GF83.55-D-2108H Component Description of Refrigerant Compressor
GF83.55-D-2108H Component Description Of Refrigerant Compressor
- with CODE (HH9) Regulated air conditioning (Tempmatic)
Shown on engine OM 646
A9 Refrigerant compressor
Shown on engine OM 642
A9 Refrigerant compressor
Shown on engine M 272
A9 Refrigerant compressor
Location
With all engine variants, the refrigerant compressor is located on the left on the engine block.
Task
The refrigerant compressor draws in the refrigerant vapor via the low pressure side, compresses the refrigerant, and returns it again as a liquid under high pressure to the high pressure side.
Design and function of the refrigerant compressor (A9)
9/1 Belt pulley
9/2 Crankcase
9/3 Alignment pin
9/4 Swash plate
9/5 Damping reservoir (pressure side)
9/6 Piston
9/7 Damping reservoir (suction side)
9/9 Valve plate
9/10 Coil body
9/11 Sliding shoe
9/12 Stop plate
9/13 Refrigerant compressor shaft
A9 Refrigerant compressor
A9y1 Refrigerant compressor control valve
Work mechanism function
The rotary motion of the belt pulley is transmitted to the stop plate via the refrigerant compressor shaft. The rotation of the stop plate is transmitted to the pivoted swash plate by means of a hinged mechanism. The rotary motion of the swash plate is converted into the oscillating motion of the pistons by means of 2 sliding shoes between the pistons and the swash plate. 7 pistons are connected at the same distance on the circumference to the swash plate. The damping reservoir (pressure side) and the damping reservoir (suction side) reduce gas pulsation in the refrigerant compressor by providing a uniform flow of refrigerant. This helps to prevent noises in the compression process
Switch off air conditioning function
If the air conditioning is governed or switched off using the AC OFF and residual heat system button (S98s4), the refrigerant compressor control valve is fully open. Refrigerant flows unimpeded from the high pressure side into the crankcase, leading to an extremely rapid increase in the crankcase pressure. As a result, the coil body is moved to the right against the valve plate and fully seals off the refrigerant flow via the suction side of the refrigerant compressor.
The coil body is designed so that, when the refrigerant compressor is switched on and when the delivery rate is less than 5 cm3 , the flow of refrigerant is interrupted by closing the intake passage.
Internal lubrication of the refrigerant compressor when the air conditioning is switched off
The refrigerant compressor is equipped with an internal lubrication circulation to ensure that the following mechanically moving parts are properly lubricated:
- Swash plate
- Piston
- Sliding shoe
- Front and rear radial shaft bearing
Lubrication is ensured by way of a minimum refrigerant compressor delivery rate. This delivery rate is regulated by the refrigerant compressor control valve.
The minimum delivery rate of 2 % of the refrigerant compressor when the refrigerant compressor is switched off causes the refrigerant to be transported together with the compressor oil located in the crankcase through the holes of the refrigerant compressor shaft.
Design and function of the refrigerant compressor control valve (A9y1)
9/16 Bypass
9/17 Control plunger
Pc Crankcase pressure
Pd High pressure
mhp Suction pressure
Ps1 Membrane pressure
A9y1 Refrigerant compressor control valve
Function of the volume control mechanism
The refrigerant compressor control valve regulates the output of the refrigerant compressor, which can be between 2 % (minimum swept volume) and 100 % (maximum swept volume). Depending on the refrigerating capacity required, the corresponding regulating current is sent to the refrigerant compressor control valve via the AAC [KLA] control and operating unit (S98). The required refrigeration capacity is essentially determined by the specified values for the interior temperature of the vehicle, the value of the Interior temperature sensor (S98b1) or of the rear interior air temperature sensor ventilation blower (M9/1), with code (HH7) Additional air conditioning in rear or with code (H08) High-performance air conditioning, and the value of the outside air temperature sensor (B14), with code (J65) Outside temperature indicator. The position of the swash plate and thus the variable swept volume is in principle determined by the crankcase pressure, the diaphragm pressure in the refrigerant compressor control valve and the suction pressure.
The change in suction pressure as a function of the regulating current on the refrigerant compressor control valve causes a change in the crankcase pressure and thus the adjustment of the swash plate in the direction either of a variable swept volume or a maximum swept volume.
Function of variable volume control in the partial-load range via the refrigerant compressor control valve (e.g. in the event of low outside temperatures or low refrigerating capacity required)
In principle, the cooling capacity is dependent on the intake pressure. If the suction pressure drops below the diaphragm pressure in the refrigerant compressor control valve and the regulating current is reduced at the same time, the passage from high pressure to crankcase pressure in the refrigerant compressor control valve is released by the control plunger. As a result, the refrigerant flows from the high pressure side into the crankcase. This causes an increase in the crankcase pressure.
The sum of the forces on the left side of the swash plate resulting from the crankcase pressure, the return force of the swash plate (centrifugal force) and the spring return force becomes higher than the sum of the forces of the pistons. As a result, the swash plate moves into a vertical position, leading to a reduction in the strokes and the swept volume.
The refrigerant compressor is automatically switched off at a volumetric flow of less than 5 cm3
Function of the refrigerant compressor control valve actuation with maximum swept volume (e.g. in the event of high outside temperatures or high refrigerating capacity required).
If the suction pressure rises above the diaphragm pressure in the refrigerant compressor control valve and the regulating current is increased at the same time, the passage from high pressure to crankcase pressure in the refrigerant compressor control valve is closed by the control plunger. The crankcase pressure drops, as no refrigerant flows from the high pressure side into the crankcase via the refrigerant compressor control valve. In the long-term, the bypass sets up a pressure compensation between the suction pressure and crankcase pressure, i.e. the reaction force on the left side from the crankcase pressure, the return force of the swash plate (centrifugal force) and the spring return force is thus smaller than the sum of the piston forces.
The angle of the swash plate increases from the "0-position", in other words the inclined position of the swash plate increases continuously until the swash plate reaches the mechanical limit at the stop plate. The strokes increase linearly as the swash plate inclines until the maximum delivery rate is reached.
Design and function of the belt pulley (9/1)
9/1 Belt pulley
9/14 Hub
9/15 Rubber
The belt pulley drives the refrigerant compressor and at the same time serves as a torque damper and torque limiter.
The hub is permanently connected to the refrigerant compressor shaft and via the rubbers to the belt pulley. If the refrigerant compressor has a tendency to lock up, the belt pulley continues to rotate and the rubbers are deformed. In this case, the rubbers act as belt protectors, since the hub and thus the refrigerant compressor shaft of the locked-up refrigerant compressor stand still.
Design and function of the pressure relief valve (9/16)
9/16 Pressure relief valve
A9 Refrigerant compressor
The pressure relief valve serves to protect the refrigerant circuit from damage caused by excess pressure. It is designed as a spring-loaded pressure relief valve and opens up in the event of a refrigerant pressure of > 40 bar.