GB2187262A

GB2187262A - Power transmission device

Info

Publication number: GB2187262A
Application number: GB08703843A
Authority: GB
Inventors: Junichi Shigeura; Haruhisa Fujita
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1986-02-25
Filing date: 1987-02-19
Publication date: 1987-09-03
Anticipated expiration: 2007-02-19
Also published as: GB8703843D0; SE8700778D0; JPS62200025A; SE464988B; SE8700778L; GB2187262B

Abstract

A power transmission device which is capable of absorbing an impact applied thereto during transmission of power includes a rotating shaft 2, a transmission member 8 loosely fitted on the rotating shaft, and a resilient member 15 provided between the rotating shaft and the transmission member. The resilient member is made of an incompressible material and has three or more free surfaces 15a. Accordingly, it is possible to readily absorb a relatively large impact without the need to increase the size of the transmission member. <IMAGE>

Description

SPECIFICATION Power transmission device The present invention relates to a power transmission device so designed that it is possible to relieve vibrations and impacts which may act thereon during transmission of power.

One type of conventional power transmission device will first be described with reference to Figs. 7 and 8.

Fig. 7 is a plan view of a conventional power transmission device for driving a vehicle which is equipped with a reduction gear, showing the way in which power transmission device is mounted on a truck, and Fig. 8 is a sectional view showing the arrangement of a conventional power transmission device disclosed in, for example, the specification of Japanese Patent Public Disclosure No. 154952/1977.In the figures, the reference numeral 1 denotes a truck frame for a vehicle, 2 an axle rotatably fitted in the truck frame 1, 3 wheels rigidly secured to two axial end portions, respectively, of the axle 2, 4 an electric motor disposed in such a manner that its longitudinal axis extends parallel with that of the axle 2, 5 a resilient support means for supporting the motor 4 on the truck frame 1 in such a manner that vibrations and impacts are absorbed, 6 a gear box which is operatively connected to the motor 4 and has openings which allow the axle 2 to pass therethrough, 7 two bearings which are rigidly fitted in the openings, respectively, of the gear box 6, 9 an outer tube which is disposed so as to extend through the openings of the gear box 6, the outer tube 9 being supported by the bearings 7 and loosely fitted on the axle 2, 8 a gear which is disposed inside the gear box 6 and rigidly fitted on the outer tube 9, the gear 8 being meshed with a gear (not shown) secured to the motor 4 so as to transmit the power derived from the motor 4 to the outer tube 9 after the speed has been reduced. A cylindrical resilient member 10 is rigidly secured to the inner periphery of the outer tube 9, the member 10 having a wall thickness t. The reference numeral 10a denotes side surfaces of the resilient member 10, that is, free surfaces. Further, a cylindrical inner tube 11 is rigidly secured between the inner periphery of the resilient member 10 and the outer periphery of the axle 2.

In operation, when the motor 4 is activated, the rotational force therefrom is transmitted to the wheels 3 secured to the axle 2 through the outer tube 9, the resilient member 10 and the inner tube 11 after the speed has been reduced by the gear 8, thus causing the truck frame 1 to travel.

When the travelling truck frame 1 passes a joint or point of rails, an impact is applied to the wheels 3, and this impact is transmitted to the axle 2. To prevent such impact from being transmitted directly to the motor 4 and the gear 8, it is buffered or absorbed by the resilient member 10 and the resilient support means 5.

In the above-described prior art, to satisfactorily absorb an impact such as that described above, it suffices to select the spring constant of the resilient member 10 so as to match with the magnitude of such impact. The spring constant in the above-described prior art is determined by the total area of the side surfaces of the resilient member 10, that is, the total area of the free surfaces 10a. Accordingly, it is necessary, in order to obtain a spring constant which is matched with an impact having a high magnitude, increase the dimension t of the side surfaces, which means that the size of the outer tube 9 must be increased. In other words, if the dimension t is left unchanged, it is impossible to absorb a relatively large impact.

Thus, the conventional power transmission device suffers from the problem that, since the free surfaces 10a are present only at both sides of the resilient member 10, it is impossible to absorb a relatively large impact unless the size of the outer tube 9 which serves as a transmission member is increased.

In view of the above-described circumstances, it is a primary object of the present invention to provide a power transmission device having excellent impact resistance which is so designed that a relatively large impact can readily be absorbed without the need to increase the size of the transmission member 9.

