Automotive Sensors and Actuators
Principles, Systems, and Electronics
Davide Scullino
Automotive Sensors and Actuators
Principles, Systems, and Electronics
●
Davide Scullino
● This is an Elektor Publication. Elektor is the media brand of Elektor International Media B.V. PO Box 11, NL-6114-ZG Susteren, The Netherlands Phone: +31 46 4389444
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● Declaration
The author and publisher have made every effort to ensure the accuracy of the information contained in this book. They do not assume, or hereby disclaim, any liability to any party for any loss or damage caused by errors or omissions in this book, whether such errors or omissions result from negligence, accident, or any other cause. The author expresses his sincere gratitude to Arrow Electronics and Trenz Electronic for granting permission to include various tables, figures, and program codes in this book.
● ISBN 978-3-89576-708-1 Print ISBN 978-3-89576-709-8 eBook
● © Copyright 2026 Elektor International Media www.elektor.com
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1.6.1 - Electromagnetism
1.6.2 - Electromagnetic Induction
1.6.3 – Self-Induction in Coils
1.7.1 - Brushed
2.5.7 - IGBT
2.6 – Protection Components
2.7 - Integrated Circuits
2.7.1 – Analog integrated circuits
2.7.2 - Voltage regulators
2.8 - Digital Integrated Circuits.
2.8.1 - Logic gates
2.8.1.1 - OR and NOR
2.8.1.2 - AND and NAND
2.8.1.3 - XOR and XNOR
2.8.2 – Microprocessor and microcontroller
2.8.3 –
Chapter 4 • Communication Links and Protocols
4.1 - The LIN Bus
4.1.1 - LIN controller
4.1.2 - LIN connector
4.1.3 - Structure of LIN sensors
4.2 - SENT Protocol
4.2.1 - SENT data format
Chapter 5 • Engine Sensors
5.1 – Intake Air Mass Detection
5.1.1 – The flowmeter
5.1.2 – Mass air flow (MAF) sensor
5.1.2.1 – Thermal flowmeter
5.1.2.2 – Bosch HFM sensors
5.1.2.3
5.2
5.3
5.10.1.2
5.10.1.3
5.10.1.4
5.10.4 – Denox sensors
5.11 – Engine Temperature Sensor
5.12 – Water-in-Diesel Sensor
5.13 – Engine Coolant Level Sensor
5.14 – Barometric Sensor
5.15 – Accelerator Pedal Sensor
Chapter 6 • Transmission Sensors
6.1 – Vehicle Speed Sensor
6.2 – Gearbox Sensors
6.2.1 – Reverse gear switch
6.2.2 – Clutch pedal switch
6.3 – Clutch-By-Wire Sensors
6.4 – CVT Transmission Sensors
6.5 – Automatic Transmission Sensors
6.6 – Limited-Slip Differential Sensors
7.1
7.4 –
7.5 – Sensors for Assisted and Autonomous Driving
7.5.1
7.5.4 – RADAR
7.5.5 – 4D RADAR technology
7.5.6 – LIDAR
7.5.7 – Cameras
7.5.8 – Blind spot assist
7.5.9 – GPS receiver
7.6 – Facial scanner
Chapter 8 • Steering and Suspension Sensors
8.1 – Power Steering Sensors
8.1.1 – Capacitive steering sensor
8.1.2 – Magnetic steering sensor
8.1.3 – Electric power steering sensors
8.2 – Sensors for Active Suspensions
8.2.1 –
8.2.1.1
10.4 – Turbocharger Actuators
10.4.1 – Electrically actuated bypass
10.4.2 – VGT actuators
10.5 – Swirl-Flap Actuation
10.6 – EGR Actuators
10.7 – Variable Camshaft Timing System
10.8 – Electrically Actuated Thermostat
10.9 – SCR System Actuators
10.10 – Diesel Fuel Heater
10.11 – Fuel Pressure Regulation in Common Rail Systems
10.12 – Fuel Pressure Regulation in GDI Systems
10.13 – Common Rail Injectors.
10.14 – Gasoline and Gas Injectors
12.7 – Brake-By-Wire Actuators
12.8 – Electric Vacuum Pump .
Chapter 13 • Steering and Suspension Actuators
13.1 – Steering System Actuators
13.1.1 – Electric power steering actuators
13.2 – Suspension Actuators
13.2.1 – Air Suspensions
13.2.2 – Electromagnetic suspensions
Chapter 14 • Vehicle Body and Electrical System Actuators
14.1 – Climate Control Actuators
14.1.1 – Auxiliary heating
14.1.2 – Climate control fan
Preface
The evolution of the automobile is now entirely driven by electronics and the software running within the various control units (ECUs) distributed throughout modern vehicles. Electronics plays an increasingly central role in managing systems and components that were once purely mechanical, hydraulic, or at most electromechanical. It now reaches every part of the vehicle to optimize performance, improve energy efficiency, reduce emissions, coordinate the internal combustion engine with the electric motor in hybrid vehicles, enhance both active and passive safety, and improve onboard comfort and travel experience for drivers and passengers.
