In addition to conventional locks, keyless-entry systems and keypads, some motor vehicles today have a number of different ways of unlocking the motor vehicle doors. How do motor vehicles keep track of all those different locking and unlocking systems and exactly what happens when the motor vehicle doors unlock?
The mechanism which unlocks your motor vehicle doors is truly quite fascinating.
It has to be extremely trustworthy because it is going to lock and unlock your motor vehicle doors tens of thousands of times over the working lifespan of your motor vehicle.
Crash sensor
Inflator Air bag
Crash sensor activated
Nitrogen gas Filters
Sodium azide
Igniter
Air bag inflation device Air bag Inflator
Methods of unlocking motor vehicle doors:
• The conventional way with a key.
• By pressing the unlock button inside the motor vehicle.
• By using the combination lock on the outside of the motor vehicle door.
• By pulling up the knob on the inside of the motor vehicle door.
• With a keyless-entry remote control.
• By electronic signal from a control centre.
We will learn just what’s inside your door that makes it unlock.
Figure 8.17: Methods of unlocking motor vehicle doors
The lock/unlock switch sends power to the actuators which unlock the motor vehicle door. But in more complicated systems that have several ways to lock and unlock the doors, the body controller decides when to do the unlocking.
The body controller is a mini computer system in your motor vehicle. It controls a number of the smaller functions which make your motor vehicle people-friendly – for example, it ensures the interior lights stay on until you start the motor vehicle and it beeps at you if you have not fastened your safety belt or it beeps at you if you leave your headlights on or you forget the keys in the ignition.
The body controller also monitors all of the possible sources of an ‘unlock’ or ‘lock’
signal. It monitors a door-mounted touchpad and unlocks the doors when the correct code is entered. It monitors a radio frequency and unlocks the doors when it receives the correct digital code from the radio transmitter in your key fob and also monitors the switches inside the car. When it receives a signal from any of these sources, it provides power to the actuator which locks or unlocks the doors.
In fact, what is happening inside the motor vehicle door?
Inside a motor vehicle door
The actuator is positioned below the latch. A rod connects the actuator to the latch and another rod connects the latch to the door knob which sticks up out of the top of the door.
When the actuator moves the latch up, it connects the outside door handle to the opening mechanism. When the latch is down, the outside door handle is disconnected from the mechanism so that it cannot be opened. To unlock the door, the body controller supplies power to the door-lock actuator for a timed interval.
Door knob Conventional key Keyless-entry remote control
Unlock button
Combination lock
159
Figure 8.18: A motor vehicle door inside panel removed
Figure 8.19: Inside of a motor vehicle door showing mechanism
Figure 8.20: A central-locking actuator
The actuator can move the metal hook shown in Figure 8.20 to the left or right. When mounted in the motor vehicle, it is vertical, so the hook can move up or down. It imitates your motions when you pull the inside door knob up or push it down.
Door knob
Door knob connecting rod Door handle
Connecting rod for unlocking door knob
Latch
Door-lock actuator
Metal hook
Actuator body
Assessment 3
1. The pressure in the hydraulic fluid in a 230 mm diameter cylinder is 0,895 MPa. Calculate in newton the force exerted when the plunger moves outwards.
2. In the figure below, the force applied to the plunger causes a force of 900 N on the ram in a hydraulic press. The ram moves 10 mm upwards. The area of the plunger is 0,2 m2 and the area of the ram is 1,8 m2.
Figure 8.21: A hydraulic system Calculate:
2.1 The diameter of the ram in mm 2.2 The force applied on the plunger
2.3 The distance the plunger moves downward in mm
3. The volume of a gas is 8 m3 at a pressure of 600 kPa. Calculate the volume of the gas if the temperature is increased to 2000 kPa while the temperature remains constant.
4. A flat-belt drive consists of a 200 mm diameter driving pulley and a 100 mm diameter driven pulley. Determine the driven pulley speed if the driving pulley rotates at 750 rev/min.
5. What is the main function of a mechanical system?
6. Complete the following sentences:
6.1 When pressure is applied to a hydraulic fluid, the liquid will … 6.2. Two spur gears will only mesh when …
6.3. The purpose of intermediate gears is to …
7. Which precision measuring tool can be used to measure the depth of a screw thread?
8. State four methods of unlocking motor vehicle doors.
9. Briefly explain the chief purpose of air bags as found in motor vehicles.
10. What is an ECU and what is its function?
Plunger
Plunger moves × mm downwards
Ram moves 10 mm
upwards Ram
900 N
S
10 mm
161
Investigation 1
Investigate and write an essay on how the speed variations are obtained in the motor vehicle gearbox below. Make reference to the components of the motor vehicle gearbox as shown below in Figure 8.19 and use your knowledge on gears, gear ratios and rotational frequencies.
Figure 8.22: Sketch of a motor vehicle gear box
Investigation 2
The diagram below depicts a hydraulic brake as in a motor vehicle. Apply all your knowledge and understanding of linkages, pressure, rams and plungers in hydraulics and investigate and explain in your own words how this brake system operates.
Figure 8.23: Hydraulic brake in a motor vehicle Brake pedal
Master cylinder
Tube T Pipeline To other wheels Brake oil
Lever system
Inner rim of the wheel Ball
spigot bearing
Clutch release fork
Clutch shaft
3rd/4th
synchroniser Primary
shaft 5th speed
synchroniser
Clutch release
bearing 4 pinion
differential Final drive
pinion 4th speed 3rd speed
2nd speed 1st/2nd synchroniser
1st speed 5th speed Secondary shaft