GB2410560A

GB2410560A - Onboard vehicle emissions measurement system

Info

Publication number: GB2410560A
Application number: GB0510355A
Authority: GB
Inventors: Alexander Willard
Original assignee: TECHNICAL CONCEPT SOLUTIONS LT
Current assignee: TECHNICAL CONCEPT SOLUTIONS LT
Priority date: 2004-11-26
Filing date: 2005-05-23
Publication date: 2005-08-03
Anticipated expiration: 2025-05-23
Also published as: GB0510355D0; GB0425964D0; GB2410560B

Abstract

An onboard vehicle system 100 to determine vehicle engine exhaust gas emissions includes an emissions unit 10, a vehicle diagnostic system 20 (e.g. OBD or OBD II system) and one or more vehicle systems 60a, 60b... (e.g. temperature sensor, ignition system, powertrain components). During calibration the emissions unit 10 is directly connected to, and receives data from, both the vehicle diagnostic system 20 and some of the vehicle systems 60a-c. Some of the vehicle systems 60d, 60e are connected to the diagnostic system 20 (figure 2). In use the emissions unit 10 is only connected to, and only receives data from, the vehicle diagnostic system 20, which in turn is connected to and receives data from the one or more vehicle systems 60a, 60b... The vehicle emissions are determined in real time based only on the data received by the emissions unit 10. The calculation of emissions may occur onboard in the emissions unit 10, or the data may be stored within the system and transmitted wirelessly via a communications interface 30 (e.g. mobile phone interface) to a remote station for processing. The emissions unit 10 may also be connected to a vehicle location unit 40 (e.g. GPS receiver) and position data used as an additional parameter in the calculation of emissions.

Description

1- 2410560

SYSTEM

The present invention relates to systems for determining the emissions of a vehicle engine, and in particular to onboard systems for real time determination of engine emissions.

It is well known that vehicle exhaust gases are a cause of environmental pollution. The gaseous pollutants are commonly subdivided into 4 broad categories: Hydrocarbons (HO), Oxides of Nitrogen (NOx), Carbon Monoxide (CO) and Carbon Dioxide (C02). Additionally, the exhaust gases comprise very small particulates (referred to as PM10s) of solid matter which have a significant effect on air quality. In North America and Europe legislation provides limits for the mass of each type of pollutant that is emitted when the vehicle is driven over a standard drive-cycle. The standard drive cycle is intended to be broadly representative of how vehicles are actually used (see for example, the Urban Dynamometer Driving Cycle from US Federal Test Procedure 72).

The emissions testing procedure cannot be expected to characterize a vehicle's emissions under all conceivable driving conditions. The standard drive cycles have been designed to be as representative as possible whilst still being a viable basis for an emissions test. Specific legislation exists in both North America and Europe to prohibit manufacturers from calibrating their engine control systems so that a significant increase in tailpipe emissions occurs when the vehicle is operating at speeds and loads not on the standard drive-cycle. This may be desirable as increased performance can be obtained from the vehicle if emissions are deliberately degraded.

The manufacturers are allowed to degrade a vehicle's emissions in order to protect the engine or emission control equipment fitted to the engine and a specific example of this is high load enrichment on spark-ignition (Sl) engines.

The speeds and accelerations required by this test are easily achievable by a modern vehicle and at no point does the engine get close to full load. At full load, - 2 depending on calibration, the Sl engine can be operating at an air-fuel ratio that is richer than the stoichiometric ratio (normally to protect the exhaust valves). When the engine is running rich, catalyst conversion efficiency is dramatically reduced and HC and CO emissions increase considerably. Additionally, there are defined windows for each gear change on the drive-cycle that last about two seconds. In practice a gear change can be performed quicker than this. Gear changes, especially fast ones, normally result in the engine being unable to control accurately the air-fuel ratio during these rapid transients. Inaccurate control of the air-fuel ratio results in poor catalyst conversion and consequently increased emissions of HC, NOx and CO.

