Method and control device for detecting a malfunction of an electric heated catalyst system

The invention relates to a method and a control device for detecting a malfunction of an electric heated catalyst system, wherein the electric heated catalyst system comprises an electric heated catalyst with a heater disc, a power supply unit which provides electric energy for heating the heater disc and a board net which transfers the electric energy from the power supply unit to the electric heated catalyst.

Conventional electric heated catalyst systems comprise different components. A first component is the electric heated catalyst with a heater disc. The electric heated catalyst is designed to increase the exhaust catalyst temperature inside exhaust aftertreatment system of a combustion engine for example by heating the exhaust gas via the heater disk. The electric heated catalyst system further comprises a control unit and an onboard diagnosis functionality. The control unit and the onboard diagnosis functionality is for example split between a control unit for an engine of the vehicle and a control unit for the electrical heated catalyst system. The data exchange between these two control units is mostly done by a CAN-Bus. Exchange data are for example control data (from engine control unit to electrical heated catalyst control unit) or measured data, or onboard diagnosis information (from electrical heated catalyst control unit to engine control unit). In the case of a defect of the heater disc, the onboard diagnosis functionality will detect a failure and can therefore switch on a malfunction illumination lamp or can trigger to make an entry in a fault memory. In such a case, the electric heated catalyst system or the vehicle with the electric heated catalyst system must be repaired. The electric heated catalyst repair could be very expensive so that the owner of the electric heated catalyst system or the vehicle with the electric heated catalyst system could be interested in a manipulation of the electric heated catalyst system so that the onboard diagnosis functionalities are no longer able to detect or to indicate the defect of the electric heated catalyst system. In a further scenario a vehicle with the electric heated catalyst system is mainly used for very short driving cycles. If the driving cycles are very short, an accumulator may be discharged step by step due to the electric heated catalyst system operation. This effect occurs if the accumulator discharge due to electric catalyst heating is greater than accumulator recharge at a remaining driving cycle. Finally, the vehicle accumulator does not contain sufficient energy to heat the electric heated catalyst system in designed and certified manner and / or to start the combustion engine. The consequence is that combustion engine does not start anymore, or a combustion engine start is possible, but exhaust emissions are above certified level up to violation of emission legislation. If such a scenario is a frequent issue for the owner of the vehicle with the electric heated catalyst system, this owner could also be interested in a manipulation of the electric heated catalyst system which could therefore reduce the overall service costs due to maintenance of the vehicle.

An approach for electric heated catalyst system manipulation is the manipulation of exchanged data between the engine control unit of the vehicle and the electric heated catalyst control unit. A small electronic device with two independent CAN-Busses can, for example, be installed. This device could be placed into the CAN communication between the engine control unit and the electric heated catalyst control unit and works like a bridge between the CAN-Busses. The electronic device can read and manipulate all exchange data between the engine control unit and the electric heated catalyst control unit. It could inhibit the heating of the heater disk by resetting the heating commands and/or it could prevent a failure detection by manipulation of the measurements or the onboard diagnosis data.

Such kind of manipulation devices are known for example from selective catalytic reduction systems (SCR systems), which manipulates the AdBlue tank filling level signal to a high filling level value, so that the vehicle owner can save the AdBlue refilling and the AdBlue costs.

State of the art electric heated catalyst systems are not secured against such kind of manipulation attacks. The conventional security measures to inhibit such manipulation is a confidential handling of CAN message definitions. A higher security level could be reached by protecting data exchange with cryptographic methods, but this increases the hardware costs because of a special cryptographic key storage. The solution with the confidential handling of CAN message definition does not protect against a reverse engineering attack because with the reverse engineering it is possible to disclose the CAN message structure and CAN message data content so that a data manipulation is doable. The solution with the cryptographic key storage produces hardware costs for handling and secured storage of the cryptographic key.

The object of the present disclosure is therefore to create a method and a control device which can detect a malfunction of an electric heated catalyst system in a reliable and simple manner.

This object is achieved by a method comprising the features of the independent claim and by a control device which is used to execute the method according to the independent claim. Advantageous embodiments of the method and the control device are specified in the dependent claims.

