Cruise Control
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itting
aftermarket cruise control can be done in one of four ways. First, if that particular car has cruise
control offered at the factory but your model doesn’t have it, you can usually
get the original equipment items (servo, stalk, electronics module) from
either a breakers yard or a dealership.
Secondly, you can have a go at making another cars’ cruise control
system fit yours, which is great if you’re into tinkering but not so good if
you’re like me. Fourth, you can engineer
your own cruise control system and finally, you can simply take the car to
somewhere that fit aftermarket cruise control, pay them some money and drive
away with the upgrade.
After careful consideration and
investigation (in the usual Dervy way) we went for the Conrad Anderson
electronic cruise control system. The
precise model we elected for uses a gear knob command module, that is, the
standard gear knob is replaced by the cruise control unit.
This
command module has five buttons - the master power plus four that operate the
cruise control system, these being SET / RESUME, ACCEL, DECEL and COAST. These work in the same way as any other
cruise control system, but as a refresher, once the system is engaged pressing
set tells the system to maintain the speed. ACCEL and DECEL increase or reduce the
cruising speed by one kilometre per hour (just over half a mile per hour)
and allow fine control over the cruising speed.
Finally, COAST temporarily disengages the cruise control speed and lets
the Ka slow down by itself (no throttle, in gear). Subsequently pressing RESUME activates the
cruise control system and it will automatically accelerate the car back up to
the original cruising speed.
We also
upgraded the standard cruise control system with the Conrad Anderson memory
module. This provides an additional
three preset speeds so can be used for predetermined cruising speeds. Whilst I freely admit that this is very much
a luxury there are certain advantages, especially when encountering roadworks
and similar. With one push of a button
I’m able to reduce the Ka’s cruising speed from seventy miles per hour to forty
or fifty miles per hour then press another button to bring the cruising speed
back up to the original speed.
Why Use Cruise Control?
There are two
primary reasons for using cruise control.
One is that it allows the driver to maintain a predetermined speed
without keeping constant pressure on the accelerator pedal. This may seem a trivial advantage to some,
but I can assure you that after several hours of driving at a constant or near
constant speed (with breaks of course) ones foot, ankle or knee muscles
can start to ache. Repeating the process
over a few days can cause serious discomfort.
The second reason is to avoid
unintentional speeding, which comes into its own when driving something that is
powerful and quiet on the motorway, thus seemingly breaks the speed limit with
little involvement or warning. In a
noisier, slower car this is less useful although in roadworks and similar, it
still has a role to play.
Other reasons
for using cruise control include making the journey easier on your passengers,
this comment applying to the many drivers out there who seem unable to maintain
a constant or near constant speed. Using
cruise control may also moderate use of the Throttle and as such can save fuel,
although by the same token since it cannot (yet) anticipate gradients
and hazards a good driver will be able to conserve fuel compared to cruise
control. The cruise system will not
start to increase the engine power before the start of a gradient, for example,
but may well progressively increase power as the car decelerates, which is a
rather inefficient way to climb a hill.
Cruise control systems can also appear rather heavy-footed in use when
changing the road speed of the car.
Kermit’s Cruise Control
Kermit has been
fitted with the Conrad
Anderson ZT-17 cruise control command module in conjunction with the
CM-8 memory module. This command module
resides in a gear knob, which is quite an unusual positioning for most cruise
control systems are operated via a stalk.
Fitting takes
most of a day at Conrad Anderson’s workshop in north
The command
module installation is especially neat.
The ZT-17E replaces the standard Ford gear knob with a slightly
oversized aluminium knob encompassing the four control buttons. The memory module is tucked on to the side of
the steering column under the left hand stalk where it’s subtle to the driver,
but less so for the passenger. It’s not
difficult to operate the memory switch by touch.
Under the bonnet, there are two new
components. One is the servo motor,
which is tucked up into the drivers side wing.
The other is the modified throttle cable. The unit connects to the Ka’s speed sensor,
which is buried behind the strut brace. I doff my hat to the Conrad Anderson engineer
because I appreciate that there is very little space to work behind the strut
brace to get to the speed sensor!
