Many luxury automobiles have thermostatically controlled air-conditioning systems for the comfort of the passengers. Sketch a block diagram of an air conditioning system where the driver sets the desired interior temperature on a dashboard panel.

1.0 INTRODUCTIONControl engineering is based on the foundations of feedback theory and linear system analysis, and it generates the concepts of network theory and communication theory. Accordingly, control engineering is not limited to any engineering discipline but is applicable to aeronautical, chemical, mechanical, environmental, civil, and electrical engineering.

A control system is an interconnection of components forming a system configuration that will provide a desired system response. The basis for analysis of a system is the foundation provided by linear system, which assumes a cause effect relationship for the components of a system. A component or process to be controlled can be represented by a block as shown in Figure 1.

Figure 1: Process under control

An open-loop control system utilizes a controller or control actuator to obtain the desired response as shown in Figure 2. The open-loop control system utilizes an actuating device to control the process directly without using device. An example of an open-loop control system is an electric toaster.

Figure 2: Open-loop control systems (no feedback)A closed-loop control system (Figure 3) utilizes an additional measure of the actual output to compare the actual output with the desired output response. The measure of the output is called the feedback signal. A feedback control system is a control system that tends to maintain a relationship of one system variable to another by comparing functions of these variables and using the difference as a means of control. As the system is becoming more complex, the interrelationship of many controlled variables may be considered in the control scheme. An example of closed-loop control system is a person steering an automobile by looking at the autos location on the road and making the appropriate adjustments.

Figure 3: Closed-loop feedback systems.

1.1 THERMOSTATICALLY CONTROLLED AIR-CONDITIONING SYSTEMS

1.1.1Air Conditioning SystemAir conditioning systems are designed to allow the driver and or passengers to feel more comfortable during uncomfortably warm, humid, or hot trips in a vehicle. Cars in hot climates often are fitted with air conditioning. In a self-contained air-conditioning unit, air is heated in a boiler unit or cooled by being blown across a refrigerant-filled coil and then distributed to a controlled indoor environment.

Figure 4: Car Air-conditioning systemA comfort air-conditioning system is designed to help maintain body temperature at its normal level withoutundue stress and to provide an atmosphere which is healthy to breathe. The heat-dissipating factors of temperature, humidity, air motion, and radiant heat flow must be considered simultaneously. Within limits, the same amount of comfort (or, more objectively, of heat-dissipating ability) is the result of a combination of these factors in an enclosure. Conditions for constant comfort are related to the operative temperature. The perception of comfort is related to one'smetabolicheat production, the transfer of this heat to the environment, and the resulting physiological adjustments and body temperature.Engineering of an air-conditioning system starts with selection of design condition: Air temperature andrelative humidityare principal factors. Loads on the system are calculated. Equipment is selected and sized to perform the indicated functions and to carry the estimated loads.Air conditioning facilitates the removal of heat from inside the vehicle. The principle applied is that heat is removed by conduction and convection. An evaporator which is cold absorbs the heat from the air that is passed through it and then cold air is forced out through the vents inside the car by the blower motor. This is done by pressurizing refrigerant (134a) with a compressor and then releasing refrigerant (134a) inside the air conditioner evaporator.

Figure 5: Air conditioning block diagram

Athermostatis adevicefor regulating thetemperatureof asystemso that the system's temperature is maintained near a desiredset point temperature. The name is derived from the Greek words thermos "hot" and statos "a standing". The thermostat does this by switching heating or cooling devices on or off, or regulating the flow of a heat transfer fluid as needed, to maintain the correct temperature.A thermostat may be a control unit for a heating or cooling system or a component part of a heater or air conditioner. Thermostats can be constructed in many ways and may use a variety of sensors to measure the temperature. The output of the sensor then controls the heating or cooling apparatus.

1.2 THE SYSTEM AND COMPONENTS WORKS

Figure 6: Features on Cooling CircuitThe air conditioner automatically controls the cabin temperature using various parameters including outside temperature, cabin temperature, solar strength, and engine cooling water temperature.Some automobiles are equipped with an automatic climate control system to regulate the temperature inside the car automatically. The climate control module is a computer whichmonitorsand adjusts to a temperature set by the user. The temperature is controlled by a combination of cold air from the air conditioner to achieve a desired temperature. The blower motor speed is controlled by a solid state speed controller. This controller electrically controls the speed of the blower motor and replaces the conventional blower motorresistorsystem.The air conditioning and heating unit provides thermal comfort to passengers inside no matter what the temperature is outside. The air inside can be heated, cooled, disinfected or ventilated. The climate control feature helps to maintain the desired temperature. The system that provides cooling, heating and climate control is known as the HVAC (heating, ventilation, air conditioning) system. Basic principles of fluid mechanics, thermodynamics and heat transfer provide cold and heat for the particular system. The climate control settings allow all three to work together to achieve good indoor air quality, thermal comfort and optimal pressure.

