WO2014033496A1

WO2014033496A1 - Hydraulic valve assembly with electronic control of flow rate

Info

Publication number: WO2014033496A1
Application number: PCT/IB2012/054318
Authority: WO
Inventors: Matteo GIBELLINI
Original assignee: Gibellini Matteo
Priority date: 2012-08-25
Filing date: 2012-08-25
Publication date: 2014-03-06

Abstract

In this invention, check valves (11), opportunely modified with position transducers(12), are used to sense the flow rate supplied to each consumer. An electronic control device (16) sets the inlet pressure and the opening of the spool in each working section (7) in order to regulate sensed flow as a function of electrical input signals. Unlike previously known load-sensing control systems, no pressure signals have to be managed to supply constant flow rate to one or more consumers regardless of their load pressure

Description

HYDRAULIC VALVE ASSEMBLY WITH ELECTRONIC CONTROL OF FLOW RATE

Technical Field

This invention relates to an hydraulic valve assembly with flow transducers and an electronic control device for powering one or more consumers regardless of their load pressure.

Background Art

The so-called load-sensing control valves assembly are known to supply constant flow rate to one or more consumer regardless their load pressure. To do this, they maintain a constant differential pressure across a variable orifice, said meter-in orifice, so that the flow rate to the consumer is determined by the cross sectional area of the orifice.

The valve assembly generally consists of one or more working sections. Each working section comprises a spool in which the meter-in orifice is machined, so that the position of the spool determines the opening of the orifice and thus the flow rate to the consumer. Each working section include means to determinate the load pressure which occurs at the highest loaded consumer in the valve assembly, said LS pressure signal. The LS pressure signal is transmitted to a variable displacement pump that adjust its delivery rate to feed the assembly valve with the requested flow rate. If the valve assembly is supplied by a fixed displacement pump a bleed valve is included in the valve assembly, generally in the inlet section, to drain the excess flow rate to tank.

When more than one consumers have to be powered in the same time, independently by their load, pressure compensators are inserted in each working section of the valve assembly. They are designed to increase the pressure drop on the less loaded sections, so as to maintain the differential pressure on the corresponding meter-in orifice equal to that of the most loaded section. The pressure compensators may be arranged upstream the meter-in orifice, said pre-compensated valve assembly, or downstream the meter-in orifice, said post-compensated valve assembly. Pre-compensated valve assemblies are generally more stable to the load pressure changes, compared to the post-compensated valve assemblies but they are affected by the inlet flow saturation.

The inlet flow saturation occurs when the sum of requested flow rate by the consumers is greater than the inlet flow rate. In this situation in pre-compensated valve assemblies, an increase of flow rate to the less loaded consumers leads to an equal decrease of the flow rate to the more loaded consumer. In post-compensated valve assemblies instead, in the event of inlet flow saturation, the flow rate is lowered equally to each consumers, regardless of their load pressure. This behavior is a problem if a consumer must be supplied in priority to other.

Furthermore, since the pressure compensators are generally located upstream of the consumers, they present a very poor behavior when the consumers supply pulling loads.

Transducers and electronic control apparatus have been added in order to simplify the valve assembly and obtain a more flexible and stable behaviour of the system.

In EP0275968 a pre-compensated valve assembly is shown wherein the pressure compensators are provided with position transducers. An electronic control device adjusts the delivery rate of the variable displacement pump in accordance with the positions of the pressure compensators removing the need of means to determinate the load pressure which occurs at the highest loaded consumer.

In EP0680565 pre-compensated valve assembly is shown wherein a position transducer is provided in the a bleed valve. An electronic control device adjusts the delivery rate of the variable displacement pump in accordance with the positions of the a bleed valve to improve the response of the pump control device.

In EP1664551 electrically operated meter-in orifices and pressure transducers are arranged with a variable displacement pump. An electronic control device adjusts the delivery rate of the variable displacement pump and the opening of the meter-in orifices in accordance with the pressure sensed by the transducers and the requested flow rate.

Technical Problem

All the load sensing valves with electronic control described above are based on the same principle of a load sensing mechanical valve, that is to maintain a constant differential pressure across a variable orifice. To do this pressure signals have to be managed by mechanical or electronic control devices.

