WO2009141697A1

WO2009141697A1 - Hydraulic actuation system with multi piston actuator

Info

Publication number: WO2009141697A1
Application number: PCT/IB2009/005592
Authority: WO
Inventors: Eero Johannes Makkonen
Original assignee: Valtra Oy Ab
Priority date: 2008-05-20
Filing date: 2009-05-14
Publication date: 2009-11-26
Also published as: EP2291587A1; GB0809112D0

Abstract

A hydraulic actuation system (10) comprising a multi-piston fluid pressure actuator (14) is provided. The actuator comprises a plurality of pistons (41,42,43) which share a common rod (40) within a cylinder. Together with internal walls (44,45) the pistons define a series of chambers (46,47,48,49,50) which have associated therewith either an inlet port or an outlet port (52,53), the latter providing a synchronised supply to respective hydraulic consumers (11). The system further comprises valve means (26,27) for selectively pressurising the chambers which have inlet ports to provide variable outlet forces for the operation of consumers connected to the outlets.

Description

HYDRAULIC ACTUATION SYSTEM WITH MULTI PISTON ACTUATOR

This invention relates to hydraulic actuation systems having a fluid pressure actuator and in particular to multi piston actuators for the control of the operation of two or more parallel consumers.

Multi piston actuators having a plurality of pistons sharing a common rod are known from GB-1, 121,956 for example. One advantage of such an actuator is the provision of two synchronised outlet ports which can drive a pair of hydraulic power cylinders with a predetermined speed ratio.

It is an object of the present invention to provide an improved form of hydraulic actuation system which includes a multi piston actuator.

Thus according to the present invention there is provided a hydraulic actuation system comprising a source of inlet pressure and a multi-piston fluid pressure actuator comprising:

a common rod on which first and second pistons are mounted at spaced locations for sliding with the rod in a cylinder having first and second inlets and first and second outlets; a first side of the first piston, when subject via the first inlet to a first input pressure admitted to a first chamber defined between the cylinder and the first piston, moving the rod and pistons in a working direction in the cylinder, a second side of the first piston generating a first outlet volume from in a second chamber defined between the cylinder, the rod and the first piston as the rod and pistons move in the cylinder, the second chamber being connected with the first outlet, a first side of the second piston generating a second outlet volume from in a third chamber defined between the cylinder, the rod and the second piston as the rod and pistons move in the cylinder, the third chamber being connected with the second outlet; and a second side of the second piston, when subjected via the second inlet to a second input pressure admitted to a fourth chamber defined between the cylinder, the rod and the second piston also moving the rod and the pistons in the working direction; wherein,

the system further comprises valve means for selectively pressurising the first and fourth chambers to provide variable first and second outlet forces for the operation of two consumers connected to the first and second outlets.

Advantageously, by providing means to selectively deliver a pressurised fluid to each of the first and second inlets, the output force applied can be changed, albeit at the expense of a change in input fluid volume. Therefore, when only a low output hydraulic force is required, the system may choose to supply a pressurised fluid to the first chamber only. When a higher output hydraulic force is demanded, the system may supply pressurised fluid to both the first and fourth chambers.

The first and second input pressures may be the same or different regardless of whether they are sourced from the same source of inlet pressure. Advantageously, by varying the respective input pressures and/or piston areas (associated with the input chambers), the range of available output powers can be broadened thereby increasing the application flexibility.

The areas of the second side of the first piston and the first side of the second piston exposed to the pressures in the second and third chambers may be equal to ensure equal outlet volumes of fluid from the first and second outlets.

The multi-piston actuator may have a third piston mounted on the rod, a first side of the third piston, when subjected to a third input pressure by admitting the inlet pressure to a fifth chamber defined between the cylinder, the rod and the third piston, also moving the rod and pistons in the working direction to provide a still higher outlet force at the first and second outlets. The second side of the third piston can be subjected to pressure by pressuring a sixth chamber defined between the cylinder, and the third piston in order to move the rod and pistons in a direction opposite to the working direction to return the actuators to an initial position.

The invention further provides a hydraulic actuation system as defined above in which the outlets are connected to respective hydraulic actuators acting between respective implement attachment links pivotally mounted on a tractor chassis so that the links can be raised in unison with different forces when the first/fourth/fifth chambers are selectively pressurised by the valve means.

