ITPR20110039A1 - HYDRAULIC DISTRIBUTOR WITH PARALLEL CONNECTION TO THE CURSOR FLOW RATE ADJUSTMENT AND LOCAL COMPENSATOR - Google Patents

Description

DESCRIPTION

TITLE: HYDRAULIC DISTRIBUTOR WITH PARALLEL CONNECTION TO THE SPOOL FLOW REGULATION NICHES AND TO THE LOCAL COMPENSATOR

FIELD OF APPLICATION OF THE INVENTION

For the needs of energy saving and containment of emissions, for several years some sectors of earthmoving machinery such as that of compact excavators have seen a progressive evolution of the hydraulic system such that alongside systems with pumps or fixed displacement pumps and free circulation or free crossing distributor systems commonly known as load sensing have spread.

In various load sensing systems, the pump has a variable displacement and only delivers the flow rate actually required by the actuators. The control of the pump displacement is done through the feedback of the pressure signal of the greater of the loads called the load sensing signal, or LS, from the distributor to the pump. The hydraulic distributor is also of the load sensing type.

The pump adjusts its displacement by means of an LS signal regulator in such a way as to keep the pressure difference between the delivery and the Load Sensing or LS signal constant; from now on this pressure difference will be called â € œdelta P of LSâ €. In a load sensing distributor, the regulation of the flow rate sent to an actuator is carried out on the basis of the position of the movable slider element by exploiting the fact that the pressure drop across the flow regulation niches is kept constant regardless of the load.

In the field of compact excavators, load sensing distributors are generally adopted which regulate the flow rate independently of the load, able to proportionally reduce the flow rates of the active sections in the event that the flow rate required by the actuators is greater than the maximum delivered by the pump.

In each working section there is a local pressure compensator which ensures that the pressure difference at the ends of the flow regulation niches is equal to the delta p of LS in each working section during the operation of two or more work sections even when the LS delta p falls below the value set by the pump's LS regulator.

To prevent the motor from switching off, on the variable displacement pump there is a device for limiting the power absorbed by the pump itself. It has the following operating principle: as the delivery pressure increases, the maximum flow rate delivered by the pump is reduced by approximating a constant power hyperbolic curve in the flow-pressure plane. When it intervenes, the power regulator prevails over the LS regulator which keeps the delta p of LS constant, with the result that the delta p of LS is reduced with respect to the value at which the LS regulator is set.

STATE OF THE ART

Among the various architectures of load sensing distributors, the patent EP1628018 (B1) of the same applicant presents one in which the local compensator is located downstream of the slider flow rate adjustment niches and in the same lapped hole two components slide, a local compensator with selector and a piston with pusher.

In the section with greater load, the group consisting of a local compensator with selector and piston with pusher constitutes a non-return valve; the selector generates the load sensing signal LS: the selector, kept open by the pusher, connects the signal downstream of the slider capacity adjustment niches with the LS signal channel. The LS signal arrives at the LS regulator of the pump and also acts between the local compensator with selector and the piston with pusher of the other sections.

In the active sections with lower load, the piston with pusher abuts against the plug and compresses the spring, while the local compensator throttles the passage of the flow directed to use, making sure that the pressure downstream of the flow regulation niches is equal to the LS pressure in channel 4. The selector is closed.

A compact excavator with

- load sensing hydraulic system with a load sensing distributor such as the one described in patent EP1628018

- a variable displacement pump with LS regulator and a power regulator,

in certain working conditions it exhibits unpleasant behaviors for the operator.

Let us assume the operating condition in which the two translation motors are powered by respective sections of the distributor and that, while the machine is moving, a third actuator reaches the end of its stroke: at this point the machine slows down conspicuously; that is, what occurs is that the section that feeds the actuator at the end of the stroke causes the pressure limiting valve to intervene on the load sensing signal LS and consequently the power limiter reduces the maximum flow rate delivered by the pump; the travel speed of the excavator can be abruptly halved.

