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A method for engine braking of an engine which has at least one exhaust-gas turbocharger with an exhaust-gas turbine acted on by an exhaust-gas flow and a charge air compressor. A device for throttling exhaust-gas flow is arranged between exhaust outlet valves and the exhaust-gas turbocharger, and a

A method for engine braking of an engine which has at least one exhaust-gas turbocharger with an exhaust-gas turbine acted on by an exhaust-gas flow and a charge air compressor. A device for throttling exhaust-gas flow is arranged between exhaust outlet valves and the exhaust-gas turbocharger, and a bypass line conducts the exhaust-gas flow past the throttling device, the exhaust-gas flow being conducted through the at least one bypass line to a turbine wheel of the exhaust-gas turbine. An exhaust gas counter-pressure and a charge air pressure are measured. Based on the measurement, an optimum position of the throttling device to obtain a predetermined braking action is determined. The exhaust-gas counter-pressure and the charge air pressure are subsequently controlled by adjusting the throttling device corresponding to the determination of the optimum position of the throttling device.

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1. A method for engine braking of an engine, the engine having: at least one exhaust-gas turbocharger with an exhaust-gas turbine acted on by an exhaust-gas flow and a charge air compressor, the exhaust-gas turbine and the charge air compressor being commonly mounted on a common shaft;an exhaust gas

1. A method for engine braking of an engine, the engine having: at least one exhaust-gas turbocharger with an exhaust-gas turbine acted on by an exhaust-gas flow and a charge air compressor, the exhaust-gas turbine and the charge air compressor being commonly mounted on a common shaft;an exhaust gas manifold disposed to conduct the exhaust-gas flow from outlet valves of the engine to the exhaust-gas turbocharger;a throttling device for throttling the exhaust-gas flow between the outlet valves and the at least one exhaust-gas turbocharger; andat least one bypass line for conducting the exhaust-gas flow past the throttling device;the method which comprises:conducting the exhaust-gas flow through the at least one bypass line to a turbine wheel of the exhaust-gas turbine, throttling the exhaust-gas flow and thus generating a pressure increase in the exhaust gas upstream of the throttling device for throttling the exhaust-gas flow, and taking a measurement of an exhaust-gas counter-pressure and of a charge air pressure;determining, based on the measurement of the exhaust-gas counter-pressure and of the charge air pressure, a position of the throttling device to obtain a predetermined braking action; andcontrolling the exhaust-gas counter-pressure and the charge air pressure by way of the throttling device in accordance with the determined position of the throttling device for throttling the exhaust-gas flow;wherein the controlling step includes performing a determination that a current exhaust-gas counter-pressure lies below a desired exhaust-gas counter-pressure and the charge air pressure corresponds to a desired value, and in response to the determination, closing the position of the throttling device further; andwherein the controlling step includes performing a further determination that the current exhaust-gas counter-pressure lies below the desired exhaust-gas counter-pressure and the charge air pressure lies below the desired value, and in response to the further determination, opening the position of the throttling device further. 2. The method according to claim 1, wherein an optimum position of the throttling device for throttling the exhaust-gas flow in a first rotational speed range of the engine is a closed position in which a cross section of an exhaust system is blocked and the exhaust-gas flow is conducted through the at least one bypass line past the throttling device. 3. The method according to claim 1, wherein an optimum position of the throttling device for throttling the exhaust-gas flow in a first rotational speed range of the engine is a closed position in which at least a part of a cross section of an exhaust system is opened up and at least a part of the exhaust-gas flow is conducted through the at least one bypass line past the throttling device. 4. The method according to claim 1, wherein an optimum position of the throttling device for throttling the exhaust-gas flow in a second rotational speed range of the engine is a closed position in which at least a part of the cross section of an exhaust system is opened up and a part of the exhaust-gas flow is conducted through the at least one bypass line past the throttling device. 5. The method according to claim 1, wherein a first rotational speed range of the engine is a rotational speed range below or equal to 1400 revolutions per minute, and a second rotational speed range of the engine is a rotational speed range greater than 1400 revolutions per minute, up to a maximum rotational speed of the engine. 6. The method according to claim 1, which comprises, in order to obtain a maximum braking action at a respective engine rotational speed, first setting a maximum charge air pressure and, after the maximum charge air pressure for the engine rotational speed is reached, carrying out a maximum exhaust-gas counter-pressure closed-loop control. 