ENGINE MANAGEMENT SYSTEM
Introduction
This study evaluates the operating principles of vehicle fuel systems, vehicle ignition systems and pressure charging of engines.
The report attempts to evaluate the operating features of actuators and sensors used in the ignition systems and engine management system of vehicles. It also analyzes the types of pressure charging systems, its shortfalls and how it affects the enhanced power of the engine.
The secondary sources which form the bulk of this report are primarily research from various sources. The paragraphs below look into the sensors and actuators and the pressure charging systems.
Sensors and Actuators
Types of Sensors and function
The types of sensors as well as their functions for the vehicle engine management and ignition systems are discussed below.
MAP sensor
Source: (Autoshop 101, n.d)
Symbol in Circuit
The Manifold Absolute Pressure abbreviated as MAP sensor is a variable resistor used in fine-tuning the pressure difference between the interior and exterior temperatures. The computer of the engine relies on this vital information to adjust the engine load. The computer adjusts the spark timings and fuel mixture when the engine is on load and thus lowers the level of emissions and improves the vehicle performance.
Source: (Pico Technology, 2016)
Waveform for MAP sensor
The figure shows the wave form for MAP sensor which measures the pressure difference existing in the intake manifold and the outside temperature. The engine system uses the information to determine how much fuel the vehicle needs as well as the load it should carry.
TPS Sensor
Source: (Autoshop101, n.d)
The Throttle Position Sensor (TPS) is affixed to the throttle shaft. This sensor improves the performance of the system by adjusting the voltage signal it receives and sending it back to the throttle. The throttle opens up, and the voltage increases. The MAP together with the voltage signal determines how air goes into the engine. The computer uses this information to decide whether or not fuel should be increased or reduced within the engine.
Source: (Pico Technology, 2016)
Wave form for TPS sensor
The TPS sensor, also known as the potentiometer, communicates the right amount of throttle opening due to the linear output. This is received by the Electronic Control Module (ECM). As its name implies, the sensor is located at the throttle spindle and are employed in most of the modern vehicle management system. Furthermore, it has about 5 volt capacity and is a 3 wire device including an earth connection and a center pin having variable output. The criticality of the output at the inside carbon track area is used in detecting the blind spots in the throttle. This results to flat spots and impacts on throttling. The oscilloscope detects the difference in output and then alerts the operator to manage the variable output within the operational range. This helps to detect any defect that may occur.
Knock Sensor
As the name implies, knock sensor prevents engine knock by controlling the vehicle’s combustion process. This functions by piezoelectricity and thus produces a voltage on activation. The system detects a knock and then communicates it to the management unit of the electronic engine. This activates the engine timings process control and fuel injection until the issue is fixed.
Symbol in Circuit
Wave form for knock sensor
Source: (Pico Technology, 2016)
Knock sensor waveform notes
Knock sensor has very rapid response timings and as a result, it must be given a time base basically about 50 ms per column and 500ms throughout as of the case discussed above. The voltage ranges from -5 volts to 5 volts. This is tested by removing the sensor and giving tapping gently with a spanner or something similar.
Technical Information
The key goal in modern vehicle engines is high performance, and this involves less fuel consumption, good power output and minimized exhaust emissions. It is imperative to ensure that the ignition advance curve is near to the detonation as possible. The detonation should be situated very near to the point where the spark plug ignites the air-fuel mixture. This knocking or detonation should normally occur at 15 kHz frequency. Thus, the detonation or knock will occur at the right timings and conditions.
The vital factor is making the timing and conditions right. This sensor is fastened to an electronic unit connected to the control system processor in the vehicle. It detects the 15 kHz frequency signal and then adjusts the air-fuel mixture timings appropriately at the right frequency. The knock is managed by the ECM by making sure that the ignition takes place at the right time. The sensor listens to determines when the knock will occur and then makes sure that it coincides with the ignition timing, ensuring that it occurs at the right time and conditions.
