Patent ID: 7624837
Filing Date: 2009-12-01
Classification: B62D,F15B

Abstract:
1. A hydraulic power steering apparatus, comprising: a variable throttle valve that has a variable throttle portion in which the degree of opening is varied by movement of a spool and varies hydraulic pressure for generating steering assist power by this variation of the degree of opening; a stepping motor for moving said spool in one direction and another direction; means for driving said stepping motor according to a number of steps; a stopper that can stop the movement of the spool in the one direction at an origin; means for storing a predetermined number of steps that is required to move said spool to said origin as a number of steps for setting origin; means for storing a number of steps that is less than said number of steps for setting origin and is predetermined for moving said spool in the one direction from a position at a time when a control of said stepping motor starts as a number of steps for setting provisional origin; means for setting a number of steps at a time when the driving of said stepping motor according to said number of steps for setting provisional origin is completed to a provisional origin for calculation, on an assumption that the spool is positioned in a provisional origin at this time; means for setting a number of steps from said provisional origin for calculation that corresponds to an amount of movement of said spool from said provisional origin in the other direction according to a vehicle driving condition; means for determining whether it is in a return to origin permission state in which conditions for return to the origin are satisfied, these conditions including a condition that the spool is disposed in the provisional origin and a condition that the number of steps from the provisional origin for calculation set according to the vehicle driving condition is zero; and means for setting a number of steps at a time when the driving of said stepping motor according to a number of steps obtained by subtracting said number of steps for setting provisional origin from said number of steps for setting origin is completed to an origin for calculation, in said return to origin permission state; wherein instead of the number of steps from said provisional origin for calculation, the number of steps from said origin for calculation that corresponds to an amount of movement of said spool from said origin in the other direction is set according to the vehicle driving condition, after said origin for calculation is set; and said spool is positioned by driving said stepping motor according to the number of steps that is set according to the vehicle driving condition.