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It's Like to Drive an Auto-Pilot Car
By Frank Rowsome Jr., from POPULAR SCIENCE Monthly, April 1958 issue.
it or not, the robots are slowly taking over a driver's chores. The
newest one is a power-operated accelerator pedal
|The automatic auto, an intriguing if faintly ominous concept, came closer this year when the Chrysler Corporation unveiled an optional supergadget for its swanky Imperials and Chryslers. Called an "Auto-Pilot" and tabbed at about $86 extra, it is a development of a device first described in Popular Science several years ago ("Educated Gas Pedal Keeps the Cops Away," Jan. '54).||
SNUGGLED on the 1958 Imperial between a vacuum tank and the power brake, the Auto-Pilot fits on the left side of the engine compartment. Its motor runs only intermittently.
Actually, the device
is a power-operated accelerator pedal. This fact alone has been enough
to distress some car critics, who argue that drivers are being increasingly
engineered out of a decent sense of participation in the new cars. The
Auto-Pilot has also hoisted the eyebrows of a few safety experts. Here
the contention has been that, with literally nothing to do except steer
and ruminate, a driver may fall victim to hypnotic goof-offs. Such judgements
appear to be academic. This writer recently made
a 4,000-mile cross-country run in an Auto-Pilot car, and ended up with
What it is. On the instrument panel there's a pushbutton and a knob that can be turned to calibrations from 30 to 80. Under the hood there's a shiny hunk of mechanism, smaller than a breadbox, that houses a reversible electric motor, a flyball governor, and associated electrical gadgetry. A flexible shaft resembling a speedometer cable feeds in car-speed information; a rod leading to the carburetor linkage executes commands to the throttle.
What it does. This is not easy to explain to women and the mechanically innocent. Not that the gadget is particularly complex; it's just that it offers two different though related services. In function No. 1 it is a speed minder--a mechanical conscience that urges you, by increased accelerator resistance, to stay under the speed it is set at. It doesn't actually prevent you from speeding, though; you can (while passing, say) readily tromp past the increased resistance.
In function No. 2 the device is a speed maintainer. Its motor depresses or releases the accelerator as needed to hold the set speed up hill or down, whether your foot is on the gas or not. You bring the car up to the speed the knob is set for and then touch the latching button. The car then eerily continues at that speed until it runs out of gas--or until you touch the brake pedal. This instantly unlatches it, returning you to conventional operation. In effect it is a robot that constantly compares an ideal speed (the knob setting) with the car's actual speed. Whenever the two begin to differ, the throttle is corrected and the speeds recompared.
Its best is very good. On the 60-m.p.h. New Jersey turnpike the Auto-Pilot showed off theatrically; it managed the throttle for 76 miles in an elapsed time of 76 minutes and 13 seconds. Even that 13 second error--less than half of one percent--wasn't really the gadget's fault. Once it had to be unlatched for a moment because of a bind in traffic, and another time for a brief debate on the tactfulness of overtaking a police car.
In hilly country, as in much of West Virginia, this remarkable precision falls off. Average speed is still close to the set one, because hill effects are usually transient and tend to cancel. But temporary variations of three or four m.p.h. above and below the setting aren't uncommon.
The reason lies, of course, in the limitations of the throttle as a speed corrective. Downhill, the most the little robot can do is take its electromechanical foot completely off the accelerator. If the grade is so steep that this isn't enough, the car necessarily goes faster. Uphill, the situation is slightly different. Chrysler's big engine has ample moxie to hold speed on any normal highway grade, given a moment or two to roll up its sleeves. The trouble is that the Auto-Pilot doesn't know a hill is coming. It gets word only on how fast the car is going now; there's no anticipation. So the robot acts only when the upgrade has begun to slow the car. It feeds a little more gas; and when in the case of a sudden hill that isn't enough, it piles on more and more power. Soon the big engine is laying into it potently and speed comes back up.
Your clever foot. Driving a few thousand miles with this robot will give you increased awareness of the sensitive, constantly corrected tasks that your right foot has been performing all these years. The most obvious one is this attack on a hill. Quite automatically, an experienced driver's accelerator foot feeds a little extra speed at the approach of a hill. Even if you don't actually crack on a few extra miles an hour (which you usually do), that foot is alerted to press down at a quickly increased rate the moment the hill load comes on the engine.
Topping a rise. A more subtle example of delicate human throttle handling comes at the top of the hill. In South Carolina, we noticed that, as you go up and over a fairly steep rise with the robot locked on, there is a strong impression of something wrong. The Auto-Pilot seems to feed more gas as you near the top; you seem to crest the hill going faster than on the middle slope.
This is an illusion, as the speedometer reveals. At first it is a puzzler: The robot is clearly whisking you over the top, but the needle shows no (or almost no) overshoot. Then it dawns on you: It feels slightly wrong because it's not the way you drive yourself. Just as the Auto-Pilot didn't know a grade was coming, now it doesn't know that near the top of a hill there is a point where your sight distance shortens rapidly. Managing the accelerator yourself, you automatically feather back, throwing away a little speed to compensate for the reduced distance you can see. The robot, knowing nothing of this, simply whisks the car up and over at a constant rate.
