Lexus Turbocharger System. Handbook

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2 Naturally Aspirated Engines Since 1989, Lexus has used naturally aspirated engines in all of the vehicles they have produced. Naturally aspirated engines, whether they are carbureted or fuel injected, use atmospheric pressure in our environment to push air into the cylinder for proper combustion. At sea level, atmospheric pressure is rated at approximately 14.7 PSI absolute (101.3 kpa). This means that there is a constant pressure of 14.7 PSI pushing on all objects at sea level. Atmospheric pressure also changes as elevation or altitude is increased. As we start to increase in elevation or altitude, the atmospheric pressure decreases. For example, the city of Denver (which is 5,280 feet above sea level) has an atmospheric reading of 12.2 PSI. So how does the atmospheric pressure have an effect on the engine? When the piston in the engine moves down in the cylinder bore it creates an area of low pressure. At this point, the high atmospheric pressure pushes air into the cylinder that has a low pressure. The air that is pushed into the cylinder mixes with fuel to create a mixture for combustion to occur. The atmosphere can only push as much air into the cylinder as the atmosphere pressure will allow. Since the atmospheric pressure is lower at higher elevations, there is a reduced amount of air entering the engine for the combustion process. During normal operation of the engine at a high elevation (Denver), the atmosphere can only push 12.2 PSI of air into the cylinder which is less than the atmospheric pressure could at sea level. Having less air in the cylinder, means that a lesser amount of fuel is needed for our stoichiometric combustion mixture. This lack of air and fuel dilutes the proper combustion mixture and causes the engine to lose power at higher elevations. Overall, the naturally aspirated engine is a tried and true method of induction. This system has less components, is reliable and cost friendly. There are a few downfalls though as power output is restricted to atmospheric pressure and power output changes as elevations change. 2

3 Naturally Aspirated Engine Benefits -Less Components -Reliable -Lower Cost Naturally Aspirated Engine Downfalls - -Less power output -Changes in Power based on elevation -Rely on Atmospheric Pressure for proper combustion mixture 2

4 Forced Induction Forced induction is the process of compressing the intake air and pressurizing the intake manifold of the engine with a higher than atmospheric pressure. This allows more air to be pushed into the cylinders during the combustion process. By allowing more air to be pushed into the engine, and in turn fuel, a larger, denser air-fuel mixture enters the cylinder for combustion. With this large, dense air-fuel mixture in the combustion chamber the engine can create additional power and torque. There are two ways to use forced induction: Supercharging Supercharged engines use a mechanical device (typically either belt or gear) driven by the engine to energize the supercharger. The supercharger than compresses the intake air supplied to the engine. Benefits more power especially at lower RPMs, no lag, heat is generally not an issue Downfalls can be noisy, cost more, consumes power to create power Turbocharging Turbocharged engines use exhaust gas to energize a turbocharger which compresses the air supplied to the engine. Benefits more power especially at higher RPMs, better efficiency, lower emissions Downfalls intake air is hotter, turbo lag, higher cost and complexity 3

5 Turbo Beginning with the 2015 Lexus NX200t, Lexus has adopted forced induction into the vehicle line-up by the means of turbocharging. The benefits of smaller turbocharged engines with less weight, better power output and increased fuel economy will help keep Lexus in front of the competition. Another concern for car manufacturers is the looming CAFÉ standards for By 2025, car manufacturers are required to meet a combined fuel economy of 54.5 MPG across their vehicle lineup and reduce the amount of CO2 for each vehicle. Turbocharging allows manufacturers to use smaller displacement engines, that get better fuel economy and lower CO2 emissions but still have the power output of a larger engine when it is needed. 4

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7 Basic Turbo Operation Turbochargers use spent exhaust gases from the combustion process to energize or propel the turbine wheel inside the turbocharger. The turbine wheel is placed in the engine exhaust stream and as the exhaust pulses from each cylinder flow out of the cylinder head, they contact the turbine wheel. Each exhaust pulse pushes on the turbine wheel blades causing it to rotate inside the turbocharger housing. Inside the turbocharger, the turbine wheel is connected via a shaft to a compressor wheel that is isolated on the intake air side. When the compressor wheel is spun, due to the turbine wheel spinning, intake air is compressed into the intake housing and pressurized to a higher than atmospheric pressure. This allows the engine to push more air than is available from the atmosphere into the engine during the combustion process. 6

