The Motor Vehicle 2010 Part 5 potx

304 The Motor Vehicle Fig. 7.64 Left, with rising fuel pressure due to increasing speed, the piston is progressively moved to the right, advancing the ignition. Right, as speed and therefore fuel pressure fall, the piston is moved to the left by its return spring regulated by the ECU, and its function is to modify the basic, or speed dependent, timing in relation to engine load and temperature. 7.32 Stanadyne rotary distributor pumps The forerunner of all the pumps of this type so far described was the invention sold in 1947 to the Hartford Division of Stanadyne by Vernon Roosa. Two features distinguished this invention: one was the substitution of two opposed plungers for the then universal arrangement of one plunger for each engine cylinder; the other was the use of inlet, instead of spill, metering. The latter feature meant that the unit was almost self-governing, so that only a simple low cost governor was needed. By virtue of its compactness and simplicity, this pump could be produced at a much lower cost than the in-line pumps. After 5 years of development, the Roosa Master Model A pump, with mechanical governing, was put in production. In 1952, it was supplied to the Hercules Motors Corporation, for fitting to the Oliver Cletrac tractors. Between 1955 and 1958, the Model B and D pumps were introduced and, in 1958, the Model DB replaced the A and D units. In 1972, the DM, with a heavier section rotor and four plungers, was introduced. The DB2, a second generation DB pump, was first produced in 1972. As can be seen from Figs 7.65 and 7.66, it is similar to the Lucas DP Series, Section 7.1, originally produced under licence from Stanadyne, but the differences are of considerable interest. The two- and all-speed governors, Sections 7.8 and 7.12, differ only in detail. On the two-speed version, however, provision is made for fuel temperature compensation. The rate of change of fuel flow per 10°C change in temperature is about 0.9% by weight and 1.8% by volume. Temperature compensation is especially desirable if the pump is mounted between the banks of engines of the V layout, where it can become very hot. Idling speed decreases with increase in fuel temperature, and adjustment for 305 Distributor type pumps Fig. 7.65 The Stanadyne DB2 pump with a solenoid-actuated mechanism in the top cover, for key start and stop operation Transfer pump Automatic advance Governor spring Governor Mech. fuel Charging annulus Housing press. reg. Plungers Rotor Delivery valve Head passage Return to tank Metering valve Main filter Fuel pressure regulator Nozzle Injection pressure circuit Fuel supply housing bypass and return circuits pressure circuit Separator compensation device Fuel tank Lift pump Vent wire shut-off To injectors Transfer pump Viscosity Fig. 7.66 Schematic diagram of the Stanadyne DB2 system 306 The Motor Vehicle increasing the idling speed to prevent stalling may be impracticable in vehicles with automatic transmission. The solution is to mount a bimetal strip in series with the idling spring, Fig. 7.67. This bimetal strip is biased in a manner such that, as the temperature of the fuel in the pump rises, the open area of the fuel metering valve increases. An entirely different thermal problem can arise during rapid acceleration at low temperatures. The shearing of the oil film in the distributor head generates a considerable amount of heat and the mass of distributor shaft is less than that of the sleeve in which it rotates. In these circumstances, this shaft can become significantly hotter and therefore expand more rapidly, closing the clearance between it and the sleeve. This can cause seizure. Stanadyne have found that this problem can be overcome by machining a peripheral groove midway between the ends of the bearing surfaces, which is the region that becomes hottest. The rotor is similar to that in Fig. 7.21, but there are no grooves in the ends of the maximum fuel adjustment plates, which Stanadyne call leaf springs. The arrangement of the fuel delivery ducting in the rotor differs from that of the Lucas pumps. Passing axially along to the end of the rotor, which is counterbored to house a delivery valve Fig 7.68, is the high pressure delivery duct from the plungers. From this illustration, it can be seen that a duct is drilled from the periphery of the rotor into the chamber that houses the delivery valve return spring. During rotation, it is aligned in turn with each Throttle shaft + Fuel Idle spring Bi-metallic element + – Fuel Effect of fuel temperature on idle speed Engine speed–(rpm) 700 600 500 Compensated Uncompensated Fig. 7.67 Above, the mechanism for temperature compensation of engine idling speed. Below, the 100 120 140 160 180 200 effect of temperature Fuel temperature (°F) compensation 307 Distributor type pumps h Fig. 7.68 This delivery valve is housed in a counterbore in the end of the distributor rotor of the ports leading to the injectors. As the delivery valve returns to its seat, following injection, its end remote from the seat enters the bore in which the valve slides and withdraws with it some of the fuel from the delivery line. This generates a negative pressure wave, which rebounds along the delivery line to each injector, to prevent secondary injection or dribbling. If the retraction volume is large, vapour-filled cavities can form just downstream