To this end, the present invention provides a power transmission device comprising a resilient member provided between the axle 2 which serves as a rotating shaft and the transmission member 9, the resilient member being made of an incompressible material and having three or more free surfaces. Free surfaces are surfaces not generally contacted by the shaft or member.

The provision of the resilient member having three or more free surfaces between the rotating shaft 2 and the transmission member 9 advantageously enables the total area of free Surfaces of the resilient member to be readily increased.

The above and other objects, features and advantages of the present invention will become more apparent from the following description of the preferred embodiments thereof, taken in conjunction with the accompanying drawings.

Fig. 1 is a sectional view showing the arrangement of a first embodiment of the power transmission device according to the present invention; Fig. 2 is a sectional view showing a second embodiment of the present invention; Figs. 3 to 6 are sectional views respectively showing third to sixth embodiments of the present invention; Fig. 7 is a plan view of a conventional power transmission device for a vehicle which is equipped with a reduction gear, showing the way in which the power transmission. device is mounted on a truck; Fig. 8 is a sectional view showing the arrangement of a conventional power transmission device; and Fig. 9 is a graph showing the relationship between the elastic modulus of rubber and the surface area.

The power transmission device according to the present invention will be described hereinunder in detail with reference to the accompanying drawings.

Referring first to Fig. 1, which is a sectional view showing the arrangement of a first embodiment of the present invention, the reference numerals 2, 4 and 6 to 9 denote constituent elements which are similar to those of the above-described prior art. A resilient member 15 is defined by a cylindrical member which is divided in the axial direction into an nular pieces with a predetermined gap W between each pair of the adjacent annular pieces and which is pressfitted into the gap t defined between the inner periphery of the outer tube 9 serving as a transmission member and the outer periphery of the axle 2 serving as a rotating shaft, the resilient member 1 5 being made of, for example, a rubber material.If this resilient member 15 is rigidly secured using an adhesive, it is possible to increase the size of power which can be transmitted. The reference numeral 15a denotes side surfaces of the resilient member 15, that is, free surfaces other than portions of the member 15 which are in contact with the inner periphery of the outer tube 9 and the outer periphery of the axle 2.

A rubber material which may be employed for the resilient member 15 is elastic and as incompressible as a liquid. Accordingly, the spring constant is inversely proportional to the total area of the free surfaces 1 5a which can be deformed when a load is applied thereto.

Fig. 9 is a graph showing the relationship between the ratio of the total area of free surfaces AF to the total area presented to pressure Ap of portions which are in contact with the rotating shaft 2 and the outer tube 9, i.e., a, = ez and the ratio of the apparent elastic modulus Ep to compressive elastic modulus Ep of rubber itself. As will be clear from Fig.

9, as the free surface area Ap increases, the ratio a of Ap to the area presented to pressure Ap increases, and if the compressive elastic modulus EF is constant, the spring constant which is proportional to the apparent elastic modulus Ep decreases.

In this way, the spring constant of the resilient member 15 can be selected to be an optimal value.

In this embodiment, if each gap W in the resilient member 15 is maintained as it is during transmission of power, the spring constant shows a substantially constant value. If the dimension W is so set that each pair of adjacent annular pieces of the member 15 are brought into contact with each other when a power of predetermined size is transmitted, the total area of free surfaces 1 5a is decreased. Accordingly, the point at which the spring constant changes can be set as desired in accordance with the size of power.

Fig. 2 is a sectional view showing the arrangement of a second embodiment of the present invention. In this embodiment, the resilient member 15 is defined by a plurality of annular pieces 15f having a circular ringshaped cross section, the annular pieces 15f being arranged in the axial direction of the axle 2 between the outer tube 9 and a cylindrical inner tube 11 which is rigidly secured to the outer periphery of the axle 2.

Fig. 3 is a sectional view showing the arrangement of a third embodiment of the present invention. In this embodiment, the inner periphery of the outer tube 9 is defined by two inner peripheral portions which have different inner diameters, and a resilient member 15 which is defined by two kinds of annular pieces 15b and 1 sic having different outer diameters is rigidly secured to the inner periphery of the outer tube 9, the side surfaces of the annular pieces 15b and 1 sic respectively defining free surfaces 15a.

In this embodiment, the respective free surfaces 15a of the two kinds of annular pieces 15b and 15c have different areas, and the resilient member 15 is therefore provided with two kinds of spring constant, which means that it is possible to suppress the occurrence of resonance which may be caused by vibrations generated during transmission of power.

