GB2105416A

GB2105416A - Rolling bearing support

Info

Publication number: GB2105416A
Application number: GB08221825A
Authority: GB
Inventors: Christopher John Mo Southworth
Original assignee: TI CHURCHILL Ltd
Current assignee: TI CHURCHILL Ltd
Priority date: 1981-08-05
Filing date: 1982-07-28
Publication date: 1983-03-23
Also published as: DE3229128A1; JPS5846223A; GB2105416B

Abstract

A rotary rolling element bearing, for example on the spindle 10 of a machine tool, is mounted in series with a hydrostatic bearing between a piston member 25, in which the outer race 22 is mounted, and a housing. The hydrostatic bearing comprises fluid under pressure in pockets around the piston and increases damping, reduces noise and accommodates thermal expansion. The piston is loaded axially to preload the bearing 11. <IMAGE>

Description

SPECIFICATION Bearing location means This invention relates to bearing location means and is applicable particularly, but not exclusively, to bearing location means for high-speed machine tool spindles.

According to the invention there is provided bearing location means, including at least one rolling element bearing mounted between two relatively rotatable bodies and a hydrostatic bearing, as hereinafter defined, mounted effectively between the rolling element bearing and one of said bodies.

Conveniently, the hydrostatic bearing is mounted between the rolling element bearing and the non-rotatable one of said bodies. Preferably, each of said fluid supplies feeds into a separate pocket bounded by part of one of said surfaces of revolution. Each pocket may be formed as a flat on the inner surface of revolution.

The bearing location means may include fluid pressure measuring or sensing means connected to each of said fluid supplies to the hydrostatic bearing, whereby the pressure differences between the various supplies enables the computation of load on the hydrostatic bearing.

Furthermore, there may be at least two rolling element bearings mounted between the two relatively rotatable bodies, said rolling element bearings being loaded in opposite directions by axial forces generated by fluid pressure.

Preferably, the fluid pressure acts on a piston in a piston and cylinder assembly to generate the axial forces, and one of the rolling element bearings is carried by the piston or the cylinder.

Advantageously the pressure of fluid applied to generate a force on one or more of the bearings is varied with the speed of relative rotation of the bodies.

Preferably there is provided means to limit the angle of rotation across the hydrostatic bearing.

The invention is described, by way of example only, with reference to the accompanying drawings, in which:~ Figure 1 is a section through two inclined planes through the axis of a spindle, along the line I-I in Figure 2, and Figure 2 is a transverse section along the line Il-Il in Figure 1.

In the drawings, a spindle 10, which may be rotated by any suitable means, such as a gear, belt or the like, is mounted on two taper roller bearings 1 1, 12. The spindle 10 is part of a high-speed machine tool, but the invention is applicable to many other forms of spindle. Indeed, in some applications the spindle 10 may be stationary and the surrounding structure may rotate.

The front end of the spindle 10 is formed with a shoulder 13, adjacent a collet holder 14, or the like.

The inner race 1 5 of the bearing 12 fits against the spindle 10 and the shoulder 13, whilst the outer race 16 is located by a bore 17 and shoulder 18 of a rigid structure 11 9, typically in the form of a ahead stock.

The inner race 19 of the rear bearing 11 is located on the spindle 10 and axially against a cap 20, which is fastened to the end of the spindle 10 by screws 21.

The outer race 22 of the bearing 11 is located by a bore 23 and shoulder 24 formed in a piston member 25.

The piston member 25 has two co-axial cylindrical surfaces 26, 27, each of said surfaces being a sliding fit in corresponding bores 28, 29 in part of the structure 11 9. It will be seen that an annular cavity 30 is thereby formed, which cavity 30 is connected to an unshown source of pressurised oil by means of a duct 31. In this way, pressure of the oil in the annular space 30 generates an axial force of pre-determined magnitude which urges the piston member 25 towards the left in Figure 1 , said force providing a required axial pre-load on the bearing 11 and thence through the cap 20 and spindle 10 provides the same axial pre-load on the bearing 12.

The piston member 25 is limited in rotation by means of a tongue 32 fastened to the structure 119 and engaging in a slot or depression 33 formed in the end of the piston member 25.

