DIRECT-INJECTION Approach by Perkins
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ALTHOUGH direct-injection combustion principles have been_ incorporated in several oil engines produced by Perkins Engines, Ltd., during the past year or so, the announcement today that a completely new 112-b.h.p. unit for vehicle use is already being produced at the Peterborough works is of great importance. Earlier direct-injection engines had principally been modifications of existing types, but the new model, known as the Six 354, has been designed from the start for direct injection.
Another difference is that the earlier direct-injection designs were used solely for industrial, agricultural and marine applications, and had never been applied to road vehicles. The new engine, however, is essentially a vehicle unit, as evidenced by its relatively high governed speed of 2,800 r.p.m.
A road test of a Seddon 7-ton goods vehicle, to be published shortly, confirms, that the Six 354 is a particularly fine proprietary unit, with sufficient power output to make it suitable for all classes of rigid goods and passenger chassis between 10 and 14 tons gross weight, and higher in the case of articulated vehicles.
Direct injection gives decidedly improved fuel economy compared with other Perkins vehicle engines having indirect injection, whilst there are added advantages in respect of running quiet ness and simplified design. Although slightly smaller in overall dimensions (particularly length) than many competitive direct-injection engines of similar capacity, the Six 354 gives high maximum torque of 260 lb.-ft. (gross) which permits good hill-climbing and acceleration, and improves part-load fuel economy.
Having a cubic capacity of 5.8 litres (354 Cu. in.), the Six 354 owes nothing to earlier Perkins designs, and there is no interchangeability between its components and those of any other Perkins G24 unit yet in production. It is not
90 unreasonable to suppose that in time a four-cylindered version
so might be produced, but it is not
De scheduled for production in the 700 immediate future.
The unit is a six-cylindered
60 engine of fairly conventional design, incorporating modern 50 features, such as a C.A.V. DPA
distributor injection pump and an eccentric-rotor oil-feed pump. This is the largest British vehicle engine to have been designed initially with a distributor injection pump, although other, smaller Perkins units have incorporated them.
A gross power output of 112 b.h.p. at 2,800 r.p.m. (105 b.h.p. net) is quoted, and the torque peak occurs at 1,450 r.p.m. The unit has a bore of 98.4 mm. (3.875 in.) and stroke of 127 mm. (5 in.), and the compression ratio is 16 to 1. Its dry weight, less flywheel, flywheel housing, starter and air cleaner, is 854 lb., and completely equipped, ready for installation, it turns the scale at 1,020 lb. Overall length, less bell housing, is 35; in. and depth is 33f; in., excluding air cleaner.
Renewable dry liners are pressed into the cast-iron cylinder block, which is
integral with the crankcase. For• increased rigidity the crankcase skirt is extended to below the line of the crankshaft, and cast-iron cylinder liners arc used.
Cast iron is employed also for the one piece cylinder-head casting. This is secured to the block by high-tensile studs, with a copper, steel and asbestos jointing gasket. Unshouldered close-grained cast-iron valve guides are fitted.
Two Springs Per Valve The inlet valves are of BS.En.18S 1-per-cent, chromium steel and the exhaust valves are of 21 4N steel. The ends of the inlet valves are flamehardened to resist wear, and the exhaustvalve stems are Stellite-tipped. Each valve has two springs, and the inner springs seat on hardened-steel pressings on top of the heads. An oil-resistant rubber collar forms an oil seal at the top of the stem of each inlet valve.
Multi-hole fuel injectors are flangemounted in the head, with two studs and nufs. The injectors fit into cast sleeves in the left side of the head, and the adjacent coolant passages direct jets of water on to the nozzle bosses and valves by means of deflectors cast into the head. These deflectors are in direct communication with the cast water rail on the side of the cylinder block.
High-duty cast iron, with chillhardened cams, is used for the camshaft, which is located low down on the right of the block. The camshaft is carried in four bearings. Cast-iron mushroomtype tappets, with chill-hardened tappet faces, actuate the cast-iron rockers through push-rods with hardened ends.
The crankshaft is a forging, using chrome-molybdenum steel to BS.En.191. The crankpins and journals are induction-hardened, the respective diameters being 2.5 in. and 3 in. A synthetic-rubber seal is provided at the front of the shaft, whilst at the rear there is a rubber-core woven-asbestos rope-type seal retained in a split housing.
End float and thrust are accommodated by two 360° steel-backed copper-lead thrust washers. The front of the crankshaft carries a Holset vibration damper as standard.
The crankshaft is carried in seven prefinished thin-wall steel-backed copperlead main bearings. Similar bearings are employed for the big-ends, whilst the wrapped small-end bushes are steelbacked lead-bronze.
Single-helical gears comprise the camshaft and auxiliary drives. The gears arc enclosed by a cast-aluminium-alloy timing case which incorporates pressedsteel inspection covers. Lubrication is provided by an intermittent feed from the two idler-gear hubs.
High-silicon aluminium-alloy pistons are employed, and, because this is a direct-injection engine, each piston has a toroidal .cavity in its crown, slightly eccentric to the piston centre-line. Of the three compression rings, the upper one is chromium plated. There is a scraper ring above and below each gudgeon pin, these pins having a floating mounting, with circlip location.
The H-section connecting rods are of high-tensile steel to B.S.En171) specifica7 lion, and the big-ends are split at right angles, the caps being located by serrations and secured by high-tensile bolts with proprietary lock nuts.
An auxiliary drive running at crankshaft speed operates the fuel-injection pump, oil pump and air compressor or exhauster. The C.A.V. injection pump is mounted vertically on the left of the cylinder block and shares a worm drive with the oil pump beneath it. The worm gear is bronze.
The C.A.V. pump incorporates automatic advance and retard mechanism and a hydraulic governor, and its location makes it readily accessible should it require attention in situ. The A.C. fuellift pump is cam-driven off the camshaft, which is on the opposite side of the block from the injection pump, and the C.A.V. filter is on the left of the cylinder head.
The oil pump is bolted to the cylinder block and driven from a serrated extension of the injection-pump worm wheel. There is a spring-loaded suction filter in the sump, and an A.C. full-flow filter is mounted on the left of the crankcase.
The oil-filler. cap is on the pressed-steel rocker cover, and its position may be reversed to suit any engine installation. The rocker cover includes a crankcase breather.
A centrifugal water pump, belt-driven from the crankshaft pulley, is carried on the front of the cylinder block, and incorporates a . six-bladed pressed-steel fan. Alternatively, the pump and fan can be mounted at the front of the cylinder head. The cooling circuit includes a bellows-type thermostat and provision is made for a thermometer.
The aluminium-alloy inlet manifold contains a Thermostart heater for use when starting the engine in very cold weather. This manifold is on the right of the cylinder head, as is the cast-iron exhaust manifold.
Belt drive from the front of the crankshaft is employed for the 12v. dynamo. The dynamo is mounted on the right of the block, where the 12v. starter motor is carried. Provision is made for fitting a hydraulic pump behind the compressor or exhauster for use with steering servos and so forth, and the standard compressor is a Tu-Flo 300 unit.
The new engine represents something of the renewed line of thought currently affecting producers of oil engines, in that it offers a comparatively high power output for its size, with added emphasis on longevity and good accessibility to the auxiliary components. Manufacturers fitting this unit to certain of their models include Dennis, Dodge and Seddon.