INTERNAL COMBUSTION ENGINE WITH OPPOSED PISTONS

Abstract: An internal combustion engine of the ''Junkers'' type, i.e. furnished with double counteracting pistons (2), whose movement between the piston (2) and the driving shaft (4) and vice versa is transmitted by a cam disc (6) on the driving shaft (4), said engine has plural cylinders (1), each having inlet and outlet gateways, the pistons (2) having a spherical cam roll (7) for transmission of movement between the piston (2) and the drivingshaft (4) and vice versa, said cam roll (7) is arranged to bear on a cam curve (11) on the driving shaft. The novelty is that the engine is arranged to work in combination with a turbo compressor equipment and that the pistons are made of steel and almost massive. With this engine a down to the indicated mean pressure of the mass forces relieved stress pressure is obtained. This implies having relieved the current corresponding remaining stress pressure of about 160 bar down to 35 bar despite a power increasing to more than twice. Hence extra low fuel consumption, low weight, small dimensions and inexpensive manufacturing.

Description: Internal combustion engine with oDDosed pistons. The invention relates to a combustion engine of the Junker type, i.e. with opposed pistons, in which the motion betwee » piston and driveshaft and vice versa is transferred with a 5 cam disc on the driveshaft. The engine has several cylinders, each with inlet and exhaust ports. The pistons of the engine have a cam roller to transfer the motion between the piston and the drive shaft and vice versa, the cam roller being arranged to be in contact with a cam curve on the 10 driveshaft. The engine according to the invention has been designated the Diesex 4 engine. Over the past three-quarters of the century our engine designers have steadily increased the number of horsepower per 100 kg weight of engines, reduced their fuel consumption 15 per horsepower-hour and increased their combustion pressure. At the beginning of the twentieth century, an engine of only a few horsepower would weigh 100 kg, the fuel consumption was about half a kilo or more per horsepower and hour, and the combustion pressure was about 20-30 kg/cm^ . By the 1950s, 20 these figures had been improved to 10-15 hp per 100 kg for heavy duty engines, and for ' aviation purposes the figures were down around 1 kg per hp, whilst the fuel consumption was around 1/4 kg per hp-hour for conventional engines and 0.16-0.20 kg per hp-hour for diesels. Combustion pressures 25 had, by the 1950s, been raised to around 100 kg per cm^ for diesels, and the stresses on connecting rods and bearings began to be high. During the 1980s, the figures have been further improved by increasing the combustion pressure, which has reached 200 kg per cm^, i.e. 200 bar, but as a result 30 connecting rods and bearings, piston bolts and crankshafts are approaching their maximum loadings, so that a change somewhere in the engine system is called for. The combustion engine according to the claims constitutes solution to these problems. In the Diesex 4 engine ther will, quite contradictorily, be a combustion pressur approaching 300 bar, but this pressure is now equalised firs and buffered down to a desired figure of 30-35 bar, which ca in this context become both a maximum, average and minimu value (see the indicator diagram in fig. 13). The combustio pressure is now extended and evenly distributed throughou the entire work stroke. As a consequence, a Diesex 4 engin for up to 200 hp need only weigh some 80 kg and has a fue consumption as low as 0.125 grams per horsepower. This has been achieved by designing a cam curve on the Diesex 4 engine such that the pistons during the work stroke only receive th very rapid acceleration required to unload, equalise an buffer the very high combustion pressure on the piston during their start and the first part of the motion o each piston stroke. This motion is then braked to stop before bottom dead centre, whereupon the mas force from the retardation of the pistons supplement the gas pressure on the pistons t which is graduall falling towards the stop position r so that it is raise to the full P m j_-value (see the indicator diagram i fig. 13) and that the acceleration and retardation of the piston during the compression stroke are chosen so that resulting line, known as the reference line (5-bar line ) is produced (see indicator diagram in fig. 13). Thi reference line, which is calculated to fall at aroun 5 bar, means that the pistons are held pressed agains the cam curve under a pressure of 5 bar, i.e. 250 kg, during the entire compression strokes . When the pistons change direction on transition to t expansion stroke, the 250 kg increases to the P m pressu (i.e. about 35 x the piston area = 35 x 50 = 1750 kg instead of the figures of 6 000 to 8 000 kg, i.e. 120 160 bar, that are current nowadays. Because, in the Diesex 4 engine, the major part of ea piston stroke takes place in less than half the time for motion period compared with current motors, and because th piston stroke happens when the engine is at its hottest, he loss is also halved. Thus the thermodynamically efficie cylinder system of the Jumkers engine has been made even