1.3 THE STRUCTURAL FEATURESTemperature control in an automobile passenger environment is more complex than that of a static room in a building. To address driver and passenger comfort and safety, many factors must be taken into account. Temperature and humidity should be controlled to provide an enjoyable ride. However, it is also critical to keep windows from being fogged, which is caused by a temperature differential between inside and outside air in combination with the interior humidity. To obtain satisfactory control results, the strength of sunshine radiation and the automobile speed must also be factored in.

Figure 7: Controller forAir Conditioning SystemIt is a controller which employs five sensors to obtain data for temperature control and humidity control in an automobile. It prevents rapid change of temperature in the car when doors or windows are opened and then closed. It even reacts to weather changes because interior humidity changes caused by the weather can be detected by sensors.

1.4 BASIC COMPONENT AND THE FUNCTION

1.4.1 AUTOMATIC TEMPERATURE CONTROL

The automatic temperature control refers to the maintenance of passenger compartment temperature and humidity at a preset level, regardless of the outside weather conditions. Therefore, the temperature control also holds the relative humidity in the compartment at a suitable level and prevents window fogging. If the preset temperature is 297 K (24 C), the automatic control system maintains the environment at 297 K with 45 to 55 percent humidity. In the hottest weather, the cooling system can rapidly cool the automobile interior to the predetermined temperature and cycles to maintain the temperature level. During cold weather, the system rapidly heats the passenger compartment to the temperature level and then automatically maintains it.Many automotive electronic temperature control systems incorporate self-diagnostic test provisions where an on-board microprocessor controlled subsystem displays a code. This code indicates the cause of the malfunction. Some systems also display a code to indicate the computer which detects the malfunction. The code usually is a number, letter or alphanumeric, which varies from car to car.

Figure 8: Typical Thermostat

1.4.2 SENSORSSensors are extremely sensitive to slight variation in temperature, though they may be different in physical appearance. The sensor is actually a resistor whose resistance value is determined by its temperature. The change in the resistance value of each sensor is inversely proportional to the change in temperature.

1.4.3CONTROL PANELThe control panel is found in the instrument panel at a convenient location giving access to both the driver and front-seat passenger, and enables the operator to provide input control to the air-conditioning and heating system. The control panel may be of manual, push button, or touch pad type (Fig. 33.53A, B and C). Provisions are made on the control panel for the selection of compartment temperature between 320 K and 330 K in one degree increments.

Figure 9

2.0SYSTEM MODELING OF SYSTEM

+-SR(s)C(s)2.1Mathematical model of each component including the disturbance/noise.

SC(s)R(s)+-

C(s)R(s)

2.2Input and output states selectionInput = User Set point Output = Thermometer display The input of the system is state as a user set point as temperature that being setup enters the temperature controller. From there, its being followed the state flow that being given and goes to the air conditioning controller. The output of the system can be defined as a thermometer display as it give a result that have exactly to be the same with the input. There have been two disturbances that we choose to fit on the programming. The disturbance that we choose for is heat sources that we can get during breathing on the car and the fan speed of the air conditioning. As we have fit it to our system, its also affecting the graph that being obtained.

Heat SourceFan External TemperatureInterior DynamicKelvin2.3Transferring the model into block diagrami) Disturbance

User Set Point (In Celsius)Temperature Control ChartAC Controlii) Air conditioning controlBDA 3073 CONTROL ENGINEERING

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2.4Transferring the model in Simulink environment

2.4.1Disturbance i. Heat Source Thermostat: Car thermostat problem can cause the heat source because of waste of gas. It can stick shut, in which case the Engine Temp light will come on or a high temperature will show on your engine temperature gauge. A high temperature indication doesnt necessarily mean a stuck thermostat; it could be a loss of engine coolant. Compressor:The most likely cause of an automotive air conditioner cooling problem is no refrigerant in the system. If the refrigerant has escaped past a leaky compressor or O-ring seal, leaked out of a pinhole in the evaporator or condenser, or seeped out through a leaky hose, the leak needs to be identified and repaired before the system is recharged. On many systems, the compressor will not turn on if the refrigerant is low because the "low pressure safety switch" prevents the compressor clutch from engaging if system pressure is low. This protects the compressor from possible damage caused by a lack of lubrication.

ii. Fan It is common for dust particles to enter into the condenser which is usually kept in front of the radiator. It is better to sometimes clean the condenser with strong air blow or with water. Those condensers which are not cleaned for years can have problems. If the fans used for cooling the condensers have problems, then also there is an issue. If there is a problem with the fan motor, relay or other electrical circuit then also the performance degrades. Some cars have a common fan for both the radiator & condenser. Moisture: If moisture enters the refrigerant, then problems can occur. Moisture will soon become ice andcause blockage in the tubes. If more air also happens to enter, that will also adversely affect the cooling capacity.

