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Automotive Electronics Part II – ECM Types by Dr David Maddison Last month, we provided an overview of how automotive electronic control modules (ECMs) work, described how they communicate and listed some of the many types used. We also described the operation of the engine control unit (ECU) in detail. Now we’ll concentrate on the other ECM types found in modern vehicles. T here are very many electronic control modules we could describe; probably enough to fill the magazine! So we have selected the following few as representative and diverse systems. others must be replaced. For details on how data can be extracted from an ACM, see the video and instructions at siliconchip.com.au/link/ab4k Also see the video titled “KIA Airbag control module (ACM) Airbags use MEMS devices to determine if a severe impact has occurred and activate pyrotechnic devices to generate gas to fill the airbags (Fig.28). The ACM usually contains capacitors to store power during a crash in case vehicle power is lost. ACMs store data about the crash that caused them to activate such as speed, throttle setting, brake application, seat belt usage and other data at the time of impact. The ACM uses data such as seat occupancy, occupant weight and crash severity to determine whether to inflate airbags, which airbags to inflate, when to inflate them and how rapidly to inflate them. We published an in-depth article on airbag systems in our November 2016 issue (siliconchip.com.au/Article/10424). In the event that a car is repaired after airbag activation, the ACM has to be either replaced or reset via hardware and/or software means. Some models can be reused a limited number of times; 10 Silicon Chip Fig.28: the Toyota Prius airbag control module is fairly typical. It integrates sensors to detect an impact with a processor to determine which airbags to fire, and components to send pulses to the airbag(s) to trigger them. The large capacitors allow it to continue operating for some time, even if the vehicle wiring or battery is damaged by the impact. Australia’s electronics magazine siliconchip.com.au Fig.30: a body control module with integral fuses from a 2017 Alfa Romeo Giulia. Note the numerous connectors which go to buses, sensors and actuators. Source: pacificmotors.com Fig.29: an ABS pump and control module from a Mazda 2. The electronic control module is the black case at the bottom, with the hydraulic valve body between it and at the pump at the top. Source: abssteuergeraet.com Soul 2016 14 15 SRS Airbag Module Reset via OBD CAN Lines” at https://youtu.be/iz14cIOZhpU Our article on OBD2 in the September 2020 issue (siliconchip.com.au/Article/14576) also described how to reset airbag computers using OBD2 in certain vehicles. Anti-lock braking system (ABS) Modern ABS systems use a speed sensor on each wheel, a hydraulic valve for each brake line, a pump (see Fig.29) and an electronic controller. If a particular wheel decelerates faster than others during braking, suggesting that locking up is imminent, hydraulic pressure is released from that brake and then rapidly reapplied to ‘pulse’ the brakes and allow the vehicle to be steered during hard braking. The pressure lost due to pulsing the brake line is made up by the hydraulic pump. An ABS can release and reapply brake pressure as much as 15 times per second. Brake assist (BAS) This system was first developed by Daimler Benz TRW/ LucasVarity. It increases brake pressure in an emergency. An emergency is sensed by such factors as the speed at which a foot is removed from the accelerator and applied to the brake. Once an emergency is assessed, full braking force is applied to the maximum permitted by the ABS system. The rationale for this system is that most drivers do not apply the brakes forcefully enough in an emergency. It has been shown to be highly effective in reducing rear-end collisions. Body control module (BCM) The BCM controls and monitors less critical devices on a vehicle’s body such as power windows, mirrors, heatsiliconchip.com.au ing and cooling, lighting, anti-theft immobiliser etc (see Figs.30 & 31). See the videos titled “BCM Trouble: Ranger & BT50” at https://youtu.be/IBEzMVtXuX4 and “Took apart a 20132017 Ford fusion BCM body control module” at https:// youtu.be/cO3FSrXfQpA Catalytic converter / oxygen sensor While not actually ECMs, cats are an essential component of the emissions control system for gasoline engines and integrate with the ECU and electronic oxygen sensors, described last month. Catalytic converters (cats) convert nitrous