Motor vehicle auxiliary unit

The present invention is directed to a motor vehicle auxiliary unit, in particular to a motor vehicle auxiliary unit for a motor vehicle with a high-voltage electrical system and a low-voltage electrical system.

Modern motor vehicles, in particular (hybrid) electric motor vehicles, often comprise a low-voltage electrical system and a separate high-voltage electrical system wherein the two electrical systems are galvanically isolated from each other. The low-voltage electrical system is typically operated with a voltage of 12 V and is provided to energize the control units of the motor vehicle as well as to energize those auxiliary units with a relatively low power demand. The high-voltage electrical system is typically operated at a voltage of 48 V and is used to energize those motor vehicle auxiliary units with a relatively high power demand such as, for example, an electric coolant pump, an electric lubricant, or an electric vacuum pump.

Because the motor vehicle control units are energized by the low-voltage electrical system, the low-voltage electrical system is typically also used for the data communication between the motor vehicle control units and the motor vehicle auxiliary units, e.g. using the "LIN over DC power line" (DC-LIN) standard. The high-voltage-operated motor vehicle auxiliary units therefore require a galvanically isolated switching unit which allows the high-voltage power supply of the motor vehicle auxiliary unit to be switched via a low-voltage communication interface. Such galvanically isolated switching units are typically based on a photocoupler with a light emitting device, typically a light emitting diode, and a photo-sensitive device, typically a phototransistor or a photodiode, which is configured to detect light emitted by the light emitting device. The light emitting device is arranged in a low-voltage input circuit of the switching unit and the photo-sensitive device is arranged in a high-voltage output circuit of the switching unit. If the input circuit of the switching unit is energized, the light emitting device generates light which is detected by the photo-sensitive device of the output circuit. This allows an output voltage of the output circuit to be switched based on an input voltage of the input circuit without requiring an electrical connection between the input circuit and the output circuit.

However, conventional optocouplers are relatively temperature-sensitive. This either limits the possible installation sites for the motor vehicle auxiliary unit, or requires the use of special, relatively high-priced high-temperature optocouplers and/or cooling arrangements for cooling the optocoupler.

An object of the present invention is therefore to provide a cost-effective and versatile motor vehicle auxiliary unit.

This object is achieved with a motor vehicle auxiliary unit with the features of claim 1.

The motor vehicle auxiliary unit according to the present invention is provided with a low-voltage electric circuit and with a high-voltage electric circuit which is galvanically isolated from the low-voltage electric circuit. The low-voltage electric circuit is configured to be electrically connected to a low-voltage motor vehicle electrical system. The low-voltage electric circuit is preferably configured to be electrically connected to a 12 V motor vehicle electrical system. The low-voltage electric circuit typically comprises a communication interface configured to provide a data communication with a motor vehicle control unit, for example a DC-LIN-type interface. The high-voltage electric circuit is configured to be electrically connected to a high-voltage motor vehicle electrical system. The high-voltage electric circuit is preferably configured to be electrically connected to a 48 V motor vehicle electrical system. The high-voltage electric circuit is configured to energize a main load of the motor vehicle auxiliary unit, for example an electric motor.

The motor vehicle auxiliary unit according to the present invention is also provided with a galvanically isolated switching unit. The switching unit comprises an input circuit which is electrically connected to the low-voltage electric circuit of the motor vehicle auxiliary unit, and comprises an output circuit which is galvanically isolated from the input circuit and which is electrically connected to the high-voltage electric circuit of the motor vehicle auxiliary unit. The switching unit is configured to switch an output voltage of the output circuit based on an input voltage of the input circuit.

According to the present invention, the input circuit of the switching unit comprises an inductor and the output circuit of the switching unit comprises a magnetic field sensor which is arranged nearby the inductor and which is configured to sense a magnetic field generated by energizing the inductor. The inductor is typically an electromagnetic coil. However, the inductor in principle can be any device which generates a magnetic field if being energized. The inductor is arranged in that way that an electrical current flows through the inductor if a defined input voltage is provided to the input circuit. The magnetic field sensor can be any device which provides a defined output voltage if being exposed to a magnetic field. The inductor and the magnetic field sensor preferably are so called "surface-mounted devices" (SMD) which can be easily mounted to a printed circuit and thus can be easily integrated into the motor vehicle auxiliary unit electronics.

If the defined input voltage is provided to the input circuit of the switching unit, the electrical current flowing through the inductor generates a magnetic field which is detected by the magnetic field sensor of the output circuit causing the magnetic field sensor to provide the defined output voltage. This allows the output voltage of the output circuit to be switched based on the input voltage of the input circuit without requiring an electrical connection between the input circuit and the output circuit.

The inductor and the magnetic field sensor are both relatively low-priced components which allows the switching unit and thus the motor vehicle auxiliary unit to be realized relatively cost-effectively. The inductor and the magnetic field sensor are both also relatively temperature insensitive which guarantees the high-voltage electric circuit of the motor vehicle auxiliary unit to be reliably switched even if being installed at relatively hot installation sites as, for example, at or close to an internal combustion engine. The galvanically isolated switching unit according to the present invention thus provides a cost-effective and versatile motor vehicle auxiliary unit.

