The Motor Vehicle 2010 Part 3 ppt

164 The Motor Vehicle 4.17 Inlet and e xhaust manif olds The stainless steel exhaust manifold is double skinned. Its inner sections are produced by internal high pressure hydraulic forming at pressures of over 2000 bar. As can be seen from Fig. 4.26, this manifold is of complex shape. Advantages of the use of high pressure hydraulic forming include light weight, the fact that there is no need for welded seams, and the walls are uniformly thin throughout. The thermal capacity of the complete manifold is low and the air gap between its double skins is a good insulator, so the catalytic converter warms up more rapidly than if the manifold had been of cast iron. Magnesium alloy is used for the combined inlet manifold and plenum chamber. In Fig. 4.27 it can be seen that the induction tracts pass round the plenum chamber before joining the inlet ports in the cylinder head. A rectangular butterfly valve in a port opening into the plenum, approximately mid-way along it, divides it into two parts, one 465 mm and the other 350 mm long. For operation above 3700 rev/min, the butterfly valve shuts off the longer portion, simultaneously opening a port between the plenum and the shorter one. At speeds below 3700 rev/min, this valve closes the port to the plenum and simultaneously connects the long and short sections in series to form a single tract 835 mm long. The basic principle of such systems is explained in Section 13.19. Fig. 4.26 The inner sections of the double skinned exhaust manifold are produced by hydraulic forming 165 Six-, eight- and twelve-cylinder engines Fig. 4.27 An integral plenum chamber is formed coaxially within the magnesium alloy induction manifold 4.18 The ASSYST maintenance system To fine tune oil change intervals, Mercedes have introduced what they term the ASSYST system. A computer-controlled instrument on the dash fascia indicates when an oil change is needed. Its reading is based on how hard and how frequently the car is driven with a cold engine. One advantage is the avoidance of unnecessarily frequent oil changes, and thus conservation of oil; furthermore the engine is protected against wear arising from failure to replace oil when it really is necessary to do so: and, of course, it can save the owner from wasting money on unnecessarily short oil change intervals. 4.19 The V-eight The straight eight engine, in addition to the liability to torsional oscillation of the crankshaft, is very long. Consequently, the alternative of a V-eight layout, with two banks of four cylinders set 90° apart, is more attractive despite its complexity. This arrangement is now of course widely used, though mainly in the USA. Following earlier pioneer designs, large-scale development was initiated by Cadillac in 1914, and aircraft and tank development produced air-cooled types. The flat or single plane crankshaft was used in these early constructions, 166 The Motor Vehicle but in 1926 Cadillac, and in 1932 Ford, introduced the 90° arrangement, the improved balance of which is described below. Side valves gave place to overhead valves from 1949 onwards. The early Ford 22 hp and 30 hp V-eight engines had some success in the UK but, because their power output was higher than was normally required for cars, production was discontinued and the traditional in-line layout remained in production in the UK. In the USA, however, the low cost of fuel, the early availability of 100 octane fuel, and the demand for large cars meant that the V layout, with swept volumes of around 4.7 litres, has remained popular. 4.20 Balance and firing intervals of V-eight With the single plane crankshaft, the 90° firing intervals are obtained by the disposition of the cylinders in two banks at right angles, whereas with the two-plane shaft, four of the intervals are due to cylinder disposition and four to crank arrangement. The flat crankshaft is a simpler and, therefore, with comparable production methods, a less expensive form to make, but the dynamic balance of the engine is inferior to that obtained with the right-angle disposition of cranks. The former arrangement is, for balancing purposes, treated as two ordinary four-cylinder engines sharing the same crankshaft, each set of four pistons being self-balanced for primary forces and couples, while the secondaries remain unbalanced in each bank. This gives a combined resultant secondary force for the whole engine which is zero in the ‘vertical’ direction, but has, in the ‘horizontal’ direction a value 40% greater than that corresponding to one set of four pistons since the horizontal components combine in the ratio √2:1, while the vertical components neutralise each other. When the right-angle disposition of adjacent cranks is adopted, the engine is treated for balancing purposes as four 90° V twins, and the primary forces are counteracted by means of revolving masses in the manner described in Section 2.2. The combined primary reciprocating effect of the two pistons, operating on the same crankpin and with their lines of stroke at right angles, is equivalent to the mass of one piston revolving at the crankpin, and the balancing problem is reduced to that of a revolving system. In the V-eight crankshaft illustrated in Fig. 4.28 the thinner webs adjacent to the journals may be regarded as circular disc webs each corrected to neutralise half of the actual revolving mass at each crankpin, that is, half the pin and one of the big ends. The heavy masses B 1 and B 2 each incorporate in effect two of these corrected disc webs, together with further masses to balance both the