Using the System
In use the
system is controlled just like any other cruise control system. You reach your intended cruising speed and
providing the system is turned on, you press the SET / ACCEL button. The system then attempts to maintain this
speed by compensating as the car goes up or down a gradient. You can make small adjustments to the
cruising speed by tapping the SET / ACCEL button to accelerate and the RESUME /
DECEL button to decelerate. Each tap adjusts
your cruising speed by approximately one kilometre per hour (around two thirds
of a mile per hour).
One can
also press and hold the button to use smooth acceleration or deceleration,
although this isn’t so useful when one has to hold on to the gear lever to do
so.
If you wish to
temporarily suspend the cruise control system, for example you need to slow
down for a junction, there are three ways of doing this. One, you can press the brake pedal. Two, you can push the clutch or three, you
can press COAST. When you suspend
operation of the cruise control system it remembers the last set speed so
pressing RESUME / DECEL will accelerate the car back up to the original
cruising speed once more (providing your forward speed is at least half of
the set speed, so if it was set for seventy miles per hour you’ll need thirty
five showing on the speedo).
You may
also switch the cruise control system off using the ON / OFF button. When you turn it off, it forgets the set
speed so you can’t use the RESUME / DECEL button.
The memory
module has three independently set speeds and when you press one of these
buttons, it simply tells the cruise control to reach that designated
speed. Although this seems superfluous,
if you regularly travel along certain roads where you know you’ll be driving at
set speeds it can be very useful. In my
particular case, the lower button is set for forty miles per hour (for one
set of roadworks), the middle to fifty miles per hour (for another set
of roadworks) and the upper button is set at fifty eight miles per hour,
this typically being close to matching a heavy
goods vehicle (when it’s busy on the A1 I’ll match the speed of a HGV in
the inside lane rather than constantly changing my speed in the outside lanes).
Cruise Control in the Wet
In some
countries, the use of cruise control has been banned on wet roads. The rationale behind this is that the cruise
control system cannot compensate for a skid and of course on a wet road there
is a much higher chance of a skid.
This law
ignores what traction and stability
control systems can do, which is to compensate for wheelspin or skidding. It also ignores the difference between high
powered and low powered cars. A low
powered car with sophisticated electronics may be unlikely to skid whereas a
high powered car with no funky electronics to keep it pointing in the right
direction is arguably at higher risk.
If the reader
has ever driven on a very wet motorway (through standing water) in a car
with traction and stability control, you may have experienced that wonderful
“what standing water?” sensation that these cars have. The electronics are clever enough to mask
what’s happening down there. This goes
some way to explain why many modern BMW and Mercedes Benz drivers hammer on at
over seventy miles per hour when conditions are pretty scary to those of us in
“normal” cars cough.
I took
heed of the warnings about not using the cruise control in the wet - to a
point. If it’s a little bit of rain I’ve
used it as normal. Kermit lacks the
power to wheelspin under most circumstances.
If I’m going through standing water I’ve disengaged it before reaching
the water (almost always because I’ve braked before hand). But as I write, I’ve only once used the
system to drive through standing water and that was just to see how it behaved.
Kermit’s
cruise control is passive. It responds
to a change in the vehicle speed by changing the throttle input. This is a feedback loop influenced by
external variables. If the car is
driving too slowly the system increases the throttle via the servo motor under
the bonnet. If the car is travelling too
quickly, it reduces throttle. If the car
ascends a gradient and decelerates, it increases the throttle and should you go
down a gradient, it starts to shut the throttle.
This particular
cruise control system is one of the most effective I’ve used on a machine
without drive-by-wire, more so with a low powered
car.
Standing water
can do strange things to the drag on the tyre.
If the tyre is ploughing through standing water there is materially more
drag on it, which causes that wheel to decelerate. This is why many cars (those without
traction control or stability protection) pull to the puddle side when
driving through puddles. If this happens
to both wheels, the car is decelerated and the cruise control increases the
throttle.
Conversely, if
the tyre skips along the surface of the puddle (it aquaplanes) then the
drag on the wheel is very much reduced.
If the level of grip experienced by the
other wheel does not change and there is no limited slip differential used, it
is possible that the aquaplaning wheel starts to wheelspin as all of the engine
output is channelled through this wheel (power
follows the line of least resistance).
If both wheels are aquaplaning the car can experience wheelspin for both
wheels.