Technical Solution

In this invention, check valves, opportunely modified with position transducers, are used to sense the flow rate supplied to each consumer. An electronic control device sets the inlet pressure and the opening of the spool in each working section in order to regulate sensed flow as a function of electrical input signals. Unlike previously known load-sensing control valves, no pressure signals have to be managed to supply constant flow rate to one or more consumers regardless of their load pressure.

Advantageous Effects

The benefits of this invention are the compactness due to less number of components and the absence of signal pressure lines. Moreover, another advantage is the stability and flexibility due to fully electronic control system which includes the management of inlet flow saturation and pulling loads, the possibility to define priority consumers, the capability to set a maximum pressure for each consumers and a reduced power consumption in stand-by also for valve assembly supplied by fixed displacement pumps.

Description of Drawings

Fig.1 shows a schematic drawing of the hydraulic circuit of the valve assembly supplied by a variable displacement pump

Fig.2 shows another schematic drawing of the hydraulic circuit of the valve assembly supplied by a fixed displacement pump

Fig.3a and Fig.3b shows two variations of the schematic drawing of the inlet section of the valve, to improve the dynamic response of the system, when the valve assembly is supplied by a variable displacement pump.

Fig.4 shows a simplified drawing of the working section of the valve assembly with the spool in idle position

Fig.5a and Fig.5b shows two possible positions of the check valve when the spool is operated.

Best Mode

Fig.1 shows a schematic drawing an hydraulic circuit related to this invention, composed by a variable displacement pump 2 with his electrical pressure control system 3, supplies the valve assembly 4 by taking the working fluid from the tank 5 to transmit to high pressure main line 6. The main line 6 brings the working fluid to the valve assembly 4 composed by one or more working section 7 that powering its own consumer, 8,9,10. Each working section is composed by a check valve 11 connected to a position transducer 12 and a four way spool 13. The spool is operated by means of electric or electro-hydraulic control, through an electronic device 16 as function of the user inputs 17 and the signals from the position transducers 12. The electronic device 16 also acts on the electrical pressure control 3 of the variable displacement pump 2 to set the pressure of the working fluid on the main line 6.

Fig.2 shows the valve assembly supplied by a fixed displacement pump 18, in this case an inlet section 19 is added to the valve assembly 4. The inlet section 19 comprises a proportional relief valve 20, that is generally of a type pilot-operated. The electronic device 16 acts on proportional relief valve 20 to set the pressure of the working fluid on the main line 6.

To improve the dynamic response of the system, the inlet section with the proportional relief valve can also be added when the valve assembly is supplied by a variable displacement pump.

Fig.3a shows the schematic of the inlet section 19 of the valve assembly 4 supplied by the variable displacement pump 2 with its electrical pressure control 3. The pilot-operated proportional relief valve 20, in the inlet section 19, is broken down into its subcomponents i.e. the main poppet 27, a restrictor 22, the repositioning spring 28 and the direct-acting proportional relief valve 21. A mechanical relief valve 23 can be added, for safety reason, to set the maximum pressure in case of failure of the direct-acting proportional relief valve 21. In this case, the electronic device sets the pressure on the proportional relief valve 21 little higher, respect to the electrical pressure control 3 of the variable displacement pump 2. This improves the dynamic response of the system, since the relief valve is much faster than the pressure control of the pump but the latter sets up, in static conditions, the desired pressure since the relief valve is closed due its higher setting.

Fig.3b shows an arrangement to use the inlet section with the proportional relief valve 21 combined with a variable displacement pump 2 with hydro-mechanical pressure control 24, since the latter is more common and cheaper respect of the electrical ones. An external hose 26, leads the pressure settled by the direct-acting proportional relief valve 21, to the hydro-mechanical pressure control 24 of the variable displacement pump 2. The force of the repositioning spring 28, is high enough to close of the main poppet 27 of the piloted-operated relief valve 20, in static conditions.

Fig.4 shows a simplified drawing of the working section 7 of the valve assembly 4. This is generally comprises the body of the section 30, a check valve with its poppet 31 and its spring 32, a position transducer 33 which senses the position of the poppet 31 and a four-way spool 34, which is normally operated by an electric or electro-hydraulic control, not shown. The inlet chamber 35 is connected to the high pressure main line 6, through a wide channel 36 so that on the opening side of the poppet 31 acts the inlet pressure. When the poppet 31 of the check valve opens, the inlet chamber 35 is connected to the intermediate chamber 37 by means of meter-in notches 46 machined on the poppet 31. The spring chamber 39 is connected to an intermediate chamber 37 through the restrictor 38 which has the function of a hydraulic damper for the poppet 31. When the spool 34 is operated, the intermediate chamber is connected to one consumer workport 42a or 42b, through the internal control notches 45a or 45b and the other consumer workport 42b or 42a is connected to the tank line 43a or 43b through the external control notches 44a or 44b.

