Hydraulic system of an automatic gearbox

1. A hydraulic system of an automatic transmission of a motor vehicle, comprising:

a hydraulic pump powered by a drive engine for supplying pressure to the hydraulic system,

a hydraulic reservoir by which, when the drive engine is at rest, for at least delaying a pressure drop in a main pressure circuit of the hydraulic system,

the hydraulic reservoir being connected to the main pressure circuit by way of either an orifice or a throttle,

wherein a valve is arranged between the hydraulic pump and a connection line of the main pressure circuit for supplying shifting elements of the automatic transmission,

the valve at least reduces leakage through the static hydraulic pump when the drive engine is switched off, and

the valve is integrated in a housing of the hydraulic pump.

2. The hydraulic system according to claim 1 , wherein the orifice is in a form of either an aperture or a bore in an intermediate plate, which is arranged between an oil supply flange and a valve housing.

3. The hydraulic system according to claim 1 , wherein the orifice is integrated in a main pressure valve of the hydraulic system.

4. The hydraulic system according to claim 1 , wherein the orifice is arranged in a connection line by which the main pressure circuit is connected to the hydraulic reservoir.

5. The hydraulic system according to claim 1 , wherein the throttle is arranged either in or in a form of a connection line by which the main pressure circuit is connected to the hydraulic reservoir.

6. The hydraulic system according to claim 1 , wherein the hydraulic reservoir is a retarder reservoir of a hydrodynamic retarder which belongs to the automatic transmission.

7. The hydraulic system according to claim 1 , wherein the valve is a one-way valve.

8. The hydraulic system according to claim 1 , wherein, when the drive engine is at rest, leakage-causing elements in the hydraulic system are switched to a low-leakage condition.

9. An automatic transmission, of a motor vehicle, comprising:

a hydraulic system having a hydraulic pump powered by a drive engine for supplying pressure to the hydraulic system,

a hydraulic reservoir by which, when the drive engine is at rest, a pressure drop in a main pressure circuit of the hydraulic system is at least delayed,

the hydraulic reservoir being connected to the main pressure circuit by way of either an orifice or a throttle;

wherein a valve is arranged between the hydraulic pump and a connection line of the main pressure circuit for supplying shifting elements of the automatic transmission,

the valve at least reduces leakage through the static hydraulic pump when the drive engine is switched off, and

the valve is integrated in housing of the hydraulic pump.

10. A method of operating a hydraulic system and an automatic transmission of a motor vehicle, the hydraulic system having a hydraulic pump powered by a drive engine for supplying pressure to the hydraulic system, and a hydraulic reservoir by which, when the drive engine is at rest, a pressure drop in a main pressure circuit of the hydraulic system is at least delayed, the hydraulic reservoir is connected to the main pressure circuit by way of either an orifice or a throttle, the method comprising:

arranging a valve between the hydraulic pump and a connection line of the main pressure circuit for supplying shifting elements of the automatic transmission,

at least reducing leakage through the static hydraulic pump, via the valve, when the drive engine is switched off,

integrating the valve in a housing of the hydraulic pump, and

acting upon shifting elements of a starting gear, when the drive engine is at rest, by pressure provided from the hydraulic reservoir as long as the pressure provided from the hydraulic reservoir is sufficient to compensate for leakage occurring the main pressure circuit.