above should preferably be carried out using a plastic material whose coefficient of thermal expansion is between the coefficients of thermal expansion of the first part and the second part.

[0031] The support boss 3 of the first part 2 is then positioned centrally and fixed in the plastic bushing 8 formed by the coating by a press fit. This results in an inner press fit between the plastic bushing 8 and the second part 1 as shown at reference numeral 7, and an outer press fit between the plastic bushing 8 and the second part 1 as shown at reference numeral 6, since the plastic bushing 8 formed by the coating contacts the second part 1 both with its radially outer side and with its radially inner side due to its H shape. Depending on the actual size values and the temperature, the transition from phase / period 1 (inner press fit 7 between the second part 1 and the coated plastic bushing 8) to phase 2 (outer press fit 6 between the second part 1 and the coated plastic bushing 8) and vice versa takes place when being positioned centrally, so that there is always a press fit force during this transition.

[0032] The plastic covering 8 thus enables reliable fixing even at high temperature differences and in the case of different materials of the first and second components.

Claims

1. A method for fixing a first component (2) in a second component (1), wherein the first component (2) is centrally positioned and fixed in the second component (1) by press fitting, the method comprising the following steps: • Overmolding at least a portion of the inner side of the second component (1) to form a plastic bushing (8); and • By means of press fitting, the first component (2) is centered and fixed inside the plastic bushing (8) of the second component (1); The bottom region of the second component (1) is covered by a plastic bushing (8) with an H-shaped cross section, and the boss (3) of the first component (2) is joined to the plastic bushing.

2. The method of claim 1, wherein, The plastic bushing (8) with a coefficient of thermal expansion that matches that of the first component (2) and / or the second component (1) is used for overmolding, such that the critical stress in the components (1, 2) does not exceed during / after the press-fit process within the operating temperature range, and there is no contact loss between the components (1, 2).

3. The method of claim 2, wherein, The plastic bushing (8) with the following coefficient of thermal expansion is used for overmolding: the coefficient of thermal expansion meets the above conditions in the operating temperature range of -40°C to 200°C.

4. The method according to one of the preceding claims, characterized in that A DC motor is used as the first component (2) and an actuator housing is used as the second component (1).

5. The method according to one of the preceding claims, characterized in that The first component (2) has a central boss (3) on its bottom side, which engages in a recess in the second component (1), and the inside of the recess is covered and shaped.

6. The method according to any one of the preceding claims, characterized in that, The first component (2) is always centered in one of the following two functional stages: the internal press fit (7) between the second component (1) and the overmolded plastic bushing (8), and the external press fit (6) between the second component (1) and the overmolded plastic bushing (8).

7. A unit formed by the method according to any one of claims 1 to 6.

8. The unit according to claim 7, characterized in that, This unit is an actuator, and the motor is fixed in the actuator housing by press fitting.

9. The unit according to claim 8, characterized in that, The motor is a DC motor.

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