Method and system for heating a catalytic converter before testing a vehicle exhaust system

Field of the invention

The present invention relates to vehicle exhaust emission systems, and in particular to a method for heating a catalytic converter of a vehicle. The present invention also relates to a method for testing exhaust systems of vehicles having a catalytic converter.

Background of the invention Due to increasing governmental concerns regarding pollution and air quality, in particular in urban areas, numerous exhaust standards or regulations from various jurisdictions, e.g., in North America, Europe and Asia, have been generated.

For example, the European emission standards are sets of requirements defining the acceptable limits for exhaust emissions of new vehicles sold in EU member states. These standards are commonly denoted Euro 1, Euro 2, Euro 3, Euro 4 and Euro 5, and consist of increasingly stringent requirements . Emissions of nitric oxides (N0 _x) , hydrocarbons (HC), carbon monoxide (CO) , and particulates are regulated for most types of vehicles in these standards. Compliance to such regulations are usually determined by running the vehicle engine at a standardised test cycle. However, even if a particular vehicle has proved to be compliant with current emission requirements, components of the vehicle exhaust emission control system eventually can be subject to a fault and need replacement. Such faults normally generate settings of, or activation of "flags" (diagnostic trouble codes) in the vehicle control system, which flags later can be read by an automobile mechanic (garage mechanic)

using a suitable vehicle diagnostics tool, implemented, e.g., in a laptop or desktop computer connected to the vehicle. The diagnostics tool can also constitute an integrated part of the vehicle. The fault is also usually indicated to the vehicle driver, e.g., by activating a warning light or text message, so as to inform the driver that exhaust emissions are too high and allow the driver to contact a garage for taking proper actions .

The activation of flags also often involve, at least with regard to trucks, consequence actions such as, e.g., reducing available torque to a percentage of the maximum torque if there is a malfunction in the exhaust system, having as result that vehicle engine use is limited, e.g., by limiting the available torque, e.g., to 60% of maximum torque. In such situations it is common that a garage mechanic performs necessary vehicle (exhaust control system) service and/or parts replacement in order to ensure proper operation of the exhaust emission control system once again.

If the vehicle is a private car, it can be enough that the mechanic performs what he believes are the proper actions, and then resets the flags of the vehicle control system so that a fault no longer is indicated.

With regard to heavy vehicles, however, such resetting of flags after service is, in many regions, not allowed. Instead, the vehicle has to perform self-tests, e.g., with regard to exhaust emissions, by measuring emissions using a vehicle onboard sensor, to ensure that the performed repairs actually have fixed the exhaust emission problem. When performing such onboard measuring, however, tests have to be performed for various engine loads, e.g. high, medium, and low engine load. Further, the components of the exhaust control system, such as

the catalytic converter, have to be heated to normal working temperature in order to ensure normal operation.

Therefore, the vehicle is many times returned to the driver without the invalidation having been performed. This has as result that when the vehicle is returned from service, it may take a while before all required self-tests have been performed, since tests may have to be performed for various driving conditions. If such a vehicle is used for urban deliveries with frequent starts and stops, it may take days or weeks before all tests have been performed, and the vehicle is back to being fully operational.

One obvious solution to this problem would be that the mechanic takes the vehicle for a longer test drive. This however, can be rather time consuming, not to mention costly. Consequently there exists a need for a simplified method of validating that a fault has been repaired.

Another solution is to bring the vehicles to a central testing facility, and perform the tests on a stationary testing apparatus, such as a vehicle dynamometer, in order to perform necessary self-tests in a controlled manner. This however, has the disadvantage that the distance between garage and testing facility easily can exceed the distance necessary to perform a successful test drive.

In conclusion, there exists a need for an improved method for testing exhaust systems of vehicles having a catalytic converter that overcomes, or at least mitigates the disadvantages of current solutions.

Summary of the invention

It is an object of the present invention to provide a method that solves the above mentioned problem. This object is

achieved by methods according to the characterising portions of claims 1 and 11, respectively.

The present invention relates to a method for heating a catalytic converter of a vehicle, said vehicle comprising an internal combustion engine and a throttling device for throttling a combustion exhaust stream from said engine. The method comprises the step of, when said vehicle is in a stationary state wherein the vehicle drive wheels supply substantially no load to said engine, controlling said throttling device and a fuel amount to be supplied to said engine such that at least a load is applied to said engine, wherein said load is above engine idling load, such that the exhaust gas generated in a combustion process of said engine is heated to such temperature that said catalytic converter can be heated to a temperature exceeding a predetermined temperature level.

This has the advantage that the catalytic converter of the vehicle can be heated to its normal working temperature without having to take the vehicle for a test drive, or use a vehicle dynamometer.