mo efficient by the Diesex 4 engine. In addition, the Diesex engine has an entirely new exceptionally easily assembl roller bearing piston motion system. This increases t overall efficiency by a further five or so percentage poin compared with conventional plain bearings . Additionally, in the Diesex 4 engine, the piston drivi system makes it possible to extend considerably the openi times for exhaust and scavenging, so that the time gain fr the short, extra-fast expansion time of the piston can overexploited. In this way the total time for exhaust a scavenging can be increased by up to a factor of 2 compar with the normal time, owing to the greatly increased ti area. Despite this it is possible to lower the port heigh in the engine by as much as 20% compared with the alarming high exhaust ports of current two-stroke engines, which turn further increases the efficiency of scavenging. Thi gives several advantages . Very heavy pistons can be used i the engine, the mass forces of the pistons reduce the load o the combustion pressures the more effectively the heavie they are, and entirely without giving rise to the damagin vibrations that are unavoidable with current engines an heavy pistons . Calculations for the 1-litre Diesex 4 engin described here were based on pistons of 4 to 6 kg . The mos suitable approach is therefore to use almost solid pistons o steel, well matched to the thermal expansion of th cylinders. Such pistons require minimum piston clearance provide maximum gas-tightness, give the most efficien possible piston ring set, low oil consumption and silen Even if the total weight of the pistons is perhaps 15 to 20 kg higher than a normal piston set, the resulting reduction in the total weight of the engine is many times this piston weight increase, owing to reduced total dimensions, the absence of connecting rods and the scope for weight reduction arising from the fact that the stress forces are far more than halved. An indicator diagram for a fast running supercharged two-stroke diesel engine according to the invention has approximately the curve shown in fig. 13, where the piston travel is the abscissa in millimetres and the pressure in bar is the ordinate. The curve is known as Pg (the gas pressure curve). See fig. 13. The P mj _ line is shown at 35 bar. It is therefore desirable that the acceleration sequence for the piston relieves the partially very high combustion pressure, if possible right down to the constant P m _ value (in this case 35 bar - compare fig. 13) during the entire expansion phase (working phase) of the piston. It is a consequence of this that the acceleration curve should follow a pressure line that continuously has a value equal to the combustion pressure known as Pg but after this has been reduced by P m ^ (i.e. in this case P m = 35 bar) and we call the new curve P r ( = ^resultant) • P r will be a curve that has a contour that is an exact likeness of the contour for Pg, but which is moved downward by 35 bar in the diagram relative to P g . If a piston weight M of 4 kp is chosen, speed N rev/min, cam curve diameter D mm, piston stroke 50 mm, then the time that must elapse for the piston, during its motion from top dead centre to bottom dead centre, to reach the various fixed points, here 5, 10, 20, 35 etc. up to 45-50 mm of the piston travel, in precisely the times that correspond to the acceleration during the piston motion, the acceleration represented perhaps the travel points (v 5, v 10, v 20, -- v 50) by the P curve, i.e. the P r curve can be said tc relieve the ?„ curve at all points down to the ?„,- value. To ensure that the necessary pressure is always present i the cylinders immediately after starting of the engine, th pressure that ensures that the pistons are constantly hel pressed against the cam curve, gas discharge from the engin should always go via a spring loaded valve providing positive pressure of about 0.5 bar, in order to preven piston slap. Thermodynamic researchers maintain that increased combustio pressure through higher supercharging and higher compressio ratio could give today's engines 20% and possibly 30% highe output, fuel economy and even more in terms of lower weigh and reduced overall dimensions, but engine manufacturers als know from ruined engines, siezed bearings and bent connectin rods that, with current combustion pressures of 200 bar, the are already approaching what is at present considered to be a maximum upper load limit for an engine. However, the Diesex 4 engine is not subject to these limitations . In the Diesex 4 engine it is its piston motion that solves these problems, and this in turn leads to great scope for additional improvement. In today's combustion engines it is the connecting rod motion that entirely defines the stages of piston motion as a motion that, on closer inspection, only to a small extent satisfies the requirements that would best serve a combustion engine. The connecting rod motion moves the pistons from top to bottom dead centre, but there is a great deal more that is asked of it. Experience of valves and cam motions from racetracks particularly highlights the importance of the combination of the weight, acceleration and retardation of fast moving parts in combustion