GB2414980A

GB2414980A - Disabled vehicle carrier

Info

Publication number: GB2414980A
Application number: GB0511738A
Authority: GB
Inventors: Colin Douglas Boswell; Denis O'donoghue
Original assignee: Edinburgh Napier University
Current assignee: Edinburgh Napier University
Priority date: 2004-06-11
Filing date: 2005-06-09
Publication date: 2005-12-14
Also published as: GB0511738D0; GB0413064D0

Description

1 Load Bearing Apparatus for a Vehicle 3 The present invention relates to

load bearing 4 apparatus for a vehicle, in particular but not exclusively for tow trucks and the like.

7 Vehicles such as tow trucks are used to tow other 8 vehicles. This may be because the vehicle being 9 towed has broken down, or because the vehicle was left illegally parked, or for other reasons. Tow 11 trucks typically use a load bearing apparatus having 12 a cantilever supporting member. Two wheels of the 13 vehicle to be towed are typically supported at the 14 free end of the supporting member which is distal from the rear end of the tow truck.

17 The load bearing apparatus can typically be lowered 18 to the ground using hydraulic means so that the 19 vehicle to be towed can be connected. This precludes having a permanent wheel or wheels at or 21 near the free end.

a * . .

. - 1 The vehicle to be towed typically has a mass of 2 between 1000 and 2000 kg and this mass acts on the 3 free end of a cantilever having a fixed end located 4 at the rear axle of the tow truck. The mass therefore generates a substantial moment about the 6 rear axle. The mass acting on the front axle of the 7 tow truck is reduced which can reduce the steering 8 control and front braking capability of the tow 9 truck. It is also possible to overload and cause failure of the rear axle, particularly due to 11 dynamic loads produced by an uneven road surface.

12 Designing the vehicle to accommodate such loads can 13 be costly and significantly add to the weight of the 14 vehicle.

16 According to a first aspect of the present 17 invention, there is provided a load bearing 18 apparatus for a vehicle comprising: 19 a cantilever supporting member having a first free end for bearing the load, the free end being 21 distal from the vehicle, and a second end; and 22 first connection means for connecting the 23 second end to the vehicle, 24 wherein at least one retractable ground engageable member is connected to the supporting 26 member and is operable to a first deployed position 27 between the first and the second end.

29 Preferably the or each ground engageable member comprises a wheel.

. ...

. . . . 8 8 8 8 8. . . . 8.

. 1 Preferably the supporting member is operable between 2 a raised and a lowered position. Preferably the 3 supporting member is operable using actuating means 4 such as hydraulic means.

6 Preferably the load bearing apparatus includes 7 suspension means.

9 Preferably the or each ground engageable member is movably connected to the supporting member such that 11 the or each ground engageable member is movable 12 between the first deploed position in which the 13 ground engageable member is in contact with the 14 ground and a second position in which the ground engageable member is not in contact with the ground.

17 Preferably the or each ground engageable member are 18 provided at a linking member which is pivotably 19 connected to the supporting member. Alternatively or in addition, the or each ground engageable member 21 is slideably connected to the supporting member.

23 Preferably the apparatus includes first retaining 24 means to retain the or each ground engageable member at the first position. Preferably the first 26 retaining means comprises a stop for preventing 27 further pivoting of the or each ground engageable 28 member beyond the first position. Preferably the 29 apparatus is adapted such that forward motion of the vehicle urges the or each ground engageable member 31 towards the stop.

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1 Preferably the apparatus includes second retaining 2 means to retain the or each ground engageable member 3 at the second position. Preferably the second 4 retaining means comprises one or more slots provided at the supporting member which align with one or 6 more slots provided at the linking member when the 7 or each ground engageable member is at the second 8 position, the slots being adapted to receive a pin 9 for retaining the or each ground engageable member at the second position.

12 An embodiment of the present invention will now be 13 described, by way of example only, with reference to 14 the accompanying drawings, in which: 16 Fig. 1 is a side view of a vehicle having a load

17 bearing apparatus according to the prior art;

19 Fig. 2 is a side view of a vehicle having a load 2 0 bearing apparatus according to the present 21 invention; 23 Fig. 3 is a perspective view of the load bearing 24 apparatus of Fig. 2; 2 6 Fig. 4 is a perspective view of a wheel assembly of 2 7 the load bearing apparatus of Fig. 2; 29 Fig. 5 is a side view of a vehicle having the load bearing apparatus of Fig. 2; and ëe e e e e ee. e e e e ee . ee e 1 Fig. 6 is a side view of a vehicle having the load 2 bearing apparatus of Fig. 2.

