From the carburettor to the age of drive by wire: a revolution from the perspective of the motorbike

During a span of time of a little less than twenty years, motorbike technology has moved from the Euro 1 type approval to the Euro 4 one. A real revolution, which forced manufacturers to invest in research and to introduce strong technological innovations. Euro 5 engines are now under development, and for two-wheeled vehicles this is going to be another historical step for their evolution. We talk about these topics, without leaving out any juicy detail, with engineer Francesco Simone, who is responsible for vehicle development at Honda Europe

 

Euro 1, Euro 2, Euro 3, Euro 4. In the 19 years since the debut of the first Euro 1 emission standard, bikes have had to adapt to progressively more stringent emission limits. An extremely hard change of pace, with test methods changing as well and forcing the houses to invest in research, to achieve the goal of homologation while maintaining optimal performances and pleasant driving experience.
An unprecedented technological revolution in its own, with its details explained by Francesco Simone, Engineer and Technical Quality Manager of Honda Europe. We asked him to tell us how motorcycles and scooters have changed over the years according to regulatory developments. Predictably, it was a long talk about electronics with, at the same time, unexpected implications. Such as investments on the engines, since the best performance and durability are also defined by a refinement of the mechanics and the study of raw materials. And now, in preparation for the future Euro 5 stage, our bikes are getting ready to change again.

 

Let’s start from the beginning, by asking Simone how the motorcycle approval cycles have evolved over the years.       
“Up to the Euro 2 stage, the approval cycle dictated a first heating phase of the engine and the exhaust system, in particular of the catalyst, for 400 seconds. The gases emitted at that stage were not taken into consideration. For the manufacturers it was a big advantage, because it allowed to enrich the air-fuel ratio, improving the operation of an engine not yet at operating temperatures; this also caused, though, strong emissions of carbon monoxide (CO) and of many unburnt hydrocarbons (HC).
The new approval cycles removed the warm-up time: starting from Euro 3, the exhaust gas analysis cycle begins from the exact moment the engine is turned on. Unsurprisingly, the first Euro 3 bikes, released in 2006, had a very poor fuelling, especially with a cold start. As a matter of fact, all those problems that were constantly occurring up to Euro 2, and that were simply bypassed at low temperatures by enriching the air-fuel ratio.
Those problems were subsequently solved by tuning the ECU accordingly.
Apart from the novelty represented by the cycle starting from a cold engine, however, the Euro 3 test was fairly similar to its predecessors: stationary profiles, made with static throttle openings and a constant regime, with stepping profiles for different speeds. At first, it was 15 km/h, then it was 30, then at last 50 km/h. The average speed of the homologation cycle, for bikes above 150 cc, was just 29 km/h, maintained for the 12.9 km covered to complete the test. The 120 km/h benchmark was reached only for a short distance.”

 

Honda SH scooters were manufactured in the Italian plant based in Atessa

When did things change?
“On the 1st of July in 2007. It was at that time that the 2006/72/EC EU directive gave manufacturers the possibility of homologating their vehicles according to a different emission test-cycle, the ECE TRANS 180, also known as WMTC (World Motorcycle Test Cycle). We’re talking about a harmonised test cycle for two-wheeled vehicles, much more detailed than the previous one. Motorcycles homologated under this protocol are divided into 3 classes, depending on displacement and maximum speed. We also have subclasses, related to the maximum speed of the vehicle.           
Most importantly, with the WMTC it is possible to simulate a much more realistic driving path compared to the previous ECE R47. In fact, there’s no longer a constant speed interrupted by accelerations and decelerations; rather, we have a series of accelerations and decelerations, in the relative absence of a constant speed. Accelerations are also much stronger, with pronounced throttle openings.
All of this translated into the need to optimise the operating map of the engine over a higher range, functionally to the missions. And clearly, pollutants emitted are necessarily higher. So much so that the limit values have been slightly increased. With the old protocol the CO was 2, the HC 0.3 and the NOx 0.15; now these values have been brought to 2.62, 0.36 and 0.22, respectively.
Honda has adopted this cycle since 2010. The first bike approved with the WMTC was the CBF1000F, the one with only one muffler on the right-hand side. Our company had self-imposed the adoption of this cycle, at the price of a more conservative engine mapping. A price we’re more than willing to pay here at Honda to contain emissions”.    

Does this mean that the novelty lies in many variations of pace and speed?
“Not only that. With the previous ECE R47, the engine was tested in a range between 10 and 20% of its operational range, depending on the type of vehicle and other parameters. With the WMTC, it goes from 35 to 60%. Therefore, the new protocol checks the operation of the vehicle on a much wider range of use”.

 

To comply with stringent emission requirements Honda choose to increase the size of catalytic converters

Has the adaptation to the new cycle proved to be a challenge for manufacturers?      
“Yes, absolutely: development costs have soared. Making a vehicle that respects the anti-pollution regulations while also offering a pleasurable driving experience requires a lot of efforts and expenses in research and development. 
It costs as far as the tests are concerned, but first of all the high cost lies in the required computing power. The fueling problem in the first Euro 3 was solved by investing in research and development, improving the control of the mass of fuel introduced with increasingly powerful ECUs and with additional systems for the elimination of pollutants.       
Here in Honda, we manage to respect these requirements without any problem at all. We produce vehicles that emit even less than half of what is allowed by the homologation standards. This can happen because our company – by policy – prefers to invest in catalysing surfaces and vehicle control.          
The volume of the catalytic converter has therefore increased, the fuel injection has been optimised, but this has also increased the cost of the vehicle. And one of the biggest costs, even if it is hard to believe, is the catalytic converter itself, because it contains noble metals like rhodium and palladium”.

 

Has something changed in the design of the engines?      
“Of course. When designing a new powertrain, significant investments must be made to guarantee the possibility of easily adapting it to future type of approval regulations. The pollutant emissions are not generated and controlled only with injection and catalysis: a well-engineered engine is also essential to keep pollutant emissions in check.    
Then we study the pistons, compression piston rings, oil control piston rings, and cylinder liners finish. It is possible to make a difference by developing the right profile for a piston ring and positioning it in the best way. Our company prefers to prioritise internal technology, to minimise frictions. A path we’re following by resorting to the best materials, processes, and treatments, rather than a cylinder liner coating. Because coating can just fall off, while a piece made with specific material will certainly have higher reliability and durability. It is clearly a philosophical choice that involves higher costs.
But the result is that today we still have engines currently on sale that started as Euro 2 and now are Euro 4. As it happens with the VFR 800 V-Tec, a power unit born in 2001. We had to make small internal improvements, but basically, the engine is just the same as the one introduced back in the days”.

Careful engineering of internal components is still fundamental to reduce friction and guarantee performances over a long time (in the photo crank, connecting rods and pistons of the Honda Africa Twin)

Lower emissions and higher motorcycle costs aside, have the new regulations brought anything else?
“The biggest impact was certainly on the great investment in the development of Electronic Control Units. Up to Euro 2 engines, you could still find some carburettors. From then on, the evolution of electronic control systems has been enormous. Now almost everyone adopted the ride-by-wire, with systems that also improve the overall efficiency of the bike. Both from a performance and an environmental point of view “.   

Why is Ride-by-Wire so important?          
“Because it makes combustion extremely efficient under any driving condition. The most common example is the one of the user who drives with a high gear at low rpm and wants to accelerate as hard as possible. In this situation, it is possible to make the mistake to flat out, which, with the traditional mechanical systems of the throttle body, can generate bad combustion, and a less effective acceleration.        
Being too hard on the gas can, in fact, cause incorrect filling and poor performance. In this situation, the best performance is achieved by gradually opening the accelerator.        
With modern electronics and ride-by-wire, the system reads the driver’s torque requirement, and adjusts the throttle opening and all engine parameters to ensure the best possible acceleration, while also safeguarding the best environmental performance.       
Additionally, all the control and safety systems are connected to the current control units. Since there were investments in fuel injection, today that branch of electronics can be exploited to perform other tasks, such as security checks. If you think about it, the very same thing happened with cars, just a few years in advance”.

 

The evaporative test monitored via multiple sensors in a controlled environment

Your judgment on the Euro 4 with WMTC protocol seems to be positive, in the end.
“It is indeed. And it’s interesting that the new Euro 4 legislation also contemplates the control of emissions of pollutants not derived from combustion processes.   
There is, for example, the evaporative test, which measures the emission of unburnt hydrocarbons from the tank and which has forced all manufacturers to install the Canister, an instrument that prevents the release of the vapours from the tank into the atmosphere. Furthermore, the emission test of the crankcase, to control the emission of vapours that occur from inside the engines.
It is also positive that was included the durability test for the emission level of the engine at 30,000 km. And the fact that with the new cycles we can test 60% of the usable range of an engine. With just a single flaw: while the range above will probably be the most frequently used for a touring bike, it will not fit for supersport models “.  

That means? 

“That the range of use not controlled during the homologation cycle, the remaining 40%, is probably the one in which supersport bikes are most frequently used. The high regimes, in any gear.”

 

How will tomorrow’s engines look like?
“We are studying the application of direct injection, a technology that could represent a big leap forward. With this, it should be possible to create more or less stratified areas of the fuel-air mix in the combustion chamber; areas where combustion is lean and areas where it is stoichiometric. It would help to reduce consumption, because if you have a 1000 cc engine and with each cycle you let a litre of air in, today for uniform combustion we need to introduce a certain amount of fuel – the ideal stoichiometric ratio is 14.7: 1. With direct injection there is the possibility – if you do not need high performances – to introduce a reduced amount of petrol to get only the performance you want, since you can focus the combustion point and create the stoichiometric ratio only at that point. But we have a problem still to solve, that of nitrogen oxides, or NOx. It is the pollutant we are talking about the most nowadays, and it is produced when there are high temperatures and large amounts of air in the engine. The petrol engine, paradoxically, produces a lot of NOx when it has to comply with the emission standards because we tend to make it work lean”.

 

 

Long-stroke engines have an advantage in homologation tests. Here the Africa Twin one

How can we solve this situation?
“Presently, we have fewer problems with bikes than with other vehicles, and we manage to keep the correct stoichiometric ratio, without having to make the fuel-air mix too lean. This because, in order to have good performance especially in acceleration, it is necessary to enrich the mix even beyond the stoichiometric ratio. Which in turn, increases the speed of the flame front. Moreover: if I put even more fuel I can not burn it all because there is not enough air, but the one that comes out without burning cools the exhaust valves, preserving them from damage. However, this increases CO and HC.          
The result is that these pollutants, CO, HC, and NOx, eventually come out in the exhaust gases, and are reduced by the catalytic converter, which decomposes them. And the chemical reactions in the exhaust produces CO2, which is not a poison, yet is a greenhouse gas”.     

An unsolvable problem, it seems.
“Maybe it is. If you want a high-performance engine, you need to enrich the air-fuel mixture to make it work, with the result of producing pollutants that the catalytic converter then turns into CO2. Otherwise, you need to stick with reduced performances.      
It also depends on the design. For the more sporty engines at low rpm – just the area where the homologation test is done – the performance will not be optimal. Because they are designed to work best at the highest regimes. That’s why our CBR1000RR 2017 nominally emits 132 g/km of CO2, while the Africa Twin is already at 109. Both are in the 1000cc range, but the latter is designed to operate at lower revs. Then there is the NC 750, which can even reach 81 g/km. That twin-cylinder is the engine that comes closest to that of a car because it is a long-stroke, it runs slowly. And it works well at the regimes of the homologation cycle, too”.   

Is this the reason why some bikes emit CO2 values similar to those of many cars?     
“It’s not just that. The most severe approval cycle that we adopted in 2010, the WMTC, is now debuting for cars, with the acronym of WLTP. Therefore, up to now, the CO2 values emitted were not even comparable. Now it is expected that, with the new approval cycle, car manufacturers will have to report values 20-25% higher than before”.

 

What will happen with the Euro 5 engines?          
“Pollutant emissions will drop even more, and HC measurement will include control of non-methane emissions, which are a fraction of total HCs. However, the real news will be the OBD2, the second phase of the On-Board Diagnostic. That is to say, the electronic controls of the operating parameters of the engine and its anti-pollutant systems. In practice, the bike will have to “realize” by itself if the emissions worsened for some reason, or if some component does not work properly; if that happens, it will have to make the driver aware with a special warning light and reduce the performance, allowing the user to reach a service centre ASAP.
To implement these features, there will be the need to introduce more sensors, and of better quality. And more powerful control units in general. Cars do already have them”.

Here Honda official video of its Atessa (Italy) plant.

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