IHKA (integrated automatic heating / air conditioning system) RR

The IHKA is used to adapt the in-car climate to the individual needs of the passengers. Information is exchanged between the vehicle components and the IHKA control unit via the K-CAN SYSTEM data bus.

Main functions (see corresponding individual function description)

• Temperature control
  
• Air distribution
  
• Air flow control
  
• Automatic recirculated air control
  
• Automatic window defrosting/defogging (DEFROST, side windows and parked wiper heater)
  
• Heated rear window (demister)
  

Components

Control unit/operating unit

The IHKA control unit records the signals of the IHKA components and controls/regulates the heating and air conditioning process. The IHKA control unit causes the heated rear window to be activated and deactivated by the power module.

The control unit functions at the same time as operating unit: The temperature selectors for the driver and passenger area as well as the adjusting wheel for the automatic window defrosting/defogging are integrated. The blower adjusters for the driver and passenger area, as well as the block of three switches for recirculated air, rear window heating and air conditioner OFF are directly connected to the front of the control unit by plug-in connections.

No distinction is made for left-hand drive and right-hand drive vehicles: The control unit/operating unit is located on the same vehicle co-ordinates for both vehicles.

Rear compartment control panel

The rear compartment control panel does not have its own processor, only switching elements. It is connected directly to the controller by means of a 12-pin cable.

The temperature selectors for the rear left and right are integrated in the rear compartment control panel. The blower adjusters for the rear left and right connected directly to the front of the rear compartment control panel via plug-in connections.

Heater/air conditioner

The IHKA air conditioner is mounted underneath the instrument cluster on the bulkhead in the middle.

The air conditioner fulfils the following tasks:

• Generation and regulation of air quantity
  
• Air distribution, air mixture (stratification) and air dehumidification
  
• Transfer of heat output delivered by coolant circuit
  
• Transfer of refrigerating output generated by refrigerant circuit
  

The air conditioner is made up of the following components/functional units:

• Evaporator and evaporator sensor
  Temperature control in the evaporator is performed by the control unit. The evaporator temperature controller operates independently of the other control loops with established controlled variables. The cold air emerging from the evaporator is increased to the desired temperature with the aid of the heat exchanger.
  
• Heat exchanger and heat exchanger sensor
  
• Expansion valve
  The expansion valve is attached to the evaporator. It serves to regulate the amount of liquid refrigerant injected into the evaporator. The liquid refrigerant is metered in such a way that only enough refrigerant as can be fully evaporated is admitted into the evaporator.
  
• Flaps with drive and mechanism
  The flaps serve to distribute the air and to mix hot and cold air.
  Fresh air flap: the amount of clean air drawn in by the blower is regulated with this flap. The flap is moved by a high-speed drive so that it can be closed in extra-quick time in automatic recirculated air mode (AUC mode). The fresh air flap also serves to compensate ram pressure.
  Recirculated-air flap: the recirculated air flap is designed as a louvre with three fins. The amount of recirculated air drawn in is regulated with this flap.
  Footwell flap: the footwell flap directs the air flow into the front and rear footwells. The front and rear footwells are supplied separately on the left and right.
  Ventilation flap: the rear ventilation flaps (left and right) serve to adjust the air flow at the rear compartment ventilation outlets and the temperature (rear compartment stratification).
  Defrosting flaps (DEFROST): The two linked defrosting flaps serve to regulate the air flow to the windscreen. These flaps are activated jointly in all adjustment and operation functions from the driver's side only.
  Hot air/cold air flaps:The air volume at the spherical vents is regulated using the warm air /cold air flaps. The temperature is also stratified with these flaps. The combination of the flap pair regulates the air flow and the temperature simultaneously. The functions are separate on the left and right.
  Different stepping motors are used for particular purposes on the flap drives.
  High-speed motor: The high-speed motor is only used on the fresh air flap. The windings of this motor is activated by the control electronics with a stepping frequency of up to 500 Hz.
  MUX motors: MUX motors are used on all the other flaps. MUX motors are provided with an integrated circuit for controlling the windings. The integrated circuit is bus- and diagnosis-compatible. All MUX drives and the blower control are activated by the control electronics via a common motors bus MUX bus). Faults reported by the integrated circuits are registered in the control electronics and result in the activation being interrupted.
  Each drive is furnished when manufactured with an unalterable address. This facilitates clear differentiation in the bus communication. Because of their individual addresses, the motors cannot be exchanged between each other.
  
