Electric vehicle climate control, function

D83.00-A002-79

Function requirements for electric vehicle climate control, general

 Control functions: Tml. 15 ON

 Automatic air conditioning activated

 Powertrain operational ("READY" status)

Electric vehicle climate control, general

The electronic ignition lock (EZS) control unit (N73/8) sends the status of terminal 15 to the automatic air conditioning control and operating unit (N22/2).

The powertrain control unit (N127) sends the "Electric drive READY" signal to the automatic air conditioning control and operating unit.

The heater control and ventilation are performed by the automatic air conditioning control and operating unit.

After system start, the thermal management automatically controls the temperatures of the vehicle interior, the high-voltage battery and electrical component parts. With the determined temperature values and the special function of this system a "heat-pump function" can be used to heat up the water.

Regulation of the "heat pump" system has been designed so that a coefficient of performance of between  1.5 and 2.5 is achieved in closed-loop operation through the use of waste heat from the high-voltage batteries and/or available energy from the environment.

As a result, the energy from the high-voltage batteries that is consumed to control the temperatures of the vehicle interior and the high-voltage battery is reduced, thus increasing the range of the vehicle.

 The coefficient of performance describes the relationship of the dissipated heat output to the consumed electrical power of the heat pump.

An important part of the system is the electric refrigerant compressor (A9/6) in the engine compartment. Due to the lack of engine noise from a combustion engine, it may be possible under certain circumstances to hear other noises, such as those from the electric refrigerant compressor, more clearly.

 Detailed information on the cooling and the thermal management is available in the separate function description for the "High-voltage on-board electrical system cooling function".

The climate control function comprises the following subfunctions:

 Ventilation system, function

 Refrigerant circuit, function

 Climate control regulation

D83.10-A008-79

Additional air vents
The code FJ6 (Center area with 2 DIN stowage compartments and air vent) contains two DIN stowage compartments and two additional air vents for improved air distribution in the center area of the instrument panel. The equipment is available as an option.

D68.10-A000-80

Ventilation system, function

The front ventilation ensures aeration of the front vehicle interior (air circulation) and also ensures the following conditions:

 the windshield and windows are kept defogged

 there is a good oxygen supply to occupants

 Constant and pleasant temperatures are quickly achieved in the front vehicle interior

Ventilation can occur in one of the following operating modes:

 Fresh air mode

 Recirculated air mode

Selection of fresh air mode or air recirculation mode is controlled using the following buttons:

 Air recirculation button (N22/2s8)

 Air distribution button (N22/2s5)

The buttons are integrated into the automatic air conditioning control and operating unit.

The flow rate is increased or reduced through the various blower setting variants of the fresh air/recirculated air flap actuator motor (M2/5) and the blend air flap actuator motors (M2 M2/6,/7) through the electronic blower regulator (N29).

The drawn in fresh or recirculated air in the front vehicle interior is then distributed to match the request for air distribution through the following air outlets:

 Left and right side window defroster vent

 Swiveling left and right side air vents

 Swiveling center air vents at left and right (with code FJ6 (Center area with 2-DIN stowage compartments and air vent))

 Right and left footwell air outlets

 Windshield defroster vents

The ventilation function comprises the following subfunctions:

 Fresh air mode

 Recirculated air mode

 Actuation of the air duct flaps

Fresh air mode

The fresh air mode is activated when the LED in air recirculation button is not on. The fresh air/recirculated air flap actuator motor (M2/5) puts the fresh air/recirculated air flap into "Fresh air open" position. In this position, the fresh air/recirculated air flap actuator motor and the blend air flap actuator motors (M2/6, M2/7) draws the fresh air/recirculated air into the air conditioner housing through the right engine compartment air inlet grille, the interior filter and the fresh air/recirculated air flap.