A method for detecting a malfunction of an electric heated catalyst system is specified. The electric heated catalyst system comprises an electric heated catalyst with a heater disc, a power supply unit which provides electric energy for heating the heater disc and a bord net which transfers the electric energy from the power supply unit to the electric heated catalyst. The electric heated catalyst system is used for example in a vehicle to treat the exhaust gas of an engine of the vehicle via increasing a catalyst temperature of a catalysts. In order to increase the temperature of the catalysts in the electric heated catalyst system, the heater disc is arranged within the electric heated catalyst system. The heater disk provides the desired heating energy when the heater disk is provides with the required electric energy. After a cold start of the combustion engine, the electric heated catalyst system has not the required temperature to treat the exhaust gas of the combustion engine to achieve the desired low emission. Therefore, the heater disc is required to heat up the catalyst portion above a light-off temperature so that the catalyst portion can treat the exhaust gas emission targets are reached. The method for detecting the malfunction of the electric heated catalyst system comprises the following steps:

- Operating the electric heated catalyst system, wherein the electric heated catalyst systems triggers an activation or a deactivation of the heater disc of the electric heated catalyst. In other words, the electric heated catalyst system is in operation, during which the electric heated catalyst system activates or deactivates the heater disc of the electric heated catalyst. An activation of the heater disc is defined that electric energy is provided / supplied to the heater disc so that the heater disc can heat, for example immediately after a cold start of the engine, which is equipped with the electric heated catalyst system. The deactivation of the heater disc is defined in that the electric energy supply to the heater disc is stopped so that the heater disc does no longer heat. This can for example be necessary after a specified period of time after a start of the engine, which is equipped with the electric heated catalyst system, for example in this case, when the temperature of the heated catalyst is high enough and does not require additional heat from the heater disc. The provided heat from the exhaust gas itself may be enough to keep the temperature of the electric heated catalyst within the desired range. Triggering the activation or the deactivation of the heater disc means that the heater disc is controlled for example by a control unit to start the heating process or to stop the heating process. It does not mean that the heater disc heats at this moment or that the heating is stopped currently (for example subordinated heating control by pulse wide modulation).

- Monitoring an electrical value of the bord net during the triggered activation and/or the triggered deactivation of the heater disc. The bord net transfers the required electric energy for heating from the power supply unit to the heater disc. Conventional heater discs are designed for an electrical power in the range of 1 kW to 4 kW or even more. The activation of such a high-power energy consumer effects the vehicle electrical system, and in particular the board net, itself. These effects can be monitored and detected in the electrical values of the bord net. In other words, an activation and/or a deactivation of the heater disc of the electric heated catalyst system effects the bord net which can be monitored, measured in the electrical values of the bord net itself. Is the electric heated catalyst system for example installed in a vehicle, then the heater disc of the electric heated catalyst system is one of the biggest consumers of electric energy. Therefore, such an activation or a deactivation causes effects on the vehicle bord net which can be monitored easily. Other words for electrical values are for example electrical parameters or electrical variables which describe the electrical behavior of the board net. Electrical values of the board net are for example an electrical system voltage at the power supply unit, an electrical system voltage at an energy consumer devices, an output current of the power supply unit, a charging / discharging current of the accumulator, an output current of an alternator, an input current of the energy consumer devices, an output power of the power supply unit, an input power of the energy consumer device, a supplied energy of the power supply unit, a consumed energy of the energy consumer devices.

- Analyzing the monitored electrical value of the board net for detecting a malfunction of the electric heated catalyst system. The monitored electrical value of the bord net can for example be stored and afterwards be analyzed. A malfunction of the electrical heated catalyst system is present, for example, when the heater disc cannot heat anymore or when heating cannot be stopped. Detecting a malfunction may imply creating a malfunction signal, which triggers an entry into a failure memory of a control unit. The monitored electrical value is for example analyzed by analyzing a gradient of its curve. If the gradient or the gradient course does not match with an expected gradient or an expected gradient course a malfunction of the electric heated catalyst system is detected. Another possible method to analyze the monitored electrical value is to search in the monitored electrical value for expected course developments (or values reached) which should occur due to the activation or deactivation of the heater disk.

