变速器英文版文献

2021年1月26日发(作者：severely)

Transmission (mechanics)

A
transmission
or
gearbox
provides
speed
and
torque
conversions
from
a
rotating
power
source
to
another
device
using
gear
ratios.
In
British
English
the
term
transmission
refers
to
the
whole
drive
train,
including
gearbox,
clutch,
prop
shaft
(for
rear-wheel
drive),
differential
and final drive shafts. The most common use is in motor vehicles, where
the
transmission
adapts
the
output
of
the
internal
combustion
engine
to
the
drive
wheels.
Such
engines
need
to
operate
at
a
relatively
high
rotational speed, which is inappropriate for starting, stopping, and slower
travel.
The
transmission
reduces
the
higher
engine
speed
to
the
slower
wheel
speed,
increasing
torque
in
the
process.
Transmissions
are
also
used
on
pedal
bicycles,
fixed
machines,
and
anywhere
else
rotational
speed and torque needs to be adapted.
Often,
a
transmission
will
have
multiple
gear
ratios
(or
simply

with
the
ability
to
switch
between
them
as
speed
varies.
This
switching
may
be
done
manually
(by
the
operator),
or
automatically.
Directional
(forward
and
reverse)
control
may
also
be
provided.
Single-ratio transmissions also exist, which simply change the speed and
torque (and sometimes direction) of motor output.

In
motor
vehicle
applications,
the
transmission
will
generally
be
connected to the crankshaft of the engine. The output of the transmission
is
transmitted
via
driveshaft
to
one
or
more
differentials,
which
in
turn
drive the wheels. While a differential may also provide gear reduction, its
primary purpose is to change the direction of rotation.
Conventional gear/belt transmissions are not the only mechanism for
speed/torque
adaptation.
Alternative
mechanisms
include
torque
converters
and
power
transformation
(e.g.,
diesel-electric
transmission,
hydraulic drive system, etc.). Hybrid configurations also exist.

Explanation
Early transmissions included the right-angle drives and other gearing
in
windmills,
horse-powered
devices,
and
steam
engines,
in
support
of
pumping, milling, and hoisting.
Most modern gearboxes are used to increase torque while reducing
the speed of a prime mover output shaft (e.g. a motor crankshaft). This
means that the output shaft of a gearbox will rotate at slower rate than the
input
shaft,
and
this
reduction
in
speed
will
produce
a
mechanical
advantage, causing an increase in torque. A gearbox can be setup to do
the
opposite and provide an increase in
shaft
speed
with
a reduction of
torque.
Some
of
the
simplest
gearboxes
merely
change
the
physical
direction in which power is transmitted.
Many typical automobile transmissions include the ability to select
one of several different gear ratios. In this case, most of the gear ratios
(often simply called
the
engine
and
increase
torque.
However,
the
highest
gears
may
be


Uses
Gearboxes
have
found
use
in
a
wide
variety
of
different
—
often
stationary
—
applications, such as wind turbines.
Transmissions
are
also
used
in
agricultural,
industrial,
construction,
mining
and
automotive
equipment.
In
addition
to
ordinary
transmission
equipped
with
gears,
such
equipment
makes
extensive
use
of
the
hydrostatic drive and electrical adjustable- speed drives.

Simple
The
simplest
transmissions,
often
called
gearboxes
to
reflect
their
simplicity
(although
complex
systems
are
also
called
gearboxes
in
the
vernacular), provide gear reduction (or, more rarely, an increase in speed),
sometimes
in
conjunction
with
a
right-angle
change
in
direction
of
the
shaft
(typically
in
helicopters,
see
picture).
These
are
often
used
on
PTO-powered agricultural equipment, since the axial PTO shaft is at odds
with the usual need for the driven shaft, which is either vertical (as with
rotary mowers), or horizontally extending from one side of the implement
to another (as with manure spreaders, flail mowers, and forage wagons).
More
complex
equipment,
such
as
silage
choppers
and
snowblowers,
have drives with outputs in more than one direction.
The
gearbox
in
a
wind
turbine
converts
the
slow,
high-torque
rotation of the turbine into much faster rotation of the electrical generator.
These are much larger and more complicated than the PTO gearboxes in
farm
equipment.
They
weigh
several
tons
and
typically
contain
three
stages to achieve an overall gear ratio from 40:1 to over 100:1, depending
on the size of the turbine. (For aerodynamic and structural reasons, larger
turbines have to turn more slowly, but the generators all have to rotate at
similar speeds of several thousand rpm.) The first stage of the gearbox is
usually a planetary gear, for compactness, and to distribute the enormous
torque of the turbine over more teeth of the low-speed shaft. Durability of
these gearboxes has been a serious problem for a long time.

Regardless
of
where
they
are
used,
these
simple
transmissions
all
share an important feature: the gear ratio cannot be changed during use. It
is fixed at the time the transmission is constructed.
For
transmission
types
that
overcome
this
issue,
see
Continuously
Variable Transmission, also known as CVT.

Multi-ratio systems
Many
applications
require
the
availability
of
multiple
gear
ratios.
Often,
this is
to
ease
the
starting
and
stopping of
a
mechanical
system,
though another important need is that of maintaining good fuel efficiency.

