Formula Hybrid MADI
DESIGN REPORT
While designing the “Colibri” our main goal was to make an efficient and reliable hybrid-­‐
powered drive train car with the agile performance of a real racing car. Our team members tried to achieve precise results and advanced features in many aspects of the design and construction of “Colibri”. Our frame is made of cheap low-­‐carbon steel. Nevertheless its structure provides high rigidity and strength. To achieve this we have made a number of experiments (analyses) in SolidWorks 2009 and its “3D Simulation” add-­‐on. We had created and tested a beam structure of the frame than included shocks and other suspension elements so that we could estimate the influence of the road bumps on the deflected mode of the frame. We simulated a static analysis that considered the weight of the car and dynamic tests as if the car rides over a road bump and a pothole. One of our most important frame features is a “Formula-­‐1” like positioning of the pilot (the basin is lower than the legs). By this the driver is provided with more comfortable and convenient fit. That’s why “Look!” has a twin floor with the steering rank and adjustable pedal box based on the lower deck and drivers’ legs positioned on the upper deck. Our suspension and steering systems were designed in accordance with the race track conditions. The kinematics of the suspension and steering was calculated in “Adams”. The most notable features are: •
Double fishbone suspension with the transversal unparallel A-­‐arms. The main idea was to get the roll center as close as possible to the center-­‐of-­‐gravity to reduce the roll of the frame while cornering or during the acceleration. •
Front sway-­‐bar – to achieve close-­‐to-­‐neutral steering and eliminate the roll of the frame while cornering. Without using a sway-­‐bar the car will tend to over steer and can cause the skidding of the rear wheels. •
The use of rocker arms that helps us to reduce the unsprung mass and that makes the adjustment of the suspension stiffness characteristics cheaper and easier – there is no need to have a number of expensive spring sets – instead of that 1 you can use either different rocker-­‐arms or even rocker-­‐arms that have multiple pushrod attachments. •
Lightened wheel hubs and duralumin steering knuckles – this also reduces the unsprung masses and the entire weight of the car. •
Identical front and rear steering knuckles with changeable steering levers (steering arms). This helps to improve the ease of the car production and maintenance. •
The use of ball couplings that increases the reaction of the car (no silentblocks). The whole steering system was designed to have a 180 degree steering wheel travel on the each side. This was matched with the minimal required turn radius of the car. The steering rank has a welded aluminum case. This helps not only to gain in weight but also saves the expensive material while the produce because it is made of separate parts that are joined by welding (there is no milling operation). Due to its design the pitch play is adjustable. Another worth to mention part of the steering system is a bronze pilot bushing inside the rank case that guides the rank – it causes lower traction and easier maintenance. The steering linkage has two cardans that work together as a single constant-­‐velocity universal ball joint. In our brake system we use high efficient Wilwood master cylinders with matched brake calipers and braided hoses. The balance between the axles can be controlled by a balance bar. We also decided to make our own steel brake disks produced on the laser cutting machine. The specific design of the ventilation holes on the disks helps to keep the whole surface clean at all the time. The fuel system features our own made and welded aluminum fuel tank. On the basement of our tests with on our previous car called “Bombus” we have corrected some technical mistakes and slightly improved the hybrid transmission on “Colibri”. The calculations were made in “Simulink MatLab”. We decided to follow the parallel hybrid system (Fig. 1). But now it consists of a more powerful Yamaha T-­‐Maxx 250cc engine and reliable and powerful LEM-­‐200 DC electric motor that doesn’t require complicated current converters. Main features of that motor are high power and relatively small size. A parallel hybrid transmission scheme is used because of its reliability. As it is known, the combustion engine is very inefficient and environment-­‐unfriendly while its starts and warms up. It is also not very efficient at low and medium RPMs. At the same time the electric motor has low time lag and high torque from the very begging. At the first 15% of the acceleration pedal the car is powered only by electric motor while the combustion engine is idling. The electric motor is connected to limited-­‐slip differential by the first chain gear with 1:4 gear ratio. After at the 15% point of the pedal travel the throttle gate is begging to be activated and the engine rises its RPMs. At the speed of 30 km/h the electric motor electronically switches off (Fig. 2). At the same speed the engine using CVT and centrifugal clutch is able to transfer the 2 torque to the input shaft of the second chain gear (CVT ratio: from 1:2.44 to 1:0.83, second chain ratio 1:2). The output shaft of the