To achieve all this, electronic control units and their software are not enough on their own. This extensive use of electronics requires accurate knowledge of the operating conditions of the systems and subsystems it is meant to control. The components responsible for providing this information are sensors, which can be seen as the “five senses” of automotive electronics. The components responsible for performing corrective actions or maintaining specific operating modes are the actuators, which function as the “arms” or hands of the control electronics.
The purpose of this volume is to list, describe, and explain the operation and structure of the main sensors and actuators used in automotive electronics. It begins with the basic concepts needed to understand the terminology and principles that appear throughout the analysis of each system.
After an introductory section consisting of the first two chapters, the content is organized by system. Sensors are addressed first, grouped by the systems to which they belong. This is followed by a study of the actuators, also organized by system. The volume concludes with a chapter dedicated to the electronic components that make up many of these sensors and actuators. This final section will be particularly useful for those interested in disassembling, testing, or repairing these devices.
Enjoy the reading!
Chapter 1 • Electrical Engineering and Physical Quantities
In this volume, we will frequently encounter concepts drawn from electrical engineering and electronics, as well as physical quantities such as voltage, current, resistance, frequency, and others, together with their respective units of measurement, including volts, amperes, ohms, and so on. Therefore, before delving into the components of sensors and actuators or analyzing their operation within a modern automobile or other vehicle, it is appropriate to begin by outlining the fundamental principles of electronics, and, more fundamentally, those of electrical engineering.
Electrical engineering studies and defines the physical phenomena associated with electricity, understood as the set of phenomena involving the release or movement of electrons. These phenomena can be static, in which case we refer to electrostatics, that is, the accumulation of electrons that generates a potential difference but does not produce a current, or dynamic. In the latter case, we refer to electric current, since it involves the movement of electrons.
For such a flow to occur, a potential difference must exist between two points. This is known as “electric voltage”. Voltage, which expresses an imbalance of electric charge between two points, is measured in volts (V), while the resulting current (which cannot exist without voltage) is measured in amperes (A).
1.1 – Materials and Electric Current
Electric current refers to the unidirectional or bidirectional movement of electrons through materials or in a vacuum. This movement may be more or less orderly, constant, or variable, and in some cases, periodic. Based on their behavior in the presence of electric current, materials are classified into three categories:
a Conductors: allow current to pass through them freely.
a Semiconductors: conduct current only under certain conditions, which is why they are essential in electronics.
a Insulators: prevent the flow of current unless subjected to a voltage high enough to break down their insulating properties.
Conductors are typically metals, whose electrons can be easily displaced by applying even a small electric field across their terminals, thereby generating current.
As it flows, electric current encounters opposition; that is, the movement of electrons requires the voltage source to perform work and continuously supply energy.
The difficulty the generator encounters in driving electrons through the circuit is known as resistance, and it is expressed and measured in ohms (Ω).
Resistance is influenced by several factors, including temperature. Higher temperatures induce “thermal agitation”, a phenomenon exploited by certain sensors to measure temperature.
In theory, electric current originates from generators, which may be either voltage generators or current generators. In practice, this distinction is largely conceptual. When a potential difference is applied between two points and connected to a load, current flows. Thus, a voltage generator also produces current, and current is always the consequence of voltage, that is, a potential difference.
An ideal voltage generator produces a constant potential difference across its terminals; the current it delivers depends solely on the resistance of the connected load. A current generator, by contrast, maintains a constant current regardless of the load’s resistance.
This distinction proves useful when analyzing devices and electronic circuits. For example, a piezoelectric sensor that generates its own voltage can be modeled as a voltage generator. In practice, however, every voltage generator is affected by an undesired internal resistance, known as parasitic resistance, which can be modeled as a resistor in series with the generator’s terminals. As current draw increases, this parasitic resistance causes a drop in the output voltage.
This phenomenon applies not only to electrical generators such as alternators and dynamos, but also to electronic circuits like power supplies. The same principle holds for batteries, which, although not generators in the strict sense, act as energy storage devices, as well as for chemical cells and photovoltaic panels.
As for current generators, they do not exist in a truly ideal form, since a parasitic resistance across the output terminals always diverts a portion of the current.