Figure 1 shows a graphical depiction of the post catalyst pollutant mass of both hydrocarbons (Line A) and NOx (Line B) as the air-fuel ratio (AFR) is varied. For fuel rich AFRs the HC emissions rise sharply and the NOx emissions are low.

For fuel lean AFRs, the NOx emissions rise and the HC emissions are low.

When there is a stoichiometric AFR then the NOx and HC emissions are equal and at a relatively low level.

Compression-ignition (Cl) engines are capable of running at a wide range of air fuel ratios. In a Cl engine, the air-fuel ratio is varied in order to vary the torque output of an engine. Sl engines use a throttle to restrict the mass of air inducted into the engine to achieve the same torque reduction effect. The emissions of HC, NOx and CO are related to the air-fuel ratio and injection timing being used for a Cl engine. Richer mixtures tend to result in lower temperature and incomplete combustion, resulting in increased HC and CO emissions.

Injection timing also has an effect on the level of emissions. A Cl engine has an optimum injection angle for efficiency, although emissions considerations may force the controller to deviate from the optimum. Injection timing affects the peak temperature achieved during combustion. At high combustion temperatures, atmospheric nitrogen is fixated and NOx emissions arise. Other factors, such as instantaneous catalyst conversion efficiency, the use of exhaust gas recirculation - 3 (EGR), time since start and particulate trap state also affect tailpipe emissions on Sl and or Cl engines. Considering this range of factors, it can be seen that there are many modes of driving which generate more pollutants than the figures predicted by standard drive cycles.

Further to the standards for vehicle emissions over a defined drive cycle, the engine control system on a vehicle must also monitor the performance of emissions control equipment. If a fault is detected in the emissions control equipment that could result in an increase in tailpipe emissions, the engine controller warns the driver by illuminating a "check engine" lamp on the instrument cluster. This lamp is referred to as the "malfunction indicator lamp" and the driver is expected to take the vehicle for service if the lamp becomes illuminated. In order to detect these faults, the engine controller contains a suite of diagnostics (OBD) software that monitors engine performance. The OBD standard also specifies a protocol that allows proprietary software tools to interrogate the engine controller. This interface allows access to fault codes that are stored inside the engine controller. OBD must also support the reporting of real-time measurements made by the engine controller, such as engine speed, calculated load, etc. As part of the homologation process for a new vehicle, it will be subjected to an emissions test, during which a driver will be required to control the vehicle's speed to a set point as determined by the drive cycle. Exhaust gases from the vehicle are stored in a bag which is subdivided into a number cells, which allows a small gas sample to be collected once a second on the drive cycle. At the end of the test, the gas samples are analysed to determine the mass of HO, NOX, CO and CO2 in each sample. The equipment used to perform the gas analysis is bulky (usually one wall of a large room) and this technology is not suitable for on- vehicle processing of emissions. - 4

Alternative measurement techniques are now available: Fast NOX and HO sensors have been developed (for example by Cambustion in the UK) and allow instantaneous measurement of pollutant mass. This equipment is expensive and still relies on bottled reference gases, rendering this technology unsuitable for use for on-vehicle emissions testing. Fast NOX sensors, suitable for on-vehicle use, are in development for advanced Diesel emissions control systems but this technology is not yet mature. An equivalent HO sensor is not currently available and the cost of retrofitting these sensors to a vehicle and interfacing them to the emissions control systems will still be high.

A known technique is disclosed by US 6 604 033, in which a system is provided that uses exhaust gas sensors and data provided by an onboard diagnostic system to determine the emissions of a vehicle and whether or not they meet a regulatory threshold. The most significant disadvantage of the system disclosed in US 6 604 033 is that the exhaust gas sensors are expensive and will need to be installed to each vehicle for which the emissions are to be measured.

According to the present invention there is provided a vehicle emissions measurement apparatus comprising an emissions unit, a vehicle diagnostic system, and one or more vehicle systems, the emissions unit being in communication with the vehicle diagnostic system and the one or more vehicle systems being in direct communication with the emissions unit, in use, the vehicle diagnostic system receiving vehicle data from the one or more vehicle systems and the emissions unit receiving vehicle data solely from the vehicle diagnostic system, wherein the produced vehicle emissions are determined solely in accordance with the vehicle data provided by the emissions unit.