This sensor is crucial because the knock can occur under any one of the conditions listed below:
High combustion temperature
Occurrence of ignition timing before time
High temperature due to air and fuel ratio
High carbon deposits
Source: (Pico Technology, 2016)
Oxygen Sensor
Oxygen sensor is a chemical generator which continuously compares the air within the exhaust and outside the engine, and it generates a voltage in the absence of oxygen. Every spark combustion engines would require this sensor to maintain the balance of air and fuel. Poor fuel economy, power lost, and excessive air pollution would result from the absence of this sensor.
Symbol in circuit
Source: (Pico Technology, 2016)
Wave form for oxygen sensor
Waveform notes
Another name for the oxygen sensor is the lambda sensor. This sensor is immensely relevant in controlling emissions from the exhaust in a catalyst equipped vehicle. The oxygen sensor is positioned in front of the catalyst converter inside the exhaust pipe. It has four electric links which react to the oxygen content in the exhaust system. This gives a varying voltage ranging from 0.5 volts to 4 volts known as the lean volt. When functioning correctly, it can also give higher voltage values.
Moreover, some oxygen sensors do not have the ability to generate their own voltage and may require external voltage supply. However, a vehicle equipped with lambda sensor has the advantage of a ‘closed loop’ system. After the combustion of fuel, the sensor analyzes the emission and resets the engine’s fuel mode.
Furthermore, some oxygen sensors come with heating elements designed to help the sensor attain the optimum operating temperature. The frequency of reaction of the sensor is 1 Hz, but it switches on when it attains the normal operating temperature. An oscilloscope can be used in detecting the switching Source: (Pico Technology, 2016).
Technical Information
The oxygen sensor is installed in most cars using the new EOBD2. On reacting with the oxygen in the exhaust system, the sensor produces a small voltage owing to the air/fuel mixture. The voltage ranges from 0.2 volts (corresponding to low mixture strength) to 0.8 volts (corresponding to high mixture strength). This sensor properly readjusts the engine’s fueling after the fuel is burnt and thus it can be described as a ‘closed loop’ mechanism. The sensor works optimally at a temperature beyond 600 oC but stops working below 300 oC. A heater element situated far away from the heat source helps in maintaining the right temperature.
Furthermore, the sensor consists of two electrodes in which the outer electrode is exposed to the exhaust gasses whereas the inner electrode is exposed to fresh air. The ECM is alerted when there is a difference in the oxygen level, and then the air-fuel mixture is properly adjusted. Zirconia is commonly used here, but Titania could also be used and in fact is a better choice since it can do faster switching.
These two oxygen sensors will both switch once per second on attaining the required temperature. An oscilloscope or a multimeter can show the result Source: (Pico Technology, 2016)
.Speedometer Sensor:
This device helps in telling the driver the vehicle’s speed. When a rotating cable is being driven, a point at the tail shaft in the transmission is selected having the other end connected to the speedometer which is a calibrated tachometer. This determines the gear reduction from the tail shaft to the flexible cable. Also, it can operate the odometer, a numeric counter (Sensoeweb, n.d).
Symbol in circuit
(Quick Reference Pro, n.d)
Respective waveform
Waveform notes
When the vehicle is slowing down or is parked, the ECM tries to adjust the engine speed with the information it receives from the speedometer sensor. The sensor has three wires. One wire is affixed to the battery supplying the voltage; the second is attached to the earth and the third to the digital wave output switching at 12 volts. The sensor could be positioned away from the gear box, in the drive output or behind the speedometer head.
Most modern cars have speedometer which gives the ECM the information required to regulate the vehicle’s speed. The speed sensor gives an analogue output from either a voltage driven unit or an inductive sensor. This sensor could either be a reed switch or a Hall Effect device. The square waveform shown above is produced by the speed sensor, and it can be viewed on an oscilloscope (Pico Technology, 2016).
Actuators Types and Names
There are many types of actuators; however, a few of them are discussed below.
