WO2009083730A1

WO2009083730A1 - Improved quick hitch

Info

Publication number: WO2009083730A1
Application number: PCT/GB2008/004303
Authority: WO
Inventors: Anthony Joseph Bianchi
Original assignee: Quick Switch (Uk) Limited
Priority date: 2007-12-31
Filing date: 2008-12-31
Publication date: 2009-07-09
Also published as: GB0725354D0; GB2451304B; AU2008345445A1; GB2451304A

Abstract

A quick hitch (10) comprises a sensor (34), for example an inductive proximity switch, which is mounted on a bracket (36). The sensor (34) is positioned to detect the presence or absence of a safety pin or safety bar (38) of a quick hitch (10). The safety pin (38) is disposed directly behind a body portion of a jaw (30) of the quick hitch 10 and engages in apertures in the body portion (24) of the quick hitch (10). When the safety pin (38) is in position, a green indicator light (48) is illuminated. When the safety pin (38) is not in position, a red indicator light (50) is illuminated and a buzzer (46) sounds.

Description

IMPROVED QUICK HITCH

The present invention relates to an improved quick hitch and particularly to a quick hitch safety device for use with a mechanical arm, for example, an excavator arm.

BACKGROUND OF THE INVENTION

An excavator arm typically includes a boom, a dipper arm and a bucket, all powered by hydraulic rams. In use, an excavator operator may have to change a bucket or other tool attachment a number of times per day in order to optimise the productivity of the machine. In some cases, an operator may change a bucket on an excavator up to thirty times per day.

Most excavators are fitted with a quick hitch or coupler in order to speed up the process of changing a bucket. A standard bucket is usually attached to the end of the dipper arm using two spaced and parallel pins. A quick hitch is a system in which one of the pins is generally located in an open-mouthed substantially C-shaped aperture and the other pin is located in a similar C-shaped aperture, but is secured within the aperture by means of a movable jaw or catch. The C-shaped apertures are arranged such that when the first pin is located in the first aperture and the second pin is secured in the second aperture and the jaw closed, the bucket is securely held to the quick hitch.

In other arrangements, custom made pins, apertures and lugs may be provided to secure a bucket or other tool, but the principal of holding the bucket or tool to the quick hitch is the same, in that a movable jaw or catch secures a pin of the bucket or tool to the dipper arm.

Some quick hitch systems are operated manually, but the majority of quick hitches are semi-automatic or fully automatic. A manual arrangement requires an operator to open and close the jaw manually, or to open a spring operated latch using a lever. This involves the operator leaving the excavator cab and is relatively slow and inconvenient. A semi-automatic quick hitch generally includes a movable jaw, which is powered by a hydraulic ram. The ram can be operated from the cab of the excavator, but because the system relies on the hydraulics of the machine, a safety pin is inserted by hand, which locks the movable jaw in its closed position. The safety pin is also known as a "safety bar" and prevents the jaw from opening in the event of a hydraulic failure or operator error.

A fully automatic quick hitch is operated entirely from within the excavator cab and utilises a movable hydraulic jaw similar to that in a semi-automatic arrangement. However, an independent locking system for the hydraulic jaw is usually provided, which does not rely on hydraulic pressure. Furthermore, a visible indicator may be provided on the quick hitch, which indicates when the bucket or tool is secure. In one arrangement, a locking pin may protrude from the side of the quick hitch if it is not in a securely locked condition. The protruding pin can be seen from the cab of the excavator by the operator and serves as a warning that the bucket or other tool is not secure.

A multi-hitch, also known as a multi-pin grab (MPG) is a quick hitch, which can be connected to attachments with different pin centres. A reason for using a multi-hitch is that different manufacturers of attachments use different pin centres. A plant company may have a mixed fleet of attachments that can only be connected or picked up by a single hitch if it is a multi-hitch. Due to the variation in pin centres, the movable jaw does not come to rest in the same position when attaching tools with different pin centres and therefore the optimum position for insertion of the safety pin, immediately adjacent the jaw to block its path, changes. The safety pin on a multi- hitch is therefore positioned in one of a number of possible apertures in the body of the hitch, depending on the distance that the movable jaw moves. Typically there are 3 holes, the central axes of which are spaced apart.

