Things About ECU Calibration
Calibration is like sharpening a knife; based on the material, hardness, and shape of the knife, we create a suitable knife. Perfect calibration brings out the best performance of the knife and highlights the key points!
1. Goals of Engine Matching Work:
1. Through engine bench matching, ensure the engine has good steady-state performance, achieving the engine’s design power, torque, and fuel consumption performance while ensuring reliability (no knocking, no overheating).
2. By matching the engine in the vehicle, ensure coordination with other systems (various electrical loads, transmission system, brake system, catalytic converter, etc.) to guarantee good starting idle performance, driving comfort, and emission performance under various environments and working conditions. A comprehensive onboard diagnostic system (OBD) matching is also required.
3. Through road environment tests such as high temperature, extreme cold, and high altitude, comprehensively validate the matched performance to ensure the engine and vehicle meet strict safety, environmental, and driving comfort standards under various conditions.
For gasoline engines, the technology involves controlling the intake (reasonable intake phase, throttle opening, etc.), fuel injection (optimal air-fuel ratio), and ignition (appropriate ignition timing) coordination.
It should be noted that the maximum potential of engine power and economy depends on the engine’s design. The engine matching work is merely an effort to excavate or coordinate these potentials. For example, a gasoline engine changes output torque and power by altering intake volume; the design of the intake and exhaust systems determines the engine’s charging efficiency. Thus, once the engine structure is determined, the maximum intake volume at a specific condition is also set, determining the engine’s power performance. Similarly, the engine’s efficiency, i.e., fuel economy, depends on combustion efficiency and mechanical efficiency. By adjusting injection timing, fuel amount, and ignition timing, fuel economy can be improved, but it cannot exceed the limits set by the engine’s design.
2. Engine Management System (EMS) and Electronic Control Unit (ECU)
The Engine Management System (EMS): In 1979, BOSCH integrated electronic control of ignition timing and fuel quantity, developing Motronic, which introduced knock control and exhaust recirculation to meet increasingly stringent performance and emission requirements. Its electronic control covers the entire engine and is centered on fuel quantity and ignition timing control.
Currently, various engine electronic management systems have become decisive factors in improving fuel economy and meeting stricter emission regulations.
The engine management system centers around the Electronic Control Unit (ECU), which receives various information from sensors, processes and analyzes it, then sends control signals to various actuators. In engine matching work, various parameters of the ECU are set through various matching experiments to achieve the goals of engine matching work.
3. Engine Matching Work
Engine matching work refers to setting appropriate values for various parameters of the engine controller (ECU) under a specific engine management system (EMS) through various matching projects to meet the requirements for the best air-fuel ratio and ignition timing under different operating conditions determined by the vehicle’s performance, economy, reliability, safety, and emissions.
Engine matching work involves setting suitable values for numerous matching parameters, which vary with the complexity of the system and the sophistication of the control software. Some of these matching parameters are characteristic values, some are two-dimensional characteristic curves, and others are matrices (three-dimensional characteristic maps). Determining matching parameters requires extensive experimentation and data analysis.
4. Standard Process for Engine Matching
Generally, once the project is determined, engine matching work can be divided into four phases: project preparation, basic matching, fine matching, and approval phase, until the final matching data is approved (SOP phase), which typically takes about 18 months (completing high-temperature, high-altitude, and high-load tests).
5. Main Content of Engine Matching Work:
1. Matching Preparation
Install the engine and its related accessories on the test bench.
Matching vehicle inspection and preparation: To ensure matching data covers manufacturing tolerances, each model state must have at least two matching vehicles.
2. Basic Matching on Engine Test Bench (Approx. 40 Working Days)
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Sensor Signal Check (Approx. 3 Days)
Ensure all sensors (water temperature sensor, air temperature sensor, HFM, etc.) input and output signals are accurate. The ECU should correctly receive signals through A/D conversion, and all actuators should function normally (carbon canister solenoid valve, fuel injectors, ignition coils, etc.). Ensure the system operates correctly.
2. Calibrate Fuel Injection End Time (Approx. 2 Days)
The fuel injection end time determines the atomization quality and the formation of the mixture, which directly affects engine combustion. The calibration of fuel injection end time is primarily based on the HC emission content in the exhaust. Determine the most suitable fuel injection end time.
