The invention is based on a steering system for a vehicle.
In a known steering system of this type (German Patent Disclosure DE 40 31 316 A1), the actuator has two planetary gears, each with one sun wheel, one ring gear, and planet wheels positioned between the sun wheel and the ring gear. The input shaft of the actuator, acted upon by the driver via the steering wheel, is the axis of the sun wheel of the first planetary gear, and the output shaft of the actuator that actuates the steering gear is the axis of the sun wheel of the second planetary gear. By the driver""s actions at the steering wheel, the planet wheels of the first planetary gear, the axes of which are connected to the planet wheels of the second planetary gear, are set into motion. The latter planet wheels in turn engage the second sun wheel and the ring gear, forming the actuator housing, of the second planetary gear. The output power of the electric motor is transmitted to the ring gear of the first planetary gear via a second input shaft of the actuator, and this shaft carries a worm. With this actuator, it is possible both to achieve steering support to the driver during steering (power steering) and also, with additional steering signals, to vary the steering of the vehicle independently of the driver, so that both driving safety and driving comfort are improved.
The steering system of the invention an advantage of reducing the engineering costs of the actuator considerably, while preserving the same functionality of the steering system. Instead of two planet wheel gears, only two simple step-down or step-gears, which can preferably be embodied as gear drives, and an electromagnetic clutch are present. The electric motor is integrated into itself and forms a compact structural unit with it that is preassembled in complete form and then inserted into the power flow from the steering column to the steering gear. Two operating modes are realized by the engagement and disengagement of the clutch. With the clutch closed, the electric motor generates a torque that is superimposed on the torque generated by the driver at the steering wheel, and power-controlled vehicle guidance is thus made possible. With the clutch open, the electric motor, on the basis of steering signals, superimposes a steering angle on the wheels, thus effecting vehicle stabilization that the driver cannot alter. As in the known steering system, there is no effect on the steering wheel. Because of the simple gears, only a few gear wheels mesh, and because the tooth play is slight, the steering play in the steering system is extremely slight. With the clutch open, it is furthermore possible in a fixedly defined angular range about the steering wheel angular position, to achieve the operating state called xe2x80x9csteer by wirexe2x80x9d, that is, purely motor-controlled steering without any mechanical connection between the steering wheel and the steering gear.
Advantageous refinements and improvements to the steering system defined hereinafter are possible with the provisions recited wherein.