Compressor for generating compressed air, compressed air supply system, pneumatic system, and method for operating a compressor

1. A compressor system for generating compressed air for a compressed air supply system in a vehicle, the compressor system comprising:

a brushed direct current electric motor (BDC electric motor);

a compressor configured to be driven by the BDC electric motor; and

a motor control circuit configured to delimit an operating current of the BDC electric motor to a time-varying current threshold value, the motor control circuit including:

a free-running current path, the free-running current path being connected in parallel to the electric motor, the free-running current path including a free-wheeling diode and a MOSFET power transistor having an integrated free-wheeling diode, and

a switch controller, the switch controller being configured to specify, in a time-varying manner, a switched-on time period (t_ON) and a switched-off time period (t_OFF) for the electric motor,

wherein the switched-off time period is determined as a function of the time-varying current threshold value so as to limit an amount of energy dissipated in the free-running current path to a dissipated energy threshold value.

2. The compressor as claimed in claim 1 , wherein the motor control circuit comprises an electronic control module including a control component and an executable program module.

3. The compressor as claimed in claim 2 , wherein the electronic control module is configured to specify the time-varying current threshold value.

4. The compressor as claimed in claim 3 , wherein the electronic control module further comprises an analyzing unit configured to determine whether the operating current of the BDC electric motor has reached the time-varying current threshold value and/or an actuating element configured to interrupt a supply of operating energy to the electric motor according to a predetermined interruption frequency when the operating current of the BDC electric motor has reached the time-varying current threshold value.

5. The compressor as claimed in claim 2 , wherein in order to delimit the operating current, the executable program module is configured to specify, as a function of time, the time-varying current threshold value, and wherein the control component is configured to interrupt a supply of operating energy or operating voltage to the electric motor.

6. The compressor as claimed in claim 2 , wherein the electronic control module is configured to control a soft start-up.

7. The compressor as claimed in claim 2 , wherein the electronic control module is further configured to control a soft switching-off procedure to specify a switch-off operating current that is delimited in a variable manner with respect to time.

8. The compressor as claimed in claim 1 , wherein the motor control circuit and the switch controller are coupled within a closed-loop and/or an open-loop control circuit, wherein the switch controller is configured to:

receive an operating current measurement for the electric motor and/or an operating voltage measurement for the electric motor, and

output, via a control signal, the switched-on time period (t_ON) and the switched-off time period (t_OFF).

9. The compressor as claimed in claim 8 , wherein the motor control circuit further comprises a first closed-loop control unit that is configured to control the operating current of the electric motor while specifying the time-varying current threshold value as a DESIRED-current.

10. The compressor as claimed in claim 8 , wherein the motor control circuit further comprises a closed-loop control module having a second closed-loop control unit that is configured to control a rotational speed of the electric motor while specifying a rotational speed upper limit that is (i) constant time section-by-time section as a function of the operating current or (ii) a variable that is derived from the operating current.

11. The compressor as claimed in claim 1 , wherein the switch controller is configured so as to specify the switched-on time period (t_ON) and/or the switched-off time period (t_OFF) in a variable but fixed, or in a variable and dynamically changeable, manner.

12. The compressor as claimed in claim 1 , wherein the switch controller is configured to maintain the operating current for the electric motor at a value below a maximum limit current of I_max=30A and/or to maintain a gradient of the operating current for the electric motor at a value below a maximum limit gradient of the operating current of G_max=300A/s.

13. The compressor as claimed in claim 1 , wherein the switch controller is configured to specify the switched-off time period (t_OFF) so as to maintain a temperature in the free-running current path to a value below 20° C. in excess of an ambient temperature of 40° C. to 100° C., to maintain an absolute temperature in the free-running current path to a value below 130° C., and/or to maintain a junction temperature in the free-running current path to below 170° C.

14. The compressor as claimed in claim 1 , wherein the switch controller is configured to specify the switched-on time period (t_ON) and/or the switched-off time period (t_OFF) to values of 200 μs or less.

15. The compressor as claimed in claim 1 , wherein the compressor is a two-stage compressor having at least a first and a second compressor stage.

16. The compressor as claimed in claim 1 , wherein the motor control circuit is configured to interrupt a supply of operating energy to the BDC electric motor in accordance with the switched-on time period (t_ON) and the switched-off time period (t_OFF).