It is an acknowledged problem of semi-automatic or fully automatic quick hitch arrangements that if the hydraulic jaw holding the bucket or tool accidentally retracts due to operator error or hydraulic failure, then the bucket or tool will fall from the dipper arm potentially causing a serious accident. In the last year approximately 13% of investigated excavator incidents in the UK have been caused by an excavator bucket detaching unexpectedly from a quick hitch and injuring or killing a ground worker. In the last year five ground workers have been killed due to the accidental release of a bucket from a semi-automatic quick hitch.

A reason for a semi-automatic quick hitch failing is the omission of an excavator operative to fit the safety pin. Reasons for this omission include the desire to speed up the changing of buckets, reluctance to insert the pin in bad weather because it is necessary to leave the excavator cab, or a misplaced pin. An operative may also incorrectly fit a safety pin.

It is an object of the invention to provide a safety device which reduces or substantially obviates the above mentioned problems.

SUMMARY OF THE INVENTION

According to the present invention there is provided a quick hitch for a mechanical arm, the quick hitch comprising a body portion having first and second tool-pin apertures therein which are in fixed spaced relationship and which have tool-pin receiving openings which face in different directions, at least one hydraulically actuated arm for closing or substantially closing a said tool-pin receiving opening of the second aperture so as to retain a respective tool-pin in the second aperture, a safety pin aperture provided in the body portion of the quick hitch, a safety pin which is locatable in the safety pin aperture for locking the at least one hydraulically actuated arm in an engaged position by blocking movement of the arm, a sensor for detecting the presence or absence of the safety pin in the engaged position, and alarm means connected to the sensor for indicating when an absence of the safety pin is detected.

The alarm means may be adapted to be positioned in close proximity to the operator of the mechanical arm. This may be, for example, in an excavator cab.

It is an advantage of the invention that the alarm can be fitted to a quick hitch and is triggered when the safety pin of the quick hitch hydraulic jaw is not inserted, or is not inserted properly, to retain the hydraulic jaw in the locked position. In other words, the operative of the mechanical arm, for example, of an excavator is warned when a bucket or other tool is not securely held to the mechanical arm. This will result in the operative seeking to secure the bucket or tool before continuing with further work and consequently accidents resulting from the unexpected release of buckets or tools from quick hitches can be substantially prevented.

The sensor may be an inductive proximity switch.

The alarm means may be an audible alarm and/or a light.

A green indicator light may be provided to indicate that the safety pin is present.

A red indicator light may be provided to indicate that the safety pin is absent.

The sensor may be connected to a quick hitch by means of a bracket.

A further sensor may be provided for detecting the presence or absence of a further safety pin, the further sensor being connected to the alarm means.

The alarm means may be adapted to be positioned proximate an operator of the quick hitch, enabling the operator to be warned by the alarm means.

A valve may be provided for diverting hydraulic flow away from control valves of an excavator, the valve being automatically operable after a pre-set time delay when an absence of the safety pin is detected.

The time delay may be adjustable. The time delay may be between 45 seconds and 2 minutes.

The time delay may be around 90 seconds.

The safety pin may be part of a safety pin arrangement including a first pin having a first length, a second pin having a second length shorter than the first length, and connection means, the connection means being connected to one end of each of the respective first and second pins and holding the first and second pins parallel to one another in spaced relationship.

The distance between central axes of the first and second pins may be adjustable.