Figure 1.1 illustrates the schematic representation of a real voltage generator, where Ro represents the parasitic resistance and Vo is the voltage measured under open-circuit conditions (i.e., when no current is drawn).
Figure 1.2 shows the graphical symbol of a real current generator, which also includes a parasitic resistance Ro.
1.2
1.1 - Schematic of a real voltage generator with its parasitic resistance (Ro) in series.
Figure 1.2 – Graphical symbol of a real current generator.
- Electric Power
One physical quantity that frequently appears in the specifications of circuits, sensors, and actuators, now more than ever due to the growing emphasis on energy efficiency, is electric power, which refers to the amount of electrical energy consumed per unit of time. Quantitatively, electric power is defined as the product of voltage and current:
P=V x I
When referring to a generator, V represents the output voltage, and I is the current flowing through the connected load. In this case, we speak of generated or delivered power. Conversely, when referring to a load (such as a resistor), the power refers to what is dissipated or absorbed: the voltage is what the load receives, and the current is what flows as a result of the applied voltage.
Figure
In the context of sensors and actuators, the term “power” always refers to absorbed power.
1.3 – Electrical Resistance
Resistance is defined by Ohm’s Law, which states that across a resistor, that is, a conductor that opposes the flow of electric current, there is a voltage drop ΔV (or simply V) proportional to the current (I), as expressed by the following equation:
V = I x R
where R represents electrical resistance, measured in ohms (Ω). Conversely, the current flowing through a resistor subjected to a voltage difference can be calculated as:
I = V / R
Ohm’s Law, for instance, allows us to calculate the voltage drop across a resistive transducer, as well as the electrical power dissipated by a resistor, which is converted into heat via the Joule effect.
Figure 1.3 illustrates the behavior of a resistor conducting current and visually represents the principle expressed by Ohm’s Law.
Figure 1.3 - A voltage drop ΔV appears across a resistor, directly proportional to the current.
1.4 - Direct and Alternating Current
Electric current may be either direct or variable. In the first case, the flow of electrons maintains a constant intensity over time. In the second case, the intensity varies, either in an irregular manner or following a regular pattern. When this variation is regular, the current is referred to as periodic and is characterized by a frequency of variation, expressed in cycles per second or hertz (Hz). Alternating current is a type of periodic current in which the direction of electron flow, and consequently the polarity, reverses cyclically. Unlike direct or irregular variable currents, AC alternates between positive and negative values.
The sinusoidal waveform (Figure 1.4) is the typical shape of the voltage supplied by the power grid and follows the behavior of the sine of an angle ranging from 0° to 360°. Since a full cycle corresponds to 360°, equivalent to the circumference of a circle (2π * radius, where π ≈ 3.1416), the angle π/2 corresponds to 90° (a right angle), π to 180° (a straight angle), and 2π to 360° (a full rotation).
1.4 – Waveform of a sinusoidal electric quantity.
1.5 – Electrostatic Phenomena
Electrostatic phenomena occur in insulating materials and in air, but not in conductors, since any imbalance of charge in a conductive material is quickly neutralized: free electrons move to restore balance, giving rise to electric current. Electrostatic effects can be triggered when an insulating material is subjected to mechanical stress, brought near a substantial electric charge, or exposed to a strong electric field induced by a voltage or a charged object.
In the case of mechanical stress, electrostatic effects arise from the piezoelectric effect, whereby deformation of certain crystal structures, such as quartz, or ceramic materials like barium titanate, causes an accumulation of negative charges (electrons) on one side and exposed positive charges on the opposite side. Similar effects can also occur when two insulating materials with different atomic structures are rubbed together.
Electric charge tends to be discharged more readily from sharp edges or pointed tips, that is, from the extremities of conductors.
Charge accumulation may lead to sudden and uncontrolled discharges, as shown in Figure 1.5, a phenomenon known as Electrostatic Discharge (ESD). This can severely damage electronic circuits based on MOS or CMOS logic. To prevent such damage, ESD protection is commonly integrated into automotive buses, as well as into certain sensors and actuators.
Various physical phenomena can lead to the accumulation of electric charge between two points in an insulating material or in air. When the potential difference between positively and negatively charged regions exceeds the insulating capacity of the material (dielectric strength), an electric discharge occurs and current flows, signaling the recombination of displaced electrons with atoms that had been lacking them.
Figure
Figure 1.5 – Electrostatic phenomena result from the accumulation of electric charge.
