VR6

The W8 uses two four-cylinder VR engines mated together, and the W16 uses two eight-cylinder VR banks. The greatest increase due to drying is in the ultimate crushing strength, and strength at elastic limit in endwise compression; these are followed by the modulus of rupture, and stress at elastic limit in cross-bending, while the modulus of elasticity is least affected. W8 and W16 designs were developed in a similar fashion. An extreme example is the case of a completely dry spruce block 5 cm in section, which will sustain a permanent load four times as great as that which a green block of the same size will support. For example, two VR6 engines mated together at 72 degrees result in a W12 configuration, which is significantly shorter than a V12 engine but only marginally wider. Drying produces a decided increase in the strength of wood, particularly in small specimens. Volkswagen has also developed a series of engines which use narrow angle designs mated together at 72 degrees. Within certain limits the greater the water content the greater its softening effect.

The Porsche Cayenne, which shares its chassis with the VW Touareg, also uses the 3.2 L VR6 as its base engine. A similar effect of common observation is in the softening action of water on paper or cloth. The VR6 is also used in other Volkswagen Group products, namely:. The general effect of the water content upon the wood substance is to render it softer and more pliable. The VR6 was used by Volkswagen in:. Even oven-dried wood retains a small percentage of moisture, but for all except chemical purposes, may be considered absolutely dry. The 3.2 and 3.6 litre VR6s will also be used to power a new MKV platform R32 (for Europe) and a new R36 model (North America). Wood that is thoroughly air-dried retains from 8-16% of water in the cell walls, and none, or practically none, in the other forms.

The introduction of the Passat VR6 also marked the first time a VR6 powered vehicle was made available in North American before Europe. In heartwood it occurs only in the first and last forms. Both the 3.2 and 3.6 feature FSI direct injection. Water occurs in living wood in three conditions, namely: (1) in the cell walls, (2) in the protoplasmic contents of the cells, and (3) as free water in the cell cavities and spaces. For North American, the Passat receives a new 3.6 L VR6 with a narrower 10.6 degree cylinder angle, producing 280 PS (276 hp/206 kW). If ease of working is prized, wood should be chosen with regard to its uniformity of texture and straightness of grain, which will in most cases occur when there is little contrast between the late wood of one season's growth and the early wood of the next. In 2005, the European market version of Volkswagen's fifth generation Passat went on sale with a revised version of the 3.2 L VR6 as its top-spec motor. In many uses of wood, strength is not the main consideration.

The 3.2 is now used as a range-topper in Audi A3 or as an entry level version in the VW Touareg and Porsche Cayenne, although the version used in the Cayenne features modifications to the heads as well as the intake and timing systems. In general it may be stated that such woods of medium growth afford stronger material than when very rapidly or very slowly grown. This variant produced 250 PS (247 hp/184 kW) and 320 Nm (236 ft•lbf) of torque in TT trim and 241 PS(238 hp/177 kW) in R32 trim. The effect of rate of growth is, therefore, not the same as in the ring-porous woods, approaching more nearly the conditions in the conifers. In 2003, a high performance 3.2 L version of the engine was introduced to power VW's limited-production Golf R32 and a new range-topping variant of the Audi TT. In diffuse-porous woods, as has been stated, the vessels or pores are scattered throughout the ring instead of collected in the early wood. The multivalve V6 was only introduced in North America in 2002 (where it retained the VR6 name). The effect of rate of growth on the qualities of chestnut wood is summarized by the same authority as follows:.

The corresponding multivalve V5 was only released in 2001, with a 20 PS power increase, to 170 PS (168 hp/125 kW). Forest Service show that:. The VR6 name was dropped as a commercial designation, and the 4WD system (4Motion) was now standard on the V6 in Europe. The results of a series of tests on hickory by the U.S. The new version was not available in the Passat (as it was incompatible with the then-current generation's longitudinal layout), but was introduced as the range topper in the Golf and Bora. Here not only strength, but toughness and resilience are important. This engine produced 204 PS (201 hp/150 kW) and 265 Nm (195 lb.ft) of torque. This is particularly the case in the choice of hickory for handles and spokes.