(a) Air-fuel ratio pulse spectrum (b) Ignition timing pulse spectrum
3. Calibrate Load Model (Approx. 15 Days)
Accurately determining the amount of fresh air entering the cylinder is the basis for engine control. Due to intake pulsation and residual exhaust gas in the cylinder, as well as changes in intake volume caused by exhaust recirculation, crankcase ventilation, and fuel tank ventilation, it is impossible to rely solely on sensors for accurate intake volume determination. The load model measures intake pressure, fuel consumption, raw emissions, and air-fuel ratio, along with various environmental and engine parameters, and calculates and simulates intake characteristics under various operating conditions using a series of mathematical models and functions to accurately determine the amount of fresh air entering the cylinder.
The workload required to calibrate the load model varies with the complexity of the system configuration, such as variable intake systems (switching between long and short intake pipes), variable valve timing systems, exhaust recirculation systems, and turbocharging systems, which significantly increase the matching time for the load model.
4. Calibrate Fuel Injection Amount (Approx. 2 Days)
After matching the load model, the theoretical calculation can determine the fuel injection amount for achieving an air-fuel ratio of λ=1 at various operating points. However, due to deviations in the fuel supply system, the air-fuel ratio may deviate from 1 in certain situations, requiring corrections here.
5. Torque Model (Approx. 15 Days)
The engine’s torque is the central variable of the engine control system, so the first step is to match the maximum torque the engine can produce at various speeds and throttle openings under conditions of air-fuel ratio equal to 1 and various ignition timing angles. This is the basic value for engine torque control (corresponding to 100% air-fuel ratio efficiency and 100% ignition angle efficiency).
Then, by measuring torque under various air-fuel ratios (generally from 1.1 to 0.9) and various ignition angles (from maximum ignition advance to misfire), efficiency characteristics regarding air-fuel ratio and ignition angle can be obtained. Thus, in future engine control, it suffices to mention engine torque and the efficiency of the air-fuel ratio and ignition advance angle that achieves that torque, allowing the engine control system to calculate the corresponding intake volume (throttle opening), fuel amount, and ignition advance angle.
6. Calibrate Ignition Advance Angle (Approx. 4 Days)
Before calibrating the ignition advance angle, preliminary matching of the knock control’s knock recognition part should generally be completed (see knock control matching).
Matching Principle: At different speeds and load points, control λ=1, and find the ignition advance angle that maximizes output torque without knocking.
7. Validate Matching Data (Approx. 2 Days)
Analyze test data, input relevant matching data into the model, and finally compare the model’s output with the actual engine test bench output. Correct deviations.
8. External Characteristics (Approx. 2 Days)
After completing the matching of knock and catalytic converter overheating protection, under full throttle conditions, adjust λ (adjust the full load enrichment coefficient) at each speed point to ensure the engine reaches the design maximum power and output torque while minimizing specific fuel consumption.
3. Knock Control Matching (Approx. 20 Working Days)
Knocking is an abnormal combustion; severe knocking can damage the engine. Modern high-compression engines are more prone to knocking, making knock matching an essential part of the engine matching process. A dedicated chip for analyzing and processing knock sensor signals is included in the engine controller. Knock control matching is a complex task requiring numerous specialized tools and equipment (such as spark plugs with combustion pressure sensors, dedicated knock matching controllers, knock measurement analyzers, etc.).
1. Knock Recognition (Approx. 15 Days)
Measure combustion pressure in the cylinder on the test bench and use a knock measurement analyzer to accurately identify and determine whether knocking occurs. Simultaneously, the knock sensor’s signal is input to the ECU, processed through amplification, bandpass filtering, rectification, and integration, and the final integrated signal is used by the ECU to determine whether knocking has occurred. This signal is also used to determine the amplification factor and the center frequency of the bandpass filter.
2. Dynamic Knock (Approx. 5 Days)
Dynamic knocking refers to accelerating knocking and high-speed knocking. Its recognition complexity arises from changes in engine speed and load causing vibrations and noise that make it difficult to identify.
Matching Method: Identify knocking under various dynamic working points, such as tip-in and rapid acceleration situations where vibrations and noise are significant, by delaying the ignition advance angle to avoid knocking.
3. Knock Function Diagnosis (Approx. 2 Days)
Test the sensor’s output in fault and normal working states, storing it in the controller for diagnosing open and short circuits in the sensor.
4. Hot Start Performance Matching (Approx. 40 Working Days)
1. Oxygen Sensor Closed-Loop Control (Approx. 10 Days)
The oxygen sensor is used to measure the excess air coefficient λ in the exhaust.
λ represents the deviation of the actual air-fuel ratio from the theoretical value (14.7:1).
