WO2004053345A1

WO2004053345A1 - Crank mechanism of combustion engine___________________

Info

Publication number: WO2004053345A1
Application number: PCT/FI2003/000670
Authority: WO
Inventors: Jukka Kalevi Pohjola
Original assignee: DAPOMOT Oy
Current assignee: DAPOMOT Oy
Priority date: 2002-12-11
Filing date: 2003-09-15
Publication date: 2004-06-24
Anticipated expiration: 2005-06-11
Also published as: FI20022177A0; AU2003262596A1; FI20022177A7

Abstract

The crank mechanism comprises a piston (3) reciprocating in a cylinder (2) so that the piston is connected by a piston pin (4) to a piston rod (5), which rotates the crank (8) of a crank shaft (10) by a circular cam (7) located at the lower part of the piston rod (5). At the vicinity of the circumference of the cam (7) there is a hole (9), eccentrically mounted into the cam, by which the cam (7) is attached to the crank (8) so that the cam can turn on the crank (8). On the cam (7) beneath the hole (9) there is a pin (12), which has been set onto the cam (7) so that the distance of the pin (12) from the hole (9) is a little greater than the rotating radius of the crank (8). The pin (12) is attached by a bearing to a slide (14) sliding along slide rails (15), which run in the direction of the cylinder (2) or the pin (12) is attached to the end of a control lever (18) swinging crosswise in respect to the axis of the cylinder so that when the crank (8) is rotating the pin (12) is reciprocating on the axis of the cylinder or in its vicinity. The motion of the pin (12) turns the cam (7) in turn to both sides of the axis of the cylinder (2) so that the cam (7) gets a motion velocity that reduces the velocity of the piston around TDC and increases the velocity of the piston around BDC.

Description

Crank mechanism of combustion engine

The invention relates to a crank mechanism of a combustion engine in which the crank mechanism decreases the velocity of the piston around the top dead center (TDC); raises the compression ratio when the engine is running with a partial load and decreases the friction between the piston and the cylinder. By decreasing the velocity of the piston around TDC it is possible to burn the fuel-air mixture in a smaller volume than by using a conventional piston road - crank shaft combination. A small combustion volume raises the combustion temperature. A high combustion temperature raises the expansion pressure, which raises the motor efficiency. The compression ratio of the engine is raised when the engine is runriing with a partial load. A partial load causes a low expansion pressure in the cylinder. The expansion pressure is raised to the right level by raising the compression ratio. By raising the compression ratio the motor efficiency is raised as well. The friction between the piston and the cylinder is decreased by decreasing the lateral motion of the piston rod, which reduces the lateral force of the piston and raises mechanical efficiency.

The crank mechanism comprises a piston reciprocating in a cylinder so that the piston is connected by a piston pin to a piston rod, which rotates the crank of a crank shaft by a circular cam located at the lower part of the piston rod. At the vicinity of the circumference of the cam there is an eccentric hole by which the cam is attached to the crank so that the cam can turn on the crank. On the cam beneath the hole there is a pin, which has been set onto the cam so that the distance of the pin from the hole is a little greater than the rotating radius of the crank. The pin is attached by a bearing to a slide sliding along slide rails, which run in the direction of the cylinder or the pin is attached to the end of a control lever swinging crosswise in respect to the axis of the cylinder so that when the crank is rotating the pin is reciprocating on the axis of the cylinder or in its vicinity.

The crank mechanism changes the velocity of the piston in such a way that when the crank is rotating the pin is reciprocating linearly or it is swinging beneath the crank in a motion of a circular arc so that the pin turns the cam on the crank in turn to both the sides of the axis of the cylinder. The swinging motion of the cam on the crank creates a velocity, which changes the height of the cam in respect to the height of the crank. The amount and the direction of the motion velocity of the cam depends on the crank angle. Around TDC the motion of the cam is contrary to the motion of the crank and therefore the velocity of the cam becomes smaller than the velocity of the crank. The cam is connected to the piston rod and therefore the velocity of the piston, which is connected to the piston rod, also decreases. Around the bottom dead center BDC the situation is the opposite and the turning motion of the cam increases the velocity of the piston.

