GB1590440A - Load-handling vehicle - Google Patents

Description

(54) IMPROVED LOAD-HANDLING VEHICLE (71) We, LINER LIMITED, formerly THE LINER CONCRETE MACHINERY COM- PANY LIMITED, a British Company of Park Road Works, Park Road, Gateshead, Tyne and Wear, NE8 3HR, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to improvements in the safety of load handling vehicles, particularly such vehicles for use on rough terrain such as building and civil engineering sites.

The invention is particularly concerned with load handling vehicles having a split chassis articulated about a vertical axis at a point between the axles of the vehicle; such vehicles usually include a mast for a fork lift carriage but may include alternative load handling attachments if desired. Vehicles of this kind are normally stable except when, for example, a loaded fork carriage is in its uppermost position. This can lead to overturning of the vehicle, as once tipping has started, the moment exerted by the load increases, and that acting to keep the wheels on the ground decreases.

An object of the invention is to provide a means whereby such tipping may be sensed, and prevented before tipping or tilting has actually started.

According to the present invention a load handling vehicle comprises a split chassis articulated about a vertical axis at a point between the axles of the vehicle and a superstructure with a lifting member cap able of raising a load and placing it at a distance from the vehicle characterised by the provision of a strain gauge mechanism mounted at a vertical pivot connecting the two parts of the chassis, to detect strains due to the superstructure and the load and an audible and/or visible alarm operable by the strain gauge mechanism to give warning when the strains are such as to render the vehicle unstable.

When a vehicle is tipped, for example by rotation on its front axles, by means of a load carried on a fully extended jib, or mast the weight acting on the vertical pivot tends to resist, so that the vertical pivot is subjected to opposing forces i.e. the leverage force transmitted by the gib or mast and the weight acting on the vertical pivot. These opposing forces between them subject the chassis to bending stresses, even, before the rear wheels have actually left the ground.

Preferably there are a plurality of strain gauges equally spaced about the vertical pivot and connected into an electrical circuit, which amplifies signals from the gauges (e.g. changes in resistance) and uses them to prevent further lowering and/or extension of the lifting member when the value of the signals from the strain gauges reach a dangerous value indicating that the vehicle is about to overturn.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a side elevation of one embodiment of load handling vehicle in accordance with the invention; Figure 2 is an enlarged side elevation of the vertical axis about which the two parts of the split chassis are articulated; Figure 3 is a plan view of the chassis of the load handling vehicle of figure 1 in which the superstructure is removed for clarity; and Figure 4 shows the preferred electrical circuit for the strain gauge.

In the drawings a load handling vehicle 1 comprises a split chassis, having a front part 2 and a rear part 3, articulated about a vertical axis 4. The two parts of the split chassis respectively support front and rear axles 5 and 6 on which the vehicle wheels 7 are mounted.

The front part of the chassis 2 supports a lifting member 8 consisting of a mast 9 and a fork carriage 10 movable therealong whereas the rear axle directly supports a propulsion engine 11, a driver's seat with controls 12 and an associated protective cab 13.

The mast 9 on the front part 2 is pivotally mounted to the chassis and, by means of a pair of hydraulic piston and cylinder assemblies 14 acting between the mast 9 and the chassis, may be tilted from the position shown in figure 1 to a position substantially parallel with an angled front portion 15 of the vehicle cab 13. The mast 9 is also extendable, to increase the operating height of the fork carriage, by a hydraulic means not shown.

The vertical axis 4 about which the two parts of the split chassis are articulated provides extra maneouvrability in rough terrain operation. The vertical axis 4 consists of two aligned pivot pins 16 which pass through coupling plates 17 connected to both the front part 2 and the rear part 3 of the chassis. Figure 2 shows two strain gauges 18 mounted to the upper pivot pin 16 and equally spaced at 180 intervals in order to sense strains operating in all directions i.e.

fore and aft and transversely; however more strain gauges may be provided if desired.

