热门搜索:

  • /?23
  • 下载费用:8 金币 ?

h42 fuel sys overview.pdf

关?键?词:
H42 FUEL SYS OVERVIEW
资源描述:
Fuel Injection System The purpose of the fuel injection system is to precisely inject a metered amount of fuel at the correct time. Based on the input sensor signals, the ECMs programming will decide when to turn each injector on and off. Fuel Delivery System The purpose of the fuel delivery system is to quietly deliver the proper volume of fuel at the correct pressure. The fuel delivery system must also meet emission and safety regulations. Major components are: ? Fuel Pump. ? Fuel Pump ECU. ? Pressure Regulator. ? Fuel Pressure Control Circuit. ? Fuel Lines. ? Fuel Tank. ? Fuel Filter. ? Pulsation Damper. ? Fuel Injectors. ? Inertia Switch. FUEL SYSTEMS #1 - OVERVIEWPage 1 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.Return Fuel Delivery System When the fuel pump is activated by the ECM, pressurized fuel flows out of the tan, through the fuel filter to the fuel rail and up to the pressure regulator. The pressure regulator maintains fuel pressure in the rail at a specified value. Fuel in excess of that consumed by engine operation is returned to the tank by a fuel return line. A pulsation damper, mounted on the fuel rail, is used on many engines to dampen pressure variations in the fuel rail. The injectors, when turned on by the ECM deliver fuel into the intake manifold. When the fuel pump is turned off by the ECM, a check valve in the fuel pump closes maintaining a residual pressure in the fuel system. Returnless Fuel Delivery System When the fuel pump is activated by the ECM pressurized fuel flows from the pump to the pressure regulator. At the pressure regulator excess fuel is directed to the bottom of the fuel tank and pressurized fuel is sent out of the fuel tank, through the fuel filter, pulsation damper, and into the fuel rail. When the ECM turns on the injectors fuel is delivered into the intake manifold. Fuel pressure in this system is maintained at a constant and higher pressure, 44-50 psi (301- 347 kPa) than the return fuel system. ECM programming and a higher fuel pressure eliminates the need for a vacuum modulated pressure regulator. FUEL SYSTEMS #1 - OVERVIEWPage 2 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.The returnless fuel delivery system was adopted because it lowers evaporative emissions since no heated fuel is returned to the fuel tank. On the return fuel delivery system, fuel heated by the engine returns to the fuel tank and has warmer fuel creating more fuel vapors. Fuel Pump The fuel pump is mounted in the tank and immersed in fuel. The fuel cools and lubricates the pump. When current flows through the motor, the armature and impeller rotate. The impeller draws fuel in through a filter and discharges pressurized fuel through the outlet port. The fuel pump's pumping capacity is designed to exceed engine requirements. This insures that there will always be enough fuel to meet engine demands. An outlet check valve, located in the discharge outlet, maintains a residual fuel pressure in the fuel system when the engine is off. This improves starting characteristics and reduces vapor- lock. Without residual fuel pressure, the system would have to be pressurized each time the engine was started and this would increase engine starting (cranking) time. When a hot engine is shut off, fuel temperature in the lines around the engine increases. Keeping the system pressurized increases the boiling point of the fuel and prevents the fuel from vaporizing. A pressure relief valve will open if the fuel system becomes restricted. This is a safety device to prevent the fuel lines from rupturing and damage to the pump. FUEL SYSTEMS #1 - OVERVIEWPage 3 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.On many models the fuel pump is part of the fuel pump assembly. This assembly contains the filters, pressure (fuel system only), sending unit, and fuel pump. Many of the components can be serviced separately. FUEL SYSTEMS #1 - OVERVIEWPage 4 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.Jet Pump The jet pump is an additional pump used when the fuel tank bottom is divided into two chambers. Excess fuel flowing through the fuel return passes through a venturi. This creates a low pressure area around the venturi, and this action will draw the fuel out of Chamber B, and sends it into Chamber A. FUEL SYSTEMS #1 - OVERVIEWPage 5 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.Fuel Pump Controls A variety of fuel pump control circuits and controls have been used over the years. The following basic