Drive system, in particular for a self-propelled construction machine, in particular a soil compactor

1. A self-propelled construction machine having a drive system, said drive system comprising:

a drive unit;

at least one hydraulic circuit with a hydraulic pump driven by the drive unit,

a hydraulic drive support unit with a hydraulic pump/motor assembly and at least one pressure fluid reservoir, wherein the hydraulic pump/motor assembly is, or can be, drivingly coupled with the drive unit or/and at least one of the at least one hydraulic circuit, wherein the hydraulic pump/motor assembly can be driven in a charge operating mode by the drive unit and at least one of the at least one hydraulic circuit as a pump to charge at least one of the at least one pressure fluid reservoir to a maximum charge and can be operated in a drive support operating mode as a motor to provide a drive support torque for the hydraulic pump of at least one of the at least one hydraulic circuit;

at least one fluid reservoir;

wherein the hydraulic pump/motor assembly can be operated in a recirculation operating mode as a pump to convey fluid out of a fluid reservoir of the at least one fluid reservoir and into the same, or another fluid reservoir of the at least one fluid reservoir;

wherein the hydraulic pump/motor assembly is operated to provide the recirculation operating mode when the charging mode of at least one of the at least one pressure fluid reservoir is above a threshold charge below said maximum charge and a drive speed of the drive unit is below a threshold speed.

2. The construction machine according to claim 1 ,

wherein the hydraulic pump/motor assembly is driven in the circulation operating mode by the drive unit.

3. The construction machine according to claim 1 ,

wherein the threshold charge is a charging mode with a charge in the range of 60 to 80% of a maximum charge of the at least one pressure reservoir, or/and that the threshold speed is a speed in the range of 1000 to 1200 rpms.

4. The construction machine according to claim 1 ,

wherein the hydraulic drive support unit comprises a charge/discharge valve unit for the selective release/interruption of a flow connection between the hydraulic pump/motor assembly and the at least one pressure fluid reservoir, at least in the flow direction from the at least one pressure fluid reservoir to the hydraulic pump/motor assembly and comprises an expansion valve unit to selectively release/interrupt a flow connection between the at least one pressure fluid reservoir and the fluid reservoir at least in the flow direction from the pressure fluid reservoir to the fluid reservoir.

5. The construction machine according to claim 4 ,

wherein the charge/discharge valve unit is pre-tensioned to a basic state interrupting the flow connection, or/and that the expansion valve unit is pre-tensioned to a basic state releasing the flow connection.

6. The construction machine according to claim 1 ,

wherein the hydraulic drive support unit comprises a recirculation valve unit in the flow path between the hydraulic pump/motor assembly and a fluid reservoir of the at least one fluid reservoir to selectively release/interrupt a flow connection between the hydraulic pump/motor assembly and the fluid reservoir of the at least one fluid reservoir at least in the flow direction from the hydraulic pump/motor assembly to the fluid reservoir of the at least one fluid reservoir.

7. The construction machine according to claim 6 ,

wherein a flow restriction arrangement is provided in the flow path between the hydraulic pump/motor assembly and the fluid reservoir of the at least one fluid reservoir.

8. The construction machine according to claim 6 ,

wherein the recirculation valve unit is pre-tensioned to a basic state releasing the flow connection between the hydraulic pump/motor assembly and the fluid reservoir of the at least one fluid reservoir.

9. The construction machine according to claim 6 , wherein a flow restriction arrangement is provided in the flow path between the hydraulic pump/motor assembly and the recirculation valve unit.

10. The construction machine according to claim 1 ,

wherein the hydraulic drive support unit comprises an open circuit.

11. The construction machine according to claim 1 ,

wherein there is no fluid exchange connection between at least one hydraulic circuit and the hydraulic drive support unit.

12. The construction machine according to claim 1 ,

wherein the drive unit comprises a diesel combustion engine.

13. The construction machine according to claim 1 ,

wherein the threshold charge is a charging mode with a charge in the range of 60 to 80% of a maximum charge of the at least one pressure reservoir, or/and that the threshold speed is a speed in the range of 1100 rpms.

14. The construction machine according to claim 1 ,

wherein the threshold charge is a charging mode with about 70% of a maximum charge of the at least one pressure reservoir, or/and that the threshold speed is a speed in the range of 1000 to 1200 rpms.

15. The construction machine according to claim 1 ,

wherein there is no fluid exchange connection between each hydraulic circuit and the hydraulic drive support unit.

16. A method of operating a self-propelled construction machine having a drive system, the drive system comprising:

a drive unit;

at least one hydraulic circuit with a hydraulic pump driven by the drive unit;

a hydraulic-drive support unit with a hydraulic pump/motor assembly and at least one pressure fluid reservoir;

at least one fluid reservoir;

wherein the hydraulic pump/motor assembly is, or can be, drivingly coupled with the drive unit or/and at least one hydraulic circuit;

wherein the hydraulic pump/motor assembly can be operated in a charging operating mode by the drive unit and at least one of the at least one hydraulic circuit as a pump to charge at least one of the at least one pressure fluid reservoir to a maximum charge and be operated in a drive support operating mode as a motor to provide a drive support torque for the hydraulic pump of at least one of the at least one hydraulic circuit, in which procedure the hydraulic pump/motor assembly can be operated in a recirculation operating mode as a pump to convey fluid out of a fluid reservoir of the at least one fluid reservoir and into the same or another fluid reservoir of the at least one fluid reservoir;

wherein the hydraulic pump/motor assembly is operated in the recirculation operating mode when a charge state of at least one pressure fluid reservoir of the at least one pressure fluid reservoir is above a predetermined threshold charge and below said maximum charge and a speed of the drive unit is below a predetermined threshold speed.

17. The method according to claim 16 ,

wherein the hydraulic pump/motor assembly is operated for a predetermined time after falling below the threshold speed to provide the recirculation operating mode when the charge state of at least one of the at least one pressure reservoir is above a predetermined threshold charge.