Archive for August, 2006

From the previous article on starter motors we can see that the motor can demand quite a large current from the battery via the supply cable. Obviously, numerous start cycles will deplete the battery power to the extent that it will no longer be able to start the engine. In order to recharge the battery vehicle manufacturers provide a generator system driven by the engine usually via a rubber belt.

Until the late sixties this generator could have taken one of two forms, the dynamo or the alternator. Gradually, over a fairly short period of time, the dynamo fell from favour and the job of battery charging and supplying electrical power has been satisfied by the alternator. As the dynamo is, to all intents and purposes, a dead issue this article will be confined to the far superior alternator.

The main reason for the rise of the alternator is its ability to provide a relatively high output without being physically large, an alternator with an output of 160 amps will be little different in size to one with half that figure. The potential for high output has become particularly relevant for today’s vehicles as the demand for power has risen many, many times, between 1960 and 1980 average current demand rarely exceeded 50 amps, today that requirement can be as high as 200 amps and it is still rising this is especially true in bigger make cars like in Alpha Romeo car parts where a bigger battery is required due to the extra size and weight of the vehicle. This factor alone has led many authorities to say that the days of the 12 volt system are numbered, current demand can be halved by simply doubling the system voltage to 24 volts and after all trucks and buses have been using this system for many years

The alternator generates power by revolving a magnetic assembly (the rotor) inside a cylinder made up of many loops of wire (the stator), this loop construction is made up of three separate phases each producing an output in turn when the rotor revolves about its centre line. The first hurdle is to change the alternating current (AC) output into direct current (DC) compatible with the battery and other vehicle systems, this is the job of the rectifier. Without going into the intricacies of rectifier construction, conversion of AC to DC is achieved by a series of one way electrical valves (diodes) wired so that a process called full wave rectification occurs. The next hurdle is one of voltage regulation, too high and battery/component damage may well occur, too low and the battery charge state will not be maintained leading directly to a non start situation. Put simply, the voltage regulator manages output by interrupting the magnetic field in the rotor. With output voltage set at around 14.2v, should output rise above the set maximum the rotor magnetic field will be switched off, dropping below this and it will be switched on. This process happens within a few milliseconds giving a very accurate voltage output. Causing the alternator to turn is a drive arrangement comprising a pulley secured to the end of the crankshaft and a similar, but much smaller, pulley at the end of the alternator with a suitable belt wrapped round the two. The difference in pulley sizes allows the alternator to be driven at a higher speed than the engine.

The whole charging system effort is to maintain the car battery and provide power for vehicle systems when the vehicle is running.

Here is a slight tip for those of you who are just about to purchase an Alfa Romeo – not that I want to put you off or anything…….but

The daily Record (via Dialog NewsEdge) states “ALFA Romeo drivers are the most accident prone in Britain�

It also shows figures of how many crashes have occurred, including up to a quarter of the 147 sports models owners having a road crash in their vehicle

Consfused.com points out BMW to be in second place with over 20% of its owners involved in a crash

On the other hand the daily record points out that the Vauxhall Nova is the safest car. Other safe vehicles include Rover, Peugeot, Nissan, Citron and Ford.

Does this mean you should not buy an Alfa Romeo? No since accidents obviously depend on who is driving the car and how fast it goes. The higher end sports models will have more crashes then a 1 liter run around version and just because this year more Alfa Romeo cars crash, does not mean next year it wont be Vauxhall. However if you do have a crash and you do need car spare parts you can always use CarSpareFinder!

In the previous two articles on basic engine operation it was explained how the four stroke cycle worked, but how do you initiate the process? With the engine running, the up and down movement of the pistons is transferred to the crankshaft to produce rotation, to start an engine we need to rotate the crankshaft by external means which will then allow the engine run cycle to take over.

The most basic method would be to use a suitably cranked handle temporarily engaged in the end of the crankshaft and turned by some athletic individual. Better still would be the fitting of an electric motor under driver control – a starter motor.