Further, according to another aspect of the present invention, it is provided a method for performing a test of the vehicle exhaust emission system, in which the above described heating method is used to set engine load to desired test points, and wherein exhaust emissions at one or more test points are used to evaluate proper function of said exhaust emission control system.

This has the advantage that tests that otherwise require quite extensive driving, e.g., in order to perform exhaust emission tests for various engine loads, such as high, medium, and low engine loads, and wherein the catalytic converter has to be heated to a normal working temperature in order to ensure

normal operation, can be performed with the vehicle standing still when using the present invention.

Brief description of the drawings

Fig. 1 shows an example an exhaust emission control system in a vehicle with which the present invention may be advantageously utilised.

Fig. 2 shows a flow diagram according to an exemplary process of the present invention.

Fig. 3 shows a flow diagram according to another exemplary process of the present invention.

Detailed description of preferred embodiments.

Fig. 1 discloses a vehicle engine 118 and exhaust emission control system of a vehicle 200. The exhaust emission control system consists of an SCR (Selective catalytic reduction) catalytic converter 201, a Urea tank 202, which is connected to a Urea Dosing System (UDS) 203. SCR is an after-treatment that requires a, usually urea-based, additive or reductant to reduce NO _x emissions. The urea, mixed with air, is injected into the exhaust gas stream resulting from the engine combustion to cause a chemical reaction in the catalytic converter, which usually is integrated in a silencer. The gaseous or liquid reductant ammonia (urea, when heated, forms ammonia) is added to the exhaust gas stream from the engine upstream from the catalytic converter. The reductant is absorbed onto the catalytic converter 201 walls, and when the exhaust gas passes through the catalytic converter 201, the reductant reacts with NO _x in the fuel gas to form water vapour (H20) and nitrogen gas (N2) .

Further, a temperature sensor 204 is arranged in, or in proximity to the catalytic converter to measure its current temperature, and a NO _x sensor 205 is provided in the exhaust

gas stream leaving the catalytic converter in order to allow measurements of the exhaust gas content so as to allow a vehicle control system to detect faults/malfunctions in the exhaust emission system. Fig. 1 also discloses an actuator operated throttling device 206 for throttling the exhaust gas stream leaving the engine, the throttling device is commonly known as an exhaust brake. Exhaust brakes are used to create a retarding effect on the driving wheels of the vehicle. When throttling the exhaust stream, the exhaust is being compressed, and while no fuel is being applied the engine will strive to retard the vehicle. The amount of negative torque generated is usually directly proportional to the back pressure of the engine.

Fig. 1 also discloses an electrical control unit 207 in form of an engine control unit which controls the engine functions of the vehicle. The control unit 207 can be connected to a communication bus (not shown) for communication with other control units and/or electrical components of the vehicle. Such communication bus systems are usually of CAN (Controller Area Network) type, although other kinds of suitable communication technologies can be used as well, e.g., TT-CAN or FlexRay. Among these functions of the control unit 207, there is an exhaust emission diagnostics system, which supervises and controls operation of the exhaust control system. For example, the diagnostics system monitors the NO _x levels by means of said sensor 205 and the catalytic converter temperature using the temperature sensor 204. If the exhaust emission control system is subject to a fault, this fault can, for example, be identified by the diagnostics system, e.g., by concluding that the current NO _x level is too high, or catalytic converter temperature diverges from a normal working temperature range. In the present description and claims, the term "normal working temperature" is intended to have the

meaning: a temperature at which the catalytic converter works with an efficiency such that, e.g., reduction of exhaust gasses leaving the vehicle engine exceeds a threshold.

The control unit 207 comprises means 208 for receiving various signals from, e.g., various sensors, such as temperature sensor 204 and NOx sensor 205. These signals can be received, e.g., via messages transmitted on a CAN bus or, as indicated in the figure, by direct links 212, 213. The received signals, together with other information, such as data transmitted from other control units, can then be used in a data processing unit 209. The data processing unit 209 can, using the received sensor signals and data, and by means of a computer program which can be stored in a computer program product in form of storage means 211 in, or connected to the processing unit 209, perform engine control calculations for controlling engine operation and generate control signals for transmission, by means of output means 210, to, e.g., various electrically operated engine functions and the UDS system 203. The storage means can, for example, consist of one or more from the group: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM) , Flash memory, EEPROM (Electrically Erasable PROM), hard disk drive.

As was mentioned above, faults normally generate settings of, or activation of "flags", which can act both as fault indicators as well as guidance for a mechanic trying to locate the probable cause of the fault. As also was mentioned above, consequence actions are usually taken, such as reducing available torque to a percentage of the maximum torque.

