Hydraulic switching assembly for a motor vehicle

The invention relates to a hydraulic switching assembly for a motor vehicle, comprising a hydraulic pump that feeds a hydraulic medium from a sump via hydraulic lines and at least via a magnetic valve assembly with a magnetically actuatable switching valve to a switching element, in order to hydraulically actuate the switching element between two switching positions.

In particular, the invention extends to a hydraulic switching assembly in motor applications of motor vehicles, wherein motor oil from an oil sump of the motor is provided as the hydraulic medium.

In general, switching valves are known that are used for controlling two-stage switchable motor elements. Here, an existing oil pressure in the motor oil circuit is used to actuate the locking mechanism of the switchable motor elements preferably by a 3/2-way directional control switching valve. The directional control switching valve is controlled corresponding to an engine characteristic map stored in the engine control module as a function of various parameters, such as engine speed, engine load, vehicle speed, operating temperature, etc. As a rule, the switching valve is mounted directly in the cylinder head and integrated in the oil circuit, wherein the switching valve includes an electromagnet and a hydraulic part. When the switching valve is energized, oil flows from the oil pump to the switchable motor elements and switches the locking mechanisms of the switchable motor elements. When the switching valve is not energized, the passage from the oil pump to the switching elements is closed and the oil flows via a bypass through the switching gallery with low pressure back to the oil pan, wherein the locking mechanisms are switched back into their original position. The switching times depend on the mechanics of the switching valve and on the design of the hydraulic circuit.

A disadvantage is that, when the engine is at a standstill, the oil pressure in the motor circuit decreases, so that the switchable motor elements are no longer controllable. Furthermore, the system has a high sensitivity with respect to oil pressure fluctuations.

The object of the present invention is to refine a hydraulic switching assembly of the previously mentioned type and, in particular, to avoid the previously mentioned disadvantages.

According to the invention, a pressure accumulator and a first check valve are arranged in a feed line upstream of the switching valve, in order to realize a reliable temporary supply of oil pressure to the switching element. In other words, the pressure accumulator is located with the hydraulic pressure medium during a closed switching position of the switching valve. An opening of the switching valve causes a loading of the switching element with hydraulic pressure medium from the pressure accumulator due to the check valve. Consequently, the switching element can be actuated independent of the operation of the hydraulic pump, in particular, when the engine of the motor vehicle is at a standstill. Furthermore, pressure fluctuations in the hydraulic lines have no influence on the actuation of the switching element. The pressure accumulator achieves the highest efficiency when it is arranged in the direct vicinity of the switching valve. Furthermore, the switching valve can be reset both by the hydraulic pressure and also by springs.

Preferably, the pressure accumulator and the first check valve are integrated in the magnetic valve assembly. Thus, the magnetic valve assembly is provided, in particular, for retrofitting on a switching assembly.

According to a respective preferred embodiment, the pressure accumulator is constructed as a membrane accumulator, gas accumulator, or piston accumulator. Preferably, the pressure accumulator has either a pneumatic spring or a mechanical spring.

The invention includes the technical teaching that a throttle valve is arranged in a bypass line upstream of the first check valve, in order to realize a flushing of the hydraulic lines via a run-back line of the switching valve leading to the sump. In particular, the switching gallery is flushed in reverse via the throttle valve.

Preferably, a second check valve is arranged downstream of the throttle valve. The check valve prevents a flow of hydraulic medium when the switching valve is open.

Preferably, the bypass line is integrated in the magnetic valve assembly. In particular, the bypass line establishes either a direct fluid connection to the run-back line or an indirect fluid connection via the switching valve.

In addition, a first pressure limiting valve is preferably arranged in the run-back line of the switching valve, in order to set a pressure when flushing the hydraulic lines. Furthermore, a second pressure limiting valve is preferably arranged in a pressure-relief line leading to the sump downstream of the hydraulic pump. A pressure increase above a predetermined pressure level thus opens the respective pressure limiting valve and enables a flow of the hydraulic medium back into the sump.

In particular, a filter device for cleaning the oil is provided downstream of the hydraulic pump. According to an advantageous embodiment, a cooling device for cooling the oil is provided downstream of the hydraulic pump.

Additional measures relating to the invention are described in more detail below together with the description of three preferred embodiments of the invention with reference to the figures. Shown are:

FIG. 1 a schematic view for illustrating the setup of the hydraulic switching assembly according to the invention according to a first embodiment,

FIG. 2 a schematic view for illustrating the setup of the hydraulic switching assembly according to the invention according to a second embodiment,

FIG. 3 a schematic view for illustrating the setup of the hydraulic switching assembly according to the invention according to a third embodiment.