For 1999, VW added further modifications to the design, with the introduction of the 24-valve 2.8 L VR6. Wide-ringed wood is often called "second-growth", because the growth of the young timber in open stands after the old trees have been removed is more rapid than in trees in the forest, and in the manufacture of articles where strength is an important consideration such "second-growth" hardwood material is preferred. It was introduced in the Passat in 1997, and later in the Golf and Bora in 1999. Such variation is very largely the result of rate of growth. This version, which had a 2.3 L capacity, was capable of 150 PS (148 hp/110 kW) and had a maximum torque of 209 Nm (154 lb.ft). In inferior oak, such fibre areas are much reduced both in quantity and quality. In 1997, VW removed a cylinder from the VR6, creating the VR5, the first block to use an uneven number of cylinders in a V design. The late wood of good oak, except for radial grayish patches of small pores, is dark colored and firm, and consists of thick-walled fibres which form one-half or more of the wood.

The corresponding Vento/Jetta VR6 versions appeared in the same years. In good oak these large vessels of the early wood occupy from 6 to 10 per cent of the volume of the log, while in inferior material they may make up 25 per cent or more. North America only received this engine in 1995, at the same time the European model started to use the 2.9 L in the VR6 Syncro model. As the breadth of ring diminishes, this middle portion is reduced so that very slow growth produces comparatively light, porous wood composed of thin-walled vessels and wood parenchyma. In 1992, with the introduction of the Golf's third generation, a six-cylinder engine was available for the first time in a lower-midsize segment hatchback in Europe. In ring-porous woods of good growth it is usually the middle portion of the ring in which the thick-walled, strength-giving fibres are most abundant. This version also had a free flowing 6 cm (2.5 in) catalytic converter, enlarged inlet manifold and larger throttle body. This, it must be remembered, applies only to ring-porous woods such as oak, ash, hickory, and others of the same group, and is, of course, subject to some exceptions and limitations.

The Passat, Passat Variant wagon and US-spec Corrado used the original 2.8 L design, while the Euro-spec Corrado and the 4WD Passat Syncro received a 2.9 L version with 190 PS (187 hp/140 kW). This may be briefly summed up in the general statement that the more rapid the growth or the wider the rings of growth, the heavier, harder, stronger, and stiffer the wood. The VR6 engine was introduced in Europe in 1991 in the Passat and Corrado, and in North America the following year. In the case of the ring-porous hardwoods there seems to exist a pretty definite relation between the rate of growth of timber and its properties. These engines produced 174 PS (172 hp/128 kW) and 240 Nm (177 ft·lbf) of torque. But in choosing a particular specimen it is not the width of ring, but the proportion and character of the late wood which should govern. The original VR6 engine displaced 2.8 L and featured a 12 valve design. In general, however, it may be said that where strength or ease of working is essential, woods of moderate to slow growth should be chosen.

There are several different variants of the VR6 engine. The quality of the site where the tree grows undoubtedly affects the character of the wood formed, though it is not possible to formulate a rule governing it. This is most similar to a DOHC Inline-6 engine. In conifers, at least, rate of growth alone does not determine the proportion of the two portions of the ring, for in some cases the wood of slow growth is very hard and heavy, while in others the opposite is true. However, later (24 valve) VR6 engines use one camshaft for all intake valves and one camshaft for all exhaust valves. Several factors may be involved. This is most similar to the operation of a SOHC V6 engine. No satisfactory explanation can as yet be given for the real causes underlying the formation of early and late wood.

In early (12 valve) VR6 engines, one camshaft is used per bank of cylinders. One can judge comparative density, and therefore to some extent weight and strength, by visual inspection. This simplifies engine construction and reduces costs. In specimens that show a very large proportion of late wood it may be noticeably more porous and weigh considerably less than the late wood in pieces that contain but little. The narrow angle between cylinder banks also allows just two camshafts to drive all of the valves, and a single cylinder head to be used. It is not only the proportion of late wood, but also its quality, that counts. As a result, it is nearly as smooth as an Inline-6. The width of ring is not nearly so important as the proportion of the late wood in the ring.

In addition, the VR6 is able to use the firing interval of an Inline-6 engine. In choosing a piece of pine where strength or stiffness is the important consideration, the principal thing to observe is the comparative amounts of early and late wood. A wider V6 engine of conventional design would have required lengthening existing vehicles to provide enough crumple zone between the front of the vehicle and the engine, and between the engine and the passenger cell. The strength is in the walls, not the cavities. By using the narrow 15° VR6 engine, it was possible to install a six-cylinder engine in existing Volkswagen models. When examined under a microscope the cells of the late wood are seen to be very thick-walled and with very small cavities, while those formed first in the season have thin walls and large cavities. The VR6 was specifically designed for transverse installation in front wheel drive vehicles. The late wood of all species is denser than that formed early in the season, hence the greater the proportion of late wood the greater the density and strength.

