[ Pobierz całość w formacie PDF ]
2
B
A
How to Use this Catalogue
Date
The date is listed in short code format,
i.e. Month/Year (01.98 = January 1998), with
an approximate manufacture/ introduction date
to last manufacture / sale date.
A
Example
0 120 006 001 is not available as a stock unit, but can be obtained from Germany upon request.
BX..... readily available as a stock item.
B
A
3
Alternator Systems
Design criteria
The following data are decisive for alternator design:
–Vehicle type and the associated operating condi-
tions,
– Speed range of the engine with which the alterna-
tor is to be used,
–Battery voltage of the vehicle electrical system,
–Power requirements of the loads which can be
connected,
– Environmental loading imposed on the alternator
(heat, dirt, dampness, etc.),
– Specified service life,
–Available installation space, dimensions.
The requirements to be met by an automotive alter-
nator differ very considerably depending upon appli-
cation and the criteria as listed above. Regarding
economic efficiency the criteria also vary along with
the areas of application.
It is therefore impossible to design an all-purpose
alternator which meets all requirements.
The different areas of application, and the power
ranges of the vehicle types and engines concerned,
led to the development of a number of basic models
which will be described in the following.
The different alternator sizes are identified by a letter
of the alphabet, and increase in alphabetical order.
A further important feature is the alternator or rotor
system (e.g., claw-pole alternator as a compact alter-
nator or alternator with compact diode assembly, or
with salient-pole rotor or windingless rotor).
This characteristic is identified by numbers or letters.
In addition, the various alternators are identified by
an alphanumeric code e.g., GC, KC, NC, G1, K1,
N1 for passenger cars, and K1, N1, T1 for commer-
cial vehicles and buses.
Further variations are possible with regard to the
type of mounting, the fan shape, the pulley, and the
electrical connections.
A
Table 1. Alternator types
Design
Application
Type No. of
poles
Compact Passenger cars,
GC, 12
motorcycles
KC,
NC
Compact Passenger cars,
G1
diode commercial vehicles,
assembly
tractors, motorcycles
Passenger cars,
Electrical data and sizes
The vehicle size is not decisive for determining the
required alternator output power. This is solely a
function of the loads installed in the vehicle.
The selection of the correct alternator is governed
primarily by:
– the alternator voltage (14V/28V),
– the power output as a product of voltage and cur-
rent throughout the rotational-speed range,
– the maximum current,
– the cutting-in speed.
With these electrical data, it is possible to define the
electrical layout, and therefore the required alterna-
tor size.
K1,
commercial vehicles,
N1
tractors, motorcycles
4
B
A
Alternators
(continued)
A
Fig. 1: Alternator types
1. Compact claw-pole alternator (KC)
2. Claw-pole alternator with compact diode assembly (N1)
1
2
B
A
5
Alternators
(continued)
Characteristic curves
Alternator performance
The characteristic performance of the alternator at
a variety of different speeds is shown by the
characteristic curves. Due to the constant
transmission ratio between alternator and engine,
the alternator must be able to operate at greatly
differing speeds.
As the engine takes the alternator from standstill up
to maximum speed, the alternator passes through
certain speeds. Each of these rotational speeds is
of particular importance for understanding the
alternator’s operation and each has therefore been
allocated a specific name.
Normally, the curves for alternator current and drive
power are shown as a function of the rotational
speed (Fig. 2).
The characteristic curves of an alternator are always
referred to a constant voltage and precisely defined
temperature conditions. For instance, an ambient
temperature of 80°C (or a room temperature of
23°C) is specified for the limit-temperature test.
A
6
B
A
Alternators
(continued)
Characteristic curves
A
Current characteristic curve (
I
)
n
0
0-Ampere speed
The 0-Ampere speed is the speed (approx.
1000min
–1
) at which the alternator reaches its rated
voltage without delivering power. This is the speed
at which the curve crosses the min
–1
abscissa.
The alternator can only deliver power at higher
speeds.
n
A
Cutting-in speed
The cutting-in speed is defined as that speed at
which the alternator starts to deliver current when
the speed is increased for the first time. It is above
the idle speed, and depends upon the preexcitation
power, the rotor’s remanence, the battery voltage,
and the rate of rotational-speed change.
Characteristic curve of power input (
P
1
)
The characteristic curve of power input is decisive
for drive-belt calculations.
Information can be taken from this curve concerning
the maximum power which must be taken from the
engine to drive the alternator at a given speed.
In addition, the power input and power output can
be used to calculate the alternator’s efficiency. The
example in Fig. 2 shows that after a gradual rise in
the medium speed range, the characteristic curve for
power input rises again sharply at higher speeds.
This is due to the increased power required to drive
the fan at higher speeds.
n
L
Speed with engine idling
I
L
Current with engine idling
With the speed increasing, alternator speed
n
L
is
reached with the engine at idle. This point is shown
as an area in Fig. 1 since the precise value depends
upon the transmission ratio between engine and
alternator. At this speed, the alternator must deliver
at least the current required for the long-term con-
sumers. This value is given in the alternator’s type
designation. In the case of compact-diode-assembly
alternators,
n
L
=1500 min
–1
, for compact alterna-
n
N
Speed at rated current
I
N
Rated current
The speed at which the alternator generates its
rated current is stipulated as
n
N
= 6000 min
–1
.
The rated current should always be higher than the
total current required by all loads together. It is also
given in the type designation.
Explanation of the type designation
Every Bosch alternator carries a rating plate contain-
ing type designation and 10-digit Part Number which
in the case of alternators always starts with 0 12...
... .
The type designation gives information on the alter-
nator’s most important technical data such as cur-
rent at engine idle and rated voltage etc.
n
max
Maximum speed
l
max
Maximum current
l
max
is the maximum achievable current at the alter-
nator’s maximum speed.
Maximum speed is limited by the rolling bearings
and the carbon brushes as well as by the fan. With
compact alternators it is 18,000 . . . 20,000 min
–1
,
and for compact-diode-assembly alternators 15,000
... 18,000 min
–1
. In the case of commercial vehi-
cles, it is 8,000 ... 15,000 min
–1
depending upon
alternator size.
Example of a type designation
K C (
) 14V 40-70A
K
Alternator size
(stator OD),
C
Compact-Alternator,
) Direction of rotation, clockwise,
14V Alternator voltage,
40A Current at
n
= 1800 min
–1
,
70A Current at
n
= 6000 min
–1
.
tors
n
L
=1800 min
–1
due to the usually higher
transmission ratio.
(
[ Pobierz całość w formacie PDF ]