The advantage of the present invention is that the vehicle emissions can be determined without needing to access any of the vehicle's systems and only requires access to the diagnostic system of the vehicle. This provides an apparatus that enables the vehicle emissions to be determined that is cheaper to - 5 install, cheaper to operate and more reliable than the system disclosed in US 6 604 033.

The invention will now be described, by way of example only, with reference to the following Figures in which: Figure 1 shows a first view of a graphical depiction of the post catalyst pollutant mass of both hydrocarbons and NOx as the air-fuel ratio is varied; Figure 2 shows a schematic depiction of a system according to the present invention under calibration; Figure 3 shows a schematic depiction of a system according to the present invention in use within a vehicle; Figure 4 shows a schematic depiction of an a alternative embodiment of the present invention; and Figure 5 shows a graphical depiction of the multiple injection pulses used with a modern Diesel engine.

Figure 2 shows a schematic depiction of a system 100 according to the present invention under calibration. The system comprises emissions unit 10, vehicle diagnostic system 20, communications interface 30, vehicle location unit 40 and a plurality of vehicle systems and sub-systems 60a, Bob, ...,. The emissions unit is connected to the vehicle diagnostic system, which may be for example, the OBD or OBD-II system. The emissions unit 10 is also connected directly to a plurality of vehicle systems and sub-systems, for example to monitor the engine temperature. This enables additional data to be measured which can not be received directly from the vehicle diagnostic system or to provide a check against the data being provided by the vehicle diagnostic system. The emissions unit is also connected to the communications interface 30 and the vehicle location unit 40 (see below). - 6

When under calibration, the vehicle emissions are measured using conventional methods across a wide range of engine speeds and loads, environmental conditions, etc. and the data received from the vehicle diagnostic system and directly from the plurality of vehicle systems and sub-systems is also recorded.

These data sets can then be correlated so that in use, the vehicle emissions can be determined solely on the basis of the data received from the vehicle diagnostic system.

Figure 3 shows a schematic depiction of a system according to the present invention in use within a vehicle. The system comprises emissions unit 10, vehicle diagnostic system 20, communications interface 30, vehicle location unit and a plurality of vehicle systems and sub-systems 60a, Bob,

.,. In use the system is configured differently to the system disclosed in Figure 2 in that the emissions unit 10 has a direct connection to the vehicle diagnostic system 20 which is in turn connected to the of vehicle systems and sub-systems 60a, Bob, There is no connection between the emissions unit 10 and the vehicle systems and sub- systems 60a, Bob, .......DTD: In use, the emissions unit receives data solely from the vehicle diagnostic system and the vehicle emissions can be determined by the emissions unit in accordance with the data received from the vehicle diagnostic system. The vehicle emissions may be directly calculated based on the data received from the vehicle diagnostic system, one or more inferences of a vehicle state or parameter may be made based on the received data and the vehicle emissions determined based on the inferences and/or one or more data values, or the emissions value(s) may be determined from accessing a look-up table. The emissions unit comprises a processing unit, such as a CPU, that interprets the data received by the emissions unit from the vehicle diagnostic system and determines the vehicle emissions. The emissions unit further comprises data storage means, and preferably both volatile and non-volatile data storage means, for storing data received from the vehicle diagnostic system and determined vehicle emissions values. - 7

The emissions unit is also connected to a vehicle location unit 40, which may be a GPS receiver or a mobile phone receiver, that determines the position of the vehicle. The position data can be fed to the emissions unit and used to correlate data received from the vehicle diagnostic system, for example validating the speed or distance travailed by the vehicle. The communications interface 30 may be used by the emissions unit to transfer emissions data and/or the parameters used to determine the emissions data. The data can be downloaded to a remoter terminal that analyses the emissions data, driving style of the driver, routes travelled, etc. such that the usage of the vehicle can be monitored and appropriate feedback passed on to the driver. The communications interface may be a mobile telephone interface, for example using GSM, GPRS or 3G technologies to transmit the data. Other suitable communication technologies may be alternatively or additionally used.