Preferably, the inductor is a low-cost rod core choke which provides a relatively concentrated and thus strong magnetic field at the axial ends of the rod core which can be sensed reliably and accurately by a magnetic field sensor arranged nearby one of the axial ends of the rod core.

In a preferred embodiment of the present invention, the magnetic field sensor is a latching-type Hall sensor, preferably a bipolar-latching Hall sensor. Latching-type Hall sensors can be considered as "magnetically-actuated" switches which are switched to an on-state by providing a sufficiently strong magnetic field with a first magnetic polarity and which are switched to an off-state by providing a sufficiently strong magnetic field with a second magnetic polarity which is opposite to the first magnetic polarity. The latching-type Hall sensor provides a relatively high on-state output voltage in the on-state and provides a relatively low off-state output voltage in the off-state. The latching-type Hall sensor "latches" the respective switching state which means that the latching-type Hall sensor remains in the on-state or in the off-state if the magnetic field is removed. The latching-type Hall sensor allows to provide the relatively high on-state output voltage for a longer time-span without the need of continuously energizing the inductor for generating the magnetic field. This provides an energy-efficient switching unit and thus an energy-efficient motor vehicle auxiliary unit.

More preferably, the input circuit comprises a capacitor which is electrically connected in series to the inductor. Preferably, the capacitor is a low-cost electrolytic capacitor or a low-cost ceramic capacitor. If the defined input voltage is provided to the input circuit, the capacitor is initially charged via a relatively high charging current which flows through the inductor in a first flow direction thus generating a magnetic field with a first magnetic polarity. The magnetic field with the first magnetic polarity causes the latching-type Hall sensor of the output circuit to switch to the on-state. If being completely charged, the capacitor prevents any current flow through the inductor and thus prevents a power consumption by the inductor. If the input voltage is removed from the input circuit, the capacitor is discharged via a discharging current which flows through the inductor in a second flow direction, which is opposite to the first flow direction of the charging current, thus generating a magnetic field with a second magnetic polarity which is opposite to the first magnetic polarity. The magnetic field with the second magnetic polarity causes the latching-type Hall sensor of the output circuit to switch to the off-state. The input circuit with the capacitor thus allows to switch the output voltage by simply switching on and off the voltage supply of the input circuit, wherein the capacitor prevents a continuous power consumption by the inductor if the voltage supply of the input circuit is switched on. This provides an energy-efficient switching unit and thus an energy-efficient motor vehicle auxiliary unit.

The output voltage provided by the magnetic field sensor is typically relatively low. In a preferred embodiment of the present invention, the output circuit of the switching unit is therefore electrically connected to a voltage controller which is configured to control a voltage of the high-voltage electric circuit based on the output voltage provided by the magnetic field sensor. The voltage controller is preferably configured to enable a power supply of the high-voltage electric circuit of the motor vehicle auxiliary unit if the output voltage provided by the magnetic field sensor is above a defined enabling threshold voltage, and configured to disable the power supply of the high-voltage electric circuit if the output voltage provided by the magnetic field sensor is below a defined disabling threshold voltage. The voltage controller can also be configured to control the voltage of the high-voltage electric circuit proportional to the output voltage provided by the magnetic field sensor. The voltage controller allows the relatively high voltage of the high-voltage electric circuit to be reliably and efficiently switched by the relatively low output voltage provided by the magnetic field sensor.

An embodiment of the present invention is described with reference to the enclosed figures, wherein figure 1 shows a simplified illustration of a motor vehicle auxiliary unit according to the present invention, and figure 2 shows a simplified electric circuit diagram of a galvanically isolated switching unit of the motor vehicle auxiliary unit of figure 1. Fig. 1 shows a motor vehicle auxiliary unit 10 which, in the present embodiment, is an electric coolant pump with a pump wheel 12 which is driven by an electric motor 14 via a rotor shaft 16.

The motor vehicle auxiliary unit 10 comprises a high-voltage electric circuit 18 and a low-voltage electric circuit 20 which are galvanically isolated from each other. The high-voltage electric circuit 18 is electrically connected to a high-voltage motor vehicle electric system 22, and the low-voltage electric circuit 20 is electrically connected to a low-voltage motor vehicle electric system 24. The low-voltage motor vehicle electric system 24, in the present embodiment, is configured to transmit data signals according to the DC-LIN standard.

The high-voltage electric circuit 18 comprises the electric motor 14 and a voltage controller 26 which is configured to control the present voltage of the high-voltage electric circuit 18. The voltage controller 26 is in particular configured to enable a power supply of the electric motor 14 from the high-voltage motor vehicle electric system 22 via the high-voltage electric circuit 18 as long as a voltage equal to or above a defined enabling threshold is provided to an enable terminal 28 of the voltage controller 26.

