The present invention relates to a sealed bearing provided with a seal for covering a rolling element from a side between an inner bearing ring and an outer bearing ring.
In recent years, due also to progress in the development of electric cars (EV), hybrid cars (HV), and the like, the number of high voltage components installed in an automobile has been increasing. An increase in the number of high voltage components leads to an increase in electromagnetic interference between the components. When such electromagnetic interference propagates to an electronic device such as in-vehicle radio, the electromagnetic interference may adversely affect the operation of the device as electromagnetic noise. As such, countermeasures for electromagnetic noise in vehicles are currently desired. In particular, the inventors of the present application have considered approaches to mitigate electromagnetic noise by using bearings installed at various locations in a vehicle.
Patent Document 1 below discloses a conductive rolling bearing as a conductive bearing. This conductive rolling bearing is provided with a conductive seal ring 10a mainly in order to prevent electrolytic corrosion of a rolling element. The seal ring 10a is a component for preventing leakage of lubricant oil, intrusion of foreign matter, and the like, and conductivity is improved by enclosing ambient temperature molten salt in a tip end portion of the seal lip 14.
Patent Document 1: JP 2009-264401A
In considering the mitigation of electromagnetic noise when using the bearing described above, the inventors of the present application considered configurations where the electromagnetic noise could be released when using the conductive seal without being influenced by operational environment changes. For example, the ease with which electricity flows through the bearing is influenced by the size of the contact area of the rolling element with the bearing rings, in other words, the thickness of an oil film between the rolling body and the bearing rings. The oil film becomes thin in situations in which the rotation speed is low and the load is large, such as when the vehicle is stopped or driving at a low speed, and becomes thick in situations in which the rotation speed is high and the load is small, such as when the vehicle is driving at a high speed. Accordingly, in order to reduce electromagnetic noise via the bearing at all times, it is important to also handle situations in which the oil film is thick.
In view of the above problems, an object of the present invention is to provide a sealed bearing that can reduce electromagnetic noise originating from the installation target at all times.
In an approach to solve the above problem, a representative configuration of a sealed bearing consistent with the present invention includes a sealed bearing comprising a seal for covering a rolling element from a side between an inner bearing ring and an outer bearing ring, the seal being formed of a conductive resin material, and when an oil film parameter of a track surface of the sealed bearing is 1.0 or more, an impedance of a circuit that passes through the inner bearing ring and the outer bearing ring via the seal is smaller than an impedance of a circuit that passes through the inner and outer bearing rings via the rolling element.
The oil film parameter is a measure indicating an extent to which friction surfaces are in direct contact with each other, and a value of 1.0 or more indicates a state in which the oil film is sufficiently thick. In the above-described configuration, when the oil film is thick, in other words, even when the bearing rings and the rolling element are not overly in contact with each other, it is possible to realize an electrical circuit that passes through the inner and outer bearing rings by using the seal. With this configuration, it is possible to reduce electromagnetic noise at all times including times when the vehicle is running and when the vehicle is stopped. Also, with this configuration, by configuring the electrical circuit by preferentially using the conductive seal, it is also possible to suppress electrolytic corrosion of the rolling element.
The above-described resin material may include at least one of nitrile rubber, acryl rubber, fluoro rubber, and silicone rubber. With these configurations, it is possible to utilize the characteristics of the materials to realize the seal having characteristics based on the installation target, such as heat resistance and abrasion resistance, for example.
According to the present invention, it is possible to provide a sealed bearing that can reduce electromagnetic noise originating from the installation target at all times.
The following paragraphs describe to some embodiments of the present invention in detail with reference to the accompanying drawings. Dimensions, materials, other specific numerical values, and the like described in the embodiments are merely examples to facilitate understanding and do not limit the present inventions unless otherwise stated. It should be noted that elements that have substantially the same function and configuration are denoted with the same reference signs in the specification and drawings and redundant description of those elements is omitted, and illustration or description of elements that do not directly relate to the present inventions are omitted.
The seal 110 is fitted into a seal groove 112 of the inner ring 102 and a seal groove 114 of the outer ring 104. The seal 110 is formed of a resin material and provided with a core metal 116 in the center in order to supplement the pressure-resistance, strength, and conductivity. A lip portion 118 is provided on the inner ring 102 side of the seal 110, and due to the lip portion 118 contacting the seal groove 112, prevention of intrusion of foreign matter and the like are performed.
The bearing 100 is assumed to be utilized in the inner mechanism of electric cars, for example, and realizes a configuration that can mitigate and/or eliminate electromagnetic noise originating from the installation target. Accordingly, with the bearing 100, it is possible for electricity to flow between the inner ring 102 and the outer ring 104 to a certain extent. Specifically, in some embodiments, an electrical circuit passing through the seal 110 may be formed in preference to an electrical circuit passing through the ball 106.
In order to achieve the above-described object, the seal 110 is formed of a conductive resin material. Specifically, the seal 110 may be formed of acrylic rubber including a conductive filler. With the above configuration, it is possible to ensure not only conductivity but also heat-resistance. Accordingly, the seal 110 can effectively function even in an environment in which the temperature tends to be high such as the inner mechanism of a vehicle and the like.