The mechanism raises the compression ratio so that the control lever moves the pin crosswise in such a way that the pin turns the cam on the crank. The turning motion of the cam changes the maximum height of the cam in the direction of the cylinder due to which the height of the piston, which is connected to the piston rod, also changes at TDC. The l irning of the cam can be carried out by turning the slide rails on a shaft so that the slide in the rails turns the cam or so that the changing length of the control lever is connected straight to the pin on the cam.

Patent application WO 95/13464 presents a circular cam fixed to the driving shaft, which is rotated by a piston rod. In that mechanism the velocity of the piston around TDC is greater than around BDC i.e. the mechanism functions contrary to the mechanism of this invention.

Patent publications EP 1143127 and EP 1160430 present a 2-lever crank mechanism in which the upper lever functions as a "piston rod" so that its lower part is connected to a lower T- shape lever, which is connected to the crank. In the T-lever there is a pin, which is connected to a control lever by which the location and the shape of the motion track of the T-lever can be changed. The crank mechanism decelerates the velocity of the piston around TDC by an elliptic motion track slanting in respect to the direction of the cylinder and increases the compression ratio so that the height of the other pin is changed in the direction of the cylinder so that the location and the shape of the motion track is changed in such a way that it simultaneously changes the height of the motion track.

In the above mechanism the velocity of the piston decreases relatively little around TDC. When the compression ratio is raised, the motion track of the lower part of the upper lever approaches the circular shape motion track of the crank, which means that the speed of the decelerating piston and the raising of the compression ratio cannot be effectively used simultaneously. The motion track of the lower part of the upper lever is a rather broad slanting "ellipse", which causes a wide lateral motion of the levers, which increases the vibration of the mechanism and the friction between the cylinder and the piston. The strength of the structure of a T-lever located above the crank is not the best possible, when it is to be used for instance in diesel engines, in which the lever is under the influence of great torques. In this mechanism the possibilities for adjusting the velocity of the piston are minor, since the small change in the velocity of the piston, which is achieved by the invention, should always be used entirely.

The mechanism according to the invention has a simpler and stronger structure and the mechanism has a different functional principle in which the velocity of the motion track of the crank is reduced around TDC by an opposite motion velocity of the cam; the compression ratio is raised by changing the location of the pin under the crank crosswise in respect to the axis of the cylinder and the mechanical friction is reduced by a narrow motion track of the cam in respect to the axis of the cylinder. The functioning of the above mechanism can be affected in six different ways:

a) The increasing of the diameter of the cam decreases the velocity of the piston around TDC. A diameter, which is about two times greater than the diameter of the revolution circle of the crank can be considered as the greatest diameter of the cam. In this case the pin can be placed into the center point of the cam. The pin located at the center point of the cam forms for the cam a linear motion track, which combines with the axis of the cylinder, when symmetrical slide rails that run in the direction of the cylinder axis are used, i.e. in this case the piston rod carries out a reciprocating linear motion that unites with the axis of the cylinder, in which case the friction between the piston and the cylinder is minimized. (Fig.4 motion track E₂) - Due to the straight motion track of the cam the mechanism can be used generally for changing a reciprocating linear motion into a revolving motion, in which case the cylinder and the piston can be replaced by a slide moving along linear slide rails.

b) The closer the hole in the cam is to its circumference, i.e. the greater the eccentricity is, the more the piston decelerates around TDC.

c) The distance of the pin from the center point of the crank shaft has the greatest effect on the functioning of the crank mechanism. The closer the pin is to the center point of the crank shaft, the greater is the swinging motion of the cam and the more the piston decelerates around TDC. However the distance always has to be a little bigger than the rotation radius of the crank so that the mechanism in general can function. d) The closer the pin is to the center point of the cam, the narrower is the motion track of the cam and the smaller is the mechanical friction between the piston and the cylinder.

e) The transfer of the pin away from the diameter of the cam, which goes through the center point of the crank, decreases the amount of the lateral motion needed for the raise of the compression ratio; it moves the motion track of the cam during the expansion phase closer to the axis of the cylinder and changes the crank angle in respect to TDC so that immediately after combustion the crank shaft has almost the maximum torque.

f) The lateral swinging motion of the control lever forms for the pin a motion track, the shape of which is a circular arc, in which the motion track moves the pin in such a way that during the expansion phase the swinging motion of the cam is increased, due to which the deceleration is increased.

