So finally Techie is having Vacation . So more time to spend in Forum!
i will explain about Tuning Boxes and remapping in detail with respect CRDI engines. Tdi engines Queries shall be answered as and when needed.
so before we start off . i will explain the basics of the Crdi injection systems. Treat this as a technical article from the real Techie. So i will be following a report kind of style and yes treat this thread as a guide to CRDi also. TDi as already told will be explained based on Queries.
So lets start off.
CRDI systems are the latest generation electronically controlled Diesel injection systems which is a major
improvement upon the DI injection systems. As the name suggests, there is a Common Rail in the system which actually makes it possible to have an engine speed independent diesel pressurisation for injection into the combustion chamber, it is also independent of the injected fuel quantity. The Common Rail System [CRS] just like the DI system has two pressure delivery sides. The low-pressure side and the high pressure side they consist of the same parts except that there is a Common Rail (a high pressure fuel accumulator) in the high pressure side.
The supply pump is either separately used in tank, which is electrically controlled otherwise it is integrated with the high pressure pump which is mechanically driven off the cam shaft. The injectors are electrically operated. This makes it possible to open the injectors for more than one time or multiple times in the same compression cycle. The CRS consists of the following main components.
Engine control module [ECM]: The CRS is controlled by the ECM. It has a metal housing. The sensors and actuators and power supply are connected to this unit through a multi pole plug in connector referred to as wiring harness.
The power components or drive circuits required to drive the actuators are integrated in the ECM such that they can dissipate their heat into the ECM housing.
Please note that different OEMs use different names for ECM.
The ECM evaluates the signal it receives from the external sensors ( more on this later) conditions it if necessary and then process the data received, by referring to the input data and predetermined data maps ( a simple look-up table. More on this also later). Once the processing is done, the ECM microprocessor calculates the injection times and the instance of injection. The outputs from the ECM are used to trigger the drive circuits for the intended actuators and the drive circuit actuates the actuators. In this case the Injectors, the rail pressure control and the engine control functions like Exhaust Gas recirculation etc. the ECM in fact takes care of the whole system functionality. The injection, turbo charging, electrical system, On Board Diagnostics [OBD] and also error information logging in the onboard ROM [read only memory].
Different manufacturers have different codes for the ECM.
Low Pressure Delivery: The low pressure delivery consists of the Pre Supply Pump [PSP]. The PSP is either an electrical pump with pre filter or a gear fuel pump.Its function is to transport the fuel in the direction of the high pressure pump from the fuel tank.
A. Electrical fuel pump: The electric roller cell pump is responsible for the delivery of fuel from tank to high pressure pump. Beginning with the engine crank, the pumps keeps on running independent of the engine speed. It permanently delivers fuel to the high pressure pump through the fuel filter.The excess fuel sent to the high pressure tank can come back to tank through an overflow valve.
B. Gear type Fuel pump: This type of pump is integrated with the high pressure pump; they both share the same drive. The main components are two counter rotating gear wheels which while rotating mesh with each other. By this procedure fuel gets trapped in the chambers formed between the gear wheels and the pump wall. In this way the fuel is transported to high pressure pump.There is a line of contact between the gearwheels which are rotating, which acts as a seal between suction and pressure ends of the pump. This prevents fuel from flowing back. This type of pump is dependent on engine speed. Itís maintenance free type.
High Pressure Delivery: The high pressure delivery side consists of the high pressure pump,
Common Rail and the Injectors. Brief explanation of these components is given below.
A. High Pressure Pump: The high pressure pump is the interface between the low pressure and high pressure sides. This is the pump that generates the required system pressure continuously in the Common Rail. This implies that in contrast to conventional systems, the fuel doesnít need to be separately compresses for each individual injection process. The high pressure pump is placed in place of the distributor pump as in conventional diesel vehicles. It is mechanically driven from the cam shaft and makes use of the diesel itself for lubricating. Inside the pump there are three radial arranged pistons at 120ļ angle to each other. The fuel is compressed by this arrangement. The driveshaft has eccentric cams which move the pump plungers up and down in accordance with the shape of the cam. The inlet valve closes when the pump piston passes through the Bottom Dead Centre (BDC). The fuel inside the pump cannot escape; hence the fuel can be compressed beyond the delivery pressure. This increased pressure opens the outlet valve as soon as the required rail pressure is met.
Now the fuel from the high pressure pump goes into the rail where this pressure can be maintained. This enables multiple injections and time controlled injection. In this way the whole system is made independent of the engine speed.
While this process goes on, whenever the pumping element chamber falls below the PSP pressure, the inlet valve to the high pressure pump opens and the pumping process starts again.