The combination of the two can be roughly translated as "in-line Vee.". If a heavy piece of pine is compared with a light specimen it will be seen at once that the heavier one contains a larger proportion of late wood than the other, and is therefore considerably darker. The name, VR6 comes from a combination of Vee and the German word Reihenmotor (straight engine). Some species, such as walnut and cherry, are on the border between the two classes, forming an intermediate group. It is similar to the V engine, but with the cylinders offset from each other and tilted by 15° instead of the usual 60°. Examples of this kind of wood are basswood, birch, buckeye, maple, poplar, and willow. VR6 is an engine configuration developed by the Volkswagen Group. In diffuse-porous woods the pores are scattered throughout the growth ring instead of being collected in a band or row.

. These fibres are the elements which give strength and toughness to wood, while the vessels are a source of weakness. SEAT Leon Cupra. The rest of the ring, produced in summer, is made up of smaller vessels and a much greater proportion of wood fibres. Audi TT. In ring-porous species, such as ash, black locust, catalpa, chestnut, elm, hickory, mulberry, and oak, the larger vessels or pores (as cross sections of vessels are called) are localized in the part of the growth ring formed in spring, thus forming a region of more or less open and porous tissue. Audi A3 Mk.II. In discussing such woods it is customary to divide them into two large classes, ring-porous and diffuse-porous.

VW Sharan/SEAT Alhambra/Ford Galaxy. They are more or less filled with vessels: in some cases (oak, chestnut, ash) quite large and distinct, in others (buckeye, poplar, willow) too small to be seen plainly without a small hand lens. VW Transporter T4 and T5. The structure of the hardwoods is more complex. VW Touareg. There are no vessels ("pores") in coniferous wood such as one sees so prominently in oak and ash, for example. VW Phaeton. In coniferous or softwood species the wood cells are mostly of one kind, tracheids, and as a result the material is much more uniform in structure than that of most hardwoods.

VW Corrado. Ordinary sap-staining is due to fungous growth, but does not necessarily produce a weakening effect. VW Bora/VW Jetta Mk.IV. Certain rot-producing fungi impart to wood characteristic colors which thus become symptomatic of weakness. VW Vento/VW Jetta Mk.III. The discoloration is merely an indication of an injury, and in all probability does not of itself affect the properties of the wood. VW Passat (B3, B4, and B6 chassis). The reddish-brown streaks so common in hickory and certain other woods are mostly the result of injury by birds.

Golf R32 MK.IV and Mk.V. The black check in western hemlock is the result of insect attacks. VW Golf Mk.III and Mk.IV. Abnormal discoloration of wood often denotes a diseased condition, indicating unsoundness. Except in the manner just stated the color of wood is no indication of strength. In ring-porous woods the vessels of the early wood not infrequently appear on a finished surface as darker than the denser late wood, though on cross sections of heartwood the reverse is commonly true.

This is particularly the case with coniferous woods. Since the late wood of a growth ring is usually darker in color than the early wood, this fact may be used in judging the density, and therefore the hardness and strength of the material. Spruce impregnated with crude resin and dried is also greatly increased in strength thereby. Stumps thus dug may actually remain a century or more since being cut.

Stumps of old longleaf pines are often dug, split into small pieces and sold as kindling for fires. Structures built of fat lighter are almost impervious to rot and termites; however they are very flammable. Such resin-saturated heartwood is called "fat lighter". This is due to the resin which increases the strength when dry.

Some experiments on very resinous Longleaf Pine specimens, however, indicate an increase in strength. This is produced by deposits in the heartwood of various materials resulting from the process of growth, increased possibly by oxidation and other chemical changes, which usually have little or no appreciable effect on the mechanical properties of the wood. In species which show a distinct difference between heartwood and sapwood the natural color of heartwood is usually darker than that of the sapwood, and very frequently the contrast is conspicuous. yew) are harder than most hardwoods.

Conversely, some softwoods (e.g. The well-known balsa (a hardwood) is actually softer than any commercial softwood. These names are a bit misleading, as hardwoods are not necessarily hard, and softwoods are not necessarily soft. oak) is called hardwood.

pine) is called softwood, and the wood from broad-leaved trees (e.g. The wood from conifers (e.g. Wood is commonly classified as either softwood or hardwood. The densest wood may be black ironwood.