The impedance of the circuit passing through the seal 110 is set to a value at which electricity can easily pass through compared to the case in which the circuit passes through the ball 106, for example, on a basis of the ball 106 being a steel ball. In general, the ease with which electricity flows between the rolling element and the bearing ring is influenced by the thickness of the oil film between the rolling element and the bearing ring. The oil film of the bearing becomes thin under a high pressure in which the mechanism is stopped or operating at a low speed, and becomes thick under a low pressure and no-load state in which the mechanism is operating at a high speed. In the present embodiment, the impedance is set so that electricity flows through the seal 110 rather than the ball the ball 106 based on the thickness of the oil film 120 so that electromagnetic noise can be eliminated in any situation such as when the mechanism is operating or stopped.
The plots in
In the present embodiment, a threshold value of impedance of the electrical circuit that passes through the ball 106 when the oil film parameter (Λ) of the track surface is 1.0 is determined (e.g. approximately 150Ω in
With the above-described configuration, it is possible to realize an electrical circuit that passes through the inner ring 102 and the outer ring 104 using the seal 110 even when the mechanism is operating at a high speed and the oil film 120 is thick. Of course, since the seal 110 is a contact-type seal, the electrical circuit is formed between the inner and outer bearing rings even in the situation in which the mechanism is stopped or operating at a low speed. In other words, with the configuration of the present embodiment, it is possible to lower the bearing impedance by passing through the seal 110 both when the mechanism is operating and stopped, and therefore electromagnetic noise can be reduced at all times. Furthermore, in the present embodiment, it is also possible to suppress electrolytic corrosion of the ball 106 by configuring the electrical circuit preferentially using the conductive seal 110 rather than the ball 106.
Particularly, since the thickness of the oil film of the track surface is thicker in a high-speed rotation region, the impedance becomes smaller and electricity flows more easily in the seal portion.
Here, an impedance (Z) of a typical capacitor is expressed by the following expression 1.
Z=−j1/ωC Expression 1
j=imaginary unit; ω=2πf (AC angular frequency); c=capacitance (electrostatic capacity)
Also, generally, the capacitance C of the capacitor in the above Expression 1 is expressed as the following expression 2. In this Expression 2, a capacitor in which a dielectric body is filled between two parallel conductors is assumed.
C=εS/d Expression 2
ε=electric permittivity of dielectric body; S=area of conductors; d=interval (or distance) between conductors
According to the above Expressions 1 and 2, it is evident that the impedance of the electrical circuit that passes through the above-described seal 110 can be adjusted by using the contact area S between the lip portion 118 and the seal groove 112, and the oil film thickness d between the lip portion 118 and the seal groove 112 in
The result of measurement of the relationship of the impedance of the electrical circuit that passes through the seal 110 with the contact area S and the oil film thickness d is shown below.
From the above description, it can be confirmed that the impedance of the electrical circuit that passes through the seal 110 can be adjusted by increasing and decreasing the contact area S of the lip portion 118 and the oil film thickness d. By adjusting in this manner, it is possible to realize the sealed bearing 100 that can form an electrical circuit having impedance that is less than or equal to the above-described threshold value (see
The bearing 100 is provided with the seal 110 formed of conductive acrylic rubber and to which the above-described impedance has been set, and therefore it is possible to effectively install the bearing 100 in electric cars, hybrid cars, and the like, especially in a differential, a transmission shaft, and the like. With the bearing 100, it is possible to reduce electromagnetic noise at all times both when the vehicle is running and when the vehicle is stopped. Furthermore, acrylic rubber is heat-resistant, and it is possible to enhance the usable temperature of the bearing to as high as 150 C.° or more as one example. Accordingly, with the bearing 100, it is possible for the bearing to function effectively even in a location in which the temperature becomes high such as the differential or the transmission.
As described above, although conductive acrylic rubber is adopted as a material of the seal 110 in the present embodiment, other resin materials can also be adopted. For example, nitrile rubber has an excellent wear resistance, and fluoro rubber has a high heat resistance and a high chemical resistance. Also, silicone rubber has a high heat resistance and a high cold resistance. With these resin materials, by imparting conductivity with a conductive filler, it is possible to utilize the characteristics of the materials to realize the seal 110 having characteristics based on the installation target, and the sealed bearing 100 that can reduce electromagnetic noise at all times.
Hereinafter, modifications of the constituent elements described above will be illustrated. In
The core metal 228 bends toward the ball along an inner circumferential surface 230 of the outer ring 222, and is in surface contact with the inner circumferential surface 230 of the outer ring 222. The seal 224 is pressed in between the inner ring 202 and the outer ring 222 (interference-fit), and the lip portion 118 slides along the outer circumferential surface 204 of the inner ring 202. With this bearing 220 as well, it is possible to adjust the impedance by increasing and decreasing the contact area between the lip portion 118 and the outer circumferential surface 204 of the inner ring 202.
As described above, the sealed bearing according to the present invention can be favorably realized as various kinds of bearings such as a deep groove ball bearing and a conical roller bearing. In any of the bearings as which the present invention is realized, due to the provision of the conductive seal, it is possible to favorably reduce electromagnetic noise originating from the installation target.
Although a preferable embodiment of the present invention has been described with reference to the drawings, needless to say, the present invention is not limited to this embodiment. A person skilled in the art will appreciate that various variations and modifications can be arrived at within the scope of the appended claims, and those variations and modifications should be understood to be included within the technical scope of the present invention.
The present invention can be used as a sealed bearing provided with a seal for covering a rolling element from a side between inner and outer bearing rings.