oxides, hydrocarbons and carbon monoxide to nitrogen, water and carbon dioxide (see Figs.32 & 33). For them to work well, the engine has to be within a narrow band of air-fuel ratios; otherwise, there is too much or too little oxygen and the converter won’t function properly. Modern vehicles have oxygen sensors before and after the converter to monitor the oxygen content in the exhaust stream. The oxygen data is sent to the ECU to ensure optimal conditions inside the converter by adjusting engine characteristics. A converter has two sections. The first reduces NOx to Security concerns The extensive computerisation and networking of cars opens up new opportunities for malicious individuals. It is possible to clone electronic key fobs, as described in our article “History of Cyber Espionage and Cyber Weapons, Part 1” in the September 2019 issue, on page 19 (siliconchip. com.au/article/11911). It’s also possible to spy on vehicle occupants, as described on page 21 of that issue. Those with malicious intent can also (possibly) take control of a car. Hopefully, security flaws are being patched as they are discovered, preferably before that! See the videos titled “How to Hack a Car: Phreaked Out (Episode 2)” at https://youtu.be/3jstaBeXgAs and “Hackers Remotely Kill a Jeep on a Highway” at https://youtu. be/MK0SrxBC1xs Australia’s electronics magazine January 2021  11 Fig.31: the architecture of a Texas Instruments body control module system. MCU is the microcontroller unit, LDO is low-dropout regulator, ESD is electrostatic discharge protection, MSDI is multiple switch detection interface, MUX is multiplexer, HS and LS refers to high side and low side switches and BTSI is brake transmission shift interlock. nitrogen, the second oxidises CO to CO2 and hydrocarbons to water and CO2. The ECU constantly cycles between slightly rich (oxygen poor) and slightly lean (oxygen rich) because the first stage needs to be oxygen-deficient and the second stage needs to be oxygen-rich to work. See the video titled “See Through Catalytic Converter” at https://youtu.be/ekQcy6GN1pM There are also catalytic converters for diesel engines. They oxidise CO and hydrocarbons but for NOx control, other systems are used, such as urea injection (“diesel exhaust fluid”, DEF, marketed as AdBlue or other names) into the exhaust and an additional special catalyst. Cylinder deactivation In some engines, especially six and eight cylinder types (but also those with four and even three cylinders!), some of the cylinders can be shut down under light driving conditions to save fuel (see Figs.34(a) & (b)). In GM vehicles, this technology is known as Active Fuel Management. It involves special valve lifters, a special manifold assembly and appropriate control by the ECU. Greater fuel economy (up to 12% improvement in GM vehicles) can be obtained without downsizing the engine. The extra power of a larger engine is available when needed. As of 2019, the GM system has now evolved to Dynamic 12 Silicon Chip Fuel Management (DFM), where as many cylinders as need be can be deactivated. Other manufacturers have similar systems. For more details, see our article in the January 2009 issue on cylinder deactivation in Honda V6 engines (siliconchip. com.au/Article/1268). Electronic stability control (ESC) ESC (also known as ESP, or electronic stability program) is an extension of the ABS or VSC system. Additional sensors are added such as a steering wheel angle sensor and a MEMS gyroscope (see Fig.35). If there is a mismatch between the vehicle’s intended direction (as determined by the steering wheel angle) and the actual direction of travel (as determined by the gyroscope), one or more wheels are braked to realign the vehicle into the intended direction. This is now a mandatory system in all new vehicles in the USA, Canada and EU. Two different ways that traction and stability control can be implemented, as used on older and newer vehicles, are shown in Figs.36 & 37. Fuel composition module This module is used in vehicles that can run on E85 ethanol as well as normal fuel (E10 or E0). They measure the exact amount of ethanol in the fuel and pass the information Australia’s electronics magazine siliconchip.com.au Fig.32: a catalytic converter with exhaust going left to right. HC stands for hydrocarbons, NOX is nitrogen oxides and CO is carbon monoxide. They are transformed to water (H2O), CO2 and nitrogen (N2). There are two different catalyst sections, plus oxygen sensors at the inlet and outlet which feed data to the ECU. to the ECU to manage timing, quantity of fuel injected and