DK149392B - DEVICE FOR AFFECTING THE WORKING POWER OF A SERVOMOTOR - Google Patents

Description

149392

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a device for influencing the workload of a servo motor having two motor connections which can optionally be connected via a switching means (control valve) to a supply line connected to a pressure medium source and to a return, whereby a return flow from the motor is provided. adjustable first throttle means and, above this, a pressure-dependent controlled reducing valve operating, whose adjusting means in one direction is loaded by a pilot pressure prevailing in the first pressure chamber, between the reduction valve and first throttle means and in the other direction by a set-point spring and a in another pressure chamber prevailing pressure.

In a known device of this kind (DE-AS 19 22 073), the throttle member and the pre-engaged reduction valve are arranged 15 in one of the motor connection lines and connected in parallel by a check valve opening in the supply line. In addition to the set value spring, the setting valve of the reducing valve is influenced by the pressure and the front and rear of the choke. The reduction valve keeps the pressure drop across the throttle constant so that the flow rate and in the final power the speed at which the servomotor moves are kept constant. The speed of movement is also kept constant when an external force is exerted on the servomotor.

When such throttle-related regulation is effective in the reflux, a pressure drop occurs, due to which the pressure level of the servomotor is high. The servomotor is therefore constantly loaded with high pressure during operation; the leakage losses are also similarly large.

It is further known (DE-AS 16 50 312) to provide the adjustable choke means with a control valve which keeps the pressure drop constant at this in the inlet line.

However, an external force attacked by the servomotor results in changes in the speed of movement and, if applicable, citation phenomena.

2 149392

Next, it is known (DE-AS 12 06 610) for a quantity divider which can be used in both flow directions to place a reduction valve both front and rear of a throttle member in each branch of the quantity divider. In this way, the 5 after-reduction reduction valve is rendered inoperative, the set-value spring being supported by a higher pressure. However, this coupling operates in dependence on the flow direction and not on external load on the servomotor.

The object of the invention is to combine the advantages of a throttle arrangement with a reducing valve with the advantages of a throttle arranged in the supply line.

This task is solved according to the invention in that an adjustable, second coupling means coupled to the first choke means is arranged in the supply line and that the pressure in the second pressure chamber is taken out between the second choke and servo motor.

By this coupling the reducing valve is brought into its open position in normal operation, so that the pressure drop occurring thereon becomes very small. The setpoint spring is supported by a pressure which is relatively large and usually corresponds to the working pressure of the servo motor on the inlet side.

If in the working direction, however, an external load is acting on the servomotor and the pressure in the inlet line thereby decreases, the reducing valve enters a throttle position which prevents a too fast flow of the backflow flow. This is especially true if there are so dangerously low pressures on the supply side that a cavitation could be induced.

30 Therefore, automatic switching occurs. In normal operation, that is, at the usual high pressures, the pressure in the servomotor is not increased by a pressure drop at the reduction valve. On the other hand, in the event of an adverse external impact, this reduction valve immediately enters the required throttle position.

With particular advantage, a control valve is connected in series with the second choke which keeps the pressure drop at the second choke constant. In this way, the workload of the servomotor is also kept constant when the back-flow reducing valve is fully equipped during normal operation.

In a preferred embodiment, there are provided that switchable coupling paths are provided which in each working position supply the second pressure chamber with the pressure between the second throttle member and the servomotor. In this case, the reduction valve can also be rendered inoperative in another way, namely that when it is in the inlet pipe it remains open at all times. For this purpose, the second pressure chamber of the reducing valve, when in the inlet line, is affected by the same pressure as the first pressure chamber. The reduction valve then operates under the influence of the setpoint spring in the opening position.

20 If a negative load can act in the two directions of movement of the motor, eg by a steering wheel, a reduction valve may also be provided in each of the motor connection lines.

Both throttle bodies always occupy approximately the same opening cross-section. This provides unequivocal conditions and also allows for the replacement of the first and second throttle bodies by reversal operation.

