Washer and Wiper

Washer and Wiper

Circuits Shown here is a circuit for fast, slow and intermittent wiper control. The switches are shown in the off position and the motor is stopped and in its park

Wiper circuit

position. Note that the two main brushes of the motor are connected together via the limit switch, delay unit contacts and the wiper switch. This causes regenerative braking because of the current, generated by the motor due to its momentum, after the power is switched off. Being connected to a very low resistance loads up the ‘motor/generator’

Operation of the Circuit ฀฀ When either the delay contacts or the main switch contacts are operated, the motor will run at slow speed. When fast speed is selected, the third brush on the motor is used. On switching off, the motor will continue to run until the park limit switch changes over to the position shown. This switch is only in the position shown when the blades are in the parked position.

Central Control Units Some vehicles use a system with more enhanced facilities. This is regulated, by what may be known as, a central control unit (CCU), a multi-function unit (MFU) or

a general electronic module (GEM)! These units often control other systems as well as the wipers, thus allowing reduced wiring bulk under the dash area. Electric windows, headlights and heated rear window to name just a few, are now often controlled by a central unit

Ford GEM and components

Electronically Controlled Facilities Using electronic control, a CCU allows the following facilities for the wipers:

• Front and rear wash/wipe • Intermittent wipe • Time delay set by the driver • Reverse gear selection rear wipe operation • Rear wash/wipe with 'dribble wipe' (an extra wipe

several seconds after washing) • Stall protection.

Wiper Blade Pressure Control A system called wiper pressure control, can infinitely vary the pressure of the blade onto the screen, depending on vehicle speed. At high speeds, the air stream can cause the blades to Bosch pressure control system lift and judder. This seriously reduces the cleaning effectiveness. If the original pressure is set to compensate, the pressure at rest could deform the arms and blades. Sensors are used to determine the air stream velocity and intensity of the rain. An ECU then evaluates the data from these sensors and passes an appropriate signal to a servomotor. When the blades are in the rest position pressure is very low to avoid damage. The pressure rises with increasing vehicle speed and heavy rain.

Linear Rear Wipers Current wiper systems that are based on an alternative rotary movement cover a wipe area, of between 50% and 60%, of the total surface area of the rear window. This limit is due to the height/width ratio and the curve of the window. The linear rear wiper concept ensures optimum visual comfort as it covers over 80% of the rear window surface. This increase in the driver's field of vision enhances safety especially during low speed manoeuvres such as reversing or parking.

Rear Screen Heating Heating of the rear screen involves a circuit with a relay, which will usually incorporate a timer. The heating elements are thin metallic strips bonded to, or built inside the glass. When a current is passed through the elements, heat is generated and the window will defrost or demist.

Windscreen Heating Front windscreen heating is used on some vehicles. This presents more problems than the rear screen, as vision must not be obscured. The technology used, is drawn from the aircraft industry; it involves very thin wires cast in to the glass. As with the heated rear window this device can consume a large current and uses a timer relay.

High Current Screen heaters can draw high current, 10 to 15 amps being typical. Because of this, the circuits often contain timer relays to

Timer relay

prevent the heaters being left on too long. The timer will switch off after 10 to 15 minutes.

 Look back over the previous section and write out a list of the key bullet points here:

HORNS, OBSTACLE AVOIDANCE AND CRUISE CONTROL

Electric Horns ฀฀ Regulations in most countries state that the horn (or audible warning device) should produce a uniform sound. This makes sirens and melody type fanfare horns illegal! Most horns draw a large current so are switched by a relay.

Horn Circuit The standard horn operates by simple electromagnetic

switching. Current flow causes an

armature, which is attached to a tone disc, to be attracted to a stop.

A set of contacts is then opened.

 Horn operation circuit

This disconnects the current allowing the armature and disc to return under spring tension. The whole process keeps repeating when the horn switch is on. The frequency of movement, and hence the tone, is arranged to lie between

1.8 and 3.5kHz. This note gives good penetration through traffic noise.

Twin Horns Twin horn systems, which have a high and low tone horn, are often used. This produces a more pleasing sound, but is still very

Horns removed

audible in both town and higher speed conditions. from vehicle

Obstacle Avoidance Radar This system sometimes called collision avoidance radar can be looked at in two ways. First, as an aid to reversing, which gives the driver some indication as to how much space System block diagram is behind the car. Second, collision avoidance radar can be used as a vision enhancement system. Obstacle avoidance radar when used as a vision enhancement is somewhat different. Shown here is a block diagram to demonstrate the principle of this system. In the future, this may be linked with adaptive cruise control.

Reversing Aid The principle of radar as a reversing aid is illustrated here. This technique is in effect a range finding system. The output

Ultrasonic

can be audio or visual, the latter being perhaps reversing aid most appropriate, as the driver is likely to be looking backwards. The audible signal is a 'pip pip pip' type sound, the repetition frequency of which increases as the car comes nearer to the obstruction becoming almost continuous as impact is imminent. The technique is relatively simple as the level of discrimination required is low and the radar only has to operate over short distances. The main problem is to ensure the whole width of the vehicle is protected.

Cruise Control ฀฀ Cruise control is the ideal example of a closed loop control system. The purpose of cruise control is to allow the driver to set the vehicle speed and let the system maintain it automatically.

