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Working principle of a standard motorcycle configuration

All modern motorcycles do have an electronic based injection system. It offers many benefits over the traditional carburettor-systems. The heart of this motorcycle electronics is provided for e.g. BMW bikes by the Motronic module. This is de main computer or ECU (Electronic Control Unit). This unit decides how much fuel needs to be injected, controls the ignition timings,... And this for the different driving situations.

The main computer or ECU can work in 2 modes. The first mode is called "open-loop" and the second one is called "closed-loop".

In both modes, the ECU needs to have some information so it can calculates for example the amount of fuel that needs to be injected. It receives this information from different sensors. In the left side picture, you can see the global overview of the electronic injection system (example taken from a BMW Boxer system, but the same principle applies to the other bike models).

Let's start to explain it briefly.

1. Hall sensors: These sensors measures the RPM of the engine and is needed by the ECU module to determine the injection timing. Every 180° rotation of the crankshaft, an electronic pulse is generated by these sensors towards the ECU module.

2. TPS or throttle-valve position sensor: The TPS is a variable resistor that changes resistance as the throttle opens wider. The computer needs this information to calculate the correct air/fuel mixture. By knowing the position of the throttle valves, the ECU knows how much air is flowing towards the cylinder this in combination with the air temperature, see later). Adjustment is very critical and is best left to a qualified professional!

3. IAT or inlet air temperature sensor: As the word already says, it measures the temperature of the air going to the cylinders. P.s. This is not the same sensor for reading the temperature at the cockpit display! This information is needed to calculated the amount of air going to the cylinders(in combination with the TPS). From the physics we know that the colder the air, the heavier the air will be. This results in a need of more fuel injection (for a same position of the TPS), if you want to keep the air/fuel mixture ratio going towards the cylinders the same.

4. Oil temperature sensor: This measures the temperature of the engine body, so the computer knows if you run with a hot or cold engine. On some of the models, this sensor information is also used by the RID (Riders Information Display). If the engine is cold, the computer will inject a little bit more fuel to avoid shutting down of the motor.

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5. CO2 potmeter or Lambda sensor: In the older motorcycles you can find a CO2 potmeter instead of the Lambda sensor. The CO2 potmeter is typically installed when no catalyst is installed. It is a variable resistor that sets (simulate) the amount of CO2 in the exhaust gases. It is a very sensitive setting. In the modern motorcycles, a Lambda sensor is used instead of the CO2 potmeter. This device measures continuously the amount of O2 in the exhaust gases and the sensor will produce an electrical signal that correspond with it.

6. Ignition coil: This device produces the high voltage going to the spark plugs, which ignites the fuel.

7. Injectors: These devices injects the fuel into the air tube going to the cylinders. It is directly connected to the fuel pump. The open/close timing signal comes from the ECU module and is a calculated value (see later).

8. ECU module: This is the main computer of your motorcycle.

The closed-loop mode on BMW systems

The closed-loop feature of the ECU system is rather simple. This uses a Lambda sensor in the exhaust to read whether there is an excess or lack of oxygen in the exhaust. The Lambda sensor is a Zirconium-dioxide sensor, and works on the principle of a galvanic oxygen cell. This is the technical way of saying that the materials used in the sensor react to their surroundings and produces a voltage in certain conditions. It does this by comparing the exhaust gas to the outside air, where there is 20% oxygen. If there is no oxygen inside the exhaust, this gives a big contrast to the outside air, a voltage will be generated. This voltage lies between 0.8 and 1 volt and is enough to give the ECU a switching signal. The ECU then uses the sensor output to either lean or richen the fuel injected (that is reduce or extend the pulse width towards the injectors) to keep the sensor’s output switching from 0.2 to 0.8 volts and back again. So it goes rich – lean – rich – lean, etc every 2 seconds. Although rich – lean means a little rich and a little lean about the stoichiermetricly correct air/fuel ratio (approx. 14.7 to 1). This cycling of the fuel mixture about the stoichiermetricly correct ratio is good for the operation of the catalytic convertor, and generally helps with fuel economy.

