EP0925427A1

EP0925427A1 - Automatic decompression system

Info

Publication number: EP0925427A1
Application number: EP97944826A
Authority: EP
Inventors: Günter Kampichler; Udo Griebl
Original assignee: Motorenfabrik Hatz GmbH and Co KG
Current assignee: Motorenfabrik Hatz GmbH and Co KG
Priority date: 1996-09-11
Filing date: 1997-09-04
Publication date: 1999-06-30
Anticipated expiration: 2017-09-04
Also published as: JP2001500209A; US6223708B1; DE19636811C2; DE59702768D1; WO1998011330A1; DE19636811A1; EP0925427B1

Abstract

Automatic decompression system for an internal combustion engine, especially a one-cylinder diesel engine with at least one output and input valve controlled by a camshaft (20) with at least one cam wherein the output valve is lifted in order to reduce starting resistance during starting whereby a lifting device that engages fully automatically into the cam (1) of the output valve is provided in order to lift the output valve below a shift speed to enable a change-over from decompression to compression. Said lifting device lifts up the output valve from the valve seat and presents an articulated bow (22) placed between the cam (1) and a cam disc (2) with two articulated arms (11) and a connecting cross-bar (14). It takes on a decompression position in the cam plane at rotational speeds below the shift speed, protrudes above the camshaft base circle and is able to be disengaged into a neutral position in the cam disc plane once the shift speed has been reached, presenting in order to control the engagement and disengagement process dependent upon the shift speed, at least one flyweight (3) biased inwardly in a radial direction by a spring (5), which is flexibly coupled with the bow.

Description

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The present invention relates to automatic decompression for an internal combustion engine, in particular a single-cylinder diesel engine, with at least one exhaust valve and one intake valve, which are controlled by a camshaft with at least one cam, the exhaust valve being vented to reduce the starting resistance when starting .

Devices are known from the prior art which reduce the starting resistance when intake of internal combustion engines. These are primarily semi-automatic devices that release the exhaust valve by a few tenths of a millimeter using a lever that can be operated manually and switch from decompression to compression after a work cycle when reversing or multiple work cycles when cranking by means of a reset or detent mechanism. Furthermore, decompression devices are known from the prior art which, controlled by centrifugal force, only lift a valve (intake or exhaust valve) a few tenths of a millimeter over a certain, short angular range around the ignition TDC and switch from decompressed to compressed state again from a certain crankshaft speed. In addition, from EP 0515183 AI a further jump starting device is known that works controlled by centrifugal force. Because of the rigid connection between the centrifugal weight and the bow, this device requires a relatively large installation space. It is therefore an object of the present invention to provide an easy-to-produce, inexpensive automatic decompression system which operates fully automatically by means of a purely mechanical control and only requires a small installation space.

This object is achieved by an automatic decompression system with the features of claim 1. A fully automatic lifting device is provided for venting the outlet valve below a switching speed for switching from decompression to compression, which causes the outlet valve to be lifted off the valve seat. In this way, the lifting device releases the valve as long as the camshaft rotates below a defined switching speed. This advantageously leads to a reduction in the starting resistance during starting, as a result of which the internal combustion engine is started either manually by means of a reversing cable or by a crank or else electrically by means of a small starter motor. Above the switching speed, the lifting device is inactive, ie the valve is not released and full compression is given. Furthermore, the invention provides that the lifting device has an articulated bracket arranged between cams and a control disk with two articulated arms and a crossbar connecting them, which assumes an indented decompression position in the cam plane at speeds below the switching speed, in which it moves over protrudes the cam base circle, and which can be disengaged into a neutral in the control disc level after reaching the switching speed. The bracket is designed such that it is about an axis of rotation arranged parallel to the cam plane can be pivoted in such a way that when the camshaft rotates slowly or is at a standstill, the bracket is engaged in the cam plane with the crossbar arranged transversely to the articulated arms and protrudes beyond the cam base circle. As a result of this space-saving arrangement, as long as it is controlled by the cam in the area of the traverse, the valve is slightly vented from its closed position, ie it is lifted off the valve seat. After the defined switching speed has been reached, a restoring force is exerted on the articulated arms, which leads to a pivoting movement of the bracket, as a result of which the crossmember is disengaged into the control disc plane. In this way, a fully automatic automatic decompression system is created in a simple manner with purely mechanical means, which only takes up a small amount of space in the assembly room. Furthermore, the invention provides that for speed-dependent control of the engagement and disengagement of the bracket for decompression or compression, at least one centrifugal weight held in a defined rest position by a biasing spring and pressurized inward in the radial direction is provided. The mass of the centrifugal weight is dimensioned such that it assumes its outermost radial position against the pressure of the spring at the defined switching speed, ie that it bears against a stop in this position. In addition, the biasing spring ensures that the centrifugal weight is held in a defined position in its rest position regardless of the gravitational forces. When dimensioning the centrifugal weight depending on the switching speed, the preload force of the spring must also be taken into account. By coupling the flyweight mechanism with the articulated bracket, in realized the switching speed-dependent engagement and disengagement of the bracket in a simple manner.