adjacent equivalent revolving masses representing the effect of the two pistons on each pin. If component couples in the plane of the paper for the lower view are considered, it will be realised that the arm of the couple due to cranks 1 and 4, which form a clockwise component couple, is greater than the arm of the component couple due to cranks 2 and 3, acting in the contrary sense. This is corrected by giving the masses B 1 and B 2 , which act in intermediate planes, a bias to assist their opposition to cranks 1 and 4. This bias accounts for the unsymmetrical form of the masses. Since the balance of the pistons involves masses incorporated in the crankshaft, it will be realized that not only should the piston masses be held 167 Six-, eight- and twelve-cylinder engines 4 3 2 8 7 6 5 Rear 1 Front Fig. 4.28 Diagram of V-eight to close tolerances among themselves, as in the four-cylinder engine, but also that their relation to the crankshaft must be carefully checked. 4.21 Secondary balance with two-plane shaft The secondary balance with the right-angle shaft is superior to that of the flat shaft. It will be found that adjacent pairs of pistons in each bank, moving in the same longitudinal plane, operate on cranks at right angles. Thus when one piston is at the position corresponding to θ = 0 (see Fig. 4.9) its neighbour in the same bank has θ = 90°, and the corresponding secondary forces will be opposed. Figure 4.28 shows the disposition of the cylinders and cranks, the shaft being indicated with five main bearing journals in order to make clear the relative disposition of the throws. The arrows represent the secondary disturbing forces in the configuration shown, and it will be seen that these are self- balanced in each bank, for both forces and couples. 4.22 Construction of V-eight A cross-section of the early Ford side-valve engine is given in Fig. 4.29, which shows the salient special features. The two banks of cylinders and the crankcase are formed in a single monobloc casting, the sump which forms the lower half of the crankcase being a light steel pressing. Detachable heads with side valves operated from a single camshaft are conventional features, while the somewhat inaccessible position of the tappets and valve springs is mitigated by the special construction adopted. The tappets are non-adjustable, and the valve stems have a wide splayed foot which minimises wear at this point. The valve stem guide is split along its centre line for assembly around the valve stem, and the whole assembly may be withdrawn upwards through the cylinder block after removal of a retainer of flat horseshoe form. Precision gauging during assembly is claimed to render adjustment between periodical regrindings unnecessary, and so enables a simpler construction to be adopted. 168 The Motor Vehicle Fig. 4.29 Cross-section of early V-eight A twin down-draught carburettor is fitted to a unit induction manifold and cover, rendering the whole assembly compact and of clean exterior form. Numbering the off-side cylinders 1, 2, 3, 4 and the near-side 5, 6, 7, 8, as in Fig. 4.28, the near-side choke feeds numbers 1, 6, 7 and 4 while the off-side choke feeds 5, 2, 3 and 8. The firing order is 1 5 4 8 6 3 7 2, resulting in a regular interval of half a revolution between cylinders fed from the same choke. The induction tracts are symmetrically arranged, but are not equal in length for all cylinders. Mounted at the rear of the induction manifold may be observed the crankcase breather and oil-filler, up which passes the push rod for operating the AC fuel pump. 4.23 A British V-eight engine A most interesting V-eight unit, because it is designed for production in large numbers and in conjunction with an in-line four-cylinder engine, is that used in the Triumph Stag, Automobile Engineer, July 1970. An in-line version, comprising in effect one bank of the V-eight unit, but incorporated in a different crankcase, is that of the 1708 cm 3 Saab 99, Automobile Engineer, September 1968. This engine was subsequently used in the Triumph Dolomite range. The bore and stroke dimensions of the Saab version were originally 83.5 × 78 mm, but the bore was subsequently increased to 87 mm, giving a swept volume of 1850 cm 3 . 169 Six-, eight- and twelve-cylinder engines For the 2997 cm 3 V-eight unit (Fig. 4.30), the bore is 86 mm and the stroke 64.5 mm. This gives a mean piston speed of 11.83 m/s at 5500 rev/ min, at which the maximum power, 108 kW, is developed. The valve overlap and lift of the V-eight are larger than those of the in-line engine, helping to give a much higher maximum torque – 235 Nm at a speed of 3500, instead of 137.3 Nm at 3000 rev/min – but steeper flanks to the torque curve. Fig. 4.30 The Triumph Stag V-eight engine has an inclined drive for the oil pump and ignition distributor, while the water pump, also driven from a spiral gear on the camshaft, is vertically incorporated between the banks of cylinders, thus economising on overall length and simplifying the drive arrangement 170 The Motor Vehicle With a V-angle of 90° – the four cylinder version is canted over at 45° – and a two-plane crankshaft, complete balance can be achieved. The first and fourth crankpins are displaced 90° from the second and third. Cylinders 1, 3, 5 and 7 are in the right-hand bank and numbers 2, 4, 6 and 8 in the left-hand one, so the firing order is 1 2 7 8 4 5 6 3. In the right-hand bank, the cylinders are set 19.8 mm forward of those in the left. At the front end of the crankshaft, a Holset viscous coupling limits the torque transmitted to the fan to 6.56 Nm and its