4 Fig 1 shows a vehicle 100 having a load bearing

apparatus 200 according to the prior art. The

6 apparatus comprises a cantilever supporting member 7 210 having a first free end 212 for supporting the 8 load F2 from a vehicle to be towed, and a second end 9 214 fixed by first connection means (not shown) to the vehicle 100. The mass of the vehicle may be 11 represented by a single point load F1 acting through 12 the centre of mass of the vehicle. The location of 13 the centre of mass is dependent on the distribution 14 of the mass of the vehicle. Also, as shown in Fig. 1 (b), a horizontal towing force is produced by the 16 vehicle to be towed.

18 The forces Fl, F2 acting on the vehicle produce 19 reaction forces R1, R2 at the front and rear axles of the vehicle. The forces F1, F2 also produce moments 21 about the front and rear axles. The value of the 22 moments is dependent on the force and the respective 23 distance a, b from the axle.

The relationship of the forces and moments can be 26 determined. For equilibrium of the forces: 2 8 F1 + F2 - R1 - R2 = 0 For equilibrium of the moments (about the rear 31 axle): e ..

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1 R1.(a+c) - F1.a + F2.b = 0 3 Typical values may be assumed. Let the mass of the 4 vehicle be 1500 kg such that F1 is about 15 kN, and the mass acting on the free end of the load bearing 6 apparatus is 1000 kg such that F2 is about 10 kN.

7 Let a, b and c be 3 m, 2 m and 3 m respectively.

9 Solving the above equations gives reaction forces R1, R2 of about 4 kN and 21 kN respectively. Thus, a 11 large force exists on the rear axle which can 12 overload and cause failure of the rear axle, 13 particularly if dynamic loads are produced by an 14 uneven road surface. Also, such a large difference between the forces on the front and rear axles can 16 reduce the steering control and front braking 17 capability of the vehicle.

19 Fig. 2 shows a vehicle 100 having a load bearing apparatus 10 according to the present invention.

21 The apparatus once again comprises a cantilever 22 supporting member 20 having a first free end 22 for 23 supporting the load F2 from a vehicle to be towed, 24 and a second end 24 fixed by first connection means (not shown) to the vehicle 100.

27 The apparatus includes two ground engageable members 28 or wheels 30 connected to the supporting member 20 29 and interposed between the free end 22 and the fixed end 24. The wheels 30 are at a distance b from the 31 rear axle and at a distance d from the free end.

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e e e e e e e e ëe e a e e. e . e e e e e e ee see *e 1 The forces F1, F2 acting on the vehicle now produce 2 reaction forces Rl, R2, R3 at the front and rear 3 axles of the vehicle and at the wheels 30 of the 4 load bearing apparatus 10.

6 The relationship of the forces and moments can be 7 determined. For equilibrium of the forces: 9 F1 + F2 - R1 - R2 - R3 = 0 11 For equilibrium of the moments (about the rear 12 axle): 14 R1.(a+c) - F1.a - R3.b + F2.b = 0 16 The same typical values may be assumed, except that 17 b is 1 m while d is also 1 m.

19 Solving the above equations gives reaction forces R1, R2, R3 of about 6 kN, 7.5 kN and 10.5 kN 21 respectively. Thus, the force on the rear axle has 22 been significantly reduced. Also, the large 23 difference between the forces on the front and rear 24 axles is now significantly smaller. Another advantage is that the highest of the three loads is 26 carried at the wheels of the load bearing apparatus 27 10. The load bearing apparatus 10 can be designed 28 to easily accommodate such loads without any 29 significant increase in cost or weight of the apparatus.

..

as. . ee ë.e. . 1 The load bearing apparatus 10 is shown in Fig. 3.

2 The apparatus 10 includes a main jib 52 for 3 connecting to the vehicle 100 and an extending jib 4 50 which extends from the main jib 52 to towing supports 54. The main jib 52 is removed for clarity 6 in Fig. 3 (b). The apparatus can be raised and 7 lowered by hydraulic pistons provided at the 8 vehicle.

The apparatus 10 is similar to a prior art apparatus 11 except that it includes a wheel assembly 32 which is 12 shown in Fig. 4. The wheel assembly 32 comprises 13 the two wheels 30 which are rotatably supported at 14 one end of a linking member 34 which is pivotably connected at the other end to the supporting member 16 20. The linking member 34 includes a link axle 36 17 which couples the two wheels 30 via a mounting 18 bracket 38.

