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Engine Control Units – Development, Functions and Tests

4007 words (16 pages) Essay in Engineering

18/05/20 Engineering Reference this

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  1. EXECUTIVE SUMMARY

Every vehicle has ECUs and ECUs are like the brain of the vehicle if we think the car as the body and the engine as the heart. The focus of Software Testing Team is to test the ECUs. The company plans to use Vehicle Spy software to test diagnostic, signal routing and network management of ECUs. However, even thought the setting of ECUs are designed to be balanced, there are lots of vehicle owners would like to flash ECUs on their vehicle to make the behaviour of ECU, power of the vehicle and torque optimized and reach to a higher level of balanced status. Here are some advantages of flashing ECUs

  • The naturally aspirated engine can increase the horsepower and torque by 5%~15%.
  • With a turbo model, it can increase power and torque by 30% or more
  • After the modification, the automatic wave model shift will become smoother and the power connection will be smoother.

              However, there are also some disadvantages for flashing ECUs:

  • The higher quality of oil is needed.
  • The upgraded ECU program should be appropriate; otherwise, it will affect the engine life.
  • Some cars have too much power after upgrading and the brakes will not met.

:          This report will introduce the development of ECUs, what are functions of ECUs, what to                                                                     test on ECUs and should people flashing ECUs on their vehicle.

  1. INTRODUCTION
  1. What is CAN Bus and ECU

Imagine that your car is like a human body. If we think the engine as the heart of a vehicle, then ECUs would definitely be the brain of the vehicle. The Controller Area Network (CAN bus) is the nervous system, enabling communication between all parts of the body. In an automotive CAN bus system, ECUs can e.g. be the engine control unit, airbags – or the audio system. A modern car can have up to 70 ECUs.

The ECU is the abbreviation of the Electronic Control Unit. It can also be called the “driving computer”. As one of the core components of modern automotive electronics, the ECU electronic control unit may have several in the car, each managing different functions; and there is information exchange between each ECU system. Although the control system on the whole vehicle is more and more complicated, it still must have the most basic structure—microprocessor (CPU), memory (ROM, RAM), input/output interface (I/O), analog-to-digital conversion (A/D) and large-scale integrated circuits such as shaping and driving. It is also well recognized in appearance – there is a control element shaped like a square box in the engine electronic fuel injection system, which is the ECU. There are many slots around the components to connect the numerous input and output circuits. Together with other electronic control components, they form the brain’s nerve center system, which monitors the input data (such as brakes, shifts, etc.). And various states of the car operation (acceleration, slip, fuel consumption, etc.), and calculate the information sent by various sensors according to a pre-designed program. After processing, each parameter is sent to each relevant actuator to execute various reservations.

  1. The communication between ECUs:

The CAN bus protocol allows ECUs to communicate with each other without complex dedicated wiring in between. In turn this allows for several features to be added via software alone like gearbox control. Further, an ECU can use data from another ECU, eliminating the need to install the same sensors in multiple devices.

Network Management is utilized by ECUs for feature implementation control when the vehicle is not powered like Initiate a vehicle wakeup utilized network management to gather vehicle information or activate a customer driven feature that requires information from another ECU.

Also, Network Management allows for the interaction between modules and provides a mechanism for feature to wakeup the network or inhibit network sleep when power distribution is off or in accessory mode.

Critical advantages of CAN bus communication:

  1. Low cost: ECUs communicate via a single CAN interface, i.e. not direct analogue signal lines, reducing errors, weight, costs.
  2. Centralized: The CAN bus system allows for central error diagnosis and configuration across all ECUs.
  3. Robust: The system is robust towards electric disturbances and electromagnetic interference, making it ideal for vehicles.
  4. Efficient: CAN frames are prioritized by ID – the top priority gets bus access, yet frames are not interrupted.
  5. Flexible: Each CAN-connected ECU can receive all transmitted messages. It decides relevance and acts accordingly – this allows easy modification and inclusion of additional nodes (e.g. CAN bus data loggers).