engines . The similarity between cam motion problems and piston motion problems is plain, and there is good reason to use the possibilities of cam motion to transfer piston motion to the rotating shaft of the engine. Here, however, the new combination of rolling bearings in the Diesex 4 engine constitutes an extremely important solution of the bearing problem. It should be noted that rolling bearing systems hitherto used for engine shafts, while admittedly easy-running, are particularly difficult to assemble. Here they have been replaced by the likewise easy-running but particularly easily assembled rolling bearing combination of the Diesex . The motion transfer system according to the invention above all performs the same function as the connecting rod motion performs today, but they also give the pistons such a high mass weight M kg that they can at any instant be given, and are given, such a speed h and an acceleration a that the combustion pressure Pg (stated in bar) minus the acceleration force at every instant P r becomes equal to P m _, thus P g - P r = P mi . The present invention is also a development of the Junkers two-stroke engine with double opposed pistons in each cylinder. As long ago as the Second World War, the Junkers engine achieved record figures. In terms of fuel economy it has hardly been surpassed since. However, because of the perhaps unduly complicated design with double crankshafts connected by means of a costly system of gears, it was not wholly successful. By combining the Diesex 4 engine according to the present invention with the Junkers combustion system and its perfect balance, a major step forward in engine development is achieved. The Diesex 4 engine's highly efficient system for the transfer of motion between piston and driveshaft not only greatly simplifies the Junkers system but also gives an extremely effective reduction down as far as one-tenth of the stress figures in currently used combustion systems before the stresses have reached the parts of the engine that are most sensitive to over-stressing. Instead of a devastatinc explosive blast of about 10 tonnes for a fraction of 0.0C1 seconds, it is reduced in the present invention down to a force during the entire compression stroke. In terms of work output, this extended force of hardly 2 tonnes far exceeds the 10-tonne explosion of the combustion processes in use today, and is, in figurative terms, delivered wrapped in cotton wool . It being well known that, the higher the combustion pressure worked with, the better the output and fuel economy obtained, but it also being known that this results in a prematurely destroyed engine, the present invention makes it possible to greatly increase the output and economy of an engine without shortening its life. By virtue of the equalised, smooth working pressure obtained according to the invention, the maximum pressure can be kept as low as around 40 bar. This is instead of the devastating forces of 150-200 bar that arise nowadays during the maximum working stokes of engines, and of which only 20-30 bar of useful working pressure can be exploited. This greatly reduced stress pressure- makes possible extra light constructions and smaller overall dimensions. A 150-200 hp engine according to the invention, with a rotation speed of 4 000 to 4 200 r/min, is calculated to weigh less than 80 kg, to be 540 mm long, 300 mm high and 400 mm wide, in a diesel version. The combustion engine according to the invention has at least one cylinder with a pair of opposed pistons . Where there are several cylinders, these are placed in a circular arrangement around and parallel to a common drive shaft. An embodiment of the engine according to the invention is shown in the accompanying drawings , where Fig. 1 shows the engine schematically, viewed from above, Fig. 2 shows the engine in fig. 1 seen from one end, Fig. 3 shows the engine in fig. 1, partly i cross-section, Fig. 4 shows the transfer of motion between a piston an the cam curve, partly in cross-section, Fig. 5 shows the piston and a groove in the cam curve an a cam roller in the cam curve in fig. 4, viewe from above, partly in cross-section, Fig. 6 shows the piston and cam curve in fig. 4, viewe from the side, partly in cross-section, Fig. 7 shows the piston and cam curve in fig. 6, viewe from above. Fig. 8 shows a cam roller for a piston, Fig. 9 shows the interaction of a cam roller with a ca curve, Fig. 10 shows a scavenging half of a cylinder, Fig. 11 shows the interaction between cylinders and ca curves in a four-cylinder version with doubl pistons in each cylinder, Fig. 12 shows indicator curves for gas pressure in conventional engine of the same size and genera type as the engine according to the invention, wit crankshaft angle 0 as the X-axis, Fig. 13 shows an indicator diagram for the engine accordin to the invention, i.e. a Diesex 4 engine. The engine according to the invention shown on the drawing works according to the "opposed piston system principle" In each cylinder 1, two pistons 2 move towards and away fro each other in the known manner. The pistons have a commo combustion chamber 3 between them. The motion of the pistons is parallel to the direction of driveshaft 4 of the engine