Cruise Control is "herky jerky"

[PBee]

I have a 09 RT with just shy of 5000 miles on it and my question is about the cruise control. When going down hill, such as the downhill side of a mountain pass, shouldn’t the operation of the cruise control be smooth?

 

I was on a six-day trip the other week and noticed each time I was descending a mountain pass, the cruise control would not maintain speed without short, and quick bursts of acceleration and deceleration. (Grief, I felt I was riding something I had picked up from the seedy part of town.) No matter if I were in 5th gear or 6th gear the action was the same. It became so irritating I disengaged the cruise control while going down each mountain pass I had crossed.

 

After getting back from my trip I went to the Seattle dealer to talk with the service manager about this situation. He told me this was normal, "all bikes with cruise control and did this, especially third-party cruise controls". When asked why he couldn't give me an explanation.

 

Am I wrong to feel a minor software adjustment would eliminate the problem, or is this something I’ll simply have to learn to live with?

 

[tchap]

I'd bet your closing sentence pretty well sums it up. I have a 2007 RT that does the exact same thing. Another annoying characteristic, if I roll on some throttle and roll back off while the cruise is set the system wants to drop back about 5 mph lower than the set speed then pick back up. I hate that!

[Albert]

My reply to the dealer would be "bunk". A cruise control is not some exotic accessory. Practially every vehicle on the road from Hundai's to Mercedes have them and they work without issue. I have just over 30k miles on my 06 RT and the cruise works flawlessly and always has. I routinely check the gps speed against the cruise when navigating mountanous terrain and it works great. Sorry I can't comment on the possible causes but there's obviously an adjustment that needs to be made.

[Joe Frickin' Friday]

The cruise control opens/closes the throttle around some "average" point.

 

On the flat or going uphill, the range of throttle movement is comfortably away from the idle/fully-closed throttle position.

 

But when going down particularly steep hills (e.g. your mountain passes) , my guess is that the "average" throttle position is very close to fully-closed, and that when the cruise control is closing the throttle down to somewhere below that "averge" position, it actually is closing the throttle all the way, and of course then taking the engine off idle to apply power. So whereas flat/uphill cruise operation has the driveline oscillating between "less power" and "more power," downhill cruise operating oscillates between "some power" and engine braking."

 

I think the problem may be exacerbated because there isn't much in the way of driveline elasticity on a motorcycle to help absorb the power/idle transitions. Contrast this with a manual-transmission car, in which there typically is some kind of spring/torque mechanism in the clutch plate. There is a torsional shock absorber on the RT's gearbox input shaft (or at least there is on oilheads, can't say for certain on hexheads), but that's designed more to absorb the pulsations of individual engine combustion cycles, not massive driveline transients. This means that every power/idle transition is felt much more harshly by the rider than would be felt by a car driver.

 

I would think that a software tweak to further limit the rate-of-change of throttle position might help to reduce the problem during steep downhills, but then the cruise will respond sluggishly to grade changes during flat/uphill operation.

[Firefight911]

Does the cruise not interface through the Boudin box? Cabling that is out of adjustment, ala too loose, can cause a hunting effect as you describe as the system takes up the slack of the cables.

 

Your fix may be a proper adjustment of the cables that lead into and out of the Boudin box.

 

This is not something you just jump in and tighten all the cables to do. It needs to be systematic and careful and, of course, needs to be followed be a good TB sync afterward.

[Boffin]

No matter if I were in 5th gear or 6th gear the action was the same.

 

Why 5th or 6th to descend a mountain pass? I would be in 3rd or 4th, but that is based on European passes.

 

Andy

[smiller]

If operation is actually annoying then it sounds to me like something is wrong. There may be a few mph lag when load varies dramatically (as in transitioning from a steep downhill to uphill or vice-versa) but even this should be smooth. Even an Audiovox aftermarket system works smoothly (about the same as automobile cruise controls) on my 1100RT, and the BMW factory cruise on my K1200GT is uncannily accurate and holds speed dead-on no matter what. In the latter example I don't know how they do it as there's virtually no lag at all even during large load transitions. Maybe has something to do with the high horsepower-to-weight ratio, not sure, but it's the best cruise control I've ever experienced.

