Valve train of a combustion piston engine

A valve train of a combustion piston engine having an actuating device which comprises a phase shift gearbox with two inputs and an output for phase adjustment of a camshaft. The first input is connected with a crankshaft, the second input is connected with a controllable braking device and the output is rotationally fixed with the camshaft. The brake is an electromagnetically controlled friction brake which comprises an electromagnet and magnetic coil. A brake rotor is connected with the second input and can be biased, by the magnetic field of the electromagnet, against a friction surface. A permanent magnet is positioned axially adjacent the brake rotor such that, by its magnetic field, the brake rotor can be pressed against a fixed friction surface for the adjustment of a basic brake torque with the respective basic pressing force.

This application is a National Stage completion of PCT/EP2011/061473 filed Jul. 7, 2011, which claims priority from German patent application serial no. 10 2010 039 861.6 filed Aug. 27, 2010.

FIELD OF THE INVENTION

The invention concerns a valve train of a combustion piston engine comprising of an actuator device with a superimposing gear, with two input elements and an output element for phase shifting a camshaft.

BACKGROUND OF THE INVENTION

Due to higher requirements with regard to power, torque, gasoline consumption, and emissions, modern four-cycle combustion piston engines are in almost all cases provided with actuator devices for the phase shifting of the inlet and/or the exhaust camshaft through which the opening times and closing times of the inlet and/or exhaust valves can mainly be modified with regard to rotational speed and load. Through adequate phase adjustment of the inlet and exhaust camshafts, stable idling, increased torque at lower rotational speed of the motor, increased maximum performance and reduced pollutant emission at partial load operation of the respective combustion piston engine can be achieved.

Known actuator devices for the phase adjustment of a camshaft are designed as hydraulic rotary adjusters or as electromechanical rotary adjusters which are positioned immediately between a hub, provided with a chain or toothed belt loop, and the axle of the camshaft wheel which is connected in a rotationally fixed manner with the camshaft. However, disadvantages of such direct rotation adjuster devices are the required actuator forces and the large control effort for the setting of a certain phase angle.

For the improvement of the control characteristics, adjuster devices are therefore proposed for the phase adjustment of a camshaft, in which in the valve train, between the crankshaft and the camshaft, a phase shifter gearbox is provided which is in an operative connection with an adjustment driver. The phase shifter gearbox has generally two input elements and an output element, whereby the first input element, for instance via a chain or toothed belt, is in an operating connection with the crankshaft, the second input element is connected to a controllable adjustment drive, and the output element is connected in a rotationally fixed manner with the cam shaft.

A preferred use of a phase shifter gearbox is a simple planetary transmission or a coupled planetary transmission which comprises components of two planetary gear sets. The actuator drive can be designed as an auxiliary power controlled rotary drive, such as for instance as an electric motor or as a hydraulic rotary adjuster, or as a controllable brake device.

In view of its construction and its control, an especially simple and cost-effective brake device is designed as a friction brake which comprises an enclosure-mounted electromagnet with a magnet body and a magnet coil, as well as a rotationally fixed and axially shiftable brake rotor which is linked with the second input element and which can be pressed against an enclosure-mounted friction surface through the magnetic field of the electromagnet. Since the second input element would be rotating in the running condition faster than the first input element, adjustment of a certain, averaged brake torque is effective at the brake rotor and thus at the second input element, and a certain phase position of the assigned countershaft is maintained. Beginning at this phase position of the camshaft, an adjustment towards early is achieved through a brief increase of the brake torque, and towards late through a brief decrease of the brake torque.

An actuator device for phase adjustment of a camshaft with a phase shifter gearbox and with its operative connection of a brake device is known through DE 10 2006 011 806 A1. The phase shifter gearbox of this actuator device is designed as a coupled planetary transmission with two sun gears with different diameters and teeth count, as well as a planetary carrier which carries several rotatably mounted, two-step planetary gears, wherein the first input element is formed through the planetary carrier, the second input element through the smaller sun gear, and the output element through the larger sun gear.

The brake device is designed as an electromagnetic controllable friction brake which comprises a enclosure-fixed electrode magnet with a magnet body and a magnet coil, as well as a rotationally fixed and axially shiftably, connected with the smaller sun gear, and the brake rotor which can be pressed through the magnetic field of the electro magnet against a friction surface which is positioned at the magnet body. When the electromagnet is turned off, the disc shaped brake rotor is axially pressed by a spring against the planetary carrier, through which at least one locking element engages in a respective recess of the planetary carrier, wherein the planetary transmission is blocked in itself and rotates rigidly. When the electromagnet is turned on, the brake rotor is pulled against the reset force of the spring axially to the outside and against the traction surface of the magnet body, wherein the coupling between the smaller sun gear, and the planet carrier is eliminated and the smaller sun gear is decelerated accordingly based on the effective brake torque.

