Electronic Engine Control & Throttle-by-Wire

New BMW motorcycles have it, as do Harley-Davidson Touring bikes, so do many models of cars and even jet aircraft. What is it? Throttle-, drive-, or fly-by-wire—electronic throttle control (H-D’s official wording) and engine management systems, of course.

To take on the entire concept of how electronic throttle control is used in every type of transportation technology is to exceed the scope of what can be covered here, but there is much that can be discussed about the positives and negatives of using such a system in motorcycles, and to examine the reasons why using electronic throttle control systems in motorcycles should be examined on its own merits as compared to them being used in almost any other mode of transportation.

As most know, throttle-by-wire replaces throttle cables with an electrically wired or electronic position sensor at the throttle handgrip that transmits a signal to a motor controlling the opening and closing of the throttle plate(s) (butterfly). Some newer and “high-end” motorcycles, such as the new touring BMW 1600GT and GTL, also integrate throttle control with traction control, anti-lock brakes, and many other facets of engine and ride control management.

So to establish why the use of throttle-by-wire (TBW) and ride control systems might be viewed differently when these systems are used on motorcycles, let’s start with the very basic differences between riding a motorcycle and driving an automobile:

• You do not have to balance a car.
• Cars rely very little on the gyroscopic effect of rotating wheels for stability.
• Cars do not lean into turns.
• There is a much greater level of physical protection while driving a car than when riding a motorcycle.

First, it should be established that some electronically controlled systems used in motorcycles are considered worthwhile by most riders and motorcycle authorities. A self-contained ABS system; a system that is limited to preventing wheel lockup in straight-line emergency stopping situations, is a benefit to the vast majority of motorcycle riders. Likewise, fuel injection systems on motorcycles are a great benefit: the fuel is dynamically adjusted for altitude, air pressure, ambient and engine temperature, and results in smoother throttle response, better drivability, and greater fuel efficiency. It also requires the use of a fuel gauge, or at a minimum a low-fuel light, giving the rider an objective indication of when they are low on fuel.

Where potential problems begin is in using a system where dynamic control of the motorcycle (or any vehicle for that matter) can be acted upon by an intermediate controlling system. Some “anomalies” in TBW systems, often in conjunctioin with electronic traction control, have been noted by motorcycle publications. An internet search turns up some very interesting, and potentially alarming, characteristics with these systems. However, some results and the consequesnces are designed into the electronics, depending on the application. For example, here’s the first paragraph of a review of the 2011 BMW S1000RR written by John Acton in February 2010: “Coming out of the long right-hand turn nine at Palm Beach International Raceway, BMW’s new S1000RR did something unexpected. Despite having the throttle pinned wide-open, the bike didn’t want to accelerate. It wasn’t until the lean angle came within 45 degrees from vertical that a blast of horsepower from the Bavarian bullet lifted the front wheel about a foot off the asphalt and hurled the bike down the 0.6-mile straightaway.”

Even a cursory read of the first paragraph of this review shows some obvious “red flags.” First, Mr. Acton says that the motorcycle “did something unexpected;” that the bike “didn’t want to accelerate,” and third, “it wasn’t until the lean angle came within 45 degrees…that a blast of horsepower…lifted the front wheel about a foot off the asphalt.” The entire opening paragraph outlines a series of occurrences where the rider was seemingly not in control of the bike! Not just one hiccup, but a list of events in a high-speed situation that were not in rider control, and it actually surprised him, as Mr. Acton describes it. What he doesn’t say though is the bike was set-up for the racetrack and in the “Slick” mode setting. With a less experienced rider it’s a scary and potentially dangerous scenario.

How often does your bike “do something unexpected?” Except in a malfunction, when was the last time you twisted the throttle and “the bike didn’t want to accelerate,” or how about the engine producing a “blast of horsepower” that unexpectedly lifted your front wheel off the ground?

Of course, it is difficult to know whether a typical street rider would be in a situation on a public road where they might be generating the combination of speed, lean angle, and throttle position that John Acton was applying on the race track, but let’s transfer the experiences he had to a possible real-world scenario: An experienced rider (“he” for simplicity) is having a great day on a new TBW-equipped bike on a twisting mountain road. He is “into the groove,” countersteering and getting some serious lean angles going and the bike is responding in stellar fashion. The rider gets a little overzealous and comes into a left-hand curve too hot, but as he is an experienced rider, he has the presence of mind to lean the bike way over and manages to make the turn. But as he starts to countersteer and apply throttle to right the bike when coming out of the turn, the bike doesn’t obey…and faced with an emergency, the rider immediately applies more counter steer to get the bike upright in order to brake. All of a sudden he gets a blast of horsepower. At that point, if he is not able to get the bike back under control very quickly, the rider is likely to crash. A far-fetched scenario? Not from what was described in Mr. Acton’s review.