An advantageous embodiment of the invention provides that the inner radius of one centrifugal weight is designed as a ramp for engaging the bracket against the resistance of a release spring. In this design, the hinge of the bracket is arranged approximately at the level of the longitudinal axis of the camshaft parallel to the cam plane. In this case, the articulated arms have a lever arm running to the cross member and a lever arm running from the joint in the direction opposite to the cross member. The lever arm is loaded by the release spring, which keeps the bracket in its disengaged position, provided that the centrifugal weight is in its extreme radial position above the switching speed. At speeds below the switching speed, the ramp-shaped surface of the inner radius of the flyweight abuts the crossmember and causes the bracket to be held in its engaged position against the pretension of the release spring.

Another advantageous embodiment of the present invention provides that the centrifugal weight is coupled to the bracket via a driver arranged on the articulated arm. In this embodiment, the driver designed as a lever is directly coupled to a driving arm of the flyweight. When the switching speed is reached, the centrifugal weight takes the driver with it so far that the bracket tilts outward into its disengaged position and is positioned in the control disc plane. Below the switching speed, the driving arm keeps the bracket in siner indented position, in which the traverse is in the cam plane.

Finally, it is advantageous that two arc-shaped flyweights are provided which are coupled to one another by a joint. This advantageously eliminates the influence of the gravitational forces by capturing two opposing flyweights. This makes it possible to achieve very low gearshift speeds, which is particularly advantageous when starting reversing.

Furthermore, an advantageous embodiment provides that the ventilation in the decompression division takes place in each case in a defined crank angle range of approximately 90 ° due to the corresponding arc length of the bracket. This is the range that is available after the inlet valve closes and before the ignition TDC is reached or after the ignition TDC and before the exhaust valve is opened. For reasons of valve clearance adjustment, there must be an area in the ignition TDC without valve lift.

It is also advantageous that the switching speed is between 300 and 600 rpm, preferably 400 rpm. With a gearshift speed selected in this way, manual starting can be carried out even at extremely low temperatures or the engine can be turned with a low-power starter.

Finally, an advantageous embodiment provides that the control cam has a groove for receiving the bracket in the engaged position. This keeps the bracket in its defined position and protects it from deformation. Another advantageous development of the present invention provides that the inlet valve can be actuated via the same cam as the outlet valve and is additionally vented in the direction of rotation of the camshaft during the decompression phase after the outlet valve. The advantage here is that, in conjunction with reversing or kickstart devices, the starting resistance is reduced by the proportion of the charge exchange work to be performed for the suction stroke. This also ensures that no unfiltered suction can take place from the outlet tract.

Finally, it is advantageous that the closing of the exhaust valve 40 ° before ignition TDC and the opening of the intake valve 40 ° after ignition TDC is provided. As a result, both valves in the ignition TDC are securely closed.

Finally, a further embodiment of the present invention provides that a valve rocker arm is provided between the cam and the valve. This can control the valve directly or via a push rod.

Finally, it is advantageous that the valve rocker arm can be raised by 0.2 mm - 0.6 mm, preferably 0.4 mm, by the lifting device. When implemented accordingly, this causes the valves to lift between 0.3 and 0.8 mm.