1.6 - Magnetic Phenomena
This term refers to physical phenomena whereby certain materials exhibit the capacity to attract or repel other similar substances. A familiar example is the compass, whose magnetized needle aligns with the Earth’s magnetic field and points toward the North Pole. It is important not to confuse magnetism with gravitational attraction: while both involve interactions between masses, magnetic phenomena arise from the intrinsic spin of electrons within individual atoms.
Magnetism forms the basis for numerous sensors and actuators, such as magnetoresistive sensors, Hall effect sensors, and even gyrocompasses.
In relation to their magnetic properties, materials are classified as ferromagnetic, paramagnetic, or diamagnetic: ferromagnetic materials exhibit strong magnetic behavior or can acquire it when exposed to a sufficiently intense magnetic field; paramagnetic materials behave similarly, though their response is weak and generally negligible. Diamagnetic materials, by contrast, are insensitive to magnetic fields and do not interact with them.
When subjected to a sufficiently strong magnetic field, ferromagnetic materials can be magnetized, that is, their molecular structure becomes permanently aligned. This process gives rise to magnets: one end acquires North polarity, while the other assumes South polarity. These magnetic properties, resulting from the alignment of individual molecules, can occur naturally or be induced artificially.
The ends of a magnet are called poles, namely the North and South poles. The North pole of a magnet is repelled by the Earth’s North Pole and attracted to the South Pole, and vice versa.
The Earth’s magnetic field allows for the use of instruments such as magnetometers, which are extremely useful in satellite-based positioning and navigation.
When two magnets are placed with like poles facing each other, they repel; when opposite poles face one another, they attract, an interaction illustrated in Figure 1.6. The ends of the magnet are referred to as pole pieces, and the region between them is traversed by magnetic field lines, also called lines of magnetic force, which flow from North to South, as depicted in Figure 1.7.
Figure 1.6 – In a magnetized material, one end assumes North polarity and the other South polarity; like poles repel each other, while opposite poles attract.
Figure 1.7 – Propagation of magnetic field lines, flowing from North to South.
1.6.1 - Electromagnetism
Magnetic phenomena are not limited to natural materials and permanent magnets. They can also be produced by electric current, which generates a magnetic field around any conductor it flows through. The strength of this magnetic field is proportional to the intensity of the current and varies in time if the current itself is variable. The magnetic field generated by electric current is referred to as an “electromagnetic field”, and its behavior is studied within the domain of “electromagnetism”. Electromagnetism plays a central role in electronics, as it enables the generation of magnetic fields with precisely defined and controllable characteristics, making it essential for the design and operation of sensors and actuators.
Since electric current generates a magnetic field, it can also interact with external magnetic fields. This interaction is reciprocal: a magnetic field, whether constant or varying, can exert a force on a conductor carrying current. This mutual interaction underlies the operation of electric motors and, more broadly, of electromagnetic actuators.
To illustrate how a magnetic field affects a current: when a freely rotating magnetized needle (or any straight magnet) is placed beneath a straight conductor carrying a strong current, the needle rotates in response to the direction of the current, as shown in Figure 1.8. Specifically, the needle aligns perpendicularly to the wire: if the current flows from left to right, the North pole of the needle points upward; if the current flows from right to left, the North pole points downward. If the needle is placed inside a coil and aligned with its axis, the North pole turns toward the side where the current exits the loop.
As for the effect of a magnetic field on a current: the force exerted by the field on a current-carrying conductor is always perpendicular to both the direction of the magnetic field lines (which flow from North to South) and the direction of the current. This interaction is illustrated in Figure 1.9, which shows the direction of the current, the orientation of the magnetic field, and the resulting force. We see that when a wire is placed within the magnetic field generated by a magnet, it is pushed by a force that acts perpendicularly to both the field lines and the direction of current flow. If the field lines, and thus the magnetic induction vector B, run from North to South, and the current enters from the rear and exits from the front of the magnet, the wire is pushed upward.
Figure 1.8 – Orientation of a rectangular magnet in response to the current flowing through a wire positioned perpendicularly to it.
Figure 1.9 – A conductor carrying current (I) and immersed in magnetic field lines is acted upon by a force perpendicular to both.
The magnetic field generated by an electric current flowing through a conductor is referred to as an “electromagnetic” field. Its lines of force are circular and concentric, coaxial with the conductor’s axis and therefore with the direction of current flow. Assuming the current is direct, the orientation of these lines corresponds to that of a right-hand screw advancing in the same direction as the current.
The force exerted by an electromagnetic field is always directly proportional to the intensity of the current flowing through the conductor, to the length of the conductor segment that lies within the magnetic field, and to the sine of the angle formed between the direction of the field lines and that of the conductor. More precisely, this force is defined by the following relation:
F = B x I x l x sena
which is known as the Laplace formula; in this expression, F is the force acting on the conductor, I is the current intensity, l is the length of the conductor segment, and a is the angle formed between the magnetic field lines and the conductor.
