Electrohydraulic steering system

1. An electrohydraulic steering system, comprising a steering unit including a steering motor triggerable via a user control element, and a continuously variable steering valve located in a flow path of an additional pressure fluid between a pressure fluid source and the steering motor for supplying the steering motor with an additional quantity of pressure fluid and triggerable as a function of an actuation of the user control element or as a function of an external signal; a blocking valve located in the flow path of the additional pressure fluid and puttable in a blocking position in order to block the flow path of the additional pressure fluid to the steering motor; pickups directly detecting a setting of the steering valve and a setting of the blocking valve and producing output signals; and a control unit receiving the output signals of the pickups and, if one of the values fails or malfunctions, adjusting a respective other valve into its blocking position.

2. An electrohydraulic steering system as defined in claim 1 , further comprising at least one sensor for detecting a desired value set with the user control element, wherein the control unit is configured for triggering the steering valve and the blocking valve as a function of the desired value.

3. An electrohydraulic steering system as defined in claim 1 , wherein the steering valve has a blocking position and also first work positions in which a first work connection communicates with the pressure fluid source and second work positions in which a second work connection communicates with the pressure fluid source.

4. An electrohydraulic steering system as defined in claim 1 , wherein the blocking valve is a switching valve.

5. An electrohydraulic steering system as defined in claim 4 , wherein the switching valve is a 4/2-way switching valve which in its blocking position blocks off the flow path of the additional pressure fluid between the pressure fluid source and the steering motor and between a pressure fluid drop in the steering motor, and in its switching position opens this flow path of the additional pressure fluid.

6. An electrohydraulic steering system as defined in claim 3 , wherein the steering valve in the first work positions connects the second work connection to a pressure fluid sink, and in the second work positions connects the first work connection to the pressure fluid sink.

7. An electrohydraulic steering system as defined in claim 4 , wherein the switching valve is located between the steering valve and the steering motor.

8. An electrohydraulic steering system as defined in claim 1 , wherein the blocking valve is a 2/2-way switching valve which in its blocking position blocks the flow path of the additional pressure fluid between the pressure fluid source and the steering motor and in its switch position opens it, and the pressure fluid flowing out from the steering motor flows out to a pressure fluid sink via the steering unit.

9. An electrohydraulic steering system as defined in claim 1 , wherein the blocking valve is a seat valve.

10. An electrohydraulic steering system as defined in claim 1 , wherein the blocking valve has a pickup which is a terminal position switch.

11. An electrohydraulic steering system as defined in claim 1 , wherein the steering valve has a pickup which is a travel pickup.

12. An electrohydraulic steering system as defined in claim 1 , wherein the pressure fluid source is a pump selected from the group consisting of a constant pump and a variable pump.