US3095692A - Two-stroke diesel engine with an exhaust gas driven turboblower - Google Patents

Description

July 2, 1963 I G. WOLF I 3,095,692

TWO-STROKE DIESEL ENGINE WITH AN EXHAUST GAS DRIVEN TURBOBLOWER Filed June 26, 1961 2 Sheets-Sheet 1 Jnvenfar:

GOTTL/EB VVOLE July 2, 1963 G. WOLF 3,095,692 TWO-STROKE DIESEL ENGINE WITH AN EXHAUST GAS DRIVEN TURBOBLOWER Filed June 26, 1961 2 Sheets-Sheet 2 Fig.3

Jnvenfor: GorruEBVVLF. 13 /K United States Patent F r 3,095,692 TWO-STROKE DIESEL ENGINE WITH AN EX- HAUST GAS DRIVEN TURBOBLDWER' Gottlieb Wolf, Winterthur, Switzerland, assignor to Sulzer Freres, S.A., Wintcrthur, Switzerland, a corporation of Switzerland Filed June 26, 1961, Ser. No. 119,611 Claims priority, application Switzerland July 11, 1960 1 Claim. (Cl. 6013) The invention relates to a two-stroke diesel engine with an exhaust gas turboblower and adjustable preexhaust by means of at least one cam-operated exhaust control device.

In order to maintain the turbine speed in low load or speed ranges of two-stroke diesel'engines having an exhaust gas driven turboblower, it is known to open the exhaust valve prematurely whereby the preexhaust angle, i.e. the angle difference measured at the crankshaft between the opening of the exhaust and the beginning of scavenging, is increased. In this way, more power is fed to the turbine at the'expense of the engine. In one known construction this is effected by turning the camshaft which operates the exhaust valves, relative to the crankshaft in dependence on the scavenging air pressure and in a direction to advance opening of the exhaust valves as the air pressure drops. This arrangement has the disadvantage that earlier opening of the preexhaust valves is accompanied by their earlier closing and that it is not possible to correctly shape the cam for the individual load ranges. Since the cams for the fuel injection arenormally disposed on the same camshaft as the cams for :the exhaust valves the cams for the fuel injection and the cams of the exhaust valves are simultaneously adjusted in a manner which is not desired. It has also been proposed to construct the exhaust valve control cam as a function body which is axially slidable in dependence on the scavenging pressure so that the cam tracks pertaining to the individual scavenging pressures can be properly constructed. With the power and space conditions prevailing in diesel engines, however, the point contact between the cams and the cam follower rollers inherent in the aforesaid mechanism makes it impossible to construct and accommodate cams which give satisfactory service.

'It is an object of the invention to provide an exhaust control device which combines the advantages of known devices and avoids their disadvantages and whichincludes an axially slidable cam having for at least one direction of rotation of the engine cylindrical control tracks for I not more than three and at least two different ranges of operation, the change-over of the exhaust control device from one of theindividual tracks to another being effected stepwise when the predetermined ranges of operation are exceeded.

The novel features which are considered characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, and additional objects and advantages thereof will best be understood from the following description of an embodiment thereof when read in connection with the accompanying drawing wherein:

FIG. 1 is a diagrammatic illustration of a diesel engine with an exhaust gas driven turbosupercharger and preexhanst control according to the invention.

FIG. 2 is an enlarged view of a cam forming part of the control shown in FIG. 1, looking in the direction of the arrow B of FIG. 1.

FIG. 3 is. a diagram illustrating the principle of the invention.