Such an actuation system applied to the operation of tractor implement attachment links has the advantage that no connection is necessary between the two links to ensure that the movement of links is synchronised as the first and second outlets provide equal outlet volumes. This results in significant cost savings as the customary cross-shaft which connects these two links in order to ensure synchronous movement can be omitted.

The present invention will now be described with reference to the accompanying drawings in which:-

Figure 1 shows schematically a tractor hitch actuation system using a multi-piston actuator in accordance with the present invention;

Figure 2 shows diagrammatically a first form of multi-piston actuator in accordance with the present invention which is used in the tractor hitch actuation system of Figure 1;

Figure 3 shows diagrammatically a second and simplified form of multi-piston actuator in accordance with the present invention;

Figure 4 shows a sectional view of an actual multi-piston actuator of the form shown diagrammatically in Figure 2; and Figures 5 and 6 show sectional and end views of a dividing wall used in the actuator of Figure 4.

Referring to the drawings, a hydraulic actuation system 10 for the control of a pair of hydraulic lift rams 11 used to raise a pair of lower implement attachment links 12 relative to a tractor chassis 13 includes a multi-piston fluid pressure actuator 14 in accordance with the present invention which supplies the two lift rams 11 with pressurised fluid from a hydraulic pump 15 which is powered from the engine 16 of the tractor.

As is conventional, the supply of fluid from the actuator 14 to the lift rams 11 is controlled by an Electronic Control Unit 17 which receives command inputs from a driver-operated control lever or dial 18 and various tractor operating parameter sensors such as draught force sensors 12a associated with the lower links 12, hitch vertical position sensors 19 associated with the lift rams 11, and one or more driving wheel speed sensors 20 which, together with a vehicle speed sensor 20a, can be used to determine the wheel slippage of the driven wheels of the tractor.

The pressurised fluid from pump 15 is supplied to multi-piston actuator 14 via a power lift valve 21 which is opened and closed via solenoids 21a and 21b which are connected with the ECU 17. The supply circuit for the lift rams 11 also includes a fluid flow control valve 22 which has a solenoid 22a which can move the control valve to a supply position in which the head end chambers 11a of rams 11 are connected with the pump pressure via check valves 23 or the head end chambers 11a are connected with the sump 24 of the circuit. There is also provided a pressure level control valve 25 which ensures that the pressure in the supply system on the ram side of valve 25 is lower than the pressure on the pump side of this valve. If the lift rams 11 are single acting the valves 22 and 25 and the connection to head end chambers 11a are not require. This is to prevent damage to the links 12 as these are primarily designed to be raised by pressure and not pressed down by a high pressure. Further fluid flow control valves 26 and 27 having solenoids 26a and 27a are also provided which are controlled by the ECU 17 and which control the admission and release of pressurised fluid to and from various chambers in the multi-piston fluid pressure actuator 14 as will be described below. A pressure limiting valve 28 is also provided which limits the pressure in an end chamber of the actuator 14 as will be described below.

The hydraulic system is completed by further fluid flow control valves 29, 30, 31, 32 each provided with their own solenoid 29a — 32a whose function will again be described below.

The multi-piston fluid pressure actuator 14, which is shown diagrammatically in Figure 2, comprises a rod 40 which carries a first piston 41, a second piston 42 and a third piston 43. These pistons and the rod 40 in conjunction with internal walls 44 and 45, through which the rod 40 slides in a sealed manner, define a first chamber 46 at the left-hand end of the actuator, a second chamber 47 between the piston 41 and the internal wall 44, a third chamber 48 between the piston 42 and the wall 45, a fourth chamber 49 between the piston 42 and the wall 44, a fifth chamber 50 between the piston 43 and the wall 45 and a sixth chamber 51 at the right-hand end of the actuator between the piston 43 and the end of the bore in which the pistons 41, 42 and 43 slide.

The first chamber 46 is connected with the outlet of the power lift valve 21. The second chamber 47 is provided with a first outlet 52 which is connected with the left-hand lift ram 11, the third chamber 48 is provided with a second outlet 53 which is connected with the right-hand lift ram 11. The fourth chamber 49 may be connected with the outlet of the power lift valve 21 when the fluid flow control valve 26 is operated. Similarly the fifth chamber 50 may also be connected with the outlet of power lift 21 when the control valve 27 is operated. Fluid pressure at a predetermined level (typically 3 bar) is provided to the sixth chamber 51 via the pressure level limiting valve 28. This ensures that the pistons and rod of the actuator are returned to the left (as viewed in Figure 2) to their initial starting position when the power lift valve 21 is in its lowering position, even if there has been some leakage in the system.