7. The method according to claim 1, wherein at least one predetermined position of the throttling device for throttling the exhaust-gas flow corresponds to a given exhaust-gas counter-pressure. 8. The method according to claim 7, which comprises detecting a correct position of the throttling device for throttling the exhaust-gas flow from a comparison of the present charge air pressure with a setpoint charge air pressure at a current exhaust-gas counter-pressure. 9. The method according to claim 1, which comprises, in a rotational speed range of the engine from 0 to 1000 revolutions per minute, setting the throttling device in a closed position in which a cross section of an exhaust system and also a cross section of at least one bypass line are blocked. 10. The method according to claim 1, which comprises closing the at least one bypass line by a pivoting movement of the throttling device for throttling the exhaust-gas flow. 11. The method according to claim 1, which comprises carrying out a closed-loop control of the exhaust-gas counter-pressure and of the charge air pressure, in addition to a closed-loop control of the throttling device, by way of a unit for charge pressure regulation, into which is incorporated a wastegate that bypasses the exhaust-gas turbine. 12. A device for engine braking of an engine, the engine having at least one exhaust-gas turbocharger with an exhaust-gas turbine subjected to an exhaust-gas flow and a charge air compressor, wherein the exhaust-gas turbine and the charge air compressor are mounted on a common shaft, the device comprising: an exhaust manifold disposed to conduct the exhaust-gas flow from outlet valves of the engine to the at least one exhaust-gas turbocharger;a throttling device for throttling the exhaust-gas flow disposed between the outlet valves of the engine and the exhaust-gas turbocharger;at least one bypass line for conducting the exhaust-gas flow past said throttling device for throttling the exhaust-gas flow;wherein the exhaust-gas flow is conducted through the at least one bypass line to a turbine wheel of the exhaust-gas turbine, the exhaust-gas flow being throttled and a pressure increase in the exhaust gas thus being generated upstream of the throttling device for throttling the exhaust-gas flow;a measuring system for measuring an exhaust-gas counter-pressure and a charge air pressure; anda control unit connected to said measuring system and configured for determining, based on a measurement of the exhaust-gas counter-pressure and of the charge air pressure, a position of said throttling device for throttling the exhaust-gas flow to obtain a predetermined braking action, and said control unit being configured to carry out a closed-loop control of the exhaust-gas counter-pressure and of the charge air pressure by way of said throttling device corresponding to the position of said throttling device determined by said control unit, and wherein said control unit is configured:to perform a determination that a current exhaust-gas counter-pressure lies below a desired exhaust-gas counter-pressure and the charge air pressure corresponds to a desired value, and in response to the determination, to close the position of the throttling device further; andto perform a further determination that the current exhaust-gas counter-pressure lies below the desired exhaust-gas counter-pressure and the charge air pressure lies below the desired value, and in response to the further determination, to open the position of the throttling device further. 13. The device according to claim 12, wherein said throttling device for throttling the exhaust-gas flow has a first closed position in which a cross section of an exhaust system is blocked but the exhaust-gas flow is conducted through said at least one bypass line past said throttling device, and a second closed position in which the cross section of the exhaust system and said at least one bypass line are blocked. 14. The device according to claim 12, which comprises a unit for charge pressure regulation configured to carry out closed-loop control of the exhaust-gas counter-pressure and of the charge air pressure is carried out in addition to the closed-loop control by the throttling device for throttling the exhaust-gas flow. 15. The device according to claim 14, wherein said unit for charge pressure regulation is formed by at least one wastegate connected to bypass the exhaust-gas turbine. 