INTRODUCTION
The purpose of this short guide is to introduce the basic principles of the most common motor, clutch and transmission of the Kombi T1.
On all Carburetor run Kombis, (hence, without injection) one can find this process. This graphic below portrays the carburetor's operation and the different elements' roles.
- 4th gear
- 3rd gear
- 2nd gear
- Front driveshaft
- Reverse gear
- Rear driveshaft
- Throw-out bearing
- Transmission shift selector lever
- 1st gear
- Drive gear
- lateral gear differential
- Differential gear
- Drain plug
- Flywheel
- Crankshaft
- Fan
- Carburetor
- Generator
- Camshaft
- Oil filter
- Camshaft drive gear
- Oil pump
- Valve
- Cylinder head
- Intake manifold
- Ignition coil
- Distributor
- Transmission oil cooler
- Fan housing
- Fuel pump
- Oil fill hole and breather tube
- Spark plug
- Heat exchanger
- Cylinder
- Oil pressure switch
- Overflow and oil pressure valve
- Connecting rod
- Piston
- Thermostat
The mechanical principles of the Volkswagen kombi engine
The mechanics of a VW Kombi are composed of 6 major elements that allow the transformation of accelerator pedal movement into forward moving speed.
The mechanical process of a VW Kombi is as follows:
1-The user presses against the accelerator pedal. This pressure tightens a cable that regulates the intake and proportion of air/gas into the engine. This mixing element is known as the carburetor.
2- The mixture enters the cylinders, generates combustion and creates a rotational movement.
3- This movement is transferred from the engine to the wheels, through the clutch, the transmission and the differential.
Foot movement
Tension on the accelerator cable
Air and fuel mixture introduced
Generation of a rotational mechanical force
Decoupling the engine from transmission
Transfer coupling and rotational speed
Synchronization of wheel speed
Accelerator pedal
Carburetor
Engine
Clutch
Transmission
Differential
THE VOLKSWAGEN KOMBI CARBURETOR
What is the difference between carburetors and fuel injection?
The carburetor and injectors are elements designed to run and control the air and fuel intake into the kombi engine. These latter is equipped with a an injection system and the former uses carburation. These parts are essential to alter the speed of the motor.
The carburetor is a mechanical organ that helps create an adjustable mixture of oxygen and fuel that will be sucked into the combustion chambers by the motor.
In contrast, the injector directly sends a stream of fuel into the combustion chambers while the air is sucked in separately.
Foot movement
Tension on the accelerator cable
Air and fuel mixture introduced
Generation of a rotational mechanical force
Decoupling the engine from transmission
Transfer coupling and rotational speed
Synchronization of wheel speed
Accelerator pedal
Carburetor
Engine
Clutch
Transmission
Differential
How does the kombi carburetor work?
The carburetor’s purpose is to mix air and fuel and control the delivery of this mixture according to the tension of the accelerator cable.
The carburetor is made of 6 elements shown with different colors in the diagram to the left:
- The housing (grey);
- The accelerator cable (black);
- Floating valve (sky-blue);
- Jet needle (green);
- Air (blue and pink fluids)
- Fuel (yellow fluid);
By pulling on the black cable the needle (the green) moves up, which gradually increases air delivery (small blue and pink channel). This results in a change in fuel volume (the blue floating valve regulates this) and leads to an increase in pressure, allowing fuel to be sucked in from the tank. The fuel travels along the yellow channel, mixes with the air and goes back into the main channel found on the right side of the diagram.
The floater valve (the sky-blue component) regulates the fuel intake through a regulated suction pressure. It is the movement of the accelerator cable on the carburetor that is controlled by your foot on the accelerator pedal that regulates the delivery of the air/fuel mixture, to ultimately change the speed and rotations of the engine.
THE VOLKSWAGEN KOMBI ENGINE
The different parts of a Kombi engine
- The combustion chamber is the cylindrical part with a variable calibrated volume in which the gases will be burned off. The intake and exhaust valves are the “doors” that allow the gases to enter or exit the combustion chamber.
- The spark-plug is for igniting the air/fuel mixture coming from the intake valves.
- The piston is a solid cylinder inside the cylinder that separates the combustion chamber from the mechanical parts of the engine. It is thanks to this part that the pressure forces are transferred to make the engine turn.
- The connecting rod is the part responsible for transforming the movement of the piston to rotate the crankshaft.
- The crankshaft is the part that spans through the whole engine. Is is connected to other cylinders to transfer the rotational movement to the transmission.
Foot movement
Tension on the accelerator cable
Air and fuel mixture introduced
Generation of a mechanical rotational force
Decoupling the engine from transmission
Transfer coupling and rotational speed
Synchronization of wheel speed
Accelerator pedal
Carburetor
Engine
Clutch
Transmission
Differential
How does a 4-stroke engine work?