The electrical energy in an electrical system (bord net) needs to be in balance. That means that the electrical energy which is generated needs at the same time a consumer. If this balance is not present, then the electrical system voltage (bord net voltage) changes up to the balance is reached again. If the generated electrical energy is higher than the consumption, then the voltage increases. If the electrical energy generation is lower than the consumption, then the voltage decreases. An accumulator is a special component in such a system which can provide and can consume electrical energy. Hence it is used at the electrical system as a buffer, when electrical energy generation and consumption are not in balance. So, the accumulator stabilizes the electrical system voltage.

The heater disc is a high energy consumer from the vehicle bord net point of view. The heater disc has a pure resistive characteristic, so that an activation of the heater disc impacts the bord net energy balance which can be monitored in the electrical values of the bord net. The disturbance of the bord net energy balance is very fast after each activation or deactivation (switching event) of the heater disc due to the pure resistive characteristic of the heater disc. It is in the range of microseconds, but the bord net energy control and the alternator power control of the power supply unit are conventionally only reacting in the range of milliseconds. So, the power supply unit must buffer the disturbance, which are caused by the activation or deactivation of the heater disc. If the monitored electrical value does not show such a disturbance when the heater disk is activated or deactivated, then a malefaction of the electric heated catalyst system is detected.

The disturbances which occur during operation of the electric heated catalyst system can be monitored via the electrical values of the bord net. Therefore, it is possible to detect a malfunction of the electric heated catalyst system by an observation of the electrical values of the bord net and analyzing the monitored electrical value. If, for example, the onboard diagnosis of the electric heated catalyst system is tampered or manipulated it would still be possible to detect a malfunction of the electric heated catalyst system due to the above-mentioned reasons. The described method does not require any additional hardware parts or expensive cryptographic storage capacities to detect a malfunction of the electric heated catalyst system. Because of that the described method provides a cheap but very reliable method for detecting a malfunction of the electric heated catalyst system.

According to one embodiment comprises analyzing the monitored electrical value of the board net comparing the monitored electrical value of the board net with a reference value, wherein a malfunction of the electric heated catalyst system is detected when the monitored electrical value differentiates from the reference value by more than a predefined threshold. The monitored electrical value of the bord net can for example be stored and afterwards compared with the reference value The reference value can for example be developed during the development of the electric heated catalyst system and could be a reference variable or a reference model depending on different parameters. The reference value defines therefore what is expected to happen with the electrical value of the bord net if the heater disc is activated or if the heater disc is deactivated. If the monitored electrical value differentiates from the reference value by more than a predefined threshold which could also be stored in the control unit, then a malfunction of the electric heated catalyst system is detected. The predefined threshold is according to an embodiment 15 %, 10 % or 5% of the reference value. The above-mentioned disturbances in the board net due to the activation or deactivation of the heater disc are predictable and can be stored in the reference values. Further, the disturbances which occur during operation of the electric heated catalyst system can be monitored via the electrical values of the bord net. Therefore, it is possible to detect a malfunction of the electric heated catalyst system by an observation of the electrical values of the bord net and comparing the monitored electrical value of the bord net with the reference value.

According to one embodiment, the electrical value of the bord net is a voltage curve of the bord net, a current curve of the board net, a power curve of the board net or an energy curve of the board net. The voltage curve of the bord net or the other electrical values can for example be measured and monitored at a specific area of the bord net and can therefore be used for comparison with the reference value. These electrical values of the bord net are immediately affected when the heater disc is activated and/or deactivated. The voltage curve of the bord net or the other electrical values are therefore a very reliable characteristic of the bord net which can be used for comparison with the reference value to detect if the electric heated catalyst system works as desired or has a malfunction. According to another embodiment, two or more of the above-mentioned electrical values of the board net are in combination used for detecting a malfunction of the electric catalyst system.