 

The R-bikes may be different but again, if operation seems incorrect then it probably is. As to TADT, I suppose I'd get a bunch of other opinions from other hexhead R-bike owners and see if they differ or agree with your experience.

[motoguy128]

I think Mitch described it well. This is a comon problem with process control valves/devices when there is a mechanical linkage involved. If you're jumping between 0% and 1%, thre is a deadband invovled. So the controller might think it's at 5%, when it's actually only at 1%. It basically gets somewhat lost.

 

 

Thsi is where having mecahnical throttle cables is a issue. If it was drive by wire, you wouldn't notice any of these issues.

 

 

The same behavior is displays going downhill, can also be found at lower speeds. Try turning on the cruise control at 30mph in 2nd gear. If will bounce on-off from 0% to 1% or some small throttle position.

 

What I'm saying is there is a deadband in the throttle control and there is inherently some deadband in the speed sensor as well. You can reduce the problem by reducing the gain value in the loop control, but then it might behave more erratically under flat road conditons at freeway speeds.

 

 

I don't think it's that annoying...but that probably because I understand what it's doing and it's limitations.

[smiller]

No doubt that for all of the reasons mentioned there's some hysteresis in the system, but the question is should a cruise control exhibit the effects described in the OP in a severe enough manner as to be problematical. My view would be that if it does then either it is very poorly designed or something is wrong, based on the fact that in most cruise control implementations these effects aren't that noticeable in operation. It's true that they often can be detected if specially looked for, but that doesn't seem to be what the OP is describing. In his case cruise control throttle corrections seem to be so abrupt as to make using the system irritating/undesirable, and that doesn't seem right.

[Kerry in Mpls]

(lots of good stuff)

Completely agree.

[RodB]

There is a torsional shock absorber on the RT's gearbox input shaft (or at least there is on oilheads, can't say for certain on hexheads)

 

Just to let you know "for certain", yes there is.

[Joe Frickin' Friday]

There is a torsional shock absorber on the RT's gearbox input shaft (or at least there is on oilheads, can't say for certain on hexheads)

 

Just to let you know "for certain", yes there is.

 

Figured there had to be, but hadn't seen it (yet) with my own eyes, and don't (yet) have the manual. Thanks for the info.

[krussell]

He told me this was normal, "all bikes with cruise control and did this, especially third-party cruise controls".

 

There are motorcycle cruise controls that are much smoother and less surprising than the RT implementation.

 

When I went from my 2008 HD Ultra Glide to the 2008 RT I was really disappointed in the cruise control performance on the RT. The HD uses throttle by wire, so the cruise is pure software, no linkage. The result is much smoother, and not as surprising. I on more than one occasion had the RT chop the throttle abruptly while in a sweeper when on cruise, I stopped using it except for straight lines and relatively straight terrain.

 

I'm really surprised that a company like BMW that likes whizzy stuff doesn't use throttle by wire.

[RodB]

My cruise is very smooth, no "herky jerky". According to my Zumo, it stays at exactly the same speed (approximately 95% of the time).

The other 5% which is on steeper hills; it will vary by no more than 2 Kph. (approximately 1.2 Mph)

 

[Eric the Blue]

I'd bet your closing sentence pretty well sums it up. I have a 2007 RT that does the exact same thing. Another annoying characteristic, if I roll on some throttle and roll back off while the cruise is set the system wants to drop back about 5 mph lower than the set speed then pick back up. I hate that!

 

You're not alone. My '09 RT does precisely the same things. Bugs the crap out of me, but after 15K miles I've just accepted it as a quirk of the bike. By the time I trailer the bike an hour to the dealer, go home, them go back again a couple days later, it's just not worth the hassle and I have better things to do with my time. Besides, I have little faith that they could/would actually fix the problem. Over the years I've come to realize that fancy electronics rarely work well in any vehicle (2 wheeled or 4).

 

--Eric the Cynic

[motoguy128]

He told me this was normal, "all bikes with cruise control and did this, especially third-party cruise controls".

