GB1570340A

GB1570340A - Indicating incipient instability of vehicles

Info

Publication number: GB1570340A
Application number: GB3157876A
Authority: GB
Original assignee: Benford Ltd
Current assignee: Benford Ltd
Priority date: 1977-10-18
Filing date: 1977-10-18
Publication date: 1980-06-25

Description

(54) IMPROVEMENTS IN OR RELATING TO MEANS FOR INDICATING INCIPIENT INSTABILITY OF VEHICLES (71) We, BENFORD LIMITED, a British Company, of The Cape, Warwick CV34 SDR, in the County of Warwick, 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 vehicles and is intended for application to a vehicle which may become unstable in use, in the sense that one or more of its wheels may tend to lift out of contact with the ground unless special precautions are taken. Such instability may arise in the use of a forklift truck by, for example, carrying an excessively heavy load on the truck.

Various devices have been proposed for incorporation in forklift trucks to warn the driver when the truck is in an unstable condition or to prevent such continued operation of the truck as would increase the instability of the truck.

In published U.K. Specification 1,223,280, there is described a lift truck comprising two hydraulically interconnected piston and cylinder units which transmit force between a back axle and a chassis of the truck. These units are connected hydraulically to valves in hydraulic circuits of the truck which control operation of a lifting mast. With this arrangement, the piston and cylinder units must be sufficiently robust to withstand the entire load which is applied to the back axle of the truck and to withstand shock loads which may arise, for example, from movement of the rear wheels over uneven ground. Furthermore, interconnection of the units provides freedom for the chassis to rock laterally relative to the back axle.

In published U.K. Specification 856,939, there is described a lift truck having leaf springs for transmitting force between a back axle and a chassis of the truck. An hydraulic valve is mounted on the chassis for sensing a condition in which little or no load is applied to the back axle from the chassis. A lever mechanism is provided for operating the sensing valve when the back axle assumes a predetermined position relative to the chassis. Because the position of the back axle relative to the chassis under a given load depends upon the properties of the leaf spring and these properties may vary somewhat during the service life of the truck, the arrangement described in this prior specification may not be reliable to provide a warning of or to prevent an unstable condition.

According to the present invention, there is provided a vehicle having a main structure, a plurality of ground-engaging wheels, a wheel mounting structure by which one or more of the wheels is mounted on the main structure, a pair of abutments associated one with the main structure and one with the wheel mounting structure and sensing means which either responds to separation of the abutments or acts to maintain the abutments in contact and responds to a decrease in the contact pressure between the abutments below a predetermined value, the abutments being so arranged that they transmit between said structures a downward load normally applied from the main structure to the wheel mounting structure, the sensing means being so arranged that it does not respond to an increase in said contact pressure above a predetermined value and there being between each of the abutments and the sensing means connections which do not undergo substantial flexing whilst the abutments remain in mutual contact.

In a vehicle in accordance with the invention, the load normally applied from the main structure to the wheel mounting structure is transmitted by the abutments, not by the sensing means. Thus, it is not necessary for the sensing means to be sufficiently robust to withstand the entire load, including shock loads, transmitted between the main structure and the wheel mounting structure. Furthermore, because the connections between each of the abutments and the sensing means do not flex during normal use of the vehicle, the arrangement is reliable and is not expected to require adjustment during the working life of the vehicle. Even in cases where the wheel mounting structure incorporates springs, such springs do not affect the reliability of the sensing means.

The vehicle may further comprise resilient biasing means arranged for urging the abutments apart. With this arrangement, the sensing means responds before the force transmitted from the main structure to the wheel mounting structure diminishes to zero.

The invention will now be described, by way of example, with reference to the accompanying drawings wherein: - FIGURE 1 shows in side elevation certain parts of a vehicle in accordance with the invention, FIGURE 2 shows an exploded perspective view of certain parts of a further example of a vehicle embodying the invention, and FIGURE 3 shows certain of the parts of Figure 2 in side elevation.

In Figure 1, there is shown a channel section member 10 which forms a part of a main structure or chassis of a fortlift truck.

A pair of plates 11 are secured to the member 10 at opposite sides thereof, these plates extending downwardly to a level below the chassis and supporting between them a horizontal pivot pin 12.

A generally horizontal arm 13 lies below the chassis member 10, one end of the arm being secured to a block 14 carried on the pivot pin 12 so that the arm can pivot about the horizontal axis of the pin 12. To an end portion of the arm 13 which is remote from the pivot pin 12, there is secured by bolts 15 a member 16 which lies below the arm. The member 16 forms a part of a wheel-mounting structure which further includes an axle or other wheel supporting component (not shown) attached to the member 16.

The vehicle includes sensing means in the form of an hydraulic load cell 17, a body of which is rigidly secured to the arm 13 at a position between the plates 11 and the member 16 by bolts 18. A load-sensing part 19 of the load cell is connected with the chassis member 10 by a further bolt 20.