Recirculated air mode

The air recirculation mode is switched on when the LED in the air recirculation button lights up. The fresh air/recirculated air flap actuator motor moves the fresh air and air recirculation flap to the "Fresh air closed" position. In this position, the fresh air/recirculated air flap actuator motor and the blend air flap actuator motors draw the recirculated air from the front vehicle interior into the air conditioner housing. Depending on the configuration of the blower setting variants and the temperature selection and air distribution variants, recirculated air passes into the front vehicle interior again through the air ducts and air outlets.

In heating mode, the system switches to fresh air mode. The transition phase (minimal heating/cooling mode), on the other hand, is controlled using variable mixed air. In cooling mode ("MAX COOL"), the system switches to air recirculation mode. Automatic flushing with fresh air takes place according to a time stored in the automatic air conditioning control and operating unit.

Actuation of the air duct flaps

The air distribution in the vehicle interior is controlled by adjusting the air ducting flaps in the air conditioner housing.

The following air duct flaps are operated:

 Defroster, footwell, side air vent and center air vent flaps (with code FJ6 (Center area with 2 DIN stowage compartments and air vent)) through the electronic blower regulator (N29) (Ventilation control)

 Blend air flaps through left blend air flap actuator motor (M2/6) and right blend air flap actuator motor (M2/7) (Temperature control)

 Fresh air/recirculated air flap via the fresh air/recirculated air flap actuator motor (M2/5) (fresh air/recirculated air control)

 The fresh air/recirculated air flap is closed after an accident (crash signal sent).

D83.00-A008-79

Refrigerant circuit, function

The refrigerant circuit generates the cooling that is required for climate control of the vehicle interior by changing the state of the refrigerant from liquid to gaseous. The refrigerant circuit can also be used to reduce the coolant temperature of the coolant circuit for the high-voltage batteries (low-temperature circuit 2).

 Detailed information on the cooling of the high-voltage batteries are available in the separate function description for the "High voltage on-board electrical system cooling function".

The refrigerant circuit is regulated by the powertrain control unit (N127). The expansion valve (Y140/1) is electrically actuated through the automatic air conditioning control and operating unit (N22/2). The requests from the vehicle occupants to regulate the climate control for the vehicle interior are also read in by the automatic air conditioning control and operating unit.

The refrigerant circuit for climate control of the vehicle interior essentially consists of the following components:

 Electric refrigerant compressor (A9/6)

 Expansion valve (Y140/1)

 High-voltage battery cooling evaporator shutoff valve (Y19/19)

 Evaporator (vehicle interior) (1)

 Evaporator/heat exchanger (2)

 Condenser (3)

 Inner heat exchanger (4)

 Accumulator (drier)

The individual components of the refrigerant circuit are interconnected through hoses and pipelines and form a closed system.

The refrigerant circuit is split up as follows:

 High-pressure side

 Low-pressure side

High-pressure side

The electric A/C compressor (A9/6) draws in the cold gaseous refrigerant, compresses it thereby heating it up, and then forwards it to the condenser. The compressed hot refrigerant is cooled in the condenser by the outside air flowing past.

The refrigerant changes its state from gaseous to liquid. The refrigerant then flows into the accumulator. The refrigerant is dehumidified when it flows through the fluid reservoir, vapor locks are separated and mechanical impurities are filtered out in order to protect the downstream components. The cleaned refrigerant flows on to the expansion valve and from there the liquid refrigerant which is under high pressure is injected into the evaporator.

Low-pressure side

The liquid refrigerant decompresses in the evaporator and changes its physical state from liquid to gaseous. The evaporation heat required for the evaporation is removed from the blow-by air at the evaporator fins, cooling it down in the process. The refrigerant, which is now completely gaseous, is drawn in again and compressed by the electric refrigerant compressor.

The cooled air is routed to the vehicle interior through actuation of the fresh air/recirculated air flap actuator motor and the blend air flap actuator motors.

Climate control regulation

The climate control is regulated through the signals recorded by the automatic air conditioning control and operating unit (e.g. interior temperature, outside temperature, coolant temperature, vehicle speed) and it matches the settings selected on the automatic air conditioning control and operating unit.