Figure 4 shows a schematic depiction of an alternative embodiment of the present invention. Vehicle 120 comprises a system 100 according to the present invention, substantially as described above with reference to Figure 3. The system 100 further comprises a remote terminal 130 which is in communication with emissions unit 10 via the communications interface 30 and wireless communications network 140. In this alternative embodiment, some or all of the determination of the vehicle emissions is performed by the remote terminal; for example the emissions unit may send the data received from the vehicle diagnostic system directly to the remote terminal for the remote terminal to determine the vehicle emissions. Alternatively, the emissions unit 10 may perform some of the processing required to determine the vehicle emissions and then pass the data to the remote terminal to perform the rest of the data processing. The remote terminal may also store the vehicle emissions for subsequent analysis, along with the driving style of the driver, routes travelled, etc. such that the usage of the vehicle can be monitored and appropriate feedback passed on to the driver. The emissions unit 10 may store a data set in the data storage means and then the data set transmitted to the terminal at an - 8 appropriate interval. Alternatively, data may be transmitted to the remote terminal when it is received by the emissions unit.

The wireless communications network may be a mobile telephone network, for example using GSM, GPRS or 3G technologies to transmit the data. It will be understood that a the remote terminal may be connected to the wireless network via one or more fixed networks. The remote terminal is stationary and located external to the vehicle but the term 'remote' need not mean that the terminal is a long distance from the vehicle. For example, the remote terminal may be sited in a garage or workshop and a Bluetooth or WiFi network used to provide the wireless communication between the system and the terminal. It will be readily understood that other suitable communication technologies may be alternatively or additionally used.

Vehicle manufacturers go to considerable effort to calibrate the on-board diagnostics software inside the engine controller and thus the control software implemented inside a controller is a very accurate model of engine performance.

Thus the present invention uses data obtained from OBD for the determination of the vehicle emissions. If additional information is required then it will be necessary to add sensors to vehicle components or systems or to extract signals from one or more vehicle systems or the wiring loom of the vehicle. This will lead to an increase in cost and complexity for the system.

The vehicle diagnostic system can report data for a number of different vehicle parameters, such as, for example, vehicle speed, engine speed, throttle angle, engine temperature, etc. Further information regarding the OBD system and its capabilities can be found at htip://www.epa. gov/otaq/obd.htm. The emissions unit may receive data from, for example, a temperature sensor measuring the temperature of a catalytic converter (for spark ignition engines, see below), powertrain components, ignition systems etc. It will be readily understood that the sophistication and complexity of the model used to determine vehicle 9- emissions will in part be determined by the type and number of parameters that are used as inputs to the model.

Spark Ignition Engines Determining the emissions from Sl engines relies on a set of key parameters being known or estimated. Wherever possible an engine controller will operate an Sl engine at a stoichiometric air-fuel ratio (AFR) under closed loop control.

The OBD interface reports whether fuelling is currently closed or open loop, but a report of the actual AFR is not guaranteed by the OBD standard. In the event that a particular implementation of the OBD standard does not include a report of the actual AFR then an estimation or inference of the ratio must be made. Tables 1 & 2 below show some of the factors that will be used to determine an open loop AFR: Reasons for a rich AFR Primary measurement method Warm- up Estimate using coolant temperature from OBD port Catalyst/engine protection Estimate using engine load from the OBD port and measured data from a reference vehicle.