Patent EP2184495 (A1) of the same applicant presents a method for limiting the maximum power required by the hydraulic system and various ways to achieve it. The method consists in introducing a connection between the channel upstream and the channel downstream of the local compensator in the translation sections. The connection must be suitably sized so that when a third actuator reaches the end of its stroke, the flow rate delivered by the pump (which goes to the two translation motors and which passes through the two connections) does not cause the pressure to rise above the intervention limit. of the power limiter. In this way the translation speed of the machine is not reduced.

The different ways of making the connection in the mentioned patent are:

- on the spool, creating a niche suitable for connecting the channel upstream of the local compensator with the one downstream when the spool is at the end of its stroke;

- in the element, making a connection hole between the channel upstream of the local compensator and the one downstream;

- on the local compensator, preventing it from closing.

PROBLEM TO SOLVE

Given that the architecture of the load sensing distributor of the patent EP1628018 (B1) provides that the local compensator of the element performs the function of non-return valve, introducing the connection as presented in the patent EP2184495 (A1) is missing the non-return valve function in the section where the connection is present.

This is not a problem in the towing sections, as there is a balancing valve on the travel motors which also acts as a non-return valve.

However, there are other work sections in which the previously described unpleasant behavior occurs for the operator, for example when the turret is rotating and at the same time a second actuator reaches the end of its stroke: the turret slows down conspicuously. Similarly, an unacceptable reduction in cycle time can occur when the first arm is rising, or when the second arm is opening or closing and at the same time a second actuator reaches the end of its stroke.

In the spools of these sections it would be possible to adopt the connection as presented in the patent EP2184495 (A1) by introducing non-return valves, inside the spool between the U-bolt and use in delivery.

However, this solution has the disadvantage of introducing an additional pressure drop always present in the power line and has the drawback of not allowing back pressure along the entire sensitivity curve of the spool due to the coverings between spool and distributor present in the distributor of the same assignee.

To overcome these problems, the following finding is presented.

PURPOSE AND ADVANTAGES OF THE FOUND

The invention consists of a hydraulic distributor having an inlet channel coming from the pump, an outlet channel connected to the tank, several working sections suitable for supplying actuators through respective uses by means of internal cursors capable of generating the deviation of the flows in the channels inside the distributor; local pressure compensators able to control the pressure drop at the ends of the spool flow regulation niches so as to make the flow delivered by the spool independent of the load, in which there is a connection between the channel that receives oil from the pump and the channel that sends oil to the actuator, closed in the central position of the spool and which opens according to the position of the spool itself, this connection being parallel with respect to the flow path through the slider flow rate adjustment niches and the compensator local.

The aforementioned additional connection requires the oil to pass through an obturator, equipped with a spring set so that the opening pressure is higher than the setting of the pump's LS regulator.

The link is operational in one of the two cursor positions or in both depending on whether it is necessary to limit the speed reduction of one or both uses of the section.

The present invention performs the same functions of the connection presented in the patent EP2184495 (A1) without presenting the problems described above, in fact there is a non-return valve suitably calibrated along the connection and this non-return valve is normally not crossed by the flow of power.

Said objects and advantages are all achieved by the hydraulic distributor with parallel connection to the flow rate adjustment niches and to the local compensator object of the present invention, which is characterized by the provisions of the appended claims.

BRIEF DESCRIPTION OF THE FIGURES

This and other characteristics will become more evident from the following description of some embodiments illustrated, purely by way of non-limiting example in the accompanying drawing tables.

- Figure 1 illustrates a hydraulic diagram of a two-section distributor, in which in one section there is the connection between the channel that receives oil from the pump and the channel that sends oil to the actuator, according to the present invention

- figure 2 illustrates an example of preferential embodiment of the connection object of the present invention inside the slider according to the scheme of fig. 1

DESCRIPTION OF THE FOUND

The following example is described with the sole purpose of clarifying the content of the invention, without thereby limiting the protection requested, whose scope of protection extends to the content of the claims.