of the delivery valve. This can be avoided by installing a snubber valve, Fig. 7.69, in each pipe connection. The snubber is a plate type valve with a hole through its centre, to damp reflected pressure waves. Its effect, therefore, is to enable a smaller retraction volume to be specified for the delivery valve. The injection timing advance mechanism is similar to those previously described. Its maximum advance for eight-cylinder engines is 10° of pump shaft rotation and for the others 12°. If, however, the fuel delivery volume is Fig. 7.69 On the DB2 pump, snubber valves are installed in the pipe connections to the cylinders. The small axial hole through the valve damps reflected waves, to reduce the potential for cavitation erosion 308 The Motor Vehicle less than 30 mm 3 per stroke, the advance may be increased by 1° or 2°. A servo-controlled advance is also available. This advance compensates for two effects: the ignition delay period and the time taken for the pressure wave to travel from the pump plungers to the injectors. The formula used to calculate the advance needed is: (Cam advance = LN 2 – N1) 16 800 where L = length of delivery line, inches N2 = rated speed N1 = minimum full load speed. This formula is based on the assumptions that there are no vapour cavities in the line and that the wave speed is 4200 ft/s or 1280.16 m/s. If metric units are used throughout, the constant 16 800 becomes 130.064. 7.33 Stanadyne DS electronically controlled pump This pump, introduced in 1993, is similar mechanically to the DB2 unit, but without the governor. It is capable of delivering 75 mm 3 per stroke at 1200 bar at the injectors of four-cylinder engines. A high capacity belt drive can be employed if required. The quantity of fuel delivered to the four plunger is regulated by an electronically controlled poppet type spill valve. A stepper motor actuates the cam-ring advance mechanism. With these arrangements, both the timing and quantity of fuel injected are accurately regulated in relation to load, speed and other engine parameters, while keeping to a minimum, under all conditions of operation, emissions of HC, CO, NO x and smoke. Accuracy of control is further assured by housing the cam rollers and tappets in the large diameter drive shaft with zero backlash. Thus the distributor is isolated from the drive, and therefore isolated from torsional oscillations that might lead to inaccuracies in the timing. The layout of the pump can be seen in Fig. 7.70. A commendable feature, and unique at the time of its introduction, is the housing of the spill valve coaxially in a counterbore in the end of the rotor. With this arrangement, the volume of fuel subjected to injection pressures is very small, so there is less risk of compressibility causing the injection characteristics to depart from those dictated by the profile of the cam geometry. Situated at the top of the unit, the fuel inlet is readily accessible, even on V engines. Other advantages claimed by Stanadyne are as follows. A heavy duty drive, and flexibility in respect of the all of the following: governing, idle speed and cold running control, fuel metering and timing control on a shot-to-shot basis. Fig. 7.71 illustrates the control system. Pump speed, angular pulse train data and data based on signals from the engine-mounted sensors are continuously updated by the electronic control module (ECM). They are processed by custom algorithms, and the resultant command signals are sent to the pump-mounted solenoid driver (PMD) and cam-ring advance stepper motor. Because a single, high speed solenoid is used for the control functions, the benefits of ease, flexibility and accuracy of signal processing associated 309Distributor type pumps Discharge fitting Pump housing Solenoid Poppet valve Advance Cam Electric shut-off (ESO) Needle bearing From electronic control module (ECM) Optical sensor timing encoder (OSTE) From pump mounted driver Advance stepper motor Drive shaft Fig. 7.70 The Stanadyne DS electronically controlled pump was introduced late in 1993 Coolant temperature Crankshaft reference Throttle sensor Closure ECM Memory Processor network Switched inputs Outputs Spare Warning lamp Inject EGR Start aids Communications Diagnostics Starting aids EGR control DS pump Pump mounted driver Lamp Fuel Temperature OSTE pump speed and reference Fig. 7.71 Schematic diagram of the DS electronic control system with digital control have been obtained. Fuel metering and timing are regulated as a function of the input data to the ECM, which controls the PMD. The latter supplies the injection command signals and a constant current. Closure of the poppet type spill valve is detected by the PMD and signalled back to the ECM. The timing and quantity of fuel needed for each injection are updated on a shot-to-shot basis, so the engine response to changes in load is virtually instantaneous. Fuel transfer pump Distributor rotor Manifold pressure Intake air temperature Start of injection optional 310 The Motor Vehicle As the control strategy is angle, instead of time, based, the performance of the system is outstandingly good. This follows from the fact that the requirements for both metering and timing are functions of crankshaft angle. The outcome is good performance under transient conditions. An encoder on the pump drive shaft serves as a high resolution clock. Its performance is