In accordance with its functional construction, a largely identical actuator device for the phase adjustment of a countershaft is published in the DE 10 2006 028 554 A1. Different from the previously mentioned actuator device, the phase shifter gearbox of this actuator device is designed as a simple planetary transmission with a sun gear, a planetary carrier which carries several, rotatably positioned planetary wheels and a ring gear, whereby the first input element is formed through the planetary carrier, the second input element through the sun gear, and the output element through the ring gear.

However, an additional type of actuator device for phase adjustment of a camshaft in accordance with DE 10 2008 043 673 A1 has an inverse control characteristic. The phase shifter gearbox is, like in the actuator device in accordance with DE 10 2006 028 554 A1, designed as a simple planetary transmission. However, the brake rotor which is rotationally fixed and axially shiftably positioned on a rigid shaft, which is connected with the sun gear, is hereby axially positioned outside of the electromagnet and clamped, by a spring, axially with reference to a freely rotatably positioned pressure disc. The pressure disc is axially positioned within the electrical magnet, adjacent the planetary carrier, and as cams to engage in recesses of the planetary carrier and for control lugs of the ring gear, which locks the planetary carrier with the ring gear in an emergency operating position, when the electromagnet is turned off. In addition, the brake rotor is pressed, when the electromagnet turned off, by a spring against an enclosure-fixed friction surface. When the electromagnet is turned on, the pressure disc is pulled axially away from the planetary carrier against the reset force of the spring and thus locking between the planetary carrier and the ring gear is eliminated. At the same time, the brake rotor is pulled away axially from the enclosure-fixed friction surface in accordance with the strength of the magnetic field against the reset force of the spring, and thus the effective brake torque is reduced.

Disadvantageously in these known actuator devices for a phase adjustment of the camshaft is the permanent energy consumption of the electromagnet during operation of the combustion piston engine and the respective actuator device. Also, in each case of the actuated devices a relatively strong magnetic field is required, against the reset force of the spring, to achieve a sufficient large brake torque for the adjustment and holding of the respective phase angle of the camshaft.

SUMMARY OF THE INVENTION

Based on this background, the objective of the invention has the task to create a valve train of a combustion piston engine with an actuator device for the phase shift of a camshaft in the above mentioned art, in which a lower amount of energy consumed and the construction of the actuator device is simplified.

This object is achieved in conjunction with the characteristics in which a permanent magnet is positioned axially adjacent the brake rotor, and its magnetic field can press the brake rotor with a respective basic pressing force against an enclosure-fixed friction surface for the adjustment of a basic brake torque.

Thus, the invention starts with a basically known valve train of a combustion piston engine which comprises an actuator device with a phase shifter gearbox with two input elements and an output element for the phase adjustment of a camshaft. The first input element is in an operative connection, for instance through a chain or toothed belt drive, with a crankshaft, the second input element is in an operative connection with a controllable break device, and the output element is connected in a rotationally fixed manner with a camshaft. The brake device is designed as an electromagnetically controllable friction brake which comprises a enclosure-fixed electromagnet with a magnet body and a magnet coil, as well as a rotationally fixed and axially shiftable brake rotor, which is connected with the second input element and which can be pressed through the magnetic field of an electromagnet against an enclosure-fixed friction surface.

Through the positioning of a shifting of a permanent magnet, axially neighboring the brake rotor, a more or less constant magnetic field is now generated, through which the brake rotor, when the electromagnet is switched off, is pressed with a defined basic pressing force against an enclosure-fixed traction surface and is therefore adjusted to a basic brake torque which is effective at the second input element. To adjust a brake torque which deviates from this basic brake torque, only an increase or decrease of the basic pressing force is required with the electromagnet, which requires a significantly lower amount of energy in comparison to known actuator devices.

The permanent magnet is advantageously designed in a way and positioned so that the camshaft, during an engine start and a failure of the power supply for the electromagnet and/or its control, is held in a defined basic position or adjusted to it through the adjusted basic brake torque. It is hereby achieved that the electromagnet needs to be turned on only for the adjustment of the actual phase position of the camshaft and that a special safety device (Fail Safe) is not needed, such as in the known actuator devices where form-fit locking is provided between the brake rotor and the second input element of the phase shifter gearbox or between the first input element and the output element of the phase shifter gearbox.

In principle, the permanent magnet could be positioned radially within or outside of the electromagnet, or at the side facing away from the electromagnet, adjacent the brake rotor. However, it would become disadvantageous due to an increased construction effort and larger dimensions of the brake device. Thus, it is here provided that the permanent magnet is positioned within the magnetic flow of the electromagnet, so that the magnet body of the electromagnet and the adjacent section of the brake rotor can be used for creating a close magnetic flow circle of the permanent magnet. In addition, the overlay of the magnetic fields of both magnets is improved, and therefore also the control of the resulting brake torque.

