Doctor Diesel

Automatic reply

You are always a good read Doctor, the bit of the magazine that I always turn to first, but donít tell the others! I am a fairly practical chap (he writes modestly! Doc) and I understand the principles of most car engineering, but I am confused by the references to different types of automatic gearboxes. I understand the old torque converter type, and have an eight-speed Steptronic in my current BMW X5, which I think is brilliant and, I am told, far more reliable than the nine-speed used in some Land Rovers and other cars, although they are also made by ZF. I also have a 4-speed automatic in a Suzuki Jimny which, although rather basic, takes me places over the hills of mid Wales where only a quad bike or a tractor can go. 

I basically also understand the more recent twin-clutch DSG, or Ford PowerShift, which I believe has a centrifugal clutch connecting the drive. There is also the CVT, but what the Dickens is an ìautomated manualî to which you refer to in the current edition of Diesel Car? I have recently noticed that Suzuki Vitara offers a TCSS transmission, which the brochure describes as an automated manual, but which the dealer tells me is in fact a twin-clutch automatic, and pretty much the same as a DSG, and is made by Fiat. Could you clarify this? Best wishes, 

Thomas Lloyd

To recap, for the benefit of readers, basically in a twin-clutch transmission there are two shafts carrying gears, each with its own clutch. Depending on what the driver or the ECU specifies, one shaft carrying gears 1, 3, 5 will be engaged, and the other carrying gears 2, 4, 6, will be spinning freely, but with one of the gears pre-engaged. Any gear change involves simply the de-clutching of one shaft and the engagement of the other clutch, thereby selecting either a higher or lower gear, odd-numbered or even-numbered, as the case may be. The gear change is, theoretically, almost instantaneous then, since the next gear expected by the ECU is already engaged, and it involves just two fast and simultaneous clutch operations. However, in some circumstances in slow-moving traffic, the ECU doesn’t know for sure which gear may be needed next, and many owners mention disturbing delays when moving away from rest swiftly, at roundabouts, where both the transmission and the interlocked automatic braking system that prevents roll-back jointly conspire to lose those few fractions of a second that can seem an age, when you’re planning a quick entry into a gap in the traffic.

Torque converter automatics have to some degree fended off the marauding hordes of twin-clutch transmissions, by virtue of the fact that they are smoother and, with the latest refinements, give little away to twin-clutch (or manual) transmissions in efficiency. Some automatics (BMW, for instance) are even marginally more economical than their manual counterparts, possibly by virtue of having more ratios, and “one more club in the bag” to cope with varied driving conditions. I don’t know much about relative reliability of ZF eight-speed and nine-speed transmissions, the eight-speed is for longitudinal engines, and the nine-speed for transverse engines.

So, to get to your main question: what transmissions are called comes down to pure terminology. In truth, any transmission that will operate without driver intervention arguably merits being termed “Automatic”, the design, or origin being irrelevant. Automatics that are derived from existing manual transmissions, but have added mechanics and electronics to dispense with driver input, are thus termed “automated manuals.” In most cases these employ an electronically operated clutch, and a powered device for operating the same gear selection device that is used in the manual variant, with computerised function involving a transmission unit that communicates with the primary ECU, and an option of manual override using the selector or steering wheel paddles. There have been quite a few of these ìautomated manualsî over recent decades (sometimes confusingly also called ìsemi-automaticsî), probably the most widely used being the EGS transmission used by Peugeot/CitroÎn, which has steering wheel paddles for manual override. Many others have been employed though, by Vauxhall (Easytronic), Fiat (Dualogic), etc., most of them on cheaper cars, usually petrol, that have been pretty horrible to use, although I do remember driving a particularly nasty automated diesel Renault Modus!

Your information that the Suzuki TCSS transmission is sourced from Fiat is correct. It stands for Twin Clutch System by Suzuki. Being pedantic though, you should not describe any twin-clutch transmission as an ìautomated manualî (as in the Suzuki brochure) since no twin-clutch manual transmissions exist!

I Hope this answers your question Thomas. Regards,

Doc Diesel

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