The invention relates to a pressure-limiting valve with feed function, comprising a valve housing having at least two connection points, in particular in the form of a work port A and a tank port T, and having a spring-loaded pressure-limiting valve piston, which is guided in a longitudinally displaceably manner in the valve housing, and having a spring-loaded check-valve piston for implementing the feed function.
Appropriate valves are used in power hydraulics as so-called shock valves. The valves safeguard the pressure between the so-called Main Control Valve (MCV) and a power cylinder or hydro motor. Thus, even if the MCV is switched off, the respective cylinder is protected in the case of shocks acting on the devices or machines from the outside.
The valve can also be used to provide individual maximum pressure relief, which can be lower than the system pressure. For that reason, the valves are installed in pairs on the A and B sides of the directional control valves (MCV). If a valve responds to a shock load, a volume flow from the hydraulic cylinder (engine) is drained into the tank, and the cylinder evades the overload. To prevent cavitation in the hydraulic system and the connected valve and machine equipment, the opposing shock valve acts as a check valve and permits the oil to be sucked back out of the volume in the tank. In the state of the art (cf. the valve solution RD18329-32/11.1 0 by Bosch Rexroth Group published online in December 2014), direct-controlled installation kit valves are usually used.
In the case of these comparable valves, the valve seat of the check piston is incorporated in the control block. The seat of the pressure-limiting valve is located inside the movable check piston. If the seat of the check piston is damaged, the entire control block must be replaced, because the seat is part of the block. The pressure-limiting valve piston is relatively small in size because it is inside the check-valve piston. In this way, the flat pressure-limiting characteristic, which is desirable for the function, cannot be achieved. Owing to the design, it is very difficult to implement suitable valve damping, resulting in a risk of instabilities in operating the valve.
Based on this state of the art, the invention addresses the problem of providing a valve design, which is suitable as a shock valve with a pressure-limiting function and which does not have the disadvantages described above.
A pressure-limiting valve having the features of Claim 1 in its entirety solves this problem.
Because, according to the characterizing part of Claim 1, the check-valve piston is designed as a continuous hollow piston and is guided directly longitudinally in the valve housing, the solution according to the invention can be designed as a so-called cartridge and can be directly replaced as a whole if the valve seat is damaged. Furthermore, the above-mentioned valve design according to the invention makes it possible to have only a single seat, which can, however, open a large cross-section. Thus, flat flow characteristics are possible in both directions, which is relevant for the shock function mentioned, the stress on the components being low even for fast evasive movements.
With the solution according to the invention, the pressure-limiting function can be dampened, allowing for a stable operation. As both the pressure-limiting valve piston and the check-valve piston have no valve cover as part of the function, the valve as a whole reacts extremely quickly to shock-like overload. As a result, virtually no pressure peaks occur during rapid opening as part of the pressure-limiting function. Further advantageous embodiments of the pressure-limiting valve solution according to the invention are the subject matter of the dependent claims.
Below, the valve according to the invention is explained in detail with reference to an exemplary embodiment in the drawings. In the schematic figures, which are not to scale,
FIG. 1 shows, in the manner of a hydraulic functional circuit diagram, the basic structure of a pilot-controlled pressure-limiting valve having a feed function;
FIGS. 2 to 4 show various functional positions of the valve according to the invention in the manner of longitudinal sectional views; and
FIGS. 5 and 6, comparable to the representation according to FIGS. 2 to 4, show the valve according to the invention having electromechanically formed pilot control.
FIG. 1 shows in the context of a hydraulic fluid supply from a connection point 1 to a connection point 2. A pressure-limiting valve 10 with a mechanical valve pilot control 12 has been installed between the two points 1, 2. Depending on the pressure setting via the mechanical valve pilot control 12 the pressure-limiting valve 10 opens towards the tank (point 2), as soon as a presettable pressure threshold value is exceeded, to protect the hydraulic circuit, in addition to the machines and equipment connected there, from damaging pressure peaks or a correspondingly damaging increase in pressure. A spring-loaded check valve 16, which opens in the direction of the connection point 1 against the action of its return spring, is connected in a bypass line 14 between the connection points 1 and 2. In this way, it is ensured that fluid can be sucked from point 2 if an amount of fluid is missing at point 1, by opening the check valve 16. In case of shock-like pressure increases at point 2, these can also be relieved in the direction of the connection point 1 via the spring-loaded check valve 16.