maximum boost level (see Fig.38). When switching between E0 and E85, the fuel could be anywhere from 0% up to about 85% ethanol. Higher ethanol concentrations require wider injector pulses as ethanol has about half the energy per litre of petrol. However, ethanol also acts as an octane booster and charge cooler, allowing for more timing advance and higher boost levels, provided there is enough fuel delivery capacity. Knock sensor The knock sensor (Figs.39 & 40) detects engine ‘knocking’ that happens when the air-fuel mixture ignites before the spark. This can be due to inappropriate fuel, excessive cylinder pressure, insufficient air-fuel ratio, excessive turbo or supercharger pressure, high operating temperature, carbon deposits or other reasons. Knock can cause severe engine damage due to the high pressures generated. A knock sensor generally uses a piezoelectric or inductive sensor attached to the engine block or head that acts like a microphone. It is tuned to be sensitive to the frequency of engine knock of the specific engine. Knock information is sent to the ECU and engine adjustments such as timing, fuel mixture or boost pressure are made to reduce or eliminate knock. Fig.33: a screengrab from the “See Through Catalytic Converter” video (https://youtu.be/ekQcy6GN1pM). Much heat is generated during the catalysis process. Catalysts also contain valuable platinum, palladium and rhodium, making them expensive and a target for thieves in some places. These sensors are sensitive enough that they can normally detect incipient knock before it is a problem and make slight adjustments to avoid it. This allows vehicles to take advantage of high-octane fuel (providing better power and economy when it is used) while still allowing lower octane fuel to be used without risk of damage. Launch control Launch control is built into a number of high-performance vehicles. Like traction control, its purpose is to limit wheel spin, but unlike traction control, it maintains the engine at the maximum RPM possible for the best acceleration from a stationary position (see Fig.41). Some wheel slip may be permitted, consistent with maximum acceleration. The GM Camaro ZL1 adjusts engine torque 100 times per second to maximise acceleration without excessive slipping. Such systems require an electronic accelerator pedal (throttle-by-wire) or a transmission brake. Traction control modules can be added to certain vehicles as aftermarket accessories, or launch control can be part of other engine control functionality. See the video from Australian company Haltech titled “How Launch Control Works” at https://youtu. be/5g2YFquhGtE Fig.34(a) & (b); in Honda’s cylinder deactivation system, the ECU uses a solenoid to control oil pressure to a set of pistons. When pressure is applied (left), the primary and secondary arms are locked together, so the intake and exhaust valves operate normally. When pressure is removed (right), the arms unlock, and the valves no longer open. The ECU switches off the fuel injectors and spark plugs for those cylinders at the same time. siliconchip.com.au Australia’s electronics magazine January 2021  13 The 42V electrical system In the 1990s, there was a proposal to change the standard voltage of a car electrical system from 12V to 42V. A fully charged regular car battery is 12.6-12.9V and a typical float charging voltage is 13.8V, which is about what the average voltage of the car electrical system runs at and what accessories are rated for. That rounds to 14V, so 42V is then triple the standard car electrical system voltage. The voltage chosen had to be under 50V due to shock hazards. A higher standard voltage was chosen because it allows for a lighter wiring harness; three times the voltage means one third the current for the same power, and the thickness of wiring is dependent on current, not voltage. A further advantage of a higher voltage is that motors such as window winders, electric power steering pumps etc can be smaller and lighter. Disadvantages are that the higher DC voltage requires more expensive switches due to more arcing, there was already a lot of support for the 12V system, and the need for the 42V system was reduced with the development of more efficient motors and multiplexed data buses requiring less wiring. Also, most hybrids have dual-voltage electrical systems anyway. The Audi SQ8 (mentioned last month) has a separate 48V volt system for its electric supercharger, and there are other vehicles with similar setups for start/stop systems etc. While there are cars out there with 42V electrical systems (mainly luxury vehicles), in the end, the benefits just weren’t worth the cost of switching and so most manufacturers haven’t bothered. 