B. Common Rail (High Pressure Accumulator): This element of the CRS is the element which takes diesel injection to the next level. Though the pump is mechanical, the rail or accumulator holds diesel at a pre set pressure level. From here individual injectors are fed through feed lines. The rail pressure modulation is a complex process and depending on the level of control available for the rail, CRS generations are defined. The generation 1 and 2 have got solenoid valve based injectors while the generation 3 has piezo valve based injectors. The rail pressure is the deciding factor for the generations. The generation 1 CRS has got a maximum possible rail pressure of 1350 Bars and generation 2 CRS has got a maximum possible rail pressure of 1600 Bars. While the generation 3 CRS system has got maximum possible rail pressure at
2000 Bars, on par with Unit injector systems. The rail pressure modulation is done using either a Pressure Control Valve [PCV] or a Metering unit referred to as MeUn. The third method makes use of both PCV and MeUn. It is known as Coupled Pressure Control [CPC] making use of PCV at low engine speeds and the MeUn in the higher engine speeds. The control can be inlet and outlet controlled. Inlet control refers to using the MeUn also known as the Magnetic Proportioning valve [MRPOP] integrated with the high pressure pump to control the fuel quantity from the PSP to the high pressure pump. Outlet control means the regulation of the output pressure from the high pressure pump using the PCV also referred to as Rail Pressure Control Valve[RPCV] the CPC control uses both inlet and outlet control and is a feature of the generation 2 and 3 CRS.
C. Injectors for CRS: The injectors used for the CRS are electrically operated and based on the applications, they are hard coded. This implies that injectors used for a particular CRS cannot be used with another CRS. The generation 1 and 2 injectors are solenoid valve based while the generation 3 CRS is based on peizo valves. The injectors used in generation 1 and 2 are rated for max 1600 Bars pressure while generation 3 piezo valve based injectors are rated for 2000Bar pressure. The injectors can open and close multiple times in the same injection cycle. Which enables multiple injections in the CRS; this is very useful for reducing noise and also for reducing emissions. There are a set of injections that happens more before TDC [Top Dead Centre].
These are known as pilot injections, there can be three of them named pilot 1, pilot 2, pilot 3. They are particularly used to bring down the noise of the engine. The main injection as always is compulsory and canít be done without. This occurs just about TDC.
After TDC a set of injections are possible, known as post injections. These also are named as post 1, post 2 and post 3. They are mainly used to bring down emission levels. But post 2 injection also delivers additional torque to the engine. In CRS systems, out of the above mentioned pilot , post and main injection, a combination of 5 injections can be used which should compulsorily have main injection.
The above paragraph is really important for this article. Boxes alters the above mentioned injections using different mechanisms. More on this later.
Features and Benefits of CRS: The principal feature of CRS is that injection pressure is independent of the
engine speed and injected fuel quantity. The principal advantages of this single feature is that, the injections can now be controlled based on time and on angle of crank. This gives more freedom to the level of fuel metering. This directly implies that more fuel can be injected even at lower engine speeds hence leading to better power and torque output at lower engine speeds. This improves the drivability of the car, making the car more suitable to be run in cities, where stop and go traffic is more.
The next major improvement over the DI engines is that electrically operated solenoid or piezo valve based injectors are used, which can open and close multiple times in the same compression cycle in individual cylinders. This has enabled the use of pilot and post injections in addition to main injection,which has made the current generation CRS cars to be as silent as their gasoline sibling and also at the same time meet stringent emission regulations with relative ease. As the name CRS suggests, the common rail has got a pressure regulation mechanism both on the inlet to the high pressure pump and at the outlet of the high pressure pump. This enables the latest generation CRS to build up higher pressures. As of now the standard max pressure available in the generation 3 CRS systems are close to 2000 Bar which is on par with the Unit injector Systems [UIS]. This results in the best possible atomization of the diesel fuel and results in increased efficiency. And since more fuel can be injected irrespective of the engine speed, the current generation CRS cars are always equipped with a turbocharger, so that more power output and lower emission levels are possible. Further more since the rail pressure can be held for longer duration, even when the engine turns off, CRS systems are more adapt to be implemented with Start Stop systems. Where the engines get turned off whenever the engine idles unnecessarily. As explained in the low pressure
side, electrical pre supply pumps can also be used for CRS. In the latest generation CRS has got a Demand Controlled Pre Supply Pump [DCPSP]. In the CRS using such PSP, the low pressure side does away with the unnecessary pressurization of the fuel and its return to tank through feed back lines into the tank, whenever over flow occurs at the high pressure pump. Thus fuel can be saved since unwanted pressurization of fuel by the PSP is avoided. The use of ECM makes the system more reliable and also easily diagnosable since the ECM diagnostic unit keeps a record of the error codes generated in every driving cycle, be it by any of the sensors or actuators. Since the system is electronically controlled. Certain basic safety features are available on the CRS equipped vehicles, since the ECM is continuously monitoring the driver demand through the accelerator pedal input, if due to any reason the accelerator pedal fails, the ECM is able to activate a Limp Home mode. In this mode the ECM recognizing that driver demand is not registered since the accelerator pedal is not giving any input, it regulates the rail pressure and injects enough fuel to keep the vehicle running in a gear till certain engine speed as set in the ECM in case of an emergency like this. In this way the driver will be able to move slowly till home or a garage.
So now having understood about the basics. we can go into the details of the tuning Boxes and the Remapping scenario.
please feel free to ask any doubts will try to clarify them to the extent of my knowledge.
Going off for a short break. will update the thread asap.
Till then happy reading..