Speed Control The system reacts to the measured speed of the vehicle and adjusts the throttle accordingly. The reaction time is

important so that the vehicle’s speed does not

Throttle

controller

feel to be surging up and down. Other facilities are included such as allowing the speed to be gradually increased or decreased at the touch of

a button. Most systems also remember the last set speed. They will resume to this speed, at the touch of a button.

System Description The main switch switches on the cruise control, this in turn is ignition

controlled. Most systems do not retain the speed setting in memory when the main switch Cruise control

switch

has been turned o ff. Operating the ‘set’ switch programs the memory, but, this normally will only work if conditions similar to the following are met:

Vehicle speed is greater than 40km/h Vehicle speed is less than 120km/h Change of speed is less than 8km/h/s Automatics must be in 'drive' Brakes or clutch are not being operated Engine speed is stable.

Set and Resume Once the system is set, the speed is maintained to within about 3-4 km/h until it is deactivated by pressing the brake or

Cruise control

clutch pedal, pressing the resume switch or

switches

turning off the main control switch. The last set speed is retained in memory except when the main switch is turned off. If the cruise control system is required again then either the set button will hold the vehicle at its current speed or the resume button will accelerate the vehicle to the previous set speed. When cruising at a set speed, the driver can press and hold the set button to accelerate the vehicle until the desired speed is reached. If the driver accelerates from the set speed to overtake for example, then when the throttle is released, the vehicle will slow down again.

Control Methods A number of methods are used to control the throttle position. Vehicles fitted with drive by wire systems allow the cruise

Throttle motor

control to operate the same actuator. A motor can be used to control the throttle cable or in many cases, a vacuum operated diaphragm is used, which three simple valves control.

Vacuum Actuator ฀฀ When the speed needs to be increased valve 'x' is opened allowing low pressure from the inlet manifold to one side of the diaphragm. The atmospheric pressure on the other side will move the diaphragm and hence the throttle. To move the other way valve 'x' is closed and valve 'y' is opened allowing atmospheric pressure to enter the chamber. The spring moves the diaphragm back. If both valves are closed then the throttle position is held. Valve 'x' is normally closed and valve 'y' normally open. In the event of electrical failure, cruise will not remain engaged and the manifold vacuum is not disturbed. Valve 'z' provides extra safety; it is controlled by the brake and clutch pedals.

Safety Switches The brake switch is very important, as it would be dangerous braking if the cruise control system was still trying to

Cruise control

maintain the vehicle speed. This switch is

system

normally of superior quality and is fitted in place development or as a supplement to the brake light switch activated by the brake pedal. Adjustment of this switch is important. The clutch switch is fitted in a similar manner to the brake switch. It deactivates the cruise system to prevent the engine speed increasing if the clutch is pressed. The automatic gearbox switch will only allow the cruise to be engaged when it is in the 'drive' position. This is to prevent the engine over speeding if the cruise tried to accelerate to a high road speed with the gear selector in position '1' or '2'.

Speed Sensor This will often be the same sensor that is used for the speedometer. If not several types are available, the most common

Road speed sensor

producing a pulsed signal the frequency of which in position is proportional to the vehicle speed.

Adaptive Cruise Control Conventional cruise control has now developed to a high degree of quality. It is however, not always very practical on many roads as the speed of the general traffic is constantly varying, and often very heavy. The driver has to take over from the cruise control system on many occasions to speed up or slow down. Adaptive cruise control can automatically adjust the vehicle speed to the current traffic situation. The system has three main aims:

Maintain a speed as set by the driver Adapt this speed and maintain a safe distance from the

vehicles in front Provide a warning if there is a risk of collision.

System Operation The operation of an adaptive cruise system is similar to a conventional system. However, when a signal from the headway sensor

Headway sensor

detects an obstruction, the vehicle speed is decreased. If the optimum stopping distance cannot be achieved by just backing off the throttle, a warning is supplied to the driver. The more complex system can take control of the vehicle transmission and brakes. It is important to note that adaptive cruise control is designed to relieve the burden on the driver, not take full control of the vehicle!

 State why many vehicles have a twin horn system.

 Look back over the previous section and write out a list of the key bullet points here:

MOBILE MULTIMEDIA

In Car Entertainment ฀฀ (ICE) Controls on most sets will include volume, treble, bass, balance and fade. Cassette tape options will include Dolby® filters to reduce hiss and other tape selections such as chrome or metal. A digital display of course, will provide a visual output of operating condition. This is also linked into the vehicle lighting to prevent glare at night. Track selection and programming for one or several compact discs is possible.

Anti-Theft Codes Many ICE systems are coded to deter theft. The code is activated if the main supply is disconnected and will not allow the set to Removable

work until the correct code has been re-entered. control panel Some systems now include a plug in electronic 'key

card', which makes the set worthless when removed.

In Car Multimedia It would be almost unthinkable to not have radio cassette players in our vehicles. It does not seem too long ago however that these were optional extras! Looking back just a little further the in car record player must have been very interesting to operate - it was evidently quite successful in large American cars in the US, but left a bit to be desired in British vehicles on British roads! Shown here is a modern, factory fitted ICE system with a CD player.