Lambda is a term used to describe the composition of the exhaust gas of combustion. Also called the Excess Air Factor, it is a ratio of the difference between the actual air/fuel ratio and the chemically correct air/fuel ratio. The chemically correct air/fuel ratio is also known as the stoichiometric air/fuel ratio, and is given by the chemical equation for combustion of a fuel in air. If combustion takes place at the chemically correct stoichiometric ratio, the air/fuel ratio for petrol is 14.7:1 and the Lambda number is 1.0. The ratio 14.7:1 means that for chemically correct combustion you need 14.7 times as much air (by weight) as you do fuel (again, by weight). By volume it’s around 9,500 litres of air per litre of petrol.

If there is excess fuel (rich) then the Lambda number is less than 1.0. If there is excess oxygen (lean) then the Lambda number is greater than 1.0. So the Lambda number is the actual air/fuel ratio divided by the chemically correct air/fuel ratio.

IMPORTANT TO REMEMBER: The signal from the Lambda sensor is only considered when the throttle is held constant and the engine is not accelerating, so on cruise basically.

The open-loop mode

Open loop simply means there is no feedback of the Lambda sensor to the ECU. It means there is no sensing or measuring of the exhaust gas to see how the motorcycle is running. The fuel injected is determined by the RPM and throttle position, derived from fuel injector pulse width numbers stored in the fuel maps, and is trimmed for environmental conditions due to air temperature, air pressure and engine temperature. The open-loop mode is needed since the Lambda sensor is not quick enough in response when you are e.g. accelerating with your bike.

So the fuel map contains the info the control software of the ECU uses to tell the injectors how long to open and the ignition circuit when to fire the spark plugs. P.s. The ECU itself is just a little, specialised control system computer, totally unaware that it is making a motorcycle go vroom vroom. The map is different for each bike model – capacity, state of tune, etc, whereas the same ECU can be used, with the appropriate map, in any bike (or car, truck, boat, etc) designed to work with it.

We can say that in all non-cruising conditions (e.g. running with a cold engine, accelerating,...) the Lambda sensor is not used. The ECU uses instead all the other sensors and the IAT plays an important role since it shifts the calculated amount of fuel (mainly RPM & throttle position) with a certain factor depending on the ambient temperature.

IMPORTANT TO REMEMBER: This is important to understand for the working of the ACCELERATOR module™ (see later)




It does appear to sometimes create a problem with surging due to the lean mixture settings in the fuel maps, forced by the stricter environmental standards (EURO-norms). The result is that a power dip arises mainly during acceleration of the engine.

In the BMW boxer engines this phenomenon is even more present, since the combustion chamber is quite large compared to a 4-cylinder engine. The adoption of twin plugs per cylinder, the so called Twin-Spark, appears to have improved this issue with the 1100S/1150/1200 models for still igniting the lean fuel mixture in the best way.

The interaction of the ACCELERATOR module™

The ACCELERATOR module™ is the perfect answer on these "lean fuel mixtures" problems and is an add-on product that adjust the ratio of the fuel mixture to the optimum ratio during mainly the acceleration of the engine. So a richer fuel mixture to accelerate the engine. Also it will helps to start the bike better.

The result is that it creates a smoother power delivery throughout the whole rpm range! (already clearly visible at much lower rpm’s compared to the standard configuration, where much less an "on-off" feeling prevails). The engine picks up faster and runs smoother. A clear improvement of a faster throttle response is immediately observed. Also, the KFR (Konstant Fahr Ruckeln) on the BMW boxer engines will in most cases disappear, as this is also a result of using a too lean fuel mixture.

How does it work?

The ACCELERATOR module™ will only work during the open-loop mode. That is de mode where most of the effects of the lean fuel mixture are seen. When cruising, you need less power to keep the desired speed. So the motorcycle doesn't encounter hereby much problems.

The ACCELERATOR module™ will interact with the IAT device. As explained above, the IAT signal is processed by the ECU module by shifting the entire result from calculating the fuel/air mixture based on RPM and throttle valve position. You can say that the IAT signal acts as a "final" multiplier.

