SENSORS AND ACTUATORS Le Thanh Phuc Faculty of Automotive Engineering University of Technical Education Ho Chi Minh City Email: phuclt@hcmute.edu.vn Introduction • In any control system, sensors provide measurements of important plant variables in a format suitable for the digital microcontroller • • Actuators are electrically operated devices that regulate inputs to the plant that directly controls its output Modern automotive electronic control systems use microcontrollers based on microprocessors to implement almost all control functions Each of these subsystems requires one or more sensors and actuators in order to operate Magnetic Reluctance Position Sensor • This sensor consists of a permanent magnet with a coil of wire wound around it A steel disk that is mounted on the crankshaft (usually in front of the engine) has tabs that pass between the pole pieces of this magnet • The magnetic field in a material is described by a pair of field quantities that can be compared to the voltage and current of an ordinary electric circuit • • One of these quantities is called the magnetic field intensity vector H It exerts a force analogous to voltage The response of the magnetic circuit to the magnetic field intensity is described by the second vector, which is called magnetic flux density vector B, which is analogous to current In these two quantities Reluctance Method • The reluctance method begins with Ampere’s law in integral where ampere-turns NI are assumed given, and magnetic field intensity H and magnetic flux density B are to be found The closed-line integral is replaced by a summation where the closed path consists of line segments of subscript k, each of which is in the direction of the field intensity Thus the direction of the field and flux is assumed known Because flux density B prefers to flow through high-permeability materials, the line segments (straight or curved) are assumed to follow a path through high-permeability materials such as steel If the steel has a gap made of air, the closed path follows the shortest part of the airgap 10 Clapper Armature 32 • Assuming for illustrative purposes that the steel permeability is infinite and that the two air gaps each have length g and poles of equal area, Ampere’s law gives the following formula for H in both airgaps H = NI/(2g) and thus the flux density in both airgaps is 33 34 35 36 (a) Use the reluctance method, assuming no leakage or fringing fluxes, to find the approximate values of the vectors B and F on left side of clapper for I = A Find F in newtons per meter depth of the solenoid into the plane of the page (b) Repeat (a) to find the vectors B and F on right side of clapper 37 38 39 Plunger Armature 40 41 42 Use the reluctance method, assuming no leakage flux, to find the approximate values of B and F on the end of the plunger 43 44 45 46 [...]... 17 18 19 20 21 SPEED SENSORS BASED ON FARADAY’S LAW 22 23 24 25 26 27 28 29 SOLENOID ACTUATORS 30 SOLENOID ACTUATORS • Solenoid actuators have a solenoidal coil, which is a coil of wire wound to a shape that is sometimes cylindrical • All solenoid actuators also have a steel armature, a term for the moving part • In solenoid actuators, the armature moves along a straight line, and thus produces linear... thus produces linear motion 31 Clapper Armature 32 • Assuming for illustrative purposes that the steel permeability is infinite and that the two air gaps each have length g and poles of equal area, Ampere’s law gives the following formula for H in both airgaps H = NI/(2g) and thus the flux density in both airgaps is 33 34 35 36 ... 10 11 12 13 14 15 16 17 18 19 20 21 SPEED SENSORS BASED ON FARADAY’S LAW 22 23 24 25 26 27 28 29 SOLENOID ACTUATORS 30 SOLENOID ACTUATORS • Solenoid actuators have a solenoidal coil, which is... microprocessors to implement almost all control functions Each of these subsystems requires one or more sensors and actuators in order to operate Magnetic Reluctance Position Sensor • This sensor consists of... sometimes cylindrical • All solenoid actuators also have a steel armature, a term for the moving part • In solenoid actuators, the armature moves along a straight line, and thus produces linear motion