US1336668A - Internal-combustion engine of compound type - Google Patents

Description

APPLICATION FILED MAR. 81 l9l8.

Patented Apr. 13, 1920.

2 SHEETS-SHEET I.

6 Ci'usfaa S. G. WlGELlUS AND N. W. UHR. INTERNAL COMBUSTION ENGINE 0F COMPOUND TYPE.

APPLICATION FILED MAR. 3. 1918.

Patented Apr. 13, 1920.

2 SHEETS-SHEET 2.

UNITED sTATES PATENT OFFICE.

SVEN GUS'I'AF WIGELIUS AND NILS WILHELM UHR, 0F GOT'IENBORG, SWEDEN.

INTERNAL-COMBUSTION ENGINE 0F COMPOUND TYPE.

Specification of Letters Patent.

Patented Apr. 13, 1920.

Application filed March 8, 1918. Serial No. 221,217.

To all whom it may concern:

Be it known that we, SVEN GUs'rAr WIGELIUS and NILs VVILHELM UHR, subjects of the King of Sweden, residing at Gottenborg, Sweden, have invented certain new and useful Improvements in Internal-Combustion Engines of Compound Type, of which the following is a specification.

The present invention refers to an arrangement in internal combustion engines of compound type in .which the cylinders are placed in communication with each other after the high pressure piston has moved through a part of its stroke, and in which the high pressure cylinder is scavenged during expansion in the low pressure cylinder. 7

The invention relates more particularly to compound engines of the type abovementioned, in which the high pressure piston also controls the exhaust from the low pressure cylinder, so as to cause an afterexpansion to take place in the low pressure cylinder when the connection between the cylinders is closed on the return stroke of the high pressure piston. The purpose of the invention is to bring about an effective scavenging of the high pressure cylinder after every charge, and to avoid losses thatmight otherwise be caused by a vacuum arising in the low pressure cylinder. To this end, accordingto this invention, the scavenging is carried on with an excess pressure sufficient to prevent a vacuum from being, produced during the after-expansion in the low pressure cylinder.

Another object of the invention is to make the expansion in the cylinders inclependent of the variations of the charge, so that the same end pressure, above atmospheric, is always obtained in the low pressure cylinder. For this purpose the time of opening of the fresh air valve is made dependent on the variations of the charge, so that the scavenging always takes place at an excess pressure sufiicient to prevent a vacuum to be produced during the afterexpansion. Preferably the scavenging is carried on at an excess pressure of 0.5 to 1 atmosphere, while the exhaust takes place at a slight excess pressure of 0.2 to 0.3 atmosphere.

' In the specification the expression variation of the charge means the Variations of the amount of fuel introduced into the high pressure cylinder for each power stroke.

The variation of the charge differs according as the invention is applied to an englne working according to the explosion method or to an engine of the Diesel type. In the former case the charge is varied by varying the proportion between the fuel and the air in the fuel mixture, and in the latter case the charge is varied by varying the length of time during which the injec tion takes place. In the case of Diesel engines different charges may be designated as in steam engines by the filling, 2'. 6., the ratio between the length of the stroke dur ing which injection takes place, and the whole length of the stroke. Thus a filling of 20% designates a charge corresponding to the injection being carried on over 20% of the stroke of the piston.

The invention will be more fully described with reference to the drawing as applied to internal combustion engines of the Diesel type.

Figure 1 is an indicator diagram of a compound engine of this character.

Fig. 2 is a fragmentary section through the two engine cylinders showing the high pressure piston in its uppermost position.

Fig. 3 is a similar section, the high pressure piston being shown at the instant at which it opens the port between the two cylinders, and the angular relation of the cranks for the pistons being indicated.

Fig. i shows the high pressure piston at its lowermost position in a section similar to that in Fig. 2.

Fig. 5 is a similar section illustrating the high pressure piston at the point where it begins to clos the communicating port, and showing the fresh air valve open for admission of scavenging air to both cylinders.

Fig. 6 is a similar section showing the high pressure piston at the point where it has closed the communicating port, and where the fresh air valve for admission of scavenging air is again'returned to closing position.