The history of ECUs

Before 1967, the gasoline engine supply system was supplied by the carburetor. This is completely different from the principle of today’s Electronic Fuel Injection (EFI) engine. The carburetor uses the pressure difference before and after the throttle to absorb oil, which not only can not accurately control the fuel replenishment. It also restricts the improvement of vehicle power and environmental performance.  A group of companies such as Bosch have developed an electronic fuel injection system like D-Jetronic in the earlier time and K-Jetronic, L-Jetronic later.

The working characteristics of the EFI system lies in “Quantitative, timing”

When fuel is injected, how much fuel is needed by the engine, and when it is injected, this has a direct relationship with the engine speed, air flow, etc. In addition, various parameters such as water temperature and oil pressure are involved, and how many parameters are processed. And send an injection command to the injection system. This requires the intervention of the engine control unit, and the ECU came into being.

  1. ANALYSIS

What to test for ECUs?

  1. Feature Based Testing

It is expected that feature-based testing will cover the behavior of the feature in the module under test.  It is not intended to test an entire distributed feature.  Feature interactions between modules will be tested when a dependent module requires a parent module input to be modified.  This level of testing will be defined by the feature owner and is not in the scope of this document.

If all the hardware variants of a specific feature are not tested, the feature cannot be claimed to be completely tested.  This includes all the configuration parameters that apply to a specific hardware variant defined in the ECU Configuration DID’s.

  1. Diagnostic Testing

The ECU defines a set of diagnostics messages that can be used to verify the presence of power on vs. running resets, watch dog resets, Data Range violations, stack over/underflow or minimum vs loss of idle time.  This information will be stored in the DID values. The ability to detect Power On resets and watchdog resets is dependent on the implementation of watchdog, the type of power source (Always switched or Powered) and if the module is a sleep node that implements cutthroat sleep or not.  The table below should be used to determine if Power on Resets (POR) and Watchdog resets can be counted.

All Diagnostic Request messages (excluding the Gateway Diagnostic Request ID) shall be routed from the default or active backbone(s) to each subnet, and not the inverse, per the respective Subnet settings where by each network is run-time configured as enabled or disabled for each or the 3 backbones.  Subnets “enabled” and asleep shall be awakened and sustained to fulfill request routing.  Following 6s of no routing activity subnet are permitted to sleep.

Figure 1 – Diagnostic Request messages

All Diagnostic Response messages shall be routed from the subnets to the backbone and not the inverse.

Figure 2– Diagnostic Response messages

  1. Gateway Message Routing

The SDLC shall also incorporate a frame gateway service that is capable of throughput of less than 2ms.  The frame gateway shall receive a message from one CAN channel and transmit the exact data frame content to another CAN channel.  The data frame is identical to the one received although the outgoing frame ID may be different.  The message shall only transfer onto the destination CAN channel when the source message is received.  Hence, it is a simple repeater.

The SDLC shall be capable to receive signals from one CAN channel and transmit that same signal value to other CAN channels as specified by the network database. Incoming signals may be packed into frame ID’s different from that received and with different transfer strategies.  Update Bit handling will also apply as dictated by the network database.  All this functionality is expected to be provided via the FNOS RP package integrated into the micro.  All signal values shall be initialized to values specified in the network database upon reset or power up.  Signal values are expected to persist through sleep durations.

Message gateway performs like the frame gateway in that it routes the exact frame data between bus but the difference it that it slows down the timing between the routing. This is used when the transmitter is sending the message faster then the receiver needs it.

Testing procedures and tools:

Gateway Message routing has three subnets which are framed gateways, signal gateways, message gateways. Those tests can be achieved by sending messages and signals through vehicle spy and monitor different buses for traffic. Here is an example and how the Vehicle Spy looks when testing sending messages:

Figure 3– Vehicle Spy Setting

Figure 4– Monitoring traffic through Vehicle Spy

  1. Network Management

Remote Wakeup

Remote wakeup is determining when an ECU wake’s up it’s network which other networks within the vehicle should also wakeup. The configuration is stored within the Build Time Configuration specification document for each program.

For Remote Wakeup: Each network node has a Remote Wakeup configuration bit for every other network node. Each network identified in the first column is configured against the other networks. When enabled, a Remote Wakeup on the network of the first column will wake up the network along the top and when disabled it will not.

