also interesting to note is that merc PU is supposed to be sacrificing around 15-20 HP because of the shorter exhaust manifold. (from the autosprint article posted above). also that merc compressor is larger. but due to bad google translation, i couldn't understand most of it, and weather it has any benefit. it says something about RPM and engine breaking and how merc MGU-H can bypass the battery and provide power directly to MGU-K and how the compressor bleed off can give more juice to MGU-K.
can anyone with italian knowledge please translate it better than google translate.
others who are more proficient in Italian will add to this, and perhaps point out a mistake or two, but here in bullet points, what I read from the linked article.
the article points out 4 main areas/benefits of the Mercedes PU
- the split turbo compressor/turbine are on opposite sides of the engine, which reduces/eleiminates the "heat flux" from the hot turbine side of the turbo, into the charge (compressed air) on the compressor side. This reduces the charge temperature for the same "work done" by the compressor (boost). Which in turn means, that you can reduce the inter cooling required to get the intake (into the engine) air temperature you want.
- unique intercooler solution, a additional benefit of the "split turbo" is, that the plumbing (pipe work) on the intake side is very short and compact, and that it allows the use of a new intercooler concept. The intercooler(s) appear to sit inside the chassis ( this part I don't fully understood, I think I know what they mean, but someone else with a better command on the Italian language may want to expand on this), and are "feed" by some duct work from the side pods. This solution, requires a rather unique "shape" of the chassis /tub, but has another benefit, as it doesn't obstruct the exit air flow from the main radiators (water coolers). Along the same lines, it is mentioned, that the main advantage from the "log style" exhaust comes from the compact packaging it allows. While they say/claim/estimate that this solution may "cost" between 15-20hp in outright engine performance, when seen from a "pure" engine point of view, the overall benefits outweigh the handicap the solutions bring. Again, the exhaust headers, are less obstructive to the airflow which comes from the main radiators on their way out of the cooling outlet towards the rear of the bodywork, and thereby allow for slimmer/narrower bodywork in this area, which benefits the aerodynamic of the car, both internal and external.
- they claim, that Mercedes is using a large® turbine then their opponents which let them extract more of the energy/power which is in the exhaust gas flow. The PU appears to be designed in a way, that it was the "plan" from the outset, to make this a integral part of the overall PU usage strategy. In the above posted energy flow schematic, you can see, that the energy flow from the MGU-H to the MGU-K is unrestricted by the rules. The only limitation is, that the total contribution of the MGU-K to the tractive/motive power (everything that propels the car forward) is capped at 120 kW. If the energy/power to the MGU-K comes out of the ES (battery) then there are additional limitations in place, as far as the energy flow is concerned.
This means, that you have a "upper limit" (time) of how long you can feed energy from the ES (battery) to the MGU-K.
But, as long as the energy comes directly out of the MGU-H and is feed directly into the MGU-K this limitation doesn't apply.
They estimate that Mercedes can augment their motive power for 50s per lap via the MGU-K, while the other teams (engine manufacturers) can do so, only for 36s.
One of the reasons is their larger turbine, which let them extract more energy from the exhaust gas flow, together with an "good" MGU-H and a refined control strategy to blend the MGU-K power with the ICE (engine) power.
- the last point is, a "clever" strategy to control the "waste gate" valve, and in general a quite elaborated and holistic control strategy which allows the power which is captured via the turbine/MGU-H to be blended via the MGU-K with the power which comes from the ICE (engine) part of the PU.
If they feed power directly from the MGU-H to the MGU-K any change in MGU-H rotational speed, will directly affect the overall power at the wheels (think traction).
In order to make this as smooth and predictable as possible, you need very good control over both parts of the PU.
You can think that the power (or torque if you prefer) at the input to the gearbox, and thereby at the wheels is the sum of the power from the engine (ICE) and MGU-K.
Total power = ICE+MGU-K
In order to be able to modulate this, and in order to give the driver good and predictable "feedback" to whatever he does with his throttle pedal, you need to have control over both the ICE and the MGU-K.
The power output of the engine, can be controlled via things like ignition timing &/or injection timing and amount of injected fuel.
The contribution of the MGU-K, you can control via the CE (Control Electronic), but this applies mainly if the energy comes out of the ES (battery) or, and this is where the waste gate control comes into the picture, you can control how fast the MGU-H spins, which in turn dictates how much power it will produce.
If you run the MGU-H (which works like a generator in this case) directly coupled to the MGU-K (which runs like a electric motor in this case) then, any change to the amount of power the generator produces, has a instant effect on how much power the motor delivers, and in turn how much power is available at the rear wheels.
And therein lies the "trick/secret" apparently. Mercedes is able to control the amount of power the MGU-H generates very precisely via a smart "waste gate" control strategy. This may also involves the actually waste gate as a hardware part, which could be different to waste gates used by the other manufacturers.
The other option, is to use the CE (control electronic) to "direct" the power from the MGU-H to the ES (battery) if it is not needed at the MGU-K, but this will be greatly affected by the "state of charge" of the ES. If the ES is "full" you can't dump any excessive power into the ES, and if you do, it will generate extra losses and heat (cooling requirements) in both the control electronic and the ES (battery) itself. So being able, to control the amount of energy the MGU-H produces and contributes to the overall "power budget" of the PU, via a clever waste gate operation, has it's merits, even if it just means, that "all what you do" is reducing the thermal stress on your control system , and produce less heat "under the skin" of your car.
The waste-gate will just dump the excessive exhaust gas, with all it's heat and energy out of the tail pipe - simple.
Any other strategy would first "extract" the energy (causing heat in the MGU-H) and then trying to "dump" it somewhere within the system, in this case trying to store it into the battery, which in turn means, that it creates additional loses, speak heat, in the control electronics, the cables and perhaps even the ES itself ( if this is the case or not, will depend on the type of ES used, capacitor vs. battery and the chemical process used in the battery). As an extreme example, Renault initially had planed to "dump" any excessive energy/power into a resistor, in case the ES couldn't take the energy at this moment. Now, dumping anywhere between 20-80 kW into a resistor (a element which turns electric energy into heat) produces a "hell of an toaster", and was one of the reasons, their customer teams suffered from massive overheating issues during the first test.
Edited by TC3000, 21 April 2014 - 15:50.