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h24 input sensors-engine control.pdf

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H24 INPUT SENSORS ENGINE CONTROL
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Overview The EFl/TCCS system is an electronic control system which provides Toyota engines with the means to properly meter the fuel and control spark advance angle. The system can be divided into three distinct elements with three operational phases.The three system elements are: ? Input Sensors ? Electronic Control Unit (A Microcomputer) ? Output Actuators ENGINE CONTROLS - INPUT SENSORSPage 1 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. The electronic control system is responsible for monitoring and managing engine functions which were previously performed by mechanical devices like carburetors, vacuum, and centrifugal advance units. In an electronic control system, these functions are managed in three phases. ? The input phase of electronic control allow the Electronic Control Unit (ECU) to monitor engine operating conditions, utilizing information from the input sensors. ? The process phase of electronic control requires the ECU to use this input information to make operating decisions about the fuel and spark advance systems. ? The output phase of electronic control requires the ECU to control the output actuators, the fuel injectors, and igniter to achieve the desired fuel metering and spark timing. In this chapter, we will explore the details of the electronic control system hardware and software. The chapter starts with a thorough examination of the system's input sensor circuits and the ECU power distribution system. It concludes with a closer look at the ECU process functions and the control strategy use( for optimum fuel metering and spark advance angle control. The Microcomputer The heart of the TCCS system is a microcomputer. A microcomputer is a device which receives information, processes it, and makes decisions based on a set of program instructions. The microcomputer exercises control over the output actuators to carry out these instructions. The use of microcomputers has taken the science of engine management into the space age by increasing the speed with which information can be processed and allowing the electronic control system to manage more engine functions. With the ability to process information so rapidly, the modern ECU is capable of carrying out its programmed instructions with extreme accuracy. Engine management can address virtually every condition the engine will encounter so that for any engine condition, the ECU will deliver optimum fuel and spark. Evolution of Toyota's Electronic Fuel Injection Systems Early Conventional EFI computers were first configured from analog circuits, and they controlled only fuel delivery and injection. The modem Electronic Control Units (ECU) utilize digital circuits and microprocessors which have served to improve EFI system capabilities. Modern TCCS engine controls, introduced to the U.S.A. market in 1983, are capable of managing fuel delivery, idle speed control (ISC), electronic spark advance (ESA), and emissions systems with extraordinary speed and accuracy. In the evolution of Toyota's fuel injection, three levels of electronic control refinements have taken place. ? Conventional EFI ? P7/EFI ? EFI/TCCS The main difference between these systems is the capability of the ECU. These capabilities have grown from simple fuel control to the addition of self-diagnostics to the control of ignition spark advance and more. The following chart summarizes basic capabilities by system and can be used as a guide in identification and troubleshooting. ENGINE CONTROLS - INPUT SENSORSPage 2 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. System identification is relatively simple. ? The Conventional EFI system has no check engine light. ? The P7/EFI system has a check engine light but has a mechanical advance distributor. ? The EFI/TCCS system has a check engine light and an electronic advance distributor. The Input Sensors, Information Source for the ECU In an electronic control system, the ECU uses its sensors in much the same manner as we use our five senses. Our sense of touch tells us when things are hot or cold; our sense of hearing allows us to distinguish one sound from another; our sense of smell tells us when fresh coffee is brewing somewhere nearby. Sensors give the ECU similar abilities: the ability to feel the temperature of the engine coolant, to listen for the sound of detonation, and to smell the exhaust stream for the presence of sufficient oxygen. This lesson on input sensors will address how each major ECU input sensor circuit works. Each sensor circuit will be broken down so you can see its individual components: the sensor, electrical wiring, and the ECU. ENGINE CONTROLS - INPUT SENSORSPage 3 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Overview The EFl/TCCS system is an electronic control system which provides Toyota engines with the means to properly meter the fuel and control spark advance angle. The system can be divided into three distinct elements with three operational phases.The three system elements are: ? Input Sensors ? Electronic Control Unit (A Microcomputer) ? Output Actuators ENGINE CONTROLS - INPUT SENSORSPage 4 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Input Sensors Used in Basic Injection and Spark Calculation Engine Air Flow Sensing Vane Type Air Flow Meters (Vs, General Information) The vane type air flow meter is located in the air induction system inlet pipe between the air cleaner and the throttle body. It is composed of the measuring plate, compensation plate, return spring, potentiometer, and by-pass passage. The sensor also incorporates the idle mixture adjusting screw (factory sealed), the fuel pump switch, and the intake air temperature sensor (which will be addressed later in this lesson). Because intake air volume is a direct measure of the load placed on an engine, the vane type air flow meter provides the most important input to the ECU for fuel and spark calculations. When air passes through the air flow meter, it forces the measuring plate open to a point where it balances with the force of the return spring. The damping chamber and compensation plate prevent vibration of the measuring plate during periods of sudden intake air volume changes. The potentiometer, which is connected to the measuring plate and rotates on the same axis, converts the mechanical movement of the measuring plate into a variable voltage signal. Movement of the measuring plate and the analog voltage signal produced by this sensor are proportional to the volume of air entering the