and is transferred to three cams that are evenly distributed each on its own end face of washers 6 facing each other. The washers 6 are fixed 5 driveshaft 4. As the drawings show, the cams 5 also produc with the aid of cam rollers 7 carried on rolling bearings pistons 2, lifting motions in a direction parallel driveshaft 4, which force the piston 2 to lift predetermined distance, i.e. its stroke, up to its t 10 position. The corresponding cam 5 of the opposite washer simultaneously works in a similar manner on the other pist 2 of the common cylinder 1 so that this other piston reaches its top position simultaneously or possibly with certain insignificant displacement. The high compressi 15 pressure in the common combustion chamber 3 in each cylind 1 of the engine then presses the pistons 2 back to the bottom position. As this happens, each piston follows i cam 5, which has been calculated with regard to t acceleration of piston 2 that is matched to the mass forc 2.0 so that at every instant p g " p r = p mi (see page 6, paragraph 3). Compare t indicator diagram in fig. 13. In an example of a motor, the piston motion of a two-cylind motor with 1 000 cc swept volume is determined by t 5 following parts: A driveshaft 4 with length L = 540 mm a with a diameter D = 100 mm. The driveshaft 4 may be in t form of a centreless-ground steel tube with 5 mm materi thickness. This is connected to each washer 6 with a 100 c bonded and pinned joint that withstands a torque 0 1 tonne-metre, corresponding to a safety factor of 20. T entire bearing arrangement of driveshaft 4 in the ends 8 cam housing 9 consists of two thrust bearings 10 of 230 outside diameter with a load capacity of about 20 tonnes. Thanks to the design of the Diesex 4 engine, these need no 5 have a higher speed than 1 400 n/min (but can withstand abou 2 200 n/min) . The carbide-reinforced cam rollers 7 are subjected to max 1 800 kg loading and a rolling speed of 17.5 m/s but a considered capable of withstanding twice the number of kg an a rolling speed of 16 000 bar/min, but they work at only 9 500 r/min. In order to match the speed of thrust bearing 10 and th rolling speed against the form of cam curves 11 of the ca rollers 7 to suitable values, each cam curve 11 has bee provided with three cams 5 on each washer . With this design, the number of cams 5 times the speed o washers 6 will determine the number of strokes per cylind and minute of the engine, a figure that should be compare with the revolutions per minute of engines in use today. I accordance with this, the present engine according to th invention has a stroke n = 4 000-4 200 per min and washe pair. The speed will then be 4 000/3 to 4 200/3 = 1 333 to 1 400 per min or 22.22-23.33 per second, corresponding to 9 100 to 9 500 revolutions per minute for the bearings 14 o cam roller 7 as against the permitted figure of 15 00 revolutions per minute. The number of cams 5 on washers 6 therefore determines th reduction ratio of driveshaf 4. For four cams, th reduction on the number of strokes will be 1:4. For helicopter engine, for example, a sevenfold gear-fre reduction can very easily be obtained simply by fitting ca curves 11 with seven cams 5 and making the engine accordin to the invention with, for example, up to 10 cylinders (th number of cylinders should not be divisible by the number o cams in order that more than one cylinder does not fi simultaneously) or up to 20 cylinders in a cylinder ring wi a diameter of only about 1 m and a length of 60 cm in a powe class of about 1 000 and 2 000 hp respectively. The washe diameter then increases in proportion to the number of ca in order that the steepness and the radii of curvature of t cam tops of cam curves II can be kept within the desir limits . The cam rollers 7 transfer the lifting motion from the cams 5 on cam curve 11 on washers 6 to the piston. Each cam roller 7 may appropriately be a roller of carbide, press-fitted to a journal 12 that is carried on rolling bearings in piston 2 by means of the two rolling bearings 14. The lifting motion is transferred from a cam 5 on cam curve 11 to the piston 2 with the washer 6 on drive shaft 4, so that the piston 2 precisely follows its P r curve in the diagram in fig. 13, the calculated motion Pg, as a consequence of which Pg - P r with the mass of piston 2 must give at each instant the value P m j_ throughout the entire expansion stroke. The diagrams in fig. 12 and 13 show curves for: P jζ = compression pressure P g = gas pressure (= combustion pressure P e χp ^ or current engines) P R = resulting pressure P ma = mass force pressure p me = effective mean pressure P m j_ = indicated combustion pressure p anh = reference pressure = a On the other hand, during the entire compression stroke P ] -PR must be equal to one contact force a for cam roller 7 (here the chosen value of a is 5 bar) . In order that cam roller 7 makes accurate contact with the curve surface of cam curve 11 along its entire contact surface with cam curve 11, the journal 12 is positioned in a bore 13 passing right through piston 2. In this bore 13 cam roller 7 is centrally carried and pressed on to journal 12, which in turn is carried between a roller bearing 14 at each end of the journal. So that cam