17. The compressor as claimed in claim 1 , wherein a start-up phase including a soft start-up of the compressor transitions to a load phase, and/or a load phase transitions to a deceleration phase including a control of the operating current of the compressor.

18. The compressor as claimed in claim 1 , wherein the motor control circuit is configured to delimit a rotational speed variability of the electric motor as a function of the operating current or of a variable that is derived from the operating current by way of a pulse width modulation (PWM) characteristic curve the PWM characteristic curve being an effective voltage ramp stored in the program module and being a function of the operating current.

19. The method as claimed in claim 18 , wherein the switched-off time period (t_OFF) is reduced for an increased operating current and/or increased operating voltage of the BDC electric motor.

20. The compressor system as claimed in claim 1 , wherein, in the free-running current path, the free-wheeling diode is connected in series with the MOSFET power transistor.

21. The compressor system as claimed in claim 1 , wherein the motor control circuit includes a switch configured to, sequentially, connect, for the switched-on time period (t_ON), a power supply to the BDC electric motor and disconnect, for the switched-off time period (t_OFF), the power supply to the BDC electric motor.

22. The compressor system as claimed in claim 21 , wherein the switch is a semiconductor switch.

23. A compressed air supply system for a vehicle, the compressed air supply system comprising:

a compressed air supply line having a compressor system, the compressor system including:

a brushed direct current electric motor (BDC electric motor);

a compressor configured to be driven by the BDC electric motor;

a motor control circuit configured to delimit an operating current of the BDC electric motor to a time-varying current threshold value, the motor control circuit including:

a free-running current path, the free-running current path being connected in parallel to the electric motor, the free-running current path including a free-wheeling diode and a MOSFET power transistor having an integrated free-wheeling diode, and

a switch controller, the switch controller being configured to specify, in a time-varying manner, a switched-on time period (t_ON) and a switched-off time period (t_OFF) for the electric motor, wherein the switched-off time period is determined as a function of the time-varying current threshold value so as to limit an amount of energy dissipated in the free-running current path to a dissipated energy threshold value;

a compressed air connection;

a ventilation connection to the environment;

a first pneumatic connection between the compressed air supply line and the compressed air connection, the first pneumatic connection including an air dryer and a separating valve; and

a second pneumatic connection between the compressed air connection and the ventilation connection.

24. A pneumatic system, comprising:

the compressed air supply system as claimed in claim 23 ;

a distributing arrangement;

at least one branch line that is connected in a pneumatic manner to the distributing arrangement;

a bellows and/or a storage device; and

a directional control valve that is arranged upstream of the bellows and/or the storage device,

wherein the pneumatic system is an air suspension system.

25. A method for operating a brushed direct current electric motor (BDC electric motor) in a compressor system for generating compressed air for a compressed air supply system of a vehicle, the method comprising:

driving a compressor of the compressor with the BDC electric motor;

controlling, by a motor control circuit, the BDC electric motor so as to delimit an operating current of the BDC electric motor to a time-varying current threshold value, wherein the motor control circuit includes a free-running current path connected in parallel to the electric motor, the free-running current path including a free-wheeling diode and a MOSFET power transistor having an integrated free-wheeling diode, and

specifying, by a switch controller in a time-varying manner, a switched-on time period (t_ON) and a switched-off time period (t_OFF) for the electric motor,

wherein the switched-off time period (t_OFF) is determined as a function of the time-varying current threshold value so as to limit an amount of energy dissipated in the free-running current path to a dissipated energy threshold value.

26. The method as claimed in claim 25 , wherein the switched-off time period (t_OFF) is determined so as to limit an amount of heat absorption in the free-running path.

27. The method as claimed in claim 25 , wherein the BDC electric motor is controlled by an electronic control module of the motor control circuit, and wherein the electronic control module comprises a control component having an executable program module.

28. The method as claimed in claim 27 wherein the time-varying current threshold value is specified as a function of time, and wherein the control component is configured to interrupt a supply of operating energy to the electric motor in a variable manner in accordance with the switched-on time period (t_ON) and/or the switched-off time period (t_OFF).

29. The method as claimed in claim 25 wherein the switched-on time period (t_ON) and/or the switched-off time period (t_OFF) are specified by the switch controller for the BDC electric motor in a variable manner and in dependence upon a measured operating current and/or a measured operating voltage of the BDC electric motor.