According to a second aspect of the present invention there is provided a safety system for an excavator having a quick hitch, the safety system comprising at least one safety pin which is adapted to be located in a safety pin aperture of the quick hitch for locking an arm of the quick hitch in an engaged position, a sensor for detecting the presence or absence of the safety pin in the engaged position; a valve for diverting hydraulic flow away from control valves of the excavator, the valve being automatically operable after a pre-set time delay when an absence of the safety pin is detected.

The pre-set time delay may be adjustable and may be between 45 seconds and 2 minutes.

The pre-set time delay may be between 1 minute and 2 minutes. Preferably the preset time delay is 90 seconds.

It is an advantage of the invention that diverting the flow of hydraulic pressure, ie pilot pressure, away from the control valves of the excavator prevents operation of the excavator when the safety pin is not in place. This will result in the operative seeking to secure the bucket or tool before continuing with further work and consequently accidents resulting from the unexpected release of buckets or tools from quick hitches can be substantially prevented. The pre-set time delay is timed to be long enough to allow a tool change, without the excavator controls being inhibited.

An audible alarm may sound when an absence of the safety pin is detected.

An indicator light may illuminate when an absence of the safety pin is detected, which is preferably a red LED. The valve may automatically allow hydraulic flow to the control valves of the excavator when the safety pin is detected.

Advantageously, once the delay period has expired, as soon as the pin is re-inserted, the valve restores the pilot pressure to the control valves of the excavator.

According to a third aspect of the present invention there is provided a quick hitch for an excavator, the quick hitch comprising a body portion having first and second tool- pin apertures therein which are in fixed spaced relationship and which have tool-pin receiving openings which face in different directions, at least one arm for closing or substantially closing a said tool-pin receiving opening of the second aperture so as to retain a respective tool-pin in the second aperture, and a safety pin aperture; a safety pin which is locatable in the safety pin aperture for locking the at least one arm in an engaged position, a sensor for detecting the presence or absence of the safety pin in the engaged position; a valve for diverting flow away from control valves of the excavator, the valve being automatically operable after a pre-set time delay when an absence of the safety pin is detected.

The pre-set time delay may be between 45 seconds and 2 minutes.

The time delay may be between 1 minute and 2 minutes. Preferably the time delay is 90 seconds.

The time delay may be adjustable.

An audible alarm may sound when an absence of the safety pin is detected.

An indicator light may illuminate when an absence of the safety pin is detected, which may be a red LED.

The valve may automatically allow hydraulic flow to the control valves of the excavator when the safety pin is detected. According to a fourth aspect of the present invention there is provided a safety pin arrangement for a multi-hitch of a mechanical arm comprising a first pin having a first length, a second pin having a second length shorter than the first length, and connection means, the connection means being connected to one end of each of the respective first and second pins and holding the first and second pins parallel to one another in spaced relationship.

It is an advantage of the invention that when the first pin of the safety pin arrangement is located in an appropriate safety pin aperture of a multi-hitch, the second pin is located in an adjacent aperture. This means that only one sensor need be provided for both apertures. The second pin is effectively a "dummy" pin, which does not act to prevent movement of a hydraulic arm of a hitch, but rather serves to indicate the presence of another adjacent safety pin. When the first pin is located in the aperture where the sensor is located, the dummy pin serves no purpose.

The second length may be less than half of the length of the first length.

Advantageously the length of the second pin is long enough to be identified by the sensor, but is short enough to be clear of the movable jaw or locking arm.

The connection means may be a substantially flat plate and the first and second pins may extend perpendicularly therefrom.

One of the first and second pins may be fixed relative to the plate and the other of the pins may be movable relative to the plate.

The first pin may be fixed relative to the plate and the second pin may be movable relative to the plate.

An elongate slot may be provided in the plate and the second pin may be adjustably mounted to the plate through the elongate slot. The first pin may have a portion of reduced diameter partway along its length.

The diameter of the portion of reduced diameter may be reduced by around 2 mm.

