Claims:We claim:
1. A controller (110) for a Secondary Air Injection (SAI) system (100), said system (100) comprising a solenoid valve (120) to control injection of secondary air in an exhaust path (102) to control emission, said controller (110) adapted to
detect fuel enrichment condition based on any one of a signal from a lambda sensor (104) and a status of a variable stored in a memory (122) of said controller (110);
compute at least one of a duty cycle and an amplitude of a drive current required to drive said solenoid valve (120) to control injection quantity of said secondary air, and
operate said solenoid valve (120), based on said computation, to maintain a desired air-fuel ratio and reduce emissions in the exhaust gas for said detected fuel enrichment condition.

2. The controller (110) as claimed in claim 1, wherein said at least one of said duty cycle and said amplitude of said drive current are computed based on an exhaust mass flow through said exhaust path (102).

3. The controller (110) as claimed in claim 1, wherein said fuel enrichment condition is at least one selected from a group comprising an open loop condition, a full load condition, at constant torque with best Brake Specific Fuel Consumption (BSFC), during transients load conditions, and during safety of components.

4. The controller (110) as claimed in claim 1, wherein said air-fuel ratio of said exhaust gas is maintained without regard to a fuel injection quantity for said detected fuel enrichment condition.

5. The controller (110) as claimed in claim 1, wherein said air-fuel ratio of said exhaust gas is maintained only by a control of said solenoid valve (120) of said SAI system (100).

6. A method for operating a Secondary Air Injection (SAI) system (100), said system (100) comprising a solenoid valve (120) to control injection of secondary air, said method comprising the steps of:
detecting fuel enrichment condition based on any one of a signal from a lambda sensor (104) and a status of a variable stored in a memory (122) of said controller (110);
computing at least one of a duty cycle and an amplitude of a drive current required to drive said solenoid valve (120) to control injection quantity of said secondary air, and
operating said solenoid valve (120), based on said computation, to maintain a desired air-fuel ratio and reduce emissions in the exhaust gas for said detected fuel enrichment condition.

7. The method as claimed in claim 6, wherein computing said at least one of said duty cycle and said amplitude of drive current is based on an exhaust mass flow through said exhaust path (102).

8. The method as claimed in claim 6, wherein said fuel enrichment condition is at least one selected from a group comprising an open loop condition, a full load condition, at constant torque with best BSFC, during transients load conditions, and during safety of components.

9. The method as claimed in claim 1, wherein said air-fuel ratio of said exhaust gas is maintained without regard to a fuel injection quantity for said detected fuel enrichment conditions.

10. The method as claimed in claim 6, wherein said air-fuel ratio of said exhaust gas is maintained only by controlling said solenoid valve (120) of said SAI system (100).

, Description:Complete Specification:
The following specification describes and ascertains the nature of this invention and the manner in which it is to be performed:

Field of the invention:
[0001] The present invention relates to a controller for a Secondary Air Injection (SAI) system and a method of controlling thereof in a.

Background of the invention:
[0002] In a conventional system, the secondary air injection is used during the start, steady state and deceleration phases based on pressure pulsations and was controlled by a mechanical unit or by the Engine Management System (EMS). There is less control on the dilution of the exhaust gas on the air injection hence the conversion efficiency in the secondary air injection zones are low and also takes some time to increase the conversion efficiency after the air injection ends. By switching the exhaust lambda close to unity using the secondary air helps the conversion to be better in the air injection zones and as well have a better transition.

[0003] According to a prior art US5675968 a secondary air control apparatus for exhaust gas purifier is disclosed. The secondary air control apparatus constituted by an exhaust gas purifier of an engine, a feed quantity control valve for feeding secondary air, a secondary air heating device, and a controller for controlling the feed quantity of secondary air and the secondary air heating device. The quantity of secondary air to be fed is set in accordance with the operation conditions of an engine, and the secondary air to be fed is modulated in quantity and heated, so that it is possible to utilize the purifying effect of a catalyst efficiently.

Brief description of the accompanying drawings:
[0004] An embodiment of the disclosure is described with reference to the following accompanying drawing,
[0005] Fig. 1 illustrates a controller for the Secondary Air Injection (SAI) system, according to an embodiment of the present invention, and
[0006] Fig. 2 illustrates a method of controlling the secondary air injection system, according to the present invention.