Example table

Figure 5– Remote Wakeup Configuration

In the table above if set HS1 bus wakes up and starts to send out a periodic autosar message, it will awake all the other buses as they have all to 1. After the buses have been awake for 3 second, they will then go back to sleep unless it has been configured in the Remote Sleep to stay awake.

NM Proxy

All Autosar NM messages Tx by GWM shall reflect the NM Proxy state of each GWM channel.  Bits of byte 5 of the GWM NM message field shall represent each CAN channel;’ 0’ when a proxy request is present, ‘1’ otherwise. Active proxy requests Rx by GWM shall be aggregated and reflected in the bit field and published with all normally occurring NM message Tx’s. No additional or prolonged GWM NM Tx’s are required due to bit field values.  E.g., if a single NM proxy request persists for the ECU’s native network and all other networks are asleep, the GWM shall only Tx NM on this network with its appropriate proxy bit set.  No other networks should awaken or sustain. Further, once a proxy request is absent for 3s it shall no longer be honored by GWM.

The functionalities of ECUs:

  1. EFI control:

The engine control unit (ECU) uses the intake air amount and the engine load as the main control signals to determine the injection pulse width (i.e., the basic fuel injection amount), and according to the circulating water temperature, the intake air temperature, the intake pressure, the exhaust gas oxygen content, and the like. The signal corrects the amount of fuel injected and finally determines the total fuel injection.

Overspeed fuel cut control: When the engine speed exceeds the safe speed or the vehicle speed exceeds the set maximum speed, the ECU automatically interrupts the fuel injection until the engine speed is lower than the safe speed and the vehicle speed is lower than the maximum speed

  1. Ignition (ESA) control:

The ignition coil primary circuit needs to ensure a sufficiently large current when disconnected to cause the secondary coil to generate a sufficiently high voltage. At the same time, in order to prevent the ignition coil from being overheated and damaged by preventing the energization time from being too long, the ECU controls the energization time of the ignition coil primary circuit based on signals such as the battery voltage and the engine speed.

  1. Idle speed control (ISC):

When the engine is in the idle condition, the ECU determines the rotation direction and the rotation angle of the idle motor according to the output signal of the idle throttle potentiometer and the difference between the engine speed and the target speed, and adjusts the opening degree of the idle throttle. When the actual engine speed is lower than the target speed, the motor rotates forward, and the motor shaft opens the throttle valve by a small opening degree through the gear mechanism, increasing the engine intake air amount and increasing the engine speed; when the actual engine speed is higher than the target speed, The motor is reversed, the throttle is closed by a small opening, the engine intake is reduced, the engine speed is reduced, and the target speed is gradually approached. When the engine is in idle condition, if the engine load increases (such as the air conditioner compressor starts), the ECU controls the idle motor to adjust the idle throttle opening to increase the engine speed and prevent the engine from stalling.

  1. Emission control:

Installing a three-way catalytic converter on the exhaust pipe of a car engine to purify the exhaust gas, Three harmful gas components, CO, HC, and NOx, but the three-way catalytic converter can only function in the range where the air-fuel ratio is close to the theory (A/F = 14.7:1). An oxygen sensor is installed in the exhaust pipe, which can obtain the air-fuel ratio of the mixture by detecting the oxygen content in the exhaust gas. The ECU corrects the fuel injection amount according to the signal input by the oxygen sensor, and realizes the feedback control of the air-fuel ratio, so that the air-fuel ratio of the mixture is close to the stoichiometric air-fuel ratio, and the three-way catalytic converter can purify more effectively and make the harmful gas Emissions are reduced to the minimum, in line with Euro III emission standards for vehicle exhaust emissions (HC ≤ 0.66%, CO ≤ 2.1%, NOx ≤ 5%, particles ≤ 0.1%)

  1. Self-diagnosis and alarm

When the engine electronic control system fails, the ECU turn on the fault indicator on the instrument panel to remind the driver that the engine has failed and should immediately check the repair.

