EP3268588B1 - Camshaft having a decompression device - Google Patents

Description

The invention relates to a camshaft having a decompression device with the features of the preamble of patent claim 1.

The predecessor of the camshaft with a decompression device used to be the decompression lever. The decompression lever actuates a so-called separate decompression valve in the cylinder head, especially in single-cylinder two-stroke engines, or opens one or more exhaust valves in four-stroke internal combustion engines to reduce the in-cylinder pressure for easier starting. In this case, it is also referred to as valve lifter lever. The decompression valve allows a part of the gas to escape from the cylinder when starting the internal combustion engine. As a result, the force required to start the engine to spin the engine is significantly reduced. Decompression devices of this type are primarily used on single-cylinder internal combustion engines of older motor vehicles, in particular of motorcycles, mopeds, occasionally also in small automobiles or tractors with diesel single-cylinder internal combustion engines.

For example, from the German patent application DE 42 21 394 A1 an automatic decompression device for internal combustion engines known. It is a decompression device with a, with the camshaft of the engine rotating flyweight, which in the area pivoted at standstill and low camshaft speeds in the region of the cam contact surface of a valve lifter vortretendes in this valve in the valve opening direction ram lifting element, which by rising at Speeds swinging centrifugal weight is guided in a Asked from the engagement with the cam contact surface of the plunger position.
Next is from the German patent application DE 196 36 811 A1 an automatic decompression for an internal combustion engine, in particular a single-cylinder diesel engine, with at least one exhaust and an intake valve as known, which are driven by a camshaft having at least one cam, wherein the exhaust valve is released to reduce the starting resistance when starting the internal combustion engine. The automatic decompression has a fully automatic, engaging in the cam of the exhaust valve lifting device for lifting the exhaust valve below a switching speed for the switching from decompression to compression, which causes the lifting of the exhaust valve from the valve seat.
Another generic camshaft with a decompression device is for example from the European patent application EP 0 407 699 A1 known.

From this is known an internal combustion engine with a combustion chamber, with an inlet and outlet valve which controls the flow of a gas-air mixture into the combustion chamber or the outlet of gases therefrom and has corresponding inlet and outlet control means. Further, a rotatable camshaft is provided, on which a camshaft pinion, an inner cam and an outer cam are fixed, wherein the inner cam is arranged axially on the camshaft between the camshaft pinion and the outer cam and the two cams are actuated such that they grasp the corresponding plungers to actuate the inlet and outlet valves. Further, a pressure release mechanism is provided which has a flyweight, wherein the flyweight between the inner cam and the camshaft pinion is arranged. Further, the pressure release mechanism on a rotatable pin which is rotatably received in axially aligned bearing bores in the two cams and extends therethrough to an axis parallel to the camshaft in the two cams, where he at two points along its axis against deflection during the circulation of Camshaft is held. The pin has a cam surface disposed in the region of the outboard cam and the cam surface is configured to extend above the outer cam to engage one of the two plungers when the pin engages a first one depending on the low engine speed Position is twisted, but then is below the outer cam, not to detect the plunger when the pin is rotated in response to high engine speed in a second position, and that the flyweight connected to the rotatable pin and together with the camshaft is rotatable to rotate the pin cam surface to said first position below an engine threshold speed and to rotate the pin cam surface to said second position above said threshold engine speed.

From the US patent US 6,250,271 B1 is a small and lightweight decompression device for a four-stroke internal combustion engine is known, which is safely deactivated when the speed of the internal combustion engine exceeds a certain speed.

A disadvantage of all these known decompression devices is that the decompression function can generate stochastic clickers, which adversely affects the noise emission of the internal combustion engine. This clicker is caused by an unstable flyweight of the decompression device.

The object of the present invention is to identify a measure which prevents or at least reduces the acoustically conspicuous clicking of the decompression device.

This object is achieved by the features in the characterizing part of patent claim 1.

A sliding element installed in the camshaft is supplied with lubricant from the lubrication circuit. As soon as the internal combustion engine starts, this sliding-moving element is displaced radially outward by centrifugal force. At the same time, the sliding-moving element is supported by lubricant pressure and remains in the desired position and pushes the flyweight to the outside. The centrifugal weight is held stable in the deflection position and according to the invention can no longer cause the clicker. Thus, the Klickern is prevented by the inventive design of the decompression function and there is no unpleasant noise of the internal combustion engine.

Advantageous developments of the invention are described in the subclaims.

