Electrical generator or motor structure – Dynamoelectric – Rotary
Patent
1999-06-08
2000-08-22
Ramirez, Nestor
Electrical generator or motor structure
Dynamoelectric
Rotary
310 91, 310 67R, 310 68B, 310 68R, 74388PS, 180 791, 180443, H02K 500
Patent
active
06107716&
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to improvements in housings for electrical devices, and in particular, but not exclusively, electric power-assisted steering systems for vehicles of the kind comprising an electric motor connected through a gearbox to an output shaft operatively connected to a steering column of the vehicle. In particular, the invention relates to reduction in the susceptibility of an electrical system to electromagnetic noise.
BACKGROUND OF THE INVENTION
It is well known to provide electrical systems which incorporate both high power electronic and low power electronic components in a single design. For efficiency of space, it is often desirable to incorporate both kinds of components into a single housing unit but this can create problems due to electromagnetic interference. Hence, it is common practice to split the high and low power devices into separate housings.
For example, in electric power assisted steering systems of the kind set forth, the electric motor is used to assist a driver of the vehicle in turning the steering column, by applying an assistance torque of the same sense as the torque applied by the driver, which makes it easier to turn the steering wheel, for example during parking. The motor is controlled by motor control circuitry and drive circuitry. The control circuitry is typically connected to a torque sensor associated with the steering column and adapted to provide a signal indicative of the torque demand by the driver. The motor drive circuitry is adapted to switch the motor drive currents between, for example, different phases in the motor under the control of the motor control circuitry. It typically comprises a plurality of high power transistors connected in a bridge as it must handle the relatively high currents demanded by the motor. The transistors are switched under the control of the control circuitry.
Electric motors are known to be relatively strong sources of electromagnetic radiation which can cause interference problems with other electronic circuitry provided in the motor vehicle and, in particular with the control circuitry in the steering system. Furthermore, because of the limited choice of positions in which the steering system can be mounted within the increasingly cramped confines of a vehicle, it is often exposed to many other sources of electromagnetic radiation. External sources of radiation, such as overhead power lines, can also produce electromagnetic radiation which can cause interference. In a safety critical application such as a power-assisted steering system, it is important to provide a high level of shielding from this electromagnetic radiation to minimise the susceptibility of the electronic control and drive circuitry from interference.
It is already known to overcome the problem of electromagnetic interference by providing the drive and control circuitry inside separate conductive casings which are bolted onto a main housing body which contains the gearbox. Another casing is provided which houses the motor. The purpose of providing the separate casings is to isolate the electronic circuitry from the motor and gearbox. However, each casing requires a separate cover or other opening to allow installation and maintenance. These openings provide potential points of leakage and entrance of radiation through the various associated seals.
SUMMARY OF THE INVENTION
According to one aspect, the invention provides a housing assembly for an electric power-assisted steering system of the kind in which an electric motor is connected through a gearbox to an output shaft operatively connected to a steering column for a vehicle, characterised in that the housing defines at least two discrete compartments, a first one of the compartments being adapted to house the motor and the gearbox, and a second one of the compartments being adapted to house a motor control circuit and a motor drive circuit, a support member being adapted to provide a physical barrier between the drive circuit and the control circuit, and in which the sup
REFERENCES:
patent: 4473128 (1984-09-01), Nakayama et al.
patent: 5738183 (1998-04-01), Nakajima et al.
patent: 5796198 (1998-08-01), Sugino et al.
patent: 5819871 (1998-10-01), Takaoka
patent: 6012347 (2000-01-01), Hasegawa
patent: 6013960 (2000-01-01), Yoshida
Lam Thanh
Ramirez Nestor
TRW Lucas Varity Electric Steering Ltd.
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