Steering system for a vehicle

A method for function checking a steering system switchable between a normal mode with a steer-by-wire level and an emergency mode with a fall-back level, the fall-back level comprising a hydraulic system which includes a manual-side double-acting piston-cylinder unit actuatable with a steering handle and positively coupled hydraulically to a wheel-side double-acting piston-cylinder unit configured to actuate steered vehicle wheels, a hydraulic charging system having a hydraulic pump with an inlet side operatively connected to a hydraulic-fluid reservoir, and a switchable hydraulic coupling for selectively coupling and decoupling hydraulically the fall-back level hydraulic system and the hydraulic charging system, wherein the manual-side piston-cylinder unit comprises two chambers positively coupled hydraulically by a left-hand hydraulic line and a right-hand hydraulic line to associated chambers of the wheel-side double-acting piston-cylinder unit, wherein the left-hand hydraulic line operatively communicates via a connecting line configured to be shut off with the right-hand hydraulic line, with a charging line being operatively connected to the connecting line, wherein a respective safety valve is arranged in the connecting line between the charging line and the hydraulic lines to selectively open and shut off the connection between the connecting line and the associated hydraulic line, comprising forming hydraulically decoupled sections by shut-off positions of the safety valves and of the charging valve in the fall-back level hydraulic system, and assigning to each of the sections a pressure sensor for checking pressure drops in the respectively assigned section to test the leaktightness of individual sections of the hydraulic system of the fall-back level.

A method for function checking a steering system switchable between a normal mode with a steer-by-wire level and an emergency mode with a fall-back level, the fall-back level comprising a hydraulic system which includes a manual-side double-acting piston-cylinder unit actuatable with a steering handle and positively coupled hydraulically to a wheel-side double-acting piston-cylinder unit configured to actuate steered vehicle wheels, a hydraulic charging system having a hydraulic pump with an inlet side operatively connected to a hydraulic-fluid reservoir, and a switchable hydraulic coupling for selectively coupling and decoupling hydraulically the fall-back level hydraulic system and the hydraulic charging system, wherein the manual-side piston-cylinder unit comprises two chambers positively coupled hydraulically by a left-hand hydraulic line and a right-hand hydraulic line to associated chambers of the wheel-side piston-cylinder unit, the left-hand hydraulic line operatively communicates via a connecting line configured to be shut off with the right-hand hydraulic line, with a charging line being operatively connected to the connecting line, and a respective safety valve is arranged in the connecting line between the charging line and the hydraulic lines to selectively open and shut off the connection between the connecting line and the associated hydraulic line, to test the gas content of the hydraulic system of the fall-back level in the case of a steer-by-wire level which has a variable steering ratio between the steering-angle actuation of the steering handle and the steering-angle actuation of the steered vehicle wheels, comprising closing the safety valves during an actuation of the steer-by-wire level of the wheel-side piston-cylinder unit and of the fall-back level wheel-side piston-cylinder unit and positively coupling said units directly or indirectly thereto;

• building up a differential pressure between the left-hand hydraulic line and the right-hand hydraulic line;
• and using the differential pressure to determine compressibility of the hydraulic fluid and thus to determine the gas content of the fall-back level hydraulic system.

A method for function checking a steering system switchable between a normal mode with a steer-by-wire level and an emergency mode with a fall-back level, the fall-back level comprising a hydraulic system which includes a manual-side double-acting piston-cylinder unit actuatable with a steering handle and positively coupled hydraulically to a wheel-side double-acting piston-cylinder unit configured to actuate steered vehicle wheels, a hydraulic charging system having a hydraulic pump with an inlet side operatively connected to a hydraulic-fluid reservoir, and a switchable hydraulic coupling for selectively coupling and decoupling hydraulically the fall-back level hydraulic system and the hydraulic charging system, wherein the manual-side piston-cylinder unit comprises two chambers positively coupled hydraulically by a left-hand hydraulic line and a right-hand hydraulic line to associated chambers of the wheel-side piston-cylinder unit, the left-hand hydraulic line operatively communicates via a connecting line configured to be shut off with the right-hand hydraulic line, with a charging line being operatively connected to the connecting line, and a respective safety valve is arranged in the connecting line between the charging line and the hydraulic lines to selectively open and shut off the connection between the connecting line and the associated hydraulic line to test the gas content fall-back level hydraulic system if a steer-by-wire level which has a variable steering ratio between the steering-angle actuation of the steering handle and the steering-angle actuation of the steered vehicle wheels, comprising closing the safety valves;