With the embodiment according to claim 2 ensures that there is always sufficient lubricant with sufficient lubricant pressure to push the sliding element movable towards centrifugal weight.

The measure according to claim 3 serves for the general stabilization of the decompression device.

The embodiments according to claims 4 and 5 are preferred embodiments.

The embodiment according to claim 6 is a particularly preferred embodiment.

Preferably, the camshaft according to the invention is installed according to claim 7 in an internal combustion engine.

Figur 1

zeigt eine Aufsicht auf eine dreidimensional dargestellte, erfindungsgemäße Nockenwelle.

Figur 2

zeigt eine Seitenansicht der erfindungsgemäßen Nockenwelle.

Figur 3

zeigt einen Schnitt A-A aus Figur 2.

The invention is explained in more detail below with reference to three figures.

FIG. 1

shows a plan view of a three-dimensional illustrated, inventive camshaft.

FIG. 2

shows a side view of the camshaft according to the invention.

FIG. 3

shows a section AA FIG. 2 ,

The following apply in the FIGS. 1 to 3 for same components the same reference numbers.

FIG. 1 shows a plan view of a three-dimensionally illustrated, inventive camshaft 1 with a decompression device for an internal combustion engine. The camshaft has two cams 3, each with a base circle 2. As long as the base circle 2 is in operative connection with a gas exchange valve, not shown, the gas exchange valve is closed. Each cam 3 is directly or indirectly via a valve cup, not shown, or a toggle or rocker arm with a gas exchange valve in operative connection, by rotation of the camshaft 1 and thus also the cam 3, the gas exchange valves can be actuated.

In a base circle 2 of a cam 3, a valve lifter 4 is rotatably mounted, which is arranged with a coaxial with the camshaft 1, rotatably mounted flyweight 5 in operative connection that the valve lifter 4 from a certain speed of the camshaft 1 of the flyweight. 5 is rotated such that the valve lifter 4 is a contour of the base circle 2. This means that from a certain speed of the camshaft 1, the valve lifter 4 is virtually ineffective, and the gas exchange valve remains closed normally.

When starting the internal combustion engine, or at a speed which is less than the defined speed, as in FIG. 3 can be seen, the flyweight of a spring element 10 is pressed into a position so that the valve lifter 4 protrudes with a slightly raised contour (0.1 to 1.0 mm) on the base circle 2 of the cam 3. Thus, from the start of the engine, up to the defined speed, the gas exchange valve is slightly opened during the normally closed phase, resulting in a decompression in the cylinder of the internal combustion engine. As a result, a much easier starting of the internal combustion engine is possible.

The camshaft 1 according to the invention with the decompression device is characterized in that the camshaft 1 in the region of the centrifugal weight 5 has a cavity 6 (FIG. FIGS. 2 and 3 ), which is acted upon by lubricant pressure, and in the camshaft 1, a radial first bore 7 is arranged from the cavity 6 in the region of the centrifugal weight 5, wherein in the first bore 7 a sliding lubricant movable sliding element 8 is arranged.

In the present embodiment, the cams 3 each have a recess 12 for weight saving.

FIG. 2 shows a side view of the camshaft 1 according to the invention with the decompression device. In FIG. 2 is the camshaft 1 facing the base circle side of the cam 3 shown. Visible are in turn the recesses 12 of the cam 3. Between the cam 3, a bearing portion 9 is arranged, in which a third bore 15 is arranged, which is connected to the cavity 6. During operation of the internal combustion engine is the camshaft 1 is rotated and the cavity 6 is acted upon by the third bore 15 with lubricant, whereby in the cavity 6, an overpressure is formed, which presses the push-movable element 8 in the first bore 7 radially outward. The cavity 6 can be represented for example by an axial bore through the camshaft 1, which is closed on both sides at the ends of the camshaft 1. This can be represented for example by a closure cover or by a screwed into the bore screw at the camshaft end. The closure of the cavity 6 thus allows the build-up of the lubricant pressure in the cavity 6, to keep the slide-moving element 8 in the desired radially outer deflection position.

By the sliding movably arranged element 8 is in FIG. 2 a section AA drawn perpendicular to the plane of the drawing, in FIG. 3 is shown.

