A DEVICE FOR INCREASING CRANKCASE COMPRESSION IN AN INTERNAL COMBUSTION ENGINE

Abstract: In order to increase the crankcase compression of an internal combustion engine, the crank portion (12) of the crankshaft (11) of the engine is provided with filling bodies (14, 15) of a lightweight material. According to the invention, the filling bodies are provided in a holder (10) having an annular, circumferential wall (10a) surrounding said crank portion (12).

Description: A DEVICE FOR INCREASING CRANKCASE COMPRESSION IN AN INTERNAL COMBUSTION ENGINE The present invention relates to a device for increasing cran case compression in an internal combustion engine, said engine comprising a crankshaft having main bearings and at least one crank portion including a counterweight, and filling bodies forming an annular unit together with said crank portion. It is previously known that the performance of a two-cycle engine can be improved by increasing the crankcase compression, which can be achieved by reducing the volume of the crankcase. To this end it has been proposed to use various types of lightweight filling bodies attached to the crank portion of the crankshaft. Such a filling body is preferably shaped so as to form an annular unit together with the crank portion. The disadvantage of such known devices is that the manufacture and mounting thereof are relatively complicated and costly and they have therefore not been used to any great extent. Although the device according to the invention is primarily intended to be used in two-cycle engines, it may also be applicable in four-cycle engines, namely such engines of the type using crankcase scavenging for the purpose of lubrication by fuel mixed with lubricating oil. Such four-cycle engines may be used for example in tools having greatly varying angular working positions preventing the use of a normal pressurised lubrication system. The invention is therefore not restricted to two-cycle engines. According to the invention, a device for increasing the crankcase compression has been provided which is uncomplicated in manufacture and can thus be produced at low cost. Another advantage is that the device can be easily mounted in the engine and is consequently well adapted to rational series production. A further advantage is that no alteration of the crankshaft is required, and neither is any costly modification of other parts of the engine. The above advantages have been achieved by means of a device of the kind mentioned in the introduction which according to the invention is generally characterized in that the filling bodies are provided in a holder comprising an annular, peripheral wall adapted to surround said crank portion. The invention will be described in more detail in the following with reference to the accompanying drawings, in which Figure 1 is a perspective view of a preferred embodiment of the device according to the invention, Figure 2 is a front plan view on a larger scale of the device shown in Figure 1, Figure 3 is a rear plan view on a larger scale of the same device, Figure 4 is a sectional view along line IV-IV in Figure 3, and Figure 5 is a perspective view of a crankshaft provided with the device according to the invention. The preferred embodiment of the device shown in the drawings comprises a cup-shaped, cylindrical holder 10, preferably made of metal, such as sheet steel or light metal, or reinforced plastic, such as glass fibre reinforced polyamide. The holder 10 comprises a peripheral, cylindric wall 10a, and a plane end wall 10b, said last mentioned wall having a central opening 10c for receiving a crankshaft 11. As is best seen in Figures 2 and 3, the end wall has recesses lOd for providing gas communication as will be described below. The cylindrical wall 10a has a diameter adapted to surrounding the crank portion 12 of the crankshaft with a suitable fit, and the crank portion has a counterweight 13, as is conventional. The holder is furthermore provided with filling bodies 14, 15 having a shape corresponding to the space between the crank portion 12 and the peripheral wall 10a. In order to minimize the influence of the filling bodies on the balance of the crankshaft the filling bodies are made of a lightweight material such as glass fibre reinforced plastic, or a light metal such as aluminium or magnesium. The filling bodies can be made as hollow shells, or as homogeneous bodies of lightweight material. For attaching the filling bodies to the holder 10 the end wall 10b is provided with two depressions 16, 17, each having two openings 18, 19, respectively. During manufacture the filler bodies 14, 15 are moulded in situ in the holder 10, the material filling also the openings 18, 19 and the depressions 16, 17, as shown in Figure 4. The filling bodies are thereby permanently attached to the holder 10. As an alternative, the filling bodies and the holder may be made integral, either of light metal by for example die casting, or of above-mentioned plastic material by injection moulding or vacuum forming. The crankshaft 11 shown in Figure 5 is of a conventional type provided with two crank portions 12 and a connecting rod 20 connected thereto. Each of the crank portions is provided with a device according to the invention. The crankshaft is rotatably journalled in a crankcase (not shown) by means of two main bearings 22, 23. As can be seen in the Figure, the holders 10 are mounted on the crankshaft between the respective main bearing and crank portion and are thereby held in place in the correct position without the need for any special attachment means. In order to achieve correct fixing of the device without play the distance between the main bearing and the crank portion is adapted to the thickness of the wall 10b. Sufficient lubrication of the main bearings is ensured by the recesses lOd of the end wall, through which fuel/oil mixture is supplied to the main bearings during operation of the engine. It is also within the framework of the invention to attach the holder 10 to the crank portion by other methods. For example, the peripheral wall 10a could surround the crank portion by a suitable press fit. In another modification, the end wall 10b could have another configuration than the shown plane shape, or could be omitted entirely, the filling bodies being instead attached to the peripheral wall 10a. Such attachment can be made as described above, or the filling bodies can be made integral with the holder. It should also be clear that the volume of the filling bodies can be modified according to the desired performance of the actual engine and need thus not have the generally maximum volume shown in the drawings.

Claims: Claims 1. A device for increasing crankcase compression in an internal combustion engine, said engine comprising a crankshaft (11) having main bearings (22, 23) and at least one crank portion (12) including a counterweight (13) , and filling bodies forming an annular unit together with said crank portion, characterized in that the filling bodies (14, 15) are provided in a holder (10) comprising an annular, peripheral wall (10a) adapted to surround said crank portion. 2. Device according to claim 1, characterized in that the holder (10) comprises an end wall (10b) connected to the peripheral wall (10a) and having a central opening (10c) for receiving the crankshaft (11) . 3. Device according to claim 1 or 2, characterized in that the filling bodies (14, 15) are made of a lightweight material, preferably reinforced plastic. 4. Device according to claim 1 or 2, characterized in that the filling bodies (14, 15) are hollow. 5. Device according to claim 1 or 2, characterized in that the filling bodies (14, 15) are homogeneous. 6. Device according to any of claims 1-5, characterized in that the filling bodies (14, 15) are made integral with the holder (10) . 7. Device according to any of claims 1-6, characterized in that the filling bodies (14, 15) and the holder (10) are made of reinforced plastic by injection moulding or vacuum forming. 8. Device according to any of claims 1-6, characterized in that the filling bodies (14, 15) and the holder (10) are made of light metal such as aluminium or magnesium, by die casting. 9. Device according to claim 2, characterized in that the holder (10) is mounted on the crankshaft (11) with the end wall (10b) clamped between the crank portion (12) and an adjacent main bearing (22, 23) . 10. Device according to any of claims 1-8, characterized in that the holder (10) is attached to the crank portion (12) by a press fit. 11. Device according to any of claims 1-10, characterized by at least one axial passage (lOd) allowing a flow of fuel mixed with lubricating oil for ensuring lubrication of the main bearing.

Inventors: CARLBAECK PER ANDERS MIKAEL, CARLBAECK, PER, ANDERS, MIKAEL
Applicants: CARLBAECK PER ANDERS MIKAEL, ELECTROLUX AB, AKTIEBOLAGET ELECTROLUX, CARLBAECK, PER, ANDERS, MIKAEL
Application year: 1996
Main classification: F02B33
IPC codes: F02B33, F16C3