Such positioning of the permanent magnets can appropriately be realized in a way so that the permanent magnet is designed in a ring shape and has an axial orientation of its poles (N, S), as well as being positioned in a respective radially inner or outer recess of the magnetic body of the electromagnet.

As an alternative hereto, it is also possible that the permanent magnet is designed in a ring shape and has a radial orientation of its poles (N, S), as well as being positioned in a respective axial outer, meaning at the side facing away from the brake rotor, recess of the magnetic body of the electromagnet.

The adjustment of the phase angle of the camshaft is now simply achieved in such a way that the magnetic field of a permanent magnet, for an increase of the effective brake torque at the brake rotor, meaning for the adjustment of the camshaft in the direction early, is increased by means of a suitable control device creating the same polarity of the electromagnet, and for a decrease of the brake torque which is effective at the brake rotor, meaning for the adjustment of the countershaft in the direction late, is reduced through a reversed polarity of the electromagnet.

To safely prevent possible assembly errors of the actuator device and excessive wear at the enclosure-fixed brake surface and at the brake rotor, effective end stops can be provided between the first input element and the output element of the phase shifter gearbox, to limit the adjustment range of the phase adjustment of the camshaft to a permitted phase angle range.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A valve train, which is presented inFIG. 1in a sectional view of a combustion piston engine, is provided with an actuator device1for the phase adjustment of a camshaft2which comprises a phase shifter gearbox3with two input elements4,5and an output element6, as well as a controllable braking device7. As presented, the phase shifter gearbox3is designed in this example as a simple planetary transmission8with a sun gear9, several rotatably positioned planetary gears10carried by the planetary carrier11and a ring gear12. The planetary carrier11forms the first input element4and is provided with a chain sprocket13through which, by means of a not shown control chain, a form-fit drive connection exists with the crankshaft of the combustion piston engine. The sun gear9forms the second input element5, which is in an operative connection with the brake device7. The ring gear12forms the output element6and is rigidly connected by several screws14with the camshaft2.

The brake device7is designed as an electromagnetically controllable friction brake15and comprises an enclosure-mounted electromagnet16with a U-shaped cross-section and is designed as a magnet body17made of ferromagnetic material and a magnet coil18, a brake rotor21is positioned rotationally fixed and axially shiftable on the axially extending outer teething20of the sun gear9. The brake rotor21is designed at least in the area adjacent to the magnet body17with a ferromagnetic material so that it is pressed, when the electromagnet16is turned on, axially against the friction surfaces22of the magnet body17due to the induced magnetic field and thereby, braking torque is created which is effective on the sun gear9.

In accordance with the invention, a permanent magnet23is provided which is designed in a ring shape, which has an axial orientation of the poles N, S, and which is positioned in a respective, radial outer recess24of the magnet body17of the electromagnet16. Hereby, the permanent magnet23is positioned within the magnetic flux of the electromagnet16such that, on one hand, the overlay of the magnetic fields of both magnets16,23is improved and, on the other hand, the common use of the magnetic body17allows an amplification of the magnetic field and its friction surfaces22for the braking of the brake rotor21through both magnets16,23.

The advantageous functionality of the inventive actuator device1is that, through the permanent magnet23and therefore without an energy effort, a constant magnetic field is create through which the brake rotor21is pressed against the friction surfaces22of the magnetic body17, thus an effective basic brake torque is created at the sun gear9of the phase shifter gearbox3.

The permanent magnet23is preferably dimensioned such that the camshaft2, when starting the engine and during a failure of the power supply of the electromagnet16and/or its control, is automatically kept in a defined basic position or adjusted to this position through the adjusted basic brake torque. Thus, the form-fit lock provided in the known actuator devices between the brake rotor21and the planetary carrier11, or between the planetary carrier11and the ring gear12, respectively, can be omitted which results in a construction space gain and cost reduction.

For the adjustment of the phase position of the camshaft2, the magnetic field of the permanent magnet23is amplified, for an increase of the brake torque which is effective at the brake rotor21, meaning for the adjustment of the camshaft in the direction early, through a same polarity of the electromagnet16, and the brake torque which is effective at the brake rotor21, meaning for an adjustment of the camshaft2in the direction late, is decreased through an opposite polarity of the electromagnet16. Through the adjustment of the brake torque which is effective at the brake rotor21, relative to the basic brake torque which is created through the permanent magnet23, the energy consumption of the electromagnet16in comparison to the known actuator devices is significantly lower and control of the brake torque is improved with the increased dynamics.

A second variation of the invented actuator device for the phase adjustment of a camshaft2, which is shown inFIG. 2, only differs from the variation shown inFIG. 1that the ring shape designed permanent magnet23′ has now a radial orientation of its poles (N, S) and is positioned, on the side facing away from the brake rotor21, in an axial, outer recess24′ of the magnetic body17of the electromagnet16.

REFERENCE CHARACTERS