mean speed to 2400 rev/min, thus reducing waste of power when the engine is operating at high speed. There are several other features of special interest. First, the auxiliary drive layout is common to both the V-eight and the four-cylinder units: a jackshaft rotating at two-thirds crankshaft speed and carried in the base of the V – an arrangement possible because of the use of the overhead camshaft layout – is driven by the timing chain for the camshaft of the left-hand bank, machined on the jackshaft are two spiral gears, one to drive the spindle for the water pump installed vertically in the V, and the other for the spindle driving the ignition distributor – inclined towards the left in the V – and the oil pump, which is on the left, near the base of the crankcase, Fig. 4.30. With this layout, the water pump does not add to the length of the engine, as it would if mounted horizontally in front. Apart from this, the drive to each single overhead camshaft is a simple run of chain from the crankshaft to camshaft pulleys with, in each case, a Renold hydraulic tensioner and a nitrile rubber-faced arcuate guide bearing against the slack run and a nitrile rubber-faced flat damping strip on the taut driving run. So that the valve gear can be completely assembled on the head before it is mounted on the block, but without impairing accessibility for tightening the cylinder head on the block, five bolts and five studs are used to secure the two: the bolts are perpendicular to the joint face, but the studs are inclined at an angle of 16 1 2 ° relative to the axes of the cylinders and, to sustain the component of the tightening force parallel to the joint face, they are a close fit in reamed holes in the head. The in-line valves are inclined at an angle of 26° inwards, and wedge- shaped combustion chambers are employed. Each exhaust valve comprises a 21-4 N steel head welded to an En18 stem. These seat on the Brico 307 sintered iron inserts in the aluminium head – the use of sintered powdered components saves a lot of machining. To clear the heads of the valves, and to form part of the combustion chambers, the crowns of the pistons are slightly dished. Two Stromberg 175-CDS carburettors are mounted on top of the manifold. Each discharges into an H-shape tract, one serving number 2, 3, 5 and 8 cylinders and the other numbers 1, 4, 6 and 7, so that the induction impulses occur alternately in each, Fig. 4.31. A balance duct is cored in the wall between the two risers. All the coolant leaving the cylinder heads passes through passages cored beneath the inlet tracts, leaving through the thermostat housing, which is integral with the manifold, Fig. 4.31, section AA. To satisfy emission regulations in the USA, an alternative exhaust heated manifold can be supplied. It has an 82.55-mm wide transverse passage, which communicates with the exhaust ports of numbers 3 and 5, and 4 and 6 cylinders, the gas leaving again through a port at the front. The alternative arrangement is shown in the scrap 171 Six-, eight- and twelve-cylinder engines 7 8 6 4 2 3 1 5 AA 1 A - A Fig. 4.31 Triumph Stag induction system. Section AA shows the water heating ducts and the upper section shows an alternative exhaust gas heating passage to meet US emission control requirements view above section AA, Fig. 4.31. In addition, a thermostatically-controlled warm air intake system is incorporated. This type of device is described in Section 14.11. 4.24 Jaguar 5.3-litre V-twelve Obviously, success with any design depends on meeting the requirements of a distinctly identifiable sector of the market. A high proportion of Jaguar cars is sold in the USA and for this reason the 60° V-twelve layout was decided upon. First, it offers something different from the common run of V -eights in that country. Secondly, with a swept volume of 5343 cm 3 , its potential is ample both to provide enough power for use with automatic transmissions and to offset limitations imposed by current or foreseeable future measures for avoiding atmospheric pollution by exhaust gas constituents. Thirdly, it is inherently in balance and, with six equally placed firing impulses per revolution, it is not only free from torsional resonances but also smooth running. In this chapter, it will be possible to outline only a few interesting features of the design, Figs 4.32 and 4.33, but a full description was published in the April 1971 issue of Automobile Engineer. To save weight, aluminium castings are used for the cylinder block and heads, the sump, oil cooler, timing cover, coolant pump casing, tappet carriers, camshaft cover, induction manifolds, coolant outlet pipes, thermostat housing and the top cover of the crankcase. Although the crankcase was designed so that it could be diecast, sand casting is currently employed. With an open-top deck and wet liners, simple cores can be used and the sealing of the liners, by compressing them between the 172 The Motor Vehicle Fig. 4.32 Transverse section of the Jaguar V-twelve engine showing how the problem of differential expansion between the aluminium crankcase and the iron liners is minimised by incorporating the flange high up around the periphery of the liner. head and the block, is relatively easy; on the lower seating flanges, Hylomar sealing compound is used to prevent any possibility of leaking of water into the crankcase. The length of the liners between these flanges and the upper ends is only about 44.4 mm, so problems due to differential expansion of the iron liners and aluminium block are reduced to a minimum, while the hottest portions of the liners