WO2007051222A1

WO2007051222A1 - Slot milling machine

Info

Publication number: WO2007051222A1
Application number: PCT/AU2006/001406
Authority: WO
Inventors: Johann Friederich Jaeggi
Original assignee: Bishop Steering Technology Limited
Priority date: 2005-11-02
Filing date: 2006-09-27
Publication date: 2007-05-10

Abstract

A machine for machining an array of longitudinally extending slots on the periphery of an input shaft for a power steering valve. The machine comprises first and second spaced apart work holding devices, each being adapted to support and index an input shaft, and first and second spaced apart rotatable tool spindles associated with the first and second work holding devices respectively. Each tool spindle has at least one milling cutter attached thereto, and each tool spindle is movable relative to its respective work holding device to effect machining of the slots. The first and second tool spindles have substantially parallel axes and are carried by a common head movable such that as the first tool spindle moves towards the first work holding device, the second tool spindle moves away from the second work holding device.

Description

SLOT MILLING MACHINE

TECHNICAL FIELD

The present invention relates to a machine for machining slots on an input shaft for a power steering valve.

BACKGROUND

A typical hydraulic power steering valve for an automotive steering gear has an input shaft with an array of slots on its periphery. These slots hydraulically co-operate with corresponding slots in the bore of a sleeve in a well known manner. These slots must be accurately machined to control the performance of the power steering valve, and accurate metering edges are typically formed on the longitudinal edges of the slots by an additional process after the slots are machined.

Special purpose mechanically operated machines have been used to machine the slots on input shafts. Such a machine is disclosed in US Patent 4,860,414 (Bishop et al). This type of machine is robust and fast but lacks flexibility and is expensive to build. Alternatively, it is known to adapt general purpose machining centres to machine the slots. This approach provides flexibility but may not be as fast or efficient a special purpose machine.

The present invention seeks to provide a machine that ameliorates one or more of the disadvantages associated with the abovementioned prior art.

SUMMARY OF INVENTION

The present invention consists of a machine for machining an array of longitudinally extending slots on the periphery of an input shaft for a power steering valve, the machine comprising first and second spaced apart work holding devices, each being adapted to support and index an input shaft, and first and second spaced apart rotatable tool spindles associated with the first and second work holding devices respectively, each tool spindle having at least one milling cutter attached thereto, and each tool spindle being movable relative to its respective work holding device to effect machining of the slots, characterised in that the first and second tool spindles have substantially parallel axes and are carried by a common head movable such that as the first tool spindle moves towards the first work holding device, the second tool spindle moves away from the second work holding device.

• Preferably, the first and second tool spindles are both disposed between the first and second work holding devices.

Preferably, at least one tool spindle has at least two axially spaced apart milling cutters of different widths attached thereto, and the common head is movable such that either of the two milling cutters can be selected to machine a particular slot.

Preferably, the first and second tool spindles rotate in opposite directions.

Preferably, each work holding device is adapted to support the periphery of an input shaft.

Preferably, each work holding device comprises an index device adapted to grip one end of an input shaft and rotate it about its axis.

Preferably, each work holding device comprises a support post adapted to support one end of an input shaft against a cutting force applied to the input shaft.

Preferably, at least one work holding device is movable along an axis parallel to the axis of an input shaft supported thereby, relative to its associated tool spindle.

Preferably, the machine further comprises a loading means adapted to load or unload an input shaft from one work holding device whilst the slots are being machined on an input shaft supported by the other work holding device. BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a side view of a typical input shaft for a power steering valve.

Fig. 2 is an end view of the input shaft shown in Fig. 1.

Fig. 3 is a plan view of a preferred embodiment of a machine in accordance with the present invention.

Fig. 4 is an elevation view of the machine shown in Fig. 3.

Fig. 5 is a detail elevation view of a work holding device of the machine shown in Fig. 3.

Fig. 6 is a detail plan view of a work holding device of the machine shown in Fig. 3.

BEST MODE OF CARRYING OUT THE INVENTION

Figs. 1 and 2 show a typical input shaft 1 for a power steering valve, having a longitudinal axis 6. An array of eight longitudinally extending arcuate slots 2 are machined on a cylindrical portion 5 of the periphery of input shaft 1. The array of slots 2 consists of alternating slots 2a and slots 2b, with slots 2a being wider than slots 2b, equally spaced around cylindrical portion 5. Slots 2 hydraulically co-operate with corresponding slots in the bore of a sleeve for a power steering valve in a well known manner. Drive end 3 of input shaft 1 is adapted to be connected to a steering wheel, and the other end of input shaft 1 has two parallel flats 4 adapted to limit relative rotation of input shaft 1 with respect to a pinion when assembled into a power steering valve.

Figs. 3 to 6 show a preferred embodiment of a machine 10 in accordance with the present invention. For clarity, some detail components of machine 10 are not shown. This includes various actuators, bearings, etc that are commonly used in machine design and do not need to be described for a person skilled in the art to understand the operation and implementation of machine 10. Machine 10 has two spaced apart work holding devices 11a and 11b, each adapted to support an input shaft 1 with its drive end 3 pointing downwards. Work holding devices 11a and 11b have respective parallel axes 19a and 19b, each defined by the axis 6 of a supported input shaft 1. Each work holding device 11a, 11b comprises an index device 12, a centreless support 13 and a support post 14, all mounted on a carriage 15.