Referring more particularly to FIG. 1, scavenging ports 6 are provided in a cylinder 1 of a reversible two-stroke marine engine including a piston 2, a piston rod 3, a crankshaft 4 and a crankcase 5. The scavenging ports 6 3,095,692 Patented July 2, 1963 are connected to an air supply socket 7 connected to an outlet 8 of a compressor 9. The latter is provided with an inlet pipe 10. A valve 12 controlling an exhaust pipe 11 is disposed in the cylinder 1 and provided with a valve spring 13. The valve is adapted to be operated by a cam element 1 7 through a rocker arm 14, a push rod 15 and a roller 16. An inlet 18 of an exhaust gas turbine 19 is connected to the exhaust pipe 11. The rotors of the turbine 19 and of the compressor 9 are connected by a common shaft 20. A camshaft 22 driven by the engine through gears 23, 24, 25 is axially slidably and rotatably supported by bearings 26. For the sake of clarity, the shaft 22 has been illustrated as being normal to the crankshaft 4. Actually, it is parallel to the crankshaft 4. The shaft 22 is provided with two collars 27 between which extends an arm of an angle lever 28. The latter is connected by a rod 29 and a two-arm lever 30 to a servomotor 31 for preexhaust control and a servomotor 32. for forward and reverse operation of the engine. The servomotors 31 and 32 are provided with supply lines 33, 34 and control slide valves 35, 35 for a hydraulic or pneumatic pressure medium. An element 36 provided withgrooves 37-39 is mounted on the shaft 22. The grooves are adapted to be engaged by a spring-loaded retaining piston 40. The-slide valve 35' is operated bya speed regulator 41 which is driven by the shaft 22 by way of helical gears 42, 43.

The cam element 17 has cams I, II and III. The cams I and II are intended for the forward operation and the cam III for the reverse operation of the engine, which is reversible. Between the individual cams transition surfaces are provided in the conventional manner affording rolling of the roller 16 from one cam onto the other upon axial displacement of the shaft 22. The cam surfaces are formed by axial generating lines .and have a noncircular cross section.

When the engine operates in forward direction and at low speeds the roller 16 is on the cam I of the cam element 17. Upon exceeding a predetermined engine speed the control slide valve 35 is moved to the right, as seen in FIG. 1, by means of the regulator 41 so that the piston of the servomotor 31-is moved into its bottom position, causing anticlockwise swinging of the angle lever 28. The angle lever 28 pushes the shaft 22 to the right and the roller 16 begins to roll on the cam II which is intended for a higher engine speed and which effects a smaller preexhaust angle. Q

If reverse operation of the engine is desired the shaft 22 is moved to: the left by means of the regulator M ami the servornotor 31 after a corresponding reduction of the speed until the roller 16 again'comes to move on the cam I of the cam element 17 Ont-he subsequently initiated reverse starting maneuver the piston of the control slide valve 35 is moved to the right and the piston of the servomotor 32 passes into its top position. The shaft 22 is thereby moved to the left by way of the angle lever 28 until the roller 16 moves on the cam III of the cam element 17, making the engine ready for reverse operation.

FIG. 2 is a view of the cam element 17 in the direction of the arrow B in'FIG. 1. FIG. 2 shows that the cam I has a lo'be causing an earlier beginning of opening a of the exhaust valve than the cam II which causes opening of the exhaust valve at the angular position b of the shaft 22. The cam I causes-full opening of the valve 1 2 at the position c whereas the cam II causes full opening at the position d. Closing of the exhaust valve begins with these cams at the same time at the position e for both speeds and terminates at the position 1 for both speeds. The cam III provided for reverse travel is symmetrical with the cam I and is shown by a broken line. If the same maximum speed is required for reverse operation as for forward operation, a cam IV is provided 3 which is symmetrical to the cam II and which is shown by a dash-dot line.