12/14V remains the dominant standard, at least for now. Fig.35: Electronic Stability Control (ESC, sometimes called ESP or VSC [vehicle stability control]) uses the ABS hydraulic actuator to brake individual wheels, to pull the vehicle back into line when traction is lost. This photo shows four wheel speed sensors, a steering angle sensor, yaw-rate sensor, the controller and the hydraulic unit. Mass airflow sensor (MAF) A MAF measures the amount of air by mass (and temperature as an auxiliary function) flowing into a fuel-injected engine (see Fig.42). This data is used by the ECU to deliver the correct air-fuel ratio in both open-loop and closed-loop modes (in conjunction with the oxygen sensor in the latter mode). It is important to measure the mass of air rather than its volume, because the volume varies according to air temperature and pressure, but a given mass of air will always have the same amount of oxygen. Most MAF devices use either a hot wire or moving vane technology for mass measurement. Airflow is controlled by the throttle body which contains a butterfly valve. These days it is usually motorised (‘drive-by-wire’) and also has a throttle position sensor to communicate throttle position to the ECU. The ECU monitors the accelerator pedal position and sets the throttle position. In the absence of a MAF, a manifold absolute pressure (MAP) sensor can be employed. In this case, mass airflow is calculated by knowing the air temperature and engine RPM and using a lookup table for fueling. For a turbo or supercharged engine (forced induction), both a MAF and MAP are normally used. Fig.36: traction and stability control systems can take various forms. This older design uses a second electronically-controlled throttle butterfly to reduce engine torque when wheel spin is detected (more modern systems would send signals to the existing motorised throttle). The main input signals are from the wheel speed sensors, which are shared with the anti-skid system. 14 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.37: more modern vehicles use a single electronic control unit for anti-lock braking ABS), traction control (TCS) and stability control (ESC). In addition to the wheel speed inputs, it has a yaw rate sensor and a steering angle sensor, which it can compare to determine if the vehicle is travelling in the intended path or not. As throttle closure takes time, traction control systems will also adjust spark timing (possibly even disabling it) to quickly reduce engine output when the wheels spin during acceleration. Parking assist or self-parking This feature was first demonstrated in 1992 on Ford’s Futura concept car. Then in 2003, Toyota offered it in their Japanese Prius model. Self-parking cars can fit into smaller spaces than many drivers can achieve manually. A self-parking system requires a motorised steering wheel (normally via the electric steering assistance system) plus several sensors such as ultrasonic distance sensors, radar and cameras to provide inputs to the car computer systems about surrounding obstacles, so the car can be manoeuvred into position (see Fig.43). Both parallel and perpendicular parking can be performed, depending on the system. See the video titled “Park Assist Pilot allows 2020 Volvo XC90 T6 to Park itself” at https://youtu.be/ujF1veCdHZs Rain sense module (RSM) The RSM detects water on the windshield and activates the wipers at an appropriate speed or interval (see Figs. 44&45). It may also perform other functions, as in the Hella brand unit shown. It operates on the principle of total internal reflection of a light beam. This occurs with no water on the upper (outside) reflecting surface, but if water is present, some light is lost and the loss of signal is interpreted as rain. Late model Teslas also use their video cameras to detect rain. These systems generally have a sensitivity setting controlled by the driver. Regulated voltage control (RVC) RVC regulates the battery charging voltage based on estimated or measured battery temperature and state-of-charge (SoC). Benefits include improved fuel economy due to the alternator only providing power when necessary, and longer lamp and switch life due to more accurate voltage control. The RVC system maintains the battery at 80% SoC or 13.0V to avoid unnecessary charging. On GM vehicles, the alternator is controlled by the “L” terminal. The PCM (powertrain control module) sends a 5V variable duty cycle signal to it to control