The bolt 20 extends through a central opening in the load cell, through respective apertures in the arm 13 and the chassis member 10 and through a washer 21 which lies within the chassis member. A head of the bolt 20 engages the washer 21 which bears against an upwardly presented surface on the chassis member. A nut 22 on the bolt bears, via a further washer, against the loadsensing part 19 so that the load to which the cell 17 is subjected is affected by pivoting movement of the arm 13 away from the chassis member 10 about the axis of the pin 12.

Resilient biasing means in the form of a pair of abutting Belville washers 23 is arranged to urge the arm 13 away from the chassis member 10 but, during normal use of the vehicle, the arm 13 remains in the position shown in Figure 1. When the arm is in the position shown in Figure 1, abutments associated with the wheel mounting structure and constituted by the heads of the bolts 15 are in contact with an abutment surface associated with the main structure of the vehicle, namely the undersurface 24 of the chassis member 10. Downward movement of the chassis member relative to the wheel mounting structure is limited by engagement of these abutments so that the downward load normally applied from the main structure of the vehicle to the wheel mounting structure is transmitted through the heads of the bolts 15.

Provided that the arm 13 remains in the position shown in Figure 1, variations in the pressure between the heads of the bolts 15 on the one hand and the surface 24 of the chassis member on the other hand do not affect the load cell 17. During normal operation, the load cell is subjected either to a substantially constant load or to no load.

Typically, the wheel associated with the wheel mounting structure of which the member 16 forms a part is a rear wheel of the vehicle and the vehicle can support a load on lift forks which project from the front of the vehicle. Any load on the lift forks reduces the force transmitted from the chassis member 10 to the member 16 and an excessive load reduces this force to zero so that there is a tendency for the chassis member to rise relative to the wheel mounting structure.

If the force transmitted from the chassis member 10 to the member 16 falls to a low value such that the resulting moment about the pivot pin 12 is slightly less than the moment about the pivot pin 12 arising from the action of the springs 23, the arm 13 will tend to pivot downwardly away from the chassis member 10 and this tendency will be sensed by the load cell 17. It will be seen that the load cell responds before the force transmitted from the chassis member 10 to the member 16 is reduced to zero.

The load cell 17 may be connected to a visual indicator to provide a driver of the vehicle with a warning when the condition of the vehicle is near to an unstable condition. Additionally, or alternatively, the load cell may be connected to hydraulic control means for preventing continued operation of the vehicle which would result in the stability of the vehicle being further reduced.

The load cell may be adapted to respond to a change in the pressure exerted on the part 19 by the nut 22, without movement of the arm 13 sufficient to separate the heads of the bolts 15 from the chassis member 10.

The moments acting on the chassis member 10 about the pivot 12, namely: the moment of the weight of the chassis member and parts carried thereby, M1, the moment of the downward force exer ted by the load cell (which may normally be zero), M2, the moment of the upward force exerted by the spring 23, M3, and the moment of the upward force exerted by the abutments 15, M4, are related by the equation M1 + M2 = M3 + M4. M4 can decrease to zero but cannot assume a negative value. Accordingly, the minimum value of M1 + M2 if stability is to be maintained is M3. If the sum of Ml + M2 falls below this value, the chassis member 10 will rise relative to the wheels.If the vehicle is loaded in such a manner that M1 approaches zero, M2 must increase towards M3. The indicator connected to the load cell would be arranged to warn the driver if the pressure to which the load cell is subjected rises to a predetermined value corresponding to a value of M2 less than M3.

With this arrangement, the warning is provided before there is any separation of the bolts 15 from the chassis member 10. Alternatively, the load cell may be adapted to respond to movement of the arm 13 from the position shown in Figure 1.

It will be noted that the load cell 17 is connected to the abutment surface 24 and to the heads of the bolts 15 by substantially inflexible elements and that the springs 23 do not form part of these connections.

In Figures 2 and 3, there are shown certain parts of a further forklift truck embodying the invention. This lift truck has four ground-engaging wheels, one pair of which, 50 and 51, is shown. The wheels 50 and 51 are rear wheels of the truck and are mounted on opposite ends of a back axle 52. The axle is carried in a housing 53 which forms a part of the wheel supporting structure.

The lift truck also has a main structure including a chassis, part of which is indicated at 54. The axle housing 53 is connected to the chassis member 54 for relative rocking movement about a horizontal axis 55 which extends longitudinally of the truck.

In an upper part of the housing 53 there are a pair of bearings 56 which are spaced apart along the axis 55 and carry a bar 57, opposite end portions of which project from the housing 53. One end of the bar 57 is secured in a block 58 which is connected to the chassis member 54 by a pivot pin 59 for pivoting relative to the chassis member about an axis 60. The axis 60 is horizontal and extends transversely of the vehicle, that is to say parallel to the axle 52.

On the end of the bar 57 remote from the block 58 there is secured an abutment member 61. The abutment member is guided for vertical movement relative to the chassis member 54 by a pair of guide blocks 62 which lie on opposite sides of the abutment member and are rigidly secured to the chassis member. Downward movement of the abutment member relative to the chassis member is limited by a pin 63 which extends between the guide blocks 62 at a level below the abutment member. During normal operation of the truck, an upwardly presented surface of the abutment member 61 remains in contact with a downwardly presented abutment surface of the chassis member 54. The downward load normally applied from the main structure of truck to the wheel mounting structure associated with the rear wheels 50 and 51 is transmitted partly through the block 58 and partly through the abutment member 61.

