GB2442700A

GB2442700A - Safety device for power take off shaft

Info

Publication number: GB2442700A
Application number: GB0620146A
Authority: GB
Inventors: James Fox
Original assignee: Individual
Current assignee: Individual
Priority date: 2006-10-11
Filing date: 2006-10-11
Publication date: 2008-04-16
Also published as: GB0620146D0

Abstract

The present invention relates to a safety device 2 for a power take off (PTO) shaft 8. The safety device 2 comprises a safety mechanism and control means 26. The safety mechanism is arranged to decelerate rotation of the PTO shaft 8 by isolating the power to the PTO shaft 8 and/or operating a brake 30 to stop the rotation of PTO shaft 8. The control means 26 is preferably a cable which extends adjacent to the PTO shaft 8, and can be pulled to activate the safety mechanism in an emergency to stop the rotation of the PTO shaft 8. The cord is preferably connected to the safety mechanism by a plug and socket construction.

Description

Safety Device This invention relates to a power take off safety device.

The invention relates to a power take off safety device more particularly but not exclusively for decelerating the rotation of the power take off.

A power take off (PTO) is a splined drive shaft, usually on a tractor or truck that can be used to provide power to an attachment or separate machine.

Generally, the PTO has rotating portions which rotate in a clockwise direction at between approximately 540 and 1000 rpm when in use.

The PTO, along with its associated shafts and universal joints, are a common cause of accidents and injury in farming and industry. If a piece of clothing, hair or body part of a person comes into contact the PTO when it is rotating it can become entangled with the PTO and may become wrapped around it. Typically, this results in injury, the loss of a limb or death.

Some PTOs are fitted with guards or shields to cover their rotating portions. Generally, these shields cover the majority of the of PlO shaft, in some instances up to 97%. However, the shields are subject to wear and tear and may also malfunction. In some cases the shields become entangled with the rotating PTO shaft. In other instances, the shields are broken exposing the PTO shaft. In both cases the PTO itself becomes a safety hazard.

In some instances a power cut off switch is fitted to an attachment or machinery which enables the power supply to the PTO shaft to be cut off.

However, such a switch is positioned such that it may not be possible for the user to reach the switch in an emergency. Alternatively, following an accident, the user may not have the strength to activate the switch or the switch may not be in the user's eye line to allow the user to locate it in order to turn off the power supply to the PTO shaft. For example, if the user, the use's clothing or hair is partially entangled with the PTO shaft his movement may be restricted. Also, if the user manages to reach to activate such a switch, the PlO shaft may not reduce its speed sufficiently quickly to avert additional damage or injury to the user. For example, the user may struggle to reach the switch and delay activating it.

In accordance with a first aspect of the invention, there is provided a safety device for a power take off (PTO) shaft, comprising: a safety mechanism arranged to decelerate rotation of the PTO shaft; a control means arranged to activate the safety mechanism to decelerate rotation of the PlO shaft, the control means being arranged to extend adjacent to a rotatable portion of the PTO shaft.

The control means is positioned in close proximity to the rotatable portion of the PTO shaft so that it is easily accessible to a user. This enables the user to manually activate the safety mechanism to decelerate and stop the rotation of the PTO shaft. For example, if the user becomes entangled with the PlO shaft and is restrained from moving the user can still reach the control means to stop the rotation of the PTO shaft.

A high proportion of agricultural accidents are associated with incidents involving PTO shafts. Therefore, it may be possible to reduce such accidents and obtain reduced insurance premiums by having such a safety device fitted.

Preferably, the control means is spaced apart from an outer surface of the rotatable portion of the PTO shaft.

Preferably, the control means is parallel to an outer surface of the rotatable portion of the PTO shaft.

Preferably, the safety mechanism comprises power connection means to enable disconnection of a power supply driving the rotation of the PTO shaft.

Preferably, the power connection means enables connection of the power supply driving rotation of the PTO shaft.