B represents the magnetic induction.
The magnetic induction at a given point in the field generated by a current-carrying conductor is directly proportional to the current intensity and inversely proportional to the distance from the conductor. More precisely, if I denotes the current and d the distance from the point of observation, the induction is given by:
B = k/d
The parameter k is a constant which, in the case of a vacuum, has the value , μo/2π; μo is the magnetic permeability of vacuum and equals 2π x 10-7 Wb/Am. Magnetic permeability expresses the ability of a material or of air to be traversed by the lines of force of a magnetic field, and it plays a determining role in assessing the behavior of components whose operation is governed by magnetic effects, such as electric motors, ABS sensors, magnetic reluctance sensors, and so forth.
When a conductor is arranged in the shape of a loop, the magnetic field generated by the current consists of concentric circles centered on the loop itself.
The magnetic induction at the center of the loop, assuming vacuum conditions, is given by the following relation:
μo x I
B = ——————
2π x r
where I is the intensity of the current flowing through the wire, and r is the radius of the loop.
This formula is useful for calculating the magnetic field intensity generated not only by individual wire loops, but also by coils (solenoids) composed of multiple turns wound in the same direction and positioned closely together. This arrangement increases the overall magnetic field strength for a given current. In such configurations, the total magnetic induction corresponds to the sum of the inductions produced by each individual turn, assuming the turns are connected in sequence and carry the same current.
If the length of the coil, measured from the first to the last turn, is much greater than its diameter (at least ten times longer), the magnetic field inside the solenoid can be considered uniform. Its direction aligns with the axis of the turns, while its orientation is determined by the current flow. Specifically, it follows the direction of a right-hand screw advancing in the direction of the current (Figure 1.10).
Figure 1.10 – Direction of the magnetic field lines generated by a coil carrying a unidirectional current.
As for the intensity of the magnetic induction, in a solenoid much longer than its diameter, the field inside is given by the sum of the individual contributions of each loop. More precisely, the total induction is calculated as follows:
μo x I x n
B = ——————————— l
where n is the number of turns, and l is the length of the solenoid.
To further increase the magnetic induction without expanding the coil’s dimensions, multilayer coils are employed. In such cases, the solenoid consists of several overlapping layers of wire, and the previous formula no longer applies.
Instead, the magnetic induction must be determined using another expression, which considers the diameter (d) of the individual loops:
μo x I x n
B = ———————————
π (l² + d²)
This formula also applies to solenoids whose length is comparable to the diameter of the turns.
1.6.2 - Electromagnetic Induction
When a conductor is immersed in a magnetic field, an impulsive electromotive force (e.m.f.) develops across its terminals. This induced voltage initially reaches a peak value and then decreases over time, eventually dropping to zero. If the magnetic induction originates from an electromagnet powered by a variable current, the phenomenon persists as long as the magnetic flux varies. In such cases, a voltage appears across the ends of the conductor, varying in proportion to the current flowing through the electromagnet (Figure 1.11). If the loop is closed on a load, a current flows, and its intensity is directly proportional to the strength of the electromagnetic field.
Figure 1.11 – A voltage is induced across a wire loop exposed to a magnetic field; when the circuit is closed, a current is generated.
If the conductor is moved within the magnetic field, a voltage is induced across it. The way this voltage varies over time depends on the orientation of the conductor with respect to the magnetic flux lines.
This is the operating principle of some electric motors and generators, such as dynamos and alternators, as well as certain types of sensors.
Magnetic flux is defined as the density of magnetic induction over a given surface and at a specific angle. It depends on the intensity of the magnetic induction and the area under consideration, according to the following formula:
F = B x S x cosa
where B is the magnitude of the magnetic induction vector, S is the surface area through which the flux is measured (expressed in webers), and a is the inclination of the conductor immersed in the magnetic field (Figure 1.12). More precisely, in the case of a straight wire, a is the angle between the perpendicular to its direction and the direction of the field lines; whereas for a loop, it is the angle between its axis and the field lines of the same field. Since the flux depends on the angle formed by the conductor and the magnetic field lines, rotating the conductor results in a variable voltage which, if the rotation is uniform from 0° to 360°, follows a sinusoidal pattern.
Figure 1.12 – A variable voltage is induced across a wire loop or rotating solenoid immersed in a constant magnetic field, depending on the angle between the field lines and the cross-section of the turns.
The induced voltage gives rise to a current (if the circuit is closed on a load), which flows in the direction of a left-handed screw advancing along the magnetic field lines produced by the electromagnet.