FIG. 1 thus shows in a symbolic circuit depiction a pilot-controlled pressure-limiting valve 10 having a feed function via the spring-loaded check valve 16, in particular for the range of necessary work functions in construction machines (not shown) of conventional design. The valve solution divided into its individual functions in FIG. 1 has been combined in a single cartridge in the valve design according to FIGS. 2 to 4. The cartridge 18 shown in longitudinal section in FIG. 2 has a valve housing 20 equipped with two connection points in the form of a work port A and in the form of a tank port T. The work port A was inserted in the valve housing 20 on the bottom side and in the axial longitudinal direction, if viewed in the viewing direction of FIG. 2, whereas the tank port T penetrates the valve housing 20 radially in the form of individual bores. Furthermore, a pressure-limiting valve piston 22 is guided in the valve housing 20 in a longitudinally displaceable manner. The piston 22 is propped by a compression spring 24, acting as an energy storage device. In doing so, the free lower end of the compression spring 24 is propped by the piston 22, which has a hollow-bore in this respect. The other upper end of the compression spring 24, on the other hand, is propped against the recess of an orifice seat body 26.
The orifice seat body 26 forms a valve seat for a seat cone 28 and has the damping orifice 30 on its underside. The orifice seat body 26 is arranged stationary in the valve housing 20 and is provided with a longitudinal bore 32, which at its upper end has the pilot control seat with the valve seat cone 28 and the damping orifice 30 is provided at its opposite lower end. The seat cone 28 is clamped between two compression springs 34, 36 with different spring stiffnesses, the upper compression spring 34 being adjustable with respect to its spring pre-load via a spindle drive 38 in a customary manner, which is therefore not described in detail. If the seat cone 28 is lifted from the orifice seat body 26 against the action of the compression spring 34 due to the pressure conditions in the valve and supported by the additional spring 36 from its pilot control seat, a fluid- or medium-conducting connection is opened from the damping orifice 30 via the pilot control seat into transverse ducts 40 in the orifice seat body 26, which in turn transitions into at least one longitudinal channel 42 leading to the tank port T as shown in FIG. 2. To form the respective longitudinal channel 42, the valve housing 20 is encompassed by a cartridge-like additional housing part 44.
The lower end of the longitudinal bore 32 opens into a spring space 46 comprising the compression spring 24 of the pressure-limiting valve piston 22 via the damping orifice 30. Viewed in the viewing direction of FIG. 2, such piston 22 is closed on its bottom by a plug 48, which is radially penetrated by a pilot control orifice 50, which is in fluid-conducting connection with the service port or work port A in every displacement position of the piston 22. The piston 22 itself is guided within the valve housing 22 between an upper travel stop 52 and a lower travel stop 54, the piston 22 abutting against the upper travel stop 52, which, just like the lower travel stop 54, is formed by housing parts of the valve housing 22, as shown in FIG. 2. The illustration according to FIG. 4, on the other hand, shows the piston 22 in its upper stop position against the lower travel stop 54.
Furthermore, the valve construction according to FIG. 2 has a check-valve piston 56, which on its underside is supported by a compression spring 58 as an additional energy storage device. The piston 56 is designed as a hollow piston and is guided along its outer circumference at least partially along the inner side of the valve housing 20. One free upper end of the compression spring 58 is supported by a step in the piston 56 and the other lower end at an end part 60 with a central opening 62, which forms a permanent fluid guide from the work port A into the cylindrical interior 64 of the piston 56.
In accordance with FIG. 2, both the pressure-limiting valve and the check valve are in their closed positions, in which the end face region of the pressure-limiting valve piston 22 is in contact with the assignable end wall region of the check-valve piston 56. Correspondingly, the fluid-conducting connection between the service port A and the tank port T is blocked or disabled. For the purpose of enabling the said fluid-conducting connection between the work port A and the tank port T, the two pistons 22, 46 have to move away from one another relative to each other and in the axial longitudinal direction of the valve body, as will be explained in more detail below. While the resetting spring 24 for the pressure-limiting valve piston 22 is mounted in the mounting space or spring space 46, the resetting or compression spring 58 for the check-valve piston 56 is mounted in the additional mounting space or spring space 66, which extends between the end part 60 and the bottom of the piston 56.
For a desired seat-tight connection of the pistons 22, 56 with each other, the check-valve piston 56 is provided with an inclined surface 68, which engages in a cylindrical receiving space 70 on the end face of the pressure-limiting valve piston 22. The pressure-limiting valve piston 22 thus represents the main stage of the pilot controlled pressure-limiting valve, the diameter of the seat edge 72, formed by the inclined surface 68 being equal to the diameter of the piston shaft 74 of the piston 22 in order to enable a functionally reliable operation in terms of the sketch. In FIG. 2, the piston 22 is already shown in its regulating position in contact with its upper travel stop 52, this only affecting the limit case stop, and the regulation can obviously be effected between the pistons 22 and 56, if the piston 22 moves out of its travel stops, in this case the upper travel stop 52. The further functional description is based on the last-mentioned case of the positioning of the piston 22.
