Utente:Fabio888/Sandbox
La sequenza di accensione rappresenta l'ordine in cui ogni cilindro eroga la spinta in un motore a movimento alternativo multi-cilindrico.
La si ottiene alimentando le candelette nell'ordine corretto per i motori a benzina oppure iniettando gasolio nei cilindri per i motori Diesel. In fase progettuale, la scelta di un appropriato ordine di accensione è importante per minimizzare le vibrazioni, per migliorare il bilanciamento del motore e ottenere un funzionamento silenzioso, per allungare la vita del motore e aumentare il comfort di utilizzo. La sequenza di accensione determina anche la geometria dell'albero motore.
Ignition[modifica | modifica wikitesto]
In a gasoline engine, the correct firing order is obtained by the correct placement of the spark plug wires on the distributor. In a modern engine with an engine management system oand direct ignition, the Engine Control Unit (ECU) takes care of the correct firing sequence. Especially on cars with distributors, the firing order is usually cast on the engine somewhere, most often on the cylinder head, the intake manifold or the valve cover(s).
Various firing orders for different engine layouts[modifica | modifica wikitesto]
| number of cylinders | firing order | example |
|---|---|---|
| 3 | 1-2-3 1-3-2 |
Saab two-stroke, Perodua Kancil engine BMW K75 engine, Subaru Justy engine |
| 4 | 1-3-4-2 1-2-4-3 1-3-2-4 1-4-3-2 1-2-3-4 |
Most straight-4s, Ford Taunus V4 engine Some British Ford and Riley engines, Ford Kent engine, Riley Nine Subaru 4-cylinder engines, Yamaha R1 crossplane Volkswagen air-cooled engine Proton Wira VDO engine |
| 5 | 1-2-4-5-3 | Straight-five engine, Volvo 850, Audi 100 |
| 6 | 1-5-3-6-2-4 1-4-3-6-2-5 |
Straight-6, Volkswagen VR6 engine, Opel Omega A Mercedes-Benz M272 engine, Volkswagen V6's (both engines are 90-degree V6's) |
| 7 | 1-3-5-7-2-4-6 | 7-cylinder single row radial engine |
| 8 | 1-8-4-3-6-5-7-2 1-8-7-2-6-5-4-3 1-3-7-2-6-5-4-8 1-5-4-8-7-2-6-3 1-6-2-5-8-3-7-4 1-8-7-3-6-5-4-2 1-5-4-2-6-3-7-8 1-5-6-3-4-2-7-8 1-5-3-7-4-8-2-6 1-2-7-8-4-5-6-3 1-2-7-3-4-5-6-8 |
1988 Chrysler Fifth Avenue, Chevrolet Small-Block engine GM LS engine, Toyota UZ engine Porsche 928, Ford Modular engine, 5.0 HO BMW S65 Straight-8 Nissan VK engine Ford Windsor engine Cadillac V8 engine 368, 425, 472, 500 only Ferrari V8's, (all are flat-plane crank) Holden V8 Cadillac Northstar Engine |
| 10 | 1-10-9-4-3-6-5-8-7-2 1-6-5-10-2-7-3-8-4-9 1-8-7-6-5-4-3-10-9-2 |
Dodge Viper V10 BMW S85 Izusu v10 |
| 12 | 1-7-5-11-3-9-6-12-2-8-4-10 1-7-4-10-2-8-6-12-3-9-5-11 1-4-9-8-5-2-11-10-3-6-7-12 |
2001 Ferrari 456M GT V12 1997 Lamborghini Diablo VT 3412E |
| 14 | 1L-1R-2L-2R-4L-4R-6L-6R-7L-7R-5L-5R-3L-3R | (Wärtsilä)-Sulzer 14ZV40/48 V14 marine diesel |
| 16 | 1-12-8-11-7-14-5-16-4-15-3-10-6-9-2-13 | 2003 Cadillac V16 engine |
Although the vast majority of automobile engines rotate clockwise as viewed from the front, some engines are designed by the manufacturer to rotate counter-clockwise to accommodate certain mechanical configurations. In these applications, the firing order is shown in a reverse order (though it still starts with 1). For the most common inline configurations, this gives firing orders of 1-3-2, 1-2-4-3, and 1-4-2-6-3-5. In addition to the reconfiguration of the plug wires or injector tubes, the valve timing must be accordingly modified.