1.6.3 – Self-Induction in Coils
The phenomenon of electromagnetic induction described earlier occurs not only when a conductor is stationary within a variable magnetic field or moving through a constant one, but also within a solenoid or even a simple wire loop. In these cases, the induced voltage exhibits a polarity and magnitude that oppose the one responsible for generating the current and magnetic field—that is, the voltage that produced the induced electromotive force (e.m.f.). This effect is known as self-induction (or mutual induction) because the element carrying the initial current is itself responsible for producing the induced magnetic flux.
Self-induction explains why solenoids behave inertially in response to current. When voltage is first applied, they initially draw no current, but gradually begin to conduct electricity over time. If the supply voltage is suddenly interrupted, they tend to maintain the current flow. If the circuit is opened at points that are very close together, an electric arc may jump across them, potentially causing the contacts to melt.
Another noteworthy aspect of coil behavior is that self-induction tends to stabilize the magnetic field and thus resists any variations. As a result, the faster or more frequent the voltage variations applied to a solenoid, the greater the opposition encountered by the current. This is because coils inherently oppose changes in current, since it is precisely these changes that produce variations in magnetic flux.
In a solenoid or wire loop carrying an electric current, the magnetic flux due to induction (Di) is expressed by the relation:
DFi = L x i
where i is the instantaneous current intensity generating the magnetic flux, and L is the coefficient of self-induction, or inductance. This coefficient expresses the solenoid’s tendency to generate both a magnetic field and an opposing induced voltage: the higher the inductance, the greater the response to a given magnetic flux, and vice versa. Inductance is measured in henries (H) in the International System of Units (SI), where one henry is equal to one watt-second (1 H = 1 W x s). It is functionally similar to electrical resistance, but this resistance-like behavior emerges only when the circuit operates under variable conditions. In such cases, the inductive opposition increases in direct proportion to the frequency.
By considering variations in flux over infinitesimally small intervals of time—which in mathematics corresponds to the “derivative”—we arrive at Lenz’s Law, which defines the self-induced voltage (ei):
This equation signifies that when a coil is energized, the current flowing through it, due to self-induction, is initially zero and reaches its steady-state value only after a certain interval. Conversely, if the voltage is removed and a resistor is connected across the coil’s terminals, the current is initially at its maximum and then gradually decays to zero.
In a coil, the value of inductance is directly proportional to the number of turns and depends on the magnetic flux. Since the flux itself is directly proportional to the magnetic permeability of the medium around which the solenoid is wound, inductance is also directly proportional to permeability.
To determine the inductance of a solenoid, two common geometries are considered: toroidal and linear. In a toroidal core, the turns are all wound in the same direction, beginning from a fixed point and progressing along the circumference of the core. Since the winding is formed over a material with uniform magnetic permeability, the flux generated by a single turn can be expressed as:
μ x I x S F = ————————— l
where S is the cross-sectional area of the loop, calculated as π x r² (with r being the radius of the loop), and l the length of the winding, imagined as if it were unwrapped into a straight line. The parameter μ represents the absolute permeability of the medium through which the magnetic flux flows; it is the product of μo (the magnetic permeability of free space) and μr (the relative permeability), which is a material-specific property. Relative permeability μr is very low (a few units) in paramagnetic materials, very high (reaching values in the thousands) in ferromagnetic materials such as soft iron, ferrite, and iron,
silicon alloys, and exactly 1 in diamagnetic materials, for which the absolute permeability μ is equal to that of a vacuum (μo).
The total inductance of the coil is defined by the following relation: μ x S x N² L = —————————
where N is the number of turns. This same formula, typically used for calculating the inductance of a toroidal coil, can also be applied to linear coils, provided their length is at least five times the diameter of the turns.
1.7 – Devices Based on Electromagnetism
Electromagnetic phenomena not only enable the acquisition of linear and angular positions or the detection of static and variable magnetic fields via dedicated sensors, but also underpin the functioning of electrical machines. These are devices capable of either generating electricity when set in motion under the action of a force, or producing mechanical motion when powered by an electric current. Electrical machines also include the transformer, a static device used to transfer electrical power between circuits while modifying voltage and current levels.
Electric machines include generators (such as dynamos and alternators) and motors in their various forms. For the purposes of this volume, we will focus on the brushed direct current motor with permanent magnets, the three-phase brushless motor, and the stepper motor.
