Safety locking device

A safety locking device 18 for a quick hitch/coupler 10 of an earth working machine. The safety locking device 18 has a locking element 21 which is biased into a locking position to automatically lock a front pin of an implement when it is engaged in the hook 14 of the coupler 10. The safety locking device 18 has an hydraulic operable mechanism to move the locking element 21 to an unlocking position. The hydraulic supply to the safety locking device 18 is independent of the hydraulic supply to a locking mechanism 16 of the coupler 10.

BACKGROUND TO THE INVENTION

This invention relates to a safety locking device for a quick hitch/coupler.

Quick hitches or couplers are used with earth working machines such as excavators whereby an implement such as a bucket can be quickly coupled to or removed from the earth working machine. The quick hitch can thus be attached to the end of the excavator arm.

The quick hitch has a hook portion which is engageable with the so-called “front pin” of an implement. A mounting portion of the quick hitch can then be engaged with the “back pin” of the implement following which a mechanism in the quick hitch is operated to retain the back pin in the mounting portion. When the back pin is so locked into position the front pin is prevented from moving out of the hook portion.

Such quick hitches are widely known and used. The mechanism to lock the back pin in place can take different forms but, in one form, can be a wedge which is moveable by a hydraulic ram. A construction of quick hitch with a wedge mechanism is shown in our New Zealand patent specification nos. 233302 and 260659.

The quick hitch permits the operator of an earth working machine to attach and remove implements without moving from the cab or operating position of the machine. However, a problem that can arise is that the operator may move the part of the machine to which the quick hitch is attached (e.g. an excavator arm) before the back pin is fixed into the mounting portion or the locking mechanism is operated before the back pin is in position in the mounting portion. This can happen because experienced operators tend to position a quick hitch with the implement, lock the quick hitch and move the implement all in one fluid action. Therefore there is the possibility of the operation not being carried out correctly with the result that the implement is not fully locked into the quick hitch.

If incomplete mounting occurs the implement may, when moved, i.e. lifted off the ground, fall from the quick hitch. This creates a situation where damage to the implement can occur or, more seriously, personal injury or death of a bystander can occur due to the uncontrolled movement (falling) of the implement.

It is known to provide in a quick hitch a safety locking device for the front pin so that if incomplete fixing of the back pin occurs, the implement will nevertheless still remain attached by the front pin. These known devices have, however, suffered from drawbacks. For example the safety device may not be failsafe i.e. automatically engage upon the front pin engaging in the hook portion of the quick hitch.

Furthermore many known safety lock devices are controlled by the hydraulic circuit that operates the primary locking mechanism. Sometimes these safety lock devices are mechanically sequenced with the primary locking mechanism which is hydraulic. Thus a failure in the primary locking mechanism hydraulics (allowing unintentional release or movement of the primary locking jaw or wedge from the back pin) could result in the safety lock failing simultaneously due to it being sequential. Thus a failure in the safety lock device hydraulics could result in the locking mechanism failing with potentially disastrous results if this leads to the implement falling from the quick hitch. For example, if there is a seal failure in the ram of the primary locking device, this can result in hydraulic fluid bypass which may cause the hydraulic ram of the locking mechanism to fail to maintain locking of the back pin.

SUMMARY OF THE INVENTION

It is thus an object of the present invention to provide a safety locking device which is of a type that automatically locks the front pin in a quick hitch/coupler and in operation is independent of the quick hitch/coupler primary locking mechanism.

Broadly the invention comprises a safety locking device for a quick hitch/coupler of an earth working machine, the safety locking device including a locking element biased into a locking position to lock a front pin in the hook of the quick hitch/coupler, the safety locking device further including an hydraulic operable mechanism to move the locking element to an unlocking position, said hydraulic mechanism including an hydraulic supply independent of the hydraulic supply to a locking mechanism of the quick hitch/coupler.

FIGS. 1 and 2illustrate a quick hitch/coupler of a type that is manufactured and marketed by Wedgelock Equipment Limited. The coupler is in accordance with conventional construction and includes a body10with a pair of upwardly projecting flanges11with mounting apertures13whereby the coupler10can be fixed to the earth working machine e.g. the end of the arm of an excavator.

The body10incorporates a hook portion14and a mounting portion15. The coupler includes a locking mechanism. This can be, as illustrated, an hydraulic ram16(seeFIG. 2) mounted within the body10and operable to move a wedge17(seeFIGS. 12 and 13) so as to lock the back pin of an implement in the mounting portion15. All of this is in accordance with conventional construction and further description is not required for the purposes of describing the present invention.

As shown inFIGS. 1 and 2a safety locking device18is fitted into the body10and, as is more evident inFIG. 1, it in part forms the hook portion14. In another form of the invention (not shown) the body19of the safety locking device18can extend further than illustrated so as to form part of the side plates20in the immediate vicinity of the hook portion14. Such an arrangement can provide manufacturing advantages as well as improve the aesthetic appearance of the safety locking device18when incorporated in the quick hitch body10.

