Hydraulic actuator assembly with rotation restraint

A hydraulic actuator assembly comprises a pair of hydraulic actuators having cylinders, pistons, and piston rods that are ganged together for extension of their respective piston rods in longitudinally opposite directions wherein at least one of the actuators comprises an anti-rotation mechanism that prevents rotation of the actuator assembly about its longitudinal axis. The anti-rotation mechanism comprises an axial anti-rotation rod rigidly attached to a cylinder having a non-circular cross-section slidably complementary to a non-circular aperture in a hollow piston rod. The piston rod can travel longitudinally along the anti-rotation rod, but is prevented from rotating by the non-circular cross-section.

BACKGROUND OF INVENTION

1. Field of the Invention

The invention relates generally to hydraulic actuator assemblies. In one of its aspects, the invention relates to a pair of hydraulic actuators rigidly ganged together wherein the piston rods of the cylinders are extendible in parallel, longitudinally opposed directions. In another aspect, the invention relates to a hydraulic actuator assembly comprising a pair of hydraulic actuators rigidly ganged together wherein at least one of the piston rods is prevented from rotating relative to the hydraulic cylinder in which it is reciprocally mounted. In another aspect, the invention relates to a hydraulic actuator assembly comprising a pair of hydraulic actuators rigidly ganged together in which at least one of the piston rods is prevented from rotating relative to a hydraulic cylinder wherein one of the piston rods is attached to a concrete delivery chute of a concrete mixer truck, and the other piston rod is attached to the chassis of the concrete mixer truck.

2. Description of the Related Art

Hydraulic actuators are well known in the art and comprise a cylinder, a piston moving longitudinally within the cylinder, a piston rod coaxially connected to the piston and extending coaxially outside the cylinder, and end caps for fluidly sealing the cylinder. The cylinder contains hydraulic fluid under pressure, the piston rod is the moving element, the piston separates the cylinder into two separate cavities, and the end caps seal the cylinder to contain the fluid inside the cylinder. The piston is typically not restrained against rotation within the cylinder. Typically some type of mounting ends are used to affix the cylinder and piston rod in place.

Hydraulic actuators are employed in numerous applications to move a first element or part of an assembly relative to a second element. As an example, hydraulic actuators have been used to selectively position a concrete delivery chute on a front unloading concrete mixer truck. The actuator enables the chute to be readily positioned by the operator for delivery of the fresh concrete to a selected location. A typical hydraulic actuator used in this application comprises a single rod, double acting actuator. The cylinder is attached to the first part of the assembly, such as an anchoring point on the transit mixer chassis, and the piston rod is attached to the second element, such as the delivery chute. The attachments prevent rotation of the piston rod relative to the cylinder.

In order to provide an extended range beyond the range enabled by the stroke of a typical single rod actuator, a dual (or piggyback) cylinder actuator assembly was developed. The dual cylinder actuator assembly comprises two cylinders laterally connected together with the piston rods extending longitudinally in opposite directions to give approximately twice the piston rod stroke of a single rod actuator. However, because the dual cylinder actuator assembly is mounted at each end by a piston rod and not by a fixed cylinder base end, as is the case with a single rod actuator, the dual cylinder actuator assembly is suspended between the concrete delivery chute and the transit mixer chassis, which are moveable relative to each other. This relative movement will translate into rotation of the cylinders relative to the pistons and piston rods.

When the transit mixer travels down the road, the dual actuator is free to swing back and forth, which can seriously damage the actuator assembly and render the transit mixer unusable. It can also cause hydraulic connecting hoses attached to the cylinders to be pulled loose, resulting in the loss of hydraulic fluid.

To solve this problem, external anti-rotation devices have been developed to prevent the cylinders from rotating. These devices are typically added to the exterior of one of the dual cylinders.