the output voltage from 11V to 15.5V. Editor’s note: this is a somewhat controversial system as it means that the battery will go flat quicker when parked and besides the inconvenience, this can also lead to premature battery failure. We have had several letters in Mailbag in the past from readers complaining about vehicle battery undercharging. Traction control system (TCS) The purpose of a TCS is to stop the driven wheels losing traction during acceleration, especially on slippery surfaces such as wet or oily roads (see Fig.46). In most modern vehicles, it is now part of the ESC system, but it might also be Fig.38: a GM ethanol fuel sensor module. It determines the percentage of ethanol in the fuel flowing through it. This is used to apply corrections to the engine map to optimise operation at a wide range of percentages. siliconchip.com.au Fig.39: a cutaway diagram of an engine knock sensor. The mass on top of the piezoelectric crystal helps tune the device to be sensitive to the frequency of the knock vibrations. It is essentially a microphone that’s very sensitive to particular frequencies. Australia’s electronics magazine January 2021  15 Fig.40: the knock sensor can be mounted directly to the engine head or attached to it via a bracket, as shown here. Some vehicles (usually those with larger engines) can have multiple knock sensors. They are sensitive enough to detect ‘incipient’ knock before it’s noticeable to the driver, or can cause any damage. Fig.41: a Lingenfelter ‘aftermarket’ combined RPM limiter, timing retard controller and launch controller intended for racing applications for GM Gen V V8 engines. integrated with the ABS system and the ECU. It monitors wheel speed and if there is a mismatch between the speed of the driven wheels, or between the driven and undriven wheels, engine power power is reduced or a wheel may be braked (via the ABS electrohydraulic system) to stop the slipping wheel spinning excessively. In our article on fluidics (August 2019; siliconchip.com. au/Article/11762), we described how traditional automatic transmissions were controlled via a complicated series of channels, valves and solenoids through which transmission fluid flowed (the valve body). This created a fluidic computer to change gears as needed. This technology has now been replaced with a TCU that operates the transmission via electronic solenoids (see Fig.47). It uses many inputs such as engine RPM, throttle position, recent driving history, speed, whether the vehicle is going uphill or downhill, whether the wheels have traction or not, torque converter slippage, transmission temperature, traction control system state, cruise control state etc. These TCU inputs are analysed and outputs are gener- ated to control the automatic transmission via solenoids to change gears, control hydraulic pressures, to lock the torque converter and to instruct the ECU to momentarily reduce or even “blip” the throttle during gear changes. The TCU also monitors natural wear in the transmission such as of the clutches, and it makes alterations to transmission operation to compensate for wear. Outputs are also sent to other control modules such as the cruise control and error codes for faults can also be generated to be shown on dash warning lights and the OBD system. Like ECUs, aftermarket TCUs are available. These might be used when a modern engine and transmission have been retrofitted into a classic car, or for drag racing. An aftermarket TCU uses the more basic inputs of engine and road speed, throttle position or manifold vacuum and selected gear. See the video titled “1966 GTO: TCI Transmission Controller V8TV” at https://youtu.be/X3EmzS7VSMk TCUs can also be remapped. Typical changes made are the point of torque converter lockup, gear change points and shift speed. Some vehicles are said not to be shipped with optimal TCU settings from the factory and benefit greatly from changes. One such vehicle is apparently the 2017 Land Fig.42: looking into a Holden Commodore MAF sensor. The wires are electrically heated and the mass of air flowing past them cools them. The current required to keep the wires at a constant temperature is therefore proportional to the mass of air moving past them. Source: Wikimedia user Jeff3205. Fig.43: a Ford Active Park Assist module for self-parking. It coordinates inputs from range sensors and controls the steering. The driver controls the accelerator (speed) and transmission (forward/reverse) via prompts from the onboard screen. Transmission control unit (TCU) 16 Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.44: the operation of a typical vehicular rain sensor. Total internal reflection is achieved with no rain, but there is some signal loss with water on the glass. Source: Wikimedia user Puppenbenutzer, CC BY 3.0. Cruiser 200; see siliconchip.com.au/link/ab4l Here is a video of how an original factory TCU is reflashed. Make sure the battery doesn’t go flat during the reflashing process! It’s titled “Programming a GM TCM with an Autel” and is at https://youtu.be/DtmiQD_pzC4 Autel is a brand of proprietary scan tool that uses J2534 communications (which was described briefly last month). Apart from the modules described above, there are numerous others, often particular to certain manufacturers or models. Other types of modules include: • adjustable pedal module • airbag control module • electronic vehicle information centre • heated seat module • instrument cluster • memory seat module • passenger and driver door module Fig.45: a schematic of an electronically controlled automatic transmission. Source: after Clemson University Vehicular Electronics Laboratory. • • • • sentry key immobiliser module sunroof module throttle control module wireless charging module for phones Drive-by-wire As in modern aircraft, in many modern vehicles mechanical linkages between the controlling device (such as a gear shifter) have been replaced with electro-mechanical servos. Examples include steering, brakes, throttle, gear shifting and when some are combined together, automatic parking. Currently, full steering-by-wire systems are illegal in most places; there is a requirement for a mechanical linkage to the Fig.46: a Hella combined rain and light sensor, which activates the wipers and headlights. They are generally attached to the windscreen above the rear vision mirror. Artificial lighting is distinguished from natural lighting due to different spectra. This particular sensor is of modular construction, and car manufacturers can choose additional functionality such as humidity measurement, a solar sensor to adjust the air conditioning, adjustment of head-up display brightness and adaption to windscreen conditions such as dirt. It is connected to the rest of the vehicle systems by both LIN and CAN buses. Source: Hella. siliconchip.com.au Australia’s electronics magazine January 2021  17 Fig.47: some components of the ABS, ECS and TCS in a typical vehicle. Some components are shared and communicate with each other over the vehicle’s data bus. In this diagram, ESC is instead labelled VSC while TSC is labelled TRAC. steering rack. However, in some countries there are already cars on the road with no such mechanical linkage, including the Infiniti Q50 from 2014 onwards. Electric servo operation of steering is possible and is used in most current vehicles. Drive-by-wire systems allow for more design flexibility, less weight and better computer control over vehicle systems and potentially, more reliability. Computer control might be seen as a bad thing as there are possible security (malicious hacking issues) enabling unauthorised persons to take control over the car, and the possibility of an electronic failure rendering the vehicle uncontrollable. However, that can happen with mechanical linkages too. The technology has proven safe and effective on aircraft and is accepted. Drive-by-wire leads the way to autonomous vehicle operation. Note that conventional mechanical systems such as powerassisted steering or brakes will still work even if the power assistance servo fails. This might not be the case in drive-by-wire or brake-bywire systems, unless safety measures are taken such as multiple levels of redundancy and a software “voting” system in the event of a communications failure between the brake SC system and the pedal (see Fig.48). Interesting videos “Reading The Extracted Memory From A Car ECU With A Raspberry Pi”: ............. https://youtu.be/zdgA86pbkw0 “Open source car engine management”: ................................................. https://youtu.be/C1D5B7BNGqA A DIY repair of an ECU: “Ford OBD-1 ECM Repair” ................................................. https://youtu.be/B0Dj40Dkszo “Airbag Crash Data Reset” ................................................. https://youtu.be/KzoKndbYgLo “Automotive Electronic Modules Types” ................................................. https://youtu.be/BG4N2dBgJrQ Fig.48: a brake-by-wire system. HMI stands for human-machine interface, BLDC is brushless electric DC motor. Note the use of 42V. Source: after Wikimedia user Rhoseinnezhad. 18 Silicon Chip Australia’s electronics magazine siliconchip.com.au