Alternatively or additionally, the safety mechanism comprises a braking means for decelerating the rotation of the PTO shaft by frictional force.

The braking means enables the rotation of the PTO shaft to be stopped more quickly and efficiently. This reduces the risk of the user become entangled or further entangled with the PTO shaft.

Preferably, the braking means is engagable with the PTO shaft.

Alternatively or additionally, the braking means is engagable with a drive means for the PTO shaft.

Alternatively or additionally, the safety mechanism comprises an engine override control arranged to cut off the engine of a vehicle to which the PTO shaft is connected.

The engine override control can cuts off the engine allowing the victim to attract attention to get assistance without being impeded by engine noise.

For example, the victim can have a mobile telephone conversation or call for help by shouting. Even the engine cutting off may in itself attract attention. If the vehicle is moving, this engine override control will cause the speed of the vehicle to reduce until it stops, preventing a victim from getting trapped under the wheels or body of the vehicle.

Preferably, the control means comprises a cord connected to the power connection means, the cord being displaceable between a first position where the power connection means connects the power supply to the PTO shaft and a second position where the power connection means disconnects the power supply from the PTO shaft.

Preferably, the cord is suspended a height above the outer surface of the P10 shaft and along the length of the PTO shaft.

The cord is suspended a height above the P10 shaft to allow for clearance. This clearance is necessary so that cord does not become entangled with PTO shaft or PTO shaft shield, even when the vehicle and attached machinery is on an uneven surface or turning a corner where sagging of the cord can occur. In general, the cord will sag around 5 centimetres when the vehicle and attached machinery are turning a corner. Therefore, the cord will not touch the PTO shaft or PlO shield even if it sags.

Preferably, the power connection means comprises a plug and a socket.

Preferably, the socket is fixed to the vehicle to which the PTO shaft is connected.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a first embodiment of a safety device according to a first aspect of the present invention and a PTO shaft coupled between a vehicle and attached machinery, and Figure 2 is a block diagram of a first embodiment of a control system according to a second aspect of the present invention for a vehicle and attached machinery.

Referring to the drawings, Figure 1 shows a safety device 2, a rear of a vehicle 4, attached machinery 6, a P10 shaft 8 and a P10 shield assembly 10.

The P10 shaft 8 couples at one end to the rear of the vehicle 4 and at its other end to the attached machinery 6. For example, the vehicle 4 can be a tractor and the machinery 6 can be farm machinery, such as a vacuum tanker.

The P10 shield assembly 10 surrounds a substantial portion of the length of the PTO shaft 8. The PTO shield assembly 10 has a vehicle P10 shield 12 attached to the rear of the vehicle 4, a machinery PTO shield 14 attached to the machinery 6 and a shaft PT0 shield 16. The shaft PTO shield 16 is cylindrical in shape with outwardly tapering frusto-conical end portions 18, 20. The shaft PT0 shield 16 is mounted coaxially with and surrounds a central portion of the P10 shaft 8. Respective end portions 18, 20 locate in the vehicle PT0 shield 12 and the machinery PTO shield 14 when in use.

The safety device 2 comprises a socket 22, a plug 24, a cord 26 and a cord mounting 28. The socket 22 is mounted on the rear of the vehicle 4.

The plug 24 locates in the socket 22. For example, the plug 24 can be secured in the socket 22 by a releasably engagable friction fit mechanism.

The cord mounting 28 is attached to the machinery 6. The cord 26 is attached to the plug 24 at one end and mounted in the cord mounting 28 at its other end. Thus, the cord 26 is suspended above and parallel to the PlO shaft 8 such that it is spaced from the PTO shaft, for example by between 7 and 20 centimetres above the outer surface of the PTO shield assembly 10 when the vehicle 4 and machinery 6 are on level ground. It will be appreciated that if there is no PTO shield assembly 10 present, the cord 22 can be suspended a suitable height above the outer surface of the PTO shaft 8.