One such device comprises a square hollow tube welded longitudinally to the side of the cylinder tube. A solid square bar adapted to slide inside the hollow tube, is inserted into the hollow tube and affixed to the mounting end of the piston rod. As the cylinders translate relative to the piston rods, the square solid bar translates along the hollow square tube (like a trombone slide), thereby preventing the piston rod from rotating relative to the cylinder. However, this assembly is very bulky and heavy, and subject to external damage. Furthermore, the assembly requires constant greasing and maintenance. The cylinder is regularly covered with cement dust which collects between the solid bar and the hollow tube, and causes them to stick together and/or travel inconsistently. Unless greasing and maintenance are performed regularly, the buildup of cement dust can harden, and the device can consequently break or no longer function properly. The device is also subject to the intrusion of water, leading to rusting which can also cause it to prematurely fail.

This device is also difficult to mount on the mixer, as the alignment between the non-rotational rod mount and the cylinder mount is critical and difficult to keep in alignment during installation. The device is also difficult to manufacture and therefore costly.

SUMMARY OF INVENTION

According to the invention, a hydraulic actuator assembly for moving a first object relative to a second object comprises a first hydraulic actuator and a second hydraulic actuator that are rigidly ganged together so that their respective piston rods are movable along parallel longitudinal cylinder axes and in opposite directions and at least one of the piston rods is non-rotationally mounted to its respect cylinder to prevent relative rotation of the one cylinder rod with respect to its respective cylinder. The hydraulic actuator assembly is preferably used to control a cement chute in a cement truck.

Typically, the first hydraulic cylinder has a first cylinder with a first longitudinal axis and a first piston, slidable within the cylinder, and attached to a first piston rod for movement along the first longitudinal axis with respect to the cylinder. The second hydraulic actuator has a second cylinder with a second longitudinal axis, and a second piston, slidable in the second cylinder, and attached to a second piston rod for movement along the second longitudinal axis with respect to the second cylinder. A non-rotation mounting is provided between at least the second piston rod and the second cylinder for non-rotational movement of the second piston rod along the second longitudinal axis. A rigid mounting is provided between the first cylinder and the second cylinder so that the first longitudinal axis is parallel to the second longitudinal axis, and the first piston rod and the second piston rod are movable in opposite directions. The second piston rod can have an axial bore therein.

The non-rotation mounting can comprise an anti-rotation rod having a non-circular cross-section and adapted for slidable translation within the axial bore. At least a portion of the axial bore can be adapted with a non-circular cross-section complementary to the cross-section of the anti-rotation rod for slidable non-rotatable receipt of the anti-rotation rod. The anti-rotation rod can have a recti-linear or hexagonal cross-section, or one of the anti-rotation rod and the axial bore can comprise a key and the other of the anti-rotation rod and the axial bore can comprise a complementary channel adapted for slidable receipt of the key therein.

The second actuator can have an end cap that is non-rotatable about the second longitudinal axis, with the anti-rotation rod rigidly attached to the end cap for insertion in the axial bore and restrained from rotational movement about the second longitudinal axis. The non-rotation mounting can further comprise a rod insert that is non-rotatably attached to the second piston rod within the second cylinder, the rod insert having a non-circular aperture coaxial with the second longitudinal axis and complementary to the cross-section of the anti-rotation rod, and the anti-rotation rod slidably received in the non-circular aperture of the rod insert to prevent rotation of the second piston rod relative to the anti-rotation rod.

The hydraulic actuator assembly can further comprise a non-rotation mounting between the first piston rod and the first cylinder for non-rotational movement of the first piston rod about the first longitudinal axis. The non-rotation mounting can alternatively comprise a cylinder end cap non-rotatably attached to the second cylinder and having a non-circular aperture therethrough, with the second piston rod having a non-circular cross-section complementary to the non-circular aperture and adapted for slidable receipt in the non-circular aperture.

