Logo Allmyblog
Logo Allmyblog
Lien de l'article    

SSSARA

auto parts
Contacter l'auteur de ce blog

CATEGORIES
- auto parts

5 DERNIERS ARTICLES
- Concept of the electronic system
-
- Ignition system timing
- Professional brake repair
- Right way to handle the warped and worn brake disc
Sommaire

CALENDRIER
LunMarMerJeuVenSamDim
01
02030405060708
09101112131415
16171819202122
23242526272829
3031
<< Juillet >>

BLOGS FAVORIS
Ajouter sssara à vos favoris
  Ignition system timing Alerter l'administrateur Recommander à un ami Lien de l'article 

Ignition occurs some time before top dead center (BTDC) during the compression stroke of the piston. This time is measured in degrees of crankshaft rotation BTDC. For a modern SI engine, this timing is typically 8 to 10 degrees for the basic mechanical setting with the engine running at low speed (low rpm). This basic timing is set by the design of the mechanical coupling between the crankshaft and the distributor. The basic timing may be adjusted slightly in many older cars by physically rotating the distributor housing. As the engine speed increases, the angle through which the crankshaft rotates in the time required to burn the fuel and air mixture increases. For this reason, the spark must occur at a larger angle BTDC for higher engine speeds. This change in ignition timing is called spark advance. That is, spark advance should increase with increasing engine rpm. In a conventional ignition system, the mechanism for this is called a centrifugal spark advance. It is shown in Figure 1.10. As engine speed increases, the distributor shaft rotates faster, and the weights are thrown outward by centrifugal force. The weights operate through a mechanical lever, so their movement causes a change in the relative angular position between the rubbing block on the breaker points and the distributor cam, and advances the time when the lobe opens the points. In addition to speed-dependent spark advance, the ignition timing needs to be adjusted as a function of intake manifold pressure. Whenever the throttle is nearly closed, the manifold pressure is low (i.e., nearly a vacuum). The combustion time for the air—fuel mixture is longer for low manifold pressure conditions than for high manifold pressure conditions (i.e., near atmospheric pressure). As a result, the spark timing must be advanced for low pressure conditions to maintain maximum power and fuel economy. The mechanism to do this is a vacuum-operated spark advance, also shown in Figure 1.10. The vacuum advance mechanism has a flexible diaphragm connected through a tie rod to the plate on which the breaker points are mounted. One side of the diaphragm is open to atmospheric pressure; the other side is connected through a hose to manifold vacuum. As manifold vacuum increases, the diaphragm is deflected (atmospheric pressure pushes it) and moves the breaker point plate to advance the timing. Ignition timing significantly affects engine performance and exhaust emissions; therefore, it is one of the major factors that are electronically controlled in the modern SI engine. The performance of the ignition system and the spark advance mechanism has been greatly improved by electronics parts control systems. Because ignition timing is critical to engine performance, controlling it precisely through all operating conditions has become a major application of digital electronics, as explained in Chapter 7. It will be shown in Chapter 7 that ignition timing is actually computed as a function of engine operating conditions in a special-purpose digital computer known as the electronic engine control system. This computation of spark timing has much greater flexibility for optimizing engine performance than a mechanical distributor and is one of the great benefits of electronic engine control.

  Aucun commentaire | Ecrire un nouveau commentaire Posté le 01-06-2011 à 05h58

 « Article précédant Retour à l'accueil du blog Article suivant »

 Articles dans la même catégorie
- Concept of the electronic system

-

- Professional brake repair

- Right way to handle the warped and worn brake disc

- Steps of installing the car speaker

- Importance of air bag and suspension system

- An overview of the auto electronics parts

- Replacing time of your brake pad


 Liste des commentaires Ecrire un nouveau commentaire


 Ajouter un commentaire
Titre
Commentaire
:) ;) :o :D :s :( :@ :clown: :$ :star: +o( ^|
8( :] (6) (h) :p 9| :'( (y) (n) :| 8-| :{
:?: :nrv: (l) (u) :o/ :pig: :hand: (h5) :yin: :nuc: :x ;D
Auteur
E-Mail (facultatif)
Blog (facultatif)
Se souvenir de mes informations
Recopier le code ci-contre :


SYNDICATION
 
Fil RSS 2.0
Ajouter à NetVibes
Ajouter à Google
Ajouter à Yahoo
Ajouter à Bloglines
Ajouter à Technorati
http://www.wikio.fr
 

Allzic en direct

Liens Commerciaux
L'information à Lyon
Retrouvez toute l'actu lyonnaise 24/24h 7/7j !


L'information à Annecy
Retrouvez toute l'actu d'Annecy 24/24h 7/7j !


L'information à Grenoble
Retrouvez toute l'actu de Grenoble 24/24h 7/7j !


Application Restaurant
Restaurateurs, demandez un devis pour votre application iPhone


Fete des Lumières
Fête des lumières : vente de luminaires, lampes, ampoules, etc.


Diffuseur
Acheter un diffuseur d'huiles essentielles

Votre publicité ici ?
  Blog créé le 16-04-2011 à 07h53 | Mis à jour le 01-06-2011 à 07h15 | Note : Pas de note