According to a fifth aspect of the present invention there is provided a multi-hitch comprising at least one hydraulically actuated arm for engaging a pin of a tool, at least two safety pin apertures provided in the body portion of the multi-hitch, a safety pin arrangement according to the fourth aspect of the invention for locking the at least one hydraulically actuated arm in an engaged position in one of at least two positions, a sensor for detecting the presence or absence of the safety pin arrangement in the engaged position and an alarm means connected to the sensor for indicating when an absence of the safety pin is detected.

Three safety pin apertures may be provided in the body portion of the multi-hitch.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding of the present invention, and to show more clearly how it may be carried into effect, reference will now be made, by way of example, to the accompanying drawings, in which:

Figure 1 shows a schematic side view of a quick hitch arrangement;

Figure 2 shows a side view of a sensor and bracket of the quick hitch safety device of Figure 1;

Figure 3 shows a schematic circuit diagram of a circuit controlling the quick hitch safety device of Figure 1 ;

Figure 4 shows a schematic circuit diagram of a circuit controlling a quick hitch safety system;

Figure 5 shows a schematic side view of a multi-hitch arrangement; Figure 6 shows a cross-sectional view through a safety pin arrangement of the invention;

Figure 7 A shows a schematic plan view of a plate and first safety pin; and

Figure 7B shows a schematic exploded view of the second pin assembly.

DETAILED DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

Referring firstly to Figure 1, a quick hitch is indicated generally at 10. The quick hitch 10 is pivotally mounted on one side to the distal end of a dipper arm 12 of an excavator about a pivot 14. The other side of the quick hitch 10 is pivotally mounted to a connecting arm 20 about a pivot 22, which is itself pivotally connected to a hydraulic ram 16 about a pivot 18. The hydraulic ram 16 controls the movement of a bucket or other tool connected to the quick hitch 10.

The quick hitch 10 includes a body portion 24 including a first open-mouthed substantially C-shaped aperture 26 facing in one direction, ie to the left of the drawing as viewed, and a second open mouthed substantially C-shaped aperture 28 facing the bottom of the page, as viewed. In other words, the mouths of the apertures 26, 28 are substantially perpendicularly disposed relative to one-another. A movable jaw 30, shown partly in dotted outline, pivots about a pivot point 31 between a closed position, as viewed, in which the jaw 30 closes over the mouth of the aperture 28 and an open position (not shown) in which the jaw 30 is rotated away from the aperture 28, allowing the aperture to receive a pin of an excavator bucket or other tool. The jaw is powered by a hydraulic ram 32, shown in dotted outline.

A sensor 34, for example a proximity switch, is mounted on a bracket 36 and is positioned to detect the presence or absence of a safety pin or safety bar 38. The proximity switch can be a micro-switch, an inductive or a magnetic switch or any other switch type capable of detecting the presence or absence of the safety pin 38. The safety pin 38 is disposed directly behind a body portion of the jaw 30 and engages in apertures in the body portion 24 of the quick hitch 10. When the safety pin 38 is located in the apertures, as shown, it blocks the path of the jaw 30, which is prevented from opening. The bracket 36 and sensor 34 are also shown in Figure 2. A cable 40 extends from the sensor 34 back to the cab of the excavator. The bracket 36 is curved to accommodate the curvature of the periphery of the safety pin 38. The sensor 34 is mounted in an aperture through the bracket 36, and may be fastened to the bracket by means of a screw thread. The shape of the bracket and proximity of the sensor to the safety pin enable the sensor to detect the presence of absence of the safety pin 38.

Referring to Figure 3, an electrical circuit for use with the sensor 34 is indicated at 42. The circuit includes the sensor or inductive proximity switch 34, a five-pin relay 44, a buzzer 46, a green indicator light 48 and a red indicator light 50. The lights 48,50 are LED's. The switch 34 is an open type switch capable of sensing mild steel at a distance of 5mm. Mild steel is the material of the safety pin 38. The buzzer 46 and warning lights 48, 50 are mounted in the cab of the excavator. The circuit is powered by a 24 volt supply, indicated at 52, and the sensor 34 is protected by a 1 amp self- resetting thermal fuse 54. The relay 44 is protected by an inline fuse 56. The circuit may be powered by, for example, a 12 volt supply, or any other supply voltage depending on the excavator battery supply voltage.

