Engineer’s Insight: For The Manual Gearbox Faithful

If you like podcasts, I discuss this in some more detail on the It’s Not That Simple Podcast

There is a very vocal crowd on the internet of what I’ll call “The Manual Gearbox Faithful” who decry the demise of the manual gearbox (or manual trans, or stick shift if you prefer) in place of smooth torque converter autos, dual clutch boxes and CVTs (continuously variable transmissions).

It seems like everyone, if you read a lot of auto blogs, but I think it is just a coincidence that those passionate enough to write articles or comments either truly prefer manuals or feel that they should share this opinion as the “car-guy” thing to say.

Manufacturers now make these changes for numerous reasons:

  • Performance
  • Smoothness
  • Compatibility with Hybrids
  • Ease of driving
  • Compatibility with driving aids (auto-park, adaptive cruise control)
  • Consumer preference
  • Accessibility

It’s definitely not done for cost, as any level of automation makes a transmission more expensive. It’s also not done for weight, as a class-equivalent auto is likely around twice the weight of the manual alternative.

Some of the reasons are justifiable. Any electronic aids or systems that have active control systems benefit from having an active control system for the gearbox as well. Adaptive cruise control, now often deployed allowing the car to speed up to your set level and slow down to a standstill, benefits from having an automatic to remove steps requiring driver intervention.

Ease of driving is true. When I bought a BMW i3, “milk float” and “golf cart” were the first comments made by my colleagues. In this case, the i3 makes it even simpler as you don’t even have to use the brake pedal, so you don’t even need to bother with the inconvenience of a 2nd pedal.

Why I prefer manual shifting

Credit: Daniel Tillotson

However, as biased as I might be with a background working in Manual Transmissions, the one thing that is missing is the connected driving experience that you cannot replace. Even paddle-shift transmissions have little appeal to me – when you know it’s an auto, it seems like you are creating an unnecessary step by telling it when to shift (I know, the shift points in Automatic mode isn’t perfect, but that’s my take).

The simplicity of the driving experience is echoed in the simplicity of the design – a lever that moves rods or cables, which moves a lever system in a transmission to select the gear you want. However, and this differs between companies, there is a lot of nuance to this that can deliver a Ford Fiesta ST shifting experience, short and precise, or a Peugeot 208 experience with less definition and a “relaxed” shift.

There are a few companies that make measurement equipment exactly for this function. The hardware tends to be similar, with force and travel measurements in 3 axes. The difference is mainly in the software This means how much processing the software can do on the raw data, and how much post processing it can do to generate useable engineering metrics. This is where the OEMs differ. Some will measure according to the supplier’s specifications, and others with develop the system to deliver to specific unique points of focus.

Source: www.atesteo.com

A demonstration of engineering in practice

The customer wants the shifting experience in their car to be nice, or at worst just not noteworthy. But how do you measure “it’s not great”? You ask more questions.

Adjectives such as rough, notchy, harsh, stiff, vague, soft need to be translated into measurable elements during the shift. In simple terms, it is usually in the geometry and feel when you move the shifter around when you are parked and the effort and feel when the engine is on and the input shaft is rotating.

Shift Assessment 101:

  • Car in Neutral, engine off.
  • Foot on the clutch, shift to 1st.
  • Return to Neutral
  • Repeat until you are used to the feel.
  • Engine on at idle, Car in Neutral.
  • Foot on the clutch, shift to 1st.
  • Return to Neutral, foot off the clutch.
  • Repeat.

You will notice there are different force peaks and the effort will change. The start of the shift will feel the same, but about 60% into the shift, there will be a larger force. That is the shift effort, or the work you are doing to synchronise 1st gear.

You might feel another force peak. That will be the end of synchronisation, and you are actually putting the transmission in gear, with the contact between the parts being felt at the shifter.

You can do this for every shift, and every shift pair (1st -2nd, 2nd-1st, etc.).

For performance cars, you might want the shift to be shorter and more precise, with very little play or softness. These things can all be measured and tweaked.

There is a challenge to balancing the wants of customers with the identity of your brand, and how much you are willing to invest in engineering it. But that is the fun part of engineering.

I could go on for a long time, but I’ll leave it there for now.

Have a go, let me know what you experience when you really pay attention to the process of shifting.

If there is anything you want to know more about, leave a comment below and I will delve deeper in a future post.

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