CIRCUIT ARRANGEMENT FOR DISCHARGING A MOTOR VEHICLE'S ENERGY STORAGE SYSTEM

Description

[0001] The invention relates to a circuit arrangement for discharging an energy storage device of a motor vehicle, in particular for discharging an energy storage device for electrical energy which is provided for supplying an electrical machine of a motor vehicle.

[0002] In mild hybrid, hybrid, and electric vehicles, additional electrical energy storage devices are used alongside or instead of a conventional 12 V or 24 V lead-acid battery to supply an electric motor in the drivetrain. Such additional energy storage devices are often designed as lithium-ion batteries or high-capacity energy storage devices. High-capacity energy storage devices based on double-layer capacitors are particularly advantageous in terms of capacity per mass. So-called ultracapacitors (also referred to as ultracaps or ultracap storage devices) are preferred for this purpose.

[0003] DE 10 2012 100 951 A1 relates to an additional circuit for actively rapidly discharging an intermediate circuit of a power converter via a PCT resistor, wherein the discharge depends on the conduction state of the load path of a power switch whose control voltage is tapped from the intermediate circuit voltage. US 2009 / 0268354 A1 discloses an approach for discharging a high-voltage bus coupled to a discharge circuit. The discharge circuit is deactivated if, during the discharge process, the values ​​of two successively determined voltage values ​​are less than a threshold value. JP 2011-250494 A discloses a vehicle energy supply system, wherein, in a parked vehicle, if a temperature exceeds a predetermined value and a double-layer capacitor is fully charged, a battery is charged with energy from the double-layer capacitor.US 2010 / 0214055 A1 discloses an inverter of an electric vehicle and a vehicle controller capable of detecting a collision condition. If this occurs, a main inverter connection switch of a high-voltage battery is opened to interrupt the voltage supply from the battery to a DC bus.

[0004] When using high-performance, low-energy energy storage devices in the drivetrain, such as ultracapacitors, these are typically charged to near their maximum usable voltage during the final braking process before the vehicle is shut down. Ultracapacitors, in particular, age most rapidly in high-voltage conditions, so storing such energy storage devices at high charging voltages, especially when fully charged, is detrimental to their service life.

[0005] On the other hand, an automatic complete discharge of the ultracapacitor when the vehicle is switched off or during a stop phase of a start-stop operation does not make sense from an energy point of view.

[0006] It is therefore an object of the invention to provide a method for discharging an energy storage device intended to supply an electric machine in the drive train, with which the charge level of the energy storage device can be adjusted in such a way that a significant impairment of the service life of the energy storage device during extended shutdowns is avoided and, at the same time, the energetic waste of the energy content of the energy storage device can be reduced. The invention is based, in particular, on the object of a simple and cost-effective design of such a discharging method.

[0007] These objects are achieved by the features of the independent claims. Advantageous embodiments and applications of the invention are subject to the dependent claims and are explained in more detail in the following description, with partial reference to the figures.

[0008] The invention is based, on the one hand, on the technical finding that, during extended periods of motor vehicle shutdown, discharging the energy storage device to a medium voltage level offers a good compromise from an energy perspective and service life perspective. It would be conceivable to discharge the energy storage device to a medium voltage level whenever vehicle shutdown is detected by opening the ignition switch - terminal 15. However, within the scope of the invention, it was determined that opening the ignition switch based on the signal from terminal 15 does not necessarily indicate a prolonged shutdown of motor vehicles, especially commercial vehicles.Rather, it was determined that an "ignition switch off" signal from terminal 15 often occurs 10 to 15 times a day in vehicles, especially commercial vehicles, so initiating a discharge process immediately after detecting a terminal 15 signal indicating that the vehicle has been turned off would be disadvantageous from an energy perspective. Rather, it is advantageous to wait for a latency phase after detecting that the vehicle has been turned off before initiating a discharge process of the energy storage device to a medium voltage level.

