Automatic transmission in motorhomes which automatic gearshift is worthwhile?
Almost all vans in the 3.5-ton class that can be used as a motorhome base are offered with an automatic option. But these transmissions differ in technology, number of gears and ease of use. An automatic guide.
For many people, the comfort of a modern vehicle means not having to change gears – in a car anyway and, if possible, in a motorhome as well. Typical automatic disadvantages such as loss of power, slow gear changes, high fuel consumption and lack of intervention are largely a thing of the past. So, tick the automatic option, sit back and let it change gear?
It’s not quite that simple – not all automatics are the same. To avoid disappointment, you should know beforehand what you can expect – and what you cannot expect – from the switching assistance offered by a base vehicle.
It’s all about principle. Four types of automatic transmissions can be distinguished: CTV, ASG, DKB and torque converter automatic.
CVT transmission
A philosophy all of its own is pursued by the CVT transmissions – also called continuously variable transmission (cvt). It is based on a link chain running over two double bevel gears. The distance between the two cone pulleys of a wheel can be varied, and thus the effective diameter on which the chain moves. This allows continuous adjustment of the speed ratio between the input and output shafts. So with the CVT, there are no fixed gears, but each intermediate stage is adjustable. However, since the transmissible force is limited, this technology is only used in compact or mid-size cars.
ASG and DKB transmissions
Type two and three – the automated manual transmissions (ASG) and that double clutch transmission (DKG) – use disc clutches, which in principle work no differently than the foot-operated clutch of a manual transmission. Only here servo motors (actuators) take over the muscle work of the calf. Two disks are pressed against each other and transfer the rotary motion from one shaft to the other by friction. When changing gears, this connection is disconnected and then closed again.
In order to equalize the different speeds of the two shafts, the pads of the discs first grind over each other until the complete frictional connection is made. A certain amount of wear is therefore associated with every start and gear change. This applies to both types of automatics, both the automated manual transmission and the dual clutch transmission.
The ASG is the technically simplest way to realize an automatic shifting gearbox. For this purpose, a robot clutch is simply flanged to the existing manual transmission instead of the manual one and the control is left to more or less sophisticated software.
Clearly more complex DKG built. You can think of it as two small gearboxes working together in one housing and alternating through the double clutch. one gearbox takes care of the even gears, the other of the odd gears. The pausing transmission always engages the gear that is likely to be requested next based on the driving situation. And the dual-clutch design – where one automatically closes while the other opens – allows for lightning-fast gear changes with almost no interruption in traction.
However, if you want to skip a gear by manual intervention, the change takes much longer, because the skipped gear must still be engaged briefly. Overall, however, the functionality is clearly superior to an ASG. Nevertheless, DKGs are not yet used in large, heavy vehicles. Reason: the higher the forces transmitted, the more waste heat is generated, which is difficult to dissipate from the complex construction. That’s why even VW, which since 2003 has been strongly relying on the DKG technology (here "DSG"), only offers this transmission variant in the transporter range for the T6, but not for the crafter.
torque converter automatic
In the 3.5-ton class, therefore, in addition to automated manual transmissions, it is mainly classic automatic torque converter for use. They can also be designed so that high torques and weights are not a problem. The heart of the system is an almost wear-free fluid clutch. In the so-called hydraulic torque converter, there are three paddle wheels, the fixed guide wheel and the movable pump and turbine wheels. When the engine is idling, just enough power is transmitted for the vehicle to creep slowly.
When the throttle is opened, the pump wheel causes the oil to move more quickly. This results in a back pressure at the fixed guide wheel. This additionally increases the effective moment at the blades of the turbine wheel, with the effect that the engine torque is practically more than doubled during start-up. A real advantage for heavy vehicles.
As soon as the engine and transmission speeds are aligned, the torque increase is a thing of the past. Since the converter always operates with a certain amount of slip, modern automatics engage a so-called converter lock-up clutch at this moment, which ensures a rigid drive between the input and output shafts and thus improved efficiency. Together with the usually higher number of gears, which allows a lower engine speed, the additional fuel consumption of a modern torque converter automatic can be significantly limited.
Advantages and disadvantages of automatic transmissions
In the 3.5-ton class, which is relevant for motorhomes, (mainly) ASG and wanderautomatic are used.
Automated manual transmission (ASG)
Relatively simple design, which tends to keep costs, weight and space requirements down.
High efficiency thanks to slip-free transmission, resulting in hardly any increase in consumption compared with manual transmissions.
Manual shifting usually possible.
Traction interruption clearly noticeable under load.
Gear changes sometimes take quite a long time.
noticeable clutch wear during start-up.
