Patent ID: 6945350

Claim:
A steering apparatus responsive to rotation of a handwheel for turning steerable wheels of a vehicle having first and second sets of steerable wheels, said steering apparatus comprising: a first steering linkage connected with the first set of steerable wheels; a first steering gear connected with said first steering linkage, said first steering gear being actuatable to effect operation of said first steering linkage and turning of said first set of steerable wheels in response to rotation of the handwheel; a second steering linkage connected with the second set of steerable wheels; second and third steering gears connected with said second steering linkage, said second and third steering gears each being independentably actuatable to effect turning of the second set of steerable wheels and thereby providing redundancy for turning of the second set of steerable wheels; said second steering gear includes a first hydraulic motor connected with said second steering linkage and a first control valve which is operable to direct fluid pressure to said first hydraulic motor; said third steering gear includes a second hydraulic motor connected with said second steering linkage and a second control valve which is operable to direct fluid pressure to said second hydraulic motor; a first electric motor connected with said first control valve and operable to effect operation of said first control valve to direct fluid pressure to said first hydraulic motor to effect operation of said first hydraulic motor and said second steering linkage under the influence of fluid pressure, and a second electric motor connected with said second control valve and operable to effect operation of said second control valve to direct fluid pressure to said second hydraulic motor to effect operation of said second hydraulic motor and said second steering linkage under the influence of fluid pressure.