The present invention provides a method that enables heating of the catalytic converter to normal working temperature with a stationary vehicle, without the need of a vehicle dynamometer, i.e., the vehicle can be standing still with the

gearbox in a neutral position, and, consequently, with no load applied to the vehicle engine by the transmission system, i.e., the vehicle drive wheels supply no load to said engine.

According to the present invention, an exhaust gas throttling device (such as the above described exhaust brake or a VGT- turbo (Variable Geometry Turbine) or a combination thereof) is used to enable heating of the catalytic converter right up to a set temperature level, e.g., the normal working temperature, which, for example, may be 190°C-300°C or even higher, e.g., up to 1000 ⁰ C.

In the prior art, the exhaust brake has been used to heat the engine, at least to some extent, and also to maintain the temperature of an already heated particulate filter. For example, if the normal engine operating temperature is 8O ⁰ C - 9O ⁰ C, it has previously been possible to heat the engine to about half that temperature. However, it has not previously been realised that the exhaust brake can be used to such extent that the catalytic converter can reach normal working temperature while the vehicle is standing still. Merely standing still with idling engine, however, will not provide a sufficient engine load to accomplish the necessary heating.

Fig. 2 shows a flow diagram 300 of an exemplary embodiment according to the present invention, according to which the catalytic converter is heated to a normal working temperature. The normal working temperature can, for example, be a minimum temperature of a temperature range that the catalytic converter must reach in order to start the desired exhaust emission control. The process starts in step 301, in which the process will remain for as long as no catalytic converter heating is requested. If, on the other hand, heating is requested, e.g., by a diagnostics system, as will be disclosed below, the process continues to step 302. In step 302 the

temperature of the catalytic converter is measured, using the temperature sensor 204. If the temperature is higher than a predetermined temperature level, e.g., the lowest temperature at which the catalytic converter is considered to operate normally, e.g., 200 ⁰ C, the process continues to step 306, where it is reported that the catalytic converter has reached its normal operating temperature. If the temperature, in step 302, is determined to be below the temperature level, the process continues to step 303, wherein a suitable engine load is determined, e.g., based on the current catalytic converter temperature. Alternatively, the load can be set to the minimum load at which exhaust gasses will reach a high enough temperature to ensure the desired heating of the catalytic converter. This load is substantially greater than the relatively low load the engine is subjected to during stationary engine idling, e.g., 5% ore more of the total power the engine can deliver. In order to obtain the desired engine load, the engine must be set to the desired operating point by adjusting engine speed and the amount of fuel and its delivery into the engine. In order to determine suitable fuel amount and engine speed, the vehicle control system can have a stored table with loads for various combinations of engine speed and fuel amount. Further, the injection time (angle) and/or injection length and/or number of injections can, if necessary, be adjusted as well. A correct load is obtained when the predetermined amount of fuel is injected, and the engine speed corresponds to the desired speed. If the engine load is too low, the desired fuel amount can not be injected without the engine speed racing. Therefore, engine speed, fuel amount and amount of exhaust brake applied is sequentially and/or concurrently controlled in step 303, whereafter it in step 304 is determined whether the desired load is obtained. If not, the process returns to step 303 for further

adjustment, otherwise it continues to step 305. When the desired load has been set, it can very accurately be kept at a constant level. When the desired engine load has been achieved, the temperature of the catalytic converter is measured again, in step 305, and if it has reached normal working temperature, the process continues to step 306. Otherwise the system waits in step 305 and measures the temperature, e.g., continuously or at predetermined intervals. However, in order to prevent the process from endlessly measuring the temperature, a maximum time T can be set, and as long as t<T the process remains in step 305. If, on the other hand it is determined that t>T the process continues to step 307, wherein it is determined that the heating is aborted.

The above described method of using the exhaust brake enables that high engine loads can be reached, e.g., up to 40-50% of the power the engine is capable of producing. In theory, the exhaust brake can be set such that the engine delivers higher power than 40-50%. This, however, may cause breakdown of components such as exhaust brake actuator. Consequently, the upper limit of the applied load using the exhaust brake should preferably be limited, e.g. to 50% of the maximum load. Still, during normal driving such high loads are only reached during conditions such as heavy acceleration, high-speed driving and hill driving. In order to reduce the stress on the exhaust brake, external aggregates such as AC compressor, air compressors can be set to apply maximum load so as to reduce the load the exhaust brake must deliver.

Further, the present invention is capable of maintaining a desired load for a desired period of time, which is advantageous, e.g., when performing exhaust emission tests in the manner described below.

Consequently, the present invention provides a method that in a simple manner is capable of heating a catalytic converter of a stationary vehicle to its normal working temperature.