FIG. 3 relates to such a regulating position, in which the check valve reaches an opening position, in which a fluid-conducting connection between the work port A and the tank port T is attained. The check valve function named is achieved in that the pressure at the service or work port A (=point 1 in FIG. 1) is lower than at the tank port T (=point 2 in FIG. 1), the check-valve piston 56 moving downwards in the viewing direction of FIG. 3, into its opening position there, whereby the assigned compression spring 58 is then tensioned. If the pressure-limiting valve piston 22 has not yet reached the upper travel stop 52, the former always follows the movement of the piston 56 until this upper travel stop 52 has been reached, as illustrated in FIG. 3. Overall, however, it should be noted that the two pistons 22, 56 separate from each other in axial direction, thereby enabling the fluid guide between the work port A and the tank port T. In this way, the feed function is achieved via the opening of the check-valve piston 56.
FIG. 4 shows the equally possible pressure-limiting function besides the check-valve function or feed function. If the pressure at the work port A is too high, the valve pilot control 12 opens and a stream of pilot-control oil flows, which builds up a pressure difference at the pilot control orifice 50 and, because of the different pressures upstream and downstream of the pressure-limiting valve piston 22, it arrives at a high piston position until it reaches its lower travel stop 54. In this case too, the check-valve piston 56 follows the movement of the pressure-limiting valve piston 22 upwards until the piston 56 reaches its upper travel stop 76 as shown in FIG. 3 after it had assumed its lower travel stop 78 there, as shown in FIG. 3, where it abuts against the upper side of the end part 60. In this respect as well, both pistons 22, 56 are again separated from one another in axial direction, but now with the option that, owing to the free travel of the piston 22 against the action of the compression spring 24, said piston acts as a pressure limiter for the fluid-conducting connection between the work port A and the tank port T.
As can be seen from FIGS. 2 to 4, the entire valve is formed like a cartridge, and if the seat edge 72 of the valve seat is damaged, the valve as a whole can be exchanged for a new valve, which is particularly cost-effective because long downtimes of the hydraulic circuit of the machine can be avoided. The inclined surface 68, which, with the seat edge 72, forms the valve seat between the two pistons 22, 56, can open a relatively large cylindrical cross-section, i.e. the desired flat flow characteristics in operation are possible in both directions, from A to T and from T to A. This results in low stresses on the components even in the case of rapid deflection movements of the two pistons 22, 56, which is extremely important for a good shock function of the valve. The valve design also permits damping of the pressure-limiting function by means of the pressure-limiting valve piston 22 via the damping orifice 30 in the orifice seat body 26. Since the two pistons 22, 56 are moved towards one another and away from one another on the front side, no valve cover is present in this respect and the valve can react extremely quickly to shock-like overloads. Thus, there are virtually no pressure peaks during the rapid opening of the pressure-limiting function when the pressure-limiting valve piston 22 is actuated against the action of its compression spring 24. The opening pressure of the pistons 22, 56 can be chosen very close to the load limit of these components, as in case of application the pressure can barely rise above the opening pressure. In this way, the construction machine or machine can be operated close to the load limit of its mechanical components.
Due to the design, it can also be operated “simply” as a proportional valve, in which case the mechanical adjustment (valve pilot control 12) has to be replaced by a magnetic actuator (actuating magnet), permitting the valve to be designed as a valve kit. Thus, the valve can be adapted to the individual maximum pressure of peripherals at any time. There is no equivalent in the prior art. FIGS. 5 and 6 show the valve solution according to the invention by way of longitudinal sectional representations; this time using electromechanical pilot control, one with a “pushing” (FIG. 5) and one with a “pulling” (FIG. 6) actuating magnet system 80. The respective actuation magnet systems 80 have a coil 82, which can be energized via a power connection 81. After the coil has been energized, the keeper 86, which is displaceably disposed in a pole tube housing 84, moves downwards, looking toward FIG. 5, counter to the action of a compression spring 88 or upwards, as viewed in the direction of FIG. 6, to effect the pilot control function of the valve function of the pressure-limiting valve according to the invention, which has already been described. Such magnet systems for controlling longitudinally displaceable valve systems are sufficiently known in the prior art, for that reason no additional details are given here.
Patent Application
20180024577
