Straddle carrier with power steering

1. A steering system for a straddle carrier having two side supports with steerable wheels, braces, a hoisting gear, and an upper frame having an operator's cab, the steering system comprising:

a steering wheel disposed in the operator's cab;

a steering computer;

a plurality of hydraulic proportional valves;

a plurality of control cylinders each disposed at one of the two side supports;

at least one potentiometer disposed at one of the two side supports; and

a servo motor disposed in mechanical connection with the steering wheel and having an inverter, the servo motor operating in four quadrants and configured to steer the steerable wheels using the steering computer, the hydraulic proportional valves and the control cylinders.

2. The steering system for a straddle carrier as recited in claim 1 , wherein the servo motor works maintenance-free.

3. The steering system as recited in claim 2 , wherein the steering computer transmits a steering angle to an anti-tip computer configured to limit a speed using a stored program control unit (SPC) so as to prevent the straddle carrier from tipping over.

4. The steering system as recited in claim 3 , wherein the at least one potentiometer sends a signal corresponding to an actual value of the steering angle for a position of each wheel to the steering computer, and the steering computer sends a set-point signal to at least one of the hydraulic proportional valves, and the at least one hydraulic proportional valve actuates at least one of the control cylinders using a hydraulic line.

5. The steering system as recited in claim 4 , wherein the at least one hydraulic proportional valve includes at least two magnets.

6. The steering system as recited in claim 4 , wherein at least one hydraulic proportional valve includes two hydraulic proportional valves redundantly provided for two control cylinders and two potentiometers.

7. The steering system as recited in claim 6 , wherein the steering system includes two feedback and control channels for feedback and control of the steering system.

8. The steering system as recited in claim 6 , wherein the steering computer is configured to reset the steering system to a position for driving straight ahead as a function of a speed of the straddle carrier.

9. The steering system as recited in claim 1 , further comprising an operator's display disposed at the operator's cab and configured to display operating states of the steering system.

10. The steering system as recited in claim 9 wherein the operating states include at least one of:

a first state indicating that the steering system is operational;

a second state warning of an impermissible operating state;

a third state indicating a failure of a redundant component;

a fourth state indicating a shutdown of the system with instructions for use of an emergency steering system.

11. A straddle carrier having a power steering system as recited in claim 1 .