Pumps – Motor driven – Electric or magnetic motor
Patent
1996-09-19
1998-09-22
Freay, Charles G.
Pumps
Motor driven
Electric or magnetic motor
4174237, 41742314, 4174103, F04B 3504
Patent
active
058105689
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a rotary pump and particularly to an electrically driven rotary pump. The present invention is suitable as a pump for vehicle power steering but not exclusively so.
Pumps used in power assisted steering of vehicles are usually driven mechanically directly from the engine. More recently though electric motor driven pumps have started to be used on vehicles, since they save engine power and fuel and are easier to package in the engine bay. Conventionally these motors are of the brushed d.c. type, and need to be powerful enough to satisfy demands for high power at low vehicle speeds and parking. These high power demands, e.g. up to 1 kilowatt account for only approximately 5% of the operational time of the motor and are short lived, that is the demand is not expected to last more than ten seconds, for example. Significantly lower power, e.g. 30 to 100 watts, is required for approximately 95% of its operational time. Brushless d.c. motors provide better control and can automatically limit in-rush current, unlike conventional motors with brushes. In addition, brushes have poor performance at very high power and will eventually wear out. Therefore, unlike brushed motors, it is possible to over power a brushless motor for brief periods for a given motor size. Conventional brushed and brushless motors consist of a rotating inner wound stator and stationary outer magnets.
The electrical motors used to drive power assisted steering pumps are commonly mounted adjacent to the pump and require separate assembly and testing. Moreover, difficulties have been experienced as a result of the very high temperatures which are generated by the motor especially when the higher power demands of low speed steering occur. One solution to this has been to completely surround the stator of the motor in oil in order to reduce the temperature of the exterior casing of the motor thereby enabling it to be used safely under the bonnet of the vehicle and preventing failure of its components due to the very high temperatures generated. This has the disadvantage though of significantly reducing the efficiency of the motor.
It is also the case not only for the above reason but also because of the physical limitation on the size of the motor to enable it to be mounted under the vehicle bonnet, that the rotor magnet conventionally consists of a rare earth to meet the power demands of the system which significantly increases the cost of the component.
The present invention seeks to overcome at least partly the difficulties identified above with respect to conventional motors for power steering pumps. In this respect the present invention seeks to provide an integral pump and motor which is compact and yet capable of meeting the power demands of a vehicle steering system and which reduces the problems associated with the high temperatures involved in a simple yet cost effective manner.
The present invention provides in a first aspect a rotary pump assembly having at least one inlet port, at least one outlet port, a housing and a pumping device in fluid communication with the inlet and outlet ports, the pumping device including a pump driver member mounted on a rotatable shaft which is connected to the rotor of an electric motor, a portion of the housing being located radially between the shaft and the rotor of the motor and having the stator of the motor mounted thereon.
The fluid pump includes a cavity in communication with the inlet port which may be located about the rotatable shaft.
With the "inside-out" construction described above, that is a stationary inner wound stator and rotating magnets, more power can be gained for a given physical size of motor. For reasons of cost and size it is preferred that a lower rated motor is employed which is capable of accommodating the brief demands for high power. With the present invention which utilises the "inside-out" construction of a brushless d.c. motor as described, it is possible to employ a lower rated motor than has formerly been the case. Ideally means of cond
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Baseley Simon John
Whitefield Kevin John
Bednarek Michael D.
Freay Charles G.
Temple Farm Works
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