Electrical System - Volvo 120 Operating & Service Manual

DESCRIPTION
Engine
The engine is a four-cylinder carburettor unit with overhead valves. The
pistons are made of light-alloy and the upper compression rings on
each piston are chromed. The main bearing and big-end bearing shells
are replaceable. The crankshaft is statically and dynamically balanced.
Engine type B 20 A has an output of 90 h.p. (SAE) and is equipped with
a Zenith-Stromberg horizontal carburettor. (On certain markets SU hori-
zontal carburettor.)
Engine type B 20 B has an output of 118 h.p. (SAE) and is equipped
with twin SU horizontal carburettors. (On certain markets twin Zenith-
Stromberg horizontal carburettors.)
Fuel system
Fuel is fed from the tank to the carburettor by a fuel pump which is
driven by a cam on the engine camshaft. There is a filter in the fuel
pump which traps water and other impurities in the fuel.
Exhaust emission control
The engine is fitted with exhaust emission control, that is, a system as a
result of better mixing and distributing of fuel and air provides a more
complete combustion and thereby cleaner exhaust gases. On the B 20 A
engine, the exhaust emission control is obtained through the carburettor
which is specially designed for this purpose. On the B 20 B engine the
exhaust emission control is provided partly through carburettors specially
designed for this purpose and partly by the engine having a special in-
duction manifold with throttles and preheating chamber. When driving at
l ow speeds the throttles are closed so that the fuel-air mixture is forced
to pass the preheating chamber.
When higher output is required, the throttles open so that the fuel-air
mixture flows directly to the cylinders.
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Air preheating
Certain variations of the 120 models are provided with thermostatically
controlled air preheating.
With this arrangement the induced air is maintained at a constant, favour-
able temperature. Air preheating counteracts ice formation in the car-
burettor and also contributes to a shorter warming up period after start-
i ng from cold.
Lubricating system
The engine lubrication is taken care of by a gear pump which sucks up
oil from the sump on the bottom of the engine and forces it through the
oil filter out to the lubricating points in the engine. A relief valve is built
It
i nto the oil filter which prevents the oil pressure from reaching exces-
sively high values.
Cooling system
The engine is water-cooled and the cooling system is of the pressure
type. Water is circulated by means of a pump fitted on the fan shaft.
A wax-type thermostat with an opening temperature of about 82
(180 F) prevents the cooling water from passing through the radiator
°
before the engine has reached its normal working temperature. On
certain markets a fan with a slip-type coupling is fitted.

Electrical system

The electrical system is of the 12-volt type and is fitted with a voltage-
regulated alternator. The starter motor is operated from the instrument
panel by the ignition key, which also switches on the rest of the electrical
system. The cables to the headlights, parking lights and internal lighting,
however, are not taken over the ignition switch but can be switched on
and off without the ignition key being in position.
DESCRIPTION
C
°
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