In use, when a bucket or tool is secured to the quick hitch 10 and the jaw 30 is closed, the safety pin 38 is inserted causing the proximity switch 34 to close. This completes the circuit back to the relay 44. The coil in the relay 44 is energised and the contact moves to illuminate the green indicator light. In this condition, safe operation of the excavator can resume.

However, should the safety pin 38 be removed or simply not be inserted, the proximity switch 34 opens and the coil of the relay 44 is de-energised. This causes the contact to switch, causing the green indicator light 48 to be switched off and the red indicator light 50 to be illuminated. The buzzer 46 is also energised and sounds in the cab of the excavator. In this condition, operation of the excavator is unsafe and the operator is warned that the safety pin 38 should be inserted.

In the event that a short circuit to the proximity switch 34 occurs, then the thermal fuse 54 will cut the power to the coil of the relay 44. This is a fail safe and has the same effect as if the safety pin 38 is removed. The green indicator light is switched off and the red indicator light and buzzer are switched on. This indicates to the operator that a fault has occurred.

The circuit 42 is an example of a suitable circuit, but has the benefit of fail safe operation. It is envisaged that use of the safety device will substantially reduce or even eradicate accidents caused by operator error and hydraulic failure. The safety device can be utilised with semi-automatic and fully automatic quick hitch devices.

Referring now to Figure 4, an alternative electrical circuit for use with the sensor 34 is indicated at 62. The circuit includes the sensor or inductive proximity switch 34, a five-pin relay 64, a buzzer 66, a green indicator light 68 and a red indicator light 70. The lights 68, 70 are LED's. The switch 34 is an open type switch capable of sensing mild steel at a distance of 5mm. Mild steel is the preferred material of the safety pin 38. The buzzer 66 and warning lights 68, 70 are mounted in the cab of the excavator. The circuit is powered by a 24 volt supply, indicated at 72, and the sensor 34 is protected by a 1 amp thermal fuse 74. If a short circuit to the proximity switch 34 occurs, the current is passed through a yellow LED 75, also mounted in the cab of the excavator, which indicates a fault in the circuit. Optionally the circuit may be powered by, for example, a 12 volt supply, or any other supply voltage depending on the excavator battery supply voltage.

The buzzer 66 and red LED 70 are connected to one of the outputs of the relay 64 and are also connected to a time relay 76, the time setting of which can be adjusted. Another output of the relay 64 is connected to the green LED 68. The output of the timer relay 76 is connected to the solenoid of a hydraulic valve 78. The valve is positioned between the hydraulic pump 80 of the excavator and the cab controls 82. In one position, the valve allows the supply of pilot pressure to the cab controls 82 of the excavator, but in an alternative position, the valve diverts pilot pressure away from the controls of the excavator and dumps the flow to the hydraulic oil tank 84 of the excavator. The valve is typically protected by a 10 amp thermal fuse.

An ignition switch 71 and starter motor 73 of the excavator are connected to the circuit 62 between the sensor 34 and the relay 64. Therefore in order for power to reach the ignition from the battery 72, the sensor 34 (proximity switch) must be closed. This means that the engine of the excavator cannot be started unless the safety pin 38 is in place and is detected by the sensor 34. This additional safety feature also provides extra security, because if an operator removes the safety pin 38 at night, or when leaving the machine unattended, the machine is immobilised.

An over-ride switch 86 is provided between the power supply 72 and the relay 64 to by-pass the proximity switch 34, thermal fuse 74 and yellow LED 75. The rest condition of the switch 86 is open and the switch 86 is only operated, when the sensor 34 is faulty or essential manoeuvres of the excavator cannot be carried out due to pilot pressure being diverted away from the controls 82 by the valve 78, or power is cut to the ignition.