Cylinder numbering and firing order[modifica | modifica wikitesto]
Notes on left/right and front/rear[modifica | modifica wikitesto]
When referring to cars, the left-hand side of the car is the side that corresponds with the driver's left, as seen from the driver's seat. It can also be thought of as the side that would be on the left if one was standing directly behind the car looking at it.
When referring to engines, the front of the engine is the part where the pulleys for the accessories (such as the alternator and water pump) are, and the rear of the engine is where the flywheel is, through which the engine connects to the transmission. The front of the engine may point towards the front, side or rear of the car.
In most rear-wheel drive cars, the engine is longitudinally mounted and the front of the engine also points to the front of the car. In front-wheel drive cars with a transverse engine, the front of the engine usually points towards the right-hand side of the car. One notable exception is Honda, where many models have the front of the engine at the left-hand side of the car.
In front-wheel-drive cars with longitudinally mounted engines, most often the front of the engine will point towards the front of the car, but some manufacturers (Saab, Citroën, Renault) have at times placed the engine 'backwards', with #1 towards the firewall. One notable car with this layout is the Citroën Traction Avant. This layout is uncommon today.
See also: Automobile layout
Cylinder numbering and firing orders for various engine layouts[modifica | modifica wikitesto]
In a straight engine the spark plugs (and cylinders) are numbered, starting with #1, usually from the front of the engine to the rear.
In a radial engine the cylinders are numbered around the circle, with the #1 cylinder at the top. There are always an odd number of cylinders in each bank, as this allows for a constant alternate cylinder firing order: for example, with a single bank of 7 cylinders, the order would be 1-3-5-7-2-4-6. Moreover, unless there is an odd number of cylinders, the ring cam around the nose of the engine would be unable to provide the inlet valve open - exhaust valve open sequence required by the four-stroke cycle.
In a V engine, cylinder numbering varies among manufacturers. Generally speaking, the most forward cylinder is numbered 1, but some manufacturers will then continue numbering along that bank first (so that side of the engine would be 1-2-3-4, and the opposite bank would be 5-6-7-8) while others will number the cylinders from front to back along the crankshaft, so one bank would be 1-3-5-7 and the other bank would be 2-4-6-8. (In this example, a V8 is assumed). To further complicate matters, manufacturers may not have used the same system for all of their engines. It is important to check the numbering system used before comparing firing orders, because the order will vary significantly with crankshaft design (see crossplane).
As an example, the Chevrolet Small-Block engine has cylinders 1-3-5-7 on the left hand side of the car, and 2-4-6-8 on the other side, and uses a firing order of 1-8-4-3-6-5-7-2.[1] Note that the order alternates irregularly between the left and right banks; this is what causes the 'burbling' sound of this type of engine.[2]
In most Audi and Ford V8 engines cylinders 1-2-3-4 are on the right hand side of the car, with 5-6-7-8 are on the left.
This means that GM LS V8 engines and Ford Modular V8s have an identical firing pattern despite having a different firing order.
An exception is the Ford Flathead V8 where the number 1 cylinder is on the right front of the engine (same as other Ford V8's) but this cylinder is not the front cylinder of the engine. In this case number 5 is the front cylinder. A similar situation exists with the Pontiac V8's 455 etc. where the cylinders are numbered like a Chevrolet V8 but the right side bank is in front(like a Ford), this puts cylinder number 2 in front of number 1.
| V8 Cylinder bank | Audi | Ford |
GM & Chrysler | GM (Northstar) | GM (Holden) |
|---|---|---|---|---|---|
| Right side of vehicle | 1234 | 1234 | 2468 | 1357 | 1357 |
| Left side of vehicle | 5678 | 5678 | 1357 | 2468 | 2468 |
Ships[modifica | modifica wikitesto]
Contrary to most car engines, a ship's engine or a power plant engine is numbered from the flywheel end towards the free end.
In ship and power plant V-type engines the numbering is A1... and B1... where the A-bank is on the left hand side and the B-bank is on the right hand side, looking from the flywheel end.
See also[modifica | modifica wikitesto]
References[modifica | modifica wikitesto]
- ^ Boxwrench.net. URL consultato il 4 febbraio 2009.
- ^ Craig Reyenga, Craig's website - V8 engines - exhaust sound, su craig.backfire.ca. URL consultato il 4 febbraio 2009.
1997 Dakota firing order diagram
External links[modifica | modifica wikitesto]
- Firing Orders, Cylinder Numbering and Distributor Rotation for American V8 engines
- V8 Engines - Analysis of firing orders and cylinder numbering of V8 engines