DETAILED DESCRIPTION

Referring now to the drawings, and toFIG. 1in particular, according to the invention a non-rotational dual hydraulic actuator assembly10comprises two hydraulic actuators12,14that are ganged together for extension of their respective piston rods30,52in opposite directions wherein at least one of the actuators comprises a mechanism that prevents rotation of the actuator assembly10about its longitudinal axis.FIG. 1illustrates the hydraulic actuator assembly10incorporated into a concrete mixer truck16for positioning of a moveable concrete delivery chute34. A first piston rod30of the dual hydraulic actuator assembly10is attached to the delivery chute34and a second piston rod52is attached to a suitable anchor point on the transit mixer chassis, such as a bumper36, a frame element, or the like. As shown also inFIGS. 2 and 3, the hydraulic actuator assembly10comprises a pair of cylinders20,40rigidly ganged together through a suitable rigid mounting72, such as by welding or casting the cylinders20,40together, in a longitudinal direction so that the piston rods30,52of the cylinders20,40are extendible in longitudinally opposed directions.

As shown inFIG. 3, the hydraulic actuator assembly10comprises a solid rod actuator12and a hollow rod actuator14rigidly ganged together in generally parallel juxta-position. The solid rod actuator12comprises a generally well-known hydraulic actuator comprising a hollow cylinder20closed at a first end with a circular end cap22and at a second end with a circular annular cap24having a circular rod aperture26extending coaxially therethrough. A circular piston28is adapted for slidable translation along the interior of the cylinder20and is rigidly attached to a second end of the piston rod30in a suitable manner, such as by threading the piston rod30into a suitable threaded aperture in the piston28and securing the piston28to the piston rod30with a lock fastener74, such as a lock nut, with the first end extending coaxially through the rod aperture26. A well-known shackle32is rigidly attached to the first end of the piston rod30and is adapted for pivotal attachment to a first movable element, such as the concrete delivery chute34shown inFIG. 1.

The hollow rod actuator14comprises a hollow cylinder40closed at a first end with a circular annular end cap42having a circular opening44extending coaxially therethrough and at a second end with a circular annular cap46having a circular rod aperture48extending coaxially therethrough. The annular end cap42is fixedly attached to the first end of the cylinder40, such as by welding or a threaded connection. A circular piston50is adapted for slidable translation along the interior of the cylinder40and is provided with a threaded aperture extending coaxially therethrough. The piston rod52is hollow and defines a rod bore54extending axially therethrough in coaxial register with the opening44. As shown inFIG. 3, the piston rod52terminates at a first end in a well-known shackle70adapted for pivotal attachment to an anchor point such as the bumper36of the transit mixer16shown inFIG. 1. As shown inFIGS. 4 and 5, the second end of the piston rod52terminates in a threaded section62extending some distance into the rod bore54. (The piston50has been removed inFIGS. 4 and 5for clarity.)

A non-rotation mounting55comprises a rod insert56and an anti-rotation rod60as hereinafter described. The rod insert56is an elongated, generally annular member shown inFIGS. 4 and 5having an insert bore58extending axially therethrough. In one embodiment, the insert bore58is provided with at least one flat side, and is preferably square or hexagonal in cross-section. The rod insert56is provided at a first end with a length of piston rod threads64, and at a second end with a length of piston threads66. The piston rod threads64are adapted for threadable register with the threaded section62so that the rod insert56can be threaded to the piston rod52to extend coaxially therefrom. A lock fastener, such as a locknut or other suitable locking mechanism such as a setscrew, can be used to lock the rod insert56to the piston rod52. Alternatively, the rod insert56can be welded or otherwise rigidly attached to the piston rod52in a well-known manner. The piston threads66are adapted so that the piston50can be coaxially threaded to the rod insert56for rigid attachment of the piston50to the piston rod52. A lock fastener76, such as a locknut threaded onto the piston threads66, or other suitable locking mechanisms, can be used to secure the piston50to the rod insert56. Alternatively, the piston50can be welded or otherwise rigidly attached to the rod insert56in a well-known manner.

In another embodiment, the insert56can be omitted, and the piston rod52provided with the piston threads66and the flat-sided bore58.

The anti-rotation rod60is a generally thin, elongated member having a cross-section complementary to the cross-section of the insert bore58and adapted for non-rotational slidable register with the insert bore58. (The anti-rotation rod60is omitted inFIG. 3for clarity.) The rod insert56is typically machined from a material, such as brass or bronze, that minimizes wear on the anti-rotation rod60as it travels in and out of the rod insert56.

