Review Car

Engine Construction And Engine Operation

FIGURE 1.1 A piston forces a crankshaft to turn

FIGURE 1.2 A flywheel is installed at the end of the crankshaft. This is a Buick opposed engine from the early 1900s.

FIGURE 1.3 Valves seal off the valve ports

FIGURE 1.4 A head gasket seals the head to the block

FOUR STROKE ENGINE OPERATION

A stroke is the movement of the piston from TDC (top dead center) to BDC (bottom dead center), or from BDC to TDC. There are four strokes in one four stroke cycle of the engine. They are called the intake stroke, compression stroke, power stroke, and exhaust stroke.

FIGURE 1.5 The opening of the valves is controlled by the camshaft

• Intake Stroke. Gasoline will not burn unless it is mixed with the correct amount of air. It is very
explosive when 1 part is mixed with about 15 parts of air. Shortly before the piston reaches TDC, the intake valve begins to open. As the crankshaft turns, it pulls the rod and piston down in the cylinder toward BDC (Figure 1.6).

FIGURE 1.6 The air-fuel mixture is drawn into the cylinder.

FIGURE 1.7 The air-fuel mixture is compressed.

FIGURE 1.8 Compression ratio is a comparison of the volume of the air space above the piston at BDC and at TDC. In this example the compression ratio is 8:1.

FIGURE 1.9 The air-fuel mixture heats up as it is compressed

FIGURE 1.11 Leakage of gases past the ring is known as blowby.

FIGURE 1.13 Cylinder arrangements

FIGURE 1.14 A radial engine from a vintage airplane

a

FIGURE 1.15 (a) Section view of an in-line six cylinder engine.   (b) Section view of a V6 engine.

FIGURE 1.16 A cam lobe forces the valve open. (a) The cam-in-block design uses pushrods to open valves. (b) In the overhead cam design, the camshaft is located in the cylinder head. FIGURE 1.17 There are half as many teeth on the crank drive as there are on the cam drive.

FIGURE 1.18 An aluminum block with cast iron sleeves

When molten iron or aluminum is poured into the core box, the heat of the casting process cooks the sand. When the casting cools, the sand breaks up. The casting is shaken out and any remaining sand is washed away through the core holes, leaving the finished casting. In another casting process, lost foam casting
(LFC), foam is “lost” or burned up during the pour. General Motors first experimented with LFC in 1982
and since then has refined the process for use in casting blocks, heads, and crankshafts. Saturn used
this process since its beginning in 1990.
With conventional sand casting, oil galleries must be machined in the block casting. With LFC, the oil galleries and coolant passages can be cast into the part. Foam also provides a more accurate casting compared to sand casting. The completed casting is smoother in appearance and there are no parting lines. More intricate castings are possible because the pattern does not need to be removed as was the case with sand castings.

FIGURE 1.19 Sand casting cores.

The LFC pattern is made of expendable polystyrene beads, otherwise known as Styrofoam. Patterns are made by injecting the beads into a die and then superheating them with steam to bond them together and form the finished mold. The foam pattern is coated with a refractory coating, which smoothes the surface of the pattern.
Gates and risers are attached to the pattern to allow for the pouring and venting of the molten metal. Unlike the conventional sand casting process, which uses binders to hold the sand together, LFC uses dry, unbonded sand that is poured around and into the internal passages in the pattern. The sand is vibrated and compacted to thoroughly fill the voids around the pattern. During the pour, the molten metal replaces the pattern as it vaporizes.
When the finished casting has cooled and become solid, the unbonded sand is dumped out. It can be reused, unlike conventional casting sand, which requires disposal. The core holes are closed off with core plugs (Figure 1.20). Core plugs are usually made of steel or brass, although rubber and copper expandable plugs are available, too. Brass core plugs are superior because they do not rust. Brass plugs are not
used in new cars because of their extra cost and because new engines are filled with coolant, which
prevents rust. Core plugs are sometimes referred to as expansion plugs, welsh plugs, freeze plugs, or soft plugs.

FIGURE 1.20 Core plugs.