The cord 26 comprises a suitable material, such as plastics or rubber, and is initially sagging in order that it can withstand wear and tear and shear forces if it is stretched out due to the vehicle 4 and machinery 6 traversing an uneven surface, for example. When traversing an uneven surface the socket 22 and cord mounting 28 can be at different levels above the surface due to the vehicle 4 and machinery 6 being on different surface levels. Thus, the distance between the mounting positions of the socket 22 and the cord mounting 28 is greater than the distance between them when the vehicle 4 and machinery 6 are on level ground. When sufficient pressure is applied to the cord 26, the plug 24 is disconnected from the socket 22.

The cord 26 includes an electric cable carrying a voltage, typically 12 Volts. The cord 26 may be earthed back to the machinery 6 or vehicle 4.

Therefore, if the cord 26 is touched by a user and it is faulty giving the victim an electric shock, such a shock is unlikely to injure the victim.

The plug 24 and socket 22 can be any conventional male and female connection paring. Typically, the plug 24 and the socket 22 engage frictionally and are usually shaped complimentary to each other. The plug 24 and socket 22 complete a power supply circuit when connected and the circuit is broken when they are disconnected.

Alternatively, it will be appreciated that the connection or disconnection of the plug 24 and socket 22 changes the state of a control signal by operating any suitable switching means. It will be appreciated that any other suitable switching means or fuse mechanism can be used in place of the plug 24 and socket 22.

The disconnection of the plug 24 from the socket 22 can change the state of the control signal to causing the power driving the PTO shaft 8 to be cut off. The PTO shaft 8 will stop rotating, for example, within a couple of seconds.

It wiN be appreciated that an emergency braking system 30 can be arranged to engage the PTO shaft 8 or its associated drive members 32 to cause the rotation of the PTO shaft 8 to decrease more rapidly by frictional force when the emergency braking system 30 engages the PTO shaft 8.

The emergency braking system 30 is activated by the safety device 2.

In addition, the safety device 2 can be connected to the vehicle engine controls to cause the power to the vehicle engine to be cut off and stop the vehicle 4. If the vehicle 4 is moving, it will come to halt. Similarly, the safety device 2 can activate the vehicle wheel brakes to cause the vehicle 4 to decelerate.

If the safety device 2 is connected to the vehicle engine controls, manual override of the safety device 2 can be allowed by driver intervention. This enables the driver to control the vehicle engine and brakes so that the driver, once alerted to the activation of the safety device 2, can manoeuvre the vehicle 4 into a different position or away from the victim and apply the brakes more vigorously, as required.

An alternative embodiment of the invention does not incorporate a means for allowing manual override by the driver so that he cannot resume control of the vehicle engine and brakes. This ensures that the vehicle 4 comes to a halt. For example, if the driver of the vehicle 4 is not immediately alerted to the activation of the safety device 2, due to natural reaction times for example, he may not be aware of any incident for a short period.

It will be appreciated that an alarm may be fitted in the cabin to alert the driver to the activation of the safety device 2.

If the PTO shaft 8 is disconnected from the machinery 6 and the safety device 2 is disconnected, the vehicle engine can be started. In this case the PTO shaft 8 is not rotating and the safety device 2 is redundant.

If the PTO shaft 8 is connected to the machinery 6 and the safety device 2 is disconnected, the vehicle engine cannot be started. In this case the PTO shaft 8 is required to rotate to drive the machinery 6 and the safety device 2 is required to stop the rotation of the PTO shaft 8 in an emergency.

There is a cabin switch operable by the driver of the vehicle enables power to the PTO shaft 8 to be activated or deactivated as required. If the power to the PTO shaft 8 is deactivated then the safety device 2 is redundant and the engine can be started irrespective of whether the safety device 2 is connected.

In use, when the PTO shaft 8 is rotating the safety device 2 is always connected as shown in Figure 1. A control signal is controlled by the safety device to ensure that the P10 shaft 8 can only rotate when the safety device is connected. In the event that a user comes into close proximity of the rotating PlO shaft 8 and becomes entangled with the PTO shaft 8, the user can grip the cord 26 and pull it downward.