Referring to detail Figs. 5 and 6, each centreless support 13 has a V-shaped recess 16 that supports the periphery of an input shaft 1. A set of four fingers 17 hold an input shaft 1 in contact with V-shaped recess 16. Fingers 17 pivot about axes 18 such that they can pivot out of the way, as indicated by the dashed outlines in Fig. 6, to provide access for loading and unloading an input shaft 1. During rotation of a supported input shaft 1 , fingers 17 are lightly preloaded against the input shaft 1 to maintain contact between the input shaft 1 and V-shaped recess 16. The preload force is increased during machining to ensure adequate support. Fingers 17 are preferably pivoted by a pneumatic or hydraulic actuator via a linkage (not shown), which may also provides the preload force when fingers 17 are holding an input shaft 1.

Each index device 12 comprises a collet 21 adapted to grip the flats 4 at the end of an input shaft 1. Collet 21 is preferably actuated by a pneumatic or hydraulic actuator (not shown). Collet 21 is supported by bearings (not shown) such that it can rotate about the axis 19a or 19b of its respective work holding device 11a or 11b. Each index device 12 has a servo motor 22 that rotates its collet 21 such that a gripped input shaft 1 can be indexed to any rotational position.

Each support post 14 is movable up and down relative to its respective centreless support 13, preferably by means of a pneumatic or hydraulic actuator (not shown). When loading an input shaft 1 into a work holding device 11a or 11b, its support post 14 is retracted downwards to provide adequate clearance. Support post 14 is then moved upwards such that it contacts the drive end 3 of a loaded input shaft 1. Support post 14 is then locked in position by a wedge or other means (not shown) such that it resists downward load applied to input shaft 1. Support post 14 is retracted downwards again before unloading input shaft 1.

Work holding devices 11a and 11b are mounted on slideways 38a and 38b respectively. Slideways 38a and 38b are mounted on the machine base 37, and are arranged to individually move work holding devices 11a and 11b along axis Z parallel to their axes 19a and 19b. Slideways 38a and 38b are driven by servo motors 39 such that work holding devices 11a and 11b can be moved to any position along axis Z within their operating range.

Machine 10 further comprises two spaced apart tool spindles 24a and 24b, associated with work holding devices 11a and 11b respectively. Tool spindles 24a and 24b are carried by a common head 27, and are each supported for rotation by bearings 29. The axes 31a and 31b of tool spindles 24a and 24b respectively are parallel to each other and perpendicular to the axes 19a and 19b of work holding devices 11a and 11b.

Attached to each tool spindle 24a, 24b are two axially spaced apart, replaceable milling cutters 26a and 26b. Milling cutters 26a and 26b have different widths corresponding to the width of input shaft slots 2a and 2b respectively. The radii of milling cutters 26a and 26b correspond to the radii of slots 2a and 2b respectively. Preferably milling cutters 26a and 26b are of the type disclosed in US Patent 5,059,068 (Scott) having replaceable carbide inserts. Motor 28, attached to head 27, drives both tool spindles 24a and 24b through gears 30. Tool spindles 24a and 24b rotate in opposite directions with tool spindle 24a rotating counter clockwise and tool spindle 24b rotating clockwise as viewed in Fig. 4.

Head 27 is mounted on a cross-slide 33 such that it is movable along axis Y parallel to the axes 31a, 31b of tool spindles 24a, 24b, by a two-position actuator 34 mounted on cross-slide 33. Actuator 34 is preferably a pneumatic or hydraulic actuator. When actuator 34 is in its extended position, milling cutters 26b align with work holding devices 11a and 11b, and when actuator 34 is in its retracted position, milling cutters 26a align with work holding devices 11a and 11b. This allows either milling cutters 26a or 26b to be selected to machine a particular slot.

Cross-slide 33 is mounted on a slideway 35 that is mounted on the machine base 37, such that cross-slide 33 is movable along axis X. Axis X is perpendicular to axis Y and to the axes 19a and 19b of work holding devices 11a and 11b. Slideway 35 is driven by a servo motor 36 such that head 27 can be moved to any position along axis X within its working range. Tool spindles 24a and 24b are disposed between work holding devices 11a and 11b. When head 27 moves along axis X such that tool spindle 24a moves towards its associated work holding device 11a, tool spindle 24b moves away from its associated work holding device 11b, and vice versa.

In the operating position of machine 10 shown in Figs. 3 and 4, an input shaft 1 can be unloaded from and loaded into work holding device 11b whilst slots 2 are machined on another input shaft 1 supported by work holding device 11a. Machining the slots 2 of an input shaft 1 supported by work holding device 11a involves feeding tool spindle 24a towards work holding device 11a by moving head 27 along axis X such that one of rotating milling cutters 26a or 26b, depending on the position of cross-slide 33, cuts a slot 2. Tool spindle 24a is then retracted and the supported input shaft 1 is indexed by index device 12. The next slot 2 is then cut. Input shaft 1 has alternating width slots 2a and 2b, so tool spindle 24a must be moved along its axis 31a by cross-slide 33 between slots so that the appropriate width milling cutter 26a or 26b is used. The same procedure applies to machining the slots 2 of an input shaft 1 supported by work holding device 11b, whilst an input shaft 1 is unloaded from and loaded into work holding device 11a.

