Electric motor assisted steering apparatus

1. An electromechanical steering device for a motor vehicle, comprising:

at least one electric motor, power electronics for controlling said electric motor and at least one temperature sensor for measuring the temperature of said power electronics and/or the ambient temperature of said power electronics, said power electronics having switching times which are variable as a function of the measured temperature, wherein:

said power electronics includes a frequency converter for pulse width modulation and has at least one power transistor, and

control voltage rise speed and/or control current rise speed on said power transistor can be varied for building up the capacities of said power transistor for varying the switching time of said power transistor.

2. An electromechanical steering device for a motor vehicle, comprising:

at least one electric motor, power electronics for controlling said electric motor and at least one temperature sensor for measuring the temperature of said power electronics and/or the ambient temperature of said power electronics, said power electronics having switching times which are variable as a function of the measured temperature, wherein:

said power electronics includes a frequency converter for pulse width modulation and has at least one power transistor,

control voltage rise speed and/or control current rise speed on said power transistor can be varied for building up the capacities of said power transistor for varying the switching time of said power transistor, and

a gate terminal and/or a source terminal of said power transistor is connected via at least two electric activation lines with different electrical resistances to a current source, and arranged in at least one activation line is at least one switch, the different activation lines being operable to be turned on and/or off alternatively and/or cumulatively as a function of the measured temperature for supplying said power transistor with control voltage and/or control current.

3. The electromechanical steering device in accordance with claim 2 , comprising at least one logic unit for activating the switch of the activation lines as a function of the measured temperature.

4. The electromechanical steering device in accordance with claim 1 , comprising at least one power transistor driver unit which includes at least one variable current source for varying the control voltage rise speed and/or the control current rise speed on said power transistor so as to vary a turn-on time and/or turn-off time of said power transistor.

5. The electromechanical steering device in accordance with claim 4 , wherein said power transistor driver unit includes at least one additional variable current source for varying the control voltage rise speed and/or the control current rise speed on said power transistor so as to vary the turn-off time and/or turn-on time of at least said power transistor.

6. The electromechanical steering device in accordance with claim 4 , wherein said power transistor driver unit is connected to at least one logic unit that controls said variable current sources as a function of the measured temperature.

7. The electromechanical steering device in accordance with claim 6 , wherein said power transistor driver unit and said logic unit are connected to one another via digital interfaces.

8. The electromechanical steering device in accordance with claim 6 , wherein said power transistor driver unit and said logic unit are connected to one another via analog interfaces.

9. The electromechanical steering device in accordance with claim 1 , wherein said power electronics are controlled such that the control voltage rise speed and/or the control current rise speed on said power transistor are varied such that the switching times become shorter as temperature increases.

10. The electromechanical steering device in accordance with claim 1 , wherein said at least one power transistor comprises a field effect transistor.

11. The electromechanical steering device in accordance with claim 1 , wherein said at least one power transistor comprises a MOSFET.

12. The electromechanical steering device in accordance with claim 2 , wherein said current source is a constant current source.

13. The electromechanical steering device in accordance with claim 6 , wherein said at least one logic unit comprises a microcontroller.

14. An electromechanical steering device for a motor vehicle comprising:

at least one electric motor;

power electronics having power transistors for controlling said electric motor, said power transistors being controlled by control signals in the form of pulses;

at least one temperature sensor for measuring temperature of one of said power electronics or an ambient temperature of said power electronics; and

said power electronics being configured to control the control signals, as a function of the measured temperature, to vary a switching time period of said power transistors which is at least one of a switching-on time period or a switching-off time period of the power transistors, wherein the switching-on time period is a period required to transition said power transistors from an off state to an on state and the switching-off time period is a period required to transition said power transistors from an on-state to an off-state, and said switching time period is shortened when said measured temperature increases, wherein one of: a control voltage rise speed or a control voltage fall speed is varied to effect the control of the at least one of a switching-on time period or a switching-off time period of the power transistors; or a control current rise speed or a control current fall speed is varied to effect the control of the at least one of a switching-on time period or a switching-off time period of the power transistors.

15. The electromechanical steering device in accordance with claim 14 , wherein one of a control voltage rise speed or a control voltage fall speed is varied to effect the control of the at least one of a switching-on time period or a switching-off time period of the power transistors.

16. The electromechanical steering device in accordance with claim 14 , wherein one of a control current rise speed or a control current fall speed is varied to effect the control of the at least one of a switching-on time period or a switching-off time period of the power transistors.

17. The electromechanical steering device in accordance with claim 14 , wherein said power electronics includes a frequency converter for pulse width modulation control of said power transistors.

18. The electromechanical steering device in accordance with claim 14 , wherein:

said power transistors each have:

a control terminal connected to at least two electric activation lines having electrical resistances situated therein, and

at least one of the two activation lines including a switch controlled as a function of the measured temperature; and

said power electronics include a logic unit controlling the switching period of said power transistors by controlling said switches in the activation lines.

19. The electromechanical steering device in accordance with claim 14 , wherein said power electronics includes variable current sources for varying at least one of a rise time or a fall time of the pulses of the control signals controlling the power transistors.

20. The electromechanical steering device in accordance with claim 14 , wherein said power transistors are field effect transistors.