Motor vehicles – Steering gear – With fluid power assist
Patent
1998-10-26
2000-11-28
Swann, J. J.
Motor vehicles
Steering gear
With fluid power assist
180421, 701 42, B62D 599
Patent
active
061522546
ABSTRACT:
A vehicle power steering system 10 achieves a substantially linear control relationship between an applied steering torque input T.sub.s and a resulting steering force output, that is, a powered assist to vehicle steering. The system 10 includes a reversible fluid pump 24 driven by an electric motor 26. A pair of fluid lines 20 and 22 supply pressurized fluid from the pump 24 and to the left and right ports 56 and 58 of a power cylinder 18. A pair of pressure transducers 54 and 55 sense the fluid pressures LP.sub.p and RP.sub.p in the lines 20 and 22. The pressure transducers 54 and 55 are connected to an electronic control 32 which establishes an internal closed servo control loop 322 or 342 over the powered assist to vehicle steering provided by the power cylinder 18, for example, over actuation of the motor 26. The system 10 is preferably regenerative and includes a variety of safety features which prevent system runaway and allow unencumbered manual steering in case of failure of the system. The system 10 is also arranged for continuous rejuvenation of its hydraulic fluid, and the structure providing such rejuvenation can be employed in a wide variety of other systems. The electronic control 32 employs the measured fluid pressures LP.sub.p and RP.sub.p to counteract a hydromechanical resonance occurring predominantly between the moment of inertia of the motor 26 and a system spring rate consisting primarily of the vehicle steering load stiffness. The system 10 substantially eliminates stability problems in EPS systems, for example, a well-recognized low frequency stability control problem which has typically not been overcome in prior EPS systems. The system 10 provides full time independent verification of instant values of steering boost, substantially eliminating prior concerns relating to auto-steer. The system 10 also eliminates concerns in prior EPS systems such as mechanical over constraint, Coulomb friction, wear and backlash.
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Lum L.
Swann J. J.
Techco Corporation
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