According to FIGS. 1, 2, and 3 , a hydraulic switching assembly according to the invention for a motor vehicle—not shown here—has a hydraulic pump 1 that feeds a hydraulic medium from a sump 2 via hydraulic lines 3 . In particular, the hydraulic medium is motor oil of the motor vehicle. The motor oil is fed via the hydraulic pump 1 through a filter device 11 for cleaning the motor oil and through a cooling device 12 for cooling the motor oil to a magnetic valve assembly 4 . A pressuring limiting valve 10 b is arranged in a pressure-relief line 3 d leading to the sump 2 downstream of the hydraulic pump 1 and upstream of the filter device 11 . When a preset oil pressure in the line section between the pump 1 and the filter device 11 is exceeded, the pressure limiting valve 10 b opens and enables the return of motor oil into the sump 2 via the pressure-relief line 3 d.

The magnetic valve assembly 4 has a magnetically actuatable switching valve 5 that is constructed as a 3/2-way directional control switching valve. A first check valve 8 a is arranged in a feed line 3 a of the switching valve 5 . A pressure accumulator 7 is arranged between the first check valve 8 a and the switching valve 5 . The pressure accumulator 7 is connected with a fluid connection to the switching valve 5 via the feed line 3 a of the switching valve 5 . Furthermore, the pressure accumulator 7 and the first check valve 8 a are integrated in the magnetic valve assembly 4 . The switching valve 5 is connected to the switching element 6 via a work line 3 e , in order to hydraulically actuate the switching element 6 between two switching positions.

The switching valve 5 has a first and second switching position 13 a , 13 b , wherein, in the first switching position 13 a of the switching valve 5 , a flow of the motor oil to the switching element 6 is blocked and thus the switching element 6 is not hydraulically actuated. For a magnetic actuation of the switching valve 5 , a fluid connection between the pressure accumulator 7 and the switching element 6 is established by the switching valve 5 , in order to realize a reliable temporary supply of oil pressure to the switching element 6 and to hydraulically actuate the switching element 6 .

According to FIG. 1 , the pressure accumulator 7 is constructed as a membrane accumulator 7 a . A throttle valve 9 is arranged in a bypass line 3 b upstream of the first check valve 8 a , in order to realize a flushing of the hydraulic lines 3 by the use of a run-back line 3 c of the switching valve 5 leading to the sump 2 . A pressure limiting valve 10 a is arranged in the run-back line 3 c of the switching valve 5 , in order to set a pressure during flushing of the hydraulic lines 3 . The flushing of the hydraulic lines 3 and especially also the flushing of the switching gallery are performed in the illustrated first switching position 13 a of the switching valve 5 . Furthermore, a second check valve 8 b is arranged in the bypass line 3 b downstream of the throttle valve 9 . The second check valve 8 b is provided to prevent leakage via the throttle valve 9 during the actuation of the switching element 6 by the switching valve 5 located in the second switching position 13 b.

According to FIG. 2 , the pressure accumulator 7 is constructed as a gas accumulator 7 b . In contrast to the embodiment from FIG. 1 , the bypass line 3 b is integrated in the magnetic valve assembly 4 in the embodiment according to FIG. 2 . Thus, the throttle valve 9 and the second check valve 8 b are also located in the magnetic valve assembly 4 . The pressure limiting valve 10 a arranged in the run-back line 3 c sets the hydraulic pressure for flushing of the hydraulic lines 3 .

According to FIG. 3 , the pressure accumulator 7 is constructed as a piston accumulator 7 c . The bypass line 3 b is connected directly to the run-back line 3 c leading to the sump 2 in contrast to the respective bypass line 3 b according to the first and second embodiment. A throttle valve 9 for flushing the hydraulic lines 3 is arranged in the bypass line 3 b . The pressure for flushing the hydraulic lines 3 is set by the first pressure limiting valve 10 a in the run-back line 3 c.

List of Reference Symbols

1 Pump

2 Sump

3 Lines

3 a Feed line

3 b Bypass line

3 c Run-back line

3 d Pressure-relief line

3 e Work line

4 Magnetic valve assembly

5 Switching valve

6 Switching element

7 Pressure accumulator

7 a Membrane accumulator

7 b Gas accumulator

7 c Piston accumulator

8 a , 8 b Check valve

9 Throttle valve

10 a , 10 b Pressure limiting valve

11 Filter device

12 Cooling device

13 a , 13 b Switching position