Bench Mark

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develops and installs homebuilt motors with external rotor. Such motors are very short in longitudinal dimension, that is an important advantage in terms of packaging. Sump is assembled by three components manufactured from milling billets of aluminium alloy. Observing the gear-box output opening, it’s easy to guess that tripod housing is integrated inside the output hub, similarly to the car of D.U.T. Racing. It’s not difficult to guess the layout of gears. Like in the previous case, a couple of double stage twin transmissions assembled with simple spur gears.

1.5.3. Green Team, Universität Stuttgart, Germany.

University of Stuttgart owns the most winning team in the history of Formula Student in Europe, Renn Team Stuttgart. A couple of years ago, the University set up a specific team which competes in the Formula Student electric, The Green Team. Car deployed in 2012 by team of Stuttgart was a two wheel drive vehicle, with drive wheels controlled independently.

By Picture 1.5-3 it’s possible to appreciate the group of motor and gear-box assembled together on a test rig. The first aspect to highlight is that motors are positioned following a longitudinal layout, differently from cars analyzed above. For this reason, it’s right to guess that transmission is realized by a couple of twin gear-boxes. A bevel gear is installed in the first stage and a spur gear in the second. In order to keep motors in the lowest position as possible, with axis parallel to the ground, axis of two stages don’t lay on the same plan identified by axis of the motors. Output of the gear-box is positioned in higher position, in order to allow the half-shaft to work parallel to the ground.

Housing of the tripod joint is integrated inside the hub of output, In this solution too. Back to the Picture 1.5-3, it’s important observe the opening below the gear-box output. It’s easy to guess that is the opening necessary to calibrate preload of angular contact bearings. Last deductive reasoning have to be made around the sump. It’s an assembly of two huge components manufactured by monolithic blocks of aluminium alloy. Surface of joint between two components is the plan that lays between the central and the output shaft.

1.5.4. T.U.G. Racing, Technische Universität Graz, Austria.

Technical University of Graz is one of the first athenaeums to take part of Formula Student in Europe. Internal combustion engine cars from Graz duelled against those of Stuttgart to claim the first positions, for a decade. In last years the team built some electric traction cars, starting from chassis of combustion cars.

By Picture 1.5-4, it’s important to meditate about the layout of the car which is a rear wheel drive equipped by two independent motors. It’s easy to guess that

Picture 1.5-3: Motors and gearbox of Green Team assembled together on a test rig

(https://www.facebook.com/greenteamstuttgart/).

Picture 1.5-4: The back of T.U.G. car at Formula Student Hungary, Gyor 2012

(https://www.facebook.com/tugraz.racing/).

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motors are positioned in parallel longitudinal position, like in the case studied at Chapter 1.5.3.

Transmissions is composed by two independent twin boxes. It’s right suppose that the gear-train is split in two stages, first realized by bevels, the second realized by spurs. Differently from the previous case, all the gears lays on the same plane. For this reason, the plan which houses axis of the gear-train components have to be tilted. That allows the half-shaft to reach the centre of the wheel hub. Half-shafts which work in angled position don’t feature their best work condition.

Anyway, this solution is excellent to keep masses as low as possible. Finally, It’s important to consider that this solution can be effective on a car equipped with 10 [inches] rims only. That’s due to the limited angle of operation of half-shafts

1.5.5. Ka-Raceing, Karlsruher Institut für Technologie, Germany.

Another important athenaeum in the European overview is the Institute of Technology of Karlsruhe. By a couple of years this university deploys two very interesting Formula Student cars, one equipped by internal combustion engine, one equipped by electric motors.

Picture 1.5-5: Rear of the car of KA-Raceing (Squadra Corse PoliTo Archive).

First of all, it’s important to appreciate the non ordinary solutions adopted in these cars. Motors are assembled together sharing the liquid cooling jacket and the box of the contacts. Gear-boxes are independent and symmetric, positioned in external position referred to the centre plan of the car.

But the most original feature of the power-train module is the structural purpose. It’s interesting appreciate that mounts of rear upper control arms are positioned on the sump structures. Rear lower control arms are assembled on a tubular frame that includes the jacking bar. Tubular frame is then bounded to the power-train. Observing the picture more in detail, it’s possible to notice that rear wing attachments are bounded to power-train module too. About gear-train it’s necessary observe that motor and half-shaft lay on the same axis. Is therefore reasonable that gear-train is realized by planetary layout, with a fixed internal crown.