According to one embodiment, the electric heated catalyst system comprises an onboard diagnosis system which observes failures of the electric heated catalyst. The onboard diagnosis system is for example implemented in a control unit of the electric heated catalyst system. This onboard diagnosis system is often target for manipulation so that the onboard diagnosis system does not send a detected failure to an engine control unit or to another further control unit. The onboard diagnosis system is therefore in addition designed to detect a malfunction of the heater disc which may result in a lack of heating the electric heated catalyst. According to this embodiment is a detected malfunction of the electric heated catalyst system which is detected via the above described method classified as a failure of the electric heated catalyst system when the onboard diagnosis system of the electric heated catalyst system detects a failure of the electric heated catalyst system. In this case, the onboard diagnosis system detects a failure of the electric heated catalyst system and the above described method using the electrical value of the board net detect a failure of the electric heated catalyst system. In this case, no tampering or no manipulation of the electric heated catalyst system is present so that a normal failure of the electric heated catalyst system is detected which can afterwards be shown to a user of the electric heated catalyst system (driver of the vehicle) so that the electric heated catalyst system can be repaired. According to this embodiment, the detected malfunction using the electrical value of the board net of the electric heated catalyst system is classified as manipulation or tampering of the electric heated catalyst system when the onboard diagnosis system of the electric heated catalyst system detects no failure of the electric heated catalyst system. In this case only the method described above using an electrical value of the bord net detects a malfunction of the electric heated catalyst system. The onboard diagnosis system does not detect a failure which is then interpreted that the onboard diagnosis system or other parts of the electric heated catalyst system are manipulated or tampered so that the onboard diagnosis system does not detect the failure of the electric heated catalyst system. In this case it is not only possible to detect a malfunction of the electric heated catalyst system besides the manipulation but is also possible to classify the detected malfunction of the electric heated catalyst system as a manipulation of the electric heated catalyst system which leads to the possibility that the detected malfunction can still be show to a user of the electric heated catalyst system (for example the driver of the vehicle) and/or that an entry in the failure memory, for example of the engine control unit, can be made.

According to one embodiment, the power supply unit of the electric heated catalyst system comprises an alternator which is designed to provide at least partially the electric energy for activating the heater disc and/or that the electric heated system comprises an accumulator which is designed to provide at least partially the electric energy for activating the heater disc, wherein the electrical value of the bord net is an output current of the alternator and/or a charging/discharging current of the accumulator. The activation of the heater disc requires a very high electric energy which is according to this embodiment provided by the alternator and/or by the accumulator. The activation of the heater disc, the switching of the heater disc from off to on, creates therefore an immediate impact in the output current of the alternator and/or of the discharging current of the accumulator. The output current of the alternator and the discharging current of the accumulator are therefore perfect electrical values of the bord net which can be used to detect the malfunction of the electric heated catalyst system. The deactivation of the heater disc, the switching of the heater disc from on to off, produces a disturbance in the bord net and in particular in the output current of the alternator and in the charging current of the accumulator because the produced electric energy of the alternator is no longer consumed by the heater disc and must therefore be stored in the accumulator. Also, in this case the output current of the alternator and the discharging or charging current of the accumulator are perfect electrical values for detecting the malfunction of the electric heated catalyst system. It is therefore possible to detect a malfunction of the electric heated catalyst system in a very reliable and secure manner if the electrical value of the bord net is the output current of the alternator and/or the charging/discharging current of the accumulator.

According to one embodiment, the alternator control commands are in addition monitored and used for the detection of a malfunction of the electric heated catalyst system. The alternator control commands are for example provided by an alternator control unit or by an engine control unit and are used to control the alternator, in particular the activation or the deactivation of the alternator and the produced electrical energy output of the alternator. An activation of the heater disc can for example be compensated at the beginning via electric energy from the accumulator. But after a specific period of time it may be required that the alternator is activated in order to produce the required electric energy for the heater disc which can no longer be provided by the accumulator alone. Is even after a long period of time during which the heater disc is activated no activation of the alternator required, it can be assumed that the heater disc does not consume the normal electric energy. It is therefore possible to detect the malfunction of the electric heated catalyst system and/or to improve the accuracy of the detection of malfunctions of the electric heated catalyst systems via monitoring the alternator control commands in view of the activation and/or deactivation of the heater disc.