In use, when a bucket or tool is secured to the quick hitch 10 and the jaw 30 is closed in normal operation, the safety pin 38 is inserted and the proximity switch 34 is closed. This completes the circuit back to the relay 64 and the contact of the relay 64 completes the circuit to the green LED 68, ie the green indicator light illuminates showing that the quick hitch is closed and secured and the excavator can be operated safely.

When a tool of the excavator is changed, the quick hitch is lowered to ground and the operator manually removes the safety pin 38. This causes the proximity switch 34 to open and the coil of the relay 64 is de-energised. This causes the contact to switch, causing the green indicator light 68 to be switched off, the red indicator light 70 to be illuminated, the buzzer 66 is to sound in the cab of the excavator and the timer 76 to be energised.

The timer relay 76 is set to switch after a duration of, for example 90 seconds, has expired. This time should be long enough for the excavator operative to return to the cab, operate the excavator controls to release the tool from the quick hitch, engage a new tool and return the new tool to ground, where the safety pin 38 can be re-inserted.

If, for some reason, the safety pin is not inserted, or is inserted incorrectly and is not detected by the sensor 34 by the time the timer relay delay has expired, then the diverter valve 78 is activated, causing pilot pressure to be diverted away from the cab control levers 82 of the excavator and dumping it back to the tank 84. In this condition, operation of the excavator is prevented.

In order to return pilot pressure to the excavator controls 82, either the safety pin 38 has to be reinserted and be detected by the sensor 34, causing the circuit to switch the relay 64 and hence the timer relay 76 and valve 78, or the over-ride switch 86 has to be operated, thus by-passing the sensor 34 and switching the relay 64. The over-ride switch should not be required during normal operation of the excavator.

The circuit 62 is another example of a suitable circuit, and has the benefit of fail safe operation, because the relay 64 switches to activate the time relay when power to the relay 64 is interrupted. It is envisaged that use of the safety device will substantially reduce or even eradicate accidents caused by operator error and hydraulic failure. The safety device can be utilised with any quick hitch device 10, where a safety pin is utilised, and provides a combined warning and cut-out device. Different excavators utilise different pilot control systems, but the principle of cutting pilot pressure to the controls of the excavator is the same for all makes of machine.

Referring now to Figure 5, an alternative quick hitch is indicated generally at 110. The quick hitch 110 is also a multi-hitch as previously described and is pivotally mounted on one side to the distal end of a dipper arm 112 of an excavator about a pivot 114. The other side of the quick hitch 110 is pivotally mounted to a connecting arm 120 about a pivot 122, which is itself pivotally connected to a hydraulic ram. The hydraulic ram controls the movement of a bucket or other tool connected to the quick hitch 110.

The quick hitch 110 includes a body portion 124 including a first open-mouthed substantially C-shaped aperture 126 facing in one direction, ie to the left of the drawing as viewed, and a second open mouthed substantially C-shaped aperture 128 facing the bottom of the page, as viewed. In other words, the mouths of the apertures 126, 128 are substantially perpendicularly disposed relative to one-another. A movable jaw 130, shown partly in dotted outline, pivots about a pivot point 131 between a closed position, as viewed, in which the hooked tip 116 of the jaw 130 closes over the mouth of the aperture 128 and an open position (not shown) in which the jaw 130 is rotated away from the aperture 128, allowing the aperture to receive a pin of an excavator bucket or other tool. The jaw is powered by a hydraulic ram 132, shown in dotted outline.