The strain gauges 18 each include as their active elements, a strip of metal the electrical resistance of which varies depending upon the strain exerted on the strip: the strips are connected into an electrical circuit shown in figure 4 by means of leads 19.

The signal from the strain gauges 18, in the form of a low voltage current modulated by the resistance changes of the strain gauges 18, is passed to an amplifier 20 which amplifies the signal and then, through a time constant device 21 which holds the signal for a set time before allowing it to pass to two level indicators 22 and 23 which analyse the signals from the strain gauges and monitor their amplitude. Should the signals approach a voltage level, predetermined as the level caused by a turning moment just under that necessary to overturn the vehicle and enough to make the vehicle unstable then the signal is passed through the indicator to a buzzer 24.If the signal continues to approach the danger level due to the load being increased on the strain gauges then the second level indicator 23 comes into operation and in turn passes the signal to a relay 25, which in its turn activates solenoid hydraulic control valves 26 and 27 which shut off the hydraulic controls for the mast, thus, preventing the driver from putting the vehicle in an unstable position. In order to bring the vehicle back to a safe condition the driver must reverse the action of the boom thereby altering the strain on gauges 18. Once the voltage level is again at a safe value the hydraulic locks effected by the solenoid valves 26 and 27 will be released and the warning buzzer 24 shut off.

Thus when a load is towards an unstable position, its reaching the unstable position is prevented, and if a load which is stable on flat ground threatens to cause instability when crossing uneven ground, warning is given and action can be taken by the driver, or automatically to reduce the risk, e.g. by lowering the load at least partially.

The strain gauges may be provided on vehicles having two or four wheel drive and the load handling attachments may be of any kind - fork lifts, grab buckets, excavator buckets, skips or crane hooks.

In addition to the strain gauges mounted at the vertical axis about which the two parts of the split chassis are articulated, the load handling vehicle in accordance with this invention may also be provided with strain gauges mounted on or adjacent the rear and/or front axle of the vehicle. In connection with this aspect of the invention reference is directed to our copending cognate application Nos. 44295/74 and 23270/75 (Serial No. 1,528,741).

WHAT WE CLAIM IS: 1. A load handling vehicle comprising a split chassis articulated about a vertical axis at a point between the axles of the vehicle and a superstructure with a lifting member capable of raising a load and placing it at a distance from the vehicle characterised by the provision of a strain gauge mechanism mounted at a vertical pivot connecting the two parts of the chassis, to detect strains due to the superstructure and the load and an audible and/or visible alarm operable by the strain gauge mechanism to give warning when the strains are such as to render the vehicle unstable.

2. A load handling vehicle according to claim 1 wherein the strain gauge mechanism comprises a plurality of strain gauges mounted at equally spaced intervals around the vertical pivot.

3. A load handling vehicle according to claim 1 or 2 wherein the strain gauge mechanism is connected in an electrical circuit including means to monitor signals from the strain gauge mechanism and means to prevent further lowering and or extension of the lifting member when the value of the signals from the strain gauge mechanism reaches a dangerous value indicating that the vehicle is about to overturn.

4. A load handling vehicle according to claim 3 wherein the signals from the strain gauge mechanism are arranged to close hydraulic control valves to prevent further lowering and/or extension of the lifting member when the value of the signals from the strain gauge mechanism reaches a dangerous value.

5. A load handling vehicle according to any one of the preceding claims wherein the lifting member comprises a mast pivotally connected to the chassis, a hydraulic piston and cylinder assembly acting between the chassis and the mast controlling the pivotal

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (6)