methods are: ? ON/OFF Control by ECM. ? ON/OFF Control by Fuel Pump Switch. ? ON/OFF Two Speed Control with a Resistor. ? ON/OFF Two Speed Control with Fuel Pump ECU. ? ON/OFF Three Speed Control with Fuel Pump ECU. The most accurate way of determining the type of fuel control circuit is to look up the circuit in the appropriate EVVD. FUEL SYSTEMS #1 - OVERVIEWPage 6 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.The following describes the basic methods of fuel pump control. An essential point to remember is that the fuel pump operates only when the engine is cranking or running. ON/OFF Control by ECM The following is an explanation of how the fuel pump circuit is activated. Engine Start When the engine is cranking, current flows from the IG terminal of the ignition switch to the L1 coil of the EFI main relay, turning the relay on. At the same time, current flows from the ST terminal of the ignition switch to the L3 coil of the circuit opening relay, turning it on to operate the fuel pump. The fuel pump is now supplying fuel to the fuel injection system. Note: The circuit opening relay in this example is ground side switched. Engine Running Once the engine starts and the ignition key is moved to the ON (IG) position, current to the L3 coil is shut off, but the ECM will keep the fuel pump on through coil L2 as long as the ECM receives an NE signal. If the NE signal is lost at any time after starting, the ECM turns the fuel pump off. FUEL SYSTEMS #1 - OVERVIEWPage 7 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.Engine Stopped When the engine stops, the NE signal to the ECM stops. This turns off the transistor, thereby cutting off the flow of current to the L2 coil of the circuit opening relay. As a result, the circuit opening relay opens turning off the fuel pump. Note: The resistor R and the capacitor C in the circuit-opening relay are for the purpose of preventing the relay contacts from opening when current stops flowing in coil L2 due to electrical noise (fuel pumps controlled by the ECM) or to sudden drops in the intake air volume (fuel pumps controlled by fuel pump switch). They also serve to prevent sparks from being generated at the relay contacts. On some models, an L3 coil is not provided in the circuit- opening relay. ON/OFF Control by Fuel Pump Switch The fuel pump switch is found on older vehicles using a Vane Air Flow Meter. The air moves the vane when the engine is running closing the fuel pump switch. The following is an explanation of circuit operation. Engine Start When the engine is cranking, current flows from the IG terminal of the ignition switch to the L1 coil of the EFI main relay, turning the relay on. Current also flows from the ST terminal of the ignition switch to the L3 coil of the circuit-opening relay, turning it on to operate the fuel pump. After the engine starts, the cylinders begin drawing in air, causing the measuring plate inside the air flow meter to open. This turns on the fuel pump switch, which is connected to the measuring plate, and current flows to the L2 coil of the circuit-opening relay. FUEL SYSTEMS #1 - OVERVIEWPage 8 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.Engine Running After the engine starts and the ignition switch is turned from ST back to IG, current flowing to the L3 coil of the circuit-opening relay is cut off. However, current continues to flow to the L2 coil while the engine is running due to the fuel pump switch inside the air flow meter being on. As a result, the circuit-opening relay stays on, allowing the fuel pump to continue operating. Engine Stopped When the engine stops, the measuring plate completely closes and the fuel pump switch is turned off. This cuts off the flow of current to the L2 coil of the circuit-opening relay. As a result, the circuit-opening relay goes off and the fuel pump stops operating. Two Speed Fuel Pump Control Large displacement engines require a higher volume of fuel during starting and heavy load conditions than small displacement engines. High capacity fuel pumps are used to meet the demand, but they produce more noise and consume more power. To overcome these disadvantages and increase pump life, a two speed fuel pump control is used. ON/OFF Two Speed Control with a Resistor This type uses a double contact relay and a series limiting resistor. FUEL SYSTEMS #1 - OVERVIEWPage 9 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.FUEL SYSTEMS #1 - OVERVIEWPage 10 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.ON/OFF Two Speed Control with Fuel Pump ECU This type is similar to other systems, but uses