Drive device comprising a drive shaft and a device for detecting torque

1. A drive device, comprising:

a drive shaft mounted so as to rotate about an axis;

two driving cranks connected to the drive shaft in a circumferential direction with respect to the axis in an angularly rigid manner; and

an output element, which is connected to the drive shaft, transmitting torque between the drive shaft and a load element,

wherein at least one magnetostrictive sensor is permanently connected to the drive shaft and is arranged axially between a driving crank and the output element,

wherein at least one axial section of the drive shaft is formed as part of the magnetostrictive sensor by magnetization,

wherein the at least one axial section of the drive shaft comprises a first region, near to a surface, with a first magnetization and a second region, remote from the surface, with a second magnetization, and

wherein the first magnetization and the second magnetization are added in a mechanically unloaded torque-free state of the drive shaft to form an essentially vanishing magnetic field outside the drive shaft.

2. The drive device of claim 1 , wherein the magnetostrictive sensor is arranged axially between each of the driving cranks and the output element.

3. The drive device of claim 1 , wherein the magnetostrictive sensor has at least two magnetostrictive bodies.

4. The drive device of claim 3 , wherein the magnetostrictive bodies are embodied as concentric cylindrical bodies.

5. The drive device of claim 4 , wherein the magnetostrictive bodies are magnetized in opposite directions in an unloaded state.

6. The drive device of claim 3 , wherein the magnetostrictive bodies are arranged lying axially one behind the other.

7. The drive device of claim 6 , wherein magnetic field components are generated with the magnetostrictive bodies by means of torsion have different directions.

8. The drive device of claim 1 , wherein a pinning zone is arranged on at least one side of the axial section, provided with the magnetization, of the drive shaft, said pinning zone limiting a magnetic field, which can be measured outside the drive shaft, of the axial section essentially to a region of the axial section.

9. The drive device of claim 1 , wherein a magnetic field sensor for measuring magnetic leakage field is assigned to each magnetostrictive sensor.

10. The drive device of claim 9 , wherein a magnetic field sensor is assigned to each magnetostrictive body and/or each axial section, provided with a magnetization, of the drive shaft.

11. The drive device of claim 9 , wherein the magnetic field sensor has at least one electrical coil with a ferromagnetic core, said coil being connected to an alternating current source for alternating magnetization of the core up to saturation.

12. The drive device of claim 9 , wherein the magnetic field sensor is arranged in a positionally fixed fashion with respect to the drive shaft.

13. The drive device of claim 1 , further comprising an evaluation device which is connected to the magnetic field sensors and assigns torque values to the measured magnetic field values.

14. The drive device of claim 13 , further comprising an analysis device in which threshold values for torques are stored in a memory device and are compared with measured torque values by means of a comparison device.

15. The drive device of claim 14 , further comprising a control device which is connected to the analysis device on the one hand, and to an additional drive and/or a shifting device for a transmission, on the other.

16. The drive device of claim 1 , further comprising a transmission device which transmits sensed measured values to a receiver by radio or IR signal.

17. A device which can be driven by means of at least one driving crank, comprising a drive device as claimed in claim 1 .

18. The device of claim 17 , wherein the device is a bicycle, an ergometer or a pedelec.