λ = intake air volume / air volume required for stoichiometric combustion
λ = 1: indicates that the intake air volume is equivalent to the theoretical requirement.
The catalytic converter has the highest conversion efficiency for HC, NOx, and CO at λ = 1.
The goal of oxygen sensor closed-loop control is to accurately control λ within 1±0.03, ensuring the catalytic converter achieves maximum catalytic conversion efficiency, compensating for λ pre-control deviations and dynamic shifts in mixture concentration.
Through λ self-learning, eliminate λ deviations caused by component manufacturing and fuel quality.
If there are downstream sensors, their functions are a) monitoring catalytic converter aging, b) improving the accuracy of oxygen sensor closed-loop control. Matching time also increases by about 10 days.
2. Exhaust Temperature Model and Catalytic Converter Protection (Approx. 10 Days)
The exhaust temperature model simulates the temperature around the oxygen sensor (before and after the catalyst) and inside the catalyst under different environmental and engine working conditions as the engine load and speed change. Establish exhaust system temperature models for various operating points through actual measurements.
Under high load conditions, if the temperature of the catalytic converter exceeds its limit, enrich the mixture to lower exhaust temperature and protect the catalytic converter from damage.
Simultaneously combine with oxygen sensor heating control to simulate the conditions at the end of the exhaust system dew point stage to protect the oxygen sensor.
3. Oxygen Sensor Heating Control (Approx. 5 Days)
This is primarily to prevent the ceramic body of the oxygen sensor from cracking. After the engine starts, water droplets may form on the exhaust system pipe wall and the oxygen sensor sheath. These droplets could splash onto the ceramic body of the oxygen sensor. If the temperature of the ceramic body is too high, it may crack. Therefore, the requirement for this test is that when the pipe wall temperature reaches 60 degrees, the ceramic body temperature of the oxygen sensor must not exceed 350 degrees.
4. Transitional Conditions (Approx. 10 Days)
When the throttle opening changes, the mismatch in load measurement and corresponding fuel amount calculation with the actual fuel injection timing leads to an excessively rich or lean air-fuel ratio, severely affecting the engine’s emission and driving performance. This phenomenon can be well explained by the different fuel film thicknesses formed in the intake manifold under different loads. The purpose of transitional condition matching is to compensate for these changes, keeping the air-fuel ratio within a reasonable range. The basic principle of matching: enrich during acceleration, lean during deceleration.
First, simulate load changes on the inertia dynamometer using a pedal position simulator. Simulate acceleration and deceleration situations, increasing and decreasing fuel injection to keep the air-fuel ratio within a reasonable range (mainly considering emissions and driving comfort). Then conduct acceleration and deceleration tests on actual roads to revise matching data.
5. Canister Control (10-30 Days)
The purpose of canister control matching is to prevent fuel vapor from escaping from the fuel tank and causing pollution, ensuring the canister has sufficient ventilation while minimizing λ deviations.
At different operating points, set the canister opening time (TEP) and correct the fuel amount through λ feedback control. When the canister is working, λ self-learning stops.
5. Idle Start Matching (Approx. 40 Working Days)
1. Idle Control (Approx. 10 Days)
The matching goal is to control λ=1, stabilizing engine speed at idle ±20 RPM. When sudden electrical loads are applied, such as air conditioning switches and power steering operation, no significant speed fluctuations or engine vibrations are allowed.
Typically, the ignition advance angle is not adjusted to maximum at idle to maintain a certain torque reserve. Sudden load increases are managed by adjusting the ignition advance angle (quickly) and increasing intake volume (slowly) to maintain idle stability.
2. Cold Start (-30 to 40 degrees)
Cold start refers to starting the engine and vehicle after being parked for a long time, allowing components to reach the ambient temperature. The temperature range is approximately from -30 to +40 degrees.
Factors causing difficulties in cold starts include: 1. Low temperature makes fuel difficult to evaporate, leading to poor atomization and ignition issues; 2. Some fuel adheres to the intake manifold walls and valves; 3. Engine lubrication has not yet formed, and increased oil viscosity leads to greater engine resistance.
The matching objectives are: 1. Ensure safe starting under various fuel qualities, temperatures, and altitudes; 2. Ensure a comfortable start, allowing the engine to start quickly and quietly; 3. Optimize emissions during starting, especially for HC and CO emissions around 20 degrees and -7 degrees.
Test temperatures: from -30 to 10 degrees, testing every 5 degrees. Test fuel must cover the gasoline quality across China (fuel evaporation pressure 40-80 kPa).