According to one embodiment, a gradient or a gradient variation of the monitored electrical value of the bord net is used for the comparison with the corresponding reference value. According to this embodiment, the monitored electrical value is analyzed by defining a gradient or a gradient variation of the monitored electrical value. For example, if the monitored electrical value is the voltage curve of the bord net, the output current curve of the alternator and/or the charging/discharging current curve of the accumulator it is possible to create the corresponding gradients or the corresponding gradient variations over time or at specific points in time. These gradients or the gradient variations can then be compared with the corresponding reference values which are in this case also gradients and/or gradient variations. According to this embodiment, it is particular easy and fast to compare the monitored electrical value with the corresponding reference value which allows a fast and accurate detection of a malfunction of the electric catalyst system.

According to one embodiment, the above described method is carried out at each triggered activation and/or each triggered deactivation of the heater disc of the electric heated catalyst system. According to this embodiment, the method is carried out during the entire lifetime of the electric heated catalyst system at each triggered activation or at each triggered deactivation of the heater disc. It is conceivable that over the life span, the malfunction probability increases. It is therefore advantageous that the method is carried out at each triggered activation and/or at each triggered deactivation of the heater disc. In this case it is possible to immediately detect a malfunction of the electric heated catalyst system and to immediately classify the detected malfunction depending on the analysis of the onboard diagnosis system. It is therefore possible to reduce possible emissions due to a malfunction of the electric heated catalyst system.

According to a further aspect of the present disclosure a control device for detecting a malfunction of an electric heated catalyst system is specified. The control device comprises a control unit which is designed to execute one of the above described method for detecting a malfunction of the electric heated catalyst system, wherein the electric heated catalyst system comprises an electric heated catalyst with a heater disc, a power supply unit which provides the electric energy for heating the heater disc and a bord net which transfers the electric energy from the power supply unit to the electric heated catalyst. The control unit is for example the control unit which is specifically designed to control the electric heated catalyst system. According to another embodiment it is also conceivable that the control unit is part of a different control unit which controls other parts of a vehicle in which the electric heated catalyst system is arranged.

According to one embodiment, the electric heated catalyst system is arranged within a vehicle and is used to treat exhaust gas of an engine of the vehicle, wherein the control unit which is designed to execute one of the above described methods in an engine control unit, a vehicle energy management unit, an accumulator control unit or an alternator control unit. According to this embodiment is the control unit which is designed to execute the method for detecting a manipulation or a malfunction of the electric heated catalyst system not the control unit which is used to control the electric heated catalyst itself. The main task of the engine control unit is to control the engine of the vehicle. The main task of the vehicle energy management unit is to control the vehicle energy management and, the main task of the accumulator control unit is to control the accumulator and the main task of the alternator control unit is to control the alternator. It is conceivable that the engine control unit is also used to control the vehicle energy management, the accumulator and/or the alternator. If the control unit which is designed to execute the method for detecting a malfunction and/or a manipulation of the electric heated catalyst system is executed on one of the above described control units it is even harder to manipulate and/or to tamper the electric heated catalyst system so that a manipulation can be detected advantageously easily.

According to a further aspect of the present disclosure, a vehicle is specified with a control device which is used for detecting a malfunction of an electric heated catalyst system, wherein the control unit is designed to execute one of the above-mentioned methods.

Further advantageous embodiments of the present disclosure will become apparent from the detailed description of exemplary embodiments in connection with the figures.

In the figures:

Fig. 1 shows in a schematic manner an electric heated catalyst system according to a first exemplary embodiment,

Fig. 2 shows an equivalent circuit diagram of an electric heated catalyst system according to a second exemplary embodiment, Fig. 3 shows a first diagram of a voltage curve over time during a switch-on event of an electric heated catalyst system,

Fig. 4 shows a second diagram of a voltage curve over time during a switch-off event of an electric heated catalyst system,

Fig. 5 shows a third diagram showing different properties of the electric heated catalyst system during its operation.