The adjustment of the compression ratio in the crank mechanism, when slide rails are used, is carried out so that the slide rails are turned on a shaft in the body in such a way that the slide in the rails moves the location of the pin, which turns the cam on the crank. The turning of the cam on the crank either raises or lowers the cam in the direction of the cylinder axis so that the height of the piston, which is connected to the crank, changes at TDC, i.e the compression ratio changes. The turning of linear slide rails is carried out by a control lever, one end of which is connected to the slide rails and the other end to a cam, which is fixed to a gear wheel rotating on a shaft connected to the body and rotated by two screws with opposite threads so that the screws are connected by gear wheels to the drive device. When the gear wheel turns the cam, it changes the functional length of the control lever. The change of the length turns the slide rails as mentioned above.

The crank mechanism can also have another kind of structure in which the slide rails and the slide are replaced by a control lever, one end of which is connected straight to the pin on the cam and the other end to the cam on the gear wheel. When the crank is rotating the control lever is swinging so that the pin at the other end of the control lever carries out a reciprocating motion track forming a circular arc. In the invention the control lever can be set crosswise in respect to the cylinder axis so that the convex motion of the pin takes place in the direction of the cylinder axis, in which case the convex shape of the motion increases the turning of the cam on the crank and thus also the deceleration of the piston during the expansion phase.

When the pin is located near the center point of the cam, the convex motion of the pin straightens the motion track of the cam during expansion, because the convex motion of the pin moves the cam during the swing towards the convex direction. The motion track, which is formed as a result, resembles a narrow "ellipse" in which the side of the expansion has become almost a straight line, which runs in the direction of the cylinder axis. (Fig. 6) The straight portion of the motion track can be united almost totally to the cylinder axis, when the location of the pin on the cam is moved away from the diameter going through the center points of the crank and the cam. The transfer of the pin also changes the position of the crank in respect to TDC. For instance when the piston is at TDC, the crank may have turned some

30° - 50° on the side of the expansion, in which case immediately at the beginning of the expansion phase, when the pressure is at its highest, the torque is also at its highest. In the following the structure of the invention is explained by referring to the attached drawings, in which:

FIG. 1 shows the front view of the crank mechanism equipped with slide rails, when the piston is at TDC.

FIG. 2 shows the exploded perspective picture of figure 1.

FIG. 3a, 3b, 3c show the crank mechanism in figure 1 with different crank angles. FIG. 4a ,4b, 4c show such a crank mechanism in which the piston rod moves linearly.

FIG. 5a, 5b show the raising of the compression ratio in figure 1.

FIG. 6a, 6b, 6c show such a crank mechamsm in which the control lever is connected to the pin on the cam.

FIG. 7a, 7b show such a mechanism of figure 6 in which the pin on the cam is in the center point of the cam.

FIG. 8 shows the stroke of the piston as a function of the crank angle with different crank mechanisms.

Fig. 1 shows the reciprocating piston 3 moving in cylinder 2 of body 1 so that piston 3 is connected with piston pin 4 to the upper part of piston rod 5. The lower part of piston rod 5 is connected by bearing 6 to the circular cam 7 that is made of two parts so that the joint of the upper part 7a and the lower part 7b of cam 7 is located on the diameter of crank 8. Hole 9 has been made into cam 7 so that its diameter is on the joint of the upper part 7a and the lower part 7b of cam 7. Hole 9 is located near the circumference of cam 7 so that the eccentricity of the hole is great. Cam 7 is connected by hole 7 to crank 8 of crank shaft 10 by bearing 11 so that the center point of cam 7 is beneath crank 8 on the diameter of the cam running through the center point of crank 8. In cam 7 beneath hole 9 there is pin 12, which is near the center point of cam 7 so that the distance between hole 9 and pin 12 is greater than the rotation radius of crank 8. Pin 12 is connected by bearing 13 to slide 14, which reciprocates linearly in slide rails 15 when crank 8 is rotating. The lower part of slide rails 15 is connected by shaft 16 into body 1 so that slide rails 15 can turn on shaft 16. In slide rails 15 there is joint pin 17 for the supporting and the turning of slide rails 15 so that pin 17 is connected by control lever 18 to cam 20, which is turned by shaft 19 located in body 1.