2.4.2Output graph

Graph A: With disturbance of 1 passenger

Graph B: With disturbance of 5 passengers

Graph C: With disturbance 1 passenger, difference engine speed and torque

Graph D: With disturbance 5 passengers, difference engine speed and torque

Graph E: With disturbance 1 passenger, difference mass flow rate and fan speed

Graph F: With disturbance 5 passengers, difference mass flow rate and fan speed

2.5Setting up the parameter / constant into Simulink2.5.1State flow chart

2.5.2Air conditioning control 2.5.3Interior dynamic

3.0BLOCK DIAGRAM MANIPULATING TO OBTAIN TRANSFER FUNCTION OF THE SYSTEM

A subsystem is represented as a block with an input, an output, and a transfer function. Many systems are composed of multiple subsystems. When a multiple subsystems are interconnected, a few more schematic must be added to the block diagram. These new elements are summing junctions and pickoff points. All components parts of a block diagram for a linear, time invariant system. We use the steps to get the transfer function by moving blocks to create familiar form or also known as reduction block diagram. This subsection basically moves the block that can make in order to establish familiar form when they almost exist. The equivalent block diagram formed when transfer function are moved left or right. These equivalences can be used to reduce a block diagram to a single transfer function.

+-SR(s)C(s)

SC(s)R(s)+-

C(s)R(s)

4.0RESULTS AND ANALYSIS

Figure shows the results of the simulation model that uses state flow as controller. The results in Figure 4 (a) and Figure 4 (b) prove that the desired temperature that being put on of like example 25C as a user set point and 35C as external temperature, respectively, can be achieved by the controller. This is because state flow is off in the air conditioning control when the current temperature in the car is 0.5C above or low than the set point temperature. The dead band of 0.5C has been implemented to avoid the problem of continuous switching.The number of passengers affects the performance of state flow controller because the base that has been used has the capability to manage just 1 passenger. In addition, the accurate blower speed proportion values cannot be achieved according to the desired temperature in order to provide a comfortable condition to the driver and passengers.Overall performance for the state flow controller is not very accurately ok. In Figure, at the beginning of the simulation, all graphs shows a performance well but when the temperature reaches 17.35C, the state flow controller response becomes slow. This is because, state flow have to wait for the current temperature to increase to 17.5C, which makes the difference values out within the dead band of 0.5C from desired temperature. Once the current temperature reaches 17.5C, the air conditioning state will switch on and the current temperature will decrease immediately to 16.5C. This action will respond continuously until the desired temperature is reached.

Graph A

Graph B Graph A and B: State flow performance with different number of passenger. (A) 1 passenger (B) 5 passengers

Other than that, the engine speed and torque also play some role onto it. As we can see from Graph A and B, the engine speed that being used is 110 with torque 15. So, what can happen when we change the value of both of it?

Graph C

Graph DGraph C and D: State flow performance with different number of passenger. (C) 1 passenger (D) 5 passengers

For the Graph C and D, the engine speed that we have used is 250 with torque 20, we can see the difference from the graph as it expand more larger rather than like in figure 4. Other than that type of the disturbance, the value of mass flow rate and fan speed rate if we make some disturbance also make some addition to obtain type of difference of graph as we can see form figure above. The graph above showed when we used the mass flow rate of 18 and fan speed rate of 20. The original one for that is mass flow rate 0.04 with fan speed of 10.

Graph E

Graph F Graph E and F: State flow performance with different mass flow rate and fan speed. (E) 1 passenger (F) 5 passengers

5.0CONCLUSION

Throughout the project, many simulations have been carried out to study the implementation of state flow as a controller in automobile climate control system. The performance of these types of control techniques is carefully studied.

For the model, as shown in Figure, if the user enters a set point temperature, which is greater than the current car temperature, the air conditioning system will be switched on and active until the current temperature in the car reaches within 0.5C of the set point temperature. Vice versa, if the set point is less than the current temperature, appropriate changes will be done by the controller.

The larger the range of temperature difference, the increase of the blower speed proportion is larger. But, the blower speed proportion values are also influenced by the number of passengers. This means that, although the range of temperature difference is the same, the output will change if the number of passengers in the car is different. The blower speed proportion will increase when the number of passengers increases.

Based on this research, the temperature control system for air conditioning for the automobile climate control system can been optimized by using state flow as a controller. The ripple in the simulation result could be reduced and the time required to achieve the desired temperature could be decreased. By studying the controllers state flow, we can really understand the characteristics of one type of controller. The knowledge gained from the analysis of from the controller, leads us to obtain the best parameter for the controller.