Electricity: motive power systems – Induction motor systems
Reexamination Certificate
2000-04-20
2001-10-23
Masih, Karen (Department: 2837)
Electricity: motive power systems
Induction motor systems
C318S049000, C318S035000, C318S051000, C318S060000, C318S432000, C318S434000, C318S567000, C318S569000, C388S903000, C388S907500
Reexamination Certificate
active
06307346
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to electric and hybrid vehicles and, more particularly, to an improved power steering system and induction motor load limiting algorithm or method for use in electric and hybrid vehicles.
The assignee of the present invention designs and develops electric and hybrid vehicles. A previous power steering system for electric and hybrid vehicles involved the use of conventional belt-driven power steering systems or power steering systems having a pressure relief valve to control load limiting. The use of relief valves has a power and cost overhead. Belt-driven power steering systems are also less responsive than is desirable.
It would, therefore, be desirable to have an improved power steering system for use in electric and hybrid vehicles. It would also be desirable to have an improved induction motor load limiting algorithm or method for use in electric and hybrid vehicle power steering systems.
SUMMARY OF THE INVENTION
The present invention provides for an improved power steering system and a software algorithm or processing method for use in electric and hybrid vehicles. The vehicle power steering system comprises a power supply that is coupled to a power steering motor. A power steering controller is coupled to the power supply and receives inputs from a plurality of software lookup tables and a frequency command such as is derived from an accelerator pedal, for example. The power steering controller implements an improved induction motor load limiting software algorithm or processing method.
The software algorithm or processing method provides for induction motor load limiting to avoid excessive power consumption and hydraulic system pressure when the power steering system is in full-lock or near full-lock position. The power steering system does not require the use of a pressure sensor or a pressure relief valve as in certain conventional systems.
The software algorithm or processing method adjusts the speed of the power steering motor by reducing the power output of the power supply (instead of using a pressure relief valve) during extremely high load conditions in order to maintain a specified system pressure. The power output of the power supply is controlled by adjusting the output frequency produced by the power supply. The output power of the power supply changes at different output frequencies. Software lookup tables are generated empirically by characterizing the output power of the power supply at a plurality of (three) different system pressures over a range of motor speeds. The tables provide a power band that implements a power limiting state machine. Power calculations are performed at the output voltage signal frequency, since AC output current can only be calculated at the output frequency.
Excessive pressure is not generated and no relief valve is used. Also, the power steering system exerts a lower power consumption using the present invention compared to conventional systems.
REFERENCES:
patent: 4702335 (1987-10-01), Cage et al.
patent: 5345154 (1994-09-01), King
patent: 5709281 (1998-01-01), Sherwin et al.
patent: 6152254 (2000-11-01), Phillips
Char Wade E.
Downer Scott D.
Fujii Stanley K.
DeVries Christopher
General Motors Corporation
Masih Karen
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