GB2054977A - Reciprocating electric machines - Google Patents

Abstract

A reciprocating electric machine which can function as a motor or a generator includes means 14, 18 for producing two magnetic fields which oppose one another. A magnetic core 32 is located in the fields and a coil 33 surrounds the core. The core is connected via drive rods 34, 36 to a converter 12 so that reciprocating movement of the coil is converted to rotary motion by the converter, or vice versa. Commutating means 56 control the direction of current flow through the coil to achieve continuous controlled motor or generator action. In the motor shown, the coil 33 is connected to a D.C. source 58 by way of the commutator 56 and conductive leads 60. <IMAGE>

Description

SPECIFICATION Improvements in or relating to electric machines This invention relates to an electric machine which depending on its mode of use, can function as a motor or a generator and may include a waveform generator.

E. R. Laithwaite has proposed a self-oscillating synchronous linear motor which suffers from the disadvantage of excessive stroke length, and, more seriously, when fitted with a linear to rotary converter is incapable of self-starting.

According to the invention, there is provided an electric machine comprising means for establishing a magnetic field, drive means, and coil means coupled to the drive means and reciprocably movable in the magnetic field, the coil means including at least one pair of terminals for connection to apparatus which determines the flow of current through the coil means.

The magnetic field means may comprise means for establishing a first magnetic field, the second magnetic field, the second magnetic field being generally of opposite magnetic sense to the first magnetic field, the coil means being reciprocably movable between the first and the second magnetic fields.

Use may be made of a power source connected to the terminal pair, the relationship of the polarity of the power source to the first and second magnetic fields being such that motor action is induced in the coil means.

Depending on the parameters of the electric machine the power source may be AC. However, where the power source is DC the machine may include commutation means for contriving the direction of current flow through the coil means.

The drive means may be connected to any device which is to be driven by the motor. The drive means, which provided reciprocating motion, may be connected directly to devices such as borehole and piston pumps, jackhammers and the like. However, if rotary motion is required use may be made of a linear to rotary converter which is driven by the reciprocating drive means.

When the machine is used as a generator, it may include means connected to the drive means for producing reciprocating movement of the coil means such that an electromotive force is induced in the coil means and appears across the terminal pair. This means may, for example, be a rotary to linear converter but clearly any suitable prime mover may be employed.

The electric machine may include a core which provides a magnetic path for the first and the second magnetic fields, the coil means surrounding, and being reciprocable along, the core.

The core may, for increased efficiently of operation, be formed a high quality magnetic material.

The first and second magnetic fields may be produced with the aid of electromagnets but in a preferred form of the invention use is made of first and second permanent magnets respectively.

The first and second permanent magnets may be formed by first and second axially aligned toroidal magnets and the coil means may be located in the bore of the toroidal magnets.

Preferably the first and second toroidal magnets respectively comprise a stacked assembly of individual toroidal magnets. The individual toroidal magnets may be selected with different magnetic strengths to obtain different characteristics from the machine. For example, the use of different strength magnets in the generating mode influences the output waveform appearing across the terminal pair, while in the motor mode the mechanical power is altered.

The invention will be further described by way of example with reference to the accompanying drawing which schematically illustrated an electric motor constituting a preferred embodiment of the invention.

The drawing illustrates an electric motor which includes a magnetic housing 10 and a crank and commutator assembly 12.

The housing 10 includes a first stack 14 of individual toroidal magnets 16, arranged in series, i.e. adjacent magnets have abutting north and south poles, and a similar stack 1 8 of toroidal magnets 20. The two stacks 14 and 18 are arranged with opposing south poles and so establish two substantially collinear magnetic fields of opposite sense. The stacks are separated by means of a toroidal, non-magnetic insert 22.

The assembled stacks are bounded by means of large upper and lower magnets 24 and 26 respectively which have polarities as indicated in the drawing and which consequently assist in concentrating the magnetic fields from the stacks 14 and 1 8 inside the bore of the housing. For a similar reason use is made of small cores 28 and 30 which are located centrally of the magnets 24 and 26 respectively, and which are of north pole polarity.

A core 32 of magnetic material is located centrally in the bore of the housing and a coil 33 wound on a spool surrounds the core. The spool is in close yet freely moving contact with the core 32.

