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h25 ECU process&output.pdf

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H25 ECU PROCESS AMP OUTPUT
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The ECU, Process Center of the Electronic Control System The ECU is an extremely reliable piece of hardware which has the capability to receive and process information hundreds of times per second. At the heart of the ECU is the microprocessor. It is the processing center of the ECU where input information is interpreted and output commands are issued. The process and output functions of the ECU can be divided into the following six areas: ? Fuel Injection Control ? ESA / VAST Spark Advance Control ? Idle Speed Control ? Self Diagnosis ? Related Engine and Emissions Control ? Failure Management (fail-safe and back-up) Fuel, spark, and failure management functions will be covered individually in this chapter. Idle Speed Control, related engine systems, emissions control systems, and the self diagnosis system will be the subject of chapters 6, 7, 8, and 9, respectively. ENGINE CONTROLS PART #2 - ECU PROCESS and OUTPUT FUNCTIONSPage 1 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. ECU Power Distribution and EFI Main Relay Circuits The ECU cannot properly function without dependable power feeds and ground circuits. The power distribution system involves several electrical circuits, protection devices, relays, and grounds. ECU Power Feeds The ECU receives its ignition-switched power from the EFI main relay on all of Toyota's EFI systems. In addition to the ignition +B power feed, all P7 and TCCS ECUs have a direct battery feed, identified as BATT, supplied from either the EFI, STOP, or ECU +B fuse. The EFI main relay +B output is the power source which feeds the ECU and related engine control circuits. The direct battery feed (terminal BATT) serves to maintain voltage to the ECU keep alive memory when the ignition switch is off. Conventional EFI has no keep alive memory capabilities and, therefore, uses only an ignition switched power feed from the EFI main relay. Main Relay Circuits Toyota utilizes several different EFI Main Relay circuits depending on application. These circuits can be categorized into four distinct types. 1) Dual contact EFI Main Relay, ignitionswitch controlled 2) Single contact EFI Main Relay, ignitionswitch controlled 3) Dual EFI Main Relays, ignition switch orECU controlled 4) Single contact EFI Main Relay, ECUcontrolled Generally speaking, the EFI Main Relay supplies current to the following major circuits: ? ECU +B and +B1 ? Injectors (dual relay or dual contact relay only) ? Circuit opening relay (power contact and pull-in windings) ? Air flow meter VB circuit (when so equipped) ? Output Actuator Vacuum Switching Valves (VSV) - Fuel Pressure Up (FPU) - Exhaust Gas Recirculation (EGR) - Throttle Opener ? ISC motor/solenoid windings ? Check connector +B terminal ENGINE CONTROLS PART #2 - ECU PROCESS and OUTPUT FUNCTIONSPage 2 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Because the EFI Main Relay supplies battery voltage to the +B terminal of the check connector when the ignition switch is in the run position, this is an excellent place to perform a quick check of the relay function. Dual Contact (Single Relay), Ignition Switch Controlled This EFI Main Relay configuration is used on the Conventional EFI system. It uses separate power contacts to supply current to the fuel injector/ignition circuits and the ECU/circuit opening relay circuit. This limits current flow that the ECU power contact must handle. This configuration improves the reliability of the relay, reduces possible voltage drop, and also isolates any inductive noise from the injectors to the EFI Computer by utilizing the battery as a large capacitor. When the ignition switch is turned to the “run“ or “start“ position, current is supplied to the pull-in winding of the relay. Pull-in ground is wired directly to the vehicle chassis. The only power feed to the ECU on this system is the +B circuit. Single Contact, Ignition Switch Controlled This EFI Main Relay circuit is one of the most popular power distribution schemes used on late model TCCS equipped engines. It is used on most applications without a stepper type Idle Speed Control Valve (ISCV). When the ignition switch is turned to the “run“ or “start“ position, current is supplied to the pull-in winding of the relay. Pull-in ground is wired directly to the vehicle chassis. ECU BATT voltage is supplied from the STOP fuse on these applications. ENGINE CONTROLS PART #2 - ECU PROCESS and OUTPUT FUNCTIONSPage 3 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Single Contact, ECU Controlled This EFI Main Relay circuit is used