1.7.1 - Brushed DC motor
The brushed direct current motor (Brushed DC motor or BDC) consists of a rotor that contains pairs of north and south pole extensions of electromagnets, positioned to face permanent magnets mounted inside the motor housing. The electromagnetic coils are powered via brushes through the commutator, which, in its simplest form, is a cylinder fitted with two arc-shaped contacts, electrically insulated from one another. In practice, there are more than two contacts, but always an even number, and arranged in opposition.
Each pair of contacts powers a coil, and each coil corresponds to a pair of pole extensions; thus, a rotor may feature four or more poles.
When voltage is applied to the brushes, current flows through the coils, generating a magnetic field in the electromagnets. This field pushes the pole extensions away from the permanent magnets. As the rotor turns, the commutator reverses the current direction, inverting the magnetic field. The pole extensions are again repelled by the permanent magnets, maintaining the shaft’s rotation. The commutator contacts are arranged around a cylinder made of insulating material and are pressed against the brushes, which are spring loaded elastic contacts that slide perpendicularly to the motor shaft. In the basic configuration of the DC motor, the stator serves as the field component (inductor) and
contains two inward-facing permanent magnets, one representing the north pole, and the other the south.
To understand how a brushed DC motor operates, refer to Figure 1.13 and imagine the rotor as a rectangular copper wire loop with axially extended ends, positioned between the pole pieces of two magnets, one oriented with its north pole facing upward, the other with its south pole facing downward. Each end of the loop is in contact with a brush. When a voltage is applied in such a way that a magnetic field is established with the north polarity aligned toward the north-facing magnet and the south polarity toward the southfacing magnet, the loop is repelled by the magnets and begins to rotate. As a result of the rotation, the commutator contacts on the shaft shift and lose contact with the brushes. The magnetic field then collapses, and with it, the repulsive force. Assuming the rotor has some inertia, the rotation continues until the brushes come into contact with the opposite set of commutator contacts, now in reverse polarity.
Figure 1.13 – Diagram and operation of a brushed DC motor with permanent magnets.
At this point, current flows through the loop in the opposite direction, generating an inverted magnetic field. However, because the loop has rotated 180°, the south pole of the electromagnetic field once again opposes the south pole of the lower magnet, and the north pole opposes the upper magnet, producing a new repulsion and another impulse that continues to drive the rotation of the rotor (the loop). As the rotor turns, the commutator contacts once again move away from the brushes. Inertia allows the rotor to continue spinning until it returns to its initial position. The cycle then repeats indefinitely, keeping the motor in continuous rotation.
The rotational speed of a brushed DC motor depends on the applied voltage (as long as it remains within the allowable range) and on the load connected to the shaft. Power output and torque, on the other hand, are determined by the current drawn by the motor.
Some brushed DC motors may use a stator without permanent magnets. Instead, they feature salient poles equipped with windings that are energized by direct current. This configuration is known as a wound-field motor, or separately excited synchronous motor (SESM).
1.7.2 - Brushless motor
The brushless motor is an electric motor without brushes, in which the stator houses the windings, serving as the fixed inductor of the excitation field, while the rotor is fitted with two or four permanent magnets arranged with alternating salient poles. This design eliminates the need for a commutator and allows for better heat dissipation from the windings, which are positioned externally. As a result, brushless motors support higher rotational speeds and deliver greater efficiency.
Having the coils located exclusively on the stator means that, to generate a rotating electromagnetic field capable of driving the rotor, the direction of the current must be periodically reversed. In practical terms, if the rotor has two pole extensions (i.e., one pole pair), the magnetic field must invert once per full rotation.
The typical brushless DC motor is a three-phase device, with three (or a multiple of three) stator windings powered by unidirectional pulses, thus enabling continuous operation. The rotor includes three pairs of pole extensions, spaced 120° apart. The stator windings are energized in either a star or delta configuration by voltage pulses sequenced with a 120° phase shift, generating a rotating magnetic field. For the motor to operate properly and produce a rotating field, the pulses must follow a precise sequence, each applied at intervals corresponding to a 120° rotation of the rotor. In this setup, the rotor’s speed is determined by the pulse frequency and the number of pole pairs on the rotor.
The brushless motor must be powered by an electronic controller, known as an ESC (Electronic Speed Controller). Control is achieved by delivering PWM-modulated voltage pulses, offset by 120° between phases. Varying the pulse frequency adjusts the rotor speed, while modifying the pulse width regulates the motor’s power output.
The absence of brushes allows the brushless motor to reach higher rotational speeds than its brushed counterpart and grants it a virtually unlimited service life.
Figure 1.14 illustrates the operation of a brushless motor with delta-connected windings.