The climate control regulation function encompasses the following subfunctions:

 Function sequence for recording and evaluating signals

 AC component actuation function sequence

 Function sequence for defroster function

 Function sequence for evaporator drying process

 Heating circuit function sequence

Function sequence for recording and evaluating signals

The following signals are recorded and evaluated:

 Outside temperature

 Interior temperature

 Temperature and moisture on windshield

 Coolant temperature

 Evaporator temperature

 Refrigerant pressure

 Solar radiation

 Vehicle speed

 Door status

Outside temperature

The SAM control unit (N10) reads in the signal of the outside temperature sensor (B14) directly, calculates the outside temperature and sends this to the automatic air conditioning control and operating unit. The automatic air conditioning control and operating unit requires this value to reach the desired interior temperature by adjusting the blend air flaps accordingly.

 If the vehicle is stationary, the measured temperature can differ considerably from the outside temperature. The outside temperature is therefore only included in the regulation process when the vehicle speed - for a period of at least 30 seconds - is  30 km/h. At speeds < 30 km/h and when the ignition is switched off and on the last measured temperature value is then used.

Interior temperature

The interior temperature is recorded by the interior temperature sensor (B10/4) and read in directly by the SAM control unit. The automatic air conditioning control and operating unit sends a request to the electronic blower regulator (N29). The fresh air/recirculated air flap actuator motor and the blend air flap actuator motors are then actuated, and they draw in the air for temperature measurement from the vehicle interior.

Temperature and moisture on windshield

The temperature and the relative air humidity (dew point temperature) on the inside of the windshield are recorded by the rain/light sensor (B38/2).

The rain/light sensor sends the signal to the SAM control unit. The SAM control unit calculates the dew point temperature and sends the signal to the automatic air conditioning control and operating unit. The automatic air conditioning control and operating unit uses the dew point temperature to calculate the relative air humidity and the temperature of the inside of the windshield.

Fogging of the windshield can thus be detected and if the windshield threatens to fog up, corresponding countermeasures are initiated, such as e.g. activation of the electric refrigerant compressor.

Coolant temperature

The temperature of the coolant in the low-temperature circuit 2 is recorded by the low-temperature coolant circuit temperature sensor 2 (B11/7). The signal is read in directly by the powertrain control unit and evaluated. The powertrain control unit sends the "Coolant temperature" signal to the automatic air conditioning control and operating unit. The value is used to regulate the air mixing flaps and to actuate the electric refrigerant compressor.

Evaporator temperature

To prevent the evaporator from icing up, the evaporator temperature is measured by the evaporator temperature sensor (B10/6). The signals from the evaporator temperature sensor are read in directly by the SAM control unit. If the evaporator temperature drops to approx. 2 °C, the electric refrigerant compressor is switched off.

Refrigerant pressure

The refrigerant pressure is recorded by the cooler pressure and temperature sensor (B161/1) and the condenser pressure and temperature sensor (B161/2). The signals from the pressure sensors are forwarded over the SAM control unit to the automatic air conditioning control and operating unit. The pressure is compared with a stored temperature/pressure curve.

At a refrigerant pressure of < 0.8 bar and > 30 bar, the electric refrigerant compressor is switched off or is not activated.

At a refrigerant pressure of between 0.8 and 30 bar, the electric refrigerant compressor is switched on or activated again.

Solar radiation

The angle of incidence and the intensity of the solar radiation in the vehicle are recorded by the rain/light sensor (B38/2). The SAM control unit reads in the signal, evaluates it and sends the signal to the automatic air conditioning control and operating unit. In the event of one-sided solar radiation, an appropriate temperature difference is set between the left and the right specified control temperatures.

Vehicle speed

The vehicle speed is sent by the ESP® control unit (N30/4) to the automatic air conditioning control and operating unit. The vehicle speed is used by the regulation for internal calculation of the outside temperature, e.g.  during operation while at a standstill.

