roof ventilating system

In the past, I designed F3000 (currently Formula Nippon) machines.  My first job at SUZUKI SPORT was developing the machine for the 1995 Pikes Peak Hillclimb.  That involved full-fledged aerodynamic tests using scale models to optimise the shapes of aero parts like wings, undercowl (*1) and diffuser (*2).  The work paid off, and our Twin Engine Escude ran successfully through tough weather to a fine victory.  After that I designed the V6 Escude, also for Pikes Peak, the first time in my career to be put in overall charge of a competition machine.  The suspension, frame, drivetrain…I designed just about all of the car; the draughts were hand-drawn back in those days.  Then I worked on formula cars for gymkhana and one-make series, after which I got the chance at fully working on a rally-car design, with the 2nd-generation Swift Super 1600 for the Junior World Rally Championship (JWRC) – the car that won the 2004 championship.  I went on to work on the current Ignis Super 1600.  The important point in WR Car design is firstly a chassis/body with low drag.  Downforce certainly is important, but the front-to-rear balance has to be maintained carefully.  Then we must see how the design affects the cooling system and the engine intake layout.  Just as for racing cars, we use ram-air pressure (*3) to feed air to the air-cleaner box to raise engine power output as much as possible.  And because of the long driving distances of rally events, we also need to consider driver comfort with measures like adding a roof ventilating system (*4).

The SX4 WRC prototype we unveiled at the 2006 Geneva Motor Show, partly due to the timing of its introduction, was still very much a work in progress, with much emphasis on showing the styling.  After that, in terms of aerodynamics, we tried very adding many shapes and forms of wings, undercowl and overfenders to the production car and performed thousands of tests.  We paid particular attention to the tendency of production vehicles to more easily lift the rear end, more than in the case of competition machines.  If we fix that by fitting a rear wing, its aerodynamics would push the rear end down but also would lift the front end, which makes it necessary to generate front downforce by using a spoiler or curving-in the bumpers.  We increased the downforce while constantly checking the front-to-rear downforce balance: first the rear downforce, then the front, again rear, front, and so on, until we reached the shape we have now.
The SX4 is basically a hatchback design, which made the design of the rear-wing section particularly difficult.  Downforce is generated by flowing air to the rear wing to create negative pressure.  What’s important is how the air coming from the roof flows away from the back of the rear wing.  The SX4 is quite tall and the rear section drops down suddenly, which makes it difficult to obtain the desired air flow into the back of the wing.  The relative positions of the spoiler, the main roof section and the wing was very difficult to get right.  We tried out many different combinations of height, angle and positioning within the limits laid out under the regulations, and we have now settled with the current layout.
We are also trying out the use of vertical fins (*5) to make the wing effective even when the car is turning corners.  Aerodynamic testing facilities at SUZUKI also perform diagonal wind-tunnel tests.  We tilted the car, to about 20 degrees, and measured the downforce at different angles to find out, quantitatively and numerically, at what angle the fins take effect.  The vertical fins don’t affect the downforce itself, but the tests also showed they become effective when the slip angle (*6) exceeds 10 degrees.  The graph readings clearly indicate the effect.  This is just one example of the way today’s rally-car building requires a lot of detailed testing and verification.

After repeatedly making and trying out different model parts at the wind-tunnel testing facility, we managed to increase total downforce by about 40 percent compared to our earlier version.  We continued making improvements at various sections – rear, front, upper – building, examining and throwing away a huge quantity of model parts before we finally reached the current shape. For some parts we would use clay models , trying out different shapes, scraping off or adding on clay.  We kept records of each test; we now have a huge accumulated data of rally car aerodynamics in many thick files.
Alongside the wind-tunnel tests, we attached stroke sensors (*7) to the suspension on the car at the proving ground and obtained precise data on the generated downforce.  We often compared the results with the wind-tunnel tests and made adjustments, such as reviewing the machine’s front-to-rear balance.
As for styling, if we only keep focusing on aerodynamics, our machine might end up looking too different from the production car’s image.   So we do take measures like adding curves for a　smoother shape or incorporating styling-design-type forms.  On the other hand, when we feel we need to emphasise aerodynamics, we make sure to choose function over form.  In the course of determining the machine shape, we hold constant talks with our design composite section and conduct styling-design reviews.

We can get a good picture of the vehicle’s characteristics by looking at data from wind-tunnel tests and test drives, but the layout of the cooling system has its own set of difficulties.  Especially since you have to foresee the vast differences in accelerator operation required for different engine loading, rpm and torque output, and different course surfaces, before deciding on the size and the position of the heat exchanger (radiator).  The big differences in temperature between rally events complicate matters.  As for the intercooler, a large cooling capacity is welcome, but its volume is restricted by the regulations; and the radiator which is positioned next to the intercooler may not fit where we’d really like it to because of the limited space, so we need to proceed cautiously in choosing its layout and size.  Currently the basic packaging of the car is being examined closely in the tests in Europe, but we are also considering a number of back-up packaging layouts.

WRC is an extremely tough, competitive category involving long driving distances, so durability, the strength to complete the run, is the absolute precondition.  The question is how to keep the car lightweight while leaving intact its strength.  To this objective Mr. Michel Nandan and Mr. Nino Frison suggested to us a new material.  Titanium is a lightweight material, but we limit its use to certain sections.  Much of the car is made of steel. In Europe, steel containing special ingredients are specified in much detail.  Among such steel, there is one that provides one-and-a-half to two times the strength with the same shape.  Using such material carefully would allow us to create a lightweight and tough car.  It’s invisible from the outside, but we have made much progress in the study of material strength, that is, we are learning to use materials with quality and characteristics that are clearly a step ahead of what we’ve used in the past.
Mr. Frison and Mr. Nandan have also given us valuable advice in other design basics, such as the structure of the roll cage, and ways to make maintenance much easier.  For example, the dampers, which we had been attaching with screws, can now be much more quickly attached/detached after removing their pins – this is just one of the very many ways in which we incorporated the special know-how of the two experts with years of top-level rally experience.
Our France-based testing team headed by Mr. Nandan and Mr. Frison are working closely together with us in Japan, as a single team.  We create a design in Japan, take it to France and we receive feedback data from them.  Such process is repeated over and over for continuous design improvement.  We at Japan also need to see for ourselves the actual testing procedures in France, and so the Japanese staff including me take turns visiting France and keep records of the tests.  We also e-mail each other on a daily basis to exchange suggestions for solving problems and making improvements.

Our October WRC test entry is looming close, and the machine is now close to completion.

We are fully aware of how hard it’s going to be for us in our first year of entry.  We went through the same process with the Super 1600, but we understand this is going to be much tougher, in light of what we’ve gone through so far.  However, it all boils down to coming up with the right technological and material solutions.  If we take the necessary measures one by one, just as we’ve done in the past, I am confident we could put on quite a performance and get some exciting results.

*1 Used partly for engine protection, but also to use airflow below the chassis to generate downforce.
*2 Placed low on the chassis rear and designed to re-route the rearwards airflow upwards, by which the chassis is pushed downwards, in stronger contact with the ground surface.
*3 Wind pressure to the front of a vehicle in motion.
*4 Ventilation inlet to draw fresh air into the cabin for driver and co-driver comfort.
*5 Fins attached perpendicular onto the rear spoiler to control chassis sideways movement.
*6 In this case, the angle formed by the directions of the wind and the car, seen from above inside a wind-tunnel testing facility.
*7 Sensors to measure suspension compression/extension when downforce is generated.