For example, while mahogany is a medium-dense hardwood which is excellent for fine furniture crafting, balsa is light, making it useful for model building. There is a rough correlation between density of a wood and its strength (mechanical properties). For every trees species there is a range of density for the wood it yields. There is a strong relationship between the properties of wood and the properties of the particular tree that yielded it.

In a large log the sapwood, because of the time in the life of the tree when it was grown, may be inferior in hardness, strength, and toughness to equally sound heartwood from the same log. In some trees, the wood laid on late in the life of a tree is softer, lighter, weaker, and more even-textured than that produced earlier, but in other species, the reverse applies. There may be decided differences in the grain of heartwood and sapwood cut from a large tree, particularly one that is mature. Upon the whole, however, as a tree gets larger in diameter the width of the growth rings decreases.

Some trees, such as southern oaks, maintain the same width of ring for hundreds of years. In the case of forest-grown trees so much depends upon the competition of the trees in their struggle for light and nourishment that periods of rapid and slow growth may alternate. As a tree reaches maturity its crown becomes more open and the annual wood production is lessened, thereby reducing still more the width of the growth rings. Since each succeeding ring is laid down on the outside of the wood previously formed, it follows that unless a tree materially increases its production of wood from year to year, the rings must necessarily become thinner as the trunk gets wider.

The annual rings of growth are for many years quite wide, but later they become narrower and narrower. If a tree grows all its life in the open and the conditions of soil and site remain unchanged, it will make its most rapid growth in youth, and gradually decline. Whatever advantages, however, that sapwood may have in this connection are due solely to its relative age and position. The larvae of many insects bore into the trees and their tunnels remain indefinitely as sources of weakness.

Every broken limb or root, or deep wound from fire, insects, or falling timber, may afford an entrance for decay, which, once started, may penetrate to all parts of the trunk. It is remarkable that the inner heartwood of old trees remains as sound as it usually does, since in many cases it is hundreds of years, and in a few instances thousands of years, old. Since in most uses of wood, knots are defects that weaken the timber and interfere with its ease of working and other properties, it follows that sapwood, because of its position in the tree, may have certain advantages over heartwood. Consequently the sapwood of an old tree, and particularly of a forest-grown tree, will be freer from knots than the heartwood.

No matter how smooth and clear a log is on the outside, it is more or less knotty near the middle. Subsequent growth of wood may completely conceal the stubs which will however remain as knots. When a tree is very young it is covered with limbs almost, if not entirely, to the ground, but as it grows older some or all of them will eventually die and be broken off. Sapwood is thicker in the upper portion of the trunk of a tree than near the base, because the age and the diameter of the upper sections are less.

As the tree gets larger, the sapwood must necessarily become thinner or increase materially in volume. If the rings are narrow, more of them are required than where they are wide. Within the same species the cross-sectional area of the sapwood is very roughly proportional to the size of the crown of the tree. There is no definite relation between the annual rings of growth and the amount of sapwood.

Thin sapwood is characteristic of such trees as chestnut, black locust, mulberry, osage-orange, and sassafras, while in maple, ash, hickory, hackberry, beech, and pine, thick sapwood is the rule. Some species begin to form heartwood very early in life, so having only a thin layer of live sapwood, while in others the change comes slowly. This is shown by the fact that a tree can thrive with its heart completely decayed. Its name derives solely from its position and not from any vital importance to the tree.

This inert or dead portion is called heartwood. As a tree increases in age and diameter an inner portion of the sapwood becomes inactive and finally ceases to function, as the cells die. Sometimes trees grown in the open may become of considerable size, 30 cm or more in diameter, before any heartwood begins to form, for example, in second-growth hickory, or open-grown pines. Hence trees making rapid growth in the open have thicker sapwood for their size than trees of the same species growing in dense forests.

The more leaves a tree bears and the more vigorous its growth, the larger the volume of sapwood required. Its principal functions are to conduct water from the roots to the leaves and to store up and give back according to the season the food prepared in the leaves. All wood in a tree is first formed as sapwood. Sapwood is comparatively new wood, comprising living cells in the growing tree.

The color of fresh sapwood is always light, sometimes nearly white, but more often with a decided tinge of yellow or brown. In some instances this distinction in color is very marked; in others, the contrast is slight, so that it is not always easy to tell where one leaves off and the other begins. Examination of the end of a log of many species reveals a darker-colored inner portion, called the heartwood or duramen, surrounded by a lighter-colored zone called the sapwood. wall panelling, knots are considered a plus as they add visual texture to the wood, giving it a more interesting appearance.

For some purposes, e.g. Sound knots do not weaken wood when subject to compression parallel to the grain. The breaking strength is very susceptible to defects. The effect of knots is to reduce the difference between the fibre stress at elastic limit and the modulus of rupture of beams.

Stiffness and elastic strength are more dependent upon the quality of the wood fibre than upon defects in the beam. Only defects of the most serious character affect the elastic limit of beams. Knots do not necessarily influence the stiffness of structural timber. Sound knots which occur in the central portion one-fourth the height of the beam from either edge are not serious defects.

Knots which occur near the ends of a beam do not weaken it. Knots in a board or plank are least injurious when they extend through it at right angles to its broadest surface. Small knots, however, may be so located in a beam along the neutral plane as actually to increase the strength by tending to prevent longitudinal shearing. The knot, especially (as is often the case) if there is a season check in it, offers little resistance to this tensile stress.

A knot on the upper side is compressed, while one on the lower side is subjected to tension. The extent to which knots affect the strength of a beam depends upon their position, size, number, direction of fibre, and condition. The weakening effect is much more serious where timber is subjected to bending and tension than where under compression. They are defects which weaken timber and depreciate its value for structural purposes where strength is an important consideration.

Knots materially affect checking (cracking) and warping, ease in working, and cleavability of timber. In grading lumber and structural timber, knots are classified according to their form, size, soundness, and the firmness with which they are held in place. Hence dead branches produce knots which are nothing more than pegs in a hole, and likely to drop out after the tree has been sawn. Subsequent layers of growth of the stem are no longer intimately joined with the dead limb, but are laid around it.

During the development of a tree the lower limbs die, but may persist for a time--often for years. Note that a small knot may also be the result of a dormant bud. The fibre direction is at right angles or oblique to the grain of the stem, thus producing local cross grain. The included portion is irregularly conical in shape with the tip at the pith.

Branches generally originate at or near the pith (central axis) of a stem, and the living portion will increase in size through the addition of annual woody layers which are a continuation of those of the stem. Knots are portions of branches included in the wood of the stem or larger branch. In the diffuse-porous woods, the demarcation between rings is not always so clear and in some cases is almost (if not entirely) invisible to the unaided eye. In ring-porous woods each season's growth is always well defined, because the large pores of the spring abut on the denser tissue of the fall before.

In hard pines, on the other hand, the late wood is very dense and is deep-colored, presenting a very decided contrast to the soft, straw-colored early wood. In white pines there is not much contrast in the different parts of the ring, and as a result the wood is very uniform in texture and is easy to work. The outer portion is the late wood or summer wood, being produced in the summer. The inner portion is formed early in the season, when growth is comparatively rapid; it is known as early wood or spring wood.

The part nearest the centre of the tree is more open textured and almost invariably lighter in color than that near the outer portion of the ring. Within a growth ring it may be possible to see two more or less well-defined parts. Where there is no seasonal difference growth rings are likely to be absent. If these seasons are annual these growth rings are annual rings.

Where there are clear seasons, this can happen in a discrete pattern, leading to what is known as growth rings, as can be seen on the end of a log. A tree increases in diameter by the formation, between the old wood and the inner bark, of new woody layers which envelop the entire stem, living branches, and roots. Wood may be broken down and be made into chipboard, engineered wood, hardboard, medium-density fibreboard (MDF), oriented strand board (OSB), paper or used to make other synthetic substances. Construction wood is commonly known as timber in International English, and lumber in American English.

Wood has been an important construction material since humans began building shelters, and remains in plentiful use today. It is also used as a material, for making artworks, boats, buildings, furniture, ships, tools, weapons, etc. One of its primary uses is as fuel. Wood has been used by man for millennia for many purposes, being many things to many people.

. Dry wood is composed of fibers of cellulose (40%–50%) and hemicellulose (20%–30%) held together by lignin (25%–30%). Wood is a hygroscopic, cellular and anisotropic material. In its most common meaning, "wood" is the secondary xylem of a woody plant, but this an approximation only: in the wider sense, wood may refer to other materials and tissues with comparable properties.

Wood from the latter is only produced in small sizes, reducing the diversity of uses. Wood derives from woody plants, notably trees but also shrubs.