GB2372490A

GB2372490A - Weight transfer system for articulated vehicles

Info

Publication number: GB2372490A
Application number: GB0104858A
Authority: GB
Inventors: David John Bowes Brown
Original assignee: Multidrive Ltd
Current assignee: Multidrive Ltd
Priority date: 2001-02-27
Filing date: 2001-02-27
Publication date: 2002-08-28
Also published as: GB0104858D0

Abstract

A tractor unit (1) has a coupling member (7), such as a fifth wheel coupling, mounted on the chassis (6) so as to be tiltable in the fore-aft direction. At least one piston/cylinder device (12) is connected between the chassis (6) and the coupling member (7) for controlling the tilt.

Description

WEIGHT TRANSFER SYSTEM FOR ARTICULATED VEHICLE This invention relates to a tractor unit for an articulated vehicle.

A conventional tractor unit has a coupling member (usually referred to as"the fifth wheel") which is connectable to a trailer unit so as to allow turning of the tractor unit relative to the trailer unit, the coupling member being mounted on the chassis so as to be tiltable in a fore-and-aft direction.

The present invention provides a tractor unit in which at least one piston-and-cylinder device for controlling tilting is connected between the coupling member and the chassis.

The invention can be used to enable an increase or decrease of the weight acting on an axle, such as a driven axle of the tractor unit.

The invention can also be used to damp oscillation of the tractor unit relative to the trailer unit, thereby improving ride characteristics.

The invention will be described further, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side elevation of part of the rear of a tractor unit, being an enlargement of the detail I in Figure 4; Figure 2 is an underside view of part of the rear of the tractor unit; Figure 3 is a diagram of a hydraulic circuit ; and Figures 4 to 6 are side elevations of an articulated vehicle, including the tractor unit, in which the weights acting on the various wheel groups under different conditions are indicated.

The articulated vehicle illustrated has a tractor unit 1 and a trailer unit 2. The tractor unit 1 contains an engine and transmission (not shown) driving a pair of rear wheels 3.

The tractor unit also has a pair of non-driven steered front wheels 4. The rear wheels 3 are carried by a rear axle (not shown) which mounts a rear chassis 6 of the tractor unit 1.

A so-called fifth wheel or coupling member 7 is mounted on the chassis 6 so as to be tiltable in a fore-and-aft direction as indicated by the double-headed arrow 8. For this purpose, the coupling member 7 is pivotally connected at each side to a bracket 9 fixed to the chassis 6, so that the coupling member is tiltable about a transverse pivot axis 11.

In the conventional way, the trailer unit 2 has a counter member (not shown) which is coupled to and bears on the coupling member 7 so as to allow turning of the tractor unit relative to the trailer unit.

A pair of piston-and-cylinder devices in the form of hydraulic rams 12 are connected between the coupling member 7 and the chassis 6. In particular, the upper end of each ram 12 is connected by a pivot 13 to a forward extension 14 of the coupling member 7, and the lower end, i. e. the free end of the rod 16 of the ram, is connected by a pivot 17 to a bracket 18 fixed under the chassis 6.

Figure 3 shows a hydraulic circuit for operating the rams 12, each of which has a piston 19 on its rod 16, running in a cylinder 21 having a first inlet/outlet port 22 in its upper end portion and a second inlet/outlet port 23 in its lower end portion. The piston 19 divides the interior of the cylinder 21 into upper and lower chambers 24 and 26 of variable volume, which communicate with the ports 22 and 23 respectively. The hydraulic circuit includes a hydraulic tank or reservoir 27, a positive displacement machine in the form of a pump 28, an accumulator 29, and valve apparatus in the form of a three-position spool valve 31 having three sections 32 to 34. The spool valve 31 has an inlet 36 and an outlet 37.