This hilltop quirk of the Auto-Pilot (more accurately of sight geometry) doesn't amount to a hazard of consequence. If the hill-creating threatens to become too brisk, you simply tap the brake and unlatch, or else just back off the speed knob.
Around the bend. On a cross-country run you inevitably notice how state highway departments compare, and particularly how they throw you their curves. On some roads the curves come up fair and square, keeping above a minimum and uniform radius of curvature. Others, though, are sneaky: They mix up their offerings deceptively, tossing in an occasional spitter that tightens up wickedly.
The Auto-Pilot dramatizes these differences. It works fine on some curvy roads, mainly the newer and more lavishly designed ones. On others, though, like the secondary highways in Georgia and Alabama, it's more trouble than not, since you are incessantly unlatching. The problem is this: How big a spread is there between cruising speed for the curves and that for the straights? On a road where the 60-m.p.h. straights are irregularly interrupted by 30- or even 25-m.p.h. curves, you don't use the Auto-Pilot.
Those top speeds. Unexpectedly, you tend to drive a little slower with the Auto-Pilot turned on that with it off. The reason appears to be this: Suppose you are traveling on a main Louisiana or Texas highway, with little or no traffic. You find, operating the accelerator by foot, that you stabilize at about 65 m.p.h. indicated as your preferred fast cruising speed. Watch closely though, and you'll see that that speed is not quite uniform, and that variations are intentional. Depending on what can be seen a half-mile ahead, on road surface, side winds, vibrations, grades and many other factors, you modulate that preferred fast cruising speed over a range of perhaps four or five miles an hour. You drive, in other words, about as fast as you think proper under the circumstances--and the circumstances keep subtly changing.
Now suppose you latch the robot at 65 m.p.h. on the same road. In the circumstances where it's the right speed or just a little slow, you don't mind. In those where it's just a little fast, you soon become vaguely uneasy. So you reach forward and twist the knob back a little.
On our trip, automatic running was consistently a little slower than conventional running. This reduction seems all to the good: It pays dividends in relaxation and improved gas mileage, and, being held with machinelike steadiness, doesn't depress average speeds.
Passing and night driving. These are, of course, the most technically demanding parts of highway travel. As might be expected, you usually want no part of the robot during a high-speed pass; it's simply not suited to those critical moments when you hang behind a car or truck, stealing glances and calculating whether or not you have a passing chance. In all our 4,000 miles we made only three automatic-control passes, each with miles-long visibility.
At night on narrow roads the Auto-Pilot also has limitations. Partly this is because your reading of what is at the far fringes of the high beam is shaky and fast-changing. And partly it is because your right foot hankers to modulate speed as headlights come toward you. (Notice what that foot does the next time you meet High-Beam Harry on an 18-foot highway.) But both the passing and nighttime limitations disappear on divided highways, especially limited-access ones. Here, if traffic is not too heavy and the weather is good, you are usually eager to let the robot do its job.
Is it really safe? The answer isn't simple, for there are at least three separate factors involved:
1. It certainly promotes safety by reducing fatigue. At the end of a 600-mile day you are noticeably fresher than you would be with a conventional accelerator. This is not solely because you are spared the leg cramps and stiffness that come from having your right leg constantly committed. It is also because you have less work to do.
2. Its design is moderately but not absolutely "fail-safe." A sticking contact could theoretically open the throttle. This wouldn't necessarily mean disaster, short of shifting to neutral, for the brake switch could still kill the latching circuit. But it would certainly startle and alarm you.
3. It does not invite highway hypnosis. The explanation for this lies in your past driving experience. You lend the Auto-Pilot a duty you have been trained to perform yourself, and this somehow makes you just a little uneasy. It is not an entirely relaxing thing to sit back at 70 m.p.h. and feel the engine get gas from some other agency than yourself; your alertness is more likely to be heightened than lulled. This slight wariness stays with you as long as the device is working, even after thousands of miles have been logged.
Does it make sense? For intercity driving, turnpike travel, and long trips generally, the Auto-Pilot is a genuine help. On curvy or mountain roads, downtown, or in heavy traffic anywhere, you will find less use for it. (Though still some: The speed-minder function is handy anywhere, and could save you some speeding tickets.) That, then, is the little robot: busy, often precise, sometimes a little stupid, and very useful.
Frank Rowsome Jr.; Popular Science Monthly, April 1958.
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electric motor controls gas pedal position
1. The desired speed is set by the speed adjustment knob. This changes
the force exerted by the governor spring.
For clarity, part of the throttle-opening linkage is omitted here, as is the circuit that unlatches the arms if the brake pedal is touched.
In its speed-warning function, the device operates with the latch "ajar." This does not open the throttle automatically, but does interpose extra spring loading on the accelerator above dialed speed.