[0009] According to general aspects of the invention, a motor vehicle is provided with a circuit arrangement for discharging an energy storage device of a motor vehicle. The circuit arrangement comprises an energy storage device for electrical energy, which is provided for supplying an electrical machine of a motor vehicle, which is preferably designed as a traction machine or as a crankshaft starter generator, and a discharge circuit. The discharge circuit is supplied with voltage via the energy storage device and has a discharge resistor, a voltage comparison element, and an activation switching device, namely in the form of a series circuit comprising the discharge resistor, the voltage comparison element, and the activation switching device.

[0010] In this case, the activation switching device initiates a discharging process of the energy storage device via the discharging resistor after a latency phase (delay phase) has elapsed since the motor vehicle was turned off. The activation switching device can be configured to initiate the discharging process of the energy storage device via the discharging resistor after the latency phase (delay phase) has elapsed since the motor vehicle was turned off. The activation switching device can be triggered externally, for example, by a vehicle control device, to initiate the discharging process of the energy storage device via the discharging resistor after the latency phase (delay phase) has elapsed since the motor vehicle was turned off.The latency phase may, for example, be set to a value that is in a range of 5 minutes to 1 hour, more preferably in a range of 10 minutes to 30 minutes, or more preferably in a range of 10 minutes to 20 minutes.

[0011] Furthermore, the voltage comparison element is configured to perform a voltage comparison between a current energy storage voltage and a voltage threshold value and to terminate the discharge process of the energy storage device if, during the voltage comparison, the current energy storage voltage is less than or equal to the voltage threshold value.

[0012] The circuit arrangement according to the invention thus enables the energy storage device to be discharged to a predetermined voltage threshold value, which corresponds to an average voltage level of the energy storage device, so that the energy storage device is not completely discharged. This avoids energy-inefficient total discharges on the one hand and a significant impairment of the service life of the energy storage device during longer shutdown processes on the other. A particular advantage of the invention is further that the partial discharge process does not occur immediately when the vehicle is parked, but rather is delayed, i.e. only after a latency phase has elapsed, so that energy-inefficient discharge processes are avoided when the motor vehicle is parked and driving is resumed after a short shutdown period.

[0013] To enable a particularly cost-effective implementation of the discharge circuit, according to a further embodiment of the invention, it is advantageous if the voltage comparison element is designed as a passive voltage comparison switch. The voltage comparison switch is closed when the current energy storage voltage is greater than the voltage threshold and open when the current energy storage voltage is less than or equal to the voltage threshold.

[0014] Furthermore, it is advantageous if the voltage comparison element has a switching hysteresis in order to avoid an undefined "oscillation" of the switching operation around the voltage threshold due to recovery effects of the energy storage device.

[0015] According to a first variant of the invention, the activation switching device comprises a timer that is closed after a predetermined latency period after the vehicle is parked, preferably after an ignition switch is turned off. Only when the timer is closed is discharging the energy storage device via the discharge resistor possible. For example only, the latency period can be in the range of 10 to 30 minutes. Such timers are cost-effective to implement and offer the advantage that the latency period for triggering the discharge process is easily adjustable and can also be preset to different values, if necessary, depending on the vehicle type and / or type of use.

[0016] In an advantageous variant of this embodiment, the activation switching device comprises a switch arranged in series with the timer, which is coupled to terminal 15 of the vehicle, such that the switch is closed when the "ignition switch off" signal is present at terminal 15. The switch is open when the "ignition switch off" signal is not present, i.e., when the ignition switch is switched on. The ignition device and the fuel supply of the motor vehicle are supplied with power via terminal 15. When an internal combustion engine is switched off, the voltage at terminal 15 drops to 0 V when the ignition switch is opened, which corresponds to the "ignition switch off" signal. When this signal appears, the loads connected to terminal 15 are switched off. According to this variant, a discharge process is therefore only possible when both the switch coupled to terminal 15 of the vehicle and the timer are closed.

[0017] According to an alternative second variant of the invention, the activation switching device comprises a temperature switch that is closed when a temperature signal falls below a predetermined temperature threshold, wherein the temperature signal indicates the temperature profile of a component that cools down after the vehicle is parked. Only when the temperature switch is closed is discharging the energy storage device via the discharge resistor possible. Preferably, the predetermined temperature threshold is selected such that the cooling time of the component from an operating temperature to the temperature threshold after the vehicle is parked lies within the range of the desired latency time for starting the discharge process. The component whose temperature is detected to determine a trigger condition for the discharge process can be the internal combustion engine.Alternatively, any other component that heats up to an operating temperature during driving and cools down again when parked can be used to detect a temperature threshold indicating that the vehicle has not been restarted for longer than a predetermined deceleration period.