second chain gear is connected to the electric motor shaft by the one way bearing. Because of that from the 30 km/h the car is only powered by the combustion engine. Starting from 50 km/h and up to 100 km/h (depend up level of charge ultracapacitors) the electric motor can be switched by the controller to the generator mode and can charge the ultracapacitors. The switch speed depends on the charge rate of the ultracapacitors. The energy recuperation mode starts when the driver actuates the brake pedal. Recuperation mode is activated when you press the potentiometer lever on the steering wheel: the sensor is triggered the inclusion of recovery and a potentiometer is integrated into the steering wheel adjusts the degree of inhibition of the motor. ICE transmits torque through the variator and freewheel. Freewheel necessary to disconnect the gasoline power unit of the wheels during motor acceleration and electrical recuperation. Because of the high loads transmitted to the OWB we decided to get rid of the reduction unit and replaced it with a two serial chains on “Colibri”. Thus we have recuperation the gear ratio on the OWB and now we use a smaller and cheaper one. We also reduced the whole time lag of the transmission (smaller sizes of the star wheels) and increased its reliability. All the listed gear ratios were calculated for the optimization of our hybrid driving mode. We considered the avoidance of the tires spin-­‐out during the forcing mode when the output of the electric motor can be increased up to 34 kW (but not longer then for 5 seconds). We use ESMA EC 503 asymmetric alkaline (KOH) ultracapacitors. Ultracapacitors can accept high rate of recovered energy while driving because of their ability to work with high charge/discharge currents (up to 1500 Amperes). It is more than other batteries. Also ultracapacitors work better at lower temperatures. Our ESMA capacitors due there alkaline design are very convenient, reliable, ecological and easy to utilize. They have low local action and a self-­‐equalizing effect (balance automatically). They are equipped with a safety valve in case of overcharge. The level of charge is controlled by the sensor of the charge. Also we use sensors which allow to provide temperature to provide sufficient range of the race in control of the ultracapacitors unit, in the case of overheating, the car automatically shut down. Blocks of ultracapacitors made in a transparent casing that allows you to monitor their condition, and able to withstand the pressure more than 20g horizontal and about of 8g vertical load. All high current plug connection certified and have extra insulation. In order to facilitate the replacement and repair of the control unit, we use for its fixation quick fasteners. All cases are grounded on the frame for the effective operation of Ground Fault Detector (or IMD). For the regulation of the driving modes we used a buck-­‐boost regulator with a microcontroller. Its parameters can be changed by the use of CAN log and key signal. The recuperation mode has a priority in case of actuating both pedals at the same time and thus it makes the driving more safety. All the high current plug connections have an additional isolation. For the ease of maintenance of the control unit it is mounted with quick-­‐release joints. The electronic cases are grounded to improve the work of the Ground Fault Detector. The high volt electric circuits are 3 galvanic isolation from the low volt lines. All the electronic and electric systems have an extra vibro-­‐ and waterproof protection. To make our ergonomics better we have put only the most important indicators on our control panel: speedometer, LED fuel level, cooling fluid temperature, voltmeter, ampere meter, sensors of charge. All of them are either LED or LCD to make them easy to see in any whether conditions an avoid vibration factor affect the necessary information. The cases for the ultracapacitors are transparent that makes it easier to check their condition. We also designed an LED stop-­‐signal that meets the requirements of the FH rules and is easy for sensing as well as the structure of the human eye for comfort and safety perception. It has a separate electrical circuit with the voltage stabilizers and filters. It also emphasizes the whole style of our car. All electrical equipment and electronics systems (electric and electronic equipment) received additional vibration protection. We paid great attention to the style of our new car. At first we had made a 3D model of the body so that it complies with our frame. After that we made 1:1 a section veneer base and filled it with foam plastic. Then we sand-­‐papered it started to make the body with glass fiber mat and polyester resin. In the end it was colored in our specialty green color. We also paid great attention to the cooling of different car components. Our engine air intake has a self made fiber glass canal with the zero resistance air filter on it. Our body has special air inlets and the ultracapacitors’ cases have a perforation to make the ultracapacitors cool better while driving. We made fiberglass air inlets for the radiator because it is mounted beyond the large aluminum firewall. The firewall itself is shaped for more comfortable and safer driving. Fig.1 4 Fig.2. Fig.3. 5 Fig.4. 6 Fig.5. 7