Without intending to single out BMW motorcycles, the problem is obvious: an engine control system that can apparently usurp operator intent, and, as it seems, possibly initiate a series of events that could cause unexpected alteration of a rider’s control of the machine. This could occur at a time when the rider must fully rely on the physics of how the machine will behave and the expectation of how it will respond at a very critical control point. While those who design these systems would be reticent to admit that this is a loss-of-control situation, it is hard to believe that the hypothetical of the rider on the mountain road described previously could never happen. The expression “that could never happen” is often used to assure the public, and everybody knows how it usually turns out. In fact, the extra cable on push-pull throttle-cable systems was a safety measure employed to be able to close the butterfly in case of cable or other malfunction in the carb.

Ask the people who have experienced unintended acceleration in their cars what they think when a corporate spokesman says that it can’t happen. And in case you think these are isolated incidents, according to a Consumer Reports article from December 2009, 52 unintended acceleration complaints were reported to the National Highway Transportation Safety Administration (NHTSA) about Toyota products (Toyota and Infinity) and 36 complaints were lodged about Ford products produced in the 2007-08 model year. While these occurrences took place in automobiles, a quote about drive-by-wire used in motorcycles from the Bosch website (bosch-engineering.de/en/boschengineeringgmbh/newsspecials/drive_by_wire.aspx) is of particular interest: “Thanks to the use of fully-electronic engine control systems, motorcyclists now have complete control over their machines, too. To do this, existing automotive systems were adapted to motorbikes within the framework of our drive-by-wire motorcycle study. The first road-capable prototype is an Aprilia RSV 1000 R. In selecting the components we rely on Bosch components from the automotive sector, which are thus now available for the motorcycle market. The development of the electronically controlled throttle valve for motorbikes is yet another example of customer-specific, individual system adaptations of Bosch components for which Bosch Engineering GmbH is internationally known.”

So basically, what Bosch is saying here is that motorcycle “fully electronic control systems” are adapted from automotive systems. It is logical then to consider that any potential hardware failures and software programming errors that by some accounts have already occurred in automotive systems could also be potential problems in motorcycle systems.

Let’s examine another point that’s very important: the anomalies in the S1000RR engine management system that Mr. Acton described were not malfunctions. The loss of throttle control, the inability to accelerate when the bike was leaned, and the (unexpected) surge of power when it was partially righted is how the electronic engine and traction control management system for this bike are designed and programmed to work under those conditions. Oddly, in the review of the S1000RR, Mr. Acton did not seem alarmed by situation where control of the bike was apparently out of his hands, and he generally gave the bike a favorable review.

So here we have an example of an anomaly in the electronic engine control system when the bike is functioning properly. How about what happens when things do malfunction?

In some recent discussions with David Hough (author of the Proficient Motorcycling book series) on the issue of throttle control and electronic engine management, he relayed to me a situation where a previously owned Can-Am Spyder (with electronic throttle) had a re-occurring drivability problem: “I had some…electronic issues, one being that the engine would suddenly go into “limp-home” mode after about four hours on the freeway. I found that shutting off the main switch for a period of time would…allow the system to reboot, and then it would start and run normally. The error message on the dash showed “Check DPS Computer.’” DPS is Dynamic Power Steering—sort of a “mother” computer, and if a fault in any of the other systems occurred, the DPS computer would signal the Engine Management Computer to initiate a loss of power…I [later] discovered that the leaf spring on the brake pedal was not giving the appropriate “brake off” signal to the DPS computer. I did a little adjusting with needle-nose pliers, and solved the limp-home problem.”

As many know, limp-home mode is where an engine management system will limit speed and acceleration in order to prevent engine damage when a problem occurs. However, in this case, the limp-home mode activated on a freeway when the problem apparently had nothing to do with an engine malfunction. Here is a case where an electronic override system caused a motorcycle-based vehicle to suddenly slow down on a freeway while other traffic around the vehicle would normally be maintaining highway speeds. While this might make sense if the limp-home mode had been activated due to an engine problem, should it have been caused by a simple mechanical problem with a brake signal switch? Most would probably argue no.

David goes on to say: “I’m not so concerned about complex systems when they are brand new. I’m more concerned about maintainability. What happens to the high-zoot electronic system five years down the road, or longer?…The owner who has all of his maintenance and repair[s] done at the dealer’s shop will buy a brand that has a nearby dealer, and be clever enough to trade it in as the warrantee expires. But for owners such as myself, who…do our own servicing and repair, there is a practical limit to how complex a machine can be.”

