Electrical generator or motor structure – Dynamoelectric – Linear
Patent
1999-06-28
2000-10-03
Enad, Elvin
Electrical generator or motor structure
Dynamoelectric
Linear
310 27, 417417, H02K 4100, H02K 3300, F04B 1704
Patent
active
061277509
DESCRIPTION:
BRIEF SUMMARY
This application claims priority from PCT Application No. PCT/GB97/01823, filed on Jul. 8, 1997, which claims priority from British Application No. 9614304.5, filed Jul. 8, 1996.
This invention relates to linear compressor motors.
Conventional electrically-driven compressors typically comprise an electric motor which drives a reciprocating piston/cylinder assembly via a crankshaft or equivalent cam arrangement. Recently, interest has been shown in linear compressors since these can be made very compact and have very long life with negligible wear and are thus suited to specialised applications, for example in refrigeration.
A known type of moving coil linear compressor motor is illustrated in FIG. 1 of the accompanying drawings, to which reference is now directed.
The motor comprises two assemblies which are movable in relation to one another along an axis 1. The two assemblies are a cylinder assembly 3 and a piston assembly 2. The assembly 3 comprises a cylinder 4, closed at one end 5, and in which reciprocates a piston 6 forming part of the assembly 2. The radial clearance between the piston and cylinder is typically in the range 5-15 .mu.m and this ensures that the reciprocating motion of the cylinder relative to the piston provides an effective pumping action.
Extending radially outwardly from the cylinder 4 is a flange 7. At its outer perimeter edge, the flange turns and has mounted thereon a cylindrical coil holder 8 made of non-magnetic material. The coil holder 8 is thus fixed to and coaxial with the cylinder 4, but spaced outwardly therefrom. Wound on the coil holder 8 is a multi-turn coil 9 of wire, the ends of which are connected to a suitable alternating supply to provide the necessary oscillatory motion.
The piston 6 is mounted on a round end cap 10 which is attached by means of axial bolts (not shown) to a cylindrical housing 11. Extending radially inwardly from the housing 11 is a flange 12 on which is mounted an annular magnet 13 and annular inner pole piece 14. The housing 11 and flange 12 are made, at least in part, of magnetic material, thus forming a magnetic circuit which also includes the magnet itself and the inner pole piece 14. It will be seen that, situated in the magnetic circuit, is a cylindrical air gap 15 formed between the inner pole piece 14 and the housing 11, which latter thus constitutes an outer pole piece.
In practice the housing 11 is split in the axial direction into three distinct components: separated at dotted lines 70,71. The central component is made of magnetic material, as required by the magnetic circuit and includes the outer pole piece. On the left side (adjacent to the air gap) there is a requirement for the material to be nonmagnetic in order to minimise flux leakage and a separate spacer is used (typically of aluminum alloy). On the right side there is no particular requirement and either the outer magnetic circuit can be extended or a separate component can be used.
The assemblies 2 and 3 are mounted together for relative axial movement by means of a pair of spiral springs 16,17. Each of these springs is made from one or more round flat discs of thin material, such as stainless steel or beryllium copper, typically 0.1-1 mm thick. A plan view of a single such disc is shown in FIG. 2 of the accompanying drawings, in which the shaded areas indicate where the spring is clamped to adjacent components: the inner area to the cylinder/coil holder assembly 3 and the outer area to the piston/magnet assembly 2. Between the areas a series of six spiral arms 18 are created by forming slots 19 in the disc. Each slot opens at each end into a hole 20 in order to provide stress relief. In the event that each spring comprises more than one disc, individual discs are separated, in the axial direction, by means of thin shims (not shown).
The stiffness of these springs in the direction of axis 1 is quite low, whereas the radial stiffness is very high. Thus the two springs 16 and 17 constrain the assemblies 2,3 to move accurately with respect to one another along the axis 1 a
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Dinh Le Dang
Enad Elvin
Isis Innovation Limited
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