Index
A
AC
16, 38, 165
Accelerator 168, 172, 206
Accumulator 68, 206, 281
Address 68, 70
B
Battery
103, 202, 301
BGA 390
Bit 69, 72, 106, 211
Brushless 278, 349, 353
Bus 68, 98, 103, 166
C
Camshaft
102, 139, 278
CAN-Bus 89, 136, 156, 225
Capacitance 32, 37, 228
Clock 68, 106, 203, 221
Coil 20, 27, 39, 192
Compressor 167, 357, 363
Connector 101, 127, 182, 261
D
DC
28, 32, 111, 261
DFN, package 387, 389
E
ECU
34, 79, 114, 178
EDC 124, 151, 287
EGT 142, 143, 158
Electromagnetic 20, 169, 196
F Feedback
35, 59, 132, 176
Ferrite 26, 40
FRS 122
FSK 86,
G
Gearbox
172, 175, 180, 307
Glow plugs 300, 301, 302
Gold 275, 390
H
Hall effect
18, 92, 139
Headlight 35, 373, 376
Heater 157, 249, 284, 366
Height sensor 236, 239, 357
I
Inductance
26, 174
Inductor 27, 39 Infrared 47, 70 242
J
Joule, effect
16, 76, 113, 287 Junction 112, 127, 143
K Khz
132, 194, 254 K-line 356
L
LIN bus
129, 176, 236 Logic 62, 70, 132, 165
M
Magnetism 18 Manifold 110, 120, 147, 274 MHz 204, 220
N NAND 62, 65 NOR 62, 63
O
Operational
78, 86 Oscillator 40, 83, 132, 165
P
Particulate
142, 154, 268 PCB 169, 275, 384
Pin 297, 308, 385 PLCC 388, 389
Power steering 200, 207, 225
Pump 122, 163, 225, 265
Q
QFN, package
201, 389
Q-factor 41
R
Ratiometric
78, 170, 303
Regulator 61, 256, 303
Reluctance 173, 192
Reluctor wheel 193, 318
Resistance 13, 33, 53, 115
RF 202, 254
S
SCU 156, 158
Sent protocol 98, 105, 179, 233
SMD 33, 378
SoC 201, 211, 257
Soldering 389, 390
Solenoid 22, 122, 176, 192
Spark plug 259, 299
Stepper-motor 27, 31, 376
Switch 52, 61, 128
T
TCS
207, 321
TCT 176, 311
TCU 175, 181, 307
Thermocouple 95, 96, 143
Trigger 60, 106, 142, 233
TSOP 386
U
Ultrasonic
77, 134, 209
Ultrasound 161, 213
Ultraviolet 48, 49
V
VCT
278, 280
Voltage 13, 15, 81, 211
W Watt 26
Wiring 31, 106, 150, 275
Xenon
240, 373 XOR 62, 66
x-by-Wire 172
Yaw
Zener
182, 207, 238, 358
46, 54, 383
Automotive Sensors and Actuators
Principles, Systems, and Electronics
This handbook provides a detailed study of the sensors and actuators at the heart of modern vehicle electronics. It begins with basic electrical and electronic concepts, introducing the principles and terminology essential for understanding automotive systems.
The book explores sensors and actuators on a system-by-system basis, including:
> Fundamentals of electrical engineering, electromagnetic phenomena, and motor principles
> Passive and active electronic components, integrated circuits, protection devices, and automotive-grade electronics
> Sensor characteristics, signal conditioning, ADCs, PWM and frequency outputs, and interface adaptation
> Automotive communication links and protocols, including LIN and SENT
> Engine sensors: air mass, pressure, temperature, speed, position, exhaust and emissions-related sensors
> Transmission sensors for manual and automatic systems
> Steering and suspension sensors for conventional and active systems
> Vehicle body and electrical system sensors for comfort, climate, access, and monitoring functions
> Engine actuators such as throttle bodies, injectors, turbo actuators, EGR systems, ignition components, and pumps
> Transmission, brake, steering, suspension, and body actuators
> Identification and coding of electronic components and packages commonly used in automotive applications
The structure and operating principles of each component are explained, with relevant electronic circuitry illustrated. Its system-oriented organization and practical focus make it a valuable reference for understanding, testing, and troubleshooting automotive electronic systems.
Davide Scullino is an Electronic Engineer who has been writing articles for applied and professional electronics magazines since his high school days.
A designer of analog and digital electronic devices and systems for audio and telecommunications, he has been active since 1987 and has authored hundreds of articles and dozens of books on technical subjects including electrical engineering, electronics, physics, automotive mechanics, automotive electronics, and model aircraft.
He is also a Technical Trainer, a speaker at professional training courses for technicians, and a teacher of automotive electronics, automotive technology, and electrical engineering.