[0018] In an advantageous variant of this embodiment, the activation switching device, analogous to the embodiment with the timer, comprises a switch arranged in series with the temperature switch, which is coupled to terminal 15 of the vehicle, such that the switch is closed when the "ignition switch off" signal is present at terminal 15.

[0019] A particularly preferred embodiment provides that the energy storage device is a capacitive energy storage device, preferably an ultracap storage device.

[0020] According to a further aspect, the motor vehicle may be a commercial vehicle.

[0021] The above-described preferred embodiments and features of the invention can be combined with each other as desired. Further details and advantages of the invention are described below with reference to the attached Figure 1 which shows a schematic block diagram of a circuit arrangement according to an embodiment of the invention.

[0022] The circuit arrangement comprises an ultracapacitor (ultracap storage) 2, which is connected via the terminals 8 to an electrical machine, e.g. in the form of a crankshaft starter generator (KSG) (not shown) of a motor vehicle, or to the on-board electrical system, sub-on-board electrical system or a high-voltage network of the vehicle, in order to supply the electrical machine with electrical energy during motor operation of the electrical machine and to store electrical energy generated during generator operation of the electrical machine.

[0023] The circuit arrangement further comprises a self-contained discharge circuit 1 for the ultracapacitor 2, which is self-powered by the ultracapacitor 2. The discharge circuit 1 is formed from a series circuit comprising a discharge resistor 3, a voltage comparator 4, and an activation switching device 5. The activation switching device 5 is configured to initiate a discharge process of the energy storage device 2 via the discharge resistor 3 after a latency phase has elapsed since the motor vehicle was turned off.

[0024] For this purpose, the activation switching device 5 is designed as a series circuit comprising a timer 6 and a switch 7, which is coupled to terminal 15 of the vehicle (not shown). The switch 7 is closed when the "ignition switch off" signal is present at terminal 15, i.e., the switch 7 is closed when the ignition is turned off, indicating a shutdown process. The timer 6 is still open at this time and is only closed after a predetermined latency period after the vehicle has been turned off, preferably after an ignition switch has been turned off and thus after the switch 7 has been closed. The latency period can, for example, have a value in the range of 10 to 30 minutes.

[0025] As already mentioned above, instead of the timer 6, a temperature switch can also be used, which is switched depending on a temperature signal that, for example, measures the temperature of the combustion engine (not shown). According to this variant, the temperature switch is closed when the combustion engine has cooled down to a predetermined temperature level after being switched off.

[0026] The voltage comparison element 4 is designed as a passive voltage comparison switch 4, which is closed when the current energy storage voltage is greater than a predetermined voltage threshold and is open when the current energy storage voltage is less than or equal to the predetermined voltage threshold. The predetermined voltage threshold is set to an average voltage level of the ultracapacitor 2.

[0027] When the vehicle is not switched off, i.e., during normal driving, switches 6 and 7 are open. If the driver switches off the vehicle, i.e., the ignition switch is opened so that the voltage at terminal 15 drops to zero or the "ignition switch off" signal is present at the terminal, switch 7 is closed. Switch 6 remains open for the time being. After the latency period has elapsed, switch 6 is also closed. If, at this point in time, the charging voltage of ultracapacitor 2 is above the predetermined voltage threshold, ultracapacitor 2 discharges via discharge resistor 3. The discharge process is terminated if the current charging voltage of ultracapacitor 2 has dropped to the predetermined voltage threshold, because then voltage comparison switch 4 opens.