In standard directional control valves, check valves are used to prevent backflow when the consumer load pressure is greater than the inlet pressure. When the inlet pressure reaches the value of the load pressure the valve will open completely with minimum pressure drop. In this invention, check valve is modified, compared to the normal ones, in order to correlate the position of the check valve with the flow through it.

Fig.5a and Fig.5b show two possible positions of the check valve when the spool, for example, is operate to the right. In this case the intermediate chamber 37, and then the spring chamber 39 through the restrictor 38, is connected to the consumer workport 42b, said feeding workport, through the internal control notches 45b while the consumer workport 42a, said drain workport, is connected to the tank line 43a through the external control notches 44a.

When the pressure in the consumer workport 42b, is greater than the inlet pressure, as shown in Fig. 5.a, the poppet 31 closes the passage between the inlet chamber 35 and the intermediate chamber 37 with a suitable overlap 41 that prevent backflow.

In Fig.5b, instead, the inlet pressure is greater than the consumer pressure, in this case the poppet opens and a flow rate is established from the inlet chamber 35 to the intermediate chamber 37. The flow rate creates a pressure drop due to the crossing of the meter-in notches 46 machined on the poppet 31. The flow rate Q is a function of pressure drop dp through the relation Q = K ·A(x) ·sqrt(dp) where K is a constant, A(x) is the minimum cross-section area of the meter-in notches 46 which is a function of the position of the poppet x , and sqrt(dp) is the square root of the pressure drop created by the flow.

In static conditions the pressure drop is reported to the sides of the poppet 31 through the restrictor 38, and the pressure forces are balanced by the force of the spring 32 which depends on its compression i.e. by the position of the poppet 31. If we assume that the force of the spring 32 is zero at the position where the poppet 31 begins to open, the balance of forces brings to the relationship dp ·Ap = Ks ·x , where, Ap is the side area of the poppet and Ks is the spring constant.

With simple algebraic passages, in static conditions we have Q = Kq ·A (x) · sqrt (x) , with Kq a generic constant, thus a relationship is established between the flow rate Q through the poppet 31 and the position x of the same. The expression says that the flow rate through the poppet of the check valve is proportional to the product between the minimum cross-section area of the meter-in notches 46, and the square root of the position of the poppet 31.

To have a linear relationship between the flow rate Q and the position of the check valve x is necessary to realize the notches 46 of the poppet 31 so that they have a minimum cross section area proportional to the square root of the position x . In this case the relationship is simplified as Q = Kg · x where Kg is a global constant.

Through the measure of the position of the poppet 31 of the check valve made by the transducer 12, the electronic device 16 can calculate the instantaneous flow rate to the consumer. The actual value of the flow rate can differ from the calculated ones, due to dimensional variations of the poppet 31 and the spring 32, in order to avoid this, a calibration can be made and stored in the nonvolatile memory of the electronic device 16.

Since the electronic device knows the actual flow rate in each section of the valve assembly, a simply control strategy can be arranged to control such value in accordance with the user input signals, changing only the inlet pressure and the position of the spools.

In idle state the electronic control device maintains the spool in each working section in central position and minimizes the inlet pressure by acting on the controls of the variable displacement pump and/or on the relief valve in the inlet section. This reduces the power consumption at the minimum also for valve assemblies supplied by fixed displacement pumps.

Suppose having to set a given flow rate to a single consumer with a resistive load type that creates counter pressure on the feeding workport. The electronic device operates entirely the spool in the corresponding working section, and gradually increases the inlet pressure.

As long as the inlet pressure is lower than the consumer load pressure, the check valve is closed to prevent backflow. When the inlet pressure reaches the load pressure, the valve begins to open and the electronic device can estimate that value. Now, the electronic device, slightly increases the inlet pressure till the position of the check valve, i.e. the flow rate to the consumer, reaches the requested value.