The anti-rotation rod60is inserted through the opening44and the insert bore58into the rod bore54, and is fixedly attached to the end cap42, such as by a weld68encircling the anti-rotation rod60along the intersection of the anti-rotation rod60with the opening44, as shown inFIG. 6, or other suitable connector, such as a locknut. (The piston50has been removed inFIG. 6for clarity.) As so assembled, the anti-rotation rod60will be fixed against rotation relative to the cylinder40through the welding of the anti-rotation rod60to the end cap42, and the end cap42to the cylinder40. The rod insert56can slide along the anti-rotation rod60with the movement of the piston50, but will be restrained against rotation by the flat-sided cross-section of the anti-rotation rod60and the insert bore58. The length of the anti-rotation rod60can be adapted to terminate at the end cap42, extending into the rod bore54sufficiently to accommodate the full stroke of the piston50. Thus, with the piston rod52pivotally but not rotationally connected to an anchor point on the transit mixer16, the cylinder40will be prevented from rotating relative to the piston rod52through the engagement of the anti-rotation rod60with the insert bore58.

By preventing the hollow rod actuator rod from rotating, the hydraulic actuator assembly10becomes non-rotating, and is prevented from swinging after it has been mounted on the transit mixer16. The hydraulic actuator assembly10has a less bulky configuration than prior art actuator assemblies, and a much lighter weight. This improves the driver's view of the road by reducing the size of the hydraulic actuator assembly, and increases fuel economy. Because the anti-rotation rod60and the rod insert56are enclosed within the cylinder40, hydraulic oil constantly bathes the entire assembly. This eliminates the need for ongoing greasing or maintenance, and insurers that the device will move freely and smoothly in operation. Because the anti-rotation device is completely contained within the cylinder40, it is fully protected from any external damage.

The entire assembly is much stronger and more rigid than the prior art devices because the anti-rotation rod60and the rod insert56are coaxial with the centerline of the cylinder40. By eliminating the mounting of the prior art external non-rotation device to the actuator, installation of the hydraulic actuator assembly10is much easier, and proper alignment is always precisely maintained. The new anti-rotation device eliminates the need to align the end mounting of the prior art external non-rotational device with the mounting of the actuator.

The hydraulic actuator assembly10can position the concrete delivery chute34through an increased distance. The dual actuators greatly increase the concrete delivery area that can be served without the need to reposition the transit mixer16. The anti-rotation device described herein effectively prevents the actuators from rotating or twisting to minimize damage to the actuators, lowers the profile and weight of the hydraulic actuator assembly10, eliminates the need for, and expense of, regular maintenance, and lowers the initial time and cost of purchasing and installing the actuator assembly10.

In yet another embodiment, shown inFIG. 7, the hollow piston rod52can be replaced with a solid piston rod86having a cross-section comprising at least one flat side. A first, distal end of the cylinder40is closed with a solid end cap82. A second, proximal end of the cylinder is closed with an annular cap84having a rod aperture88complementary to the piston rod cross-section. The cylinders20,40are ganged together as previously described to form the non-rotational dual hydraulic actuator assembly10.

The invention can also comprise an embodiment wherein the non-rotation mounting55is incorporated into both hydraulic actuators12,14. In such embodiment, the solid piston rod30is replaced with a hollow piston rod, and both piston rods30,52are prevented from rotating relative to their respective cylinders20,40.

In yet another embodiment, the anti-rotation rod60can be provided with a radially-outwardly extending longitudinal key extending the length of the anti-rotation rod60, rather than a flat side, which is keyed to a complementary channel formed in the insert bore58to prevent rotation of the anti-rotation rod60in the insert bore58. Conversely, the channel can be formed in the anti-rotation rod60, and the key can be provided in the insert bore58.

While the invention has been specifically described in connection with certain embodiments thereof, it is to be understood that this is by way of illustration and not of limitation. Reasonable variation and modification are possible within the scope of the forgoing description and drawings without departing from the spirit of the invention, which is described in the appended claims.