• Blower with controller
  Blower: The blower is mounted with the blower motor as an assembly in the glovebox area. The blower can be detached from the motor. Because the blower is mounted on the passenger side, there are different versions for LHD and RHD cars.
  Controller: The controller is mounted on the blower motor housing. The controller is activated by the control electronics in the control panel of the IHKA via the MUX bus in the same way as the MUX motors and is capable of on-board diagnosis. The diagnosis information is transmitted to the control electronics for evaluation. If on-board diagnosis identifies a fault which would cause components to overheat, the current is reduced or cut off until the fault criterion has been eliminated.
  The blower draws in air as a function of the flap setting either
  
  • through the cleaners and the fresh air duct o r
    
  • through the recirculated air flap.
    
  Air can be drawn in through both channels depending on the operating state.
  

Refrigerant compressor (KMV)

The refrigerant compressor (KMV) compresses the refrigerant gas drawn in by the evaporator and forces it to the condenser. It is always in operation when the vehicle engine is running. Infinitely output regulation is possible on account of its design and activation of a regulating valve with pulse-width-modulated signals by the control electronics. For the purpose of load reduction, only the refrigerating output that is directly needed is generated. The control and switching criteria for this purpose are:

• Compressor speed (engine speed)
  
• Compressor load torque (from IHKA to DME)
  
• Torque limitation (from DME to IHKA: possible limitation of load torque in event of kick-down mode or excessive coolant temperature)
  
• Refrigerant pressure limitation
  

Exchange of information between the IHKA and DME takes place via the body data bus CAN SYSTEM.

NOTE: The compressor must be broken in without fail in the following cases:

• Initial operation of the IHKA
  
• Replacement of the refrigerant compressor (KMV)
  
• Refilling of the cooling circuit with refrigerant
  

Compressor breaking-in: To ensure fault-free compressor lubrication, it is necessary to mix the amount of oil added by the manufacturer uniformly with the liquid refrigerant. For this purpose, the compressor must be operated for a specific period at a speed of between 300 and 1500 rpm.

If the engine idle speed exceeds 1500 rpm, the breaking-in procedure is automatically cut off and a message issued. The breaking-in procedure must then be repeated in its entirety.

Specifications: The air conditioning must be set to OFF when the engine is started. Do not switch on the air conditioning before being prompted.

Carry out the following steps:

• Set all air outlet nozzles in instrument cluster to OPEN.
  
• Start engine and allow idle operation to stabilize.
  
• Set blower output to at least 75% of maximum output.
  
• Switch on air conditioning and run for at least 2 minutes without interruption.
  

Coolant pressure sensor

The pressure sensor in the pressure line between the condenser and the evaporator supplies the control electronics with signals relating to the system pressure.

Condenser with integrated drier

The thermal energy generated by compression of the refrigerant gas in the heat exchanger is dissipated by air cooling to the surroundings at the condenser surface. The refrigerant condenses and turns liquid. In order to prevent corrosion damage, any water present in the refrigerant circuit is bound in the integrated drier. The drier insert can be replaced. It incorporates a filter screen to provided protection against particles.

Auxiliary water pump

An electric auxiliary water pump is installed in order to ensure adequate water flow through the heat exchanger at low engine speeds.

Water valves

The water valves on the left and right serve to regulate the heat exchanger. The water valves are activated with pulse-width-modulated signals. The control unit calculates the valve opening times dependent on certain input variables, e.g. engine speed. The valve opening times are 0 ms at max. COLD and 3600 ms at max. WARM.

Microfilter/air intake

A microfilter is located in both of the filter housings for the intake of air. The microfilter is a combination of a particle and activated charcoal filter. The activated charcoal filter holds back disruptive and toxic gases.

Rear compartment blower

For the rear compartment air conditioning, two additional blowers are located beneath the front seats.

The two rear compartment blowers are activated by the control unit with analog control voltage, which is converted by a final stage to the actual activation of each rear compartment blower.