 On V-type blocks, cylinders are cast in two rows called left and right banks. V8 blocks are cast with the cylinder banks separated by a 90° angle. V6 blocks have either 60° or 90° between banks. There are also unusual engine designs, such as Volkswagen’s V6, which has 15° between banks. There are big block and small block engine designs. Smaller, lighter blocks are more popular in passenger cars because of their fuel efficiency. Some intake manifolds cover the area between the heads known as the valley ,whereas others use covers and a separate intake plenum. A complete block assembly with the entire valvetrain (cylinder heads and related parts) included is called a long block.

Youve closely tracked the Porsche Cayennes success by scanning parking lots outside fancy restaurants. You understand that the Cayennes omnipresence in Orange County translates directly to the mere presence of a 918 Spyder in Porsches lineup, which is important to you, the owner of a knackered E36 BMW 328i.

As a result, you know that the Macan is simply the next rung on Porsches ladder. Oh, its the lesser of the two SUVs; smaller in size and price and probably status, too. But this is the vehicle which moves Porsche from niche luxury player closer to the mainstream premium arena. Three sports cars wont do it, not even with the addition of an SUV and a massive four-door hatchback.

Thanks in part to an additional 3947 Macan sales in the U.S. over the last four months, Porsche USA has sold 31,759 total vehicles through the first eight months of 2014. This moves Porsches market share up to 0.284% from 0.268% a year ago.

An incremental improvement? Most definitely, but the rate of Porsches improvement is in excess of what the overall market is averaging. Total new vehicle sales are up 5% in the United States in 2014. Porsche USA volume is up 12%.

The figure achieved by the Macan in its first month on the market, when 1263 were sold, was both representative of some pent-up demand and Porsches ability to meet that demand, if only at first. But it was also a tell-tale that the Macan, as if there was ever any doubt, was not another low-volume Porsche sports car. (Porsche sold 312 Caymans in May; 411 Boxsters.)

August told another, different story. The Panameras 3945 year-to-date sales represent a 14% year-over-year improvement for the brands people-carrying passenger car. Yet the Macan has generated more sales activity for Porsche in the last four months than the Panamera has over the last eight. That the Macan can quickly muster more sales in a shorter period than the Boxster or Cayman is no surprise. Yet in August, the Macans 969 U.S. sales nearly matched the 1056-unit total achieved by the Boxster, Cayman, and Panamera combined.
Now, the Panamera is not exactly Americas favourite car. Mercedes-Benz sold 1855 S-Classes and 1150 CLS-Class sedans last month. The Lexus LS, Audi A7, BMW 5-Series, BMW 6-Series, and Audi A8 were just a few of the other high-end premium brand cars which found more new customers than the Panamera.

But from a purely inward-looking Porsche perspective, the Macans early-onset success and the Panameras inability to keep up speaks to the current state of the automotive industry. Crossover tops car. Porsche USAs Panamera volume met a monthly peak in April 2012, when 868 were sold. The Macan has surpassed that peak in three of its four months on the market. Yes, its been helped along by a much lower sticker price than the Panamera, but also by its bodystyle.

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• Historical Monthly & Yearly Porsche Macan Sales Figures
• U.S. Vehicle Sales Rankings By Model - August 2014 YTD
• U.S. SUV/Crossover Sales Rankings By Model - August 2014 YTD

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This isnt just something were seeing at Porsche, nor is it a trend we see only with oddly-styled large hatchbacks and especially sporty small crossovers. By recent standards, Mercedes-Benz USA will report particularly strong S-Class sales this year, but the current pace suggests at least a 25% decline compared with 2006 levels. Yes, 2006, the year Mercedes-Benz USA sold their first 18,776 GLs to go along with nearly 31,000 S-Classes. Over the last three years, Mercedes-Benz has averaged 27,000 GL sales per year in the U.S., the kind of number they havent achieved with the S-Class since 2007.

BMW will sell less than half the number of 7-Series sedans this year than they did in 2003 while likely selling close to 110,000 total SAVs, around 2.5 times the number of X5s sold in 2003. Tatas JLR? 60% of Jaguar-Land Rovers volume in 2002 was Jaguar-derived, now its 77% Land Rover.

No matter which data point you use, its remarkably easy to see that the Macan went from non-existence to Porsche USAs deuteragonist in the matter of one summer. Its perhaps easier to see that big luxury cars are quickly being pushed to the sidelines, while the Macan and its more common premium cohorts move in on their territory.