EP1700012B1 - Electrical valve actuating device comprising a rotary actuator - Google Patents

Abstract

The invention relates to a valve actuating device (1) for an internal combustion engine comprising a valve (2) that can be axially displaced between an opening position and a closing position and is pre-stressed by a closing spring (3) in the direction of the closing position thereof. A cam (6) connected to a camshaft (5) is provided for actuating the valve. Said camshaft is arranged in such a way that it can pivot back and forth along a longitudinal axis (17) of the camshaft by means of an electric motor (7). A pressure element (14) that can be pivoted about a pivoting axis is pre-stressed by a spring element (11) which exerts a torque on the camshaft by means of the pressure element, said momentarily exerted torque depending on the pivoting position of the cam. The pressure element is pivoted back and forth about the pivoting axis thereof at the same time as the back and forth movement of the camshaft. The invention is characterised in that the angular momentum of the pressure element relating to the pivoting axis is larger than the angular momentum relating to the longitudinal axis of the camshaft and created by the camshaft and the cam.

Description

The present invention relates to a valve train according to the preamble of claim 1.

Such a valve train is known from DE 101 40 461 A1. In conventional internal combustion engines, the camshaft is mechanically driven via a timing chain or timing belt from the crankshaft. To increase the engine power and to reduce the fuel consumption, it would bring significant benefits to individually control the valves of the individual cylinders, but at least the intake valves and the exhaust valves of the individual cylinders. This is possible through an electromagnetic valve train. In the case of an electromagnetic valve drive, an "actuator unit" is assigned to each valve or "valve group" of a cylinder. Currently, different basic types of actuator units are being researched. In a basic type, an opening and a closing magnet are assigned to a valve or a valve group. By energizing the magnets, the valves can be moved axially, ie opened or closed. However, such valve trains are difficult to control in terms of control engineering. In the other basic type, a control shaft is provided with a cam, wherein the control shaft through an electric motor is pivotable back and forth. This is also referred to as the so-called "rotary actuator principle". In the aforementioned DE 101 40 461 A1, the cam acts on a rocker arm. From the rocker arm, the opening force generated by the cam is then transmitted to the valve. At one end of the control shaft, a lever-like member is further provided, which has the form of a "hand crank". Further, a leg spring is provided which has a protruding spring arm which presses against the lever-like element. The spring arm of the pivot spring exerts a torque on the control shaft or on the cam. The torque depends on the position of the lever-like element, ie from the pivot position of the control shaft.

As already mentioned, the control shaft pivots cyclically with the cam in a valve train, as described in DE 101 40 461 A1, cyclically. So there is a permanent reversal of direction instead. The electric motor must thereby accelerate the control shaft and the cam and the lever-like element attached thereto from the idle state to a relatively high rotational speed. When opening the valve, the electric motor is indeed supported by the leg spring, but he has to work against the force of the closing spring, which requires a relatively high electrical power. A major problem here is that when accelerating the control shaft, the cam and connected to the control shaft lever-like element, the electric motor "starts" each time from hibernation. It takes a certain amount of time for each cycle until the electric motor reaches a speed at which the electric motor operates at a favorable electrical efficiency. Especially at very low speeds, the efficiency of the electric motor is relatively unfavorable, resulting in high energy consumption.

The object of the invention is to provide a working on the "Drehaktuatorprinzip" electric valve train, which is improved in terms of electrical energy consumption.

This object is solved by the features of claim 1. Advantageous embodiments and further developments of the invention can be found in the dependent claims.

The starting point of the invention is a valve train for an internal combustion engine with a valve which is arranged axially displaceable between an open position and a closed position. By a closing spring, the valve is biased in the direction of its closed position. Further, a control shaft is provided with a cam which actuates the valve. The control shaft is coupled to an electric motor which pivots the control shaft back and forth about a longitudinal axis. Furthermore, a pivotably arranged "pressure element" is provided, which is biased by a spring. The biased by the spring pressure element exerts on the control shaft torque. The momentarily applied to the control shaft torque depends on the pivoting position of the cam. During the reciprocation of the control shaft, the pressing element is also pivoted back and forth about its pivot axis.