**WARNING** start of CLMS field may overlap end of DESC **. assemblies 14 acting between the mast 9 and the chassis, may be tilted from the position shown in figure 1 to a position substantially parallel with an angled front portion 15 of the vehicle cab 13. The mast 9 is also extendable, to increase the operating height of the fork carriage, by a hydraulic means not shown. The vertical axis 4 about which the two parts of the split chassis are articulated provides extra maneouvrability in rough terrain operation. The vertical axis 4 consists of two aligned pivot pins 16 which pass through coupling plates 17 connected to both the front part 2 and the rear part 3 of the chassis. Figure 2 shows two strain gauges 18 mounted to the upper pivot pin 16 and equally spaced at 180 intervals in order to sense strains operating in all directions i.e. fore and aft and transversely; however more strain gauges may be provided if desired. The strain gauges 18 each include as their active elements, a strip of metal the electrical resistance of which varies depending upon the strain exerted on the strip: the strips are connected into an electrical circuit shown in figure 4 by means of leads 19. The signal from the strain gauges 18, in the form of a low voltage current modulated by the resistance changes of the strain gauges 18, is passed to an amplifier 20 which amplifies the signal and then, through a time constant device 21 which holds the signal for a set time before allowing it to pass to two level indicators 22 and 23 which analyse the signals from the strain gauges and monitor their amplitude. Should the signals approach a voltage level, predetermined as the level caused by a turning moment just under that necessary to overturn the vehicle and enough to make the vehicle unstable then the signal is passed through the indicator to a buzzer 24.If the signal continues to approach the danger level due to the load being increased on the strain gauges then the second level indicator 23 comes into operation and in turn passes the signal to a relay 25, which in its turn activates solenoid hydraulic control valves 26 and 27 which shut off the hydraulic controls for the mast, thus, preventing the driver from putting the vehicle in an unstable position. In order to bring the vehicle back to a safe condition the driver must reverse the action of the boom thereby altering the strain on gauges 18. Once the voltage level is again at a safe value the hydraulic locks effected by the solenoid valves 26 and 27 will be released and the warning buzzer 24 shut off. Thus when a load is towards an unstable position, its reaching the unstable position is prevented, and if a load which is stable on flat ground threatens to cause instability when crossing uneven ground, warning is given and action can be taken by the driver, or automatically to reduce the risk, e.g. by lowering the load at least partially. The strain gauges may be provided on vehicles having two or four wheel drive and the load handling attachments may be of any kind - fork lifts, grab buckets, excavator buckets, skips or crane hooks. In addition to the strain gauges mounted at the vertical axis about which the two parts of the split chassis are articulated, the load handling vehicle in accordance with this invention may also be provided with strain gauges mounted on or adjacent the rear and/or front axle of the vehicle. In connection with this aspect of the invention reference is directed to our copending cognate application Nos. 44295/74 and 23270/75 (Serial No. 1,528,741). WHAT WE CLAIM IS:

1. A load handling vehicle comprising a split chassis articulated about a vertical axis at a point between the axles of the vehicle and a superstructure with a lifting member capable of raising a load and placing it at a distance from the vehicle characterised by the provision of a strain gauge mechanism mounted at a vertical pivot connecting the two parts of the chassis, to detect strains due to the superstructure and the load and an audible and/or visible alarm operable by the strain gauge mechanism to give warning when the strains are such as to render the vehicle unstable.

2. A load handling vehicle according to claim 1 wherein the strain gauge mechanism comprises a plurality of strain gauges mounted at equally spaced intervals around the vertical pivot.

3. A load handling vehicle according to claim 1 or 2 wherein the strain gauge mechanism is connected in an electrical circuit including means to monitor signals from the strain gauge mechanism and means to prevent further lowering and or extension of the lifting member when the value of the signals from the strain gauge mechanism reaches a dangerous value indicating that the vehicle is about to overturn.

4. A load handling vehicle according to claim 3 wherein the signals from the strain gauge mechanism are arranged to close hydraulic control valves to prevent further lowering and/or extension of the lifting member when the value of the signals from the strain gauge mechanism reaches a dangerous value.

5. A load handling vehicle according to any one of the preceding claims wherein the lifting member comprises a mast pivotally connected to the chassis, a hydraulic piston and cylinder assembly acting between the chassis and the mast controlling the pivotal

movement of the mast, and a fork lift carriage movable up and down the mast.

6. A load handling vehicle substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.