Projecting from the body19of the safety locking device18is a safety knuckle21. InFIG. 1this is shown in its normal extended position i.e. locking position. It therefore projects downwardly from the body19and, as shown inFIG. 13, engages with the front pin P so as to lock the front pin P into the hook portion14.

The locking knuckle21is biased into this projecting position by a spring bias. Therefore, when the front pin P is introduced into the open end of the hook portion14it will cause the locking knuckle21to move upwardly against the spring bias as the pin P moves into its position fully inserted into the hook portion14(seeFIG. 12). Once it has reached this position the lock knuckle21will, under the spring bias, move back to its projecting position (i.e. as shown inFIG. 13).

Referring now toFIGS. 2-10, the safety locking device18is shown in more detail.

The lock knuckle21is mounted on a rotatable shaft23(seeFIG. 4) and is biased by the coil spring25. This coil spring25is engaged on the shaft23. One leg26of the coil spring25engages with a surface27of the lock body while the other leg28engages against a surface29of the knuckle21.

The shaft23has a bore extended diametrically there through and into which is engaged an engagement element in the form of a lug30. A bolt31fixes the lug30into place. In the illustrated form of the locking device an opening or passage32extends through the body19so that the lug can be located into the bore when the shaft23is in location within the body19. A further passage33with blanking off plug34screwed therein, is provided in order to enable access to the bolt31to be achieved.

Fixed into the body18is a small linear actuator which can be a single acting hydraulic ram35. The piston36of this ram35is engageable with the lug30.

Under the action of the coil spring25the knuckle21extends, in its normal or rest position, downwardly as shown inFIG. 7. In this position the piston36is pushed back into the body of the ram35by virtue of the restoring action of spring25. This retracted position establishes a limit to the extent to which the shaft23can rotate.

When the hydraulic ram35is operated the piston36extends and pushes against the lug30thereby moving the lug until it reaches an end point established by stop surface37. This is shown inFIG. 10. The knuckle21is thus raised into its unlocked position against the action of the bias of spring25.

When the hydraulic pressure is released from the ram35the action of the spring25will cause the shaft23to rotate and hence the interaction between the lug30and the piston36will cause the piston to move back into the position shown inFIG. 7. Hence the knuckle21will move back into its locked position.

The hydraulic supply conduit (not shown) which connects at point35aof the ram35is a separate conduit to that which operates the ram of the locking mechanism. Hence the hydraulic circuit for the safety locking device is independent of the hydraulic circuit used for operating the ram16of quick hitch locking mechanism. As a result of this any failure in the hydraulic circuit e.g. failure of the seal38in the piston36will have no effect on the locking mechanism of the quick hitch.

In a preferred embodiment of the invention the safety locking device is operated by a switching arrangement which, as shown inFIG. 14, is in one preferred form of the invention, a rotary switch40. This switch40is formed as part of a control or solenoid driver circuit as shown inFIG. 14.

The solenoid41of the quick hitch locking mechanism is coupled to the rotary switch40. As shown inFIG. 14this circuit includes a visual warning device (e.g. an LCD42and a buzzer43.

Also connected to the rotary switch40is a solenoid44for operation of the safety locking device. This circuit includes its own visual indicator such as LCD45.

To further describe the circuit diagram and the hydraulic circuits of the quick hitch and safety locking device reference will be now made to the quick hitch operation sequence. This is a description which is based on the different positions of the rotary switch40.

In position1, or the lock position of the rotary switch40, the normal operating position of the quick hitch will exist i.e. the locking wedge17will be extended and locked onto the back pin under hydraulic pressure and the safety locking device will be in its locked or safe position.

As a result no power will be supplied to the directional control solenoid valves. The quick hitch and safety locking device solenoids41and44will be closed allowing “low” pressure oil to the extended side of the quick hitch cylinder16only thereby causing the wedge17to extend. As is apparent from the foregoing description the knuckle21of the safety locking device18is in the extended position and held therein due to the load of the spring25.

With the rotary switch40moved to the release wedge17or “unlock” position, the wedge can be disengaged from the back pin but the safety locking device18will remain in its closed locking position.

In this situation the LED42will illuminate and the buzzer43will sound. Power is supplied to the quick hitch solenoid41only allowing “high” pressure oil to flow into the retract side of the hitch cylinder16opening the pilot operator check valve thereof and causing the wedge17to retract. The “low” pressure oil on the extend side of the cylinder16is able to flow back to the hydraulic tank (not shown) of the hydraulic system bypassing the “low” pressure reducing valve which forms part of the hitch hydraulic circuit.

The rotary switch40can now be moved to the release position where the implement attached to the hitch can be disengaged i.e. the wedge17will be in its retracted position and the safety locking device18will be in its open or unlocked position (i.e. knuckle21retracted).