As David points out, what happens to drivability of the motorcycle when a totally integrated throttle/traction control/braking system experiences failures or components wear out? The increasingly higher levels of technology may start to yield diminishing returns when the engineering that goes into them gets so complex that a machine can no longer be reasonably maintained by an owner, and very high expense is necessary for maintenance and repair. Have you had your motorcycle in the shop for repairs lately? Even the simplest procedures performed in a motorcycle-repair shop often yield an expensive bill. Try to imagine the bill when electronic engine management components begin to fail and problems have to be diagnosed and repaired at a dealership. Having to trade-in a bike before the warranty period expires is an option that most in this day and age typically cannot afford to or want to make.

Perhaps a “simpler” TBW system that is not part of an overall engine management system may not be significantly more complicated in principal than throttle cables, but there are some notable differences: finding the source of a cable problem will usually only require visual inspection, maybe getting the bike back to your garage and removing the fuel tank or body panels to locate a cable restriction, or to lubricate a cable or to replace a broken one. Repairing an electronically controlled throttle system would typically require troubleshooting knowledge that exceeds that of a typical DIY mechanic, and the use of diagnostic equipment that most will not own or even know how to use.

So how much more will the costs be to repair the higher level of complexity of systems that incorporate motorcycle TBW, traction control, and braking into an engine management system? How much of an effect on the ability to continue to operate the bike and even the safety of the rider if a failure of even one of the systems occur? As these systems are still relatively new, the jury will be out for some time.

Of course, it is understood that a tremendous amount of R&D goes into getting these systems to be useable, functional, reliable, and safe, and that in the vast majority of riding circumstances, riders will find the increased options for choice of ride type, handling, and braking capability will take motorcycle riding to new levels of comfort and convenience. While in the majority of situations the computer will choose the best combination of handling characteristics in a given riding situation, some of the reviews and reports indicate that this may not always be the case. David Hough’s experience with his Spyder going into limp-home mode due to a simple mechanical problem is one example; John Acton’s description of the behavior of the BMW is another.

There are also discussions posted on several Harley-Davidson owner group sites concerning idle variation problems on some 2008 models using TBW, most notably v-twinforum.com and hdforums.com, with the latter having a link to a service bulletin released by Harley-Davidson referring to a TBW problem. Several posts say that the throttle control problems occurred while the bikes were being ridden, rather than just at idle. Further, in the cases of claimed unintended acceleration in automobiles, throttle and engine management computers may have no direct “cause and affect” as to how they may operate should a control system get an errant control input. That it uses an electronic signal rather than cables, a system malfunction could conceivably result in a variety of unexpected control problems, simply because a triggering electrical short, open circuit, or component failure could cause an electronic hardware problem, a software error, or both. A bike may accelerate, go to idle, shut off, go into limp-home mode—any of a number of unexpected behaviors based on a wrong signal in an electronic engine management system.

Conclusion

In the engineering career field, there is a concept known as “elegance.” It refers to the idea that the more you strive to keep electronic systems and their software programming simple, the less likely that bugs or unintended outcomes will result. The idea of keeping motorcycle control systems simple is worth considering for this reason. Consider also that following the “KISS” principle here may also be a good idea due to the lower level of physical protection for the rider of a motorcycle, as opposed to a car. There is a logical connection between these two thoughts: if a throttle system were to malfunction causing unintended de- or acceleration, a resulting accident would certainly have a greater potential for serious physical injury on a motorcycle than in a car.

Technology with a proven track record of decades in use are logical additions to motorcycles, and while electronic fuel injection and ABS brakes are more complex systems (respectively) than carburetors and simpler hydraulic brakes, you get a lot for the trade off for the relatively small increase in complexity. ABS brake systems are generally passive systems, where their effect on motorcycle operation is secondary to the rider’s input. Not so the case in more complex engine management systems, and some consideration should be given to fully “working the bugs out” before applying these systems to a motorcycle.

Some thoughts to ponder: will there be high-mileage TBW motorcycles still around and usable in 20 years? 30 or 40? Will the cost of repair exceed the value, as is the case with many current buy it, drive it, junk it philosophies with automobiles? Planned obsolescence as it’s called; it’s seemingly designed into everything these days.

Please share your thoughts on this with us. Have you had any odd experiences or lack of control from a TBW system or expensive repairs? We’ll print some of the responses and opinions in an upcoming issue of Baggers. B