are in direct contact with the water. Cast iron main bearing caps are used, and they are each held down by four studs. This ensures adequate rigidity, for avoidance of crankshaft rumble. It also reduces to a minimum variations in clearance due to thermal expansion. A shallow combustion chamber depression in the crown of the piston, beneath the completely flat face of the cylinder head, was found to give a clean exhaust gas – originally, a deep chamber with clearances machined beneath the valves was tried. To reduce emissions it was also found necessary to lower the compression ratio to 9 : 1 from the 10.6 : 1 originally conceived. The stroke : bore ratio is 0.779 to 1 (70 to 90 mm) and the maximum torque 173 Six-, eight- and twelve-cylinder engines Fig. 4.33 On the Jaguar V-twelve engine, cast-iron main bearing caps are used, each being held down by four studs screwed into the aluminium crankcase [...]... output goes through a filter to the engine, while the other half passes through the relief valve, which lifts at 4 83 kN/m2, to the oil cooler integral with the filter housing at the front end of the sump The return flow from the base of the radiator to the water pump inlet passes through this cooler, lowering the temperature of the oil by about 22°C and increasing that of the water by only just over 1°C... is formed to constitute the combustion chamber As the valve rotates the cell is presented in turn to the inlet port I, the sparking plug P and the exhaust port E During compression, ignition and combustion the cell is on the cool side of the cylinder, and after ignition the plug is shielded from the hot gases These conditions play a great part in the thermodynamic properties of the engine In this early... though the form of the combustion chamber has an important influence, the longer the delay period the steeper will be the second phase and the rougher the running, as a greater proportion of fuel is present The nature of the fuel, the temperature and pressure of compression, and initial rate of fuel injection are all factors in deciding the length of the delay period apart from the form of the combustion... corresponding to the full vertical throw of the ball B while the extent of the rotational movement produced by the horizontal throw of the ball depends upon the distance between the centre of that ball and the axis of the sleeve 5.2 Arrangement of ports The form and arrangement of the ports are arrived at as the result of considerable theoretical and experimental investigation in order that the maximum... and limits the maximum pressure The pre-chamber represents about 40% of the total clearance volume, and the fuel is injected into this air and partly burned, the spread of ignition being helped by the turbulence arising from the passage of the air through the communicating pepper-castor holes during compression The products of this partial combustion and the remaining fuel are then forced by the excess... 188 The Motor Vehicle the accompanying bulk of blast air, which was from 2 to 3% of the total air, lengthened the injection period with the result that the pressure did not rise during combustion, but was merely maintained at approximately the compression pressure as the piston moved outwards until combustion was completed This led to the use of the expression constant pressure cycle to describe the diesel... respect with the petrol engine 6.4 Power : weight ratio The above ratio of mean to maximum pressure is the determining factor in the value of the power : weight ratio, since the power depends on the mean pressure while the sturdiness and therefore weight of the parts will depend on the maximum pressure to be provided for Thus, the compression-ignition engine is inherently heavier than its rival the petrol... roller chain passes round the drive sprocket on the crankshaft, the two camshaft sprockets and, in the base of the V, the jackshaft sprocket for driving the Lucas Opus contact breaker and distributor unit A Morse tensioner bears against the slack run of the chain and a damper strip against each of the other runs between the sprockets This tensioner is described in Section 3. 51 For the lubrication system,... 175 With the May Fireball combustion chamber there are two zones in the cylinder-head casting One is a circular dished recess in which is the inlet valve, and the other, extending further up into the cylinder head, accommodates both the exhaust valve and the sparking plug Because the compression ratio is required to be high, the combustion chamber has to be fully machined, otherwise both the tolerances... forms of rotor Recesses in the curved faces are provided to obviate strangling of the charge during passage from one zone to the next The form of these faces, subject to the necessary compression ratio being provided, is not limited to any particular profile Fig 5.7 184 The Motor Vehicle Cooling has not presented many problems, because the complex movements of the rotor, and the resultant changing accelerations, . one to drive the spindle for the water pump installed vertically in the V, and the other for the spindle driving the ignition distributor – inclined towards the left in the V – and the oil pump,. compressing them between the 172 The Motor Vehicle Fig. 4 .32 Transverse section of the Jaguar V-twelve engine showing how the problem of differential expansion between the aluminium crankcase and the. through the relief valve, which lifts at 4 83 kN/m 2 , to the oil cooler integral with the filter housing at the front end of the sump. The return flow from the base of the radiator to the water