This force on the cord will pull on the plug 24 causing it to disconnect from the socket 22. The disconnection of the plug 24 and socket 22 changes the state of the control signal causing the power to the PlO shaft 8 to be cut off and the engine to be cut off and the emergency braking system 30 for the PTO shaft 8 to be activated. This causes a decrease in the rotational speed of the PTO shaft 8 which will stop rotating after a short period of time. Thus the user does not become entangled or further entangled with the PTO shaft 8.

The same control signal may also control the operation of the engine of the vehicle 4. When the plug 24 is disconnected from the socket 22, the control signal switches the engine off and the wheel brakes of the vehicle 4 may also be activated, If the vehicle 4 is in motion, it will come to a halt so that the user can avoid being run over by the vehicle 4 while entangled with the PTO shaft 8.

Referring now to Figure 2, a vehicle 100 is attached to machinery 102.

The vehicle 100 comprises a PTO control circuit 104, an engine 106 driving a PTO clutch 108, a PTO brake 110 and a PTO shaft 112.

An output shaft 114 of the PTO clutch 108 is coupled to the PTO shaft 112. The output shaft 114 drives the PTO shaft 112 when the PTO clutch 108 is engaged. The PTO shaft 112 is connected to the machinery 102, via a coupler 116, to drive the machinery 102.

The PTO brake 110 is arranged to engage the output shaft 114 to inhibit rotational motion of the output shaft 114. This in turn causes the rotational speed of the PTO shaft 112 to decrease.

The P10 control circuit 104 has various inputs including inputs from a PTO cabin switch 118 and a safety device switch 120. The PTO cabin switch 118 is mounted in the vehicle cabin and is operable by the driver.

The safety device switch 120 is on when the safety device is enabled and a user can turn the safety device switch 120 off, for example in an emergency situation. The means for switching the safety device switch 120 is located in close proximity to the P10 shaft 112 so that the user can switch the safety device switch 120 off, if required, for example in an emergency situation.

The control circuit 104 has various outputs to control various components of the vehicle 100. These outputs include a PTO brake output 122, a PTO clutch output 124 and an engine output 126. The PTO brake output 122 and PTO clutch output 124 are connected to control valves 128,130 which control the PTO brake 110 and P10 clutch 108 respectively. The engine output 126 provides a control signal to the vehicle engine 106 to switch it off. It will be appreciated that the engine output 126 may also activate the vehicle wheel brakes.

Table 1 below shows various states of vehicle engine 106 and PTO shaft 112 which are controlled by the safety device switch 120 and cabin switch 118.

Safety device Cabin switch for Vehicle engine PTO shaft switch the PTO shaft ON ON Enabled ON ON OFF Enabled OFF OFF ON Disabled OFF OFF OFF Enabled OFF If the cabin switch 118 is "on", the state of the PTO shaft 112 is controlled by the safety device. If the cabin switch 118 is "off', the PTO shaft 112 is "off'.

When the safety device switch 120 is "on" the safety device is activated and the engine 106 can be started by the driver at any time. However, if the safety device switch 120 is "off" the safety device is deactivated and the engine 106 can only be started if the cabin switch 118 is off also meaning that the PTO shaft 112 is off. In this case, the safety device need not be activated since it is not required when the PTO shaft 112 is not rotating.

In use, the safety device switch 120 and the cabin switch 118 are both "on". The safety device is enabled as is the engine 106 and the driver can start the engine. With the engine 106 started, the PTO clutch 108 is engaged and the output shaft 114 rotates. The output shaft 114 in turn rotates the P10 shaft 112 to drive the machinery 102.