8 Types of Turbocharger Systems Single or Dual Turbochargers Single turbochargers can be added to vehicles to increase performance. There are many aftermarket turbocharger applications that are available and it is a common accessory to add to a vehicle to increase performance. One downfall to a vehicle equipped with a single turbocharger is that the vehicle will experience a phenomenon known as turbo lag. Turbo lag is the amount of time that is takes for the turbocharger to spool up before it starts creating boost pressure in the intake manifold. Turbo lag varies and is dependent on the turbocharger that is being used. For example a large turbocharger will take a longer time to spool up than a smaller turbocharger. There are a few ways to overcome the effects of turbo lag on a vehicle. One way is to use two turbochargers. This type of setup can be accomplished by using a smaller turbocharger that will spool up quickly and provide quick response at low rpm s and a larger turbocharger that will continue to provide boost and the air volume needed for response at high RPM s. By having both turbochargers the vehicle gets great response and performance across all RPM ranges with a minimal amount of turbo lag if any is felt at all. This type of dual turbocharger set-up is also known as sequential turbocharging. Sequential turbocharger systems provide a way to decrease turbo lag without compromising ultimate boost output and engine power. Lexus has not used a dual turbocharger setup in its history, but Toyota used the dual turbocharger setup in the infamous Toyota Supra. Variable Vane Turbochargers - Variable vane turbochargers allow the same benefits of a sequential turbocharger system, but with only the use of a single turbocharger. Inside a variable vane turbocharger there are plates or vanes that direct the exhaust flow in the turbocharger. These vanes are placed before the turbine wheel and 7

9 are adjustable. The adjustability of these vanes allow them to direct more or less air to the turbine wheel and also how the air is directed to the turbine wheel. In low RPM situations, the turbine wheel needs to spool up quickly to reduce turbo lag, so the vanes are adjusted to close off more creating a higher back pressure in the exhaust system which increases the velocity of the exhaust gases to the turbine and directs the exhaust gases into the turbine blades. At higher RPM s, the vanes open up more to allow a larger volume of exhaust gases to move through the turbocharger and directs the exhaust gases to flow onto the turbine blades. By constantly changing the angle of the vanes inside the turbocharger, the vehicle has great response and power throughout the full RPM range of the engine. Twin Scroll Turbocharger The twin scroll turbocharger was also developed to provide power throughout the RPM range of the engine with reduced turbo lag. As with the variable vane turbochargers, the twin scroll turbocharger is a self contained single turbocharger. What makes the twin scroll turbocharger unique is that is separates the cylinder exhaust streams to the turbine wheel in the turbocharger. One exhaust stream is designed to increase velocity of the exhaust gases to the turbine wheel for low RPM performance and the other exhaust stream is designed for high exhaust volume which helps provide power at higher RPM s. To provide a comfortable ride with almost no turbo lag, Lexus has decided to use a twin scroll turbocharger for the NX200t. 7

10 Twin Scroll Turbocharger Details Like a VGT, a twin scroll turbocharger can be used to maximize the amount of boost across a larger RPM range, this is accomplished in two ways. First, in the case of a 4 cylinder engine, the exhaust gases from cylinders 1 and 4 are separated from the exhaust gases from cylinders 2 and 3. This is done to prevent the exhaust gas pulses that are output by the cylinders from interfering with each other. When the piston is on the exhaust stroke there is a spike in exhaust pressure from that cylinder, immediately following the spike in pressure there is a moment of vacuum caused by valve overlap. This moment of vacuum occurs at the same time that the next cylinder is on its exhaust stroke causing an interference. By separating the exhaust from the cylinders, this interference can be avoided. Now that the exhaust is separated into two channels it can be routed through two different size/shape scrolls (channels) before the exhaust gas energizes the turbine. One of the channels is larger to accommodate larger amounts of exhaust gases at higher RPM ranges. This channel routes larger amounts of exhaust gases at a high enough velocity to spin the turbine effectively and create effective boost at higher RPMs. The other channel is smaller in order to effectively use smaller amounts of exhaust gases at lower RPM ranges to create boost. This channel routes smaller amounts of exhaust gases through a smaller space, which increases the velocity of the exhaust gases used to spin the turbine to create effective boost at lower RPMs. 8