enhanced by a phase lock loop (PLL) circuit in the ECM, which gives a resolution of 0.04 °. Control over the metering and timing events is exercised, by a series of digital counters in the ECM, on the basis of signals received from the angular clock. Fig 7.72 Chapter 8 Some representative diesel engines Presented in this chapter are some examples of what have been and, in some instances still are, outstanding diesel engine designs. The Perkins three- cylinder indirect injection engine, for example, has found many applications including in some of the earliest diesel cars produced in small numbers and, of course, light commercial vehicles. Designed and produced by the same company, initially in association with Austin-Rover for installation in some of their cars and Freight Rover vehicles, the Prima was the first of the 2.5 litre direct injection engines. The Gardner LW is a classic heavy diesel engine, while the Cummins 10 litre engine is a modern design in which unit injection is employed. 8.1 Perkins P3 diesel engine This engine was developed for installation in or as a conversion unit for light commercial vehicles and tractors. Its attraction was the flat torque characteristic and fuel economy of the diesel engine. Prior to this, diesel engines were ruled out for this type of vehicle because of the difficulties associated with the design of injection equipment for them and obtaining satisfactory combustion characteristics in small cylinders. The solution to the problem then appeared to be reducing the numbers of cylinders. Perkins were able to rationalise production and the supply of spare parts by basing the P3 three-cylinder engine on the P4 and P6, four- and six- cylinder units. In fact, the P3 was basically half of the P6 engine. The only new parts required where those related to the length of the unit, principally the crankshaft, cylinder block and sump. With only three cylinders, the unit was of convenient size for substitution for an alternative petrol engine. Longitudinal and cross-sectional views of the engine are shown in Fig. 8.1, from which the sturdy and yet compact design will be noted. Dry cylinder liners are fitted into a nickel or chromium cast iron block which extends from the head face to the crankshaft centre line in the conventional manner. The bore and stroke are 89.9 and 127 mm respectively and the connecting rods are 228.6 mm long between centres. A sturdy four-bearing crankshaft, with Tocco hardened journals, is employed. 311 312 The Motor Vehicle Fig. 8.1 Perkins P3 engine Some representative diesel engines 313 With three cranks at 120° pitch there are no primary or secondary unbalanced reciprocating forces, and the rotating couple is balanced by the two attached balance weights on the end crank webs. Primary and secondary couples remain to be absorbed by the engine mounting, and this disadvantage and the massive flywheel required to absorb the variations in turning moment are the penalties to be paid for the convenience of the three-cylinder lay-out. 8.2 Perkins Prima DI engine The alternative to reducing the number is, of course, to reduce the size of the cylinders. This had, until 1986, been impracticable for the reasons given in Section 6.12. Though, as mentioned previously, Perkins was first with its Prima engine, Ford had about a year earlier introduced a 2.5-litre DI diesel engine rated at 4000 rev/min for their Transit van. Some of the disadvantages of indirect injection are outlined in Section 6.12 and the problems to which it is a solution in Section 6.18. As can be seen from Fig. 8.2, the Prima is a four-cylinder unit with an enclosed, 30 mm wide, HTD toothed belt drive from the crankshaft to the injection pump and overhead camshaft. The alternator on the side of the crankcase, and the spindle of the fan and water pump above the crankshaft, are both driven by a V-belt from a pulley on the front end of the crankshaft. On the other hand, the oil pump is interposed between the toothed wheel for the HTD drive and the crankcase wall and driven by a gear on the crankshaft. It is of interest that, unlike the Prima, the larger and more powerful Phaser engine has an all-gear drive for its auxiliaries, Sections 6.16 and 6.17. On the Prima, a toothed belt is more suitable because it is lighter yet adequate for the loading and, particularly important for a car engine, quieter. Another factor that may have influenced by choice is the fact that the crankcase was designed to be machined by Austin-Rover on the same production line as the O-Series petrol engine described in Section 3.65, which also has a toothed belt drive. Structurally, the engine is similar to the O-Series, with siamesed cylinders and a fully balanced SG iron crankshaft carried in five main bearings. However, whilst the crankcase, because of the need for good bearing properties in the cylinder bores, is of the same high quality, flake graphite cast iron as that of the O-Series, the main bearing caps are of the stronger SG iron to react to the higher peak gas pressures of the diesel engine. In the turbocharged version, peak combustion pressure is of the order of 12 000 kN/m 2 . One of the advantages of DI head, as compared with one for an IDI engine, is the freedom to position generous coolant passages all round the valve seats, owing to the absence of a pre-chamber, and the consequent reduction in thermal fatigue loading. The eight valves are in line, with their axes in a vertical plane slightly offset to one side of that containing the axis of the crankshaft, so that the injector nozzles, on the other side, can be sited appropriately relative to the bowl type combustion chambers in the pistons. Sintered iron valve seats are shrunk into the head. The pistons have steel inserts for expansion control. They are of the three- ring type, the top ring being armoured, which means that its groove is machined in a steel ring bonded in the periphery of the piston, the appropriate distance below its crown. Armoured ring grooves, which are a useful aid to reducing the rate of wear of the very hot top grooves, especially in the more severely [...]