While the safety device is enabled, if the safety device switch 120 is turned "off' the PTO clutch 108 disengages causing the output shaft 114 to stop rotating. Consequently, the PTO shaft 112 stops rotating since it is driven by the output shaft 114. The PTO brake 110 engages the output shaft 114. The rotational motion of the PTO shaft 112 can be stopped, if the PTO shaft 112 is still engaged with the PTO clutch 108. The PTO shaft 112 and PTO clutch 108 may be engaged if they are beginning to disengage or if they fail to disengage. Alternatively, it will be appreciated that the PTO brake 110 may engage the PTO shaft 112 directly and cause itto decelerate. The engine 106 is disabled. Wheel brakes may also be activated to slow down the vehicle 100 if it is in motion.

It will be appreciated that any one or combination of these actions may occur as a result of the safety device being turned "off" when it is enabled.

The safety device effectively enables the user to stop the rotation of the PTO shaft 112, turn off the vehicle engine 106 and, if the vehicle 100 is in motion, to stop the vehicle 100. Only the safety device switch 120 must be turned off to cause all these actions to occur. The means for controlling the safety device switch 120 is located in close proximity to the PTO shaft 112 so that the user can reach it in an emergency, particularly, if such an emergency involves an incident in the vicinity of the P10 shaft 112.

After the safety device switch 120 has been turned off and the engine 106 is deactivated, the driver can enable the engine 106 by switching the cabin switch 118 off, as shown in Table 1. The engine 106 may then be started by the driver with the PTO shaft 112 off.

Alternatively, after the device switch 120 has been turned off and the engine is deactivated, the driver can enable the engine 106 by switching the safety device switch 120 on again. The engine 106 may then be started by the driver with the PTO shaft 112 on.

While various embodiments of the invention have been described, it will be apparent to those skilled in the art once given this disclosure that various modifications, changes, improvements and variations may be made without departing from the scope of the invention.

Claims

Claims 1. A safety device for a power take off (PTO) shaft, comprising:

a safety mechanism arranged to decelerate rotation of the PTO shaft; a control means arranged to activate the safety mechanism to decelerate rotation of the PTO shaft, the control means being arranged to extend adjacent to a rotatable portion of the PTO shaft.
2. A safety device as claimed in claim 1, wherein the control means is spaced apart from an outer surface of the rotatable portion of the PTO shaft.
3. A safety device as claimed in claim 1 or claim 2, wherein the control means is parallel to the outer surface of the rotatable portion of the P10 shaft.
4. A safety device as claimed in any of claims I to 3, wherein the safety mechanism comprises power connection means to enable disconnection of a power supply driving the rotation of the PTO shaft.
5. A safety device as claimed in claim 4, wherein the power connection means enables connection of the power supply driving rotation of the PlO shaft.
6. A safety device as claimed in any of claims I to 5, wherein the safety mechanism comprises a braking means for decelerating the rotation of the PTO shaft by frictional force.
7. A safety device as claimed in claim 5, wherein the braking means is erigagable with the PTO shaft.
8. A safety device as claimed in claim 6 or claim 7, wherein the braking means is engagable with a drive means for the P10 shaft.
9. A safety device as claimed in any of claims 1 to 8, wherein the safety mechanism comprises an engine override control arranged to cut off the engine of a vehicle to which the P10 shaft is connected.
10. A safety device as claimed in any of claims 4 to 9 when dependent on claim 4, wherein the control means comprises a cord connected to the power connection means, the cord being displaceable between a first position where the power connection means connects the power supply to the PTO shaft and a second position where the power connection means disconnects the power supply from the PTO shaft.
11. A safety device as claimed in claim 10, wherein the cord is suspended a height above the outer surface of the P10 shaft and along the length of the P10 shaft.
12. A safety device as claimed in claim 10 or claim 11 wherein the cord is suspended at least 5 centimetres above the outer surface of the PTO shaft.
13. A safety device as claimed in any of claims 4 to 12 when dependent on claim 4, wherein the power connection means comprises a plug and a socket.
14. A safety device as claimed in claim 13, wherein the socket is fixed to the vehicle to which the PTO shaft is connected.