3. Hot Start (>95 degrees)
The matching goal is to enrich the mixture due to the presence of gasoline vapor in the fuel line or due to excessively high temperatures of the fuel injectors, causing the mixture to become too lean.
This test is conducted in a 40-degree high-temperature chamber.
6. Emission Matching (Approx. 30 Working Days)
Calibrate the catalytic converter window (5 Days)
Typically, each catalytic converter has an optimal conversion efficiency point, usually near λ=1.
The matching goal is to find the area of optimal conversion efficiency for the catalytic converter, adjusting the λ control closed-loop correction factor to keep λ as close as possible to this working area.
2. Optimize starting, idle, warm-up, and transitional conditions (>20 degrees) (5 Days)
To meet emission requirements, keep λ as close to 1 as possible.
3. Calibrate the catalytic converter heating function (10 Days)
After starting, delay the ignition advance angle to allow the mixture to burn in the exhaust pipe, helping the catalytic converter reach working temperature quickly.
4. Emission tests for fresh, rapidly aged, and real vehicle aged catalysts (10 Days)
Tests must be conducted using new catalytic converters, those aged at high temperatures in furnaces, and those on vehicles with 80,000 km endurance, all meeting emission requirements.
7. Road Testing (Approx. 37 Working Days)
1. Plateau Testing (Approx. 8 Days) (up to 4700 meters)
In high-altitude areas, the air pressure is lower, and the air is thinner, requiring different fuel amounts for combustion compared to plains. The controller must be able to recognize and adjust accordingly. Key focuses during system assessment in high-altitude areas include: adjusting altitude correction factors, cutoff speed, cold start, hot start, warm-up start, hot idle, mixture pre-adjustment, driving performance, knock control, and adjusting exhaust and catalytic converter temperatures under high loads by delaying the ignition advance angle.
2. Summer Testing (Approx. 15 Days) (40℃)
In hot regions, key focuses during system assessment include: hot start and repeated hot start, hot idle, mixture pre-adjustment, cold driving, driving performance, knock control, and self-learning, switching to specific ignition advance angle regions for poor fuel quality, and adjusting exhaust and catalytic converter temperatures through fuel enrichment under high loads, canister control.
3. Winter Testing (Approx. 15 Days) (Minimum -30℃)
The main testing focus is on cold start and cold driving performance.
(1) Cold Start: Poor gasoline evaporation at low temperatures necessitates starting enrichment. Tests are conducted at various temperatures, including -30℃, -25℃, -20℃, etc.
(2) Cold Driving Performance: Increased oil viscosity at low temperatures affects lubrication, and poor gasoline atomization leads to greater resistance during cold driving.
8. Driving Performance Matching (Approx. 30 Working Days)
1. Optimize acceleration and deceleration performance, optimize fuel cutoff and restoration (Approx. 20 Days)
Avoid acceleration shudder by adjusting the ignition angle to ensure smooth RPM increases without fluctuations.
Avoid deceleration shudder caused by rapid reduction of throttle. After releasing the throttle, keep the throttle open for a period. Then enter the fuel cutoff phase, restoring fuel injection smoothly as the RPM approaches idle (the RPM point for restoring fuel injection varies across models).
2. Calibrate engine and vehicle speed limit functions (Approx. 5 Days)
To protect the engine, limit RPM by delaying the ignition advance angle and cutting off fuel when approaching maximum RPM (E-GAS through throttle closure).
Vehicle speed limits are set to protect tires and other vehicle components, with the control method being the same.
3. Optimize dynamic idle (Approx. 5 Days)
Monitor RPM control during idle with throttle pressed and coasting.
9. OBD Diagnostic Function (40-60 Working Days) and Monitoring Function Matching (40 Working Days)
The control system of electronically fuel-injected engines is very complex; any failure of a component in the system, or issues like broken wires or loose connections, can lead to system failures. The On-Board Diagnosis (OBD) system has two functions: first, to continuously monitor for abnormalities in the system and, when necessary, record faults with codes for maintenance; second, to implement temporary remedial measures to get the vehicle to a repair station.
1. Reasonableness Check
The reasonableness check function is used to monitor the hardware of the electronic control system, including checking for faults in various sensors and actuators, whether sensor signals are reliable, and whether there are circuit short circuits or open circuits. This function must set reasonable fault judgment thresholds for each sensor and actuator to avoid misjudgments that prevent the engine from functioning normally.