The most common starter motor found on modern vehicles is the pre-engaged type which uses an electro-magnet to operate switching and engagement functions, this differs from the older inertia type which requires a separate heavy current switch and engages by throwing a drive gear into engagement. This engagement with the engine is achieved by the use of a toothed ring secured to the outer rim of the flywheel (the ring gear), when the starter is engaged drive is transmitted from the motor drive gear onto the ring gear and the engine turns over.

For the average engine to start, a minimum speed of 100rpm is required, less than this will not produce the levels of compression and fuel vapour mixing required for proper combustion. During the cranking phase the starter motor will demand around 150 – 200 amps from the battery, however, under extreme climatic conditions even the average family 2 litre hatchback can ask for 450 – 500 amps to overcome the initial resistance to rotation and friction found within the engine. To give some idea of the torque required for this freezing cold morning scenario, the average wheel nut is tightened to around 90 – 110Nm, the amount required to start the engine moving can be as much as 450 – 500Nm dropping to 160 – 200Nm to maintain the 100rpm minimum crank speed. It must be noted that cranking should be restricted to a maximum of 10 seconds at a time, extended crank times, more than 3 seconds, will cause the motor and associated wiring to heat up leading to increased fatigue and a much shorter service life.

So that’s what the starter motor does, but how does it do it and how is it controlled?
As the pre-engaged type is by far the most common the following will be restricted to this type. The two main parts of the starter motor are the motor itself and the solenoid which is usually mounted on the top of the motor casing, the motor is devoted purely to rotating like most other electric motors, the solenoid has two functions 1) to handle the high current switching, and, 2) to push the drive gear into mesh with the ring gear. It would be impractical to run the large high current cables from the battery to a switch mounted in the cab then down to the starter, so the pre-engaged system uses the solenoid to handle the heavy current switching required. This is done under the control of a much lower current circuit using far smaller wires from the starter switch which can now be incorporated into a combined ignition/start switch assembly. The second job for the solenoid is to facilitate the engagement of the starter drive gear into the engine ring gear. Both of these tasks are carried out by an electro-magnet making up the solenoid assembly. The high current feed from the battery is connected to one of the large terminals of the solenoid; the other large terminal feeds the motor itself. In the at rest position this circuit is open (no current flow), when the solenoid is operated by a low current feed from the starter switch the centre plunger of the solenoid pulls the drive gear into mesh with the ring gear and closes the high current circuit so powering the motor. As the engine starts, the driver releases the ignition key from the crank position thereby cutting the low current feed to the solenoid which in turn breaks the supply to the motor and brings the drive gear out of mesh assisted by a return spring.

Car modification is one of the many hobbies to do with cars, or should I say lifestyle. Although this pastime is a relatively expensive one it is also worth while.

There are several good Blogs out there on car modification, for example Auto Truck Blog and Drivers Drive. These blogs include how to start,why and examples of modifications.

One interesting car modification enthusiast was Tom Sakowski and he installed a start button on his car. If you don’t want to mod and just want an import, try some importing companies such as jm – imports.

Whatever you’re into, you could always get your required car parts from CarSpareFinder in the spare parts directory.

[PICTURE FROM jm-imports]

Work can be one of the most boring places you can spend your time. Even though you cannot just go home when boredom starts driving you insane admit it we all have one of those days when all you want to do is run out the office and go down the pub we can help make time that bit more bearable my personal way of doing this is to play a flash game (when the boss is out the office).

Car Sparefinder currently have 3 games for passing the time click here to go to the page.

For those interested in engine history Dr Rudolf Diesel took out patent 7241 in 1892 which detailed an engine design relying on the induction of coal dust for fuel. Prior to this, the English engineer Herbert Ackroyd-Stuart filed patent 7146 in 1890 which contained a design for an engine which ran on the timed, high pressure injection of fuel oil. Whichever camp you decide to pitch in, it cannot be denied that the work of Ackroyd-Stuart preceded that of Diesel. To avoid being dragged into the argument the term “compression ignition� or “CI� will be used throughout.

