Welcome back! Like the title suggests, this week we are going Old-School – looking at what entails a NON-computerized transmission. Yes…they do exist! But before we get into that, like always, time for a quick recap & review some definitions.
Previously on Anthony’s Automotive Blog….
Previously, we did a recap of the past few weeks – just to clear up any confusion any of you might have had. You can do a re-read of it here.
And prior to that (check it here), we discussed all the fun parts like Servo, Solenoid and just how the computerized transmission knows when to shift gears.
Our Growing Automotive Vocabulary
This week we added the following to our vocabulary: Governor, Vacuum, Modulator, Cable, Hinged, Spring, the combined specific terms of Vacuum Modulator and Throttle Cable as well as brought back a term we used awhile ago – Centrifugal. You can find them at the bottom of the list. As always, you can find our entire and current automotive dictionary here. Feel free to save its link so that you can find it again in case we use a word that happens to not be on this week’s list.
Here are the related words for this week’s topic. Enjoy expanding your vocabulary.
Automatic Transmission – An automotive transmission that can automatically change gears as the vehicle moves, freeing the driver from having to shift gears manually.
Hydraulic – Operated by the movement and force of liquid; specifically, operated by the pressure created when a liquid is forced through an aperture, tube, etc..
Valve – Any device in a pipe or tube that permits a flow in one direction only, or regulates the flow of whatever is in the pipe, by means of a flap, lid, plug, etc. acting to open or block passage.
Throttle – The valve that regulates the amount of fuel vapor entering an internal-combustion engine or controls the flow of steam in a steam line. This is also known as the Throttle Valve.
Governor – A mechanical device for automatically controlling the speed of an engine or motor as by regulating the intake of fuel, steam, etc..
Vacuum – An enclosed space, as that inside a vacuum tube, out of which most of the air or gas has been taken, as by pumping.
Modulator – Something that regulates, adjusts or adapts to the proper degree.
Cable – A thick, heavy rope, now often of wire strands.
Hinged – Jointed device on which a door, gate, lid, etc. swings.
Spring – A device, as a coil of wire, that returns to its original form after being forced out of shape: springs are used to absorb shock, and as the motive power in clocks and similar mechanisms.
Vacuum Modulator – A device that monitors the vacuum pressure in an engine and moves the throttle valve in a specific direction that is dependent upon the load of the engine.
Throttle Cable – A cable that is connected between the gas pedal and the throttle valve and monitors the position of the gas pedal.
Centrifugal – Moving or tending to move away from a center.
Look Ma – No Computers!
It’s hard to believe that there was a time when computers did not exist. They are wonderful and exasperating machines that make our lives both easier and more complicated. They are fantastic when they work properly and not so much when they don’t. And it’s also hard to believe that there was a time when there was not a single computerized part in our vehicles.
So exactly how did they work without computers? By simply using centrifugal forces, vacuums and cables.
It all starts with the use of the Governor. Arnold here is attached to the output shaft and regulates the hydraulic pressure in the system based on the speed of the vehicle. It does this by spinning a pair of hinged weights against a pair of springs. The spinning causes a centrifugal force that pulls on the weights. As the weights get pulled out by the force, it pulls and stretches the springs. The further out the springs move, the more oil pressure is allowed to go past the Governor to then engage on the shift valves that are in the valve body. This would signal the engine on when to shift.
Also factored into this equation is the load that the engine is under. This is just simply how hard the engine is working. The higher the load on the engine, the longer the transmission will hold a gear before it will shift to the next one.
How to Lighten the Load
Non-Computerized monitoring of the load of the engine is done using one of two devices in conjunction with Arnold (aka the Governor). It is with either the Vacuum Modulator or the Throttle Cable.
The Vacuum Modulator is a device that is attached to the engine via a vacuum hose. When the engine is under a light load, a high vacuum is produced. Naturally, when an engine is under a heavy load, the vacuum pressure decreases down to non-existant. The other side of the Modulator is attached to the transmission, specifically the throttle valve in the valve body. Based on the vacuum level present, the modulator prompts the transmission to either shift early and softly or shift later and firmly.
The Throttle Cable just monitors the position of the gas pedal and prompts the throttle valve to shift based on its position.
For Next Week
And that’s a wrap on all things Automatic Transmission! You now know how this intricate piece of machinery works. Next Week, we’re going to discuss all the many things that can go wrong and we will give you some things to watch for in case your car needs a mechanic’s attention.
Until Next Time….