In order to improve the yield of thermal motors (in our case a 125cm3), a new concept of motor with a variable compression rate has been created. This project deals with the installation of a compression rate regulation system.
This subject is at the heart of a company creation project lead by Mr Michel Marchisseau. This project obtained the following awards:
1- Price of the 3rd millenium delivered by the Lépine competition
2- National competitionl « en émergence » organised by the high education and research ministery
3- Admission to the 23th promotion HEC Challenge +
4- Acceptation to the Limousin Incubator(A.I.L.E.)
The volume between the cylinder head and the piston when this one is at the high static point (PMH) represents the combustion chamber (or dead volume) v. The volume between the cylinder head and the piston when this one is at the lowest static point (PMB) is called V.
The piston run variation permit to change the values of v and V, and so the value of their ratio wich is called the compression rate ε. The volumetric ratio ρ whisch appear in the performance expression, is defined with the following formula:
If we reference to the formula (1), we understand than to rise the compression rate is equal to minimize and/or maximize, because the surface cylinder is constant. One of the ways to change the PMH and PMB volumes consist to change the piston run: this is the method used in this project.
The prototype is composed of an eccentric (yellow) built in the crank shaft, where is fixed the lever (orange) in pivot connection with the eccentric (travel of ±22°compare with the average position) allowing that way to rise or reduce the piston run (blue) as we need (Fig.1 et 2). The leve movement is controlled with a hydraulic circuit localised inside the crank shaft and the eccentric.
down under, 2 videos to help you to understand the device functionment. On the left, a video with the lever in neutral position. On the right, a video with the lever in max position. If we watch well, we can see the piston amplitude is more important on the right.
The energetic stock of a such device permit to draw the following figure in order to well understand the energetic transfomation, and disclose the importance of a control on the compression rate.
| Advantages: | The main interest of this technology are: |
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In order to control the compression rate of a motot, we need to measure it to integrate it in clod loop. That is why we had to find a sensorwhich is able to transmit the information in a hostile environment according to the following specifications:
The choice were on a giant magnetoresistance sensor from the company "NVE CORPORATION", because they are one of the rare sensor able to work at his temperature.
In order to work correctly, We need to integrate on the lever a magnet which is the magnetic source enough powerful to work in all position of the lever. Following the position of the lever, we can read after calibration the compression rate value.
Finally, after an electric signal treatment delivered by the sensor, we can transmit the compression rate information to the calculator which could command the TCV in a closed loop.
Once we found the best magnet position on the lever, we can connect the sensor to a Labview acquisition card which permit us to filter the signal and start to calibrate the sensor. Down-under, the curves measured directly with the sensor on a digital oscilloscope.
We get with this measure a dynamic amplitude of peaks of : 225 – 30 = 195 mV. On the following curves, it is represented the Labview signal after digital treatment in order to raise the measures precision.
Thanks to Labview, a information acquisition software was created (see annex 4). However, a correct calibration of the sensor must be done. We regret to not have seen this project materialised in order to check if the sensor integrated on the motor housing deliver an information in accordance to the specifications (precision < 10 %...).