Driveability Estimate from engine load and data from a calibration exercise Exit from over-run fuel Estimate from engine load, calibration data and the shutoff closed loop fuelling flag Fault conditions Determine from malfunction indication on OBD Aged components Estimate from durability measurements on the reference vehicle and open loop fuelling flag from

OBD

Poor transient control Estimate from load and measurements on the reference vehicle Deliberate perturbation for Infer from diagnostics monitor status, reported over diagnostics tests the OBD link

Table 1 - 10

Reasons for a Primary measurement method lean AFR Fast catalyst lightDetermine from closed loop fuelling flag, time since start off and coolant temperature Fault conditions Determine from malfunction indication on OBD | Aged components Estimate from durability measurements on the reference vehicle and open loop fuelling flag from OBD Poor transient Estimate from load and measurements on the reference control vehicle Special operating Examples are over-run fuel shut-off and cylinder cutout for modes rev or torque limiting

Table 2

A modern three-way catalytic converter must have a high temperature in order to convert HO and NOx into H2O, CO2 and N2 and the conversion efficiency is dependent on a number of factors (see Table 3) below: Reasons for Primary measurement method reduced conversion efficiency Temperature Estimate from load (OBD), time since start, engine temperature (OBD), air-fuel ratio (estimated by the model) and ignition advance (OBD). It is believed that this estimation technique may lack the required accuracy and thus it may be necessary to directly measure this parameter AFR history A catalyst can be regarded as an oxygen storage device.

When a large amount of oxygen has been stored in the catalyst, it will be most efficient at HO and CO conversion.

When little oxygen is stored in the catalyst, it will be more efficient at NOx conversion. The history of the estimated AFR will be used to compute conversion efficiency.

Catalyst age A brand new catalyst does not exhibit the same conversion efficiency properties as one that has been fitted to a vehicle that has covered several thousand miles. A new catalyst will have unpredictable oxygen storage properties and measurements across a range of reference vehicles will be used to correlate conversion efficiency with vehicle age.

Table 3

Once the conversion efficiency and current AFR are known, the HO, CO and NOx emissions can be determined. - 12

Compression Ignition Engines It is anticipated that Cl engines will require direct monitoring of the injection pulse sequences and timing to determine accurately the emissions (this monitoring will typically be carried out in addition to the measurement and monitoring steps described above with reference to spark-ignition engines). Detailed injector pulse data is not available over OBD and will therefore have to be directly measured with accurate pulse timing being required if useful emissions data is to be calculated. Figure 5 shows a graphical depiction of typical Diesel injection multiple pulses as used for with a modern engine. Typically a short duration pilot injection 70 is followed by a main injection 80 having a much greater duration. A software or hardware timer may be used to capture the pulse duration. The measurement of the engine angle at which the pulse occurs requires timing against a pulse from a known reference point on the engine. An electronically controlled Cl engine will typically have Hall effect or variable reluctance sensors connected to the engine camshaft and crankshaft. These sensors are used by the Cl engine controller to schedule fuel injection and it may be possible to use non- invasive inductive coupling to sense the injector activity. Other sensing techniques which may be used include, without limitation, single- or multiple-axis accelerometers, serial connections, probes and pump sensors.

It is common for modern Cl engines to use exhaust gas recirculation (EGR) to reduce NOX emissions. It is proposed to estimate the amount of EGR being used, although direct measurement may alternatively be performed. Testing can indicate which approach is to be preferred for different vehicle types. Table 4 indicates some factors that influence the amount of EGR commanded by a typical control strategy: - 13 Input variable Primary measurement method Engine load Available over OBD Engine speed Available over OBD or direct measurement from injection sensing Engine temperature Available over OBD Air charge Available over OBD temperature Inducted air mass Available over OBD Time since start Calculated internally by the system

Table 4

The models for both spark- and compression-ignition engines will allow an accurate prediction of actual fuel used, independent from any calculations done inside the engine controller. However, vehicle emissions are known to be strongly dependent upon driver performance and thus a number of different driver behaviours can be measured or inferred, such as, for example: Time spent at or close to full load - minimising full load operation reduces a vehicle's emissions.

Time spent at high loads when the engine is cold - this leads to increased emissions.

Time spent in top gear at light loads - lower gears result in increased fuel usage and emissions for a given mileage.

Time spent with engine running and vehicle stationary.

Number of short journeys.