roller 7 sets itself automatically in accordance with the profile of cam curve 11, the profile of cam roller 7 rolling against cam curve 11 is shaped as the middle sector of a sphere (for example with 35 mm diameter). The cam curve II must therefore have a groove 15 with a cross-section profile that exactly fits the spherical rolling surface of cam roller 7. The bearing arrangement of cam roller 7 permits an even distribution of the load on its two roller rolling bearings 14 is exploited. An example of a suitabl diameter for cam roller 7 is 35 mm and, for the radius curvature of the top rounding of a cam 5, 15 mm. Several advantages are gained with the present invention With the engine according to the invention it is possible obtain a load reduction and equalisation of the combusti pressure down to a constant value of P m _ (calculated here to 35 bar) throughout the entire work stroke as shown in th diagram in fig. 13. This diagram also shows how a reduction of the pressure P during the compression strokes can be achieved down to suitable constant value (calculated here to 5-10 bar) b which the piston 2 should be held in contact with cam curv 11 throughout the entire compression stroke, in order neve to lose contact with it. This guarantees that the motion fo which it is calculated is followed. The calculations ar illustrated by the curves in the indicator diagram i fig. 13, with the following values of max pressure P raax an the corresponding P mj _ at the piston travel V in mm. For P max corresponding to P m ^ 500 bar " 45 bar 250 bar " 38 bar 200 bar' " 35 bar With the motor according to the invention, a power gain i also achieved by the greatly shortened heat loss time durin the hottest part of the work period. Such an engine is also advantageous owing to the greatl extended time that is available, owing to the shortene expansion time, for exhausting and scavenging, both i accordance with the previous paragraph and as a result of th shape of the piston motion curve. Fig. 10 shows the scavenging half of a cylinder 1. I piston 2 transfers its motion by means of a plunger 23 to compressor piston 22 in a compressor cylinder 17 to scaven cylinder 1 of the motor via a scavenge cooling battery 21 a a scavenge duct 19. The induction and exhaust openings compressor cylinder 17 are fitted with leaf springs 24. T cylinder also has an exhaust duct 20 (see fig. 3). Compared with engines of the type with "opposed pist two-cycle engine" (or the Jumos system) the engine accordin to the invention has additionally improved balancin efficiency determined by the cam curves . The motor is also advantageous through the absence of gear for reduction. The cam curve 11 is its reduction system. Allowing the gas pressure to ensure the return motion of th pistons in the engine according to the invention is not mor dangerous than allowing the return motion of valves to b .ensured by springs in a four-stroke engine. To guarantee that the fuel is supplied to the cylinders wit maximum reliability, the engine should be provided with tw independent entirely separate and complete fuel suppl systems . A condition for reliable operation of the Diesex 4 engine i that the scavenge air system in the engine is guaranteed t provide 0.5 to 1 bar positive pressure at the instant o starting, and that a corresponding counterpressure exists i the exhaust system at the same time. This is made possible by giving the cam curves such a shap that the dynamic mass forces, the acceleration and th retardation of the piston are balanced against the pressure, ignition pressure and combustion pressure of the indicato diagram. It should also be noted that the Diesex 4 engine probably ha or will have its most important fields of application i combination with turbo compressor equipment, in other word in the super-high-pressure engine field, precisely where th stress-relieving characteristics of the Diesex 4 will be o extra value and where new areas of power and economy open u which have not been possible for today's engine types owin to problems with material overloading. Although the diesel Diesex 4 engine is suitable for vehicl engines, the engine is even more suitable for most othe types, from the smallest at 50 hp and a weight of 10 kg fo aircraft and helicopters (single-seater) to the largest, u to more than 100 000 hp with weights of 2 kg per hp an possibly fuelled with a mixture of water and powdered coal o peat, the latter with turbo-compressor of course. This open up considerable additional possibilities for increased outpu and economy. All dimension data relate to an engine size in which th swept volume of the cylinder 1 is 500 cm^, the pisto diameter is 80 mm, the stroke is 50 mm, the number o cylinder strokes per minute is is 3 600 - 4 200, P^ Q i 22.4 bar, the output is 200 hp, the weight is less than 80 k and the front area of the engine is of the order of 12 dm 2 . The Diesex 4 engine is even more attractive if it is provide with internal water spray cooling with a simple bum mechanism. The cooling water can be recovered from the exhaust gasses. In this way 30% extra heat becomes availabl as f el. Already within one start revolution the Diesex 4 engin delivers the necessary positive pressure for starting.