In this situation the LED45will be illuminated and the LED42and buzzer43will continue to operate. Power will thus be supplied to the safety device solenoid44allowing “high” pressure oil to flow to the extend side of the cylinder35thereby extending the piston36to cause the knuckle21to rotate out of the hook section14opening and into the body19of the safety locking device18. At this point the hitch16cylinder will have no pressure to either side as both sides of the cylinder will be open to the tank.

The attachment or implement can therefore be removed from the quick hitch.

The safety locking device18is, via the circuitry connected to the latch solenoid44, able to be “re-set” by one of two different methods.

By returning the rotary switch40to the release wedge position, power supply to the latch solenoid44will be removed thereby allowing the safety knuckle21to rotate back into the opening of hook section14under the action of the spring25.

The circuitry also provides a time delay which is adjustable in duration of, say, between 4 and 10 seconds. After the elapsed time the timer switches off the power supply to the solenoid44allowing the knuckle21to rotate into its closed position.

When the safety locking device is reset safety cylinder35has no pressure on the piston36and the piston is retracted back via the spring25acting on the safety knuckle21as described above. The hitch is therefore ready for engagement to another attachment or implement.

FIGS. 15 to 20graphically illustrate the use of a coupler with an attachment, the coupler incorporating the safety locking device according to the present invention.

FIG. 15illustrates the coupler C mounted to an excavator arm E in accordance with conventional procedure. The coupler C is approaching the attachment (e.g. bucket) A. The knuckle21is shown in its extended or projecting position.

FIG. 16illustrates the coupler C having engaged with the front pin P and with a locking knuckle21engaged over the front pin P so that the pin is locked into the open end of the hook portion14of the coupler C.

FIG. 16shows the coupler having been moved so as to engage with the rear pin P′ and the locking wedge17extended and locked onto the back pin P′ under the hydraulic pressure of the ram16. The coupler is now engaged with the attachment A and ready for use as normal.

FIG. 18illustrates the attachment A having been lowered onto a surface and the primary locking wedge17disengaged which enables the coupler C to disengage the back pin P′ from the mounting portion15. It will be noted that the locking knuckle21is still engaged with the front pin P so that front pin P cannot be disengaged from the hook portion14.

FIG. 19shows that the lock knuckle21has been released thereby enabling the coupler C to be detached from the attachment A.

FIG. 10shows the coupler C ready to re-connect with the attachment A. It will be noted that the locking knuckle21has now reverted to the extended or projecting position and therefore when the coupler C is presented to and engages with the front pin P the locking knuckle will retract then under the spring bias will re-extend to automatically lock the front pin P into position once the pin P has moved into the throat of the hook portion14.

It will be appreciated by those skilled in the art that the safety device is open to modification. For example the knuckle could be of a sliding construction rather than rotating. It could also have a pivoting action.

A further worthwhile modification is shown inFIGS. 21 to 24which illustrates how the lug30can be formed with a hook type profile (in cross section) which ensures that the centre line of the piston36remains in full contact with the lug30. This modification overcomes any possibility that the piston36can slide off the lug30especially when the lug30is towards the end of its movement as shown inFIG. 10.

FIGS. 21 and 22show a further modification that can be made to the locking device.FIG. 21shows the knuckle in the raised or retracted position whileFIG. 22shows the knuckle extended.

In the event that the bucket/attachment A is not latched correctly (or fails) at the primary locking mechanism (wedge) end and the bucket/attachment rotates and swings uncontrolled in the hock section14, the front bucket pin P will usually come into contact with the face of the knuckle21as the attachment/bucket swings pivotally in an arc. In such a situation the safety knuckle21carries out its required function of preventing unintentional release of the entire attachment/bucket from the coupler C.

However, with the more radial face shape as shown in the embodiment of for example,FIGS. 3,6and7, this contact between the pin P and the face of the knuckle21could tend to result in the contacting surfaces working like two meshing gears and roll the knuckle up into the retracted position and thereby enable the pin P to be released from the hook portion14. With the modified more angular face surface of the knuckle shown inFIGS. 21 and 22, this possibility of meshing/rolling is prevented and thereby overcomes any possibility of the knuckle being forced upwardly by the pin P.

The present invention thus provides a safety locking device which is operable independent of the hydraulics of the coupler/quick hitch. The safety locking device is of a fail safe construction and either via manual re-set or timing out of the circuitry controlling the solenoid44will always return to a position whereby it will automatically latch the front pin upon the front pin being inserted into the opening of the hook portion14of the quick hitch.

The present invention differs from other safety systems used with couplers in that with known safety systems the coupler engages with the front pin and the primary lock (e.g. sliding wedge) is engaged and following this the secondary or safety lock is operated. There is thus a period of time when the attachment is engaged with the coupler but the safety lock is not engaged. Thus there is a risk period before the engagement of the safety lock. With the present invention, however, the coupler engages with the front pin and the safety lock device immediately operates and does so before the primary lock (e.g. sliding wedge) is activated. Therefore, there is minimal time between the coupler C coming into engagement with the attachment before the safety lock device becoming effective.

This minimal time period also applies in the unlocking sequence.