Three apertures 134, 136, 138 are provided through the body portion 124 of the quick- hitch 110 for receiving a safety pin as described in further detail below for locking the jaw 10 in a closed position. The jaw 130 is opened and closed by means of the hydraulic ram 132 and comes to rest in different positions depending on the distance between the attachment pins of a tool. For example, one pin of the tool is located in the base of the aperture 126, but the other pin may be positioned at any lateral position in the base of the aperture 128, depending on the pin centres of the tool. Apertures are also provided through the jaw 130 for receiving the safety pin and the apertures align with at least one of the respective apertures, 134, 136, 138 depending on where the jaw comes to rest. For example, as shown in Figure 1, the safety pin should be positioned in the first aperture 134 to most effectively prevent opening movement of the jaw 130. In other arrangements, the jaw 130 may not be apertured, but the safety pin may bear against the back of the jaw to prevent the jaw from opening. In some arrangements, the jaw 130 extends above the pivot 131 and in this case, the safety pin may bear against the front of the jaw above the pivot 131 to prevent the jaw from opening, ie in a clockwise direction about the pivot 131, as viewed.

A sensor 140, for example a proximity switch, is mounted on a bracket 142 and is positioned to detect the presence or absence of a safety pin or safety bar in the aperture 136. The proximity switch can be a micro-switch, an inductive or a magnetic switch or any other switch type capable of detecting the presence or absence of the safety pin. When the safety pin is located in the aperture 136, it blocks the path of the jaw 130, which is prevented from opening.

Referring to Figure 6, a safety pin arrangement is indicated at 150. The safety pin arrangement 150 includes a first safety pin 152 and a second dummy pin 154. The pins 152, 154 are mounted to a connecting plate 156 and are arranged spaced apart and parallel with one another. The pins 152,154 are the same diameter, but the second pin 154 is shorter than the first pin 152. This enables it to be inserted in one of the apertures 134, 136, 138 and not impede movement of the jaw 130. The first pin has a portion of reduced diameter 151, part-way along the pin 152, and substantially beginning at the position where the second pin terminates. An aperture 153 is also provided through the diameter of the pin 152 at its end, for receiving a spring clip or split pin. The first pin 152 is permanently attached to the plate for example by welding and the second pin is adjustably mounted to the plate 156 by means of a locking cap 158 and cap screw 160. Referring also to Figures 7 A and 7B, an elongate aperture 162 is provided through the plate, the longitudinal axis of the aperture 162 being aligned with the central axis of the pin 152.

A threaded bore 164 is provided in one end of the second pin 154 which is adapted to receive the threaded cap screw 160. The locking cap 158 is apertured to receive the head and shaft of the cap screw 160 and has a portion 168 of large diameter and a stepped down portion 170 of reduced diameter, which is adapted to slide in the elongate slot 162 of the plate 156. When assembled, as shown in Figure 6, the pin 154 sits on one side of the plate, the same side as the pin 152, and the locking cap 158 and cap screw 160 secure the pin 154 to the plate 156 from the other side. When tightened, the cap screw 160 does not rigidly connect the locking cap 158 and the pin 154 to the plate 156, but the locking cap 158 is able to slide freely within the elongate slot 162. In other words, the tolerance between the locking cap 158 and elongate slot is tight enough to hold the pin 154 securely to the plate 156, but loose enough to allow adjustment of the position of the pin 154.

In use, when a bucket or other tool is secured to the quick hitch 110 and the jaw 130 is closed, the pins 152,154 of the safety pin arrangement 150 are inserted in two adjacent apertures of the hitch. The pin 152 is inserted in the appropriate aperture to prevent undesired movement of the jaw 130 and at least one of the pins 152, 154 enters the central aperture 136 of the hitch body 124, and thus is detected by the sensor 142. In this condition, safe operation of the excavator can resume. If for some reason, the pins should start to move back out of their respective apertures, then when the step down in diameter of the pin 152 to the reduced diameter portion 151 moves past the sensor, this change in diameter is detected and the machine alarm sounds. This warns the operator to stop operating the machine and check the location of the safety pin arrangement 150. The size of the pins 152, 154 and the distance between the apertures 134, 136 and 138 depends on the size of the multi-hitch. In a typical example for use on an excavator, the first pin 152 is between 400mm and 500mm long and the second dummy pin is between 120mm and 150mm long. The diameter of the pins is typically between 20mm and 70mm. The space between the peripheries of the first and second apertures 134, 136 is typically around 9mm and the space between the peripheries of the second and third apertures 136, 138 is typically around 13mm. Therefore in this example, adjustment of at least 4mm is required on the plate 156.