Cam 20 can be turned by control mechanism 21, which comprises the above mentioned cam 20 and gear wheel 22 which is fixed to cam 20 so that cam 20 is eccentric in respect to shaft 19 and the center point of gear wheel 22 is on the axis of shaft 19. Cam 20 is connected into hole 23 , which is at one end of control lever 18. Gear wheel 22 is connected to two opposite screws 24a, 24b with opposite threads so that the screws rotate gear wheel 22 together with cam 20 fixed to gear wheel 22 so that the distance between pin 17 and shaft 19 changes. Screws 24a, 24b are rotated by gear wheels 25a, 25b, which are turned by gear wheel 26, which is connected to drive device 27. The functional change of the length of control lever 18 turns slide rails, due to which cam 7 at the lower part of piston rod 5 turns on crank 8 in such a way that cam 7 either raises or goes down in respect to crank 8. The change in the height of the cam causes a change in the compression ratio. The amount of the rising motion of cam 7 can be increased by moving the location of pin 12 in cam 7 a little away from the diameter of cam 7.

Figure 2 shows the exploded perspective picture of figure 1 without body 1 and cylinder 2. Figure 3 a shows the engine in figure 1 at the beginning of the expansion phase when piston 3 is at TDC; in figure 3b crank 8 has turned 90° from the former; in figure 3c piston 3 is at BDC. Figures 3 also show motion track Ei of cam 7 and the motion of center point Pi of cam 7 along motion track Ei. The motion track E_t of cam 7 is symmetrical in respect to the cylinder axis and the motion track E_t resembles a narrow ellipse running in the direction of the cylinder axis, in which the upper part has expanded and the lower part has become narrower. Figures 4a, 4b, 4c show such a special case of figure 1, in which the diameter of cam 7a is about two times greater than the revolution diameter of crank 8 and pin 12a in cam 7a is located in the center point P₂ of cam 7a. In this case the motion track E₂ of cam 7a is a straight line E₂ which unites with the axis of cylinder 2. This mechanism can be used especially when there is no need to change the compression ratio, as in diesel motors. Motion track E decreases the velocity of piston 3 considerably and motion track E₂ is ideal, because piston 3 doesn't have any lateral forces which press piston 3 against cylinder 2. Thus the friction between piston 3 and cylinder 2 is at its minimum. Piston rod 5 doesn't either have any lateral motion due to which the engine doesn't vibrate crosswise. Because of the linear motion of the piston rod slide rails 15 have been replaced by fixed slide rails 15 a. In figure 4c slide rails 15b have been fixed to the upper part of body 1 so that crank 8 can rotate between slide rails 15b above slide 14b and piston rod 5b has been fixed to piston 3. - The mechanism can be used in general for changing reciprocating linear motion into revolving motion, in which case cylinder 2 and piston 3 can be replaced by a slide moving along linear fixed slide rails.

Figure 5a shows figure 1, in which piston 3 is at TDC. In figure 5b the compression ratio of the former figure 5 a has been raised so that the height of piston 3 has been increased by distance h. The increase of the compression ratio has been carried out in such a way that slide rails 15 have been tilted on shaft 16 by an angle α , in which case pin 12 on cam 7 has turned cam 7 on crank 8 so that the rise of cam 7 has lifted piston 3 by the distance h.

