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The present invention relates to a method for operating a hydraulic system of a self-propelled road paver, in particular, for the supply of hydraulic oil as needed to a closed hydraulic circuit of the road paver, a hydraulic system of a road paver for performing the method and a road paver having su

The present invention relates to a method for operating a hydraulic system of a self-propelled road paver, in particular, for the supply of hydraulic oil as needed to a closed hydraulic circuit of the road paver, a hydraulic system of a road paver for performing the method and a road paver having such a hydraulic system. The extraction and/or return of the quantity of hydraulic oil occur depending on at least one operating parameter of the road paver.

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1. A method for operating a hydraulic system of a self-propelled road paver, comprising: supplying hydraulic oil to a closed hydraulic circuit, wherein at least one hydraulic motor is driven by the hydraulic circuit by at least one operating pump;taking a quantity of hydraulic oil in operation per u

1. A method for operating a hydraulic system of a self-propelled road paver, comprising: supplying hydraulic oil to a closed hydraulic circuit, wherein at least one hydraulic motor is driven by the hydraulic circuit by at least one operating pump;taking a quantity of hydraulic oil in operation per unit of time from the closed hydraulic circuit for cooling and/or filtering purposes; andsupplying a quantity of hydraulic oil per unit of time back to the hydraulic circuit at another location,wherein the supply of hydraulic oil to the closed hydraulic circuit occurs by a feed pump arranged as a variable displacement pump, with a delivery rate of the feed pump being variable and controlled by at least one operating parameter as needed,wherein a closed-loop control of the delivery rate of the feed pump occurs on the basis of a pressure of the hydraulic oil in a load signal line and the pressure of the hydraulic oil is for this purpose monitored in this region,and further wherein a scavenging circuit is present with a scavenging pump arranged as a constant pump, via which, independently of the closed hydraulic circuit, a continuous scavenging and/or cooling of the at least one operating pump and/or the at least one hydraulic motor occurs for cooling and/or lubricating purposes, which scavenging and/or cooling is independent of the at least one operating parameter. 2. The method according to claim 1, wherein the quantity of hydraulic oil taken from the closed circuit is controlled depending on at least one operating parameter of the road paver, wherein the at least one operating parameter is currently determined and an actuating quantity for extracting the hydraulic oil is calculated therefrom on the basis of a predetermined algorithm, or that the actuating quantity is determined by a comparison of the currently determined operating parameter with predetermined characteristic quantities. 3. The method according to claim 1, wherein a division of the hydraulic oil conveyed by the constant pump occurs downstream of the constant pump in the scavenging circuit among operating pumps and/or hydraulic motors of at least two closed hydraulic circuits, wherein hydraulic oil is returned independently thereof in a controlled manner to both closed hydraulic circuits as needed. 4. A hydraulic system of a road paver, comprising: a closed hydraulic circuit with at least one operating pump and a hydraulic motor which is driven by said pump, wherein a quantity of hydraulic oil is taken from the closed hydraulic circuit in operation per unit of time for cooling and/or filtering purposes, and a quantity of hydraulic oil per unit of time is supplied back at another location, the supply occurring via a feed pump supplied from a tank,wherein the feed pump is a variable displacement pump with variable delivery rate, with a delivery rate of the feed pump being controlled as required by at least one operating parameter, such that the feed pump supplies hydraulic oil as needed to the hydraulic circuit,wherein a closed-loop control of the delivery rate of the feed pump occurs on the basis of a pressure of the hydraulic oil in a load signal line and the pressure of the hydraulic oil is for this purpose monitored in this region,and further wherein the hydraulic system comprises a scavenging pump arranged as a constant pump, which, independently of the feed pump and in a constant manner, conveys hydraulic oil to a scavenging circuit, the scavenging circuit being arranged in such a way that the at least one operating pump and/or the at least one hydraulic motor is scavenged and/or cooled by said scavenging circuit independently of the operation of the feed pump. 5. The hydraulic system according to claim 4, wherein the closed hydraulic circuit further comprises a scavenging aperture and a pressure-maintaining valve, wherein the scavenging aperture is provided downstream with a proportional valve with a variable valve opening cross-section, which is triggered depending on the operating parameter, so that the valve opening cross-section and thus the quantity of hydraulic oil taken from the circuit and supplied back to the hydraulic oil tank depends on the operating parameter. 6. The hydraulic system according to claim 5, wherein the proportional valve comprises a control input on the basis of an electrically actuatable magnet, a wax expansion element or a bimetallic element. 7. The hydraulic system according to claim 5, wherein the proportional valve is triggered by an electronic control unit (ECU), and that the at least one operating parameter is determined by a temperature sensor and/or a pressure sensor. 8. The hydraulic system according to claim 5, wherein the proportional valve is triggered by an electronic control unit (ECU), and that the at least one operating parameter is derived from a motor controller or a machine controller. 9. The hydraulic system according to claim 4, wherein a data memory is present in which characteristic quantities of the at least one operating parameter for comparison with the current operating parameter are stored for determining an actuating quantity for the extraction of the hydraulic oil. 10. The hydraulic system according to claim 4, wherein several closed hydraulic circuits are present, and that each circuit is controlled separately. 11. The hydraulic system according to claim 4, wherein the supply of hydraulic oil as needed to the several closed hydraulic circuits occurs jointly via the feed pump arranged as a variable displacement pump, wherein a distributor is provided downstream of the feed pump, via which the hydraulic oil is fed to the several closed hydraulic circuits. 12. The hydraulic system according to claim 4, wherein the feed pump comprises a pressure controller which is arranged for setting the operating pressure of the feed pump at its output within a control range. 13. A road paver having a hydraulic system according to claim 4. 14. The road paver according to claim 13, wherein at least two closed hydraulic circuits with at least one respective operating pump and at least one respective hydraulic motor are present, wherein a distributor is present downstream of the scavenging pump, which distributor allocates the hydraulic oil conveyed by the scavenging pump in parallel to the at least one respective operating pump and/or the at least one hydraulic motor of the two hydraulic circuits. 15. The road paver according to claim 14, wherein the several operating pumps are combined as a modular unit and simultaneously comprise separate inputs and outputs for the hydraulic oil conveyed by the scavenging pump for scavenging and/or cooling purposes. 16. The road paver according to claim 4, further comprising a tamping screed, a right running gear and a left running gear, and that the hydraulic circuit comprises a respective closed hydraulic circuit for driving the tamping screed, the right running gear and the left running gear, and closed hydraulic circuits for the drives of a right and/or left scraper belt, a right and/or left screw conveyor and/or a vibration device.