Claims: Claims 1) Combustion engine of the Junkers type, i.e. provided wi double opposed pistons, in which motion between the pist and the driveshaft and vice versa is transferred by a c disc on the driveshaft, the said motor having centr cylinders, each having inlet and exhaust ports, whose pisto have a cam roller to transfer motion between the piston a the driveshaft and vice versa, the said cam roller bei arranged to bear on a cam curve on the driveshaf cha ra c ter is e d in tha t , the engine is arranged to work in combination with a turbo compressor system and the pistons (2) are almost solid and may conveniently made of steel. 2) Internal combustion engine according to claim 1 cha ra c te r is e d in tha t the masses of the pistons (2) are made approximately te times heavier than the masses of normal pistons, the product of the masses of the pistons (2) and their instantaneous motion acceleration at any instant reduces o supplements the piston force of the combustion pressure dow to its indicated mean pressure within a margin of about 10% whereby the pistons, during the working stroke of the engine first receive the very high acceleration that is needed t relieve, equalise and buffer the very high combustio pressure on the pistons during the start and the first par of the motion of each piston stroke, after which this motio is breaked to stationary before the bottom dead centre, whe however the gas pressure successively falling towards th stationary position is supplemented by the mass force fro the retardation of the pistons in such a way that the ga pressure is raised to the full ~ P m value (see the indicato diagram in fig. 13) . 3) Internal combustion engine according to claim 2, cha ra c ter ised in tha t the acceleration and retardation of the pistons (2) during the compression stroke of the engine are designed such that a resultant line, known as the reference line (the 5-bar line) is achieved, as a result of the pistons (2) constantly being held pressed against the cam curve during the entire compression stroke of the engine with their pressure of 5 bar, i.e. with a pressure of 250 kg. 4) Internal combustion engine according to one of claims 1-3, cha rac ter ised in tha t each piston (2) of the engine is designed to work in conjunction with a compressor cylinder 17 for scavenging the engine cylinder (1), as a consequence of the motions of the piston (2) being transferred by a plunger (23) to the compressor piston (22) of compressor cylinder 17. 5) Internal combustion engine according to claim 4, cha ra c ter ised in tha t the compressor cylinder (17) is connected to the cylinder (1) of the engine via a cooling battery (21) for the scavenge air and a scavenge air duct (19). 6) Internal combustion engine according to one of claims 1-5, cha ra c te r is ed in tha t the exhaust of the engine is connected to a spring loaded 0.5 bar pressure valve. 7 ) Internal combustion engine according to any of the preceeding claims, cha ra cte r ised in tha t the masses of pistons (2) are of an order of magnitude such that the product of the masses and the instantaneous motion acceleration periodically relieves and periodically supplements the force of the combustion pressure down to its indicated mean pressure within a margin of 10%, which means a reduction of the maximum stresses on the most vital parts of the Diesex 4 engine to 1/3 to 1/4, which, by virtue of this, in combination with other aspects of the design of the Diesex 4 engine, permits an increase in power output by a factor of up to 2 compared with conventional corresponding motors cf

Inventors: MANNERSTEDT FOLKE, MANNERSTEDT, FOLKE
Applicants: MANNERSTEDT FOLKE, MANNERSTEDT, FOLKE
Application year: 1987
Main classification: F01B9
IPC codes: F01B3, F02B3, F02B75