[0028] Although the invention has been described with reference to specific embodiments, it will be apparent to a person skilled in the art that various changes may be made without departing from the scope of the invention. In addition, many modifications may be made without departing from the scope thereof. Consequently, the invention is not intended to be limited to the disclosed embodiments, but is intended to include all embodiments falling within the scope of the appended claims. List of reference symbols

[0029] 1Discharge circuit 2Ultracap memory 3Resistance 4Voltage comparison switch 5Activation switching device 6Timer 7Switch, coupled to terminal 15 8Connection to the vehicle electrical system

Claims

1. A motor vehicle, comprising a circuit arrangement for discharging an energy storage device of the motor vehicle, the circuit arrangement comprising an energy storage device (2) for electrical energy, which is provided for supplying an electrical machine of the motor vehicle; and a discharge circuit (1), which is supplied with voltage via the energy storage device (2) and comprises a discharge resistor (3), a voltage comparison element (4), and an activation switching device (5), wherein the activation switching device (5) is configured to start a discharging process of the energy storage device (2) via the discharging resistor (3) after a latency phase has elapsed since the motor vehicle has been parked, and / or wherein the activation device is triggered to start the discharging process of the energy storage device (2) via the discharging resistor (3) after the latency phase has elapsed, and wherein the voltage comparison element (4) is configured to perform a voltage comparison between a current energy storage device voltage and a voltage threshold value and to terminate the discharging process of the energy storage device (2) if the current energy storage device voltage is less than or equal to the voltage threshold value during the voltage comparison; characterised by a series connection of the discharge resistor (3), the voltage comparison element (4), and the activation switching device (5); in that the activation switching device (5) comprises a timer switch (6), which is closed after a predetermined latency time after an ignition switch is switched off; and in that the voltage threshold value corresponds to an average voltage level of the energy storage device (2), so that the energy storage device (2) is not completely discharged.

2. The motor vehicle according to claim 1, characterised in that the activation switching device (5) comprises a switch (7), which is arranged in series with the timer switch (6) and which is coupled to terminal 15 of the vehicle in such a way that the switch (7) is closed when the "ignition switch off" signal is present at terminal 15.

3. The motor vehicle according to one of the preceding claims, characterised in that the energy storage device (2) is a capacitive energy storage device, preferably an ultracap storage device (2).

4. The motor vehicle according to one of the preceding claims, wherein the motor vehicle is a commercial vehicle.

5. A motor vehicle, comprising a circuit arrangement for discharging an energy storage device of the motor vehicle, the circuit arrangement comprising an energy storage device (2) for electrical energy, which is provided for supplying an electrical machine of the motor vehicle; and a discharge circuit (1), which is supplied with voltage via the energy storage device (2) and comprises a discharge resistor (3), a voltage comparison element (4), and an activation switching device (5), wherein the activation switching device (5) is configured to start a discharging process of the energy storage device (2) via the discharging resistor (3) after a latency phase has elapsed since the motor vehicle has been parked, and / or wherein the activation device is triggered to start the discharging process of the energy storage device (2) via the discharging resistor (3) after the latency phase has elapsed, and wherein the voltage comparison element (4) is configured to perform a voltage comparison between a current energy storage device voltage and a voltage threshold value and to terminate the discharging process of the energy storage device (2) if the current energy storage device voltage is less than or equal to the voltage threshold value during the voltage comparison; characterised by a series connection of the discharge resistor (3), the voltage comparison element (4), and the activation switching device (5); in that the activation switching device (5) comprises a temperature switch, which is closed when a temperature signal falls below a predetermined temperature threshold value, the temperature signal indicating the temperature profile of a component, preferably of an internal combustion engine, which cools down after the motor vehicle has been switched off; and in that the voltage threshold value corresponds to an average voltage level of the energy storage device (2), so that the energy storage device (2) is not completely discharged.

6. The motor vehicle according to claim 5, characterised in that the activation switching device (5) comprises a switch (7), which is arranged in series with the temperature switch and which is coupled to terminal 15 of the vehicle in such a way that the switch (7) is closed when the "ignition switch off" signal is present at terminal 15.

7. The motor vehicle according to one of claims 5 or 6, characterised in that the energy storage device (2) is a capacitive energy storage device, preferably an ultracap storage device (2).

8. The motor vehicle according to one of claims 5 to 7, wherein the motor vehicle is a commercial vehicle.