Hydraulic Actuators
This type of actuator makes mechanical processes in a vehicle easy through hydraulic power. The mechanical process in turn activates the linear, rotary or oscillatory motion. The actuators can ensure accurate control of the movement produced by exerting a significant amount of force. They can be used manually or hydraulically in systems such as car pumps and jacks. According to The Greenbook (2016), cylindrical type actuators are the most used actuators in cars, and they use piston dipped mostly in oil. This type of actuators can either be double acting or single acting actuators. The figure below illustrates this more clearly.
A double acting actuator is shown in the left side of the above figure, and it is used in choke valves, and the single acting actuator is shown in the right, and it is used in integrated safety issues.
Symbol in circuit
Waveform
The waveform for the linear system is shown above. It is characterized by three properties namely, homogeneity, time invariability and additivity. Homogeneity refers to the change in input amplitude which results due to an equal change in output amplitude. When two signals are added, the two signals remain intact, this is additivity. Time invariability implies that the response time or reaction remains the same with time (Team Corp., n.d).
Pneumatic Actuators
This actuator works just like the above actuator. However, unlike a hydraulic actuator in which liquid is used, a compressed gas is used in pneumatic actuators. Furthermore, with compressed gas, this actuator can convert energy in linear or rotary motion. The engine controls can be started or stopped with quick reaction with the energy from the pneumatic actuator. In addition, unlike the hydraulic actuators, the pneumatic actuators have an advantage that they do not leak. But they have a disadvantage against mechanical actuators since they have a probability of leaking. Pneumatic actuators are bulky, difficult to move from one place to another and also make noise which is their major disadvantage (The Greenbook, 2016).
The figure above illustrates the basic actuator. The actuators make use of gas laws with basically three inputs which include thermodynamic temperature (T), volume (V) and pressure (P). The Boyle's law, Gay-Lussac law, and the Charles' law explains these relationships.
Symbols in circuit
Source: (Scribd, n.d)
Waveform
Source: (Jeong, 2007)
The different efficiencies of the actuator under different waveforms and types of ratios are summarized in the above waveform. Moreover, the deflection deficiencies decrease as the frequencies increase.
Electrical Actuators
These actuators have different features from the aforementioned ones. Firstly, they are driven by motors which generates electricity and which is converted into mechanical force. This produces motion in the vehicle’s components that requires globe or gate valve. One interesting feature of this type of actuator is that they are cleaner than both the pneumatic and hydraulic actuators discussed already. They do not have leakage issues, and they are very appropriate for car engines where a lot of valves to be opened and closed (The Greenbook, 2016).
Symbol in circuit
Source: (Festo-didactic, n.d)
Waveform
Source: (Piezo Technology, 2016).
Mechanical Actuators
These actuators are relevant when it becomes necessary to convert rotary motion to linear motion. They come handy in operating gears, chain belts, and other devices. They are also employed in turning screws and to make the crew shaft to move in a straight line the wheel and the axle which makes the wheel of a car to make the belt move in a linear motion (The Greenbook, 2016).
Symbol in Circuit
Source: (Wikipedia, 2016).
Mechanical actuator waveform
The waveform diagram shows the short term SPL spectrum for mechanical actuator that has one-third resolution measured with TRF model (Klippel, n.d)
Linear Actuators
These are general purpose actuators which have a lot of applications. They come handy in quite a number of applications and most especially in automating a process.
Symbol in Circuit
Source: (Thomas, n.d)
Waveform for linear actuators
The linear actuator shown above is one of the various types of this kind of actuator. The figure shows the actuator being driven by AC signal. The more preferred signal is the sine wave at a resonant frequency as shown in the diagram above (Precision microdrives, 2016).
Pressure Charging Systems
Mechanically Driven
Supercharging is achieved and regarded as an alternative approach to achieve intensive downsizing in a mechanically driven passenger car engines. The performance of the pressure charging system is identified either by the supercharger or by the combination of the supercharger and the turbocharger. This is the case because the car engine directly is driven by the crankshaft. Observations show that by involving the latter system, the following conclusions can be made:
Two types of compressors namely centrifugal and positive-displacement compressors are included in the mechanical systems used in passenger car engines to activate the pressure charging systems.