a Fuel Pump ECU. In this system, however, ON- OFF control and speed control of the fuel pump is performed entirely by the Fuel Pump ECU based on signals from the ECM. In addition, the Fuel Pump ECU is equipped with a fuel pump system diagnosis function. When trouble is detected, signals are sent from the D1 terminal to the ECM. High Speed During starting and heavy load condition, the ECM sends a HI signal (about 5 volts) to the FPC terminal of the Fuel Pump ECU. The Fuel Pump ECU then supplies full battery power to the fuel pump. Low Speed After the engine starts, during idle and light loads, the ECM outputs a low signal (about 2.5 volts) to the Fuel Pump ECU. Then, the Fuel Pump ECU supplies less voltage (about 9 volts) to the fuel pump. Three Speed Fuel Pump Control With this system, the fuel pump is controlled in 3 steps (high speed, medium speed, and low speed). High Speed When the engine is operating under a heavy load at high RPM or starting, the ECM sends a 5 volt signal to the fuel pump ECU. The fuel pump ECU then applies battery power to the fuel pump causing the fuel pump to operate at high speed. Medium Speed Under heavy loads at low speed, the ECM sends a 2.5 volt signal to the fuel pump control. The fuel pump ECU applies about 10 volts to the fuel pump. This is considered medium speed. FUEL SYSTEMS #1 - OVERVIEWPage 11 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.Low Speed When idling or under light loads, the ECM sends a 1.3 volt signal to the fuel pump ECU. The fuel pump ECU applies 8.5 volts to the fuel pump, preventing excessive noise and decreasing power consumption. Inertia Switch The fuel pump inertia switch shuts off the fuel pump when the vehicle is involved in a collision, minimizing fuel leakage. FUEL SYSTEMS #1 - OVERVIEWPage 12 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.Operation The inertia switch consists of a ball, spring loaded link, contact point, and reset switch. If the force of the collision exceeds a predetermined value, the ball will move causing the spring loaded link to drop opening the contact point. This opens the circuit between the ECM and Fuel Pump ECU causing the fuel pump to turn off. If the fuel pump inertia switch has been tripped, it can be reset by pushing up on the reset switch for at least 1 second. FUEL SYSTEMS #1 - OVERVIEWPage 13 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.Pressure Regulators The pressure regulator must consistently and accurately maintain the correct fuel pressure. This is important because the ECM does not measure fuel system pressure. It assumes the pressure is correct. There are two basic types of pressure regulators. Modulated Pressure Regulators The return fuel delivery system uses a pressure regulator located on the fuel pressure rail between the fuel pressure rail and the return line to the fuel tank. There are two types of pressure regulators. One type is modulated by vacuum, the other by atmospheric pressure. Vacuum Modulated Pressure Regulator To maintain precise fuel metering, the vacuum modulated pressure regulator maintains a constant pressure differential across the fuel injector. This means that fuel rail pressure will always be at a constant value above manifold absolute pressure. FUEL SYSTEMS #1 - OVERVIEWPage 14 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.Low intake manifold pressure (idle for example) pulls on the diaphragm decreasing spring pressure. This allows more fuel to return to the fuel tank decreasing pressure in the fuel rail. Opening the throttle increases manifold pressure. With less vacuum on the diaphragm spring pressure will increase restricting fuel flow to the fuel tank. This increases pressure in the fuel rail. Atmospheric Modulated Pressure Regulator The atmospheric modulated pressure regulator modifies fuel pressure with changes in atmospheric pressure. A hose is connected from the pressure regulator to the air intake hose between the air filter and throttle plate. Spring pressure and atmospheric pressure keep the fuel pressure at a constant value, 226-265 kPa (38-44 psi). As air pressure changes, such as climbing from low to high altitude, fuel rail pressure decreases because there is less force on the diaphragm. FUEL SYSTEMS #1 - OVERVIEWPage 15 ? Toyota Motor Sales, U.S.A., Inc. All Rights Reserved.
? 汽车智库所有资源均是用户自行上传分享,仅供网友学习交流,未经上传用户书面授权,请勿作他用。
0条评论

还可以输入200字符

暂无评论,赶快抢占沙发吧。

关于本文
本文标题:h42 fuel sys overview.pdf
链接地址:http://www.autoekb.com/p-2806.html
关于我们 - 网站声明 - 网站地图 - 资源地图 - 友情链接 - 网站客服客服 - 联系我们

copyright@ 2008-2018 mywenku网站版权所有
经营许可证编号:京ICP备12026657号-3?

收起
展开