A variation of the consumer load pressure results in a variation of the flow rate to it and consequently the opening of the check valve. To maintain a constant flow rate to the consumer the electronic control device only needs to increase the inlet pressure to a reduction in the opening of the check valve and vice versa.

Suppose now having to set a given flow rate to a second consumer with a resistive load type that creates a different counter pressure, on the second feeding workport, respect to first one. The electronic device gradually operates the spool in the second working section until the control notches of its check valve begin to open and therefore the load pressure of the second consumer reaches the intermediate chamber of its working section.

If the second consumer has a load pressure lower then the inlet pressure, the check valve opens and a flow is established from the main line and the consumer. The amount of flow on the second consumer depends both on the pressure difference between the input and the consumer, and both on the opening of the control notches machined on the spool. The control notches machined on the spool are used to create a pressure drop that balance the pressure difference between the inlet and the consumer. More the spool is opened and lower is the pressure drop created by its control notches.

Now, the electronic device, slightly increases the spool opening till the position of the check valve, the flow rate to the consumer, reaches the requested value. To maintain a constant flow rate to the lower pressure consumers the electronic control device only needs to increase the opening of their spools to a reduction in the opening of their check valves and vice versa.

In this situation, the spool has the same function of the pressure compensators present in the previously known load-sensing control valves, but is driven only by the electronic device without the management of pressure signals. The internal control notches of the spool create a pressure drop that don't affect the consumer load pressure, on the contrary the external control notches create a pressure drop that increase the consumer load pressure.

Suitable control notches, of different size and shape, can be machined on the spool to suit different types of consumer load, for example a pulling load. The pulling loads create underpressure on the feeding workports to suck up the required flow. The flow rate to the pulling load can be controlled trough the increase of the load pressure in the drain workports by means of suitable external control notches.

If the second consumer has a load pressure higher than the inlet pressure, the check valve remains closed also when its spool is totally opened. In this case the electronic device gradually increases the inlet pressure and consequently decreases the opening of the first spool to keep constant the flow rate to first consumer. When the inlet pressure reach the value of the load pressure of the second consumer its check valve begins to open and its flow rate is regulated by the inlet pressure.

As described above, a simple control strategy can be implemented in the electronic device, wherein the more loaded consumer is recognized by the behavior of the check valves and not by means of pressure signals. The flow rate to the more loaded consumer is controlled by adjusting the inlet pressure, while the flow rate to the other consumers is controlled by the opening of their spools. To better control the more loaded consumer especially for low flow rates, its spool can be partially closed to create a pressure drop which helps to achieve the balance of the system.

The condition of inlet flow saturation can be recognized and managed in a simple manner by the electronic device. If the maximum flow rate of the supply pump is known, the condition of inlet flow saturation is easily detected by the electronic device from the sum of flow rates required by the inputs. If the maximum flow rate of the supply pump is not known, the condition of inlet flow saturation can be detected by the electronic device by the fact that, in this situation, an increase of flow rate to one of the less loaded consumers, results in a decrease of the same amount of flow rate to the more loaded consumer. In condition of inlet flow saturation, the electronic device can simply lower the requested flow rate to all consumers or supply a consumer in priority to others.

Since the electronic device sets the inlet pressure is possible to set a maximum inlet pressure for each consumers.

In the system described above, the electronic device sets the inlet pressure, but does not know its actual value. To prevent damage, a mechanical relief valve can be added to set the maximum admissible inlet pressure.

The system can operate only by means of the electronic device, in fact, in the idle condition, a movement of a spool will not operate the consumer because the inlet pressure is almost zero. However, emergency manual controls can be added on each spool and on the proportional relief valve in order to operate the consumers in case of power failure.

Claims

A valve assembly consisting of one or more working sections comprising at least a 4-way spool, a position transducer and a check valve consisting of a spring and a poppet on which are machined notches, characterized in that the pressure drop due the crossing of the flow through the notches is reported to the sides of the poppet and the pressure force thus created is balanced by the spring force generated by the movement of the poppet which is measured by the position transducer.
A valve assembly in accordance with claim one, characterized in that the notches on the poppet of the check valve have a minimum cross section area proportional to the square root of theirs position.
A valve assembly in accordance with claim one, characterized in that at least one electronic device operates the spool and sets the inlet pressure by suitable means, in accordance with the user signals and the position transducers.