Thus it is possible to determine what the effect of the driving style an individual driver has on the emissions of their vehicle. This enables driver training to be provided as appropriate. - 14

The rate at which the vehicle emissions are computed needs careful consideration. If it is too slow, transient conditions where high emissions are likely may be missed. As the OBD port provides data-updates fairly slowly (a few samples per second) then there is little value in calculating the emissions value at a significantly greater rate than this. Thus, in the context of the present invention, real-time determination of vehicle emissions may be interpreted to mean that an emissions value is determined at least once a second, and preferably approximately 10 times per second.

It will be readily understood that the present invention may be used with any type of vehicle having an internal combustion engine and also with other internal combustion engines. -

Claims

1. A vehicle emissions measurement apparatus comprising an emissions unit, a vehicle diagnostic system, and one or more vehicle systems, the emissions unit being in communication with the vehicle diagnostic system and the one or more vehicle systems being in direct communication with the emissions unit, in use, the vehicle diagnostic system receiving vehicle data from the one or more vehicle systems and the emissions unit receiving vehicle data solely from the vehicle diagnostic system, wherein the produced vehicle emissions are determined solely in accordance with the vehicle data provided by the emissions unit.

2. A vehicle emissions measurement apparatus according to claim 1, wherein, in use, the determination of the emissions produced by the vehicle is made onboard the vehicle.

3. A vehicle emissions measurement apparatus according to claim 2, wherein, in use, the emissions unit determines the emissions produced by the vehicle.

4. A vehicle emissions measurement apparatus according to claim 1, wherein the system further comprises a communications interface and a remote terminal, the communications interface, in use, providing a connection to the remote terminal such that, in use, the vehicle data received by the emissions unit is transmitted to the remote terminal.

5. A vehicle emissions measurement apparatus according to claim 4, wherein the remote terminal determines vehicle emissions solely in accordance with the vehicle data provided by the emissions unit.

6. A vehicle emissions measurement apparatus according to any preceding claim wherein a determination of the emissions produced by the vehicle is made at a rate of at least 1 per second.

7. An vehicle emissions measurement apparatus according to claim 6 wherein a determination of the emissions produced by the vehicle is made at a rate of 10 per second.

8. A vehicle emissions measurement apparatus according to any preceding claim wherein the vehicle comprises a spark injection engine and the system is configured to determine the air-fuel ratio in the engine.

9 A vehicle emissions measurement apparatus according to claim 8, wherein the air-fuel ratio is determined by the vehicle diagnostic system.

10. A vehicle emissions measurement apparatus according to claim 8, wherein the air- fuel ratio is determined by the emissions unit in accordance data received from a plurality of vehicle systems.

11. A vehicle emissions measurement apparatus according to any of claims 8 to 10, wherein the system further determines the conversion efficiency of the catalytic converter.

12. A vehicle emissions measurement apparatus according to any of claims 1 to 7 wherein the vehicle comprises a compression injection engine and the system is configured to determine one or more parameters or one or more injection pulses.

13. A vehicle emissions measurement apparatus according to claim 12, wherein the system is further configured to determine the exhaust gas recirculation in the engine. - 17

14. A vehicle emissions measurement apparatus according to claim 12 or claim 13 wherein the vehicle comprises a spark injection engine and the system is configured to determine the air-fuel ratio in the engine.

15. A vehicle emissions measurement apparatus according to any of claims 12 to 14, wherein the air-fuel ratio is determined by the vehicle diagnostic system.

16. A vehicle emissions measurement apparatus according to any of claims 12 to 15, wherein the air- fuel ratio is determined by the emissions unit in accordance data received from a plurality of vehicle systems.

17. A vehicle emissions measurement apparatus according to any of claims 12 to 16, wherein the system further determines the conversion efficiency of the catalytic converter.

18. A vehicle emissions measurement apparatus according to any preceding claim wherein the system further comprises a vehicle location unit in communication with the emissions unit.

19. A vehicle comprising a vehicle emissions measurement apparatus according to any preceding claim.