What is ECU flashing:

Someone believes that stock ECUs are generally far from optimal and developed to allow for a wide range of riding styles, fuel quality and operational conditions. The result of this is often a compromise resulting in suboptimal performance. Significant improvements can be achieved through correcting the stock ECU’s deficiencies and tuning the engine to take full advantage of it’s potential. ECU Flashing is the process of updating the software that runs on your vehicles ECU. This allows you to change various maps and settings in your ECU and significantly improve the performance of your engine. Therefore, lots of people choose to flash ECU on their car to improve and seek for a higher performance of their car, including both power and torque.

The drawback of flashing ECU:

  1. The higher quality of oil is needed. After upgrading the ECU, the most basic one and a parameter that the ECU must modify is the ignition advance angle. The original car was shipped to adjust the ignition advance angle to the most adaptable advance angle because of the differences in oil products across the country. Therefore, the problem arises. For most areas, unleaded petrol is used. After upgrading with premium gasoline, the engine with the upgraded ECU can be optimized. On the contrary, some cities currently use ethanol gasoline. Ethanol gasoline has flammability and short combustion characteristics. Properly igniting the ignition will make ethanol gasoline burn more fully. Then, upgrading the ECU will advance the ignition, which will cause engine knock and weakness. Long-term use will damage the engine. However, if unleaded gasoline is the opposite, proper advancement will make the combustion of the engine mixture more complete, the carbon deposit will be relatively reduced, and the engine life will be extended.
  2. The upgraded ECU program should be appropriate, otherwise it will affect the engine life. It is a professional matter to upgrade the ECU power program. It is not just a matter of adjusting the injection time and the mixture. Unsatisfactory adjustments can lead to fault lights turn on, unbalanced power output, and even directly affect engine life.
  3. Some cars have too much power after upgrading and the brakes are not met. Some models have some large power upgrade space. Proper modification with good gasoline is very beneficial to the car, but excessive modification may damage the hardware beyond the car’s tolerance. Therefore, in the case that the power and torque of the engine output are greatly improved, the hardware method is recommended to be properly upgraded, otherwise the braking distance may be lengthened, and the safety may be affected.

         The advantages of flashing ECU:

  1. The naturally aspirated engine can increase the horsepower and torque by 5%~15%. The best torque is better than the original factory setting. Therefore, the trembling problem of the original car in the first and second gear shifts will disappear and become smoother.
  2. With a turbo model, it can increase power and torque by 30% or more. In addition, the original turbo model usually sets the engine speed to about 1800, and the turbine will work. After the ECU is modified, the turbine will intervene earlier, and the turbine will intervene about 1500 rpm, so that the torque can be played earlier, and the maximum torque output curve. It becomes wider and therefore makes the car more fuel efficient than the original car.
  3. After the modification, the automatic wave model shift will become smoother and the power connection will be smoother. Normally, the driver will shift gears earlier than the original car to achieve fuel-saving purposes. On the contrary, when the acceleration is accelerated, the shift will be delayed, and the speed increase will be more rapid, so that a stronger pushback pleasure will be enjoyed.
  4. At present, it is the easiest, fastest and most effective modification method, most models do not need to disassemble any original car hardware and can read and write ECU programs only through the OBD2 on-board diagnostic interface that comes with each car.

4. CONCLUSIONS:

The earliest application of the ECU upgrade was on the racing car, which improved the performance of the car through professional ECU tuning.

Due to differences in gasoline quality, temperature, atmospheric pressure, humidity, and engine form in each country, the ECU program software must be used in accordance with the conditions of each country, so as not to cause soil and water, and must be durable and economical. Environmental protection and other multi-party conditions, so the range set by the original car computer is more conservative, so reserve a certain space for modification.

We must know that the state of a car is the most balanced when it is in the original factory. Any modification is just to break the balance of the original factory and seek the next balance point. Therefore, the engineers will make the original ECU calibration and comprehensively consider the fuel consumption and reliability. Sex, power output and other factors to make a setting that is most suitable for the majority of consumers. Flashing the ECU to increase horsepower and torque will certainly destroy the engine’s performance in other aspects.

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