Air flap modules

In addition to the step motors fitted in the heating and air conditioning system, 14 other MUX motors (see above) are used. These are connected to the control unit across two other motor buses.

The step motors are use to adjust the following ventilation flaps:

• Ventilation flap at outside front left, centre, knee and indirect
  
• Ventilation flap at outside front right, centre, knee and indirect
  
• Rear mixing flap, left and right
  
• Rear ventilation flap, outside left and right
  
• Rear ventilation flap, left and right centre console
  

Potentiometer air vents

The air volume and distribution can be adapted to the needs of the occupants by manual intervention. To do so, the control unit takes account of the potentiometer setting and activates the step motors to bring the ventilation flaps into the corresponding position.

Hall sensors, knee vents

In each case a Hall sensor reports to the control unit whether the ventilation flaps at the knee vents are to be opened or closed on the driver and passenger side.

AUC sensor

The AUC sensor registers the pollution gas content of the outside air and reports it to the control unit as a pulse-width-modulated signal. The evaluation electronics necessary for this sensor is integrated in the sensor. After vehicle start, the sensor always needs a warm-up time of 60 seconds.

Solar sensor

A solar sensor is fitted to the dashboard. It provides two voltage signals that are proportional to the heat generated by solar radiation to which the occupants are subjected at the front left and right.

Relay for parked wiper heater

Relay for side window heating

Auxiliary fan

The auxiliary fan is needed to cool the condenser. The required fan speed depends on the refrigerant pressure and is transferred by the IHKA across the body CAN SYSTEM data bus.

At vehicle speeds > 80 km/h, the auxiliary fan is switched off. At speeds below 70 km/h, the auxiliary fan is switched on again.

CAN messages

The IHKA communicated with various other control units across the body CAN SYSTEM data bus:

• DME Digital Engine Electronics
  The IHKA control system informs the digital engine electronics via the body data bus CAN SYSTEM of the activation status of the refrigerant compressor. The compressor is activated by the IHKA if no shutdown criterion (e.g. excessive coolant temperature or kickdown mode) prevents such an activation. When the compressor is activated, it is possible to switch between operation with and without an increase in idle speed.
  The idle speed is increased at an
  
  • outside temperature of ≥ 15°C a n d a
    
  • setting for controlled variable Y on left or right ≤ 10%.
    
  The idle speed is not increased at an
  
  • outside temperature of ≤ 13°C a n d a
    
  • Setting for controlled variable Y on left or right ≥ 20%.
    
• LM Light Module
  The LM light module provides the IHKA with information on the dimming setting and the light status (e.g. low beam activated). The IHKA controls the brightness of the function and locator lights in accordance with this information.
  
• PM Power Module
  The power module monitors the battery charge state and the quiescent current consumption of the car. It also activates or deactivates the heated rear window depending on activation by the IHKA. Information is received and sent via the K-CAN PERIPHERALS body data bus.
  

Safety function

Load deactivation

In the case of a ”control system peak reduction priority” signal from the power module, the consumers have their power output reduced or are shut down by the IHKA control system according to priority:

• Priority 6: heated rear window in timed mode (normal operation only)
  
• Priority 5: heated rear window in timed mode (normal operation only)
  
• Priority 4: heated rear window in timed mode, blower at max. half output
  
• Priority 1: parked wiper heater OFF, heated rear window in timed mode, blower at max. half output
  

In the case of a ”stationary consumers status” signal - DEACTIVATION by the power module, the stationary consumers are deactivated by the IHKA control system.

The DEFROST function is relevant to safety and always operates at maximum blower output.

Sleep/wait/power down modes

Sleep mode: In order to achieve the required closed circuit current consumption, the control unit is intentionally switched via the network management into a state of minimum current consumption (< 100 µA). The wait mode must be taken into account here.

Wait mode: The wait mode starts after the following overshoot times have elapsed:

• The overshoot time for the water valves must have elapsed (filling station effect).
  

Power down mode: With the power down command, the vehicle electrical system is placed for the purpose of rapid closed circuit current measurement in a state that it would normally adopt automatically after the overshoot time has elapsed.

The command is given with the DIS Tester. The overshoot time is thus reduced to max. 5 seconds.