1 is the high pressure cylinder, 2 the high pressure piston, 3 the low pressure cylinder and 4' low pressure piston, 5 is the exhaust channel and 6 an annular recess in the piston 2 for blowing out from the low pressure cylinder chamber through the port 7 in the wall between the two cylinders.

8 is the fueland air inlet valve and 9 the air valve for scavenging the high pres sure cylinder.

Under the low pressure piston & there is an air inlet valve 10 to, and an air outlet valve 11 from, the chamber 12 under the piston. By means of the channel 13 the chamber 12 is in communication with the chamber 14: above the valve 9.

The method of working is as follows Fig. 2 shows the parts in the position which they occupy at the beginning of the charging operation and of the combustion. The piston 2 now moves downward, but the piston 4, on the other hand, upward, blowing out taking place at the same time from the low pressure cylinder chamber through the recess 6 and the exhaust channel 5. When the piston 2 has completely covered the port 7, the piston 1 is in such a position that its upper edge has reached about the lower edge of the port 7, and compression begins in the low pressure cylinder. In consequence of the angular crank-position, which, suitably, is about 110 (between 90 and 180) the piston 2 now runs with great speed, and the piston 4, on the other hand, at low speed.

Approximately when the upper edge of the piston 2 has passed the upper edge of the port 7, the two cylinders are placed in communication with each other, and the low pressure piston begins its return stroke at about the same instant. The pressure at that instant is about the same in both cylinders. Both the pistons now move downward, and expansion goes on in both cylinder chambers.

When the high pressure piston 2 begins its return stroke, the low pressure piston 4: has not yet reached the end of its stroke, but has just gone beyond the middle of its stroke. During the following movement, therefore, the expansion is continued as, firstly, the low pressure piston is considerably larger than the high pressure piston, and, as, secondly, the low pressure piston moves at this time with considerably greater speed than the high pressure piston, for which reason the increase of volume in the low pressure cylinder is many times greater than the volume diminution in the high pressure cylinder per time unit.

During the downward movement of the low pressure piston 4, the air which has been drawn inby suction in through the valve 10 during the up-stroke is compressed in the chamber 12, the channel 13 and the chamber 14, and when the pressure on. the air amounts to about 1.5 atmosphere, the pressure in the two cylinder chambers has, at the same time, fallen to the same, or a somewhat lower value, for which reason the valve 9 opens automatically. The low pres sure piston still moves downward, and the scavenging of the high pressure chamber continues during the downward movement of the piston 4.

During the scavenging period the opening of the channel 5 is kept closed by the solid portion of the piston 2, so that, during the whole of the scavenging period the low pressure cylinder chamber is cut oil from the channel 5. At no instant is the high pressure cylinder chamber stand in direct communication with channel 5.

During the continued up-stroke of the high pressure piston 2, the port 7 is first covered by that piston, and then a further expansion, that is, an after-expansion, takes place in the low pressure cylinder, while the low pressure piston is still moving downwardly. At the same time the compression of the fresh air previously introduced into the high pressure cylinder chamber goes on until the piston 2 has reached its highest point, when the fuel injection and combustion begin.

As soon as the port 7 has come into communication with the recess 6 and, consequently, with the exhaust channel 5, which has taken place during the latter part of the up-stroke of the piston 2, and as soon as the piston f has started on its return stroke, the blowing out operation begins from the low pressure cylinder chamber, and it continues even after the piston 2 has begun its return stroke. The continued method of working has been described above.

The pressure conditions of the two cylinders appear from Fig. 1, which shows the pressure curve of the high pressure cylinder designated by small letters and the pressure curve of the low pressure cylinder designated by capitals. Fuel injection takes place along the line (0-6, the length of which represents the degree of admission. At '0 and C respectively the two cylinders are put in communication with each other. C-D represents the simultaneous expansion in both cylinders. At D the scavenging begins. DE represents the scavenging and EF the after-expansion.

