How does an automatic transmission work?

May 28, 2015

Despite the huge number of automatic vehicles on our roads, most drivers are completely unaware of how an automatic transmission works. Have you ever stopped to consider how your car shifts gears automatically or why the engine does not die when you come to a stop?

Well, if you have, then this blog is for you. While we don’t promise to give you a deep understanding of this complex system, we pledge to simplify it to point where you have some idea of what’s going on in a traditional, torque converter-based system.

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What is the Purpose of a Transmission?

Your vehicle’s engine creates rotational power, otherwise known as torque. To be able to move your vehicle, this power needs to be transferred to the wheels. However, in order to operate efficiently, an engine must spin at a specific speed. If it spins too fast, the engine could potentially self-destruct. Too slow and your vehicle won’t budge.

Your transmission sort of acts like a power switchboard for your car. It provides your wheels with the perfect amount of power depending on the situation. For example, if your vehicle is starting from a standstill or going up a hill, it will increase the amount of power. However, if you are going downhill or slam on your breaks, it will decrease. Your transmission will ensure that your engine always spins at the optimal rate.

Main Parts of an Automatic Transmission

1. Bell Housing

To get a better understanding of how an automatic transmission works, the best place to start is the bell housing, which contains a torque converter as opposed to a clutch found in manual vehicles.

The bell housing is the place where the transmission connects to the engine. Inside the transmission is the planetary gear sets, which are responsible for providing different gear ratios.

The torque converter and the planetary gear sets are the two main components of an automatic transmission – so let’s look at them a bit closer.

2. Torque Converter

You know how you have a clutch on a manual transmission? A torque converter basically takes its place in an automatic transmission.

The major parts of a torque converter are the impeller, turbine, stator and the lock-up clutch. So how do all these parts work? Well, the impeller is part of the torque converter that connects directly to the engine. It drives the turbine, which in turn is connected to the transmission input shaft where it provides torque.

Transmission oil flows in a loop between the impeller and turbine. Between these two components sits the stator, which redirects the fluid as it returns from the turbine to the impeller. This minimalises churning loses and increases torque output.

By providing you with more torque, it assists you with accelerating or when your vehicle is stationary (the reason your car never stalls).

3. Planetary Gear Set

The torque converter clarifies how the engines send power to the transmission, but the planetary gear sets explain how an automatic transmission changes gear.

The planetary gear set is really the heart of an automatic transmission. This one part creates all the possible gear ratios that the transmission can produce.

All planetary gear sets have three main components, which are:

The sun gear
The planet gears (also the planet gear’s carriers) and
The ring gear

As you can probably work out, the planet gears rotate around the sun gear, while the planet carrier connects the planet gears.

The ring gear is on the outside and meshes with the planet gears. By using the clutches and brakes, it alters the input and output of the system, which changes the overall gear ratio.

All three parts can be the input, output or remain stationary. Depending on what role each part plays, it will determine the gear ratio for the gear set. That is how an automatic transmission knows when to change gears.

Contact the Automatic Transmission Experts Today!

As you can see, automatic transmissions aren’t some kind of black magic – it’s just a set of parts working together.

We hope this has illuminated your understanding of automatic transmissions and helped to foster an appreciation of how ingenious this system is.

We think they are great, but we may be biased as we work with them every day. For all automatic transmission enquiries, contact the Automatic Transmission R Us team by calling us on (08) 9240 5449, emailing info@autotransrus.com.au, or submit a contact form!

      Excellent rating  
 Based on 280 reviews 
    
  
 
 
      I must say, I’m not one to often leave reviews, especially when it comes to services like this. However I was really pleasantly surprised with the service here. I’m quite new to the Perth area and had a whining issue with my 2010 rav4, so did some digging for transmission shops around the area, the review of this one definitely stood out and they didn’t disappoint! I went to the Toyota dealership to get the same issue looked at and they just took my 250$ and told me to completely change the Trans and Front diff and quoted me 20k. I came here for a second opinion. I got a call back from cam, who told me after looking at the car it is indeed noisy but it isn’t something that actually deteriorates the life of the car. He proceeded to tell me he has dealt with a lot of the callbacks for this exact model and problem. He told me if I could live with the noise and couldn’t afford a repair he’d recommend I just drive with it. He told me if you put the noisy piece next to one that isn’t noisy you wouldn’t even be able to tell the difference. I really really appreciated the transparency and honesty here, he didn’t try and upsell me or quote me an expensive repair, he just gave me the god honest truth (you can drive with it, if you want the noise gone only way to fix it is to replace it). If there is any other issues with my car at all I’ll be sure to come back here as I was truly impressed by the transparency and quality of service. Many many thanks to the team and especially cam! Bloody legend!
     
   Obey Summer 
 1 days ago
 
 
 
 
    The team at Automatic Transmissions R US were fantastic. Their service was excellent. Pam and the team made the process easy, especially as I was transporting my vehicle by courier. They were able to book my car in for as soon as I could get it delivered. The service team did great work inspecting and then completing the repairs. They kept in contact with any updates and were fast, reliable and reasonably priced.
Thank you Automatic Transmissions R US
     
   Michelle Te Aho-Woodbrook 
 9 days ago
 
 
 
 
    
     
   H S 
 48 days ago
 
 
 
 
    Came here to check my card transmission, very satisfied with the results and they give me good feed back that I need to do, luckily the transmission is no issue so, no charge for that, thanks very much for best service :)
     
   Faisal 
 55 days ago
 
 
 
 
    Ongoing issues with my car others couldn't fix, they sorted first visit, no issues since. Highly recommended 👍👍
     
   markymark9172 
 56 days ago
 
 
 
 
    Cameron and the team are the go to for transmission issues. I could not be happier with the service provided.
     
   Chris Parker 
 84 days ago
 
 
 
 
    I booked the vehicle in for a noise I thought was coming from the gearbox. Graham inspected the vehicle and found it was not a gearbox issue. Graham pointed out other possible faults that could result in the problem i was experiencing. I felt reassured and can highly recommend this repairer who didn't charge me for the diagnosis. Thanks to Cameron and the team at Automatic Transmission R Us a job well done.
     
   George Doneo 
 84 days ago
 
 
 
 
    Trailblazer/ Colorado TC shudder
Had to fight with Holden for many years for a repair for the TC shudder, offered a band aid fix from Holden that failed on two previous occasions.
The team at Transmissions R us were completely honest, as a mechanic in a previous life the explanation of the common problem made sense. (Phoenix Holden constantly denied this issue)
Had the  Transmission  repaired and drove like new, I literally drove the vehicle across Australia towing a boat. After 10 months noticed some slight leaking of ATF on the bell housing. The team repaired the leak that included removal of the Transmission without question.Highly recommend this business.
     
   Darren Ginnane 
 107 days ago
 
 
 
 
    Took my car in recently on short notice when I was informed of a auto trans issue from my normal mechanic. I was met with exceptional customer service and expertise which lead to a quick diagnosis to confirm my true issue which was a crappy ac compressor making the noise.

Will definitely be returning to these guys in the future for any auto trans work.
     
   luke sampson 
 116 days ago
 
 
 
 
    Was just booking in my car,great conversation very up front with the information I needed to know  very helpful
     
   James Taylor 
 119 days ago