Moreover, modern novel technologies attempt to effectively bring together the mechanical engines with the pressure charging systems. The synergetic systems are referred as downsized supercharged engines.
The pressure charging systems with mechanical engines are designed to achieve low force engine enhancement as well as transient drivability improvement and low load reduction. This will give rise to a supercharger process which will supercharge a passenger car mechanically (Hu et al., n.d).
Power increase and limitations
In pressure charging systems, mechanical engines compress the air intake with the aid of the force obtained directly from the engine crankshaft. This helps in boosting mechanically driven vehicles. This helps in improving the drivability of the vehicle that has excessive fuel consumption. Moreover, the engine and driver behavior cannot coordinate the consolidated point methodology and the kinetic model of a mechanically driven vehicle. As a matter of fact, existing mechanical driven vehicles can experience it as a limitation.
Exhaust drive
The supercharged mechanical engines are run by a drive belt or train gears operated by engines, however, the exhaust driven cars are different. Burned exhaust gasses exeunt from the engines on running the air compressor with turbine wheel placed in the engine exhaust manifold. This is referred to as exhaust driven supercharger and commonly known as a turbocharger.
Power increase and limitations
This employs the same principle, but the only difference is that the wheel turbine creates the intake air compression. This increases the pressure from 5 to 15 psi. In addition, this will increase the vehicle's power. This is partially used at high altitude where there is a need for extra power as a result of the reduction in air density.
The exhaust driven vehicle has a shortfall since they consume fuel. Vehicles obey a very simple rule: the more air is burned, the more fuel it will burn. The turbocharging process in exhaust driven vehicles makes them less fuel efficient (Severson, 2008).
Electrically driven
Cars driven by electric motors, as against those driven by petrol engines, are termed electrically driven cars. The set of rechargeable batteries supplies power to the controller which in turn supplies power to the electric motor.
Power increase and limitations
Electric cars are efficient in reusing the energy and makes sure it does not go waste. The battery is recharged each time the break is applied. Moreover, since the car is built with light material, a lot of energy can be saved and used in running the car. Furthermore, since the engine is lighter and smaller, it can supply more power but uses less fuel. Thus, in comparison to other cars, it is environmentally friendly and also there is power increase (Brain n.d)
Furthermore, electric energy is evidently good on fuel, but its short fall is that it is not good on speed and acceleration and as a result, it is best used for city driving. Electric cars have twin engines, but it is limited because the twin-engine produces less power compared to a single gas-powered engine.
Chemical boosting
This implies the boosting of the vehicle’s speed and power by the use of chemicals such as nitrous oxide. Phosphates could sometimes be added so as to make the gas purer.
Power increase and limitations
The power is increased when nitrate is injected into the intake manifold. This leads to the increase in the supply of oxygen and as a result the engine would burn more fuel and air. Moreover, the increased air consumption by the vehicle results in enhanced power production.
However, the chemical boosting is also limited because so much power is produced in the engine sufficient enough to destroy the engine itself. Interestingly, the engine power can increase beyond 100% and even up to 300% and as a result it is necessary to reinforce the mechanical structure of the engine to withstand such pressure and power surge (Yahoo Answers, n.d).
Conclusion
In short, it can be noted that there are various types of sensors and actuators as discussed above. These sensors and actuators function differently from one another and also have different characteristic features. This report has carefully taken a look at their symbols and waveform. Careful study has also been made on the power increase, and limitation of various types of power charging systems and these could range from mechanical and exhaust to supercharging of vehicles and electrical and chemical boosting systems. These technologies and systems are different from one another, and each of them attempts to reduce fuel consumptions and improve power. Basically, a lot about vehicle ignition systems, fuel system and power charging systems have been comprehended in this discussion.