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12 Turbocharger System Components The turbocharger assembly is the main component that provides the additional air need to increase performance in a turbocharged engine. For the turbocharger to function correctly and accurately there are other components that are needed to help control the turbocharger and the boost pressure that it provides to the engine. Listed below are a few of the main components that help the turbocharger control boost: 1. Wastegate Valve 2. Wastegate Actuator 3. Vacuum Regulating Valve 4. No. 2 Check Valve 5. Vacuum Pump 6. No. 1 Turbo Pressure Sensor 7. No. 2 Turbo Pressure Sensor 8. Intercooler 9. Air Bypass Valve 10. Ejector Valve 10

13 Wastegate Valve and Actuator The wastegate valve controls turbo pressure and is opened and closed via the wastegate valve actuator. The default position of the actuator with no vacuum applied is the OPEN position, this is achieved with a spring in the actuator assembly; conversely, when vacuum is applied to the actuator the valve is closed. This type of vacuum actuator control is opposite from other turbocharger control systems that were adopted by other vehicle manufacturers. By having the wastegate valve normally open, the chances of mechanical failure that will cause an over boost condition are minimized and it creates an area of opportunity to make the engine more fuel efficient. By timing the wastegate valve and the boost pressure, Lexus can reduce fuel consumption of the engine and increase the MPG. The ECM cooperatively controls the throttle valve, VVT-iW, VVT-i and wastegate valve to achieve a driving condition with optimal fuel efficiency and power during normal driving. 11

14 Wastegate Valve Control During Engine Start - The ECM controls the vacuum regulating valve assembly to block the vacuum from the vacuum pump assembly to the actuator and open the wastegate valve. As a result, high temperature exhaust gases are supplied to the catalyst and warm-up time has been reduced. During Light Loads - The ECM controls the vacuum regulating valve assembly to block the vacuum from the vacuum pump assembly to the actuator, opening the wastegate valve and decreasing the exhaust manifold pressure. As a result, fuel economy has been enhanced due to reduced pumping loss and improved combustion (reduction of remaining gas). During Acceleration and High Loads - The ECM controls the vacuum regulating valve assembly to control the vacuum from the vacuum pump assembly to the actuator and close the wastegate valve. As a result, engine torque increase and response during acceleration have been achieved. 12

15 Vacuum Regulating Valve The Vacuum Regulating Valve (VRV) is a ECM duty cycled controlled device that limits the amount of vacuum going to the wastegate actuator. The VRV receives vacuum from the vacuum pump and check valve and provides this vacuum source to the wastegate actuator through vacuum lines in the system. During diagnosis of the turbocharger system, the VRV can be active tested. This active test is labeled as Wastegate Valve Control Duty Ratio. 13

16 Vacuum Pump Assembly A vacuum pump assembly is used on turbocharged engines since intake vacuum will not be sufficient at all times due to the use of a turbocharger. The vacuum pump supplies vacuum to the Vacuum Regulating Valve (VRV), which in turn controls the operation of the wastegate valve. The vacuum pump also supplies vacuum to the brake booster. The pump assembly is installed on the rear of the engine and is driven by the exhaust camshaft (No. 2 camshaft). Inside the vacuum pump is a rotor with two end caps. The rotor spins inside the housing and creates a vacuum for the turbocharger and brake booster systems. The Vacuum Pump also has a maintenance interval of 124,000. At this time, the pump is supposed to be disassembled and checked for wear. If any wear is noticed on the rotor, end caps, housing or cover the components should be replaced. 14