Figure 6a shows a modification of figure 1, in which the straight motion of slide 14 has been replaced by the circular arc motion Bi of pin 12 located at the end of control lever 18a. The change has been accomplished in such a way that slide 14 has been converted into control lever 18a, into one end of which is made hole 23 by which control lever 18 is connected to cam 20. Figure 6b shows the mechanism of figure 6a when crank 8 has turned 90°. Point P₃ demonstrates the motion of the center point P₃ of cam 7 along its motion track E₃. In the crank mechanism according to the invention it is possible to set control lever 18a crosswise in respect to the axis cylinder 2 so that the convex motion Bi of pin 12 in control lever 18a begins on the axis of cylinder 2 and ends on the axis of cylinder 2. The convex motion B_Ϊ of pin 12 improves the shape of the motion track E₃ of cam 7 in such a way that motion track E₃ during the expansion phase becomes almost a straight line, which runs in the same direction as the axis of cylinder 2. This is due to the fact that the convex motion Bi of pin 12 changes the location of pin 12 during the swing of the pin. The convex motion Bi of pin 12 also adds the swing of cam 7 on crank 8, which during the expansion phase increases the deceleration of piston 3 around TDC. The straight part of motion track E₃ can be united with the axis of cylinder 2 when the location of pin 12 in cam 7 is transferred away from the diameter of cam 7. In this new motion track the mechanical friction of piston 3 is almost at its minimum.

Figures 7a, 7b show such an application of the mechanism presented in figures 6, in which pin 12b in cam 7b is located at the center point P₂ of cam 7b. In this case the motion track of cam 7b has the same motion track E as pin 12b at the end of control lever 18b, i.e. the shape of the motion track E is a circular arc. If pin 12b is transferred away from the center point of cam 7b, motion track E₄ approach the shape of a narrow ellipse resembling motion track E3 presented in figures 6. The said motion track E₄ decreases the velocity of piston 3 so much that piston 3 is almost stopped around TDC in a sector of 65°, during which the "stopped" piston 3 enables combustion in an almost constant volume. Combustion in a constant volume creates a high pressure at the beginning of the expansion phase due to which the meaning of the raising of the compression ratio decreases as a motor efficiency raising factor. Therefore in figure 7b the control mechanism 21 of the compression ratio has been omitted and the swinging control lever 18b is connected straight to the shaft in body 1 in which case shaft 20b replaces cam 20. The location of the circular arc shape motion track E₄ can be changed in respect to cylinder 2 axis by moving shaft 20b in body 1 ; for instance so that the motion track begins approximately in the direction of cylinder 2 axis due to which the friction between piston 3 and cylinder 2 is at its minimum when the load on piston 3 is at its maximum. The mechanism presented above suits especially well diesel engines, since the slow motion of the piston around TDC allows a long time for injecting fuel, which makes it possible to run the engine with higher RPM and accordingly with higher engine power.

Figure 8 shows graphically the length of the piston stroke as a function of a crank angle. The lowest curve Si shows the motion of the piston in a conventional crank mechanism. The following upper curve S₂ illustrates a T-lever crank mechanism with two pins. The second highest curve S₃ shows a curve according to the invention, when from all the factors affecting the shape of the curve (points a - f) some kind of lowest limit has been taken. The highest curve S₄ shows the functioning of the mechanism presented in figures 7, in which pin 12b in cam 7b is located in the center point of the cam. The shaded area in general demonstrates the functioning area of the mechanism according to the invention. It can be seen from the curves that with the invention it is possible to achieve around TDC such a deceleration that is necessary for obtaining an ideal combustion process for different types of engines. The combustion can first take place in a constant volume and after that in a constant pressure in such a way that at the beginning of the expansion phase the mechanism creates a great torque on crank shaft 10. The curve S₄ in figure 8 doesn't present the greatest deceleration of piston 3, which can be reached by the mechanism. The velocity of piston 3 decelerates even more, if pin 12b is located between the center point of cam 7b and crank 8.

The crank mechanism presented in the invention is not restricted for use only in combustion engines, like otto- and diesel engines with several cylinders, but it can be used in heat engines, steam engines, pumps and in all the machines and devices, in which the conventional combination of piston rod and crank shaft is presently used in order to change the reciprocating motion into a revolving motion.