What we learned from above is that when the air is colder, the heavier the air will be. Meaning that there will be more air molecules per volume. If you want to keep the air/fuel ratio at the same level, you need to increase the portion of the fuel at colder temperature, given the same driving conditions at warmer temperatures. This is the part where the ACCELERATOR module™ will work.

It basically shifts the IAT temperature with -20°C. This means that the ECU or computer is fooled and thinks that the temperature is 20 °C colder than in reality. The result is that more fuel will be injected and that is the goal we want! Why -20°C? Calculations and field proven tests have shown that this gives the engine the best technical performance! You need however to be careful that you don't inject too much fuel. This is the case at temperatures below 0°C! Under 0°C you need to offset the temperature less than 20°C to avoid problems of too rich fuel mixtures which results in bad starting of the engine, too high fuel consumption,...)

To keep the various motorcycle configurations and different temperatures under control, I made a calculation model. I can lay perfectly the offset curve where I want, by using different electronic components. The main component of the ACCELERATOR module™ is a sensor that measures the outside air temperature very well. The other components bent the curve in some temperature ranges, to avoid the problems below zero degrees as mentioned before. The ACCELERATOR module™ is designed to work in all temperature ranges, i.e. from -30°C up to +80°C.

There are two versions of the ACCELERATOR module™. Which one should I choose?

Let me start to say that both models work fantastic! With over many thousands modules out there and the very positive reactions of the users, the concept has proven itself. Both versions of the module are made with high quality components, to deal with rough environments when riding the motorcycle.

The compact version came out as the first product on the market. Although very compact, it incorporates the necessary electronics to do the job. (I know that some people may find hard to believe it, but it is true. And I can tell you it is not a fixed resistor as some people do want to believe.) The design criteria was to create a module that is easily to install, to do the job perfectly and in a cost effective manner.

So why create an extension version, I hear you asking. Well some people like to have maximum flexibility and options. The extended versions allows the user to place the sensor on a different , free to choose, location on the motorcycle. The length of the cable is long enough to put the sensor at the front or the rear of the motorcycle, more directly in contact with the ambient air. The construction is very rigid and weather (water, snow,..) resistant. The installation takes a little bit longer than the compact version and the module is more fixed to the motorcycle.

IMPORTANT: It is really up to you which model you prefer!

Does the fuel consumption increases dramatically?

It is true, that during the acceleration more fuel will be injected with the ACCELERATOR module™. However, this results in a faster progress towards the desired RPM’s and speed. This because the ACCELERATOR module™ works with a fuel ratio which gives the highest yield.

Once we drive with a constant speed (cruising mode), the ECU module (engine management) will work in the "closed-loop" operation. Now the fuel ratio is determined by the Lambda probe and no longer by the ACCELERATOR module™. The fuel ratio is set back to a poorer mix. This is OK because the engine needs to deliver the least power. If we go back with the engine in acceleration mode, then the ECU module works back in a “open cycle” and the optimum fuel ratio will be back determined by the ACCELERATOR module™,with the known gains.

Is this a new technology?

Not really.

This method is applied for many years in the automotive and motorcycle industry. It is a proven technology where there is no danger to the engine, but only benefits. Because of the technical better fuel mixture, there will be less harm done to the engine! The motorcycle can be put at any moment back into an original state, without leaving any trace. The ACCELERATOR module™ is a complete Plug-n-Play tuning module where no DYNO test bench is needed!

Why choose the ACCELERATOR?

There are many good reasons to purchase this module.

It allows you to increase the smoothness of your engine, smoother throttle response and more power (even at very low rpm’s). In short, more fun driving your motorcycle! The ACCELERATOR module™ compensates for the high environmental demands settings of your bike engine.

It is a true compact Plug-n-Play module, which you can install in less than 10 minutes (for BMW R1100x and R1150x series in less than 1 minute! ). No wire cutting needed! You can always go back to your original engine configuration, without the bike dealer may find something. There are no error codes generated!

Most importantly, the ACCELERATOR module™ is far cheaper than any similar product on the market, such as the “POWER FRK MODULE”, “BOOSTERPLUG”, "OPTIMIZER",.. . And this at least equal or better performance!

The ACCELERATOR module™ benefits summary: