If you’ve read anything about the top road-going superbikes of the last couple of years you’ve probably seen the term IMU bandied about. Standing for Inertial Management Units, they’re the centrepieces of the latest traction control and ABS systems.
These little black boxes that tie together the electronic control systems of the latest generation of bikes look just as mysterious as every other piece of electrical gubbins, but are actually so clever that they achieve something that was considered impossible just a few years ago; they give standard, production road bikes a level of traction control that’s above anything even a top-level GP racer could have dreamt of a decade or so ago.
In the early 2000s, traction control was almost unheard of away from the race track. Yes, rudimentary systems had appeared on a couple of production bikes like the Honda ST1100 back in the Nineties, but they didn’t work well and never caught on.
Given that the average age of bikes on UK roads is 13 years, most riders have yet to experience even the first of the new generation of traction-controlled road bikes, which emerged in 2008 when Ducati introduced the first modern-generation system on the 1098R. But it’s spread so fast that there’s a good chance that if you don’t have it already, your next bike will be equipped with it.
So we picked up the phone to Matthias Mörbe (pictured) – Bosch’s Vice President of Engineering Two-Wheeler and Power Sport, Europe, and Product Manager for Sensors, World – to get an explanation and to see what we can expect next from this fast-moving technology.
“We have a lot of suspicious minds when it comes to electronics and motorcycles,” he said, “Nevertheless most riders are already using electronics without deeper knowledge. Injection systems are so perfectly adjusted that most people don’t really want to get back to the carburettor!
“With the upcoming more advanced and more sophisticated systems we certainly see that there’s a requirement to understand at least to what extent the electronics actually influence the driving behaviour of the motorcycle. One of the key messages we always try to highlight is that our main intention is not to distract the driver and not to be an influence during normal driving conditions. Only when a limit is achieved, or you are close to the physical limits, will those systems be of assistance, to catch up with the situation.
“Take ABS as an example. You don’t brake at each corner using the ABS. You only use the life-saving functionality when the friction changes in corners, or on wet roads when the friction is low. Under normal circumstances the systems are in the background and you don’t really recognise they are there.”
Bosch’s first lean-sensitive traction control system was launched in 2007, and used a gyroscope to sense the bike’s lean angle. That’s vital, as because of their rounded profiles and the differing sizes of a bike’s front and rear tyres, you can’t use wheel speed sensors alone to sense whether the rear is starting to spin. Mörbe explained: “If you have a 45 degree lean angle, for example, the rear wheel, due to its tyre shape, has a smaller diameter. If you compare it to the front wheel speed you’ll already find a theoretical slip value that is at the limit of having traction. So a good traction control at that time could only be made with a lean angle sensor.”
Bosch actually developed a lean angle sensor many years earlier, towards the end of the last millennium, but had to wait for other elements of bike technology to catch up before it could implement traction control.
Mörbe said: “The key element to realise traction control was the engine management and the introduction of the electronic throttle body. Without an electronic throttle body, or at least a double-flap design, you are not able to control the torque in a way that you can achieve a good traction control in corners. The first approach, which was done by just influencing spark advance and to reduce ignition and injection, with Ducati, was pretty rough and was not suitable for public road applications with average rider abilities. With the introduction of an electronic throttle body, all of a sudden there was a chance to get much better control of the torque of the engine and then with this feature the question appeared “what do we do in corners”. As I said before, comparison of wheel speed was not possible to do this.”
That’s where the lean angle sensor came in.
“We actually had our first lean angle sensor device much earlier than 2007,” said Mörbe, “Before 2000 actually, but the industry wasn’t in favour of any significant traction control algorithms, because most of them were still running on carburettors. It was more or less a coincidence that the introduction of much better controlled engine management systems and throttle controls came at the same time as the requirement to have traction control with high powered bikes, in a way that you also get control in corners.”
The key to the lean sensors in those early traction control systems, and to the IMUs that they have developed into today, is MicroElectronic Mechanical Systems, or MEMS. These look just like computer chips, but inside there are actually tiny mechanical devices rather than purely electronic ones.
Mörbe said: “We introduced the micro-machine technology in 1998, and in principle it’s always the same. We have very small units which contain a seismic mass, which moves inside a sensing element. The detection is made by a change in electrical capacitance. There’s a comb structure internally, and the distance between the forks of the comb [as the mass moves], is changed, and with the change in the distance you get a change in capacitance.
“The seismic mass is held in place by springs made of silicone, which is one of the most interesting design features of these micro-machine devices. The springs are etched out of the silicone layer and the seismic mass is hanging virtually free in a vacuum inside the unit. We have special processes that enable us to take away the material underneath the mass. So we are able to create all sorts of designs of springs, of masses, of comb structures. We can precisely design the spring rate. We have also done tests of the durability and silicone springs do not age at all in comparison to metal ones. If they are not destroyed by extreme acceleration, they last forever.”
When we talk about gyroscopes the image of a spinning weight might spring to mind, but the MEMS gyros in IMUs are quite different. Instead, they’re ‘vibrating structure’ gyroscopes based on the idea that a vibrating mass will try to continue to vibrate in the same direction even if the structure holding it is turned.
On a MEMS accelerometer the mass doesn’t need to vibrate. It’s simply a weight mounted on a spring (all microscopically tiny, of course) which can move back and forth to measure acceleration in a single direction.
All these micro-mechanical parts are sensitive enough to measure movements of the mass inside them by as little as the radius of a single atomic nucleus.
The IMU is basically a single piece of electronics that combines both accelerometers and gyros to be able to measure both linear acceleration and changes in orientation. If you’ve got a smart phone, it probably already contains sensors that work in much the same way to measure its movement. By comparing these measurements against one another as well as readings from wheel speed sensors, a modern IMU-equipped bike knows precisely what’s going on at all times. It can tell if a wheel is starting to spin or to lock-up, whether both wheels are on the ground, your lean angle and even the angle that you’re wheelying at, if that’s your thing. And with the ability to influence braking pressure via the ABS and engine torque via the ignition, electronic throttles and injection, the extent of the ability to operate things like stability control, wheelie control, anti-lift systems for the rear wheel or cornering ABS all come down to the programming of the electronic brain that ties everything together.
You’ll see that IMUs are often referred to as being ‘six-axis’ or ‘five-axis’. This refers to the sensors – three accelerometers and either two or three gyros, giving a total of five or six measurements. Although we live in a 3D world, there are actually six movements that can be measured, three linear (i.e. changes in position) and three rotational (i.e. changes in orientation). The linear ones are left-right, up-down and back-forward. There are also the pitching movements as the bike angles forwards and back under acceleration or braking, the side-to-side roll as it leans and the yaw as the bike changes direction. Combined, these are referred to as the six degrees of freedom.
Mörbe explained that there are five sensors inside the latest Bosch IMU: “We are currently in the fifth generation, the MM5.10. We have three acceleration sensors, in the X, Y, and Z axis. The Z axis is vertical, the Y is left and right and the X is forwards and backwards. We also have two gyroscopes. These gyroscopes are orientated in the Z axis and either the Y or the X axis, depending on how the unit is placed on the vehicle. With a special algorithm we are able to work out the missing gyro axis, so by means of computing it’s possible to have six-degree functionality.”
So there’s a huge amount of information coming from those sensors. The next job is to apply that information to other systems so it can be helpful. Obviously two key beneficiaries are the bike’s ABS brakes and its traction control.
“The main elements are the drivetrain and the braking system,” said Mörbe, “On top of that, suspension systems can be influenced by data we receive from the sensors on the bike. That can give better adjusted suspension for the average 90 percent of motorcycle riders. My personal experience is that most of them, if they adjust their suspension at all, only do it once in the time they own the bike. They then ride it like that for the next 15,000km. They are not using the entire performance of that the suspension systems actually provide.
“So this is one of the options we have, to modify the suspension to have comfort, more stability and even up to the point of having shorter braking distances by reducing the dive of the fork and changing the rebound adjustment at the rear during braking.”
The progress that’s been made in just a handful of years is already astounding, and the adoption of these electronic systems is what makes today’s crop of new bikes stand out so much from their forebears. But there’s still more to come from the fast-improving.
Mörbe said: “What we have now, and this is a very good view into the future, is a technology which allows us to staple the micro-machine functionality on top of the amplification device, which is a micro-controller with some specific hardware. With this technology we can reduce the size of the package, to get smaller devices on the circuit board and to place more units on one circuit board. In future we will see generations with more features and more performance than the one that is currently in production.
“Technology wise, we are working on reduction in dimensions but in principle the micro-machine technology remains the same. In terms of performance, it’s always a question of what is the ultimate reference? The reference so far in the motorcycle industry is a fibre-optic sensor that works using light. It’s a fibre-optic gyro that’s used for satellites and rockets, coming from the military side. We use these as a reference, and the latest generation of sensor is very close to the reference already. The deviations we had five or six years ago are almost gone. I can say with a bit of confidence that we are close to the reference now. The sensor itself will not be the limiting factor anymore.”
If the sensors are reaching the point where it’s hard to improve them, the bottleneck moves elsewhere in the system.
“Interpretation of the signals is then the most important thing,” said Mörbe “Of course, you have some limitations. On motorcycles, these limitations come specifically from the nature of the motorcycles. We have very high vibrations, the engines are mounted sometimes directly to the frame, and you can get a high disturbance into the signal just due to the vibrations on the vehicle itself.
“We have to live with that, so our approach is to use some special placements on the bike, or even a damping element to get rid of these disturbances. If you keep these disturbances away from the foreground, the sensing accuracy and long term stability meets almost all future requirements of the systems we will see.
“These systems are the ones that take the dynamics of the motorcycle to a much higher degree than today, to sort out specific dynamic situations and even going up to the point of detecting accidents before they actually happen. From our point of view, the aim of the future is to have no accidents at all, so we can save the lives of motorcycle riders.”
That’s a lofty goal, but even a few years ago – before MEMS technology and the advent of electronic throttles – many experts reckoned that viable traction control for production bikes was a virtual impossibility.
Just recently we’ve seen both Honda and Yamaha reveal concepts that show computers not only controlling the throttle and braking but also able to steer bikes. Honda’s self-balancing ‘Riding Assist’ concept was shown in January, able to balance itself by automatically moving the steering. And Yamaha’s wilder-looking Motobot appeared in late 2015, a robot that hopes eventually to be able to rival human riders in terms of ability and speed.
Many new cars have steering-assist systems to help prevent accidents, too, so does Bosch think that this is the next step for bikes? Mörbe isn’t convinced.
“Influencing the steering is a very interesting point,” he said, “There have been studies into modifying the steering system. But due to the fact that the rider is an entire part of the steering dynamics, so far there is no solution visible which has a chance to influence steering. It’s completely different to cars, where you have the opportunity to influence the steering system. Maybe I’m wrong, but I strongly believe that in the near future we won’t see any approaches to go into the steering side. It’s theoretically possible, but the technical solution, in my personal opinion, is not feasible for the time being.
“I saw the Honda concept. It was a very interesting approach and it shows what technology can do, but at the end of the day what is the user benefit? If my motorcycle is following me when I’m walking on the street? I don’t think that’s the main purpose for having a motorcycle.
“I’ve seen the mechanical effort needed to achieve what they have done, and it’s horrendous. But it’s very interesting. Compared to other solutions, it actually works. You might also have seen the Yamaha approach, with the self-riding motorcycle (pictured). That shows the extent to which technology is currently able to go, but…
“There’s a study available which says that 45 percent of all accidents in corners could have been avoided if the rider had applied more lean angle. So if you take this into consideration you have to discuss the ability to overrule the rider’s intent. This is a very interesting question – to what degree is such overriding acceptable, and also safe enough to be done. I guess we currently have no strategy available which gives us the opportunity to go to this extent of influencing the riding combination of machine and human.”
Bosch dominates the market for motorcycle electronics, particularly when it comes to ABS and traction control, and the fact its systems are used by so many manufacturers mean that in future we’ll be seeing this kit on a majority of bikes. Since January 1 this year, ABS has been mandatory on new bikes over 125cc. Those that use the Bosch MSC (Motorcycle Stability Control), which is cornering ABS, effectively incorporate all the sensors needed for the latest in traction control. So while at the moment there’s no regulation to make traction control mandatory, it might well become ubiquitous anyway.
Mörbe said: “With our MSC motorcycles, we virtually have this functionality on board. So the target is to implement MSC to all bikes, not just ABS, and that means you get traction control, let’s say, ‘for free’.
“Of course, with very low power there’s always a question as to how big the risk is that you will overshoot the grip level of the rear tyre. I’d say that above about 35hp it’s good to have traction control.”
The other element that’s likely to spread fast is semi-active suspension tied in to the same sensors.
“This is on some bikes already,” said Mörbe, “We will see a higher population in the next two years, and Bosch is working on electronics for this purpose. Our sensors are supporting these systems with signals to make a really functional algorithm.”
What’s perhaps the real genius of the latest layer of electronic control technology is that for ninety nine percent of the time you don’t even know about it. It’s such a seamlessly-integrated setup that there’s no excuse for traditionalists to moan about dilution of the riding experience. But that one time you do need it, you’ll be glad it’s there.
Share on social media:
