Voltage control system for heating a selective catalyst reduction device

1. An exhaust gas treatment system for an internal combustion engine, comprising:

an exhaust gas conduit in fluid communication with, and configured to receive an exhaust gas from the internal combustion engine;

an electrically heated catalyst (“EHC”) device in fluid communication with the exhaust gas conduit, the EHC device including an electric heater and an EHC that is heated to an EHC light-off temperature;

a generator selectively operable in a target voltage mode to supply a target voltage to the electric heater, wherein the target voltage represents a voltage required by the electric heater in order to maintain the EHC at a catalyst temperature;

a selective catalytic reduction (“SCR”) device in fluid communication with the exhaust gas conduit, wherein the SCR device includes an SCR catalyst that is selectively heated by the EHC device to a SCR light-off temperature;

a hydrocarbon supply selectively activated to introduce hydrocarbons into the exhaust gas conduit; and

an electronic control unit (“ECU”) in communication with the generator, the EHC device, the hydrocarbon supply, and at least one temperature sensor of the SCR device, the ECU configured to:

determine an SCR temperature of the SCR catalyst;

determine whether the EHC is above the EHC light-off temperature and whether the SCR catalyst is below the SCR light off temperature; and

operate the generator in the target voltage mode based on determining that the EHC is above the EHC light-off temperature and the SCR catalyst is below the SCR light off temperature, wherein operating the generator in the target voltage mode comprises continuously monitoring one or more parameters of the exhaust gas treatment system and continuously controlling an output voltage of the generator based on the one or more parameters so as to responsively adjusting adjust the target voltage to maintain the catalyst temperature based the SCR temperature,

wherein the catalyst temperature represents a temperature required by the EHC to sustain combustion of the hydrocarbons introduced into the exhaust gas conduit and sustain the SCR light-off temperature of the SCR catalyst so as to improve conversion efficiency of the SCR catalyst.

2. The exhaust gas treatment system of claim 1 , wherein the ECU activates the hydrocarbon supply to introduce hydrocarbons into the exhaust gas conduit if the target voltage is provided to the electric heater by the generator.

3. The exhaust gas treatment system of claim 1 , further comprising an energy storage device that is selectively connected to the generator by a vehicle bus switch.

4. The exhaust gas treatment system of claim 3 , wherein the generator is connected to the energy storage device if the generator is operated at the target voltage mode.

5. The exhaust gas treatment system of claim 1 , wherein the ECU is further configured to operate the generator at an elevated voltage mode if the EHC is below the EHC light-off temperature.

6. The exhaust gas treatment system of claim 1 , wherein the ECU determines the target voltage based on a temperature of the EHC, an exhaust flow, a temperature of the exhaust gas, and a fuel mass flow.

7. The exhaust gas treatment system of claim 1 , further comprising an oxidation catalyst (“OC”) located immediately downstream of the EHC device.

8. The exhaust gas treatment system of claim 1 , wherein the electric heater is selectively connected to the generator by an EHC switch.

9. The exhaust gas treatment system of claim 8 , wherein the ECU is in communication with the EHC switch, and wherein the ECU opens the EHC switch to disconnect the electric heater from the generator if the EHC is above the EHC light-off temperature.

10. A method of operating an exhaust gas treatment system, comprising:

monitoring an electrically heated catalyst (“EHC”) device by an ECU to determine if an EHC is heated to an EHC light-off temperature, wherein the EHC device is in fluid communication with an exhaust gas conduit;

monitoring a selective catalytic reduction (“SCR”) device by the ECU so as to determine a SCR temperature of SCR catalyst included in the SCR device and to determine if the SCR catalyst is at a SCR light-off temperature, wherein the SCR device is located downstream of the EHC device;

determining whether the EHC is above the EHC light-off temperature and whether the SCR catalyst is below the SCR light off temperature by the ECU;

providing a hydrocarbon supply selectively activated to introduce hydrocarbons into the exhaust gas conduit, wherein the ECU is in communication with the hydrocarbon supply; and

based on determining the EHC is above the EHC light-off temperature and the SCR catalyst is below the SCR light off temperature, controlling a generator to operate in a target voltage mode to control the temperature of the EHC, wherein the target voltage represents a voltage required by an electric heater in order to maintain the EHC at a catalyst temperature, wherein operating the generator in the target voltage mode comprises continuously monitoring one or more parameters of the exhaust gas treatment system and continuously controlling an output voltage of the generator based on the one or more parameters so as to responsively adjusting adjust the target voltage to maintain the catalyst temperature based on the SCR temperature,

wherein the catalyst temperature represents a temperature required by the EHC to sustain combustion of the hydrocarbons introduced into the exhaust gas conduit and sustain the SCR light-off temperature of the SCR catalyst so as to improve conversion efficiency of the SCR catalyst.

11. The method of claim 10 , further comprising activating the hydrocarbon supply to introduce hydrocarbons into the exhaust gas conduit if the target voltage is supplied to the electric heater by the generator.

12. The method of claim 10 , further comprising providing an energy storage device that is selectively connected to the generator by a vehicle bus switch.

13. The method of claim 12 , wherein the generator is connected to the energy storage device if the generator is operated at the target voltage mode.

14. The method of claim 10 , wherein the ECU is further configured to operate the generator at an elevated voltage mode if the EHC is below the EHC light-off temperature.

15. The method of claim 10 , wherein the ECU determines the target voltage based on a temperature of the EHC, an exhaust flow, a temperature of an exhaust gas, and a fuel mass flow.

16. The method of claim 10 , further comprising providing an oxidation catalyst (“OC”) that is located immediately downstream of the EHC device.