• actuating a manual-torque actuator which is coupled to and simulates at the steering handle the manual torque corresponding to side forces acting at the steered vehicle wheels to actuate the manual-side piston-cylinder unit;
• actuating a control valve of the steer-by-wire level hydraulic system such that the wheel-side piston-cylinder unit does not adjust the steering angle at the steered vehicle wheels;
• and building up a differential pressure between the left-hand hydraulic line and the right-hand hydraulic line to determine compressibility of the hydraulic fluid and gas content of the fall-back level hydraulic system.

A method for function checking a steering system switchable between a normal mode with a steer-by-wire level and an emergency mode with a fall-back level, the fall-back level comprising a hydraulic system which includes a manual-side double-acting piston-cylinder unit actuatable with a steering handle and positively coupled hydraulically to a wheel-side double-acting piston-cylinder unit configured to actuate steered vehicle wheels, a hydraulic charging system having a hydraulic pump with an inlet side operatively connected to a hydraulic-fluid reservoir, and a switchable hydraulic coupling for selectively coupling and decoupling hydraulically the fall-back level hydraulic system and the hydraulic charging system, wherein the manual-side piston-cylinder unit comprises two chambers positively coupled hydraulically by a left-hand hydraulic line and a right-hand hydraulic line to associated chambers of the wheel-side piston-cylinder unit, wherein the left-hand hydraulic line operatively communicates via a connecting line configured to be shut off with the right-hand hydraulic line, with a charging line being operatively connected to the connecting line, wherein a respective safety valve or valves are arranged in the connecting line between the charging line and the hydraulic lines to selectively open and shut off the connection between the connecting line and the associated hydraulic line comprising conducting a plausibility check for checking equality of the safety values determined by a plurality of pressure sensors assigned to the sections wherein a plurality of the sections are coupled hydraulically to test the operation of pressure sensors assigned to individual sections of the hydraulic systems.

A method for function checking a steering system switchable between a normal mode with a steer-by-wire level and an emergency mode with a fall-back level, the fall-back level comprising a hydraulic system which includes a manual-side double-acting piston-cylinder unit actuatable with a steering handle and positively coupled hydraulically to a wheel-side double-acting piston-cylinder unit configured to actuate steered vehicle wheels, a hydraulic charging system having a hydraulic pump with an inlet side operatively connected to a hydraulicfluid reservoir, and a switchable hydraulic coupling for selectively coupling and decoupling hydraulically the fall-back level hydraulic system and the hydraulic charging system, wherein the manual-side piston-cylinder unit comprises two chambers positively coupled hydraulically by a left-hand hydraulic line and a right-hand hydraulic line to associated chambers of the wheel-side piston-cylinder unit, the left-hand hydraulic line operatively communicates via a connecting line configured to be shut off with the right-hand hydraulic line, with a charging line being operatively connected to the connecting line, and a respective safety valve or valves are arranged in the connecting line between the charging line and the hydraulic lines to selectively open and shut off the connection between the connecting line and the associated hydraulic line, comprising, test switching of the valves, switching a charging valve and the safety valves to a shut-off position thereof;

• setting in a section of the charging line which adjoins the charging valve and is operatively coupled to the steer-by-wire level hydraulic system, a pressure different from pressure in the other sections of the fall-back level hydraulic system which are connected to the charging valve and thereby forming a pressure difference between the sections adjoining the charging valve;
• switching that the charging valve to open and, if the charging valve opens effecting a pressure equalization which can be sensed between the sections adjoining the charging valve and forming a pressure difference between the sections adjoining the safety valves;
• switching one of the safety valves to open and, if the one safety valve opens, effecting a pressure equalization which can be sensed between the sections adjoining the one safety valve, and switching another safety valve to open and, if the other safety valve opens effecting a pressure equalization which can be sensed between the sections adjoining the other safety valve.