exclusively on applications equipped with the stepper type Idle Speed Control Valve. This relay is powered by the ECU rather than the ignition switch to allow control of the relay for approximately two seconds after the ignition is switched off. This allows the ECU to step the ISCV back to engine restart position after ignition power down. When the ignition switch is turned on or engine cranked, the ECU receives a voltage signal at the IG SW terminal. This causes the ECU to supply current from the MREL terminal to the EFI Main Relay pull-in winding. The pull-in winding is grounded directly to the vehicle chassis. ECU BATT voltage is supplied from the EFI fuse on these applications. When the ignition switch is turned off, the ECU will maintain current flow through the EFI Main Relay pull-in winding for a few seconds after power down to allow time to reset the stepper ISCV. Dual Relays, Ignition Switch or ECU Controlled This configuration utilizes two separate relays identified as EFI Main Relay #1 and EFI Main Relay #2. Relay #2 supplies current to the fuel injector circuit. Relay #1 supplies current to the ECU, Circuit Opening Relay, and other circuits depending on application. If a stepper ISCV is used ('85 and '86 5M-GE), the ECU will drive relay #1 so the ISCV can be operated after the ignition is switched off. ENGINE CONTROLS PART #2 - ECU PROCESS and OUTPUT FUNCTIONSPage 4 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. ECU Grounds and Quick Checks No electrical circuit will function normally without a dependable ground. Toyota EFI systems use a redundant ground system which significantly reduces the chance of ground problems; however, this circuit should never be overlooked when troubleshooting ECU related systems. The E2 circuit serves as a signal return or sensor ground. Referring to an EWD, you will notice that the throttle position sensor, water and air temperature sensors, and air flow meter all flow current to ground through circuit E2. The ECU supplies a chassis ground through the E1 circuit which typically terminates somewhere on the engine. Circuits E01 and E02 serve as grounds for the fuel injector driver circuits. To provide a redundant ground for the ECU, these two grounds are tied to the E1 circuit through a diode. In the event that the E1 wiring to chassis is open circuit, E1 circuit current could flow through the diode to ground. The diode serves to prevent voltage spikes from the injectors from interfering with other ECU circuits. It is not uncommon for many or even all ECU grounds to terminate at the same point and fasten to the engine with the same fastener. Sometimes a ground fault is due to one fastener being left loose after a service procedure has been performed. It is a fairly simple task to confirm the integrity of all ECU ground circuits in fairly short order. Two methods can be used to identify and isolate a ground fault; these are the circuit continuity check and the voltage drop check. These procedures along with checks of the power distribution circuits are addressed in exercises 5-1 and 5-2. ENGINE CONTROLS PART #2 - ECU PROCESS and OUTPUT FUNCTIONSPage 5 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Fuel Injection Control ENGINE CONTROLS PART #2 - ECU PROCESS and OUTPUT FUNCTIONSPage 6 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Injector Timing Injection Timing Control Injection timing control determines when each injector will deliver fuel to its corresponding intake port. There are three different methods of injector timing used on Toyota engines, depending on application. These methods are Simultaneous, Grouped, and Independent injection. Simultaneous Injection All injectors are pulsed simultaneously by a common driver circuit. Injection occurs once per crankshaft revolution just prior to the crankshaft reaching TDC cylinder *1. This means that twice per engine cycle one half of the calculated fuel is delivered by the injectors. This is the simplest and most common injection timing method in use. Grouped Injection Injectors are grouped into pairs. The pairs consist of two consecutive cylinders in the firing order; each pair is driven by a separate driver circuit. Four cylinder engines use two groups, six cylinder engines three groups, and the 1UZ-FE V8 engine uses four groups of injectors. Injection is timed to deliver fuel immediately preceding the intake stroke for the leading cylinder in the pair. The entire group is pulsed once per engine cycle, delivering the entire calculated charge of fuel. This timing method ensures that fuel does not linger behind the intake valve, thereby, reducing emissions, improving fuel economy and throttle response. Independent Injection Injectors are driven independently and sequentially