Generac Power Systems 941-2, 940-2 Section GENERAL INFORMATION, Cycle Engine Theory, Introduction

Section 2.1

GENERAL INFORMATION

INTRODUCTION

The engine used on Impact 36 plus Series recreational vehicle AC generators is a Generac Series GV-220, vertical shaft, single cylinder, overhead valve type.

These engines are not equipped with a mechanical engine governor. Instead. variable engine speeds are controlled by a computer circuit board. The circuit board signals a stepper motor to move the carburetor throttle linkage.

4-CYCLE ENGINE THEORY

GENERAL:

Series GV-220 engines require four (4) strokes or cycles to complete one power cycle. This is often called the "4-stroke, 5-event" cycle. The 4 strokes and 5 events that occur are (1) Intake, (2) compression,

(3) Ignition, (4) power and (5) exhaust

INTAKE STROKE (FIGURE 1):

The intake valve is open. The exhaust valve is closed. The piston travels downward, creating a suction which draws the air-fuel mixture from the carburetor into the cylinder and just above the piston.

COMPRESSION STROKE (FIGURE 2):

As the piston reaches bottom dead center (BDC), the intake valve closes. The exhaust valve remains closed, as well. The piston starts to move outward in the cylinder. Since both valves are closed, the air-fuel mixture in the cylinder is compressed.

POWER STROKE (FIGURE 3):

Both valves remain closed. At some point before the piston reached top dead center (TDC), the spark plug fires to Ignite the fuel-air mixture. The piston moves to its top dead center position and the burning, expand- ing gases of combustion force the piston downward.

EXHAUST STROKE (FIGURE 4):

The expanding gases of combustion force the piston downward to its bottom dead center (BDC) position. The exhaust valve then opens, as the piston starts its movement toward top dead center (TDC). Piston movement then forces the exhaust gases out through the open exhaust valve. The 4-stroke cycle of events then starts over again.

Figure 1. Intake Stroke

Figure 2. Compression Stroke

Figure 3. Power Stroke

Figure 4. Exhaust Stroke

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