 

 

I'm really surprised that a company like BMW that likes whizzy stuff doesn't use throttle by wire.

 

But that would eliminate some of the traditional boxer maintenance procedures. I mean, could you imagine...throttle by wire along with pressure transducers that allow the system to even synch itself.

 

In reality, you'd either still need a cable to each throttle body, or use 2 electronicaly actuated throttle bodies. The 3rd option would be to go the way of automobiles and use a single throttle body. But I think throttle response would get pretty muddy, expecially with a lightweight flywheel.

 

How does Harley do theit TBW? 2 throttle bodies or a single throttle body for both cylinders? I'm not up ot speed on HD's engien designs.

[T__]

 

How does Harley do theit TBW? 2 throttle bodies or a single throttle body for both cylinders? I'm not up ot speed on HD's engien designs.

 

motoguy128, Harley uses a single throttle body with a short “Y” type intake manifold.. The intake ports are close together & facing each other.. Due to the short intake tracts it is pretty responsive & smooth..

 

The BMW boxer has some issues in that area.. Too far between cylinder heads to easily use a single TBI unit without major redesign on the intake system..

 

 

 

Twisty

 

[smiller]

motoguy128, Harley uses a single throttle body with a short “Y” type intake manifold.. The intake ports are close together & facing each other.. Due to the short intake tracts it is pretty responsive & smooth..

Is that perhaps the reason (or a reason) why the factory cruise control works so well on the K-GT? In spite of all the reasons posted why cruise controls cannot work smoothly, this one does... virtually no lag and very smooth in operation. I can't make it hiccup even if I try. A bit of a puzzlement since I would imagine the cruise control hardware at least is the same as on the R-bikes. Is it the engine configuration that makes the difference?

[T__]

Seth, obviously (2) large throttle plate bores,, lean running engine,, high TBI return spring pressure,, cam timing designed for higher RPM power,, a 2.62:1 final drive,, & fuel shutoff on decel all make the 1200RT a more difficult package to tune the cruise control on..

 

If it is too responsive & quick to react it will hunt all the time.. If it is too slow to respond it will lag on speed increase or decrease.. There is very fine line to getting a cruise control on a higher performance manual trans vehicle to do everything correctly..

 

On my 1200RT I am pretty happy with it’s performance in the range I use it in.. On the freeway it holds true & tracks with other vehicles on the road.. Works quite good at 50- 100 mph,, has nice clean steps both up & down.. It is less than stellar at slower speeds in lower gears & descending long down hills where it tries to completely close the throttle plates..

 

I’m not sure why your K-GT is better.. It could be the engine tuning,, or the final drive gearing,, or the smoother 4 cylinder engine,, or better low RPM engine drivability & tractability..

 

I do know that on my 1200RT even holding a steady speed with the twist grip at lower speeds is not easy & low throttle opening throttle modulation is not as smooth as I would like.. Some of that could be mitigated with different TBI cable cam profiles (or 2 stage throttle bodies) & I have no idea why BMW engineering didn’t address that area.. Unless they did & marketing overrode that by deciding that a quicker throttle action made the bike feel faster than it is..

 

I do know that when I bought my 1200RT the cruise was acting strange & struggling to hold a steady road speed so I thought I would make sure the cruise throttle cable was free,, routed correctly,, & adjusted correctly but when I started checking it out I found the stepper to cable drive tape had a 1/2 twist in it.. Once I took the twist out of the tape it worked as it should..

 

Twisty

 

[smiller]

Seth, obviously (2) large throttle plate bores,, lean running engine,, high TBI return spring pressure,, cam timing designed for higher RPM power,, a 2.62:1 final drive,, & fuel shutoff on decel all make the 1200RT a more difficult package to tune the cruise control on..

Most of those characteristics are present on the K-GT as well, nor am I sure I'd say that the K bikes have better low RPM engine drivebility & tractability than the R. Certainly more power, but not better drivability.

