Pumps – Motor driven – Electric or magnetic motor
Patent
1995-11-29
1997-01-28
Gluck, Richard E.
Pumps
Motor driven
Electric or magnetic motor
F04B 3504, F04B 3900, F16J 124
Patent
active
055972942
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to electromagnetic reciprocating compressors or pumps, particularly compressors for pumping gas such as air. Such devices can also act as vacuum pumps, but the term "compressor" will be used generally in this specification and claims for convenience.
BACKGROUND ART
Such compressors, which may pump relatively large amounts of air with little compression, have an axially reciprocating piston carrying an armature which is moved through a magnetic field generated by one or more coils. The return stroke of the piston is typically caused by a compression spring. There are many examples of such compressors in the prior art, and reference is made to the following patent specifications as examples, particularly of interest in relation to the present invention: GB-A-1529597) US-A-4718832, US-A-4867656 and US-A-5100304.
Such compressors are required to operate without lubrication and with as little maintenance as possible, for long periods. Their typical rate of operation is the mains frequency, e.g. 50 Hz or 60 Hz. Consequently, the compressor must be designed so that wear caused by the moving piston is minimized, so as to avoid the creation of leakage paths which lead to inefficiency. Another problem is noise, particularly where the compressor is to be used in a quiet environment such as a hospital. Noise may arise as a result of wear of the piston or a surface which it contacts, or from contact of the piston with the cylinder head.
The simplest and most reliable form of return spring for the piston in such an electromagnetic linear compressor is a helical coil spring, applied at one end to the movable piston and at its other end to a fixed abutment. A coil spring cannot be fully constrained laterally, because of its radial expansion and contraction during compression and relaxation. Due to asymmetry in the spring, or in its mounting, it tends to deflect from a truly axial position, thus applying lateral force to the piston, which may result in uneven wear. Also, the compression of a coil spring causes a torsional force to be applied between its ends. It has been proposed (in US-A-5100304) to support the coil spring rotatably at one end against the pump casing by means of a spring retainer seated on a spherical ball, so that the spring causes the piston to rotate gradually by torsional forces generated as the spring returns to its relaxed state. The stated aim is to prevent the piston from suffering uneven wear. US-A-5100304 itself proposes a modification of the same principle, in which the spring retainer is supported by a ball bearing having a plurality of balls spaced from the axis. The aim is firstly to cause the piston gradually to rotate during the reciprocating movements of the piston, as a result of the torsional forces of the spring, and secondly, due to the mounting of the spring retainer, to prevent the coil spring from flexing away from its central axis and exerting radial biassing forces on the piston. It is not clear from these disclosures how the use of a low-friction or substantially friction-free mounting of one end of the coil spring will result in a gradual rotation of the piston in a consistent unidirectional manner. It seems more probable that the effect will be a small reciprocating rotation of the piston about its axis, which will not solve the problem of uneven wear. This is discussed more below.
DISCLOSURE OF THE INVENTION
It is an object to the present invention to reduce or minimize the effects caused by the torsional forces exerted by the spring and the tendency of the spring to deflect from its axis.
In accordance with the present invention in a first aspect there is provided an electromagnetic linear compressor having a linearly reciprocating piston biassed in one direction by a spring system comprising two helical coil springs acting in series to bias the piston and a rotational bearing permitting relative rotation of the two springs about their axis, transmitting thrust between the two springs. A first advantage of this arrangement is tha
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patent: 2954917 (1960-10-01), Bayer
patent: 4090816 (1978-05-01), Takahashi
patent: 4357915 (1982-11-01), Monsour
patent: 4718832 (1988-01-01), Takahashi
patent: 4799421 (1989-01-01), Bremer et al.
patent: 4854833 (1989-08-01), Kikuchi et al.
patent: 4867656 (1989-09-01), Hirose
patent: 4966533 (1990-10-01), Uchida et al.
patent: 5100304 (1992-03-01), Osada et al.
Gluck Richard E.
Pegasus Airwave Limited
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