Welcome back! I know last time we said that we’d look at how the non-computerized transmissions work but we’re going to hold off on that. Instead, let’s review all that we have learned over the past several weeks. We want to make sure you have a good understanding of how the transmission works before we add any new data and concepts to this.
The Automatic Transmission
In this photo, you will see exactly what we’ve been talking about for the past several weeks. This is the side view of your car’s transmission. You can even see the Gear Shift attached. This photo gives a great perspective on how the transmission looks and where everything is placed in relation to each other.
Now…how does it work again?
You put your key in the ignition and you turn your car on. The engine is now running and the Torque Converter has been engaged. Transmission fluid is now pumping through your car’s transmission via the Pump, through the Turbine, into the Stator and into the One Way Clutch. This essentially keeps your engine running and keeps your car moving while its shifting gears, idling, etc..
When you shifted your Gear Shift into the Drive position, you have basically put it into First Gear and told your car that you want all the gears available for it to use while you are moving forward.
Now back to the One Way Clutch – the transmission fluid doesn’t just stop there. It keeps moving. Through a complex series of passages and tubes, the fluid moves into the Valve Body of your car’s transmission. And it does this only because it is under pressure the entire time.
This pressure is generated by the Oil Pump when you turn your engine on. It is connected to the torque converter which means it is connected to both the engine and the transmission. As long as there is sufficient oil located in the oil pan (on the bottom side of the transmission), it will create pressure and will allow the transmission fluid to flow through the transmission.
Now back to the Valve Body – transmission fluid is directed to the channels that lead to specific valves required to allow a gear shift to occur.
And how exactly does it know which channels to use?
In a computer controlled transmission, there are sensors that are used to capture lots of data related to your engine: brake pedal position, engine load (how ‘hard’ it’s working), engine speed, vehicle speed and many more. By compiling all this information, it can exactly pinpoint when a gear shift needs to occur. AND when it has properly identified that moment, it transmits to the Solenoid Packs in the transmission so that they can redirect the transmission fluid as needed to the correct clutch pack/band/servo to shift the gear.
Remember – a Solenoid Pack is simply a coiled wire that acts like a magnet when an electrical current is running through it and it can easily open and close valves.
In a Nutshell
You turn your car on. This causes the oil to create pressure that allows the transmission fluid to flow through the valve body, which selects the optimum gear for your car to be in at that specific moment. All you do is turn the car on, tell your car you want ALL the gears (putting in Drive) and put your foot on the gas pedal.
Until Next Time….
Welcome back! This week we’re still on the topic of Transmissions. But this time, let’s get a little more technical know-how under your belts. But before we jump right in, let’s do a quick recap & review some definitions.
Previously on Anthony’s Automotive Blog….
Last week, we talked about just the basics when it comes to transmissions. If you wish to do a quick re-read of it, you can find it here. For a quick recap, keep reading.
Basically, your car’s transmission is what keeps it moving. They come in two flavors: Automatic or Manual (aka Stick Shift). Automatic transmissions require little to no interaction from the driver, while Manual transmissions require 100% interaction from the driver. Your transmission needs a special fluid to keep all of its parts working together. We also touched on some common problems that can occur & how to tell if it’s about to die.
We also covered some basic definitions of various automotive-speak words that you could understand exactly what it was that I was saying. Let me recap a couple of those words here just in case. I will also add some new ones, as they do pertain to this week’s particular topic.
Transmission – The mechanism by which power is transmitted from an engine to the wheels of a motor vehicle.
Torque Converter – A device that transmits or multiplies torque generated by an engine.
Gear – One of a set of toothed wheels that work together to alter the relation between the speed of a driving mechanism (such as the engine of a vehicle or the crank of a bicycle) and the speed of the driven parts (the wheels).
Automatic – A device or process that works by itself with little or no direct human control.
Automatic Transmission – An automotive transmission that can automatically change gears as the vehicle moves, freeing the driver from having to shift gears manually.
Manual – A thing operated or done by hand rather than automatically or electronically, in particular.
Manual Transmission – An automotive transmission consisting of a system of interlocking gear wheels and a lever that enables the driver to shift gears manually.
Neutral – A disengaged position of gears in which the engine is disconnected from the driven parts.
Clutch – A mechanism for connecting and disconnecting a vehicle engine from its transmission system.
Epicyclic – A circle whose center moves along the circumference of another, larger circle.
Planetary Gear System – A gear system that consists of one or more planet gears (the gears in the middle area) that rotate or revolve around a sun gear (the gear in the center) and a ring gear (the gear on the outer edge).
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..
The Nuts and Bolts of an Automatic Transmission
As you recall, an automatic transmission is the type of transmission that requires little to no interaction from the driver (outside of putting your foot on the gas pedal that is) in order to work. But it is so much more complex than you think.
An automatic transmission system works by utilizing a series of gears that lock and unlock in order to change the gears of the vehicle. The transmission also uses a torque converter instead of a clutch to disconnect the transmission from the engine when the car needs to come to a stop.
The series of gears used actually have their own name. They are referred to as the Planetary Gear System (or Gear Set). The system has three main parts: the Ring Gear, the Planetary Gears and the Sun Gear. The Ring Gear is on the outer edge. The Planetary Gears are in the middle area (usually mounted to a carrier or plate). The Sun Gear is in the very center. The Planetary Gears rotate and revolve around the Sun Gear in the center and the Ring Gear on the outer edge.
This system works by moving two of these parts, while keeping the third one still. By doing this, it can transmit the torque created by the engine to the wheels of the car, which, in turn, makes it move.
In addition to the above gear set, you also have what is called the Valve Body. It is what allows the automatic transmission of your car to smoothly shift gears as you are driving down the road. It is a hydraulic system that uses a pump to bring transmission fluid into the valve body. It then directs the fluid through a maze of channels and valves that, in turn, activate whatever gears are needed to shift to.
This maze is quite intricate and specialized. For example, if the car needs to shift from second to third gear, the transmission fluid needs to flow through the channels to the specific valve that is for that function. This valve is often called the 2-3 valve. And oddly enough, there is a specific valve for shifting from third back to second and it’s commonly called the 3-2 valve. In this system, there is a valve for everything!
Food for Thought
I hope you were able to learn a little more this week about exactly how an Automatic Transmission works. In a nutshell, fluid is pumped through the system and through a specific valve which tells the vehicle which gear it needs to shift to.
Next week, we’ll continue to learn more about how an Automatic Transmission works. In truth, we’ve just begun to scratch the surface.
Until then, I’ll leave you with something to think about. We’ve all seen those big semi trucks that are always slow to start moving and we all curse and moan when we get stuck behind them at a stoplight. They typically have anywhere from 12 to 18 gears that their engine has to shift through to get moving. Just imagine the number of valves that transmission would need in order to shift up and down all of those gears IF they were an automatic transmission. How big would that engine be??!!??
Until next time,