17 Turbo Pressure Sensors There are two turbo pressure sensors in the intake system. No.1 Turbo Pressure Sensor Is located after the throttle body assembly. It is comprised of the turbo pressure sensor and a thermistor type intake air temperature sensor. The ECM uses the temperature sensor in the No.1 turbo pressure sensor along with the temperature sensor in the MAF sensor to monitor the turbo charger intercooler efficiency. The pressure sensor in the No.1 turbo pressure sensor is only used for on F-Sport models as an input for the turbo boost gauge on the multi information display. No. 2 Turbo Pressure Sensor Is located before the throttle body assembly and detects turbo pressure. It is connected via a hose to the intercooler assembly on the back side of the engine. The turbo pressure sensors have a semiconductor that utilizes the characteristics of a silicon chip which changes its electrical resistance when pressure is applied to it. The sensor converts the intake air pressure into an electrical signal and sends it to the ECM in an amplified form. 15

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19 Air Bypass Valve The air bypass valve is designed to reduce the surge phenomenon and turbo lag. When the accelerator pedal is released, the throttle valve closes and compressed air from the turbocharger hits the closed throttle valve, increasing intake pressure. The surge phenomenon occurs when the intake air flow reverses, resulting in an abnormal noise during deceleration. Turbo lag is caused when this extra pressure slows the compressor turbine. On deceleration the ECM commands the air bypass valve to open, diverting excess pressure upstream to the turbocharger, reducing both of these conditions. The air bypass valve includes: Air bypass valve -- controlled by ECM Resonator to reduce sound Lexus decided to use a bypass valve instead of a blow-off valve for two reasons: 1. Blow-off valves vent to the atmosphere and provide that distinct turbocharger sound. Being a luxury model, Lexus did not want to introduce any unwanted noises into the vehicle. The bypass valve provides a direct path back to atmosphere within the intake side of the turbocharger housing reducing noise. 2. The bypass valve can be precisely controlled allowing the system to spool the turbo up quicker and reduce turbo lag. 17

20 Air Bypass Valve During Turbo Operation The Bypass Valve is closed allowing all intake air to be pressurized in the intake before the throttle body. This allows the compressor wheel to create a pressure higher than atmospheric for the engine. During Deceleration When the throttle plate is closed while the vehicle is by turbocharged, the intake air surges to a higher pressure. This happens because the turbocharger is still spinning and creating boost, but the throttle plate is closed, so the air is trapped in the intake. With the sudden increase of intake air, the pressure surges and tries to flow backwards through compressor wheel. This incorrect path of air flow puts stress on the compressor wheel, slows it down considerably and creates a whistle type noise. This is known as the surge phenomenon and can damage the compressor wheel if not controlled. To allow the air to escape when the throttle plate is closed, the air bypass valve is opened. When the air bypass valve is opened it provides a path for the high intake air pressure to escape back to atmospheric pressure, reducing the pressure in the intake and minimizing the surge phenomenon. The high pressure air is routed back to the atmospheric side of the turbocharger allowing the air to enter the turbocharger again when it is needed. During Acceleration If the vehicle is requesting a higher than atmospheric pressure, the air bypass is closed and the turbocharger will spool back up in a relatively short amount of time reducing turbo lag. 18

21 Intercooler A turbocharger compresses and forces more air into the cylinders of the engine to produce a larger, denser combustion charge. During the intake air compression process the intake air is heated up. Cooling the incoming intake air is needed to help maintain a dense air/fuel charge for proper combustion and to also minimize possible pre-detonation or knock within the engine. Lexus has equipped the NX200t with a small, but efficient intercooler that is mounted to the backside of the engine assembly. This intercooler is an air to water intercooler. An air to water intercooler uses an outside coolant source to cool and maintain the proper temperatures for the intake air. Lexus found that using an air to water intercooler over an air to air intercooler decreased the vehicles 0-60MPH times by 0.3 seconds. 19

22 Turbocharger/Intercooler Cooling System Heat is one of the worst enemies for a turbocharger system and precautions need to be taken to prevent the turbocharger from constantly being overheated. Lexus has developed a dedicated turbocharger and intercooler cooling system that is separate from the engine cooling system. This system has its own radiator, electric water pump and reservoir. The ECM varies the pump motor speed based on various inputs in order to achieve an optimal coolant flow rate. The turbocharger/intercooler cooling system makes sure that the system stays at the right temperatures. If the turbocharger is constantly overheated, oil coking and turbocharger bearing failure may occur. The capacity of this system is 3.1 quarts of SLLC. 20