intake manifold. Vane Air How Meter Electrical Circuit The sensor movable contact is attached to the measuring plate and rides on a fixed resistor wired between the reference voltage input and the ground. As the volume of air entering the engine increases, the movable contact moves across the fixed resistor, causing a change in signal output voltage. There are two designs of vane air flow meters used on Toyota L type EFI systems. The first design generates a signal which varies from low voltage at low air volumes to high voltage at high air volumes. The second design sensor has opposite signal characteristics. These sensors also operate on different reference voltages. Both sensor designs integrate an intake air temperature sensor into the air flow meter. ENGINE CONTROLS - INPUT SENSORSPage 5 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. First Design Vane Air How Meter The first design air flow meter is found on all Conventional EFI engines and many later model TCCS equipped engines. This sensor has an electrical connector with seven terminals, four of which are used for air flow measurement. Air Flow Sensor Terminal Identification (First Design Sensor) The air flow meter and ECU are wired as shown in the diagram. Signal characteristics are depicted by the accompanying graph. The use of battery voltage, VB, as a sensor input necessitates the use of the Vc terminal as a constant reference signal for the ECU. This is because battery voltage may change with variances in electrical load and ambient temperatures. Without the use of a constant reference voltage, these changes would cause a change in the Vs signal value recognized by the ECU. ENGINE CONTROLS - INPUT SENSORSPage 6 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Second Design Air How Meter The second design air flow meter was introduced on the '85 5M-GE engine, and its use expanded with many late model TCCS equipped engines. This sensor has an electrical connector with seven terminals, three of which are used for air flow measurement. Air Flow Sensor Terminal Identification (Second Design Sensor) The air flow meter and ECU are wired as shown in the diagram; signal characteristics are depicted by the accompanying graph. The use of a regulated 5 volt reference eliminates the need for the VB terminal with this sensor circuit. Resistors R1 and R2 provide self diagnostic capabilities and allow for a fail-safe voltage at the ECU in the event of an open circuit. These two resistors have a very high resistance value (relative to r1 and r2) and essentially have no electrical effect on the circuit under normal operating conditions. They will, however, affect the open circuit voltage measured on the Vs wire at the ECU. ENGINE CONTROLS - INPUT SENSORSPage 7 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Karman Vortex Air Flow Meter (Ks) The Karman vortex air flow meter is currently used on the 7M-GTE Toyota engine and the 2JZ-GE and 1UZ-FE Lexus engines. It is located in the air induction system inlet pipe between the air cleaner and the throttle body. The sensor is composed of a photocoupler and mirror, a vortex generator, and an integrated circuit (IC) which together, measure the frequency of the vortices generated by air entering the intake system. When compared with the vane type air flow meter, the Karman vortex meter is smaller, lighter, and offers less restriction to incoming air. Similar to the vane type air meter, the Karman vortex meter integrates the intake air temperature sensor into the meter assembly. The sensor has an electrical connector with five terminals, three of which are used for air flow measurement. Karman Vortex Air Flow Meter Terminal Identification ENGINE CONTROLS - INPUT SENSORSPage 8 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. The Karman vortex air flow meter and ECU are wired as shown in the diagram. Signal characteristics are represented by the illustration of the variable frequency square wave. Because of the pull-up resistor wired between the Vcc and Ks circuit, the Ks signal will go to 5 volts if the circuit is opened. When air passes through the air flow meter, the vortex generator creates a swirling of the air downstream. This swirling effect is referred to as a “Karman vortex.“ The frequency of this Karman vortex varies with the velocity of the air entering the air flow meter and other variables. The photocoupler and metal foil mirror are used to detect changes in these vortices. ENGINE CONTROLS - INPUT SENSORSPage 9 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. The metal foil mirror is used to reflect light from the LED to the photo transistor. The foil is positioned directly above a pressure directing hole which causes it to oscillate with the changes in vortex frequency. As the mirror oscillates, the 5 volt Vcc reference is switched to ground by a photo transistor within the sensor. The resulting digital signal is a 5 volt square wave which increases in frequency in proportion to increases in intake air flow. ENGINE CONTROLS - INPUT SENSORSPage 10 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Manifold Absolute Pressure Sensor The manifold absolute pressure sensor (sometimes referred to as vacuum sensor) is used on engines equipped with D type EFI. It is typically located somewhere on the bulkhead with a vacuum line leading directly to the intake manifold. It measures intake air volume by monitoring changes in manifold absolute pressure, a function of engine load. The sensor consists of a piezoresistive silicon chip and an Integrated Circuit (IC). A perfect vacuum is applied to one side of the silicon chip and manifold pressure applied to the other side. When pressure in the intake manifold changes, the silicon chip flexes, causing a change in its resistance. The varying resistance of the sensor causes a change in signal voltage at the PIM (Pressure Intake Manifold) terminal. ENGINE CONTROLS - INPUT SENSORSPage 11 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. The manifold absolute pressure sensor has an electrical connector with three terminals. Manifold Absolute Pressure Sensor Terminal Identification The sensor and ECU are wired as shown in the diagram. As manifold pressure increases (approaches atmospheric pressure) there is a proportionate increase in PIM signal voltage. This analog signal characteristic is depicted in the accompanying graph. TO check sensor calibration, signal voltage should be checked against the standards shown on the graph, and a voltage drop check should be performed over the entire operating range of the sensor. ENGINE CONTROLS - INPUT SENSORSPage 12 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
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