In fig. 3 is shown a flow diagram 400 of a process for self- invalidating activated fault flags. As was mentioned above, tests relating to fault in the exhaust emission control system has to be performed for various engine loads. It is a further object of the present invention to provide an inventive method for performing diagnostics tests of the vehicle exhaust emission system, in which the above described heating method is used to set engine load to desired test points.

The process starts in step 401, wherein it is determined whether the catalytic converter temperature is above a predetermined temperature level, the temperature level being a normal working temperature, e.g., the above mentioned 200 ⁰ C. If the current temperature is below the temperature level, i.e., below a normal working temperature, the process continues to step 402, wherein the above mentioned heating process is initiated for execution. If it is determined, in step 401, that the working temperature is at or above the minimum normal working temperature, an engine load test point TP is set to test point 1. For example, there may be a number of engine loads for which the exhaust emissions must be measured and approved. The process then continues to step 403, wherein the engine is set to work at TP 1, e.g., in a similar manner as was described above with reference to fig. 2. It is then determined, in step 404, if the desired engine load is reached. If it is determined that the desired engine load is not reached, the process can, e.g., wait for a predetermined time to see if the desired load is achieved. When the predetermined time lapses an error message can, e.g., be generated. If the desired load is reached, on the other hand,

the process continues to step 405, wherein urea dosing is set to zero, whereafter the process waits for a predetermined time. This is done in order to consume ammonium remnants in the catalytic converter, so that measurements can be started using a "clean" system. When said predetermined time has lapsed, which can be in the order of minutes, e.g., 5 or 15 minutes, the process continues to step 406, wherein the exhaust emissions are measured for the system using no urea additive. This measurement is performed in order to provide the system with a reference value, i.e., emission value for the catalytic converter without addition of any additive, for the particular test point TP. The process then continues to step 407, wherein urea dosing is started. When it is determined that the dosing is at a normal level, a new measurement is performed in step 408. When both the "raw" emission measurement and the urea influenced measurement have been performed, an emission ratio is calculated for these measurements in step 409. If the improvement, i.e., emission reduction is above a predetermined ratio, the behaviour of the exhaust emission system is approved for the test point, and the process continues to step 410, otherwise the process continues to step 414. In step 410 it is determined whether measurements are to be carried out for further test points. If so, the TP counter is incremented by one in step 411, and the process returns to step 403, wherein the engine is set to work at TP 2 (or 3 or 4 or...) . If not, the process continues to step 412, wherein it is determined whether all test points have been approved, and if so, fault indicating flags, and consequence actions thereof, are reset in step 413, and the vehicle is determined fully operational. If not, a message indicating remaining fault is generated in step 414, e.g., for alerting the driver or garage mechanic. As an alternative to requiring that all test points are approved, it can, e.g., be

enough that only specific test points fulfil the set criteria, or that the result of individual test points are weighted together, and the approval/disapproval of the exhaust emission system is based on the weighted result, in which case the process of fig. 3 is changed in accordance therewith.

As was mentioned above, the load can be very accurately controlled, and this has the advantage that emissions for a particular test point, the expected emissions can be stored in a memory in the system, and compared to the measured emissions. Therefore, the present invention also allows a method wherein only the "treated" emissions are measured, since absolute values of maximum emissions for a particular test point can be stored and compared with. Preferably, engine temperature is monitored during the test, so as to prevent engine overheating due to poor ventilation.

Further, the present invention allows that the same load can be accomplished for, in principle, an arbitrary engine speed. This has the advantage that emission for a few, beforehand known to be critical, test points, and if emissions at these points are ok, the system function is approved of. Instead of requiring acceptable emissions at all test points, it can be enough that only part of the test points have approved emissions, e.g., 3 or 4 out of 5.

Consequently, the present invention allows that exhaust emission control system diagnostics can be performed while the vehicle is standing still, and since this process may take a while, the diagnostics test can be initiated, whereafter the garage mechanic can attend to another vehicle while the test is running. The present invention also has the further advantage that while the exhaust emission diagnostics test is running, other onboard tests requiring a loaded engine working at its normal operating temperature can be performed as well,

thereby further reducing the need for time consuming test drives .

In the above description, an onboard exhaust emission sensor is used to perform exhaust emission measurements. In principle, however, an onboard sensor is not necessary to perform the measurements according to the present invention, since measurements sensors of, e.g., a garage can be used instead since the required measurements can be performed while the vehicle is standing still. The onboard sensor, however, has the advantage that the required measurements can be performed, in practice, anywhere the vehicle can be parked. For example, the tests can be initiated by the driver when found suitable.

Further, in the above description the normal operating temperature of said catalytic converter has been described as a specific temperature or temperatures above a predetermined temperature level. It is to be understood that the normal working temperature can be determined to be within a certain temperature range, e.g., between 200 ⁰ C and 300 ⁰ C.