1. This invention introduces a new range of D.C. motors, made possible by the new manner of manufacture of commutator motors and generators covered by our company's Provisional Patent Application titled COMMUTATION OF MOTORS AND GENERATORS. A NEW APPROACH. The new range is also provisionally patented under our application titled D.C. MOTORS. A NEW APPROACH TO FIELD EXCITATION

2. As stated in past D.C. motor literature and confirmed by modeling we did some years ago, main field excitation is possible by exaggerated brush shift from the neutral axis. The problem has been the excessive commutation arcing which has so far resulted when this has been tried. Our new approach to commutation overcomes this problem and ushers in a new range of D.C. motors. Field windings can be entirely omitted, in which case a series torque-speed characteristic results, or windings or permanent magnets can be included to give compound characteristics, when acting together with brush shift.

3..  DESCRIPTION OF MOTOR.

In a typical execution of this invention, the armature and field are as used in current permanent magnet motors, except that:

3.1. The armature has the new commutator assembly fitted, see 1 above. The use of this new arrangement is essential for satisfactory commutation.

3.2..Brush sets, resistors, diodes, transistors and control module are as per the new commutation approach.

3.3..The salient poles P are high permeability low remanence magnetic material, e.g. soft iron, without windings. This configuration gives a series characteristic.

3.4..Alternatively, the salient poles P are permanent magnets, or shunt wound poles. These give a compound characteristic when combined with brush shift.

3.5..The brush axis is displaced from neutral in the manner shown. This displacement may be fixed or mechanically variable, in order to produce the desired torque-speed characteristics in either of the 3.3 or 3.4 configurations. The brush axis should remain outside the pole tips by an angular displacement to be established during the development phase. This is to avoid excessive speed voltage generation in the commutating coils.

4..THEORY.

The manner in which brush shift causes the non-air gap conductors (shown green) to take the place of conventional field windings is immediately evident in the preceding Schematic Layout . The ensuing motor analysis then proceeds along well established lines and there is no need to reiterate it here.

5..APPLICATIONS.

This new range will be preferred in applications requiring higher start torques and/or higher speeds than are available from current permanent magnet motors of similar size.

Consider, for example, a simple traction application like electric bicycles, where permanent magnet motors are generally used. Manufacturers have so far had to include gears or two motors (series/parallel combinations) to obtain the torque required for starting and hill climbing, and the high speed required for flat travelling.

Using the new motor range here introduced, the approach to this application will be:

In this example and in any similar application, rotating the brush axis has the same effect on output torque as adding a smoothly variable gearbox after the motor. The "gear ratio" is altered, in effect, by varying the air gap field, the field itself being dependent on the amount of brush shift.

This capability to vary the torque and speed (their product remaining constant) for a given input voltage and current is not available on permanent magnet motors and is one of the advantages which should ensure the commercial attraction of this new range. Another will be the ability to compound predominantly permanent magnet motors so as to achieve, with moderate fixed brush shifts, sensibly constant (ie. non-drooping) speed vs current characteristics.

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