23 Turbocharger/Intercooler Cooling System In addition to the turbocharger\intercooler cooling system, the Owner s Manual for the Lexus NX200t outlines some precautions to take after driving the vehicle. In order to make sure that the turbocharger is not overheated after certain high speed driving conditions, it is required that the vehicle be idled for a period of time before shutting off the vehicle. The graph above shows the amount of idling time required for each driving scenario. 21

24 Blowby Gas Ventilation System Because a larger volume of blowby gas is present in a turbocharged engine compared to an normally aspirated engine, and because naturally aspirated engines rely in intake manifold vacuum to draw the blowby gases from the crankcase, the 8AR-FTS uses two methods to control blowby gases. A conventional PCV valve is used and is effective when vacuum is available (when turbocharger is not being utilized) in the intake manifold. An ejector is also used to forcibly ventilate the crankcase when the turbocharger is operating. The ejector uses the venturi effect to draw gases from the crankcase: pressurized intake air supplied by the turbocharger is routed through the ejector nozzle which creates venturi vacuum in the ejector to draw the blowby gas out of the crankcase. 22

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26 Turbocharger Reference Information In good repair practice, it is critical to know and understand how a system actually works before trying to repair any of the components. A component that you think may be faulty because of its operation, may actually be working as designed. For example, the Lexus wastegate actuator is normally open. If you did not understand the system, you may think that this is at fault since most other manufacturers keep the wastegate valve normally closed. The repair manual and new car features books can help you understand the system. When diagnosing an actual concern with the vehicle, use the repair manual to help guide you through the repair process. The repair manual lists Diagnostic Trouble Codes that are related to the turbocharger system and will have you perform specific tests in a particular order to determine the root cause of the concern. The repair manual also lists out repair and test procedures for customer concerns that are not related to a specific failure with a DTC, such as turbocharger noise and white smoke from the turbocharger system. 24

27 Turbocharger Diagnosis After thoroughly understanding the turbocharger system and using the reference information to come up with a specific repair process, the technician will have to perform a few tests. Most of the tests for the turbocharger system can be performed with some basic hand tools, a vacuum gauge and a vacuum tester. Since the control part of the turbocharger system uses vacuum, most of the tests that are performed are checking for a constant source of vacuum or making sure that components can hold a source of vacuum. The Techstream scan tool is also a vital tool that is needed in the repair and diagnosis of the turbocharger system. The Techstream allows a technician to retrieve DTC s, perform active tests and monitor live data on the vehicle to see exactly what is happening. 25

28 Techstream Diagnosis Using the Techstream the technician can monitor the specific data lines that allow them to see what is happening in the turbocharger system. The data lines listed below are data that is directly related to the turbocharger system and should be used during the diagnosis of the turbocharger system. Intake Air Temperature B1S1 (Turbo) Intake temperature coming from the No. 1 Turbo Pressure Sensor located in the intake manifold. This sensor reports the intake air temperature after going through the intercooler. Can be used to diagnose intercooler efficiency. Wastegate Valve Control Duty Ratio Target duty cycle that the VRV is receiving from the ECM to control the wastegate valve actuator. Intercooler Water Pump Speed The RPM of the intercooler water pump. The intercooler water pump can range from 2,000 to 7,000 RPM s when operating. Intercooler Water Pump - The drive request duty ratio of the electric water pump assembly. Target Boost Pressure The intake air pressure that the ECM is trying to receive from the turbocharger system. This data list item is labeled in absolute PSI reading. Therefore the technicians will see a target boost of close to 15 PSI when the vehicle is at idle. This is a normal condition, because atmospheric pressure is close to 15 PSI absolute. During boost conditions under WOT, the target boost will reach approximately 30 PSI, which means the ECM is requesting the maximum boost pressure of 17.4 PSI from the turbocharger system. Boost Pressure Sensor - The absolute pressure inside the intercooler. This pressure reading comes from the No. 2 Turbo Pressure Sensor. The data list item is also read in absolute PSI. 26

29 Air Bypass Valve Control - Operation status of the air by-pass valve assembly. Determines if the air bypass valve is requested open or closed. The air bypass valve is normally off which means that it is closed in the turbocharger system. 26

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