Two drive rods 34 and 36 extend from the spool and are connected to a link 38 by means of a yoke 40.

The link 38 is connected to the mechanism 12 by means of a pin 42. The mechanism includes a crank 44, a shaft 46 which is mounted in bearings 48 and 50, a flywheel 52 on the shaft, and an output pulley 54. A commutator disc assembly 56, mounted on the shaft, is connected to a DC source 58 and via supply lines 60 to a terminal pair 62 and 64 respectively. The terminal pair in turn is connected to the coil 33 by means of conductors mounted on the drive rods 34 and 36.

The direction of current flow from the source 58 via the lines 60 to the coil 33 is controlled by means of the commutator assembly 56, in relation to the magnetic field polarity inside the housing 10 and the physical position of the coil 33, in accordance with well known electromagnetic laws to produce motor action on the coil 33. Thus the coil 33 reciprocates along the core 32 and the crank action of the mechanism 12 converts the linear movement into rotary motion which may be taken off at the pulley 54.

In a test conducted on a small model of the motor, output speed of 700 rpm was obtained from the crank mechanism. The output power, measured by means of a pony brake test, was 2.2 watts. The input voltage was 6.75 volts and the input current was 1.5 amp. Thus the input power was 10,25 watts and the motor had an overall efficiency of 2,2/10,125=22%.

For comparison purposes a similar test was conducted on a small, high quality, conventional rotating DC motor. With an input voltage of 9 volts the motor drew 0,4 amps, i.e. 3,6 watts.

The output speed was 600 rpm and the output power was 0,47 watts giving an efficiency of 0,47/3,6=13%.

Clearly if the motor is used only in the linear mode then friction losses in the mechanism 12 are eliminated and the efficiency is increased.

If the machine is used as a generator then the coil 33 may be reciprocated by means of the mechanism 12. An alternating output is obtained across the contact pair 62 and 64 and this may be rectified, if desired, by means of the commutator assembly.

The motor speed is easily controlled by varying the potential of the source 58 applied to the coil 33 and the speed of the shaft 46 may readily be controlled from tens of revolutions per minute.

Another apsect is that two or more of the housings 10 can be connected in V- or other configurations to drive a single mechanism 12 to obtain a fairly constant output power.

It has also been found in practice that minimal heat is developed by the machine during operation.

Claims (11)

1. An electric machine comprising means for establishing a magnetic field, drive means, and coil means coupled to the drive means and reciprocably movable in the magnetic field, the coil means including at least one pair of terminals for connection to apparatus which determines the flow of current through the coil means.

2. An electric machine as claimed in Claim 1, in which the magnetic field means comprises means for establishing a first magnetic field, and means for establishing a second magnetic field, the second magnetic field being substantially collinear with the first magnetic field and being generally of opposite magnetic sense to the first magnetic field, the coil means being reciprocably movable between the first and the second magnetic fields.

3. An electric machine as claimed in Claim 2, including a power source connected to the terminal pair, the relationship of the polarity of the power source to the first and second magnetic fields being such that motor action is induced in the coil means.

4. An electric machine as claimed in Claim 3, wherein the power source is a direct current power source and includes commutation means for controlling the direction of current flow through the coil means.

5. An electric machine as claimed in Claim 3 or 4, including a linear to rotary converter arranged to be driven by the reciprocating drive means.

6. An electric machine as claimed in Claim 2, including means, connected to the drive means, for producing reciprocating movement of the coil means such that an electromotive force is induced in the coil means and appears across the terminal pair.

7. An electric machine as claimed in any one of Claims 2 to 6, including a core for providing a magnetic path for the magnetic field, the coil means surrounding and being reciprocal along the core.

8. An electric machine as claimed in any one of Claims 2 to 7, wherein the means for establishing the first and the second magnetic fields respectively comprise first and second permanent magnets.

9. An electric machine as claimed in Claim 8, wherein the first and second permanent magnets t are respectively formed by first and second axially aligned toroidal magnets and the coil means is located in the bore of the toroidal magnets.

10. An electric machine as claimed in Claim 9, wherein the first and second toroidal magnets respectively comprise a stacked assembly of individual toroidal magnets.

11. An electric machine substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.