Interposed between a rearwardly projecting part 64 of the abutment member 61 and the chassis member 54, there is sensing means in the form of an hydraulic load cell 65. A body of the load cell is maintained in contact with, and may be secured to the abutment surface of the chassis member.

A load sensing part of the load cell is engaged by a stack of Belville washers 66.

The washers 66 and the load cell 65 are carried on a bolt 67 which extends through a clearance aperture in the chassis member 54. A head of the bolt 67 lies between the washers 66 and the part 64 of the abutment member. The dimensions are such that, whilst the abutment member remains in contact with the abutment surface of the chassis member 54, the stack of washers 66 is compressed and applies a predetermined load to the cell 65.

On the upper end of the bolt 67, there is a nut 68 which prevents the bolt falling out of the chassis member. There is normally a gap between the underside of this nut and an adjacent upwardly presented surface of the chassis member 54 so that the nut does not prevent downward movement of the bolt 67 relative to the chassis member from the position which the bolt normally occupies.

Variations in the pressure between the abutment member 61 and the chassis member 54 do not affect the load cell 65, since such pressure variations do not result in any movement of the abutment member 61 and bolt 67.

If the force which is transmitted from the chassis member 54 to the housing 53 falls towards zero, a stage will be reached at which the bolt 67 tends to move downwardly under the action of the spring 66 and so tends to move the abutment member 61 out of contact with the chassis member 54. Such downward movement of the bolt will permit the springs 66 to expand and so change the load which is applied to the cell 65. The cell responds to such movement by providing an output signal. The cell may be connected to a visual indicator or to means for controlling operation of the lift truck as hereinbefore mentioned with reference to the load cell 17.

It will be noted that the springs 66 are not subjected to flexing during normal use of the lift truck. Accordingly, the properties of these springs are not likely to change significantly during the working life of the truck. Furthermore, the form of the springs 66 is such that a small movement of the bolt 67 will result in a substantial change in the load to which the cell 65 is subjected. There is substantialy no risk of the cell failing to respond when the abutment member 61 moves into contact with the pin 63.

WHAT WE CLAIM IS: - 1. A vehicle having a main structure, a plurality of ground engaging wheels, a wheel mounting structure by which one or more of the wheels is mounted on the main structure, a pair of abutments associated one with the main structure and one with the wheel mounting structure and sensing means which either responds to separation of the abutments or acts to maintain the abutments in contact and responds to a decrease in the contact pressure between the abutments below a predetermined value, the abutments being so arranged that they transmit between said structures a downward load normally applied from the main structure to the wheel mounting structure.

the sensing means being so arranged that it does not respond to an increase in said contact pressure above a predetermined value and there being between each of the abutments and the sensing means connections which do not undergo substantial flexing whilst the abutments remain in mutual contact.

2. A vehicle according to Claim 1 further comprising resilient biasing means arranged to urge the abutments apart.

3. A vehicle according to Claim 1 or Claim 2 comprising an arm pivotally connected adjacent to one of its ends to the main structure and connected at a position between its ends to the wheel mounting structure, the abutment associated with the wheel mounting structure being provided on the arm at a position adjacent to the end thereof which is remote from the pivotal connection between the arm and the main structure.

4. A vehicle according to Claim 3 wherein the abutment associated with the wheel mounting structure is situated between the sensing means and the pivotal connection between the arm and the main structure.

5. A vehicle according to Claim 1 arranged substantially as herein described with reference to and as shown in Figure 1 of the accompanying drawings.

6. A vehicle according to Claim 1 arranged substantially as herein described with reference to and as shown in Figures 2 and 3 of the accompanying drawings.

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the chassis member 54 to the housing 53 falls towards zero, a stage will be reached at which the bolt 67 tends to move downwardly under the action of the spring 66 and so tends to move the abutment member 61 out of contact with the chassis member 54. Such downward movement of the bolt will permit the springs 66 to expand and so change the load which is applied to the cell 65. The cell responds to such movement by providing an output signal. The cell may be connected to a visual indicator or to means for controlling operation of the lift truck as hereinbefore mentioned with reference to the load cell 17. It will be noted that the springs 66 are not subjected to flexing during normal use of the lift truck. Accordingly, the properties of these springs are not likely to change significantly during the working life of the truck. Furthermore, the form of the springs 66 is such that a small movement of the bolt 67 will result in a substantial change in the load to which the cell 65 is subjected. There is substantialy no risk of the cell failing to respond when the abutment member 61 moves into contact with the pin 63. WHAT WE CLAIM IS: -

1. A vehicle having a main structure, a plurality of ground engaging wheels, a wheel mounting structure by which one or more of the wheels is mounted on the main structure, a pair of abutments associated one with the main structure and one with the wheel mounting structure and sensing means which either responds to separation of the abutments or acts to maintain the abutments in contact and responds to a decrease in the contact pressure between the abutments below a predetermined value, the abutments being so arranged that they transmit between said structures a downward load normally applied from the main structure to the wheel mounting structure.