The invention is based on the finding that the energy required for the valve actuation or the electric power required for the valve actuation depends very substantially on the ratio of the mass moments of inertia of the "pivotable valve train components". The greater the mass moment of inertia of the control shaft and the cam, the more power must be provided by the electric motor for the acceleration of the control shaft and the cam. When opening the valve, the acceleration of the control shaft and the cam by the biased by the spring pressure element supported. When the valve is closed, the spring is maximally tensioned. In the experiment, it can be demonstrated that, in particular, the mass moment of inertia of the pressure element or the mass moment of inertia formed by the spring and the pressure element has a decisive effect on the electrical power required for the operation of the electric motor. A good "electrical efficiency" is achieved when the related to its pivot axis mass moment of inertia of the pressing member is greater than the formed by the control shaft and the cam, related to the longitudinal axis of the control shaft mass moment of inertia.

The pressing element is thus executed "solid", as it would actually be required for the transmission of the biasing force generated by the spring.

In the design of the electric motor, it is favorable not to set the maximum speed of the electric motor too high. Although, with an increase in the mass moment of inertia of the control shaft and the cam, the maximum speed of the electric motor could be reduced. However, as already mentioned, as the mass moment of inertia of the control shaft and the cam increases, the dynamics of the valvetrain decreases as the mass moment of inertia of the control shaft and the cam also in the "stable end positions", i. must first be electrically accelerated by the electric motor and then additionally mechanically by the springs from the rest positions of the control shaft out. Likewise, this moment of inertia must be electrically accelerated in a "Minihubbetrieb".

An increase in the mass moment of inertia of the pressure element, however, has the advantage that the pressure element when opening the valve just not by the electric motor out of the rest position must be accelerated, but is moved by the spring element with.

During a first phase of the opening process of the valve, the control shaft and the cam are first accelerated by the electric motor to a certain speed without the valve already being opened. During this first phase, the pressure element is accelerated and thus stores a certain amount of rotational energy. During the second phase, the actual opening movement of the valve begins, in which the valve is opened against the closing spring force of the valve. The energy required for opening the valve is applied primarily by the spring element and the "kinetic energy" stored in the pressure element.

By increasing the mass moment of inertia of the pressure element, correspondingly more kinetic energy is stored in the pressure element. This part of the energy no longer needs to be stored in the camshaft. In other words, according to the invention, part of the energy required for the valve opening is "shifted" from the camshaft to the pressure element. This allows a reduction in the maximum control shaft speed required for the valve opening. The increase in the mass moment of inertia of the pressure element acts in this operating state as an increase in the mass moment of inertia of the control shaft. Since the "rotary actuator" has to be electrically accelerated out of the two end positions, a low mass moment of inertia, in particular at the beginning of the acceleration movement, is favorable both with regard to the actuator dynamics and with regard to the electrical energy consumption.

Another advantage achieved by the invention is that with the invention, the average speed of the electric motor in a higher Speed range is shifted. As a result, the ohmic losses, in particular when accelerating the electric motor from low speeds out, resulting in an improvement in the overall electrical efficiency. This reduces the total energy consumption and the dissipated heat loss.

According to a development of the invention, the spring element is a torsion spring. This may be a torsion bar whose first end is firmly clamped, e.g. is attached to an actuator housing and at its other end the pressing element is fixed and projects substantially perpendicularly from the Torsionsfederstab. The torsion spring rod can be arranged parallel with respect to the control shaft and thus very space-saving.

Preferably, the "increased" mass moment of inertia of the pressure element is achieved by a mass concentration at the end remote from the torsion spring. This results in a relatively high mass moment of inertia with a comparatively small total mass of the pressure element. The pressure element can be made, for example, from a plate-shaped component and have a closed contour with a recess in the central region. The pressing element may be a stamped part. In particular, the recess may be punched out in the middle region.