Another important detail to focus in, is the presence of the hoses on the sumps. It’s sure that the cover of the motors houses a liquid cooling jacket. But, observing position of the hoses it’s right to suppose that the cooling liquid and the transmission oil are the same fluid. The fluid with this double purpose, is then cooled in a radiator positioned in the back of the driver’s cell.

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1.5.6. DART Racing, Technische Universität Darmstadt, Germany.

Another interesting team to take in example is DART Racing from Darmstadt. Like many others, a couple of years ago, this team switched from the conventional power-train to the electric one with good results. It’s possible appreciate in Picture 1.1-10 the duel for the podium between S.C.12e and eta2012. during Formula S.A.E. Italy of 2012.

Picture 1.5-6: Disassembled gear-box from DART Racing car. Note the scavenge rotary pump circled in red (https://www.facebook.com/TUDarmstadtRacingTeam/).

Motors shown in Picture 1.5-6 features a very tight axial dimension but quite large radial. It’s obvious that chosen layout is the transversal one. All power-train components are roomed inside the monocoque chassis. That solution, which is very similar to the one described at Chapter 1.5.2, is in reality more interesting and refined.

Basically, layout adopted is the same shown in chapters 1.5.1 and 1.5.2, but there are some details that make the solution of DART very interesting. Analysis starts from the sump, which is assembled by only two components, machined by billets of aluminium alloy. Central wall of the sump, displayed in the solution of A.M.Z., is therefore removed. As consequence, there isn’t a central support to house bearings. From deep observation of Picture 1.5-6, it’s possible to notice that twin gear-trains feature a single stage of reduction with offset grown by idle gear. Moreover, it’s possible to notice that gearwheels aren’t equal to their homologues. One gearwheel is provided by an integral shaft which is shared with the homologue wheel too. In order to guarantee that two homologue wheels on the same shaft are decoupled, one of the wheels is supported by a radial and an axial bearings.

Returning to analyze the sump, it’s possible to appreciate the labyrinth walls under the gear-box input opening. It’s sure that these barriers protect the admission of a scavenge pump by the oil surging. As matter of fact, it’s possible notice a small rotary oil pump which in the picture is underlined by a red circle. It’s sure enough that the rotor of the pump is connected to the idle shaft of the gear-box. That solution which looks very interesting by point of view of the packaging but impairs the efficiency of the two “branches” of the gear-train. Another detail to appreciate is the couple of spray nozzles useful to lubricate heavily stressed gear in meshing zone. That example is very relevant by lubrication point of view. Traditionally, gear-boxes exploited on Formula Student vehicles are lubricated by the classic wet sump. It’s now useful take in consideration the possibility of install a system devoted to cool and to direct gear-box lubrication oil.

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1.5.7. Racetech, Technische Universität Bergakademie Freiberg, Germany.

By point of view of materials and technology, some of the most interesting cars are made by the Technical University of Freiberg.

Gears shown in Picture 1.5-7 suggest a layout of the transmission like that described in Chapter 1.5.3. As explained in advance, students of TU Freiberg are particularly skilled in the choice of the materials and in the employ of advanced manufacturing technologies. Gears shown in Picture 1.5-7 are supported in a quite sophisticate sump produced by additive manufacturing of magnesium alloy.

Gears shown, are quite conventional by point of view of geometry which exploits sp-lined profiles and spiral bevel profiles of tooth. The most interesting detail to take in consideration, is the finish of the gears. Seen from the picture, it looks a PVD coating which is fundamental in order to tear down the friction. That leads to a higher efficiency and to a lower wear that affects the components.

1.5.8. R.M.I.T. Racing, University of Melbourne, Australia.

R.M.I.T. Racing is the team of the Melbourne University which competes in the Formula Student Australasia, unique event to take place in Oceania.

Layout of motors and of Gear-train looks very similar to examples shown in chapters 1.5.3 and 1.5.7.

Components, gears in particular, looks quite heavy to be installed on a race car.

Anyway, it’s important appreciate the sump.

Differently from the example described in chapter 1.5.3, it’s useful observe how sump is disassembled. In this example, the surface of joint is perpendicular to that of Green Team gear-box. This fact simplify a lot the manufacturing of the sump because housing of bearings are integral. Another detail to notice in the sump, is the spacing of the screws. Bolts are very near each others, in order to ensure the proper stiffness in the connection of the different components of the sump. That ensures the proper operation of the bevel gears and the retain of lubricant oil.

Picture 1.5-7: Gear assembly from Racetech car (https://www.facebook.com/Racetech.Racingteam/).

Picture 1.5-8: R.M.I.T Racing partially assembled gearbox (https://www.facebook.com/RMITElectricRacing/).

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