Hydraulic Activation for a Sliding Carriage
A hydraulic system for moving a carriage guided for movement along a linear path by a support frame, such as a backhoe or an excavator. The system comprises two hydraulic jacks, each having a cylinder body and a piston rod. The cylinder bodies of the two jacks are joined to one another, the end of the piston rod of one jack is connected to the support frame and the end of the piston rod of the other jack is connected to the carriage. In the invention, the two piston rods project from the same side of the joined cylinder bodies and in each end position of the carriage, the piston rod of a respective one of the jacks is extended while that of the other jack is retracted.
This application is the US National Stage filing of International Application Serial No. PCT/EP2010/057748 filed on Jun. 2, 2010 which claims priority to Italian Application TO2009A000421 filed Jun. 3, 2009, each of which is incorporated herein by reference in its entirety.
FIELD OF THE INVENTIONThe present invention relates to hydraulic actuation of a sliding carriage guided for movement along a linear path.
BACKGROUND OF THE INVENTIONA backhoe is an item of excavating equipment comprising a digging bucket on the end of a two-part articulated arm, the two parts being termed a main boom and a dipper. Backhoes are typically mounted on the back of a vehicle, such as a tractor or front loader, and can be used for example to dig trenches.
It is known from EP 0 692 579 to connect the lower end of the boom arm of the backhoe pivotally to a king post assembly which allows pivotal slewing movement of the main boom about a vertical axis, so that the main boom can be rotated from one side to the other of the centre line of the vehicle. The king post assembly is itself mounted upon a guide and is movable along the guide in a direction transverse to the vehicle centreline. A fluid operated ram is connected between the king post assembly and an anchor point on the vehicle, so that extension or contraction of the ram causes movement of the king post assembly along the guide.
The present invention is concerned with a hydraulic system which may serve the purpose of the fluid operated ram in EP 0 692 579 but may alternatively be used to move any carriage that is guided for movement along a linear path.
There are several criteria that need to be taken into consideration in the design of such a hydraulic actuator. A first consideration is the size of the actuator, in that it must be capable of being accommodated within the path of travel of the carriage yet it must not limit the movement of the carriage. Another consideration is that the actuator needs itself to be supported in a suitable manner to ensure that its piston rod and cylinder axis always remain in alignment, even when under load. A further consideration is that it should be possible to offer protection to any extended piston rod as it risks being damaged in the dirty environment in which heavy equipment, such as a backhoe, operates.
Two solutions proposed in EP 0 692 579 involve repositioning the cylinder of the ram, either relative to the track or relative to the carriage. In this way, the maximum displacement of the carriage is not determined by the stroke of the ram. However, when operating in a dirty environment, neither of the embodiments described in the latter patent specification offers a solution satisfying the above criteria.
In
The present invention provides an improved hydraulic system that avoids several shortcomings of the system illustrated in
First, it will be noted from
Second, the separation between the pivot pins 22 and 24 in the position of
A still further problem arises when pressure is applied to move the carriage 10 away from its right hand end position shown in
With a view to overcoming at least some of the above shortcomings, the present invention provides a hydraulic system for moving a carriage guided for movement along a linear path by a support frame, the system comprising two hydraulic jacks, each having a cylinder body and a piston rod, wherein the cylinder bodies of the two jacks are joined to one another, the end of the piston rod of one jack is connected to the support frame and the end of the piston rod of the other jack is connected to the carriage, characterised in that the two piston rods project from the same side of the joined cylinder bodies and in each end position of the carriage, the piston rod of a respective one of the jacks is fully extended while that of the other jack is fully retracted.
In the preferred embodiment of the invention, the two jacks have strokes of unequal length and the second piston rod is connected to the side of the carriage that is nearer to the side of the frame connected to the first piston rod.
Advantageously, the joined cylinders are formed with a projecting pin engaged in a slot in a guide movable with the carriage in order to prevent misalignment between the axes of the piston rods and the cylinders when under load.
The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:
To avoid unnecessary repetition, in
Instead of using two hydraulic jacks of equal stroke length and with the piston rods projecting from their respective cylinders in opposite directions, the hydraulic circuit of
A guide plate 118 secured to the carriage 110 has a slot which receives a pin 120 fixed to joined cylinders 114a and 116a near to the end of the cylinder 116a from which the piston rod 116b projects. It would be possible to secure the slotted guide plate 118 to the cylinders 114a, 116a and the pin to the carriage 110 as was the case in the hydraulic circuit of
In
To move the carriage to the intermediate position shown in
To return the carriage 110 to its left hand end position of
It will be seen from the above description that the hydraulic circuit of
First, is it noted that, because the bracket 126 does not project beyond the side of the frame, it does not interfere with the carriage reaching either of its end position.
Second, the maximum separation between the ends of the piston rods, as shown in
Third, to initiate movement of the carriage in either direction, hydraulic fluid always acts on the large face of the piston of one of the two hydraulic jacks. There is therefore always available sufficient force to overcome static friction and to start the carriage moving. Furthermore, in contrast to the prior art, the same force is available to move the carriage in both of its end positions.
Last, it will be seen that the hydraulic system can be mounted above the carriage where it is less exposed to dirt. Furthermore, it is readily possible to mount a fixed shield on the frame 22 to protect the piston rod 114b when it is extended. Another shield may be fixed to the underside of the part of the hydraulic cylinder 114a that projects beyond the cylinder 116a to protect the piston rod 116b when it is extended.
Claims
1. A hydraulic system for moving a carriage along a linear path by a support frame, the system comprising
- two hydraulic jacks, each having a cylinder body and a piston rod, wherein the cylinder bodies of the two jacks are joined to one another,
- the end of the piston rod of one jack is connected to the support frame and the end of the piston rod of the other jack is connected to the carriage; and
- the two piston rods project from the same side of the joined cylinder bodies and in each end position of the carriage, the piston rod of a respective one of the jacks is extended while that of the other jack is retracted.
2. A hydraulic system as claimed in claim 1, wherein the joined cylinders are provided with a projecting pin engaged in a slot in a guide movable with the carriage to prevent misalignment between the axes of the piston rods and the cylinders when under load.
3. A hydraulic system as claimed in claim 1, wherein the two jacks have strokes of unequal length and the second piston rod is connected to the side of the carriage that is nearer to the side of the frame to which the first piston rod is connected.
4. A hydraulic system as claimed in claim 3, wherein a fixed shield is mounted on the frame to protect the piston rod of the longer hydraulic jack when it is extended.
5. A hydraulic system as claimed in claim 3, wherein a shield is fixed to the part of the longer hydraulic cylinder that projects beyond the shorter cylinder to protect the piston rod of the short cylinder when extended.
6. A kingpost assembly comprising
- a carriage and guiding support frame
- a hydraulic system arranged for moving the carriage along a linear path by the support frame, the system comprising two hydraulic jacks, each having a cylinder body and a piston rod,
- wherein the cylinder bodies of the two jacks are joined to one another, and
Type: Application
Filed: Jun 2, 2010
Publication Date: Jun 14, 2012
Inventor: Giuseppe Burgo (Imola (Bo))
Application Number: 13/375,761
International Classification: F01B 29/00 (20060101); E02F 9/22 (20060101);