GB2466646A

GB2466646A - Safety System for a Quick Hitch Coupler

Info

Publication number: GB2466646A
Application number: GB0823666A
Authority: GB
Inventors: Anthony Joseph Bianchi
Original assignee: QUICK SWITCH
Current assignee: QUICK SWITCH
Priority date: 2008-12-31
Filing date: 2008-12-31
Publication date: 2010-07-07
Also published as: GB0823666D0

Abstract

A quick hitch safety device 10 comprises a sensor 34, preferably an inductive proximity switch, 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 coupler 10 used to couple an attachment tool to an excavator arm. 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 not in position, a valve diverts the flow of hydraulic pressure away from the control valves of the excavator to immobilise the machine. The valve operates after a time delay following the detection that the safety pin is absent, where the time delay is long enough to allow a tool change without the excavator controls being inhibited.

Description

Safety System for an Excavator The present invention relates to a safety system and particularly to a safety system for use with a quick hitch of a mechanical arm an excavator.

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 arid 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.

It is an acknowledged problem of semi-automatic and 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 injuling 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 system for an excavator which reduces or substantially obviates the above mentioned problems.

According to a first aspect of the present invention there is provided a safety system for an excavator having a quick bitch, 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.

Preferably the pre-set time delay is between 1 minute and 2 minutes and more preferably the pre-set 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.

Preferably an audible alarm sounds when an absence of the safety pin is detected.

Preferably an in indicator light illuminates when an absence of the safety pin is detected, which is preferably a red LED.

Preferably the valve automatically allows 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 second 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.

Further preferred features are described in dependent claims 11 to 18.

For a better understanding of the present invention, and to show more clearly how it may be earned 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; and Figure 3 shows a schematic circuit diagram of a circuit controlling a quick hitch safety system.

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. In alternative affangements, the pin 38 may extend through an aperture in the jaw 30 or may abut the jaw 30 in a different position, depending on the shape of the jaw.

The bracket 36 and sensor 34 are also shown in Figure 2. A cable 40 extends from the sensor 34 hack 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, 150 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 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 thermal fuse 54. If a short circuit to the proximity switch 34 occurs, the current is passed through a yellow LED 55, 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 46 and red LED 50 are connected to one of the outputs of the relay 44 and are also connected to a time relay 56, the time setting of which can be adjusted.

Another output of the relay 44 is connected to the green LED 48. The output of the timer relay 56 is connected to the solenoid of a hydraulic valve 58. The valve is positioned between the hydraulic pump 60 of the excavator and the cab controls 62.

In one position, the valve allows the supply of pilot pressure to the cab controls 62 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 64 of the excavator. The valve is typically protected by a 10 amp thermal fuse.

An ignition switch 51 and starter motor 53 of the excavator are connected to the circuit 42 between the sensor 34 and the relay 44. Therefore in order for power to reach the ignition from the battery 52, the sensor 34 (proximity switch) must he 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 66 is provided between the power supply 52 and the relay 44 to by-pass the proximity switch 34, thermal fuse 54 and yellow LED 55. The rest condition of the this switch 66 is open and the switch 66 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 62 by the valve 58, 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 44 and the contact of the relay 44 completes the circuit to the green LED 48, 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 44 is de-energised. This causes the contact to switch, causing the green indicator light 48 to be switched off, the red indicator light 50 to be illuminated, the buzzer 46 is to sound in the cab of the excavator and the timer 56 to be energised.

The timer relay 56 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 58 is activated, causing pilot pressure to be diverted away from the cab control levers 62 of the excavator and dumping it back to the tank 64. In this condition, operation of the excavator is prevented.

In order to return pilot pressure to the excavator controls 62, either the safety pin 38 has to he reinserted and he detected by the sensor 34, causing the circuit to switch the relay 44 and hence the timer relay 56 and valve 58, or the over-ride switch 66 has to be operated, thus by-passing the sensor 34 and switching the relay 44. The over-ride switch should not be required during normal operation of the excavator.

The circuit 42 is an example of a suitable circuit, and has the benefit of fail safe operation, because the relay 44 switches to activate the time relay when power to the relay 44 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 he 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.

Claims

CLAIMS1. 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 time delay when an absence of the safety pin is detected.
2. A safety system as claimed in claim 1, in which the time delay is adjustable.
3. A safety system as claimed in claim 1, in which the time delay is between 45 seconds and 2 minutes.
4. A safety system as claimed in claim I or claim 3, in which the time delay is between 1 minute and 2 minutes.
5. A safety system as claimed in any one of claims 1, 3 and 4, in which the time delay is 90 seconds.
6. A safety system as claimed in any preceding claim, in which an audible alarm sounds when an absence of the safety pin is detected.
7. A safety system as claimed in any preceding claim, in which an in indicator light illuminates when an absence of the safety pin is detected.
8. A safety system as claimed in claim 7, in which the indicator light is a red LED.
9. A safety system as claimed in any preceding claim in which the valve automatically allows hydraulic flow to the control valves of the excavator when the safety pin is detected.
10. 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 provided directly or substantially directly behind the arm; 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 time delay when an absence of the safety pin is detected.
11. A quick hitch as claimed in claim 10, in which the time delay is between 45 seconds and 2 minutes.
12. A quick hitch as claimed in claim 10 or claim 11, in which the time delay is between 1 minute and 2 minutes.
13. A quick hitch as claimed in any one of claims 10 to 12, in which the time delay is 90 seconds.
14. A quick hitch as claimed in claim 10, in which the time delay is adjustable.
15. A quick hitch as claimed in any one of claims 10 to 14, in which an audible alarm sounds when an absence of the safety pin is detected.
16. A quick hitch as claimed in any one of claims 10 to 15, in which an in indicator light illuminates when an absence of the safety pin is detected.
17. A quick hitch as claimed in claim 16, in which the indicator light is a red LED.
18. A quick hitch as claimed in any preceding claim in which the valve automatically allows hydraulic flow to the control valves of the excavator when the safety pin is detected.
19. A safety system for an excavator substantially as described herein with reference to and as illustrated in Figures 1 to 3 of the accompanying drawings.
20. A quick hitch for an excavator substantially as described herein with reference to and as illustrated in Figures 1 to 3 of the accompanying drawings.