by separate driver circuits. Injection is timed to deliver the entire fuel charge just prior to each intake valve opening. This timing method provides optimum engine performance, emissions, and fuel economy. ENGINE CONTROLS PART #2 - ECU PROCESS and OUTPUT FUNCTIONSPage 7 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Input Signals Required to Pulse Injectors There are three signals which are necessary to operate the fuel injectors. These are the Ne, G, and IGf signals. Inside the ECU, the Ne Signal is used to produce an injection chive signal. The G signal is used to determine the timing of the injection signals. The IGf signal is monitored for fuel delivery fail-safe. (With Conventional EFI, the IG signal is used to produce the injection drive signal.) The ECU cannot pulse the injector without an Ne signal and will not start or run if this signal is not present. If the G signal is not present while cranking the engine, the ECU will not be able to identify when to produce the injection signal. The result will be the same, no injection pulse. If the IGf signal is not present, the ECU will go into fuel fail-safe by stopping injection pulses. If, however, the ECU loses the G signal with the engine running, the engine will continue to run because the timing of injection signals is locked in once the engine starts. ENGINE CONTROLS PART #2 - ECU PROCESS and OUTPUT FUNCTIONSPage 8 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. Injector Operating Modes There are two injection operating modes used by the ECU, depending on engine operating conditions. These modes are called synchronous and asynchronous. Synchronous Injection Synchronous injection simply means that injection events are synchronized with ignition events at specific crankshaft angles. Synchronous injection is used a great majority of the time. Asynchronous Injection Asynchronous injection is only used during acceleration, deceleration, and starting. It occurs independently of ignition events based on change in idle contact (IDL) or start switch (STA) status without regard to crankshaft angle. ENGINE CONTROLS PART #2 - ECU PROCESS and OUTPUT FUNCTIONSPage 9 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved. ECU Control of Injector Duration An Overview of Injection Duration Calculations Determination of final injection pulse width is the function of a three-step process. Step 1, Basic Injection Duration The first step involves calculation of basic injection duration. Input sensors used in basic duration calculation are: ? Air Flow Meter (Vs or Ks) ? Manifold Pressure Sensor (PIM) ? Engine rpm (Ne) The ECU calculates basic injection duration based upon engine speed and air flow volume. These two inputs considered together establish an engine load factor. The ECU monitors the Air Flow Meter signal or Manifold Pressure Sensor for intake air volume information and the Ne signal for engine speed information. ? As either of these parameters increase, injection duration is increased. Step 2, Injection Duration Correction Factors The second step involves duration corrections. Input sensors used for injection duration corrections are: ? Engine Water Temperature (THW) ? Intake Air Temperature (THA) ? Throttle Angle (VTA or IDL & PSW) ? Exhaust Oxygen Content (OX) Once basic injection duration is calculated, the ECU must modify the injection duration based on other changing variables. Variables considered in the correction calculation are coolant and intake air temperature, throttle position and exhaust oxygen sensor feedback (when operating in closed loop). ? As engine and intake air temperatures move from cold to warm, injection duration is reduced. ? As the throttle opens (IDL contact break), injection frequency is momentarily increased. ? Fuel injection duration swings back and forth between longer to shorter durations to correct conditions detected by the exhaust oxygen sensor. Step 3, Battery Voltage Correction The final step is a battery voltage correction. The input signal used in battery voltage corrections is: 0 Battery Voltage (+B) There is an operational delay between the time the ECU sends the injection signal to the driver circuit and the actual opening of the injector. This delay changes with the strength of the magnetic field around the injector coil. The delay increases as battery voltage falls. To determine final injection duration, the ECU corrects for injector opening delay by using a battery voltage correction coefficient. ? The battery voltage correction coefficient increases injection duration as sensed battery voltage falls. ENGINE CONTROLS PART #2 - ECU PROCESS and OUTPUT FUNCTIONSPage 10 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
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