With particular reference to Figure 1, 2 indicates as a whole a load sensing distributor 2 which comprises inside a channel 10 in which pressurized oil flows arriving from a variable displacement pump 1; through said channel 10 the pressurized oil passes through specific internal channels and can reach at least two sections A and B, each of which controls respective actuators 3A, 3B, through channels or uses 13A, 14A (in section A) and 13B , 14B (in section B); the uses are in turn connected to the collection tank through a channel (15).

In addition, the distributor 2 further comprises a pressure limiting valve 5, placed on a channel 4 of the load sensing or LS signal of the largest of the loads and a flow rate regulating valve 6 for unloading said channel 4 of the LS signal.

Each work section A and B is defined by an element 50A, 50B inside which the sliders, the local compensators and the other components necessary to realize the invention are housed.

With specific reference to element 50A of working section A, the oil coming from pump 1 (via channel 10) encounters a spool 7A, crosses the area of the flow regulation niches 27A (23A) when the spool 7A is driven by V1A (V2A), passes a local compensator 8A, goes to use 13A (14A), returns from use 14A (13A) and unloads through channel 15.

On channels 13A and 14A there are secondary shockproof and anti-cavitation valves 25A and 26A.

A piston 9A with pusher 28A slides in the same lapped hole of the local compensator 8A. The local compensator 8A has a selector 18A inside it for selecting the LS signal. The local compensator is normally closed; on the one hand it is subjected to the upstream pressure reigning in 11A which acts in opening through the channel 16A, on the other by the signal LS 4 and to the contact force of the piston 9A which act in closing. The piston 9A is subjected on the one hand to the pressure of channel 4 of the signal LS and to the contact force of the local compensator 8A, on the other to the downstream pressure reigning in 12A through channel 24A and to the force of a spring 19A of negligible strength.

When section A is operated individually or when it is operated at the same time as other sections and has the load at the greatest use (section A is dominant), the local compensator 8A is open and against the piston 9A since the pressure in 16A is higher than the pressure in 24A; the set of local compensator 8A and piston 9A works as a non-return valve. The LS signal is taken from the channel 11A through the channel 17A and is sent to the channel 4 through the selector 18A kept open by the pusher 28A of the piston 9A. In this case, the pressure drop across the flow control niches 27A (23A) of the spool 7A between 10 and 11A is controlled by the pump and is equal to the `` delta p of LS '', i.e. the difference between the pressure in the channel 10 and the pressure in channel 4.

When section A is operated at the same time as other sections and has the load on use that is not the greatest, the local compensator 8A throttles the passage of the direct flow to the actuator 3A causing the pressure in channel 16A is equal to the pressure LS of channel 4; the piston 9A is pushed all the way towards the spring side 19A and is not in contact with the local compensator 8A. In this case the pressure drop across the flow rate adjustment niches 27A (23A) of the spool 7A between 10 and 11A is controlled by the local compensator 8A and also in this case it is equal to the â € œdelta p of LSâ €.

As can be concluded from the operating modes described above, a distributor having sections such as section A delivers flows independent of the load and reduces them proportionally in the event that the flow rate requested by the actuators is higher than the maximum flow delivered by the pump, because the pressure drop at the ends of the flow regulation niches is equal to the â € œdelta p of LSâ € on all sections.

Referring now to the specific case of element 50B of working section B, as in section A the oil coming from pump 1 meets the cursor 7B, it crosses the area of the niches) for regulating the flow rate 27B (23B) when the spool 7B is driven by V1B (V2B), passes the local compensator 8B, goes to use 13B (14B), returns from use 14B (13B) and unloads through channel 15.

On channels 13B and 14B there are secondary anti-shock and anti-cavitation valves 25b and 26b.

In section B the group consisting of the local compensator 8B with selector 8B, piston 9B with pusher 28B and spring 19B is similar to that of section A, therefore please refer to its description.