Normally, i. e.'at a degree of admission of 20%, the expansion in the low pressure cylinder is carried down to a pressure of 1.5 or 2 atmospheres, and this pressure is reached at the point D, where scavenging begins. During the after-expansion D--E the pressure is lowered to about 1.2 or 1.3 atmospheres. If now the degree of admission is changed to say 15%, as indicated by ab, the expansion would follow the clotted line bc and a pressure of 1.5 atmospheres would be reached already at the point D." This would result in a vacuum being produced during the following expansion were it not for the fact that according to the invention the fresh air valve is opened at an earlier moment when the degree 'of admission is reduced. Thus in this alternative case thefresh air valve is openedatthe point D'. I I .7

We claim:

1. In an internal combustion compound engine of the type wherein a high pressure cylinder is in communication with a low pressure cylinder, and wherein the high pressure piston controls the communication between said cylinders so as to cause an after-expansion in the low pressure cylinder upon closing this communication, means for introducing scavenging air to the cylinders at an excess pressure suflicient to prevent the creation of a vacuum during said afterexpansion, the relation between the high pressure piston and low pressure piston being such that the high pressure piston closes the communication to the low pressure piston after the scavenging operation is finished.

2. In an internal combustion compound engine of the type wherein a high pressure cylinder is in communication with a low pressure cylinder, the high pressure piston controlling the connection between said cylinders so as to cause an after-expansion in the low pressure cylinder 011 closing the connection between the cylinders, means for introducing scavenging air to the cylinders at an excess pressure sufficient to prevent the creation of a vacuum during said afterexpansion, and means for automatically varying the supply of fresh air in accordance with the variations of the charge, the relation of the high pressure'piston to the low pressure piston being such that the com- 'munication between the two cylinders is closed by the high pressure piston after the scavenging operation is finished.

3. In an internal combustion compound engine of the type wherein a high pressure cylinder is in communication with a low pressure cylinder, the high pressure piston controlling the connection between said cylinders so as to cause an after-expansion in the low pressure cylinder on closing the connection between the cylinders, means for introducing scavenging air to the cylinders at an excess pressure to prevent the creation of a vacuum during said after-expansion, and a pressure-controlled fresh air valve on the high pressure cylinder, the relation of the high pressure piston to the low pressure piston being such that the communication between the cylinders is closed after the scavengin operation is finished.

4. 11 an internal combustion compound engine of the type wherein a high pressure cylinder is in communication with a low pressure cylinder, the high pressure piston controlling the connection between said cylinders so as to cause an after-expansion in the low pressure cylinder on closing the connection between the cylinders, means for introducing scavenging air to the cylinders at an excess pressure suificient to prevent the creation of a vacuum during said after-expansion, a pressure controlled valve on the high pressure cylinder, and a passage-way leading from said valve to an air outlet port in the suction chamber of the low pressure piston.

5. In an internal combustion compound engine of the type wherein a high pressure cylinder is in communication with a low pressure cylinder, the high pressure piston controlling the connection between said cylinders so as to cause an after-expansion in the low pressure cylinder on closing the connection between the cylinders after the scavenging operation is finished, means for introducing scavenging air to the cylinders at an excess pressure sufiicient to prevent the creation of a vacuum during said after-expansion, a passage connecting the outer compartment of the low pressure cylinder with the high pressure cylinder, and a pressurecontrolled fresh air valve provided in said passage and adapted to open only after the high pressure piston has turned and begun its return stroke.

6. In an internal combustion compound engine of the type wherein a high pressure cylinder is in communication with a low pressure cylinder, the high pressure piston controlling the connection between said cylinders so as to cause an after-expansion in the low pressure on closing the connection between the cylinders after the scavenging operation is finished, means for maintaining the pressure in the low pressure cylinder above atmospheric pressure during the entire expansion movement of the low pressure cylinder.

In testimony whereof we aflix our signatures in presence of two witnesses.

SVEN GUSTAF WIGELIUS. NILS WVILHELM UHR.

Witnesses GUsTAr SANDBERG, ALFRED ANDERssoN.

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