Linear motor
AssigneeFisher & Paykel Limited
InventorsGerald David Duncan, John Henry Boyd
Life of this patent
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Abstract
The present invention provides an improved design of linear motor as well as an improved control strategy. The design allows for a shorted stator, where the armature magnets are controlled to reciprocate to a greater maximum displacement than for a equivalent conventional linear motor. The control strategy is such that a minimum of external sensors are required. The linear motor is driven at its resonant frequency ensuring optionally efficient operation. A determination of the maximum current is made based on a relationship with the resonant frequency and the evaporating temperature/pressure of the vapor entering the compressor. The current is then limited to control the maximum displacement to avoid damage.
Claims16
A vapour compressor comprising:
- a piston,
- a cylinder,
- said piston being reciprocable within said cylinder, the vibrating system of piston, spring and the pressure of said vapour having a natural frequency which varies with vapour pressure,
- a linear brushless DC motor drivably coupled to said piston having at least one winding,
- a DC power supply,
- commutation means for electronically commutating said at least one winding from said DC supply to provide a supply of current to said at least one winding to reciprocate said piston,
- resonant driving means which initiate commutation of said at least one winding to thereby drive said piston at the resonant frequency of said vibrating system,
- current controlling means which determine the amount of said supply of current supplied by said commutation means, said determined amount of current being related to said resonant frequency, and which initiate commutation of said at least one winding to thereby limit the amplitude of reciprocation of said piston.
Dependencies are inferred from the claim text.