Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2000-04-14
2002-01-01
Nguyen, Tran (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S085000
Reexamination Certificate
active
06335581
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to an electric motor intended for use in an aggressive medium and, in particular, for a fuel pump of a motor vehicle, with a rotor rotating within a stator, the rotor having an outer surface susceptible to corrosion in respect of the intended medium.
Such electric motors are often used for driving fuel pumps and are known in practice. In this case, the fuel flows through the electric motor. The electric motor therefore does not require complicated sealing, so that it can be produced highly cost-effectively. The rotor usually has an armature core bundle composed of a soft-magnetic steel which is therefore highly susceptible to corrosion. In particular, alcohol-, water- or acid-containing fuels therefore result in the rotor being destroyed.
It would be conceivable to injection-mold corrosion-resistant plastic or wrap foil around the rotor completely. However, this increases the distance between the rotor and the stator, so that the efficiency of the electric motor decreases. Furthermore, injection-molding around the rotor leads to a pronounced unbalance. Wrapping necessarily has overlaps which likewise result in an unbalance. Since, due to the high density of the armature core bundle, the rotor has to be balanced, for example by milling out, before being injection-molded around it or being wrapped with foil, the injected-around or wrapped armature requires a second balancing. This leads to a particularly cost-intensive manufacture of the rotor.
It would also be conceivable for the rotor to be covered with a corrosion-resistant lacquer. However, such lacquers require high curing temperatures. The high temperatures may, however, destroy components of the rotor.
SUMMARY OF THE INVENTION
The problem on which the invention is based is to design an electric motor of the type initially mentioned, in such a way that it can be produced particularly cost-effectively and affords a high degree of protection for media which are aggressive toward components of the rotor.
This problem is solved, according to the invention, in that the rotor has a hose-like casing resistant to the intended medium.
By virtue of this design, there is no need for high temperatures in order to protect the rotor against corrosion, so that damage to the rotor is ruled out by the attachment of the hose-like casing. Since the casing, because of its hose shape, can be provided with the same thickness at every point, the true-turned and balanced rotor is not unbalanced as a result of the attachment of the hose-like casing. A suitable choice of material for the hose-like casing gives the outer surface of the rotor particularly reliable corrosion protection. Since curing or stoving of the corrosion protection is not necessary, in contrast to lacquer or to injection-molding around, the electric motor according to the invention becomes particularly cost-effective.
According to an advantageous development of the invention, the unbalance caused by the hose-like casing can be kept particularly low if the hose-like casing is seamless.
According to another advantageous development of the invention, the mounting of the hose-like casing becomes particularly simple if the hose-like casing is designed elastically. Furthermore, the hose-like casing is thereby connected reliably to the rotor. It is therefore possible to avoid the situation where the hose-like casing is stuck fast.
According to another advantageous development of the invention, particularly high prestressing forces of the hose-like casing can be applied in a simple way if the hose-like casing is designed as a shrinkable hose which contracts plastically as a result of heating. Another advantage of this design is that the shrinkable hose can be fixed to the end faces of the rotor by means of a slight projection beyond the outer surface. The hose-like casing is consequently fastened to the rotor particularly reliably. Moreover, another advantage of this design arises when the hose-like casing is mounted on the rotor, since, by virtue of the invention, the casing does not have to be stretched at the same time.
A contribution to further reducing the manufacturing costs for the electric motor according to the invention is made if the hose-like casing contains polyester, Polyvinyl Chloride (PVC) or Polytetrafluoro Ethylene (PTFE).
The edges of the hose-like casing which are contiguous with the rotor could, for example, be adhesively bonded to the rotor for sealing purposes. Alternatively, a clamping ring could also be fastened on the rotor for sealing off the hose-like casing. This results, however, in an increase in the costs of the electric motor and also in an unbalance being introduced into the rotor. However, according to another advantageous development of the invention, it becomes particularly simple to seal off the hose-like casing if the rotor has a smooth continuous annular surface in each of the contiguous regions of its outer surface and if the hose-like casing is prestressed against the annular surfaces.
REFERENCES:
patent: 3718830 (1973-02-01), Philofsky et al.
patent: 4120618 (1978-10-01), Klaus
patent: 5779453 (1998-07-01), Nagayama et al.
patent: 5816782 (1998-10-01), Nagayama et al.
patent: 1089468 (1959-02-01), None
Mannesmann Vdo AG
Mayer Brown & Platt
Thimmig David M.
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