Claims

1. A crank mechanism of a combustion engine comprising a piston (3) reciprocating in a cylinder (2), in which the piston (3) is connected by a piston pin (4) to a piston rod (5), which rotates the crank (8) of a crank shaft (10) by a circular shape cam (7) located at the lower end of the piston rod (5) wherein the cam (7) is equipped by a hole (9) eccentrically mounted into the cam (7) so that the hole (9) is on the crank (8) in such a way that the cam (7) can turn on the crank (8) and a pin (12), which is located at the center point of the cam (7) or in its vicinity so that the distance of the pin (12) from the hole (9) is greater than the rotation radius of the crank (8) and that the pin (12) is connected to a slide (14), which while the crank (8) is rotating reciprocates along the slide rails (15) attached to the body (1) in such a way that the pin (12) turns the cam in turn to both sides of the axis of the cylinder (2).

2. A crank mechanism of a combustion engine comprising a piston (3) reciprocating in a cylinder (2), in which the piston (3) is connected by a piston pin (4) to a piston rod (5), which rotates the crank (8) of a crank shaft (10) by a circular shape cam (7) located at the lower end of the piston rod (5) wherein the cam (7) is equipped by a hole (9) eccentrically mounted into the cam (7) so that the hole (9) is on the crank (8) in such a way that the cam (7) can turn on the crank (8) and a pin (12), which is located at the center point of the cam (7) or in its vicinity so that the distance of the pin (12) from the hole (9) is greater than the rotation radius of the crank (8) so that the pin (12) is connected to the free end of the control lever (18a) swinging crosswise in respect to the axis of the cylinder (2) on a shaft (19) attached to the body (1) in such a way that the pin (12) turns the cam (7) in turn to both sides of the axis of the cylinder (2) so that during the expansion phase the transfer of the pin (12) caused by its convex motion increases the turning of the cam (7) on the crank (8) and straightens the oval motion track E₂ on the side of the expansion phase in such a way that the friction between the piston (3) and the cylinder (2) decreases during the expansion phase.

3. A crank mechanism according to Claim 1, in which the compression ratio is changed by changing the functional length of the control lever (18) by ttirning the cam (20) at the end of the control lever (18) on the side of the body (1) in such a way that the change of the length of the control lever (18) turns the cam (7) on the crank (8) so that the distance between the crank (8) and the piston pin (4) changes wherein the other end of the control lever (18) is connected to the pin (17) on the slide rails (15) so that the motion of the pin (17) turns the slide rails (15) on the shaft (16) in the body (1) so that the pin (12) on the slide (14) of the slide rails (15) turns the cam (7) on the crank (8).

4. A crank mechanism according to Claim 2, in which the compression ratio is changed by changing the functional length of the control lever (18a, 18b) by turning the cam (20) at the end of the control lever (18a,18b) on the side of the body (1) in such a way that the change of the length of the control lever (18a, 18b) turns the cam (7, 7b) on the crank (8) so that the distance between the crank (8) and the piston pin (4) changes wherein the control lever (18a, 18b moves the pin (12, 12b) so that the length of the stroke remains almost the same and the lateral motion of the motion track (E3, E4) of the lower part of the piston rod (5) remains small and that by moving the pin (12, 12b) away from the diameter of the cam (7, 7b) the motion of the pin (12, 12b) needed for the raising of the compression ratio can be decreased and that by a certain transfer of the pin (12) the straight part of the motion track (E3) of the expansion phase can be moved to the axis of the cylinder (2).

5. A crank mechanism according to Claim 2, in which the compression ratio is changed by changing the functional length of the control lever (18a, 18b) by turning the cam (20) at the end of the control lever (18a, 18b) on the side of the body (1) in such a way that the change of the length of the control lever (18a, 18b) turns the cam (7, 7b) on the crank (8) so that the distance between the crank (8) and the piston pin (4) changes wherein the cam (20) is fixed eccentrically on a gear wheel (22), which is rotated by two opposite screws (24a, 24b) with opposite threads so that at one end of the screws there are gear wheels (25a, 25b), which are connected to the driving gear wheel (26).