In use, if neither the first pin 152 nor the second pin 154 is detected by the sensor 142, then an alarm is activated. In this condition, operation of the excavator is unsafe and the operator is warned that a safety pin should be inserted.

It is envisaged that use of the safety pin arrangement 150 will substantially reduce or even eradicate accidents caused by operator error and hydraulic failure with multi- hitches. The arrangement 150 provides for the use of a single sensor to monitor the presence or absence of a safety pin in three separate apertures.

It is understood that variations may be made in the foregoing without departing from the scope of the invention. For example, the elements and teachings of the various illustrative embodiments may be combined in whole or in part in some or all of the illustrative embodiments. In addition, one or more of the elements and teachings of the various illustrative embodiments may be omitted, at least in part, and/or combined, at least in part, with one or more of the other elements and teachings of the various illustrative embodiments.

Although illustrative embodiments of the invention have been shown and described, a wide range of modification, changes and substitution is contemplated in the foregoing disclosure. In some instances, some features of the invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the invention.

Claims

1. A quick hitch for a mechanical arm, the quick hitch comprising a body portion having first and second tool-pin apertures therein which are in fixed spaced relationship and which have tool-pin receiving openings which face in different directions, at least one hydraulically actuated arm for closing or substantially closing a said tool-pin receiving opening of the second aperture so as to retain a respective tool- pin in the second aperture, a safety pin aperture provided in the body portion of the quick hitch, a safety pin which is locatable in the safety pin aperture for locking the at least one hydraulically actuated arm in an engaged position by blocking movement of the arm, a sensor for detecting the presence or absence of the safety pin in the engaged position, and alarm means connected to the sensor for indicating when an absence of the safety pin is detected.

2. A quick hitch as claimed in claim 1, in which the sensor is an inductive proximity switch.

3. A quick hitch as claimed in claim 1 or claim 2, in which the alarm means is an audible alarm.

4. A quick hitch as claimed in any preceding claim, in which the alarm means is a light.

5. A quick hitch as claimed in any preceding claim, in which a green indicator light is provided to indicate that the safety pin is present.

6. A quick hitch as claimed in any preceding claim, in which a red indicator light is provided to indicate that the safety pin is absent.

7. A quick hitch as claimed in any preceding claim, in which the sensor is adapted to be connected to a quick hitch by means of a bracket.

8. A quick hitch as claimed in any preceding claim, in which a further sensor is provided for detecting the presence or absence of a further safety pin, the further sensor being connected to the alarm means.

9. A quick hitch as claimed in any preceding claim, in which the tool is an excavator bucket.

10. A quick hitch as claimed in any preceding claim, in which a valve is provided for diverting hydraulic flow away from control valves of an excavator, the valve being automatically operable after a pre-set time delay when an absence of the safety pin is detected.

11. A quick hitch as claimed in claim 10, in which in which the time delay is adjustable.

12. A quick hitch as claimed in claim 10, in which the time delay is between 45 seconds and 2 minutes.

13. A quick hitch as claimed in any one of claim 10 or claim 12, in which the time delay is 90 seconds.

14. A quick hitch as claimed in any preceding claim, in which the safety pin is part of a safety pin arrangement including a first pin having a first length, a second pin having a second length shorter than the first length, and connection means, the connection means being connected to one end of each of the respective first and second pins and holding the first and second pins parallel to one another in spaced relationship.

15. A quick hitch as claimed in claim 10, in which the distance between central axes of the first and second pins is adjustable.