It is also convenient to size the reduction valve so that the pressure drop affected by this first choke means is at most equal to the pressure drop determined by the control valve 30 at the second choke means. This design ensures that the pressure between the first throttle body and the servomotor never falls below the tank pressure, so that no cavitation phenomena can occur.

This prevents more pressure fluid from flowing out of the servomotor at negative load than flows to it. The same advantage can also be obtained at different opening cross sections of the two choke members when the pressure drops are similarly converted.

In particular, the first and second chokes may be joined to a four-way valve with throttling intermediate positions. At such a valve, the parallel cross sections of the opening cross sections are secured in a simple manner.

Further, the four-way valve may serve as a switching means and be provided with the switchable switching paths.

The invention is further described below with reference to the exemplary embodiments shown in the drawing, which are shown in FIG. 1 is a circuit for a dual-acting servo motor in which the negative load can only affect one direction; and FIG. 2 shows a modified part of FIG. 1 with a dual acting 20 servomotor, at which the negative load can have influence in both directions.

In the embodiment of FIG. 1, there is shown a servomotor 32 having a cylinder 33 and a piston 34 which can be loaded by an external load L. As a result, there are also two motor closures 35 and 36, both of which over each a safety valve 37 and 38 is connected to a tank conduit 23. For refilling, the motor connection line 36 is connected to a tank conduit 39 via a check valve 23. The motor connection 35 is connected to a reduction valve 9 in connection 30 with a connection 40, the motor connection 36 is directly connected to a connection 41. of a four-way control valve 42 which is adjustable by a handle 43.

For each direction of operation, there is a first choke means 10 and 10 'for the backflow and a second choke means 44 and 5 44' for the inflow. Both throttle bodies can be displaced together. For the working position b (setting path x) and the working position c (setting path y), they have the same opening cross-section in pairs. In addition, there is a neutral position a. As a pressurized source, a pump 6 serves with the pump pressure Pp, which 10 is connected to a safety valve 29. This opens when a predetermined pump pressure is exceeded. The pump delivers pressure fluid from a tank 11 over an inlet line 7 to the four-way control valve 42. In the inlet line there is arranged a control valve 21, which on one side is affected by the pressure per 15 in the inlet line 7 and on the other side a set point value. spring 28 and the pressure in a conduit 24. The reduction valve 9 in one motor connection 35 has a first pressure chamber 15 which is connected to a point 16 between the reduction valve 9 and the throttle means 10 and 10 'containing control valve 42, 20 as well as a second pressure chamber 17 , which is connected to conduit 24 and whose pressure acts in the same direction as a set-value spring 18. Pressure chamber 17 and conduit 24 are connected in neutral position a over coupling paths 25 in the bypass valve 42 to the tank pressure on leading conduits 23 and 25. is connected in each of the two working positions b and c over a coupling path 26 to a pressure pd leading point 27 behind the throttle 44 and 44 '.

This results in the following operating modes When the control valve 42 is displaced a setting path x to the working position b, pressure fluid flows from the pump 6 over the control valve 21, the second throttle member 44 'and the reduction valve 9 on the left side of the servomotor 32. At the same time, pressure means flows over the first throttle member. 10 'to the tank. Over coupling paths 26, pressure Pd is applied to pressure chamber 17 and conduit 24. As a result, the reduction valve 9 is completely opened by the set value spring 18. The control valve 21 keeps the pressure drop at the control valve 42 constant. The flow rate is therefore determined by the setting path x and the corresponding choke opening in the choke 44 '.

