Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1998-12-14
2001-06-05
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S181000, C310S171000, C310S168000, C310S184000
Reexamination Certificate
active
06242834
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is generally concerned with rotating machines such as motor vehicle alternators.
A conventional motor vehicle alternator is a polyphase generator generally including a stator within which turns a rotor provided with an excitation coil. The coil is energised via brushes in contact with two collector rings on a projecting part of the rotor shaft.
Using brushes has disadvantages, including the need for a relatively great axial length of the alternator, a set of brushes and collectors that increase the unit cost and malfunctions due to faulty contact between the brushes and the collector rings, in particular as a result of wear.
There exist in the prior art certain proposals aimed at providing rotating machines that can be used as motor vehicle alternators that have no brushes.
In one prior art alternator the claws of the two pole wheels of the rotor, which normally interpenetrate, are truncated to provide space in a transverse plane for a support for a fixed excitation coil disposed inside the pole wheels. However, this approach is detrimental to the efficiency of the machine, because the areas of the air gap are then very significantly reduced. What is more, for a given output/speed curve, a machine of the above type is significantly heavier than a conventional machine, which is particularly disadvantageous in the case of vehicle alternators.
In another prior art alternator two pole wheels with interleaved claws are mounted cantilever fashion at one axial end of the machine between an internal fixed excitation coil and external stator coils.
This prior art solution also has disadvantages, in particular the fact that the axial dimension and the weight of the machine are necessarily increased. Also, the enlarged air gaps in the rotor reduce the efficiency of the machine.
What is more, in both cases referred to above, the design of the machine makes it essential to take into account electromagnetic phenomena not only in the plane perpendicular to the rotation axis, i.e. in two dimensions, but also in the direction of the axis, i.e. in the third spatial dimension.
This necessity for three-dimensional design of the machine makes it extremely difficult and time-consuming to model and to optimise the various parameters.
A flux commutating machine with no brushes, known in particular from document EP-0 707 374, has the advantage of being easily modelled and optimised in two dimensions only.
This prior art machine nevertheless has the drawback of being restricted to single-phase operation, although three-phase machines can be desirable in a large number of applications, in particular in terms of electromagnetic efficiency and in terms of the simplicity and economy of the associated rectifier and smoothing means.
BRIEF SUMMARY OF THE INVENTION
The Applicant has found that it is possible to use the flux commutation technique to produce various polyphase machines with great flexibility while retaining two-dimensional design and two-dimensional optimisation.
Accordingly, the present invention proposes a flux commutating electrical machine including a stator and a rotor, the stator having on its inside face a series of notches housing a series of stator coils and further including a series of housings for excitation means and a rotor including a plurality of flux commutator teeth adapted selectively to establish pairs of closed magnetic circuits through the stator coils, characterised in that the stator includes a plurality of independent stator coils defining the same number of phases and situated in a series of individual cells angularly distributed around its circumference and in that the teeth of the rotor are equi-angularly spaced so that the angular positions of the various pairs of teeth have predetermined phases relative to the various individual cells.
Preferred but non-limiting aspects of the machine in accordance with the invention are as follows:
each individual cell has a stator structure defining a pair of spaced notches for two portions of a stator coil, said notches being delimited laterally by two stator teeth, and excitation means adapted to establish in one or other of the stator teeth within said stator coil a magnetic field varying in accordance with the mutual angular position of the rotor teeth and the stator teeth;
the individual cells are separated from each other by gaps;
the individual cells are separated from each other by decoupling permanent magnets the field orientation of which is opposite to that of the excitation means;
the excitation means of each cell include a permanent magnet disposed between two stator elements having a generally U-shaped profile defining said notches and said stator teeth;
the excitation means of each cell include an excitation coil disposed in two notches of a single stator element one of which is substantially half-way between two stator coil notches also formed in said stator element;
the excitation coil is disposed in two notches in the inside surface and in the outside surface of the stator element to generate an essentially tangential magnetic field at said coil;
the excitation coil is disposed in two notches both in the inside surface of the stator element to generate an essentially radial magnetic field at said coil;
the various excitation coils are connected in parallel to the same source of current;
the machine comprises pairs of cells formed in a common structural element housing two stator coils corresponding to two different phases, a magnet for exciting one of the stator coils and an excitation coil for exciting the other stator coil;
the stator coils are angularly equidistant over all of the inside circumference of the stator, the angular gap between the various cells being substantially equal to the angular dimension of a notch receiving one run of a stator coil;
the portions of the stator coils in the same cell or the same group of cells are separated by a constant angular gap and the angular gap between portions of successive stator coils in two separate cells or groups of cells is different from said constant angular gap;
said constant angular gap is identical to the angular gap between two adjacent rotor teeth;
the geometry of the rotor and stator structures of the machine satisfies the following condition:
N
M.q.[(N
c
+1).&Dgr;&thgr;
R
+(m/q).&Dgr;&thgr;
R
]=k.&Dgr;&thgr;
R
=2&pgr;
where
N
M
is the number of individual machines on the circumference of the stator,
q is the number of phases of each individual machine,
Nc is the number of excitation means, such as magnets, per phase of each individual machine,
m is a positive or negative integer representing the value of the phase difference between two individual machines and is in the range −(q−1) to +(q−1),
&Dgr;&thgr;
R
is the constant angular gap between two adjacent rotor teeth, or rotor pitch,
&Dgr;&thgr;
S
is the constant angular gap between two adjacent runs of stator coils, or stator pitch, and
k is an integer;
the rotor pitch and the stator pitch satisfy the following condition:
(⅞).&Dgr;&thgr;
S
≦&Dgr;&thgr;
R
≦(5/4).&Dgr;&thgr;
S
the stator pitch is equal to the rotor pitch and in that the geometry of the rotor and stator structures of the machine satisfies the following condition:
N
m
.q
. (N
c
+1)+N
M
.m=k
the machine comprises a single individual machine with three regularly distributed individual cells respectively accommodating the stator coils of three phases and the rotor includes a number of rotor teeth equal to 4, 5, 7 or 8 and preferably equal to 5;
the machine comprises two individual machines each with three regularly distributed individual cells respectively accommodating the stator coils of three phases and the rotor includes a number of rotor teeth equal to 8, 10, 14 or 16 and preferably equal to 10;
the machine comprises a single stator frame including at least two series of internal notches adapted to accommodate respectively the stator coils and the excitation magnets or the excitation coils.
A
Morgan & Finnegan LL
Tamai Karl
Valeo Equipements Electriques Moteur
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