When
driving through standing water, one or both of the front wheels can push
themselves to the surface of the puddle.
For a front wheel drive car this can causes a sudden dose of wheelspin. The driver may experience a skip to the side
or a “power wriggle,” caused as each individual wheel spins off the excess
power. Most drivers’ immediate reaction
is to lift off the throttle when this happens, which should reduce the
wheelspin and improve grip. Good news.
In theory the
cruise control system will behave in the same way, except its reactions are not
as quick as the human driver (in theory).
Under
certain circumstances, the cruise control contributes to a bout of
wheelspin. This happens when the wheels
plough through standing water, thus the system increases the throttle, then
both wheels skip to the surface of the water.
The system does close the throttle but not before a Sketchley’s Moment!
Sensitivity
Although cruise control is designed to
maintain a constant speed, it should be remembered that it will always maintain
a speed very close to that set but it will vary ever so slightly as the car
goes up and down gradients or around corners.
This is because
the system reacts to changes in speed as they happen rather than anticipates
them, as a skilled driver will do. A
skilled driver over a road he or she knows should be able to match a cruise
control’s ability to maintain speed or perhaps even better it over some roads.
Therefore, when
going up a gradient it is usual for the speed to drop off ever so slightly and
when descending one would expect the speed to rise. In top gear inside the United Kingdom speed
limit, the Conrad Anderson unit maintains the selected speed within one or two
miles per hour with the exception of a long downhill motorway gradient, where
the car will exceed this boundary.
Conrad
Anderson’s cruise control system has an automatic sensitivity process. It is possible to change how sensitive the
system is but the automatic option has provided a balanced set up. If the system is too sensitive, it “hunts” at
a steady speed by over-reacting to small (and often undistinguishable)
changes in speed. If the sensitivity is
set too low, the cruise control will react too slowly to changes in speed so it
will decelerate when going up a gradient and accelerate when going down a
gradient. If the car encounters a series
of changes in gradient the slow reactions may be enough to cause it to exceed
the twenty five percent speed boundary threshold and the cruise control system
will de-activate itself.
This isn’t a
problem with Kermit, indeed the default setting is so good that when
accelerating up to a preset speed (or after pressing RESUME) the system
backs off the throttle just enough to maintain the given speed rather than
overshoots it. Similarly, when
decelerating the system starts to apply power as the preset speed approaches
rather than undershoots. It is in this
respect that the cruise control system is especially impressive because it is
as good as a skilled driver at matching a speed.
Problems In Use
After just over
a week in use, the gear knob command module came loose and subsequent rotation
of this broke the wires that connected this with the rest of the kit. I had to take Kermy back to Conrad Anderson,
where the technician fixed the device and reassured me that it wouldn’t come
loose again. Actually the chap concerned
wouldn’t tell me how to tighten the command module because there was no way it
would come off...
A couple of
days after getting back from Conrad Anderson, Charlie, Kermit and I set off on
the Italian Job Road Trip, and sure
enough approximately 1,700 miles after the repair, the gear knob came loose again... Just for dramatic effect, here’s the video we
took right after we stopped to fix it: clicky
(approximately 1·5 Mb
in size, no sound, QuickTime video).
This was rather
frustrating but a little part of me was expecting it to come loose and I’d
ascertained enough information about how it worked and how the command module
was attached to the gear stick to be able to effect a repair.
First, I gently
unscrewed the lower collar of the cruise control system, being very careful not to rotate the entire
command module.
Then align the
gear knob command module up with the alignment of the Ka...
And finally, using a 2·5mm allen key,
tighten each individual grub screw so that the command module is nice and
tight.
There are three
grub screws and when the command module came loose during the Italian Job Road Trip, one grub screw
was especially loose, one was partially loose and the third was still tight.
Once you’ve
tightened the screws back up, gently re-attach the collar and you’re done!
What Causes The Screws To Loosen
Well it’s
certainly not brute force when changing gear on our part. Kermit had driven approximately 1,700 miles
since having the command module re-attached and the vast majority of these were
on the motorway (in the
My theory is
that it’s the vibration of the gearstick that causes the screws to come
undone. Holding on to the gear lever
whilst driving along seems to confirm this: it’s vibrating at quite a rate!