When the spool 7B is piloted by V1B, the connection 20 opens between the channel 10 coming from the pump upstream of the flow regulation niches 27B and the channel 12B downstream of the local compensator 8B and therefore to the use 13B; this connection is parallel to the flow path through the flow control niches 27B and the local compensator 8B. Along connection 20 there is a shutter 21 held in the closed position by a spring 22 calibrated so that the opening pressure of the shutter 21 is higher than the â € œdelta p of LSâ € imposed by the LS regulator of the pump.

When the cursor 7B is driven by V2B, the connection 20 remains closed, as when the cursor is in the central position, therefore in this case the operation of the section is identical to that of section A previously illustrated.

Consider the case in which the cursor 7B is operated individually by the pilot V1B. The pressure drop at the ends of the flow control niches 27B, equal to the pressure in 10 minus the pressure in 11B, being the latter equal to the pressure LS in channel 4, is equal to the â € œdelta p of LSâ € imposed by pump 1. Since section B is the only one to be active, the group consisting of local compensator 8B plus piston 9B works as a non-return valve, therefore the pressure difference between 11B and 12B is for example 7-8 bar at maximum flow rate for use; supposing that the LS regulator of the pump is set so that the delta p of LS is equal to 20 bar, the pressure difference between 10 and 12B is at most 28 bar. By calibrating the shutter spring 21 so that its opening pressure is 30 bar, the shutter 21 remains closed. In this case, therefore, the oil passes all through the flow regulation niches 27B and the local compensator 8B and does not pass through the connection 20, although it is available. Section B behaves exactly like section A.

If both sliders 7A and 7B are operated, for example by pilots V1A and V1B, and the load on use 13B is greater than the load on use 13A (dominant section B), what has just been described applies, in fact the pressure in 11B is equal to the LS pressure in channel 4 and therefore the pressure difference between 10 and 12B is at most 28 bar, not sufficient to open the obturator 21.

If both sliders 7A and 7B are operated for example by pilots V1A and V1B and the load on use 13B is not the greatest, i.e. section B is dependent, when the pressure difference between 10 and 12B exceeds 30 bar the shutter 21 opens. In this case, the oil, in addition to passing through the flow regulation niches 27B and the local compensator 8B or the controlled flow channel, crosses the path 20 from delivery 10 to use 13B. This path 20 is equivalent to a calibrated passage, therefore the flow rate that passes through it depends on the pressure difference between 10 and 12B. The flow rate that arrives at use 13B is given by the sum of that which comes from the regulation niches of the flow rate 27B and that which comes from connection 20.

Suppose that both sliders 7A and 7B are operated for example by pilots V1A and V1B and the actuator 3A reaches the end of its stroke. If connection 20 were not present, this working condition would result in the opening of the pressure limiting valve 5 on signal LS, channel 4, and reaching the maximum system pressure, with the consequent intervention of the pump torque limiter. 1 and, if the flow rate required by the actuators is higher than the maximum flow rate delivered by the pump, with the consequent reduction in the speed of the actuator 3B. The presence of connection 20 causes the flow rate passing through connection 20 to increase as the pressure difference between 10 and 12B increases. Since the oil from channel 10 to use 13A is a static column, the pressure signal in 10 passes through the flow regulation niches 27A, channel 11A, is taken from channel 17A and sent to the LS signal of channel 4; consequently the local compensator 8B is kept closed by the pressure LS in channel 4 equal to the pressure in channel 10 and therefore the only possible path for the oil in section B to use 13B is through passage 20.

The connection 20 causes the oil in the channel 10 to be at a pressure lower than that set by the limiter 5 which therefore remains closed. In this way the pump delivers a flow rate greater than that which it would deliver at the set pressure of the pressure limiter 5 and consequently the reduction in speed of the actuator 3B is contained.