FIG. 3 shows the section AA FIG. 2 by the sliding movable member 8 and the decompression device. Central in FIG. 3 the cavity 6 can be seen, in which the sliding movable element 8 projects in the first bore 7. The flyweight 5 is rotatably mounted on a rotation axis 14. A direction of rotation of the centrifugal weight 5 upon rotation of the camshaft 1 from a defined speed is shown schematically by an arrow, as well as an associated rotation of the valve lifter 4. At the same time the sliding movable element 8 abuts on a stop 11 of the centrifugal weight 5.

The spring element 10 presses via a pressure element 13 at a standstill of the camshaft 1, the flyweight 5 about the axis of rotation 14 with the stop 11 on the sliding element 8 on the side facing away from the spring element 10, the flyweight 5 with the valve lifter 4 in operative connection. In the in FIG. 3 shown position, ie at standstill of the internal combustion engine, the valve lifter 4 in the region of the base circle 2 of the cam 3 is formed so that it protrudes about 0.1 to 1.0 mm above the base circle 2 for a decompression of the cylinder.

If now the internal combustion engine is started, a lubricant pressure builds up in the cavity 6, at the same time the centrifugal weight 5 rotates radially outward, with a support of the lubricating pressure, which also pushes the sliding-moving element 8 radially outward. Here, the centrifugal weight 5 rotates clockwise according to the arrow and rotates the valve lifter 4 such that it assumes the same contour in the base circle 2 as the base circle 2 itself. A decompression is thus safely avoided from a defined speed.

As in FIG. 3 is shown, the element 8 is preferably against the spring force of the spring element 10 of the lubricant in the direction of flyweight 5 slidably. Furthermore, the flyweight 5 preferably has a stop 11 for the sliding-moving element 8. In a further preferred embodiment, the element 8 is a needle roller. Particularly preferably, the camshaft 1 with a decompression device is used as an exhaust camshaft of a valve train of an internal combustion engine.

In other words:

The built in the camshaft 1 sliding movable element 8 is supplied with lubricant from the lubricant circuit. As soon as the internal combustion engine starts, the sliding-moving element 8, preferably a needle roller, is displaced radially outwardly through the lubricant pressure building up in the cavity 6. As soon as the internal combustion engine starts, the sliding-moving element 8 is displaced outward by centrifugal force. At the same time, the sliding-moving element 8 is supported by lubricant pressure in the cavity 6 and remains in the desired radially outer position. The flyweight 5 is held stable in the deflection position and can no longer cause the acoustic conspicuousness. This means thus in accordance with the invention no clicking the decompression device and thus no unpleasant noise of the internal combustion engine.

LIST OF REFERENCE NUMBERS

1. 1st camshaft
2. 2nd base circle
3. 3. cam
4. 4. Valve lift
5. 5. Flyweight
6. 6. Cavity
7. 7. first bore
8. 8th element
9. 9. Storage area
10. 10. spring element
11. 11. Stop
12. 12. recess
13. 13. Pressure hull
14. 14. axis of rotation
15. 15. second bore

Claims (7)

1. A camshaft (1) with a decompression device for an internal combustion engine, wherein a valve lifter (4) is rotatably mounted in a base circle (2) of a cam (3) which can be brought into an operative connection with a gas exchange valve by rotation, which valve lifter is in an operative connection with a flyweight (5) which is rotatably mounted and arranged coaxially to the camshaft (1), in such a way that the valve lifter (4) from a certain speed of rotation of the camshaft (1) onwards forms a contour of the base circle (2) in the region of action with the gas exchange valve,
   characterised in that the camshaft (1) in the region of the flyweight (5) has a cavity (6) to which lubricant pressure can be applied, and in the camshaft (1) a radial first bore (7) is arranged from the cavity (6) to the flyweight (5), with a slidingly movable element (8) which can be displaced by the lubricant pressure being arranged in the first bore (7).
2. A camshaft according to Claim 1,
   characterised in that lubricant can be applied to the cavity (6) via a second bore (15) from a bearing region (9) of the camshaft (1).
3. A camshaft according to Claim 1 or Claim 2,
   characterised in that the element (8) is displaceable, counter to a spring force of a spring element (10), by the lubricant in the direction of the flyweight (5).
4. A camshaft according to one of Claims 1 to 3,
   characterised in that the flyweight (5) has a stop (11) for the element (8).
5. A camshaft according to one of Claims 1 to 4,
   characterised in that the element (8) is a needle roller.
6. A camshaft according to one of Claims 1 to 5,
   characterised in that the camshaft (1) is an exhaust camshaft.
7. An internal combustion engine having a camshaft according to one of Claims 1 to 6.

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