16. In a method for engine braking of an engine, the engine having for each cylinder, at least one outlet valve connected to an outlet system, and a throttle device installed in the outlet system, wherein the throttle device, for engine braking, is actuated in such a way that the exhaust-gas flow is throttled and a pressure increase in the exhaust gas is generated upstream of the throttle device, wherein the exhaust gas flows back into a combustion chamber after an intermediate opening of the outlet valve and serves to provide an increased engine braking action during a subsequent compression stroke with the outlet valve still held partially open, wherein during engine braking, an intermediate opening of the outlet valve effected by the pressure increase generated in the exhaust gas when the throttle device is in the throttling position is subjected to a control-based intervention by virtue of the outlet valve, which tends toward closing after the intermediate opening, being forcibly prevented from closing, and then being held partially open at the latest until a cam-controlled outlet valve opening, by the interception of a control unit installed remote from the camshaft in the outlet valve actuating mechanism;the engine further having at least one exhaust-gas turbocharger with an exhaust-gas turbine acted on by an exhaust-gas flow and a charge air compressor, with the exhaust-gas turbine and the charge air compressor being commonly mounted on a common shaft, having an exhaust manifold which conducts the exhaust-gas flow from outlet valves of the engine to the exhaust-gas turbocharger; andthe throttle device for throttling the exhaust-gas flow being arranged between the outlet valves and the at least one exhaust-gas turbocharger, and at least one bypass line for conducting the exhaust-gas flow past the throttle device for throttling the exhaust-gas flow, wherein the exhaust-gas flow is conducted through the at least one bypass line to a turbine wheel of the exhaust-gas turbine, the exhaust-gas flow is throttled and a pressure increase in the exhaust gas is thus generated upstream of the throttle device for throttling the exhaust-gas flow;the method which comprises:measuring an exhaust-gas counter-pressure and a charge air pressure;based on a measurement of the exhaust-gas counter-pressure and of the charge air pressure, determining a position of the throttle device to obtain a predetermined braking action; andcarrying out a closed-loop control of the exhaust-gas counter-pressure and of the charge air pressure by way of the throttle device for throttling the exhaust-gas flow corresponding to the determined position of the throttle device, andwherein the closed-loop control includes performing a determination that a current exhaust-gas counter-pressure lies below a desired exhaust-gas counter-pressure and the charge air pressure corresponds to a desired value, and in response to the determination, closing the position of the throttle device further; andwherein the closed-loop control includes performing a further determination that the current exhaust-gas counter-pressure lies below the desired exhaust-gas counter-pressure and the charge air pressure lies below the desired value, and in response to the further determination, opening the position of the throttle device further. 17. The method according to claim 16, which comprises, at an end of the expansion stroke, when a control of the outlet valve by a camshaft takes effect again, eliminating a holding function of the control unit which previously acted as a hydraulically blocked buffer, and then controlling an opening of the outlet valve up to a full stroke thereof, a holding of the outlet valve and a renewed closing of the outlet valve during an exhaust stroke by way of an associated normal outlet valve control cam via an outlet valve actuating mechanism with the control unit which then acts therein only as a mechanical buffer. 18. The method according to claim 16, wherein the control unit is installed and acts in a rocker arm mounted on a cylinder head and is composed of a control piston, which is movable with low leakage in a bore of the rocker arm axially between two end positions delimited mechanically by stops and which acts at a front on a rear end surface of the outlet valve shank and which is acted on at a rear side by a compression spring and hydraulically, and a control bush which is screwed into a threaded section of the same rocker arm bore and in whose pressure chamber, which is open in the forward direction toward the control piston, is installed the compression spring acting on the control piston and a check valve, which check valve permits only an introduction of pressure medium from a pressure medium supply duct and has a compression-spring-loaded closing member, the pressure medium supply duct being supplied with pressure medium via a feed duct within the rocker arm, wherein a relief duct leads from the pressure chamber through the control bush to an upper end thereof, and the method comprises holding the outlet opening of the relief duct closed during a braking process in an interception and holding phase of the control unit, for building up and holding the pressure medium pressure in the pressure chamber and for an associated deployment and holding of the control piston in a deployed outlet valve interception position, by a stop fixedly mounted on a cylinder cover. 19. The method according to claim 18, which comprises, during a braking process, with an exhaust-gas-counter-pressure-induced intermediate opening of the outlet valve, pushing the control piston out into a deployed end position thereof on account of forces acting in the pressure chamber and following the outlet valve shank, and as a result filling the pressure chamber which becomes larger in volume with pressure medium, and therefore the control piston is subsequently hydraulically blocked in the outlet valve interception position and in said position, by way of an end surface thereof, intercepts and correspondingly holds open the outlet valve which is moving in the closing direction. 