Patent ID: 8689716

Claim:
A servo-assisted steering device for vehicles comprising: a manual control member; a shaft ( 12 ) connected to the control member, a pressurized control fluid supplying and conveying unit ( 13 ) driven by the shaft when the control member ( 11 ) is rotated; at least two fluid conveying lines connected to the supplying and conveying unit, pressurized fluid flowing through the conveying lines in and out of the supplying and conveying unit depending on a rotational direction of the shaft, the conveying lines being further connected to one of two chambers ( 16 , 17 ) of a steering actuator ( 18 ) and comprising hydraulic pipes ( 14 ) for supplying the pressurized fluid alternately to one or the other of the two chambers ( 16 , 17 ) of the actuator ( 18 ) depending on the rotational direction of the control member; and a hydraulic power unit ( 2 ) connected to the supplying and conveying unit ( 13 ) with a fluid supplying and conveying circuit, the hydraulic power unit comprising a reservoir ( 21 ) for the pressurized fluid and powered pumping means ( 22 ) driven by an electric motor ( 23 ) and by electrical connection means of the electric motor ( 23 ), the pumping means connected to the fluid supplying and conveying circuit and supplying the pressurized fluid alternately to the one or the other of the two chambers ( 16 , 17 ) of the actuator ( 18 ) depending on the rotational direction of the control member ( 11 ), wherein the electric motor ( 23 ) is energized or de-energized upon operation of the control member ( 11 ), such that the pumping means ( 22 ) increase an amount of pumped fluid and increase a pressure exerted by the supplying and conveying unit ( 13 ) to reduce resistance upon a steering of the control member, wherein the hydraulic power unit ( 2 ) is connected to a control unit ( 24 ) and is operatively communicating with the electric motor ( 23 ) and the control member ( 11 ), the control unit ( 24 ) setting operation of the electric motor ( 23 ) depending on rate or number of rotations of the control member ( 11 ), wherein the electric motor ( 23 ) has a plurality of operating conditions, which are different from one another depending on a number of revolutions of the electric motor ( 23 ) or of the amount of fluid required by the control member ( 11 ) corresponding to typical mean operating modes of the control member under a plurality of travel conditions, the operating conditions being settable in alternating mode from one to another, wherein the operating conditions are manually settable by an operator with an input unit ( 25 ) connected to the electric motor ( 23 ), the input unit changing settings driving the electric motor ( 23 ) according to the number of revolutions thereof, imposing a limit to a power of a power signal, and wherein three different operating conditions are provided.