As already mentioned, according to the invention, the mass moment of inertia of the pressure element related to its pivot axis is greater than the mass moment of inertia formed by the control shaft and the cams and related to the longitudinal axis of the control shaft. A particularly favorable mass moment of inertia results if the mass moment of inertia of the pressure element related to its pivot axis is greater than that by a factor which lies in the range between 1.7 and 2.3 formed by the control shaft and the cam, related to the longitudinal axis of the control shaft mass moment of inertia.

Figur 1

einen elektrischen Ventiltrieb mit Drehaktor gemäß dem Stand der Technik, wie er aus der DE 101 40 461 A1 bekannt ist;

Figur 2

ein durch eine Torsionsfeder vorgespanntes Andrückelement gemäß der Erfindung;

Figur 3

ein Drehzahl-Drehwinkel-Diagramm zur Erläuterung des mit der Erfindung erreichten Energieeinsparpotenzials.

In the following the invention will be explained in connection with the drawing. Show it:

FIG. 1

an electric valve drive with rotary actuator according to the prior art, as it is known from DE 101 40 461 A1;

FIG. 2

a biasing spring biased by a torsion spring according to the invention;

FIG. 3

a speed-rotation angle diagram for explaining the achieved with the invention energy saving potential.

Figure 1 shows a rotary actuator as it is known from DE 101 40 461 A1. The content of DE 101 40 461 A1 is hereby incorporated in full in the content of the present patent application. It is expressly pointed out that all the features described in DE 101 40 461 A1 are also the subject of the present patent application.

FIG. 1 shows an electric valve drive 1 which is based on the rotary actuator principle. An axially displaceably arranged valve 2 is biased by a closing spring 3 in the closed position shown here. At the shaft end of the valve 2, a rocker arm 4 is arranged. Further, a control shaft 5 is provided with a cam 6 acting on the rocker arm 4. The control shaft 5 with the cam 6 is pivoted by an electric motor 7 back and forth. Furthermore, a lever-like element 8 is provided, against which an arm 9 of a leg spring 10 presses. The leg spring 10 thus exerts a torque on the control shaft 5 which is dependent on the pivot position of the control shaft 5. At the back and forth Herbewegung the control shaft 5 and the cam 6 and the arm 9 of the leg spring 10 is moved in accordance with the movement of the lever-like element 8 with. In the rotary actuator shown in FIG. 1, the mass moment of inertia of the arm 9 of the leg fields 10 is comparatively small compared with the control shaft 5 and the cam 6.

A reduction in the motor power required for the valve control or a reduction in the electrical energy required for the valve control can be achieved by using an "arm" or a "pressure element" cooperating with the lever element 8, which has a "higher" mass inertia , As a result, on the one hand, the maximum engine speed required for the valve control or the idling speed of the electric motor can be reduced. In other words, this results in an improved overall electrical efficiency.

Figure 2 shows an improved arrangement according to the invention. Instead of the leg spring shown in Figure 1, a torsion bar 11 is provided in the arrangement of Figure 2, one end 12 is clamped firmly, for example on an actuator housing not shown here. At the other end 13 of the torsion bar 11, a "pressure element 14" is fixed, which presses against a lever-like element 15 which is fixedly connected to the control shaft 5 and thus pivoted back and forth with the control shaft 5 by an electric motor, not shown in Figure 2 , The lever-like element 15 is arranged eccentrically to the control shaft 5. The pressing element 14 has with respect to its pivot axis, ie with respect to the longitudinal axis of the torsion bar 11 a high moment of inertia, which is achieved primarily by a local "mass concentration" in the region of the free end 16 of the pressing member. The moment of inertia of the pressing element 14 is greater than the mass moment of inertia formed by the control shaft 5 and the lever-like element 15 relative to the longitudinal axis 17. But the pressing element has a Comparatively small total mass, which is achieved by a recess 18 in the central region of the pressing member 14. The pressure element 14 is thus formed by a closed contour.