 

I would guess that it may be just easier to maintain precise control of a four-cylinder engine with solidly-linked throttle bodies and short intake tracts than a large twin with long tracts and throttle bodies in different time zones. But then again as I mentioned the el cheapo Audiovox aftermarket unit works quite well on my R1100RT, or at least as well as any typical automotive cruise control (and from what I'm reading better than the factory system on the R bikes, oddly enough.)

[T__]

Seth, is your 1100 still using stock fueling control or have you worked with the system to get better off-idle drivability?

 

A lean spot just off idle will make cruise control messy at best..

 

I’m not real sure what the difference is between the K bike & R bike as far as cruise control is concerned & I never installed a cruise system on my 1100 or 1150.. I do know my 1200RT cruise works about as I would expect on a manual transmission large throttle body lean running vehicle..

 

 

Twisty

 

 

[smiller]

I do have a Power Commander installed but I'm not sure what off-idle drivabilty has to do with cruise control operation as in my case it's primarily used at high speeds at reasonably high power settings (the two go together on an 1100 )

[PBee]

No matter if I were in 5th gear or 6th gear the action was the same.

 

Why 5th or 6th to descend a mountain pass? I would be in 3rd or 4th, but that is based on European passes.

 

Andy

The decent side of the passes I was on were not so steep that simple engine braking in 5th or 6th gear wasn't enough to prevent a run away.

 

I didn't mention, and should have, on the level, slight decline and going up those passes the cruise control did perform flawlessly. Considering most of the responses perhaps I should accept the downhill "herky jerky" as a quirk and disengage the cruise control whenever it starts.

 

Other than that one thing I'm happy with the bike.

[motoguy128]

I do have a Power Commander installed but I'm not sure what off-idle drivabilty has to do with cruise control operation as in my case it's primarily used at high speeds at reasonably high power settings (the two go together on an 1100 )

 

It makes the power curve less linear, which can;t really be tuned out of a typcial control Loop. Yu have ot assume a sconsistent cureve or linear performance. So dips in power delivers will cause a lead/lag scenario. Look at it this way. If the biek is at 5% throttle and the speeds start dropping so it goes to 6%. But at 6% pwoer actually drops. The control loops assumes the load has actually increased, so it goes ot 7% or 8%, now power resumes the previous curve, and it overshoots the setpoint. SO it backs off. If it's tuned incirectly, a dip in the pwoerband, could cause the CC to "yo-yo" between to throttle positons. But that's why you use PID control, not just directly proportional control with a gain value. The intergral and derivative should prevent those kinds of problems. Espeically if you have a analog to digital conversion. Normal loop error can cause the value of the control vairable to jump back and forth, then causing the output ot bunce up and down. I hd this happend of a variable speed AC drive. the intergral value was set to 0. So you could actully hear the motor in the field bouncing up and down every 1/2 second (the I/O scan rate) by 0.1 Hz. Now don;t ask me how ot tune a PID loop. I only know the very basics. Mitch probably knows more on that.

[motoguy128]

No matter if I were in 5th gear or 6th gear the action was the same.

 

 

I didn't mention, and should have, on the level, slight decline and going up those passes the cruise control did perform flawlessly. Considering most of the responses perhaps I should accept the downhill "herky jerky" as a quirk and disengage the cruise control whenever it starts.

 

 

Rather than turn it off. You can also just manually hold the throttle position manually ot a point where you're going at least 1 mph faster than the CC setpoint. I do that near the bottom of some downhills where I know the CC will cut back in abruptly. its' also a way to save fuel in rolling hills. IF you allow your bike to gain a little speed on the downhill, you're "storing" energy for hte uphill. Of course increased speed will increaes wind drag, so it's not as good as having an actual hybrid, but it does help a little. I cna gain about 2mpg on my car doing just that when I'm driving on backroads in Missouri.

[Sailorlite]

I just returned from 2100 mi. in AZ, UT and CO and used the cruise control extensively. The only time I got any "jerking" was to RES to 72 MPH from 80 MPH, or similar. And even that wasn't really annoying. Otherwise it operated as well as the average modern car's CC. I'd say the OP's CC is not up to par, and the mechanical cabling sounds to me the likely culprit.