If the control valve 42 is displaced an adjustment path y to the working position c, the flowing pressure fluid flows over the throttle body 44 directly to the right side of the servomotor 10 32. At the same time, the pressure chamber 17 in the reduction valve 9 is again supplied with the pressure p ^, while the pressure ps at the point 16 is controlled by the reducing valve 9. The refluxing fluid flows through the now regulated reduction valve 9 and then the adjustable choke means 10. If 15 does not have a negative load L, the pressure p 2 in the pressure chamber 17 is substantially greater than the pressure ps in the pressure chamber 15, so that the reduction valve 9 is completely open and control of the workload is only effected by the throttle means 44. However, if the negative load h becomes larger, the pressure p <3 decreases until the pressure ps finally becomes so high that the reduction valve 9 is moved in the closing direction. This reduces the flow rate, so that the supply line control can be maintained. However, if the pressure in the motor connection line 36 due to the negative load L 25 becomes so low that a control is no longer possible on the inlet side, the pressure in the pressure chamber 17 is also so low that the pressure ps from the reduction valve 9 can be kept constant and the control of the flow rate is caused by the throttle member 10. The mode of operation is more precisely shown in the calculation example below. It is assumed that the pressure drop across the throttle means 44 and 44 * can be kept constant at 4 bar by means of the control valve 21, that the load corresponds to a pressure of 200 bar, that the cross section of the cylinder is twice as large as left and right. the spring 18 exerts a pressure of 3 bar and the throttle members 10, 44 and 10 ', 44' are paired in the same opening. Furthermore, the adjustment must be made so that the throttle means 44 'is flowed through 5 liters per minute. unit of time.

a) If the control valve 42 is moved to the working position 5 b, the pressure drop at the throttle 10 'can be calculated to 1 bar. If the tank pressure equals 0 bar, the ps pressure of 201 bar and the pump pressure of 204 bar appear.

b) If the control valve 42 is moved to the working position c, the pressure drop at the throttle 10 can be calculated to 10 16 bar. Since this pressure is equal to the pressure p <3 in the supply plus a constant pressure originating from the spring 18, this pressure p <fj 13 bar and thus the pump pressure pp 17 bar.

In the embodiment of FIG. 2 only the portion of the control valve 42 'located on the other side of the control valve is shown. This time, both connecting lines 35 and 36 are connected to the associated connections 40 and 41 over each of a reduction valve 9 and 9 '. Both are shunted by a check valve 45, 45 'towards the motor 32. Pressure chamber 20 communicates with point 16, pressure chamber 15 'with point 16'. The pressure chamber 17 communicates with a point 46 at the connection 41 and the connection line 36, respectively, and the pressure chamber 17 'communicates with a point 46' at the connection line 35 and the connection 40, respectively.

If the connection 41 carries inflow pressure, the servomotor 32 is supplied over the check valve 45 '. The reducing valve 9 enters the opening position so that the pressure fluid can flow undisturbed. Only if the load L is too large and the pressure in the connection 41 decreases does the reduction valve 9 act in a manner that is described in the manner described. The same also applies to a change of the motor 32 in the reverse direction at the corresponding reverse acting external load.

Instead of the check valves 45, 45 ', reduction valves 9, 9' which are controlled in the same way as the reduction valve 9 in FIG. 1 over the control valve 42.

Claims (3)

149392 Device for influencing the workload of a servomotor (32) having two motor connections (35, 36) which can be optionally connected via a switching means (control valve) respectively to a supply line (7) connected to a pressure source (6) and a reflux, whereby for the return flow from the motor there is an adjustable first throttle member (10, 10 ') and above this a pressure-dependent controlled reducing valve (9, 9') operable, the adjusting means of which in one direction is loaded by one in a first pressure chamber (15, 15 ') here, between the reduction valve and the first throttle body, the pilot pressure taken out and in the other direction of a burner di-spring (18, 18') and one in a second pressure chamber (17, 17, prevailing pressure, characterized by 15 being arranged in the supply line (7) an adjustable second throttle member (10, 10 ') coupled to the second throttle member (44, 44') and the pressure (p <g) in the second pressure chamber (17) being taken out between second throttle body and servomotor (32). Device according to claim 1, characterized by a control valve (21) connected in series with the second choke member (44) which keeps the pressure drop at the second choke constant. Device according to claim 1 or 2, wherein the reduction valve (9) is arranged in a motor connection line (35), characterized in that switchable coupling paths (26) are arranged as in each working position (b, c). supplies the second pressure chamber (17) with the pressure (pd) between the second throttle member (44, 44 ') and the servomotor (32).