Fig. 2 shows the preferential way of carrying out the present invention in accordance with the diagram of Fig. 1. In the cross-section of the element 50B of the working section B the lapped hole 48 within which the slider 7B slides, shown in a central position, is visible. The cursor 7B can be operated to the right by the pilot V1B to make the connection 10> 11B by opening the flow adjustment niches 27B, 12B> 13B by opening the cover 34, 14B> 15 by opening the niche 36; It can also be operated to the left from the V2B pilot to make the connection 10> 11B by opening the flow adjustment niches 23B, 12B> 14B by opening the cover 35, 13B> 15 by opening the niche 36.

In detail, the connection 20 is visible consisting of the radial passages 40 which carry oil to the obturator 21, the radial holes 42 which discharge oil from the obturator 21, the axial hole 41 which connects the radial holes 40 and 42 together. The radial holes 40 are always connected to the channel 10, while the radial holes 42 are covered in a central position and open to the channel 12B and therefore to the relative use 13B when the slider 7B is piloted from the side V1B.

Between the axial hole 41 and the radial holes 42 there is the sealing seat 44 of the obturator 21. The obturator 21 is housed in the hole 43 together with the spring 22 from which it is kept in the closed position; in opening the obturator 21 abuts against the pin 32. On the obturator 21 the pressure in 41 acts in opening and therefore in 10, in closing the pressure in 42 equal to that in 12B, when the spool is piloted from V1B, plus spring force 22.

Claims (4)

CLAIMS 1. A load sensing distributor (2), of the type comprising a. a channel (10) in which pressurized oil flows from a variable displacement pump (1) with LS delta p regulator; b. a drainage channel or outlet (15) for the pressurized oil, c. one channel (4) of the load sensing signal or LS of the largest of the loads, d. at least two sections (A, B) with a plurality of channels or uses (13A, 14A, 13B, 14B) for connection to respective actuators (3A, 3B); each section being defined by elements (50A, 50B) inside which are housed corresponding cursors (7A, 7B) comprising a series of flow regulation niches (23A, 27A; 23B, 27B) and local pressure compensators ( 8A; 8B) capable of controlling the pressure drop at the ends of the flow rate adjustment niches (23A, 27A; 23B, 27B) of the spool making the flow rate delivered by the spool independent of the load, characterized by the fact that at least one of said sections (A, B) comprises a connection (20) between the channel (10) which receives oil from the pump (1) and at least the channel (13B) which sends oil to the actuator (3B ); said connection (20) being parallel with respect to the flow path through the flow rate adjustment niches (23B, 27B) of the relative spool (7B) and the local compensator (8B); said connection (20) being closed in the central position of the relative cursor (7B) and open when the cursor (7B) is piloted on one side (V1B); in said connection (20) the oil passes through a shutter (21) kept normally closed by a spring (22) set so that the opening pressure is higher than the delta p of LS at which the LS regulator is set. pump (1). 2. Hydraulic distributor (2), according to claim 1, characterized in that said connection (20) is made inside the slider (7B) through radial (40, 42) and axial (41) holes, shutter (21) and spring (22) being both housed inside the slider (7B). 3. Hydraulic distributor (2), according to claim 2, characterized in that said radial holes (40) which carry oil to the shutter (21) are always connected to the channel (10), while the radial holes (42) which they discharge oil from the shutter (21) are covered in a central position and open to the channel (12B) and therefore to its use (13B) when the spool (7B) is piloted on one side (V1B); the sealing seat (44) of the obturator (21) is located between the axial hole (41) and the radial holes (42), while the obturator (21) is housed in the hole (43) together with the spring ( 22) from which it is kept in the closed position; when opening, the shutter (21) abuts against the pin (32); the pressure in (41) and therefore the pressure of the oil entering the pump in (10) acts in opening on the shutter (21), while the pressure in (42) is closed at the same level as that of use in ( 12B), when the slider is piloted from one side (V1B), plus the force of the spring (22). 4. Hydraulic distributor (2), according to claim 1, characterized in that the local pressure compensators (8A; 8B) are placed downstream of the respective cursors (7A; 7B) between the flow regulation niches (23A, 27A ; 23B, 27B) and the uses (13A, 14A; 13B, 14B).