191 Dealing With Air Conditioning Refrigerant

Refrigerants that are used in air conditioning systems can be harmful to persons who come into contact with them and they are also considered to be harmful to the environment. For these reasons the servicing of air conditioning systems requires the use of specialized equipment, and technicians must be trained for the specific application that they are working on. Most garage equipment manufacturers market air conditioning service equipment and the Bosch Tronic R134 kit is an example. Equipment suppliers and vehicle manufacturers provide training for air conditioning systems and I strongly recommend that all garage technicians receive such training as air conditioning is now found in many vehicles that are used in Europe.

Some points of general application are as follows.

• There are strict rules about releasing refrigerant into the atmosphere. Technicians must familiarize themselves with the local rules and abide by them.

• The refrigerant is held in the system under pressure. Any small leak must be repaired.

• Some refrigerants produce poisonous gas when a flame is introduced near them. This eventuality must be avoided.

• If refrigerant gets on to the body it can cause cold burns and damage to the eyes - this must be avoided.

These are some of the reasons why special training is so important.

1.10 Computer controlled damping rate

Forcing oil through an orifice is a commonly used method of providing the damping in vehicle suspension systems. The amount of damping force that is applied is dependent, among other factors, on the size of the orifice through which the damping fluid is forced by the action of the suspension damper. The damping force can thus be changed by altering the size of the damping orifice. In practice this can be achieved by means of a valve which, under the control of the ECM, varies the size of the damping orifice to provide softer or stiffer damping, as required. Figure 1.30 shows the location of a solenoid-operated damping valve that is used on some Ford systems. The solenoid is controlled by the adaptive damping computer and provides two damping rates, a soft one and a stiff one.

The suspension damping rate is varied to suit a range of driving conditions, such as acceleration mode, braking (deceleration), bumpy roads and cornering etc. In order to provide the required damping for the various conditions the computer is fed information from a number of sensors. The input data is then compared with the design values in the computer ROM and the processor then makes decisions that determine the required damping rate. Figure 1.31 gives an indication of the types of sensors involved for adaptive damping.

The speed sensor can be the one that is used for other systems on the vehicle and it will probably be of the electromagnetic type. The steering position sensor is frequently of the opto-electronic type. This utilizes an infrared beam which is interrupted by the perforated disc as shown in Fig. 1.32. The wheel speed sensor signal can be derived from the ABS computer, and the brake light signal is derived from the stop light switch.

1.11 Computer controlled diesel engine management systems

Diesel engines rely on the compression pressure being high enough to ignite the fuel when it is injected into the combustion chamber. In order to achieve the

Location of solenoid valve on front axle

1 Solenoid valve

2 Damper

Location of solenoid valve on front axle

1 Solenoid valve

2 Damper

Location of solenoid valve on rear axle

1 Solenoid valve

2 Damper

Location of solenoid valve on rear axle

1 Solenoid valve

2 Damper

Fig. 1.30 The adaptive damping solenoid required pressure and temperature the mass of air that is compressed in each cylinder remains approximately constant throughout the engine's operating range. The power output is regulated by varying the amount of fuel injected. This means that diesel engines have a very weak mixture at idling speeds and a richer mixture for maximum power.

The operating principles of diesel engines therefore preclude the use of the exhaust oxygen sensor feedback principle that is used to help control emissions from petrol engines. However, only relatively small amounts of HC and CO appear in diesel engine exhaust gas and these can be reduced further by the use of an oxidizing catalyst. The reduction catalyst that is normally used to

Fig. 1.31 Computer controlled variable rate damping - inputs and outputs

reduce NOx emissions, however, cannot be used. A commonly used alternative method of NOx reduction on diesel engines is electronically controlled exhaust gas recirculation.

Steering angle sensor

Steering angle sensor

Turn signal switch assembly Slotted disc

Fig. 1.32 The steering position sensor

Turn signal switch assembly Slotted disc

Fig. 1.32 The steering position sensor

Another emission that causes concern is soot. Soot emission can be reduced by electronic control of the mass of fuel injected, injection timing and turbocharging (exhaust system particulate traps also have a beneficial effect).

Figure 1.33 shows a computer controlled diesel engine management system. The exhaust system is equipped with an oxidizing catalyst that converts CO into carbon dioxide and HC into carbon dioxide and steam. There is no exhaust oxygen sensor because diesel engines, when operating correctly, have a certain amount of excess oxygen in the exhaust and this aids the operation of the catalytic converter. NOx is kept within the required limits by careful control of fuelling and exhaust gas recirculation. The effectiveness of the emissions system is, in the UK, checked by means of a smoke meter, and the emissions test is part of the annual inspection. The emissions are also subject to spot checks by the enforcement authorities at any time.

The power output of a diesel engine is controlled by the quantity of fuel that is injected into each cylinder, whilst the quantity of air that is drawn into the cylinder on each induction stroke remains approximately the same. The main aim of computer control is to ensure that the engine receives the precise amount of fuel that is required, at the correct time and under all operating conditions. There are three areas of computer control. If we examine these in detail we shall find that for their operation they rely on well tried devices, such as solenoids and valves. The three items are:

1. fuel quantity (spill control)

2. injection timing control

3. idle speed control.

Do It Yourself Car Diagnosis

Do It Yourself Car Diagnosis

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