Detailed description of the embodiments:
[0007] Fig. 1 illustrates a controller for the Secondary Air Injection (SAI) system, according to an embodiment of the present invention. The SAI system 100 comprises a reed valve 116 (also known as one way valve) which functions based on pressure difference. The reed valve 116 is connected to an air intake path (not shown) of the engine through a conduit 118. The reed valve 116 is connectable to an independent air source as well. A solenoid valve 120 is positioned in the conduit 118 to control the flow of air. The reed valve 116 opens into an exhaust path 102 of the engine. The exhaust path 102 comprises a lambda sensor 104, a catalyst 114 and an optional at least one temperature sensor 106. The temperature sensor 106 is positioned either before or after the catalyst 114, or at both the positions. A controller 110 controls the solenoid valve 120 to control injection of secondary air. The controller 110 is adapted to detect fuel enrichment condition based on any one of a signal from the lambda sensor 104 and a status of a variable stored in a memory 122 of the controller 110. The controller 110 then computes at least one of a duty cycle and an amplitude of a drive current required to drive the solenoid valve 120 to control injection quantity of the secondary air. The controller 110 then operates the solenoid valve 120, based on the computation, to maintain a desired air-fuel ratio and reduce emissions in the exhaust gas for the detected fuel enrichment condition. The lambda sensor 104 is also referred to as oxygen sensor or air-fuel ratio sensor.

[0008] The controller 110 calculates the quantity of secondary air required and then calculates the duty cycle and/or the amplitude of the drive current. The at least one of the duty cycle and the amplitude of drive current are computed based on an exhaust mass flow through the exhaust path 102 and a lambda value. The controller 110 then supplies the calculated drive current to the solenoid valve 120 to perform optimal conversion of the emissions in the exhaust gas. The pattern of the duty cycle and the amplitude is varied by the controller 110. The duty cycle and the solenoid excitation amplitude (also known as lift of the solenoid valve 120) is specific to the fuel enrichment condition of the engine. The amplitude and/or the duty cycle is decided based on the exhaust mass flow and the lambda value of the exhaust gas. At lower load and lower engine speeds the exhaust mass flow is less and the amount of air to be fed into the exhaust path 102 is also less, therefore the corresponding amplitude is low with a higher frequency of the solenoid valve 120. The higher speed and higher load zones of the engine require more air mass, hence the operating conditions changes to low frequency and high lift. The conditions are specific to a given conditions.

[0009] The exhaust mass flow is calculated based on the quantity of air intake and the engine speed. The engine speed is measured by an engine speed sensor 108 and the air intake mass is measured by the Manifold Absolute Pressure (MAP) sensor (not shown). The temperature of the catalyst 114 is either measured using the temperature sensor 106 or is calculated using a model stored in the memory 122 of the controller 110. A temperature sensor 106 to measure the exhaust temperature may also be used.

[0010] In an embodiment, the controller 110 is an Engine Control Unit (ECU) of the vehicle. Alternatively, the controller 110 is a dedicated control unit in communication with the ECU. The controller 110 comprises a processor, the memory elements 122 such as Read Only Memory (ROM), Random Access Memory (RAM), input/output ports, low/high-side drivers, Analog-to-digital and vice-versa convertors, all interconnected with communication channels such as bus. In accordance to an embodiment, the controller 110 is independent to the ECU. In another embodiment, the ECU is connected to the controller 110 to provide a trigger signal for initiation of control over the solenoid valve 120. The controller 110 controls the SAI system 100 independent of the fuel injection. The ECU controls fuel injection as per the desired torque demand by the driver, even though the requirement leads to rich combustion, but at the same time the controller 110 ensures optimal reduction of emissions while maintaining lambda value of the exhaust gas nearly equal to unity (average unity). The lambda sensor 104 of either version is usable i.e. one which gives the value of the air-fuel ratio and the one which detects only rich and lean combustion.