Automotive basics
The need for a transmission in an automobile is a consequence of the
characteristics
of
the
internal
combustion
engine.
Engines
typically
operate over a range of 600 to about 7000 revolutions per minute (though
this varies, and is typically less for diesel engines), while the car's wheels
rotate between 0 rpm and around 1800 rpm.
Furthermore,
the
engine
provides
its
highest
torque
outputs
approximately in the middle of its range, while often the greatest torque is
required
when
the
vehicle
is
moving
from
rest
or
traveling
slowly.
Therefore,
a
system
that
transforms
the
engine's
output
so
that
it
can
supply high torque at low speeds, but also operate at highway speeds with
the
motor
still
operating
within
its
limits,
is
required.
Transmissions
perform this transformation.
Many
transmissions
and
gears
used
in
automotive
and
truck
applications
are
contained
in
a
cast
iron
case,
though
more
frequently
aluminium is used for lower weight especially in cars. There are usually
three shafts: a mainshaft, a countershaft, and an idler shaft.
The mainshaft extends outside the case in both directions: the input
shaft towards the engine, and the output shaft towards the rear axle (on
rear wheel drive cars- front wheel drives generally have the engine and
transmission
mounted
transversely,
the
differential
being
part
of
the
transmission assembly.) The shaft is suspended by the main bearings, and
is
split
towards
the
input
end.
At
the
point
of
the
split,
a
pilot
bearing
holds the shafts together. The gears and
clutches ride on the mainshaft,
the gears being free to turn relative to the mainshaft except when engaged
by the clutches.
Types
of
automobile
transmissions
include
manual,
automatic
or
semi- automatic transmission.

Manual
Main article: Manual transmission
Manual
transmission
come
in
two
basic
types:a
simple
but
rugged
sliding-mesh
or
unsynchronized
/
non-synchronous
system,
where
straight-cut spur gear sets are spinning freely, and must be synchronized
by the operator matching engine revs to road speed, to avoid noisy and
damaging

clash
and
the
now
common
constant-mesh
gearboxes
which
can
include
non-synchronised,
or
synchronized
/
synchromesh
systems, where diagonal cut helical (and sometimes double-helical) gear
sets
are
constantly

together,
and
a
dog
clutch
is
used
for
changing gears. On synchromesh boxes, friction cones or
are used in addition to the dog clutch.

The former type is commonly found in many forms of racing cars,
older heavy-duty trucks, and some agricultural equipment.
Manual transmissions are the most common type outside North America
and Australia. They are cheaper, lighter, usually give better performance,
and
fuel
efficiency
(although
the
latest
sophisticated
automatic
transmissions
may
yield
results
slightly
better
than
the
ones
yielded
by
manual
transmissions).
It
is
customary
for
new
drivers
to
learn,
and
be
tested,
on
a
car
with
a
manual
gear
change.
In
Malaysia,
Denmark
and
Poland
all
cars
used
for
testing
(and
because of
that,
virtually
all
those
used
for
instruction
as
well)
have
a
manual
transmission.
In
Japan,
the
Philippines,
Germany,
Italy,
Israel,
the
Netherlands,
Belgium,
New
Zealand,
Austria,
Bulgaria,
the
UK,
Ireland,
Sweden,
Estonia,
France,
Spain,
Switzerland,
the
Australian
states
of
Victoria
and
Queensland,
Finland and Lithuania, a test pass using an automatic car does not entitle
the driver to use a manual car on the public road; a test with a manual car
is transmissions are much more common than automatic
transmissions in Asia, Africa, South America and Europe.
Most
manual
transmissions
include
both
synchronized
and
unsynchronized gearing, such as a reverse gear and a low-speed
gear
granny
gear
to
a
low
synchronized
gear
is
generally
available
while
in
motion, while shifting out of reverse to any other gear typically requires
the vehicle to be stopped.

Non-synchronous
Main article: Non- synchronous transmissions
There
are
commercial
applications
engineered
with
designs
taking
into account that the gear shifting will be done by an experienced operator.
They
are
a
manual
transmission,
but
are
known
as
non-synchronized
transmissions. Dependent on country of operation, many local, regional,
and
national
laws
govern
the
operation
of
these
types
of
vehicles
(see
Commercial
Driver's
License).
This
class
may
include
commercial,
military,
agricultural,
or
engineering
vehicles.
Some
of
these
may
use
combinations of types for multi- purpose functions. An example would be
a
PTO,
or
power-take-off
gear.
The
non-synchronous
transmission
type
requires
an
understanding
of
gear
range,
torque,
engine
power,
and
multi-functional clutch and shifter functions. Also see Double-clutching,
and
Clutch-brake
sections
of
the
main
article
at
non- synchronous
transmissions

Automatic
Main article: Automatic transmission
Epicyclic
gearing
or
planetary
gearing
as
used
in
an
automatic
transmission.
Most modern North American and Australian and many larger, high
specification European and Japanese cars have an automatic transmission
that will select an appropriate gear ratio without any operator intervention.
They
primarily
use
hydraulics
to
select
gears,
depending
on
pressure
exerted
by
fluid
within
the
transmission
assembly.
Rather
than
using
a
clutch to engage the transmission, a fluid flywheel, or torque converter is
placed
in
between
the
engine
and
transmission.
It
is
possible
for
the
driver
to
control
the
number
of
gears
in
use
or
select
reverse,
though
precise control of which gear is in use may or may not be possible.
Automatic
transmissions
are
easy
to
use.
However,
in
the
past,
automatic transmissions of this type have had a number of problems; they
were complex and expensive, sometimes had reliability problems (which
sometimes
caused
more
expenses
in
repair),
have
often
been
less
fuel-efficient
than
their
manual
counterparts
(due
to

in
the
torque converter), and their shift time was slower than a manual making
them
uncompetitive
for
racing.
With
the
advancement
of
modern
automatic transmissions this has changed.
Attempts to improve the fuel efficiency of automatic transmissions
include the use of torque converters which lock up beyond a certain speed,
or in the higher gear ratios, eliminating power loss, and overdrive gears
which automatically actuate above certain speeds; in older transmissions