It should be noted that, although in this embodiment the annular pieces 15b and 15c which define the resilient member 15 have different outer diameters, they may be made different from each other in terms of inner diameter, and in such case also, advantages sim ilar to those described above are obtained.

Fig. 4 is a sectional view showing the arrangement of a fourth embodiment of the present invention. In this embodiment, the resilient member 15 is a cylindrical member and has ring-shaped grooves 15d provided in the inner and outer peripheries thereof, so that the side surfaces of the resilient member 15 and the inner surface of each groove 15d define free surfaces 15a, respectively.

It should be noted that, although in this embodiment the grooves 15a have a ring-shaped configuration, they may be defined by grooves which are provided in both the inner and outer peripheries of the resilient member 15 so as to extend in the axial direction thereof.

Fig. 5 is a sectional view showing the arrangement of a fifth embodiment of the pre sent invention. The resilient member 15 in this embodiment is a cylindrical member and has annular hollows 15e which extend in the circumferential direction thereof. The side surfaces of the resilient member 15 and the surface of each hollow 15e define free surfaces 15, respectively.

Fig. 6 is a sectional view showing the arrangement of a sixth embodiment of the present invention. In this embodiment, the outer tube 9 extends on the side of the gear box 6 which is closer to the motor 4, and the inner tube 11 and the resilient member 15 are provided in the extended portion of the outer tube 9. Although the resilient member 15 in this embodiment is defined by a plurality of annular pieces 15f arranged in the axial direction of the member 15 and having a circular cross section, and one of the resilient members 15 shown in the above-described embodiments may be employed in place of the illustrated one.

It should be noted that, although the resilient member 15 shown in each of the abovedescribed embodiments has the shape of a cylinder defined by constituent elements which are continuous in the circumferential direction, the resilient member 1 5 may consist of a combination of sectional pieces which are formed by dividing a cylindrical member circumferentially and are circumferentially disposed side by side to form generally cylindrical configuration.

Further, although a reduction gear for a vehicle has been exemplarily shown in each of the above-described embodiments, the illustrated example is not necessarily limitative, and it is a matter of course that the present invention may be applied to any types of power transmission to which impacts may be applied.

As has been described above, according to the present invention, the resilient member 15 which is made of an incompressible material and has three or more free surfaces 15a is provided between the rotating shaft 2 and the transmission member 9. It is therefore possible to readily absorb a relatively large impact without the need to increase the size of the transmission member 9.

Although the present invention has been described through specific terms, it should be noted here that the described embodiments are not necessarily exclusive and various changes and modifications may be imparted thereto without departing from the scope of the invention which is limited solely by the

Claims

appended claims. CLAIMS

1. A power transmission device comprising: a rotating shaft; a transmission member loosely fitted on said rotating shaft; and a resilient member provided between said rotating shaft and said transmission member to transmit power therebetween, said resilient member being made of an incompressible material and having three or more free surfaces.

2. A power transmission device according to Claim 1, wherein said resilient member is cylindrical and axially divided into annular pieces.

3. A power transmission device according to Claim 2, wherein said resilient member has a gap between each pair of the adjacent annular pieces even during transmission of power.

4. A power transmission device according to Claim 2 or 3, wherein at least one of said annular pieces has a different outer diameter from the others.

5. A power transmission device according to Claim 1, wherein said resilient member is a cylindrical member and has a ring-shaped groove circumferentially extending along one or both of its inner and outer surfaces.

6. A power transmission device according to Claim 1, wherein said resilient member is a cylindrical member and has an annular hollow extending in the circumferential direction thereof.

7. A power transmission device according to any preceding claim wherein said resilient member is press-fitted between said rotating shaft and said transmission member.

8. A power transmission device according to any one of claim 1 to 6 wherein said resilient member is rigidly secured in position by means of bonding.

9. A power transmission device according to any preceding claim wherein said resilient member is made of a rubber material.

10. A power transmission device according to any preceding claim, wherein said resilient member is rigidly secured to said rotating shaft via a cylindrical inner tube.

11. A power transmission device according to any preceding claim, wherein said resilient member consists of a combination of sectional pieces which are formed by dividing a cylindrical resilient member so that it is not continuous in the circumferential direction.

12. A power transmission device substantially as hereinbefore described with reference to and as illustrated in any one of Figures 1 to 6 of the accompanying drawings.