Steering system for vehicles

Claim 2

A steering system for a vehicle having a steerable front wheel and a steerable rear wheel, comprising: a front wheel steering mechanism for steering said front wheel; a rear wheel steering mechanism for steering said rear wheel in dependence on travelling state quantities of said vehicle; and said rear wheel steering mechanism (7, 8, 9, 10, 12, 13, 14, 15) including: actuation means (7, 8, 9, 10) for actuating said rear wheel; detection means (13, 14, 15) for detecting said travelling state quantity (δ f , V, α a ); control means (12) connected to said detection means and adapted to supply a control signal (d) to said actuation means; and said control means having: first process means (A, B) receiving an output signal (x, y, α 0 ) from said detection means to produce a first signal (d 0 ) representing an ordinary steering angle for said rear wheel; second process means (13, 14, 15, D, E, F, G) also receiving said output signal (X, Y, α 0 ) from said detection means for deriving data (K r , μ r , P r , W r ) ) relating to at least a cornering power (K r ) of said rear wheel and for producing a second signal (d 2 ) for correcting said first signal on the basis of said data; and synthesizing means (C) for synthesizing said first signal and said second signal to produce said control signal.

Claim 3

A steering system according to claim 1, wherein: said second process means is adapted to produce, when a ratio of said cornering power of said rear wheel to a vertical load of said rear wheel is larger than a predetermined value, said second signal so as to steer said rear wheel, additionally with respect to said ordinary steering angle, in the opposite direction to a steering direction of said front wheel, to decrease a slip angle of said rear wheel while said vehicle is turning.

Claim 4

A steering system according to claim 1, wherein: said second process means is adapted to produce, when a ratio of said cornering power of said rear wheel to a vertical load of said rear wheel is smaller than a predetermined value, said second signal so as to steer said rear wheel, additionally with respect to said ordinary steering angle, in the same direction as a steering direction of said front wheel, to increase a slip angle of said rear wheel while said vehicle is turning.

Claim 5

A steering system according to claim 1, wherein: said second process means is adapted to produce said second signal so as to steer said rear wheel, additionally with respect to said ordinary steering angle, in the opposite direction to a steering direction of said front wheel to decrease a slip angle of said rear wheel while said vehicle is turning, when a ratio of said cornering power of said rear wheel to a vertical load of said rear wheel is larger than a predetermined value, and in the same direction as said steering direction of said front wheel to increase said slip angle of said rear wheel while said vehicle is turning, when said ratio of said cornering power of said rear wheel to said vertical load of said rear wheel is smaller than said predetermined value.

Claim 6

A steering system according to claim 4, wherein: said control means comprises a computer system (12) mounted on said vehicle having at least a memory; said computer system being connected to said detection means and to said actuation means.

Claim 7

A steering system according to claim 5, wherein: said first process means comprises given data (A) on various travelling states of said vehicle and a first operation program (B) for producing said first signal on the basis of said output signal from said detection means and of said given data, said given data and said first operation program being stored in said memory of said computer system, respectively; and said synthesizing means comprises an addition program (C) stored in said memory of said computer system.

Claim 8

A steering system according to claim 6, wherein: said second process means receives said output signal from said detection means; and said second process means comprises: a conversion process program (D) for computing a plurality of values (α i ) of a lateral acceleration (α) of said vehicle corresponding to a variety of probable values (K i ) of said cornering power (K), on the basis of at least a first component (x, y) of said output signal from said detection means relating to a steered angle (δ f ) of said front wheel and to a vehicle speed (V) of said vehicle; a comparison process program (E) for comparing said values thus computed of said lateral acceleration with a second component (α 0 ) of said output signal from said detection means relating to an actual value (α a ) of said lateral acceleration, to determine an actual value (K r ) of said cornering power of at least said rear wheel; a second operation program (G) for producing said second signal (d 2 ), on the basis of a signal (d 1 ) relating to said actual value thus determined of said cornering power and of given data (F) on various values of said cornering power; and said conversion process program, said comparison process program, and said second operation program being stored in said memory of said computer system, respectively.

Claim 9

A steering system according to claim 6, wherein: said second process means receives said output signal from said detection means; and said second process means comprises: a conversion process program (D 2 ) for computing a plurality of values (α i ) of a lateral acceleration (α) of said vehicle corresponding to a variety of probable values (μ i ) of a coefficient (μ) of friction between a tire of said vehicle and the road surface, on the basis of at least a first component (x, y) of said output signal from said detection means relating to a steered angle (δ f ) of said front wheel and to a vehicle speed (V) of said vehicle; a comparison process program (E 2 ) for comparing said values thus computed of said lateral acceleration with a second component (α 0 ) of said output signal from said detection means relating to an actual value (α a ) of said lateral acceleration, to determine an actual value (μ r ) of said coefficient of friction between at least a tire of said rear wheel and and the road surface, a second operation program (G 2 ) for producing said second signal (d 22 ), on the basis of a signal (d 2l ) relating to said actual value thus determined of said coefficient of friction and of given data (F 2 ) on various values of said coefficient of friction; and said conversion process program, said comparison process program, and said second operation program being stored in said memory of said computer system, respectively.

Claim 10

A steering system according to claim 6, wherein: said second process means comprises: air pressure detection means (16, 17, 18, 19) for detecting an air pressure (Pr) of a tire of at least said rear wheel; a second operation program (H) for producing said second signal (d 32 ), on the basis of a signal (p) from said air pressure detection means relating to said air pressure of said tire and of given data (F 3 ) on various values of said air pressure; and said second operation program being stored in said memory of said computer system.

Claim 11

A steering system according to claim 6, wherein: said second process means comprises: vertical load detection means (26, 27, 28, 29) for detecting a vertical load (Wr) of at least said rear wheel; a second operation program (J) for producing said second signal (d 42 ), on the basis of a signal (w) from said vertical load detection means relating to said vertical load and of given data (F 4 ) on various values of said vertical load; and said second operation program being stored in said memory of said computer system.

Claim 12

A steering system according to claim 10, wherein: said vertical load detection means comprises a stroke sensor (26, 27, 28, 29) for detecting a vertical stroke of a suspension unit for at least said rear wheel.

Claim 13

A steering system according to claim 1, further including: select means (Sw) for manually selecting an override mode in which said control signal has a component thereof forced to change so as to render a slip angle (β) of said rear wheel smaller than it would be in a normally controlled mode of the steering system.