The direction of rotation of tool spindles 24a and 24b is such that the cutting force is always downwards and is reacted by support posts 14. Milling cutters 26a and 26b can only cut in one direction of rotation, so the milling cutters 26a and 26b must be selectively oriented with respect to tool spindles 24a and 26a such that their cutting edges travel in the correct direction. This means that the milling cutters 26a and 26b attached to tool spindle 24a are oriented such that they are turned over compared to the milling cutters 26a and 26b attached to tool spindle 24b, which is why machine 10 has two tool spindles 24a, 24b, instead of one tool spindle that can reverse its rotation direction.

Input shafts 1 can be loaded and unloaded using a variety of well known loading means, such as gantry loader or a robot. The arrangement of machine 10 is such that ample time is available for loading and unloading. Providing unloading and loading of a work holding device 11a or 11b is completed within the time taken to machine the slots at the other work holding device, then the loading and unloading process does not interfere with the cycle time of the machine. Typically, the cycle time is of the order of 10 seconds per input shaft.

The overall layout of machine 10 is very efficient and compact in that it requires only one slideway 35 to move both tool spindles 24a and 24b, and both tool spindles 24a and 24b can be driven by a single motor 28.

Slideways 38a and 38b can be used to feed work holding devices 11a and 11b along axis Z, relative to their respective tool spindles 24a, 24b, during the machining of a slot if it is desired to produce a slot having a flat bottom, or if the slot must be extended such that it is open at one or both ends to suit a particular valve design. In other not shown embodiments of the present invention, slideways 38a and 38b can be eliminated, in which case work holding devices 11a and 11b are mounted directly to the machine base 37. This simplified arrangement is suitable where the extra flexibility of moving work holding devices 11a and 11b along axis Z is not required, such as when the machine is only required to machine arcuate slots all having the same axial position on the input shaft. Input shaft 1 , for example, has a slot arrangement that can be machined using a machine without slideways 38a and 38b.

In other not shown embodiments of the present invention, each tool spindle 24a and 24b may have only one milling cutter attached thereto. In this case, cross-slide 33 can be eliminated and head 27 can be mounted directly on to slideway 35. This arrangement is suitable when the machine is only required to machine a single slot width. Alternatively, in other not shown embodiments of the present invention, each tool spindle may have more than two milling cutters attached thereto. In this case, cross-slide 33 must be moved by an actuator having more than two positions, such as a servo motor. This arrangement is suitable for input shafts having more than two slot widths, or where it is desired to quickly change slot width without replacing the milling cutters.

Whilst the present invention is described in detail with respect to machining the particular slot arrangement of input shaft 1 , it should be understood that it is equally applicable machining any other arrangement of input shaft slots, such as input shafts having other than eights slots, equal width slots, or unequal slot spacing.

The term "comprising" as used herein is used in the inclusive sense of "including" or "having" and not in the exclusive sense of "consisting only of.

Claims

1. A machine for machining an array of longitudinally extending slots on the periphery of an input shaft for a power steering valve, the machine comprising first and second spaced apart work holding devices, each being adapted to support and index an input shaft, and first and second spaced apart rotatable tool spindles associated with the first and second work holding devices respectively, each tool spindle having at least one milling cutter attached thereto, and each tool spindle being movable relative to its respective work holding device to effect machining of the slots, characterised in that the first and second tool spindles have substantially parallel axes and are carried by a common head movable such that as the first tool spindle moves towards the first work holding device, the second tool spindle moves away from the second work holding device.

2. A machine as claimed in claim 1 , wherein the first and second tool spindles are both disposed between the first and second work holding devices.

3. A machine as claimed in claim 1 , wherein at least one tool spindle has at least two axially spaced apart milling cutters of different widths attached thereto, and the common head is movable such that either of the two milling cutters can be selected to machine a particular slot.

4. A machine as claimed in claim 1 , wherein the first and second tool spindles rotate in opposite directions.

5. A machine as claimed in claim 1 , wherein each work holding device is adapted to support the periphery of an input shaft.

6. A machine as claimed in claim 1 , wherein each work holding device comprises an index device adapted to grip one end of an input shaft and rotate it about its axis.

7. A machine as claimed in claim 1 , wherein each work holding device comprises a support post adapted to support one end of an input shaft against a cutting force applied to the input shaft.

8. A machine as claimed in claim 1 , wherein at least one work holding device is movable along an axis parallel to the axis of an input shaft supported thereby, relative to its associated tool spindle.

9. A machine as claimed in claim 1 , further comprising a loading means adapted to load or unload an input shaft from one work holding device whilst the slots are being machined on an input shaft supported by the other work holding device.