[0011] In accordance to an embodiment of the present invention, the controller 110 detects the fuel enrichment condition, even before the combustion with the input of high torque demand from a driver. Whenever a high torque demand is detected, the ECU sets the variable in the memory 122 of the controller 110 or a memory of itself, and activates the SAI system 100. The variable is then used by the ECU to perform the fuel injection to meet the driver demand. In the meantime, the controller 110 performs the secondary air injection to reduce emissions and also maintains the lambda value close to unity or on average unity. In the alternative embodiment, the controller 110 detects the fuel enriched state from the signal received from the lambda sensor 104 and then enables/activates the SAI system 100. The controller 110 controls the SAI system 100 in a closed loop manner with the help of lambda sensor 104, and maintains the lambda values between a pre-determined zone/values for optimal conversion of the emissions in the exhaust gas. The predetermined values is within three percent or less of the unity lambda value.

[0012] In an embodiment, the fuel enrichment conditions is at least one selected from a group comprising but not limited to an open loop condition, a full load condition, at constant torque with best BSFC, during transients load conditions, and during safety of components. The open loop condition corresponds to a failure of the lambda sensor 104, in which case, a modeled value of the lambda value pre-stored in the memory 122 of the controller 110 is used. The open loop condition also corresponds to a carburetor system, i.e. carburetor based fuel delivery system. In the carburetor system there exists no control over the fuel injection unlike the Electronic Fuel Injection (EFI) system. The fuel quantity is fixed for the given engine operating conditions based on the throttle opening and the engine speed. A closed loop SAI system 100 with the help of a lambda sensor 104 helps in maintaining the oxygen concentration of the exhaust gas before the catalyst 114 and also helps in switching the oxygen concentration of the catalyst 114 to improve the conversion efficiency of the catalyst 114. In the carburetor system, the closed loop SAI system 100 is used in at least one of the following fuel enriched conditions, during deceleration when the fuel cutoff is not possible the emissions are converted effectively, during higher load and higher engine speed zones and enrichment is needed based on torque requirement and engine overheat protection, during deviation occurrence due to ageing of mechanical components where the fueling is affected, and the like. Even possible during engine start, once the lambda sensor 104 is active.

[0013] The full load condition usually induces rich mixture for combustion which must be addressed in the exhaust path 102. The full load condition is detected based on the signal received from a Throttle Position Sensor (TPS) 112 for a throttle valve for a Wide Open Throttle (WOT) condition. The constant torque demand with best Brake Specific Fuel Consumption (BSFC), corresponds to case of hybrid vehicle, where the vehicle is operated at constant load but with rich combustion. To meet a higher torque demand the fuel mixture is enriched. The condition is detected by the signal from the status of the variable and/or the lambda sensor 104. The resultant exhaust gases are then treated with the secondary air for optimal reduction of emissions. The transient conditions correspond to sudden or abrupt changes in the throttle valve opening such as tip-in, during which, a rich air-fuel mixture is induced in the engine for combustion. The condition is detected by monitoring rate of change of the throttle position as detected by the TPS 112. The safety of components corresponds to safety of turbocharger or catalyst 114 which is required when the temperature of the exhaust gas is above a safe temperature level of the components. The temperature is lowered if above the safe level by the use of SAI system 100. The condition is detected by the respective temperature sensor 106.

[0014] In accordance to an embodiment, the controller 110 maintains a necessary oxygen concentration in the catalyst 114 for best emission conversion. The selection of catalyst 114 with respect to size and loading is specific to requirement and design. The oxygen holding capacity of the catalyst 114 is analyzed and the switching time of the exhaust lambda is found. A higher time of the lambda switching leads to the oxygen storage quantity going above the storage limits and reduction in the conversion efficiency of NOx and when deprived of oxygen, leads to the reduction in the conversion efficiency of hydro carbons and the oxides of carbon. In this condition if the oxygen is supplied the carbon molecules interact with the oxygen available and this leads to the exothermic reaction leading to very high temperatures. Hence, the oxygen concentration in the catalyst 114 is to be carefully maintained. Thus, the control of the solenoid valve 120 is used for maintaining the oxygen content of the catalyst 114, which enables for optimal emission reduction for both Carbon Monoxide (CO) and Hydrocarbon (HC) in rich combustion mixture and the NOx reduction during lean combustion mixture in the engine.