Figure 3 shows a diagram in which the speed of the control shaft is plotted against the rotation angle of the control shaft. Qualitatively, the curve 21 corresponds to the conditions in a rotary actuator according to the prior art, as shown for example in Figure 1. The curve of the curve 22 qualitatively corresponds to a rotary actuator according to the invention. When the valve is fully closed and the control shaft and the cam are in their rest position, this corresponds to a rotation angle 0. In the range between 0 and α ₁ , the control shaft and the cam is accelerated by the electric motor and by the spring or the pressure element , In the rotation angle range between 0 and α ₁ , about 1/4 or 1/3 of the mechanical energy stored in the spring is converted into kinetic energy of the pressure element. The valve is still completely closed up to the angle of rotation α ₁ . Illustratively, the control shaft and the cam in the rotation angle range between 0 and α _{1 get} momentum, in order then to open the valve against the force of the closing spring in the rotation angle range between α ₁ and α ₂ (see FIG.

In the prior art, the pressure element has a comparatively low mass inertia. Thus, the control shaft and the associated cam must be accelerated to a relatively high speed n ₁ .

A reduction in the required for the valve actuation maximum speed to n ₂ can be achieved if the relative to the pivot axis of the pressing member mass moment of inertia of the pressing member is increased, especially if it is greater than that formed by the control shaft and the cam, on the longitudinal axis of the control shaft referred mass moment of inertia. As can be seen from FIG. 4, the "Stellmotorkurve" much flatter. With respect to the maximum engine speed n ₁ and n ₂ is the "mean" operation speed at which the electric motor operates at a pressure member with increased mass inertia larger than in the prior art. In absolute terms, the average working speed in a rotary actuator according to the invention may be smaller. However, the average operating speed related to the maximum engine speed or to the idling speed is greater. The ratio between the average operating speed and the maximum engine speed n ₁ or n _2, in turn, is decisive for the "economy" of the electric motor. By increasing the mass inertia of the pressure element, ie at a flatter speed-rotation angle characteristic results in a better overall overall electrical efficiency.

Claims (9)

1. A valve drive (1) for an internal combustion engine, comprising a valve (2) axially movable between an open position and a closed position and biased towards its closed position by a closing spring (3), a cam (6) connected to a camshaft (5) and adapted to actuate the valve (2), wherein the camshaft (5) is pivotable in reciprocation around its longitudinal axis (17) by an electric motor (7), and a pressure element (14) pivotable around an axis of rotation and biased by a spring element (11), wherein the spring element (11), via the pressure element (14), exerts a torque on the camshaft (5) and the torque exerted at any moment depends on the rotary position of the cam (6), and wherein the pressure element (14) is also swung round its axis of rotation during the reciprocating motion of the camshaft (5),
   characterised in that the mass moment of inertia of the pressure element (14) relative to its axis of rotation is greater than the mass moment of inertia of the camshaft (5) and cam (6) relative to the longitudinal axis (17) of the camshaft (5).
2. A valve drive (1) according to claim 1, wherein the spring element (11) is a torsion spring.
3. A valve drive (1) according to claim 1 or claim 2, wherein the spring element is a torsion spring bar (11) having a first end (12) firmly clamped and a second end (13) fastened to the pressure element (14), which projects at right angles from the said end (13).
4. A valve drive (1) according to claim 3, wherein the torsion spring bar (11) is disposed parallel to the camshaft (5).
5. A valve drive (1) according to any of claims 1 to 4, wherein a part (5) eccentric relative to the camshaft (5) and firmly connected to the camshaft (5) is pressed against by the pressure element (14).
6. A valve drive (1) according to any of claims 1 to 5, wherein the centre of gravity of the pressure element, relative to the centre of area of its projection, is nearer the end (16) of the pressure element (14) remote from the torsion spring (11).
7. A valve drive (1) according to any of claims 1 to 6, wherein the pressure element (14) has a closed contour with a recess in its middle region.
8. A valve drive (1) according to any of claims 1 to 7, wherein the pressure element (14) is a punched part.
9. A valve drive (1) according to any of claims 1 to 8, wherein the mass moment of inertia of the pressure element (14) relative to its axis of rotation is greater by a factor between 1.7 and 2.3 than the mass moment of inertia of the camshaft (5) and cam (6) relative to the longitudinal axis (17) of the camshaft (5).

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