20. The method according to claim 19, wherein the return of the control piston from its outlet valve interception position into its retracted basic position at the end of the holding phase takes place in that, upon the actuation of the rocker arm by the camshaft with the normal outlet cam directly or indirectly via a push rod, as a result of the pivoting of said rocker arm away from the cylinder-cover-side stop, the outlet opening of the relief duct within the control bush at the upper end of the control bush is opened up, and therefore the pressure medium situated in the pressure chamber is relieved of pressure and is released from the volume of the control piston which can now move back and is no longer blocked by the rocker arm, the release taking place until the control piston has assumed its fully retracted basic position. 21. The method according to claim 16, wherein the engine is an internal combustion engine with an underlying camshaft from which the actuation of an outlet valve takes place via a push rod and a following rocker arm, wherein the control unit acts in the chamber between the push rod and force introduction member of the rocker arm in a holding sleeve arranged in or on the cylinder head, and the control unit has a control sleeve coaxially movable with low leakage in the holding sleeve and supported on the upper end of the push rod and has a control piston installed so as to be coaxially movable with low leakage in a blind bore of the control sleeve, which control piston is supported at the top on a thrust transmission part articulatedly connected to the force introduction member of the rocker arm and is acted on at the bottom by a compression spring which acts in the direction of said thrust transmission part, which compression spring is installed in that part of the blind bore provided below the control piston and the hydraulic pressure chamber thus delimited, which pressure chamber is supplied with pressure medium, in particular engine oil, via a feed duct within the cylinder head or block and via a feed duct within the holding sleeve and via a supply duct, which communicates with said feed duct within the holding sleeve, within the control sleeve, wherein a check valve installed in the pressure chamber prevents, by means of its spring-loaded closing member, a return flow of pressure medium from the pressure chamber into the supply duct. 22. The method according to claim 21, wherein, during a braking process, with the exhaust-gas-counter-pressure-induced intermediate opening of the outlet valve, deploying the control piston on account of the forces acting in the pressure chamber, and here, the rocker arm is made to perform a follow-up movement, wherein during the deployment of the control piston, after a stroke travel coordinated with the spring-open stroke of the outlet valve, the outlet opening of a relief duct within the control piston is opened up by emerging from the blind bore in the control sleeve, and the pressure medium within the pressure chamber is relieved of pressure via said relief duct, and in that, at the start of the subsequent closing movement of the outlet valve, the control piston is moved in the direction of its non-deployed basic position again by means of the rocker arm which has performed a corresponding follow-up movement and the thrust transmission part until the outlet opening of the relief duct is closed again by the wall of the blind bore, as a result of which the pressure chamber is shut off again, the control unit is therefore hydraulically blocked, and the outlet valve remains held intercepted in the corresponding partially open position. 23. The method according to claim 21, wherein the elimination of the hydraulic blocking of the control piston in the control sleeve and the return of the control piston out of the outlet valve interception position into its non-deployed basic position take place when, during actuation of the push rod by the camshaft with the normal outlet cam, and the associated stroke of the control sleeve, after a certain stroke, coordinated with the maximum opening stroke of the outlet valve, of the control sleeve, as a result of the emergence thereof from the holding bore of the holding sleeve, the outlet cross section of a relief bore extending transversely from the pressure chamber is opened up, the pressure medium situated in the pressure chamber is relieved of pressure and is released from the volume of the control piston which can now move back, said release taking place until said control piston has assumed its fully retracted basic position, attained when the thrust transmission part sets down on the end side of the control sleeve. 24. The method according to claim 16, which comprises holding the outlet valve, after the exhaust-gas-counter-pressure-induced intermediate opening, in an interception position, wherein a distance from the closed position amounts to approximately ⅕ to 1/20 of a full camshaft-controlled outlet valve opening stroke. 25. The method according to claim 16, which comprises also taking into consideration the control unit as a hydraulic valve play compensating element, and compensating for a degree of play occurring in the valve actuating mechanism by way of corresponding pressure medium replenishment into the pressure chamber with corresponding follow-up movement of the control piston in a direction of a member to be acted on.