Figure 1 shows an electric heated catalyst system 100 in a schematic manner. The electric heated catalyst system 100 comprises an electric heated catalyst 110 (EHC), an electric heated catalyst control unit 120, an engine control unit 130, a power supply unit 140, and a bord net 150. The electric heated catalyst 110 comprises a heater disc 160 which is used to create heat inside the electric heated catalyst 110. The electric heated catalyst system 100 supports the aftertreatment of exhaust gas of a combustion engine. The electric heated catalyst control unit 120 is designed to control the electric heated catalyst system 100. The engine control unit 130 is designed to control the engine and further to send and receive data to and from the electric heated catalyst control unit 120 to control the electric heated catalyst system 100 and in particular to control the electric heated catalyst 110 with its heater disc 160. The power supply unit 140 comprises for example an alternator and/or an accumulator which provides energy to the electric heated catalyst 110 in particular to the heater disc 160 to create heat inside the electric heated catalyst 110. The bord net 150 is arranged to transfer the required energy from the power supply unit to the heater disc 160. The bord net 150 further may comprise communication and control wires within the entire electric heated catalyst system 100 for example from the control units 120, 130 to the power supply unit 150 and/or to the electric heated catalyst 110. According to this embodiment, the communication between the electric heated catalyst control unit 120 and the engine control unit 130 is processed by a CAN-bus system.

An activation of the heater disc 160 requires that electric energy is provided from the power supply unit 140 via the bord net 150 to the heater disc 160. A deactivation of the heater disc 160 requires that the electric energy is no longer provided to the heater disc 160 which affects the energy balance of the bord net 150. A malfunction of the heater disc 160, the electric heated catalyst 110 or the entire electric heated catalyst system 100 is for example diagnosed via an onboard diagnosis system which is for example implemented in the electric heated catalyst control unit 120. In the case of a manipulation or tampering of the electric heated catalyst system 100, a malfunction or a failure of the electric heated catalyst system 100 is not transferred from the electric heated catalyst control unit 120 to the engine control unit 130 which then may not lead to an entry into the failure memory of the engine control unit 130. It is therefore necessary to create a method which is able to detect a malfunction of the electric heated catalyst system 100 even if the electric heated catalyst system 100 itself is manipulated or tampered. In order to achieve this, the bord net 150 itself is monitored. As explained above, the bord net 150 is affected during activation or deactivation of the heater disc 160 due to the high energy consumption of the heater disc 160 to create heat inside the electric heated catalyst 110. The method according to the present disclosure monitors an electric value of the bord net 150 for example like the voltage curve of the bord net 150 during a triggered activation or triggered deactivation of the heater disc 160. If the monitored electric value differentiates from a reference value by more than a predefined threshold, then a malfunction of the electric heated catalyst system 100 is detected. The reference value is for example stored in the engine control unit 130. Therefore, the detection of a malfunction of the electric heated catalyst system 100 can be executed outside of the electric heated catalyst control unit 120 so that a malfunction of the electric heated catalyst system 100 can be detected even if the electric heated control unit 120 is manipulated. The threshold value is for example also stored within the engine control unit 130.

Figure 2 shows an equivalent circuit diagram 200 of an electric heated catalyst system 100 according to a second embodiment. The equivalent circuit diagram 200 comprises an alternator 210, an accumulator 220, an electric heated catalyst control unit 230/120, an electric heated catalyst 240, an engine 250, a DC/DC converter 260 and further consumers 270. The alternator 210 and the accumulator 220 form the power supply unit to provide electric energy for the electric heated catalyst 240. According to another embodiment it is also conceivable that additional electrical energy sources like a 400 Volt or an 800 Volt Accumulator are provided as part of the power supply unit. In addition, the accumulator 220 and the alternator 210 provide electric energy for the engine 250, for the DC/DC converter 260, and/or for additional consumers 270. The DC/DC converter 260 is for example used to reduce the voltage to 12 Volt for the additional consumers 270 or to transfer energy from the 12 Volt system to the 48 Volt system. The electric heated catalyst control unit 230 is designed to activate or to deactivate the electric heated catalyst 240 and in particular to activate and/or deactivate the heater disc of the electric heated catalyst 240.

