RARE EARTH MAGNET PMDC MOTOR / ALTERNATORS

TECHNICAL FIELD OF THE INVENTION

This invention relates to the improvement in out put with smaller volume and weight by using rare earth magnets in PMDC motors / alternators used in automobiles and other similar applications.

BACK GROIJM) OF THE INVENTION

PMDC motors have been used from the early 50's and 60's to do the functions which were done manually earlier to that period or have been done by elaborate electro magnetic motors which were far more bulkier than the current motors and were drawing far more power from the battery or DC source ex. starter and wiper motors.

Many DC Motors are used in the modern Automobile. Of them PMDC motors are used in power windows, wipers, windshield washers central locking mirror and seat adjustment motors. These motors are built with ceramic magnets, which are the permanent magnets in the PMDC (Permanent Magnet Direct Current) motors.

As technology improved it was found that more applications for the motors were introduced where in it was expected for these motors were required to produce more output in terms of power. This requirement made the motors bulkier since the magnets, had to be made longer and thicker and the armatures had to be made longer as well and increased in diameter in order to accept more turns and produce better output. This created a major problem of space constraints.

As a general rule among the permanent magnet field DC motors it is difficult to maintain the output with the diameter of the armature (3) reduced. Especially in a motor using Ferrite magnet, whose maximum energy product [BH] max in low irrespective of whether it is fabricated by sintering, compression moulding or any other process in order to get the required dimensional accuracy.

It requires to make the magnets more powerful without increasing its size. The better option was to go in for rare earth magnets. But these magnets are upto 10 times more powerful having a [BH] max value of about 40 Mega Gauss Oersteads MGOe as against the best of Ferrites, which give about 4 MGOe.

In order to make it suit the requirements at hand a much smaller volume and in turn weight, of rare earth magnets may be used. This in turn would also make the other components of the PMDC motor smaller. Overall the motor itself will be made much smaller both in volume and consequently in weight.

We also have the option of increasing the power as per our requirement for a much smaller volume than the prior art motors.

But using a rare earth magnet in a motor used in the automobile has to be done in a fashion, which will allow the magnet to be protected on all sides than be exposed. This is because the rare earth magnet does not have a very strong structural integrity. Hence these magnets are enclosed in a stainless steel (non magnetic) cladding, which will protect the magnet from loosening and provide a strong enough encasement fig (1). This will also prevent the ingress of any magnetic material to come in between the gaps between the magnets and the armature teeth.

BRIEF DESCRIPTION OF THE DRAWING

Fig 1 : Shows the relative size of the two motor stators.

Fig Ia : Shows the exploded view of the conventional ceramic magnet fitted stator of the PMDC motor called the prior art.

Fig Ib : Shows the exploded view of the preferred embodiment with the rare earth magnets fitted stator of the PMDC motor called the invention and also shows the stainless steel cladding and the two notches on the soft iron yoke to hold the rare earth magnets in position.

Fig. 2 : Shows the comparative hysterisis curve of the present invention (2a) with that of the conventional one (2b).

Fig. 3 : Shows the PMDC motor working principle

DETAILED DESCRIPTION OF INVENTION

The magnets (1) are placed outside with one magnet's north pole and one magnets south pole at 180 degrees to each other in-side a yoke (2) is of soft magnetic material.

The armature (3) consists of an electro magnet of laminated design, which can have a winding and a commutator (4).

The windings, when a supply is given by carbon brushes (5) on the commutator which is a connector connected to the two ends of the winding, the armature produces a North pole opposite to the north pole of the permanent magnet and south pole against the south pole of the permanent magnet thus repelling the armature.

When the armature is moved in this way the commutator terminals will be against the brushes with reversed polarity thus creating the same effect again and again making the armature / rotor to rotate. More number of pole segments are provided in the armature to make it move continuously without jerk. This is a PMDC motor.

In the case of preferred embodiment, the magneto-motive force of the magnets becomes more and to repel this magnet more turns are wound on the armature to make the armature rotate. When this is done the motor gives a better output by repelling more forcefully.

The cladding (6) is added to give more structural integrity to the construction in preventing the magnet (1) from coming loose.

This invention by primary objective seeks to improve output by the more powerful yet smaller in size ceramic magnets. Thus solving the problem of bulkiness or more volume of the magnet. It is also noticed that though more turns are added to the armature the current in the armature is lesser because of the length of the armature core is less comensurate with the less length of the Rare Earth Magnet.

This invention also relates to alternators, fly wheel generators, flywheel magnetos alternators etc; using permanent magnet.

Permanent magnets produced from alloys containing iron in combination with at least one rare earth element and boron /cobalt provide magnets having energy product which may be of the order of upto 45 MGOe. (Mega Gauss Oersteads) Energy product is a measure of the usefulness of a magnet since the MMF upto 10 times that of commercial ceramic magnet, which have a max energy products of value 4 MGOe.

It is therefore a main object of the present invention to use a rare earth magnet in place of an ordinary ceramic magnet to produce a better output for a smaller volume and weight.

A smaller motor will provide more space utilisation when used in an automobile.

A lower weight will provide greater leave way for better fuel efficiency.

Although by providing an effective air gap equivalent to that of the conventional motor, this motor can be made still smaller and / or more powerful for the practical purposes of using the same motor in place of the existing motor suitable reduction in volume of the magnet and increase in air gap have been made.

The main advantage of the present invention is explained in Figure 2, which proves that the comparative hysterisis curve of the demagnetisation portion of the present invention is 10 times better than the conventional one, whose operation is

almost at saturation levels of remnance throughout the working cycle of the motor, making the motor more efficient, due to the higher value of both remnance and coercivity. Thus rare earth magnets of the present invention are more useful and better than that of the conventional ceramic magnet.

The following table shows the percentage reduction in terms of weight, volume and power consumption of the present invention over the prior art for a typical power window application.

The above savings in weight, volume and power consumption is valid for all other applications also.

Example 1 : With the reduced size of mating parts also, the motor has been made still smaller giving a saving in cost.

Example 2 : The stainless steel cladding acts like a protective shield in:

a) Preventing the rare earth magnet from falling down on to the armature.

b) Preventing ferrous particles from outside gaining access to the air gap between the magnets (stator) and armature (rotor) thus damaging the magnets and the motor. c) Facilitating increase in air gap effectively for replacement of conventional motor without much modification.