Less smooth starting and usually no creep function when maneuvering (exception: Renault master).
Partly nonsensical back and forth shifting if the speed connection does not fit after the gear change.
Converter automatic
Gear changes without noticeable interruption of tractive power.
Almost wear-free starting.
Creep function with torque increase when maneuvering.
Converter dampens vibrations in the driveline.
Compact design realizable through planetary gear sets.
Manual shifting is usually possible.
Mostly higher number of gears.
Complex design, tends to increase weight, costs and space requirements.
Slight loss of power and slightly higher fuel consumption.
Shifting to manual transmission
All automatic transmissions now allow manual intervention. It is therefore possible to select the desired gear by hand – whether by stick, rocker switch or paddle on the steering wheel. However, the control computers interpret the shift command with varying degrees of indifference. While the fiat-comfort-matic, for example, tries to comply with the shift request immediately – of course after checking whether nonsensical speed regions are reached in the process – the mercedes 9G-tronic only makes a vague promise to move in the desired direction when the opportunity arises.
Pleasantly, almost all automatics accept temporary intervention by the driver without having to switch completely to manual mode. The accelerator pedal can also be used to influence the automats according to the situation. But while, for example, Renault and VW attentively follow every accelerator pedal movement, the Fiat does not react at all in some cases.
The ASGs from fiat and renault provide for a general shift of the shift points to higher engine speeds by pressing a button, which is particularly advisable when driving through passages, with a full load and when towing a trailer. A similar situation can be found in the power or S-mode of the automatic transmissions from iveco and VW/MAN.
Leveling and maneuvering
To leveling of the vehicle is precise maneuvering about balancing wedges a common task in motorhome use. It’s true that all vans now have electronic hill start assist – at least as an option. But they usually do not intervene in such cases yet. A valuable aid, on the other hand, is the for automatic converter typical creep function. Just by applying the brakes, this allows the vehicle to weigh accurate to the centimeter get into position.
In such tricky situations, it’s best to operate the fiat with comfort-matic with one foot on the gas and one foot on the brake, otherwise it will keep rolling backwards. The renault, which nevertheless has a creep function, shows that things can also be better with an ASG – but the clutch wear can soon be smelled.
Automatic shifting in the 3.5-ton class
the automatic transmissions of the common base vehicles with 3.5 tons differ not only in the type of transmission, but also in the number of gears, the drive, the engine variants, the extra weight and, of course, the price.
Ford transit
Name: select-shift
type: torque converter automatic
number of gears: 6
DRIVE: front
engine variants: 130/170 HP
more weight: 45 kg
surcharge*: 1964 euro
Fiat ducato
name: comfort-shift
type: automated manual transmission
number of gears: 6
drive: front
engine variants: 130/150/177 HP
extra weight: 17 kg
surcharge*: 1990 euro
Iveco daily
Name: hi-matic
type: torque converter automatic
number of gears: 8
drive: rear/all wheel
engine variants: 116-205 hp (all 6 diesel engines, except 150 hp engine, also 136 hp natural gas engine)
MORE WEIGHT: 6-12 kg (low weight)
surcharge*: ca. 2400 euro
Mercedes sprinter
Name: 9G-tronic
type: torque converter automatic
number of gears: 9
drive: front
engine variants: 114/143/177 HP
more weight: 29 kg
surcharge*: 2504 euro
Name: 7G-tronic-plus
type: torque converter automatic
number of gears: 7
drive: rear/all wheel
engine variants: 114/143/163/190 HP
more weight: 48 kg
surcharge*: 2504 euro
Renault master
Name: quickshift
type: automated manual transmission
number of gears: 6
drive: front
engine variants: 170 HP
extra weight: 10 kg
surcharge*: 1131 euro
VW crafter / MAN TGE
Name: 8-speed automatic
type: converter automatic
number of gears: 8
drive: front/rear/all-wheel
engine variants: 140 hp (front-wheel drive only) / 177 hp
extra weight: 32 kg
surcharge*: 2446 euro
*surcharge of the base vehicle manufacturer, may differ for the bodybuilder.
Conclusion
Automatic is always better? It is really great what has happened in the field of automatic transmissions in the last few years. The torque converter automatics have become even more comfortable and at the same time lighter, cheaper and more efficient. Automated manual transmissions, on the other hand, seem to be on the decline. If you take the quick-shifting, well-tuned renault quickshift with creep function as a yardstick, there is little reason to do so. The results for the fiat comfort-matic are more ambivalent: clearer shift jerks, sometimes nonsensical gear changes and difficulties when maneuvering detract from the comfort gain. It’s time for a function update or a change to a torque converter automatic transmission.