The basic four stroke cycle of induction, compression, power, exhaust, used in the CI engine is exactly the same as that used in the petrol engine of such makes as Alfa Romeo. Two main differences exist; 1) engine construction tends to be heavier and more robust to handle the much higher compression and combustion pressures, and 2) ignition of the fuel/air mixture does not require an external source (a spark).

So we have an engine which will run without having any external form of starting the burn process, how can this happen? Put simply, pressure; cast your mind back to when you last used a bicycle pump, notice the fixed end of the barrel becoming warmer, this was not entirely due to the warmth of your hand it was caused by the air in the pump tube getting hotter as its pressure increased. Now imagine this scenario magnified many, many times and instead of generating 30-45 pounds per square inch (psi) or 2-3 bar you generate 500psi or 34 bar, at this pressure created over a very short period of time temperatures usually reach well over 600 C. Just before top dead centre, fuel oil is injected at very high pressure, around 2500psi or 175 bar, via an injector which produces a very fine mist. The fuel mist will self ignite at around 400 C so its introduction into this cylinder will produce almost instant combustion thus producing the power stroke.

So why use a CI engine over a similar sized petrol engine? Until relatively recently the CI engine was the sole power unit of choice for heavier duty applications, trucks, buses, taxis etc, the greater fuel efficiency over the petrol engine was guaranteed  to give the operator lower fuel costs and its better power characteristics produced high power output at lower engine speeds thus promoting a longer service life. The flip side to this was the CI engines higher noise and harshness levels plus its ability to belch black smoke under heavy acceleration. In more recent times however, CI engine development has come on in leaps and bounds offering noise, harshness and exhaust emissions levels virtually identical to its petrol driven cousins whilst still delivering the old attributes of excellent power output at relatively low engine speeds.

According to an article in AutoExpress by Ross Pinnock a system is being implemented where car salesmen can tell in seconds what your old car is worth and only using your registration number. Currently the system is being developed by Car Supermarket Motorpoint.

Whether or not this will work as an advantage to the customer is yet to be seen. Maybe you will get a better price on a car if you own a newer car, but those trading in a old car might get less than they would now.

Although this system may take a while before it is the norm, it may be feasible to trade used auto parts in part exchange e.g. part exchanging your old exhaust in trade for this new one. It would make MOT’s and Garage visits cheaper since when you need new car parts you could get some money for your old one and thus increasing the value of used auto parts

Ever wondered how car salesmen are good at selling cars? or how you walk into a dealership with a car in mind and then come out worth a totally different car? well Mike Brewers reveals these tricks in a series coming this fall. To find out more visit Mike Brewers column. He describes it as “an exciting new programme that lifts the lid on the tricks car salesmen use” Mike Brewer (2006)

Maybe Mike will answer such questions as ‘How do you know your car has new car parts or simply used car parts’?

This news was found in the Auto Express website in the Mike Brewers column.

According to Autoblog.com several sources are reporting that the SAIC group will be purchasing the Rover name from BMW. The selling of the Rover name is supposed to occur later this year; however nothing has been written in stone yet.

SAIC are not the only ones interested in the rover name, competition includes Nanjing Auto and the Ford Motor Company.

Will this see a new era for Rover, will car parts change? Since it’s a new company does this mean parts such as a car engine will be re modelled? with we will just have to wait and see!

A recent article from autoexpress.co.uk revealed than the number of petrol stations has decreased to around 10,000 in the uk. Many people suggest this will keep decreasing due to soaring fuel prices, as you might agree. If this continues bigger firms will have the greater profits and many small petrol stations will be at risk of closure since they gain less profit due to less pumps or have higher fuel prices to accomodate this.

Will UK fuel keep rising. Hopefully Honda’s 3 approached for better fuel will come into play and create more fuel efficient cars or better, non foreign fuel source (see http://www.hybridcars.com/blogs/hyview for more details) or otherwise i will strip my car down and will sell the individual car parts.