As indicated above, the raising and the lowering of the lift rams 11 is controlled by the power lift valve 21 which receives its control signals via solenoids 21a and 21b to raise and lower the associated lower links 12 in response to the tractor driver's commands which are inputted through the input device 18 and also the feedback of the tractor operating parameters from the various draught force, draught link position, vehicle speed and wheel slip sensors in a conventional manner.

In accordance with the present invention, if control valves 26 and 27 are closed then opening of the power lift valve 21 supplies the pump pressure to the first chamber 46 only which displaces the piston 41 arid the rod 40 together with the second and third pistons 42 and 43 to the right as shown in Figures 1 and 2.

As will be appreciated, as piston 41 is moved to the right this displaces fluid from the second chamber 47 which is fed to the first out at 52 and hence to a left-hand lift ram 11. Similarly piston 42 moves to the right generating at output volume in the third chamber 48 which is delivered by the second outlet 53 to the right-hand lift ram 11. If the cross-sectional areas of the pistons 41 and 42 which are exposed to the pressure in the second and third chambers are equal the output volumes at the first and second outlets 52 and 53 will be equal and thus equal amounts of fluid will be displaced into both the left-hand and the right-hand lift ram 11 so that the two lower links 12 are both raised in synchronism at the same speed even if different loads are applied to the links.

Thus P1.A46=P2.A47+P3.A48

(Where Pl, P2 and P3 = pressures in chambers 46, 47 and 48 respectively and A46, A47 and A48 = areas of pistons 41 and 42 exposed to pressures Pl, P2 and P3 respectively.)

If it is desired to increase the hydraulic force applied to the lower links 12 the control valve 26 may be opened using the solenoid 26a to also admit the output pressure from the power lift valve 21 to the fourth chamber 49 so that additional force is applied to the piston rod 40 by the piston 42 to increase the output volume and force applied to rams 11 by the fluid in the second chamber 42 and also the third chamber 48.

Thus P1.A46+P1.A49=P2.A47+P3.A48 An even higher outlet volume/force can be generated by also opening the control valve 27 so the output pressure from power lift valve 21 is also admitted into the fifth chamber 50 so that further force is applied to the rod 40 by the left-hand side of the piston 43.

Thus P1.A46+P1.A49+P1.A50=P2.A47+P3.A48

Thus three volume/force outputs are possible from the outlets 52 and 53 depending on whether the output from power lift valve 21 is only delivered to the first chamber 46 or to additionally the fourth chamber 49 and still further additionally to the fifth chamber 50.

As will be appreciated from the above, since the output volume from the first and second outlets 52 and 53 is matched the movement of the lower links 12 is completely synchronised without any need to have any mechanical connection between the two lower links. This results in significant cost savings since the customary cross shaft which links the two lover links 12 is no longer necessary to ensure synchronism movement of these lower links.

As indicated above, if the lift rams 11 are to be double acting then the fluid control valve 22 is used to apply the system pressure to the head end of the lift rams 11 to force the lift rams downwardly rather than simply relying on the weight of any implement connected to the lower links 12 to cause the lower links to fall.

Also, using the control valves 29, 30 and 31, 32 it is possible to add or remove fluid from the rod end of the lift rams 11 to, for example, adjust the relative height of the lower links 12 when the tractor is being used on a slanting field. Also, by admitting hydraulic fluid into the rod end of the lift rams it is possible to limit the lowest position to which the lower links can fall during operation of the control system.

Figures 4 and 5 show details of one form of the multi-piston fluid pressure actuator 14. It will be noted from Figure 4 that the rod 40 can conveniently be in two parts 40a and 40b which are joined together within the central piston 42. Also, the first outlet 52 is provided within the dividing wall 44 and the second outlet 53 within the dividing wall 45. Figure 5 shows the internal details of the dividing wall 44 with an axial drilling 44a connecting the left-hand side of wall 44 with the second chamber 47 and with an outlet drilling 44b which extends through the body of the actuator. The inlet from valve 26 into chamber 49 is via a port 61 in dividing wall 44 which opens into a central bore 62 in wall 44 through which rod part 40a and piston 42 slide. The internal details of wall 45 are similar to wall 44.

As can be seen from Figure 4, the body of the actuator is in fact formed in three parts 14a, 14b and 14c which are joined together by the two wall members 44 and 45. The ends of the body of the actuator 14 are closed off by end caps 14d and 14e which include ports 14f and 14g which communicate with the first and sixth chambers respectively.