... it is ignited and expands in the usual way The indicator diagram takes the form shown at (a) in Fig 9.2, which differs from that of the four-stroke cycle only in the rather more sudden drop of pressure as the exhaust ports are uncovered and the 328 The Motor Vehicle T T E E I I 1 2 Fig 9.1 Three-port two-stroke engine 1400 BDC (a) +50 + 25 0 – 25 50 TDC kN/m2 MEP about 27 .5 kN/m2 Inlet 80° 0 nsfer 100°... cooling of the underside of the piston crown 322 The Motor Vehicle Fig 8.8 On the Cummins engine, the two outer rockers actuate the valves and the central one the injector Rocker type cam followers actuate the very short pushrods Fig 8.9 As can be seen on the left, the piston skirts are shortened locally to clear the crankwebs This is done by means of a metal jet in a plastic moulding in the form of... serve the four adjacent valves, two each side of them, while each of the exhaust ports serves the two valves beyond the adjacent pair of inlets, the layout of the porting for the latter being visible through the sectioned end of the head As can be seen from Fig 8.7, the turbocharger is mounted just below the exhaust manifold, and delivers air up to the inlet trunk in the rocker cover above All the exhaust... constraint for the location of the spring blades, which have less free curvature than have the retainers, with the result that when blown open by the air flow the blades are 332 Fig 9 .5 Trojan engine The Motor Vehicle The two-stroke engine 333 R V B R B V V Fig 9.6 Trojan automatic valves and cage strained against the retainers, and spring back sharply to the closed position on reversal of the flow The rolled... against the cylinder walls Because the connecting rods are short, the lower ends of the skirts have to be cut away to clear the balance weights on the crankshaft as the piston passes bottom dead centre To keep vibration, and thus cavitation erosion, to a minimum and to confine the water jacket to their top ends, the seating flanges of the wet liners are only about 75 mm from the top, Fig 8.10 There is... its stroke The transfer port T, through which the charge is pumped from the crankcase, opens slightly later than the exhaust port, as shown in 1, to reduce the risk of hot exhaust gas passing into the crankcase and igniting the new charge It follows that the transfer port is closed by the rising piston slightly before the exhaust port, so that the final pressure in the cylinder, and therefore the total... 4800 50 00 Engine speed (rev/min) 140 120 100 154 N m (114 lbf ft) 80 80 1000 59 .5 kW (80 bhp) 160 140 800 600 120 100 80 30 40 30 20 20 Power output (kW) 60 450 0 rev/min Power output (bhp) 50 40 900 220 800 700 60 70 50 1000 Bmep (kN/m2) 80 160 Torque (N m) 100 B.m.e.p (kPa) 120 Bmep (lbf/in2) Torque (lbf ft) 1000 150 0 2000 250 0 3000 350 0 4000 450 0 Engine speed (rev/min) 600 230 50 0 240 400 300 250 2 75. .. valves The general construction should be clear from the two sectional views given in Fig 9 .5, while Fig 9.6 shows to a larger scale the details of the interesting automatic valves The bore of the working barrels is 65. 5 mm and of the charger cylinders 96.8 mm, the stroke of all being nominally 88 mm, but owing to the offset cylinder axes, the actual stroke is fractionally greater than twice the crank... incorporating the induction manifold partly 320 The Motor Vehicle in the head casting, Fig 8.6, and partly in the rocker cover, Fig 8.7, not only is weight again saved but compactness is achieved too Fig 8.6 Arrangement of the valves and ports on the Cummins 10-litre engine Fig 8.7 The exhaust manifold of the Cummins 10-litre unit is designed to take advantage of the pulse effect in serving the turbocharger... downstream into the air The toroidal recess in the piston crown has the effect of increasing the rotational swirl when the piston reaches the top of the stroke, on the principle of the conservation of angular momentum in a space of reduced diameter, as utilised by Ricardo in the cylindrical head of sleeve-valve engines Tin-plated cast iron pistons are fitted, and the great length of these above the gudgeon . cylinders and the low height of the engine, associated partly with the use of short connecting rods. Also, by incorporating the induction manifold partly 320 The Motor Vehicle in the head casting,. oil cooling of the underside of the piston crown. 322 The Motor Vehicle Fig. 8.8 On the Cummins engine, the Fig. 8.9 As can be seen on the left, the two outer rockers actuate the valves and. 220 230 240 250 2 75 300 400 50 0 350 140 900 120 100 800 80 700 60 600 50 0 Power output (kW) 400 40 300 30 200 20 0 1000 150 0 2000 250 0 3000 350 0 4000 450 0 1000 1400 1800