Door status

The status of the respective door is determined by the following control units:

 Driver's door control unit (N69/1)

 Front passenger door control unit (N69/2)

The respective control unit sends the status to the automatic air conditioning control and operating unit. If the door is open, the automatic air conditioning control and operating unit retains the current blower setting, in order to prevent any unnecessary readjustment in the event of high temperature differences between the inside and outside air.

AC component actuation function sequence

The function sequence for actuating the A/C components encompasses the following subfunctions:

 Actuation of blower actuator motors

 Actuation of the air duct flaps

 Actuation of electric refrigerant compressor

 Actuation of high voltage PTC heater control unit

 Actuation of circulation pump

Actuation of blower actuator motors

The fresh air/recirculated air flap actuator motor and the blend air flap actuator motors are used for ventilation. The automatic air conditioning control and operating unit forwards the request to the electronic blower regulator.

 The electronic blower regulator switches off the actuator motors in the event of an accident (crash signal sent).

Actuation of the air duct flaps

The air distribution in the vehicle interior is controlled by adjusting the air ducting flaps in the air conditioner housing.

Actuation of electric refrigerant compressor

The electric refrigerant compressor is responsible for drawing in the refrigerant and compressing it.

The automatic air conditioning control and operating unit actuates the electric refrigerant compressor.

 The electric refrigerant compressor is switched off via the interlock circuit in the event of an accident.

Actuation of high voltage PTC heater control unit

The high-voltage PTC heater control unit (N33/16) is switched on as required by the automatic air conditioning control and operating unit.

 The high voltage PTC heater control unit is switched off in the event of an accident.

Actuation of circulation pump

The heated coolant passes through the heater heat exchanger, which dissipates heat to the air blowing by.

The circulation pump (M13/4) is also actuated to ensure there is a sufficient volumetric flow rate to heat up the blowby air. The circulation pump is actuated by the automatic air conditioning control and operating unit.

Function sequence for defroster function

When the defroster button (N22/2s7) is pressed, all air flaps are closed with the exception of the defroster flaps and the fresh air/recirculated air flap. These are fully opened. The defroster flaps are adjusted so that the maximum air flow is directed to the windshield and the front side windows. The blend air flaps are set to full warm air supply.

The automatic air conditioning control and operating unit actuates the fresh air/recirculated air flap actuator motor and the blend air flap actuator motors so that an optimum defrost mode is achieved that matches the vent air temperature.

The electric refrigerant compressor is switched-in to ensure that the vent air is dried. The air is dried and then heated up to the maximum temperature.

Additional function requirements for evaporator drying

 Air conditioning system was active at least once during the last activation cycle.

 Outside temperature > 20 °C

 Doors closed

 Kilometer reading > 250 km

Function sequence for evaporator drying process

To counteract evaporator odors in the vehicle interior and fogging of windows when starting the air conditioning or climate control, an evaporator drying process is performed.

A timer is activated in the instrument cluster_(A1) when the electric vehicle is switched off. The "Electric drive READY" status is sent by the powertrain control unit to the instrument cluster.

After a one hour waiting period the instrument cluster sends the request to dry the evaporator to the automatic air conditioning control and operating unit, which initiates drying of the evaporator.

The automatic air conditioning control and operating unit sends the request to the electronic blower regulator. The electronic blower regulator actuates the fresh air/recirculated air flap actuator motor and the blend air flap actuator motors at the lowest stage for 30 minutes. The air supply serves to reduce residual moisture in the evaporator.

Heating circuit function sequence

The coolant is circulated by the circulation pump in the heating circuit. Here, it absorbs the heat from the high-voltage PTC heater control unit or from the high-voltage battery, depending on the given operating condition.

The heated coolant also passes through the heater heat exchanger, which dissipates heat to the blowby air.

The condensation prevention switchover valve (Y16/9) regulates the flow of coolant to the heater heat exchanger or to low-temperature circuit 2 (coolant circuit of high-voltage batteries) and the heater heat exchanger, if actuated by the automatic air conditioning control and operating unit.