The low-voltage electric circuit 20 comprises an auxiliary unit control electronics 30. The auxiliary unit control electronics 30 comprises a data interface 32 which is configured to send and receive data via the low-voltage motor vehicle electric system 24 according to the DC-LIN standard. The auxiliary unit control electronics 30 is configured to activate the electric motor 14 if a respective data signal is received from a motor vehicle control unit via the data interface 32. The motor vehicle auxiliary unit 10 comprises a galvanically isolated switching unit 34 with an input circuit 36 and with an output circuit 38 which is galvanically isolated from the input circuit 36.

The input circuit 36 comprises an inductor 40 and a capacitor 42 which are electrically connected in series to each other. The inductor 40, in the present embodiment, is a rod core choke with a rod-shaped core 44. The inductor 40 is selectively electrically connectable to a voltage potential VI of the low-voltage motor vehicle electric system 24 by a switch 46, wherein the switching state of the switch 46 is electrically controlled by the auxiliary unit control electronics 30. The capacitor 42, in the present embodiment, is an electrolytic capacitor. The capacitor 42 is electrically connected to a ground potential GNDI of the low-voltage motor vehicle electric system 24. A voltage potential of a feed line of the inductor defines an input voltage Vin of the input circuit 36.

The output circuit 38 comprises a magnetic field sensor 48 which is arranged nearby the inductor 40, in particular nearby an axial end of the rod-shaped core 44 of the inductor 40. The magnetic field sensor 48, in the present embodiment, is a latching-type Hall sensor. The magnetic field sensor 48 is electrically connected to a voltage potential Vh as well as to a ground potential GNDh of the high-voltage motor vehicle electric system 24. An output terminal 50 of the magnetic field sensor 48 is electrically connected to the enable terminal 28 of the voltage controller 26.

The magnetic field sensor 48 is configured to switch to an on-state if a magnetic field MF with a first magnetic polarity is sensed, and is configured to switch to an off-state if a magnetic field MF with a second magnetic polarity, which is opposite to the first magnetic polarity, is sensed. The magnetic field sensor 48 is configured to provide an output voltage Vout with a relatively high amplitude at the output terminal 50 in the on-state, and configured to provide a output voltage Vout with a relatively low amplitude at the output terminal 50 in the off-state, wherein the high amplitude of the output voltage Vout is above the enabling threshold of the voltage controller 26 and wherein the low amplitude of the output voltage Vout is below the enabling threshold of the voltage controller 26.

If the switch 46 is closed by the auxiliary unit control electronics 30, the input circuit 36 is provided with an input voltage Vin corresponding to the voltage potential VI of the low-voltage motor vehicle electric system 24. This causes the capacitor 42 to be charged via a charging current which flows through the inductor 40 in a first flow direction thereby generating a magnetic field MF with a first magnetic polarity. The magnetic field MF with the first magnetic polarity is sensed by the magnetic field sensor 48 causing the magnetic field sensor 48 to switch to the on-state. The magnetic field sensor 48 in the on-state provides the output voltage Vout with the high amplitude to the enable terminal 28 of the voltage controller 26 causing the voltage controller 26 to enable the power supply of the electric motor 14 via the high-voltage electric circuit 18.

Although the input voltage Vin still corresponds to the voltage potential VI of the low-voltage motor vehicle electric system 24, the charging current stops if the capacitor 42 is fully charged, which causes the magnetic field MF to vanish. Because the magnetic field sensor 48 is a latching-type Hall sensor, the magnetic field sensor 48 however remains in the on-state so that the electric motor 14 remains powered.

If the switch 46 is opened by the auxiliary unit control electronics 30, the input circuit 36 is separated from the voltage potential VI of the low-voltage motor vehicle electric system 24 causing the input voltage Vin to decrease e.g. to the ground potential GNDI of the low-voltage motor vehicle electric system 24. This causes the capacitor 42 to be discharged via a discharging current which flows through the inductor 40 in a second flow direction, which is opposite to the first flow direction, thereby generating a magnetic field MF with a second magnetic polarity which is opposite to the first magnetic polarity. The magnetic field MF with the second magnetic polarity is sensed by the magnetic field sensor 48 causing the magnetic field sensor

48 to switch to the off-state. The magnetic field sensor 48 in the off-state provides the output voltage Vout with the low amplitude to the enable terminal 28 of the voltage controller 26 causing the voltage controller 26 to disable the power supply of the electric motor 14 via the high-voltage electric circuit 18.

Reference List

10 motor vehicle auxiliary unit

12 pump wheel

14 electric motor

16 rotor shaft

18 high-voltage electric circuit

20 low-voltage electric circuit

22 high-voltage motor vehicle electric system

24 low-voltage motor vehicle electric system

26 voltage controller

28 voltage controller enable terminal

30 auxiliary unit control electronics

32 auxiliary unit electronics data interface

34 switching unit

36 switching unit input circuit

38 switching unit output circuit

40 inductor

42 capacitor

44 inductor core

46 switch

48 magnetic field sensor

50 magnetic field sensor output terminal

MF magnetic field

Vh voltage potential of the high-voltage motor vehicle electric system

Vin input voltage

VI voltage potential of the low-voltage motor vehicle electric system

Vout output voltage

GNDh ground potential of the high-voltage motor vehicle electric system

GNDI ground potential of the low-voltage motor vehicle electric system