Figure 3 shows a first diagram 300. The first diagram 300 displays on its x-axis the time 320 and on its y-axis the voltage 310. The first diagram 300 shows a first voltage curve at a voltage source 330 and a first voltage curve at a voltage sink 340. The voltage source is the power supply unit. The first voltage curve at the voltage source 330 is therefore measured near the power supply unit, near the alternator 210 and the accumulator 220 shown in the equivalent circuit diagram 200. The voltage sinks are electric consumers of the electric energy provided by the power supply unit. A big voltage sink is the heater disc of the electric heated catalyst system. The first voltage curve at the voltage sinks 340 shows therefore the voltage curve near the consumers, near the electric heated catalyst in the equivalent circuit diagram. The first diagram 300 shows the first voltage curve at the voltage source 330 and the first voltage curve at the voltage sinks 340 during an activation event of the heater disc 160. In figure 3 it is clearly shown that the first voltage curve at voltage sinks 340 drops immediately after the switching-on event of the heater disc. This drop is the result of the high energy consumption of the heater disc 160, the internal resistance of power supply unit 140 and internal resistance of bord net 150 and parasitic inductance of bord net 150. After this undershot of the first voltage curve at the voltage sinks 340, the power supply unit 140 reacts and provides the necessary electric energy to heat up the heater disc 160 as required. Over time both, the first voltage curve at the voltage source 330 and the first voltage curve at the voltage sinks 340 approach each other until both reach an equilibrium. These voltage curves are specific and occur at each activation of the heater disc. The undershot at voltage sinks 340 occurs mainly due to component internal resistances, parasitic inductances and high current gradient at activating the heater disk 160. If a monitored voltage curve of the bord net deviates basically from such a shape, if the heater disc is triggered to be activated, then the electric heated catalyst system 100 has a malfunction.

Figure 4 shows a second diagram 400. The x-axis of the second diagram 400 is the time 420 and the y-axis of the second diagram 400 is the voltage 410. The second diagram 400 shows a second voltage curve at the voltage source 430 and a second voltage curve at the voltage sinks 440. Contrary to the first diagram 300, the second diagram 400 shows the second voltage curves 430, 440 during a deactivation, a switching-off event, of the heater disc. Immediately after the switching-off event of the heater disc, an overshot of the second voltage at the voltage sinks 440 occurs due to the additional electric energy within the bord net which is not consumed by the heater disc. After that, the voltage source, the power supply unit can react and can reduce the provided electric energy due to the reaction of the power supply unit, the second voltage curve at the voltage source 430 and the second voltage curve at the voltage sinks 440 approach each other until both reach an equilibrium. The accumulator works as a buffer during such a switching-off event. Also, here, each switching-off event, each deactivation of the heater disc produces such voltage curves within the bord net. If the monitored electric value of the bord net differentiates from the shown voltage curves of the second diagram during a deactivation of the heater disc, during an switching-off event of the heater disc, then the electric heated catalyst system 100 has a malfunction which can be detected.

Figure 5 shows a third diagram 500. The third diagram 500 comprises four sub-diagrams. Each of the four sub-diagrams show on its x-axis the time and on its y-axis different parameters. The first sub-diagram shows the electric heated catalyst switching curve from on to off and from off to on. The second sub-diagram which is located below the first sub-diagram shows a voltage curve at the electric heated catalyst 520. The third sub-diagram which is located below the second sub-diagram shows the voltage curve at the voltage sources 530, at the power supply unit. The fourth sub-diagram shows the alternator power 540 over time. The fourth sub-diagram shows a first alternator output power which follows the EHC switching 580 and a second constant alternator power during EHC heating 590. All the sub-diagrams show a first PWM cycle 560 and a last PWM cycle 570. Each PWM cycle 560, 570 starts at a switching event from off to on of the heater disc and end at another switching event from off to on of the heater disc. Within each PWM sub cycle 560, 570 a deactivation of the heater disc is present. In figure 5 shows that the different voltage curves 520 and 530 correspond to the voltage curves shown in figure 3 and 4 which correspond to the deactivation or activation of the heater disc. Figure 5 further shows that voltage curves 520, 530 depend on the alternator power output. The voltage curves 520, 530 are slightly different depending on how the alternator is controlled. The brighter depictured voltage curves of the second and third sub diagram correspond to the alternator control which follows the EHC switching 580. The darker depictured voltage curves of the second and third sub diagram correspond to the constant alternator control 590.