In FIG. 3 the curve a shows the optimal preexhaust angle V, for example, with respect to fuel consumption and smoke at steady operating conditions, in dependence on the speed n in the case of a marine engine with direct drive of the propeller. Tests have shown that the curve a is horizontal between 40% and full load speed, i.e., for this range a single adjustment of the preexhaust angle is sufficient. Below 40% of the full load speed it is necessary to increase the preexhaust angle, as shown by the inclined curve portion a. According to the invention, for the range from about 40% of full load speed up to maximum speed the preexhaust angle adjustment used is the one obtained by the cam II of the cam element 17. Below this speed range the cam I comes into operation, which produces an increased preexhaust angle. The diagram shows that the actually eifected preexhaust angle considerably exceeds (the theoretically required preexhaust angle. This means that the turbosupercharger group receives more energy than required for static conditions as regards fuel consumption and so on. On the other hand, however, an increased air pressure is obtained for scavenging and charging and the acceleration power of the engine is considerably boosted. The result of this is that while in the higher speed range when the cam II is in operation an optimum engine economy is obtained, in the lower speed range when the cam I is in operation improved acceleration is obtained, which is particularly important for this speed range. This advantage is particularly striking in the case of marine engines directly driving the propeller. With these engines the power is dependent on the speed in accordance with the known propeller characteristic, 40% of full load speed corresponding approximately .to 6% power. This means that such an engine can be designed for optimum economy in practically the entire power range but receives its maximum acceleration in the range below 40% speed and 6% power, i.e., in the idling range. A somewhat increased specific fuel consumption can be tolerated in the lower speed range since the total fuel consumption is small in the low power range. In addition there is the important fact that with such engines a reversing mechanism is always provided and the system according to the invention requires only slight changes of the cam and of the reversing mechanism. The engine can be used without additional scavenging pumps or blowers.

Although an engine having two cams for forward direction of rotation has been described as an example, it is possible to provide three cams, i.e. three ranges of operation for special purposes, for example for locomotive engines and the like.

The paraxial surfaces of the cams permit line contact between the cam and the roller, causing only moderate stresses at the lines of contact in comparison with point contact and extending the life of the cams and of the roller.

4 The transition surfaces permit simple displacement of the cams during the change-over movement whereby the roller can roll from one cam to another. A cam construction without transition surfaces is possible, necessitating, however, a device to lift the roller during the change-over, as is known in devices for changing from forward and reverse operation and vice versa.

The control of the forward operation, reverse operation and preexhaust may also be effected by apparatus different from that illustrated, for example, by a displacer servomotor mounted on the camshaft. The speed regulator may also be replaced by a speed responsive hydraulic or pneumatic system.

Furthermore, the adjustment of the cam need not be effected in dependence on engine operating ranges determined by the speed. This adjustment may be effected in dependence on other operating variables of the engine, for example the scavenging pressure. In that case, the regulator 41 would be formed by a pressure-sensitive element known per se, which is connected to the scavenging air line.

I claim:

In a reversible two-stroke diesel engine operating under variable load and having an exhaust gas driven turbocharger, an exhaust valve for controlling flow of exhaust gas to said turbocharger, and control means for said exhaust valve, said control means including an axially movable shaft rotating at a speed corresponding to the engine speed: a cam mounted on said shaft and having three cam surfaces, cam follower means operatively connected to said valve and engaged by one of said cam surfaces for operating the engine in one direction of rotation and engaged by the second or third cam surface, depending on the axial position of said shaft for operating the engine in the opposite direction of rotation, means responsive to the speed of the engine and connected to said shaft for axial movement thereof to eifec-t engagement of said second cam surface by said cam follower means upon an engine speed below a predetermined value and to effect engagement of said third cam surfiace by said cam follower means upon an engine speed above said predetermined value, to stepwisely advance beginning of the opening of said exhaust valve upon a reduction of the engine speed below said predetermined value and to retard beginning of the opening of said exhaust valve upon increase of the engine speed above said predetermined value.

References Cited in the file of this patent UNITED STATES PATENTS 1,159,692 McKeen Nov. 9, 1915 1,161,464 Enrico Nov. 23, 1915 2,097,883 Johansson Nov. 2, 1937 2,670,594 Crooks Mar. 2, 1954 2,977,943 Lieberherr Apr. 4, 1961 2,991,616 Miller July 11, 1961

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