The pressure regulating valve 28 ensures that the sixth chamber 51 is typically subjected to a pressure of approximately 3 bar which ensures that when the pressure is relieved from the first, fourth and fifth chambers there is a return force applied to the rod 40 to move the rod to the left as shown in Figures 1 and 2 to return the rod to its initial position.

Figure 3 shows a simplified form of multi-piston fluid pressure actuator 60 which is basically the same as the actuator shown in Figure 2 except that the third piston 43 and chambers 50 and 51 are not present. In the Figure 3 construction the components similar to those previously described with reference to Figure 2 have been similarly numbered and it will be appreciated that from the outlets 52 and 53 two levels of volume/force output are now possible depending on whether only the first chamber 46 is connected to the output of the power lift valve 21 or additionally the fourth chamber 49 is connected to the output from valve 26. Chamber 61 can again be supplied with pressure via valve 28 to return the rod 40 to its left-hand starting position.

It should be appreciated that the multi piston hydraulic actuator may comprise any practical number of pistons and corresponding chambers, inlets and outlets without deviating from the scope of the invention. The more selectively controllable inlets then the more available outlet powers are made available due to the increase in input permutations. The respective input pressures may be sourced from a common pressure supply or, alternatively, separate pressure supplies. In the former case, different input pressures can still be obtained by including restrictors in the valve gear, 26,27 for example. In summary, there is provided a hydraulic actuation system comprising a multi-piston fluid pressure actuator. The actuator comprises a plurality of pistons which share a common rod within a cylinder. Together with internal walls the pistons define a series of chambers which have associated therewith either an inlet port or an outlet port, the latter providing a synchronised supply to respective hydraulic consumers. The system further comprises valve means for selectively pressurising the chambers which have inlet ports to provide variable outlet forces for the operation of consumers connected to the outlets.

From reading the present disclosure, other modification will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the field of hydraulic actuation systems and component parts therefore and which may be used instead of or in addition to features already described herein.

Claims

1. A hydraulic actuation system comprising a source of inlet pressure and a multi-piston fluid pressure actuator comprising: a common rod on which first and second pistons are mounted at spaced locations for sliding with the rod in a cylinder having first and second inlets and first and second outlets; a first side of the first piston, when subject via the first inlet to a first input pressure admitted to a first chamber defined between the cylinder and the first piston, moving the rod and pistons in a working direction in the cylinder, a second side of the first piston generating a first outlet volume from in a second chamber defined between the cylinder, the rod and the first piston as the rod and pistons move in the cylinder, the second chamber being connected with the first outlet, a first side of the second piston generating a second outlet volume from in a third chamber defined between the cylinder, the rod and the second piston as the rod and pistons move in the cylinder, the third chamber being connected with the second outlet; and a second side of the second piston, when subjected via the second inlet to a second input pressure admitted to a fourth chamber defined between the cylinder, the rod and the second piston also moving the rod and the pistons in the working direction; wherein, the system further comprises valve means for selectively pressurising the first and fourth chambers to provide variable first and second outlet forces for the operation of two consumers connect to the first and second outlets.

2. A hydraulic actuation system according to Claim 1, in which the areas of the second side of the first piston and the first side of the second piston exposed to the respective pressures in the second and third chambers are equal to ensure equal first and second outlet volumes of fluid.

3. A hydraulic actuation system according to Claim 1 or 2, wherein the first and second input pressures are different.

4. A hydraulic actuation system according to Claim 1, 2 or 3, wherein the actuator further comprises a third piston mounted on the rod, a first side of the third piston, when subjected to a third input pressure by admitting the inlet pressure to a fifth chamber defined between the cylinder, the rod and the third piston, also moving the rod and pistons in the working direction.

5. A hydraulic actuation system according to Claim 4, in which the other side of the third piston can be subjected to pressure by pressuring a sixth chamber defined between the cylinder, and the third piston in order to move the rod and pistons in a direction opposite to the working direction to return the actuator to an initial position.

6. A hydraulic actuation system according to any preceding claim, in which the outlets are connected to respective hydraulic actuators acting between respective implement attachment links pivotally mounted on a tractor chassis so that the links can be raised in unison with different forces when the first/fourth/fifth chambers are selectively pressurised by the valve means.

7. A multi-piston fluid pressure actuator constructed and arranged substantially as hereinbefore described with reference to and as shown in the accompanying drawings.