The wheels 30 are therefore pivotably connected to 21 the supporting member 20 such that the wheels 30 are 22 movable between a first position in which the wheels 23 30 are in contact with the ground and a second 24 position (as shown in Fig. 3) in which the wheels 30 are not in contact with the ground. Therefore, the 26 supporting member can be fully lowered when the 27 wheels 30 are in the second position.

29 The apparatus 10 includes first retaining means to retain wheels 30 at the first position. The first 31 retaining means is in the form of a stop 40 for 32 preventing further pivoting of the or each ground a .

. ë ë 1 engageable member beyond the first position. The 2 stop 40 is provided by the underside of the 3 extending jib 50. Forward motion of the vehicle 4 urges the wheel assembly 32 towards the stop 40.

6 The apparatus 10 also includes second retaining 7 means to retain the wheels 30 at the second 8 position. The second retaining means comprises two 9 slots 42 provided at the supporting member 20 which align with two slots 44 provided at the linking 11 member 34 when the wheels 30 are at the second 12 position. A pin (not shown) is inserted in the 13 slots for retaining the wheels 30 at the second 14 position.

16 The apparatus 10 also includes suspension means to 17 minimise the effect of dynamic loads on the 18 apparatus 10.

Fig. 5 shows the apparatus 10 at three stages of 21 use. In Fig. 5 (a), the apparatus 10 has been 22 lowered to the ground and the towing supports 54 23 connected to the vehicle to be towed. In Fig. 5 24 (b), the apparatus 10 has been raised which raises the front end of the vehicle to be towed and which 26 produces a load on the rear axle. In Fig. 5 (c), 27 the retaining pin has been removed allowing the 28 wheels 30 of the apparatus 10 to move to the first 29 position, and the apparatus 10 has then been lowered slightly so that the apparatus takes up a proportion 31 of the load. The apparatus 10 is now ready for use.

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1 Various modifications and improvements can be made 2 without departing from the scope of the present 3 invention. For instance, the wheels 30 may be 4 permanently in the first position.

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Claims

1 CLAIMS 3 1. A load bearing apparatus for a vehicle 4 comprising: a

cantilever supporting member having a first 6 free end for bearing the load, the free end being 7 distal from the vehicle, and a second end; and 8 first connection means for connecting the 9 second end to the vehicle, wherein at least one retractable ground 11 engageable member is connected to the supporting 12 member and is operable to a first deployed position 13 between the first and the second end.

2. A load bearing apparatus as claimed in Claim 1, 16 wherein the or each ground engageable member 17 comprises a wheel.

19

3. A load bearing apparatus as claimed in Claim 1 or 2, wherein the supporting member is operable 21 between a raised and a lowered position.

23

4. A load bearing apparatus as claimed in Claim 3, 24 wherein the supporting member is operable using actuating means.

27

5. A load bearing apparatus as claimed in any 28 preceding claim, including suspension means.

6. A load bearing apparatus as claimed in any 31 preceding claim, wherein the or each ground 32 engageable member is movably connected to the . e :: e ë e e 1 supporting member such that the or each ground 2 engageable member is movable between the first 3 deployed position in which the ground engageable 4 member is in contact with the ground and a second position in which the ground engageable member is 6 not in contact with the ground.

8

7. A load bearing apparatus as claimed in Claim 6, 9 wherein the or each ground engageable member is provided at a linking member which is pivotably 11 connected to the supporting member.

13

8. A load bearing apparatus as claimed in Claim 6 14 or 7, wherein the apparatus includes first retaining means to retain the or each ground engageable member 16 at the first position.

18

9. A load bearing apparatus as claimed in Claim 8, 19 wherein the first retaining means comprises a stop for preventing further pivoting of the or each 21 ground engageable member beyond the first position, 22 and wherein the apparatus is adapted such that 23 forward motion of the vehicle urges the or each 24 ground engageable member towards the stop.

26

10. A load bearing apparatus as claimed in Claim 9, 27 including second retaining means to retain the or 28 each ground engageable member at the second 29 position.

31

11. A load bearing apparatus as claimed in Claim 32 10, wherein the second retaining means comprises one . . . . . . ... . . . . ..

. . . 1 or more slots provided at the supporting member 2 which align with one or more slots provided at the 3 linking member when the or each ground engageable 4 member is at the second position, the slots being adapted to receive a pin for retaining the or each 6 ground engageable member at the second position.

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