The fundamentals of a 4-stroke ignition engine are relatively simple. The air/fuel mixture is highly compressed by the piston. The sparkplug creates a spark that ignites the compressed gas that pushes forcefully against the piston. Consequently, this movement moves the crankshaft, engaging the mechanical system that turns the wheels and makes the vehicle go forward.
In this 4-stroke engine, the piston must move up and down twice to move the connecting rod once. To enable the 4-stroke cycle, the values must open and close. This synchronization is carried out by the camshaft. This is the purpose of the distribution system.
To prevent friction and seizing, the moving pieces must be greased. This is the purpose of the lubrication system.
It is essential to discharge some of the heat during combustion to maintain the integrity of the engine parts. This is known as the cooling system.
There are also a specific number of parts that bring air and fuel into the engine, known as the fuel system.
In the old days, one needed to turn a starting handle three-quarters of a turn to start the engine. In effect, it was the last quarter turn that sparked ignition. Since then, the engine sparks thanks to a small electric motor connected to the battery.
Stroke 1: Intake
The intake valve opens and the piston goes down, while sucking in the air/fuel mixture coming from the carburetor.
Stroke 2: Compression
The intake and exhaust valves close and the piston goes up compressing the air/ fuel mixture.
Stroke 3: Combustion
With both valves closed, the spark-plug emits a spark that causes an explosion of the mixture. The pressure from the explosion enables the piston to go down again. This movement cycles the engine.
Stroke 4: Exhaust
The exhaust valve opens and the piston goes up allowing the burnt gases to exit through the tailpipe.
THE VOLKSWAGEN KOMBI CLUTCH
Even though the architecture of the clutch seems to be rather complex, the basics are quite simple. Its function is to separate or bind the output shaft from the engine to the shaft connected to the transmission
To change gears, you push down the clutch pedal that decouples these two shafts allowing you to shift. When you take your foot off the pedal the two shafts reengage to transfer the rotational movement. This coupling is done by rubbing different disks (pressure, smooth, conical) that are part of the transmission shaft and the shaft exiting the engine. The pressure springs help control the friction necessary to couple the two shafts.
Foot Movement
Tension on the accelerator cable
Air and fuel mixture introduced
Generation of a mechanical rotational force
Decoupling the engine from transmission
Transfer coupling and rotational speed
Synchronization of wheel speed
Accelerator pedal
Carburetor
Engine
Clutch
Transmission
Differential
THE VOLKSWAGEN KOMBI TRANSMISSION
The transmission is a mechanical part that enables the transferal of movement between the engine shaft and the drive shaft with the help of gears. By increasing the reduction ratio of these gears, the moving parts turn faster, increasing the torque and reducing the engine rotations (by decreasing the reduction ratio, the inverse effect is observed).
The idler sprockets turn loosely (not connected to the shaft). The clutches select gears. When we move the gear shifter, we act on these clutches. The clutch moves onto an idler sprocket. This action will connect the gearwheel to the shaft and consequently change gears. In order to unite these two parts, the primary shaft from the transmission and the engine shaft must be disconnected. That’s where the clutch comes in.
Foot movement
Tension on the accelerator cable
Air and fuel mixture introduced
Generation of a mechanical rotational force
Decoupling the engine from transmission
Transfer coupling and rotational speed
Synchronization of wheel speed
Accelerator pedal
Carburetor
Engine
Clutch
Transmission
Differential
THE VOLKSWAGEN KOMBI DIFFERENTIAL
During a turn on the road, the inner wheel travels less distance than the outer wheel. This creates driving instabilities like friction and undesired wear on the pneumatic system. To counter these events, the rotational speed of the wheels must be shared in an adaptive, immediate and automatic fashion.
The differential is a part on the axle of each wheel set that addresses these issues. It is made of a conical gearwheel (apart from the engine shaft) connected perpendicularly to a conical gear ring supporting a Rotating cage that engages two planetary gears separated from the moving axles.
Foot movement
Tension on the accelerator pedal
Air and fuel mixture introduced
Generation of a mechanical rotational force
Decoupling the engine from transmission
Transfer coupling and rotational speed
Synchronization of wheel speed
Accelerator pedal
Carburetor
Engine
Clutch
Transmission
Differential
Case 1: The two wheels turn at the same speed
The two wheels sustain the same level of force. The central cog is immobile and the two wheels turn at the same speed.
In the figure the two output shafts (The left in red and the right in yellow) turn at the same speed. Thus, the rotational force is split equally and the intermediate cog (in green, also known as the satellite gear) does not turn.
Case 2: The left wheel is immobile
As the left wheel is blocked, only the right is turning by the central cog. In the image, the red shaft is slowed down. The middle cog is now moving and transferring an additional rotational force to the yellow shaft that turns at a higher speed.
