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Discussion in 'Technical' started by mpg, Dec 3, 2010.
It seemed to work well in F1, so why don't newer supercars like the Enzo have it?
well there are different forms under different names. such as adaptive suspension. one thing to note though I wouldn't say it worked in F1 well overall because of the troubles coming out of pits and things. the other problem is the fact that road cars can't have every street with all its contours and bumps/potholes loaded into a computer whereas a circuit is much easier to do that with.
Weight is a big reason. The ferromagnetic shocks they use are heavy as fuuuuuu, and a really good damper can do nearly as well. Very high research/testing costs to get them set up properly too.
Wait, I thought they had computers making adjustments in real time. Are you saying that the suspension adjustments were preprogrammed?
you still have to program those computers on how to make adjustments. Race cars see a much narrower set of operating parameters/conditions than street cars.
As I understand it, the constant road height that active suspension provided to F1 cars was primarily used to implement quite sophisticated ground effects for downforce. In modern road cars, although obviously aerodynamics are going to be significant, they are typically not the limiting factor for any vehicle. The benefits that minor increases in downforce provide are never going to be realized by the vast, vast majority of drivers, and will only result in a net hindrance given the added weight. Efforts are much better spent in attempting to reduce the potential-cap: trying to augment driver skills with sophisticated control systems which might serve to close some of the gap left by skill.
Active suspension in road cars is mostly relegated to luxury cars, where the nil body roll is actually seen as worth it.
Simplified we can say that there are three different types of active suspension systems.
The first kind is what you would find on many production automobiles. Basically the system can keep the cars ride height the same when for instance you add weight in the luggage compartment. The system works with a low frequency, perhaps one time per second or so. The system is not really useful for a racing or high performance car.
The next system is what is sometimes refered to as a reactive suspension system. This was the system used by for instance Williams. Unlike the previous system, this system work with a much higher frequency, so it can prevent the car from diving during braking, rolling during turning and such. It still uses passive springs for regular suspension movement though, hence the name "reactive".
The third system is what is commonly refered to as an active suspension system, raced by for instance Lotus in F1. This system does not use any passive springs, but operates at a very high frequency so every movement is taken up by the hydraulic actuators the car rides on. Basically this system can do whatever you tell it to do, but its operation will depend on the hydraulic pump and the electro-hydraulic valves controlling it. Lotus tested the system on production cars before they raced it in F1. They also built a number of prototypes for car manufacturers, for instance Chevrolet (Corvette) and Volvo. Chevrolet did however had problems with the system when they tried to adapt it for production, and the costs were high.
Basically the systems used in F1 used an engine powered hydraulic pump, a closed aerospace type hydralic system (this prevents air bubbles to form, and keep the amount of oil in the system to a minimum). The weight of the aerospace type pump is no more than a few kg, but they do consume quite some engine power, so the car have to be competitive on power. Also the servovalves are very lightweight, but also very expensive.
Some pictures of the reactive suspension system found on the Williams FW14B below. At the front end you can see the the hydraulic actuators taking up the suspension movement and the MOOG servovalves controlling the system. Some general drawings of the system can be found in Williams US patent.
Also, if you don't mind me asking, what profession are you in?
The fact that it consumes a lot of power, is also a disadvantage in racing. So then it boils down to cost?
Well, for a racing car that uses ground effects to generate downforce the system can obviously be a significant advantage since it can keep the car at an optimum distance of the ground. But cost is one issue yes, I know Lotus couldn't afford to race it in F1 some seasons, and for a while when they used Renault engines, Renault didn't allow them to install the hydraulic pump.
Williams system is said to consume about 5 hp and the Lotus system perhaps some more. Lotus roadcar system consumed as much power as an aircondition system. The Lotus system of 1987 added about 10-12 kg to the car.
Since the Enzo has AC, the lost power and extra weight don't seem to be issues, and the Enzo has ground effects too.
the ground effects on the enzo provide relatively small gains relative to the weight of the vehicle, while something like an F1 car is generating downforce numbers of several times the vehicles weight.
streetable cars are also designed with ride heights high enough that the undertrays arent super height sensitive, as in an F1 car.
OK, so it doesn't aid the aerodynamic grip on the Enzo nearly as much as it aids the aerodynamic grip on an F1 car, but it still aids it, right? What about mechanical grip? Is it better or worse than a conventional suspension for mechanical grip?
Im sure the enzo's undertray was specifically designed to not be upset by roll/dive/squat much. remember were talking 3+" ground clearance, where .5" of height change is a much less significant chunk compared to a ground effect car which is only an inch off the ground. combine this with the fact youre only generating a couple hundred pounds of downforce at speed, and the gains are going to be maybe 50 pounds of aero grip while going over bumps or something inconsequential like that.
significant gains could probably be made in a car where you could lower it into something like a skirted track setting and actually get some serious ground effect going.
and no clue about mechanical grip. Id imagine you could see gains if programmed properly, but to what extent? I have no idea.
The Enzo has 1700 lbs of downforce. Perhaps that's partially because of the conventional suspension. Certainly it compresses with that much downforce, which decreases ground clearance and increases downforce. I guess I'm mostly curious about mechanical grip.
1700 pounds at 200 miles an hour. Going around a circuit, it would indeed be only a couple hundred pounds. Google says about 750 pounds at 125 mph, which is probably higher than it would average on a road circuit as well.
Enzo produce a quite significant amount of downforce, 775 kgf @ 356 km/h and higher, which is roughly 56% of the cars curb weight. Downforce obviously follows velocity squared so the gain in high speed corners are much higher than the gain in low speed corners. In any case, that is still a significant amount of downforce for a road car and the closer the car can run to the ground (without choking the flow under the car), the more downforce the car will produce without adding drag. In general a road car uses a too high ride height and a too soft suspension to make good use of ground effects aerodynamics. At the same time, a race car has a too low ride height and a too stiff suspension to be usable on public roads. With active ride this would not be an issue, or at least a much smaller problem.
Keeping the car at the right distance from the ground and in the correct angle is crucial for the performance of ground effects aerodynamics. Infact Lotus started development on the active ride system after the Lotus 88, the "twin chassis car" was banned. At the time the ground effect cars in F1 were able to produce more downforce than they could use due to problems with 'porpoising'. Porpoising was a result of the cars being very pitch sensitive which caused the center of pressure moving around depending on pitch angle, ground clearence and so on. This could introduce a rocking motion of the car, hurting the performance and limit how much downforce they could use in practice.
With the twin chassis car being banned, which had a separate floor section mounted on the wheel uprights to keep ride height and pitch angle under control, the next solution to that same problem was to use active suspension.
Most downforce producing cars rely on heave springs (you now, the spring that got loose from Barrichellos car and hit Massa in the head) to handle the forces created by downforce at speed. It's also refered to as the "third spring", since the cars got one spring for each wheel, then they have a linkage which connects the left and right suspension to this third spring. If both wheels at one axle are under load at the same time, just like when downforce presses the car down to the ground, the heave spring will take up the load and control ride height and pitch angle of the car. In F1 today, they usually use a springless rear suspension; basically the heave spring is the only spring used in the rear suspension. Obviously, these are only passive devices and not exactly ideal, but they are what the regulations allow.