Advantageous embodiments of the present invention are explained in more detail below with reference to the attached figures. Show: 1 shows a front view of a first embodiment of the automatic decompression system according to the invention;

FIG. 2 shows a sectional side view of the automatic decompression system according to FIG. 1;

Fig. 3 is a front view of the automatic decompression system shown in Fig. 1 with the inlet valve vented;

4 shows an automatic decompression system according to FIG. 1 after the switching speed has been reached;

5 shows a sectional side view of the automatic decompression system according to FIG. 1 after the switching speed has been reached;

6a-6c different embodiments of a bracket according to the invention;

7 shows a further embodiment of the automatic decompression system according to the invention in a sectional side view;

Fig. 8 is a valve timing diagram with decompression.

1 shows a front view of a first embodiment of the automatic decompression system according to the invention with cam 1 arranged on camshaft 20 and a control disk 2. In the control disk plane there is a first flyweight 3, which is supported at a point 4 and by a spring 5 in the radial direction inwards is pressed, a second flyweight 6 with a further bearing point 7 and the common joint 8 as well as the driving arm 9 and the bracket 22 are mounted. The driver 10, the associated articulated arm 11, the second articulated arm 13 and the cross member 14 form the bracket 22. The toothing 15 of the control disk 2 and the cam base circle 19 are indicated by a dash-dotted line. Furthermore, are indicated by dash-dotted lines Lines of the rocker arm 16 for the exhaust valve and the rocker arm 17 for the intake valve are shown. In addition, the nose 18 of the first flyweight 3 and the nose 19 of the second flyweight 6 are shown, which are each arranged at the ends of the arcuate flyweights opposite the bearing points 4 and 7.

In the following, identical parts are provided with the same reference symbols.

FIG. 2 shows a sectional side view of the automatic decompression system according to FIG. 1. Only the rocker arm 16 of the exhaust valve is shown. This has a sliding surface 21 which rests on the cam 1 and opens or closes the exhaust valve depending on its stroke movement. The bracket 22 with the cross member 14 and the articulated arm 11 and the driver 10 is pivotally mounted on the two articulated arms in a bearing 23 in the control disc 2. Furthermore, the camshaft 20, the first centrifugal weight 3 and the second centrifugal weight 6 and the toothing 15 of the control disk 2 are shown.

1 and 2 describe a state of the automatic decompression at standstill or at speeds below the switching speed. In this state, the first centrifugal weight 3 is pressed inwards by the spring 5 in the radial direction and the second centrifugal weight 6 is likewise held in the inner radius direction via the articulated connection 8. As a result, the driving arm 9 holds the driver 11 in a position distant from the camshaft axis 24, as a result of which the cross member 14 of the bracket 22 is in a moved state in the camshaft plane. When a switching speed is reached, the centrifugal force of the two centrifugal weights 3 and 6 is greater than the radially inward force of the spring 5, as a result of which the centrifugal weights are pressed radially outward until the lugs 18 and 19 strike the groove base 25 of the control disk. In this state, the driver 10 is moved into a position approximated to the axis 24 of the camshaft, as a result of which the bracket 22 is disengaged into a neutral position in the control disk plane. This state is shown in FIGS. 4 and 5.

In the engaged state, the cross member 14 engages in a groove 26 of the cam 1, whereby the cross member 14 of the bracket 22 protrudes a few tenths of a millimeter above the cam base circle N. If the control disk from FIG. 1 continues to rotate clockwise, the engaged bracket first lifts the rocker arm 17 of the intake valve by a few tenths of a millimeter, the effective crank angle range being determined by the arc length of the bracket 22, i.e. is determined by the length of the cross member 14. This state is shown in Fig. 3. When turning further, the cam 1 first opens the outlet valve, then the inlet valve and, after closing, lifts the outlet valve again slightly through the engaged bracket. As already described, the engagement and disengagement of the bracket is controlled by centrifugal force, and engagement can only take place when the bracket is not exactly at the level of a rocker arm.

