Double Clutch: This Article Is About The Driving Technique. For The Semi-Automatic Transmission With Two Clutches, See

Double clutch
This article is about the driving technique. For the semi-automatic transmission with two clutches, see dual clutch
transmission.
A double clutch (also called a double declutch) is a driving procedure primarily used for vehicles with
an unsynchronized manual transmission. The double clutching technique involves the following steps:
 The throttle is released, the clutch pedal is pressed, and the gearbox is shifted into neutral.
 The clutch pedal is then released, the driver matches the engine RPM to the gear RPM either by throttle or
wait for RPM to decrease until they are at a level suitable for shifting into the next gear.
 At the moment when the revs between engine and gear are closely matched, the driver then instantly
depresses the clutch again and shifts into the next gear. The whole maneuver can, with practice, take no more
than a fraction of a second, and the result is a very smooth gear change.
Contents
[hide]
1 Manual transmission
shifting
2 History and theory
3 Heel-and-toe shifting
4 External links
[edit]Manual transmission shifting
In a gearbox with neutral between each gear, a typical shift actually involves two gear changes, once into neutral, and
again into the next gear. During any shift, disconnecting drive components via a clutch properly unloads the engine
and transmission of undue pressure applied by the opposing components. Fully utilizing the clutch for each shift out
of, and then into each gear is double clutching. Due to the absence of a neutral spacing, double clutching is ill-
advised for sequential gear changes, as in a fully sequential gearbox such as a typical motorcycle.
Keeping the clutch pedal pressed while in neutral, as is performed during a typical shift, gives more economy of driver
motion and effort compared to double clutching. Taken to extreme, sequential gearbox shifts and non-clutched shifts
are also very quick and effortless. However, significant wear can take place on the separated clutch plates any time
the engine and transmission have varying drive loads. In simple terms, wear occurs the more the clutch has to "slip"
to match revolutions between the engine and transmission. Double clutching can minimize this clutch plate wear by
encouraging matching of engine and transmission RPMs before the clutch plates are engaged.
[edit]History and theory

Before the introduction of transmission synchronizers (in the 1920s) and helical cut gears, double clutching was a
technique required to prevent damage to an automobile's gear system. Due to the difficulty and most often
unnecessary redundancy involved in learning the technique, coupled with the advent of synchronized gearing
systems, it has largely fallen into disuse. However, drivers of large trucks often use the double clutching technique
when unable to keep the transmission unloaded during shifting, as large vehicles are usually equipped with older,
simpler and more durable unsynchronized gearboxes.
The purpose of the double-clutch technique is to aid in matching the rotational speed of the input shaft being driven
by the engine to the rotational speed of the gear you wish to select (directly connected to rotating wheels). When the
speeds are matched, the gear will engage smoothly and no clutch is required. If the speeds are not matched, the dog
teeth on the collar will "crash" or grate as they attempt to fit into the holes on the desired gear. A modern
synchromesh gearbox accomplishes this synchronization more efficiently. However, when the engine speed is
significantly different than the transmission speed, the desired gear can often not be engaged even in a fully
synchronized gearbox. An example is trying to shift into a gear while travelling outside the gear's speed or directional
range, such as accidentally into 1st from near the top of 2nd, or intentionally from reverse to a forward gear whilst still
moving at speed.
Double clutching, although time consuming, eases gear selection when an extended delay or variance exists
between engine and transmission speeds.
Although double clutching is a testing requirement when obtaining a commercial driver's license, many experienced
truckers have learned when it is possible to shift gears without using the clutch. This is known as float gears or skip
shift, which thus eliminates the clutch except for starting and stopping.
Conversely, in order to shift down, engine RPM must be increased while the gearbox is in neutral and the clutch is
either engaged or disengaged. This requires the driver to shift into neutral, apply throttle to bring the RPM up to a
suitable speed, and finally shift into gear. This operation can be very difficult to master, as it requires the driver to
gauge the speed of the vehicle and throttle accurately. Double clutching occurs if the clutch pedal is released while
matching engine speeds in neutral and again engaged prior to shifting into the next gear.
[edit]Heel-and-toe shifting
A related downshifting technique is called heel-and-toe, in which the brake and accelerator pedals are pressed
simultaneously. Classically, the brake is pressed with the ball of the right foot and the accelerator pedal is controlled
by the right heel, while the clutch pedal is pressed by the left foot. However, many variants are possible, with the
brake and accelerator pressed by sides of the right foot.
Proper heel-and-toe technique aids both slowing the vehicle while at the same time accelerating the engine for a
matched downshift. Note that neglecting to rev-match in any downshifting scenario can be extremely dangerous,
especially in low-traction conditions. Heel-and-Toe may be used with any type of gearbox when simultaneous braking
and downshifting is necessary. Though difficult, mastering the heel-and-toe technique in conjunction with necessary
clutching is essential for high performance driving (e.g., rally racing) to stay in the optimal gear regardless of the
simultaneous braking, accelerating, and clutching required for shifts. This allows the engine to stay in the RPM
"powerband" and allows one to drive as fast as possible. Left foot braking while accelerating the engine with the right
foot to accommodate downshifting in a clutchless situation accomplishes the same feat.
The purpose of the heel-toe-double-clutch is to downshift into the correct gear, and thus optimal engine RPM, for
exiting the corner while placing the least wear and tear on the entire drivetrain. Note that racers will sometimes skip
gears during downshifts depending on the vehicle speed. With double-clutching there is no need to shift through
every gear when significant velocity has been lost.

Double Clutch: This Article Is About The Driving Technique. For The Semi-Automatic Transmission With Two Clutches, See

Uploaded by

Copyright:

Available Formats

Double Clutch: This Article Is About The Driving Technique. For The Semi-Automatic Transmission With Two Clutches, See

Uploaded by

Document Information

Original Description:

Original Title

Copyright

Available Formats

Share this document

Share or Embed Document

Sharing Options

Did you find this document useful?

Is this content inappropriate?

Copyright:

Available Formats

Double Clutch: This Article Is About The Driving Technique. For The Semi-Automatic Transmission With Two Clutches, See

Uploaded by

Copyright:

Available Formats

Double clutch

2 History and theory

advised for sequential gear changes, as in a fully sequential gearbox such as a typical motorcycle.

[edit]History and theory

simpler and more durable unsynchronized gearboxes.

between engine and transmission speeds.

brake and accelerator pressed by sides of the right foot.

foot to accommodate downshifting in a clutchless situation accomplishes the same feat.

every gear when significant velocity has been lost.

You might also like