2. ECU Drive-Level Monitoring
This is used to check whether the ECU itself is functioning normally.
3. Emergency Home Function
This allows the vehicle to be driven to a repair station after certain faults occur, mainly striving for the two basic control functions of fuel quantity and ignition timing to be implemented.
Emergency measures are divided into two main parts: ECU input failures and output failures.
Input failures can be handled using signal substitution, signal setting, and program switching methods. Output failures should adopt specific emergency measures for different issues, such as shutting off the fuel injector of a faulty cylinder.
The implementation of the emergency home function must consider handling methods for failures of all sensors.
4. Fault Code Management
Fault code management essentially involves FMEA analysis, i.e., setting the conditions for generating fault codes. Comprehensive fault code management facilitates the ECU to take measures based on the situation and helps users quickly identify the causes of vehicle issues.
5. Check Diagnostic Device Communication
Users typically read fault information and operating conditions of the electronic fuel injection system using diagnostic devices like VAG1552, VAS5051, etc. Checking the communication of diagnostic devices involves first defining the outputs of each diagnostic block, then checking the communication status between the diagnostic device and the ECU.
6. Electronic Throttle Monitoring
Electronic throttle monitoring includes performance monitoring and safety monitoring, focusing on the throttle pedal and electronic throttle body. First, ensure that the output signal from the throttle pedal accurately reflects the driver’s request, then ensure that the electronic throttle body correctly executes the desired throttle opening. When signals are unreliable, fuel cutoff control must be implemented to ensure vehicle safety.
10. Additional Matching Projects in Some Models
1. EGR Matching
Exhaust Gas Recirculation (EGR) lowers the maximum combustion temperature by diluting the mixture, thus optimizing the combustion process to reduce fuel consumption and NOx emissions. The ratio of CO2 concentration in the intake and exhaust pipes is called the EGR rate. EGR generally operates under moderate load at mid-high RPM, not during startup or idle. Its operation is limited in high-load regions.
2. Secondary Air Pump Matching
Secondary air is introduced just behind the exhaust valves of each cylinder. This helps oxidize HC and CO in high-temperature exhaust gases; additionally, the heat generated by the combustion of HC and CO raises the temperature of the catalytic converter to working temperature. The secondary air pump typically operates during cold starts when the engine water temperature is below 60 degrees.
3. Long-Short Intake Pipe Switching Matching (Approx. 10 Working Days)
The basic concept of intake pipe switching is to use short intake pipes during high-speed engine operation and long intake pipes during low-speed operation to take advantage of the intake wave effect, improving charging efficiency under various operating conditions. The matching work for long-short intake pipe switching primarily involves determining the engine RPM for switching pipes at various loads. This is done by analyzing data from speed characteristics when using only long or short pipes under specific loads to select reasonable RPM switching points to ensure a good torque curve.
4. Cruise Control Matching
For vehicles using E-GAS systems, throttle opening can be directly controlled by the engine controller, making it easier to implement cruise control. The focus of matching is similar to idle control, primarily ensuring stability in engine speed changes during load variations.
5. Variable Valve System Matching
Control of the intake and exhaust systems determines the engine’s charge exchange process. For variable valve systems, matching parameters include valve opening phase, valve opening duration, and valve lift. Variable valve systems can be classified into many types based on adjustable valve quantity and degrees of freedom. For specific operating points, numerous orthogonal tests must be conducted to determine the matching parameters of the valve system at that point. If calibration is conducted across all operating conditions, the workload is enormous.
Additionally, related changes can impact matching.
Parts related to engine combustion, such as the cylinder block, cylinder head, piston, intake manifold, exhaust manifold, etc., are generally not allowed to be changed, as structural changes will require all projects to be rematched. Factors like wind resistance and vehicle weight have little impact on matching work but will affect the vehicle’s performance and economy indicators. Furthermore, the following component changes can also affect matching to varying degrees:
1. Catalytic Converter
2. Exhaust Muffler, Air Filter, etc.
3. Engine Accessories: such as the air conditioning compressor, power steering pump, etc.
4. Transmission System: such as gearbox, axle, tire specifications, etc.
5. Air Conditioning Compressor Bracket and Generator Bracket.
6. Engine and Transmission Mounts
In summary, as one of the most critical electronic control modules in modern vehicles, ECU calibration plays a vital role, but it cannot be entirely relied upon; for example, fuel consumption, maximum power, and torque performance mainly depend on the engine’s efficiency, and the role of calibration is to bring out the best performance.
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