It is frequently an essential requirement of high speed spindles, that they are accurately located radially relative to their supporting structure and are mounted in a radially rigid manner thereto. In the present case, the provision of necessary clearances to enable the piston member 25 to slide axially within the structure 19 may diminish such accuracy and stiffness of location of the spindle 10. This problem can be alleviated by providing a positive hydrostatic bearing arrangement between the piston member 25 and the surrounding structure 11 9. A hydrostatic bearing is defined as a bearing between two surfaces of revolution, one of said surfaces having.

a plurality of circumferentially spaced fluid supplies each bounded by part of said surface of revolution. Such hydrostatic bearings are inherently very stiff, whilst avoiding metal-to metal contact which might lead to unacceptable fretting.

An appropriate form of the hydrostatic bearing is shown in Figure 2, where the cylindrical surface 26 of the piston member 25 is formed with six circumferentially-spaced flats 34, which do not extend for the full axial length of the surface 26, thereby forming six isolated pockets. Each pocket 35 is fed with a supply of pressurised oil through interconnected ducts 36.

By means of the hydrostatic axial and radial loadings of the piston member 25, the required axial pre-load on the bearings 11, 12 and a high radial stiffness may be sustained despite axial and radial expansions of the various components during use.

The number of pockets 35 is chosen to suit the size of the assembly. The oil supply to the ducts 36 may be any of the usual methods employed with hydrostatic bearings, e.g. capillaries, orifice jets or flow control valves. Furthermore, the pressure of the oil in each pocket 35 may be monitored and the values of said oil pressures may be used to determine the radial force acting on the bearing 11.

The provision of the hydrostatic bearing tends to increase radial damping, decrease the transmission of bearing noise and compensate for differential radial expansion due to heat generation in the rolling element bearing.

Although the hydrostatic bearing is shown to be located between the non-rotary race 22 of the bearing 11 and the structure 119, for some embodiments it may be preferable to locate the hydrostatic bearing effectively between the rotary race 19 of the bearing 11 and the spindle 10.

The hydrostatic bearing is shown as a purely radial bearing, but for some embodiments it may be arranged as a hydrostatic thrust bearing or in an inclined manner to provide combined radial and axial location.

In some embodiments it may be advantageous to increase or decrease the pressure supplied to the cavity 30 and/or to the pockets 35 as the spindle speed increases.

Claims

1. Bearing location means, including at least one rolling element bearing mounted between two relatively rotatable bodies and a hydrostatic bearing, as hereinbefore defined, mounted effectively between the rolling element bearing and one of said bodies.

2. Bearing location means, according to Claim 1, in which the hydrostatic bearing is mounted between the rolling element bearing and the non-rotatable one of said bodies.

3. Bearing location means, according to Claim 1 or 2, in which each of said fluid supplies feeds into a separate pocket bounded by part of one of said surfaces of revolution.

4. Bearing location means, according to Claim 3, in which each pocket is formed as a flat on the inner surface of revolution.

5. Bearing location means, according to any preceding claim, including fluid pressure measuring or sensing means connected to each of said fluid supplies to the hydrostatic bearing, whereby the pressure differences between the various supplies enables the computation of load on the hydrostatic bearing.

6. Bearing location means, according to any preceding claim, including at least two rolling element bearings mounted between the two relatively rotatable bodies, said rolling element bearings being bonded in opposite directions by axial forces generated by fluid pressure.

7. Bearing location means, according to Claim 6, in which the fluid pressure acts on a piston in a piston and cylinder assembly to generate the axial forces, and one of the rolling element bearings is carried by the piston or the cylinder.

8. Bearing location means, according to any preceding claim in which the pressure of fluid applied to generate a force on one or more of the bearings is varied with the speed of relative rotation of the bodies.

9. Bearing location means, according to Claim 8, in which the pressure of the fluid is increased as the speed increases.

10. Bearing location means, according to any preceding claim, in which one of the bodies is nonrotatable and the other of the bodies is a spindle.

11. Bearing location means, according to Claim 10, in which the spindle is a high-speed machine tool spindle.

12. Bearing location means, according to any preceding claim, including means to limit the angle of rotation across the hydrostatic bearing.

13. Bearing location means constructed and arranged and adapted to operate substantially as described herein and as shown in the accompanying drawings.

14. A machine tool including bearing location means according to any preceding claim.