[0015] The air-fuel ratio of the exhaust gas is maintained without regard to a fuel injection quantity for the detected fuel enrichment condition. The fuel injection, even though rich mixture, is continued by the ECU, however at the same time the controller 110 operates the solenoid valve 120 to bring the air-fuel ratio of the exhaust gas to unity and also to reduce the emissions by switching between rich and lean values of the lambda value of the exhaust gas. Thus, the required torque is maintained as per the driver demand and still the emissions are controlled within the predetermined level. The air-fuel ratio of the exhaust gas is maintained only by a control of the solenoid valve 120 of the SAI system 100. The controller 110 is adapted in any one of a fuel based vehicle and a hybrid vehicle. The hybrid vehicle is any one of a series hybrid and a parallel hybrid vehicle. Further, the vehicle is any one of a two-wheelers such as motorcycle, scooter, moped, three-wheelers such as auto-rickshaw, a four-wheeler such as cars and the like.

[0016] In accordance to an embodiment of the present invention, the controller 110 is provided to generate oscillations of lambda value of the exhaust gas using only the SAI system 100 by injecting/purging air intermittently in the exhaust path 102. The lambda value of the exhaust gas is controlled similar to closed loop lambda control by the fuel injection, but here the fuel is not controlled, only the secondary air is controlled. The present invention is applicable for steady state operating applications like range extender, gensets etc. to reduce emission while combusting slightly richer lambda.

[0017] Fig. 2 illustrates a method of controlling the SAI system, according to the present invention. The SAI system 100 comprising the solenoid valve 120 to control injection of secondary air. The method comprising the steps of a step 202 comprising detecting fuel enrichment condition based on any one of the signal from the lambda sensor 104 and the status of the variable stored in the memory 122 of the controller 110 or the ECU. A step 204 comprises computing at least one of a duty cycle and an amplitude of a drive current required to drive the solenoid valve 120 to control injection quantity of the secondary air. A step 206 comprises, operating the solenoid valve 120, based on the computation, to maintain a desired air-fuel ratio and reduce emissions in the exhaust gas for the detected fuel enrichment condition. The method is performed by the controller 110.

[0018] The step 204 comprising computing the at least one of the duty cycle and the amplitude of drive current is based on an exhaust mass flow through the exhaust path 102. The fuel enrichment condition is at least one selected from a group comprising an open loop condition, a full load condition, at constant torque with best BSFC, during transients load conditions, and during safety of components. The air-fuel ratio of the exhaust gas is maintained without to fuel injection quantity for the detected fuel enrichment condition. The method is performed in any one of a fuel based vehicle and a hybrid vehicle.

[0019] In accordance to an embodiment of the present invention, the controller 110 is able to reduce the emissions by using only the SAI system 100 and without any specific change to fuel injection (controlled by the ECU). The fuel injection is done by the ECU to meet the driver demand, for example providing rich combustion mixture for specific time or continuously. In contrast to the prior art, where the fuel injection is also controlled along with the SAI system 100 to control emission but results in not meeting with the driver demand. In the present invention, the controller 110 controls the SAI system 100 and operates the solenoid valve 120 to control the injection quantity of the secondary air. The ECU controls the fuel injection to meet the driver demand, whereas the controller 110 performs emission reduction for the intended rich mixture without any compromise in the driver demand. The SAI system 100 and mass flow rate of the secondary air is controlled by the controller 110 to get a better conversion efficiency through the catalyst 114. The solenoid valve 120 is used in series with the reed valve 116 which does not allow the reverse flow of exhaust gases into the conduit 118. The solenoid valve 120 controls the secondary air flow acts like a gate/valve programmed to open and close (switching) at different frequencies based on the exhaust mass flow rate in order to maintain lambda value. The switching is continuous throughout the engine operating conditions/zones enhancing the overall conversion efficiency. The present invention also results in reduction in exhaust gas temperature hence providing a scope for ignition angle changes and reduction in enrichment requirement. The controller 110 enables reduction of exhaust emissions for an enriched lambda using secondary air injection modulation.

[0020] It should be understood that embodiments explained in the description above are only illustrative and do not limit the scope of this invention. Many such embodiments and other modifications and changes in the embodiment explained in the description are envisaged. The scope of the invention is only limited by the scope of the claims.