6a to 6c show side views of different embodiments of an inventive Bracket. In addition to the articulated arm 11 and the cross member 14, the driver 10 and a cutting edge 23 serving as a joint are shown. 6b shows a bracket in which the bearing is formed by a ball 60. 6c finally shows the side view of an embodiment of a bracket according to the invention, in which the bearing is formed by an axis 61.

7 shows a further embodiment of an automatic decompression system according to the invention. This differs on the one hand from the embodiment described above in that the first centrifugal weight 70 has an inner radius formed as a ramp 71 and on the other hand in that the bracket 72 is pivotable about an axis 73 leading through the center line of the camshaft. In addition to the articulated arm 74 and the cross member 75, the bracket 72 has a lever arm 76 which is loaded by a spring 77. As a result, the bracket is disengaged above the switching speed and held in this position. Below the switching speed, the bracket is pushed against the spring pressure of the spring 77 by the ramp 71 into its engaged position in the cam plane and held in this position until the centrifugal weight again moves outwards.

8 shows a valve control diagram of the decompression, in which the valve lift curve of the exhaust valve is shown at 100, the valve lift curve of the intake valve at 102, the valve lift through automatic decompression at the intake valve at 103 and the valve lift through automatic decompression at the exhaust valve at 104 is pictured. With 105 the ignition TDC is designated and with 106 the over intersection OT. This diagram clearly shows that the valve is not lifted around 40 ° before ignition TDC and 40 ° after ignition TDC.

Claims

claims

Automatic decompression for an internal combustion engine, in particular a single-cylinder diesel engine, with at least one exhaust and one intake valve, which are actuated by a camshaft (20) with at least one cam (1), the exhaust valve being vented to reduce the starting resistance when starting, whereby To vent the exhaust valve below a switching speed for switching from decompression to compression, a fully automatic lifting device engaging in the cam (1) of the exhaust valve is provided, which causes the exhaust valve to be lifted off the valve seat, the lifting device providing an articulated between cams (1) and a control disc (2) arranged bracket (22, 72) with two articulated arms (11, 13; 74) and a crossbar connecting this (14; 75), which assumes an engaged decompression position in the cam plane at speeds below the switching speed, in which he over the cam base circle (N) protrudes, and which can be disengaged into a neutral position in the control disc plane after reaching the switching speed, characterized in that for speed-dependent control of the engagement and disengagement process at least one centrifugal weight (3; 70) is flexibly coupled to the bracket.

2. Automatic decompression system according to claim 1, characterized in that the inner radius of the flyweight (70) is designed as a ramp (71) for engaging the bracket (72) against the resistance of a release spring (77).

3. Automatic decompression device according to claim 1, characterized in that the centrifugal weight (3) with the bracket (22) via a on an articulated arm (11) arranged driver (10) is coupled.

4. Automatic decompression device according to claim 1, characterized in that two arc-shaped flyweights (3, 6; 70; 78) are provided which are coupled to one another by a joint (8).

5. Automatic decompression system according to claim 1, characterized in that the ventilation in the decompression position takes place in a defined crank angle range of approximately 90 ° by a corresponding arc length of the bracket (22; 72).

6. Automatic decompression device according to claim 1, characterized in that the switching speed is between 300 and 600 rpm, preferably at 400 rpm.

7. automatic decompression device according to claim 1, characterized in that in the control cam a groove (25) for receiving the bracket (22) is provided in the engaged position.

8. Automatic decompression system according to claim 1, characterized in that the inlet valve can be actuated via the same cam (1) as the outlet valve and is additionally vented in the direction of rotation of the camshaft (20) after the outlet valve in the decompression phase.

9. Automatic decompression device according to claim 8, characterized in that the closing of the exhaust valve 40 ° before ignition TDC and the opening of the intake valve 40 ° after ignition TDC is provided.

10. Automatic decompression device according to claim 1, characterized in that a valve rocker arm (16; 17) is provided between the cam (1) and the valve.

11. Automatic decompression system according to claim 10, characterized in that the valve rocker arm (16; 17) can be raised by the lifting device by 0.2 mm to 0.6 mm, preferably by 0.4 mm.