The pump 28 draws hydraulic fluid from the reservoir 27 and supplies it under pressure to the inlet 36 through a line 38 which contains a check valve 39 and is connected to the accumulator 29. The outlet 37 is connected to the reservoir 27 by a drain line 41. The upper and lower ports 22 and 23 of each ram 12 are connected to the spool valve 31 by respective lines 42 and 43, one or both of which (in this case the line 42) is provided with a flow restrictor 44.

In the state shown in Figure 3, the middle section 33 of the spool valve 31 is operative to connect the upper and lower chambers 24,26 of the ram to each other by way of the port 22, the line 42, the restrictor 44, a bypass duct 46 (in the section 33), the line 43, and the port 23. This allows the hydraulic fluid in the rams 12 to circulate in a damped manner as the rams extend and contract when the trailer unit 2 oscillates about the transverse pivot axes 11, so that the relative oscillation of the tractor unit and the trailer unit is damped.

When the left-hand section 32 of the valve spool is operative, the first port 22 of each ram 12 is connected to the inlet 36 of the spool valve 31 and is therefore supplied with

hydraulic fluid under pressure, while the second port 23 is connected to the outlet 37 of the spool valve 31. Accordingly, the upper chamber 24 is pressurised and the lower chamber 26 is drained, with the result that the rams 12 are extended and the upper and lower pivots 13,17 are pushed away from each other.

When the right-hand section 34 is operative, the second port 23 is connected to the inlet 36 so that pressurised hydraulic fluid is supplied to the lower chamber 26, while the first port 22 is connected to the outlet 37 so that the upper chamber 24 is drained.

Accordingly, the rams 12 are retracted, drawing the upper and lower pivots 13,17 towards each other.

In each case the check valve 39 prevents the hydraulic fluid from flowing back to the pump 28 from the rams 12, and the accumulator 29 maintains the pressure in the hydraulic circuit within acceptable limits as relative movement (arrow 8, Fig. 1) occurs between the tractor and trailer units.

Figure 4 shows, beneath the figure, the weights in metric tons acting on the various wheel groups of the laden vehicle without the above described hydraulic circuit (upper figures) and with the above described hydraulic circuit having the rams retracted (lower figures). It will be seen that, with the rams retracted, the weight on the steered wheels 4 decreases from 7t to 5t, the weight on the driven wheels 3 increases from 1 It to 14t, and the weight on the rear wheels of the trailer unit 2 decreases from 22t to 21t. The laden weight is 40t.

Figure 5 gives the same information for the unladen vehicle having a weight of 15t.

Again, the lower set of figures relates to the situation in which the rams are retracted.

Figure 6 again relates to the laden vehicle, but in this case the lower set of figures corresponds to the rams being extended.

Thus, the above described hydraulic circuit provides a weight transfer system for the articulated vehicle, in which the weight on an axle or axles adjacent to the coupling member or fifth wheel connecting the tractor unit to the trailer unit can be increased or decreased by contracting or extending piston-and-cylinder devices connected between the fifth wheel and the chassis. Furthermore, by restricting the flow of fluid from each end of the cylinder, a damper is created between the tractor unit and the trailer unit.

Various modifications may be made within the scope of the invention. For instance, the hydraulic ram can be replaced by a pneumatic ram, in which case the pump will be replaced by a compressor and, if the gas used is air, a reservoir can be dispensed with.

Although two rams have been shown, it is possible that one ram may be sufficient.

Additionally, or alternatively, one or more rams may be connected between a rear extension of the coupling member and the chassis. The tractor unit may have more than one pair of driven wheels or more than one pair of steered wheels.

Claims

Claims: 1. A tractor unit for an articulated vehicle, the tractor unit having a chassis and a coupling member which is connectable to a trailer unit so as to allow turning of the tractor unit relative to the trailer unit, the coupling member being mounted on the chassis so as to be tiltable in a fore-and-aft direction, at least one piston-and-cylinder device for controlling tilting being connected between the coupling member and the chassis.
2. A tractor unit as claimed in claim 1, in which the piston-and-cylinder device functions as a damper.
3. A tractor unit as claimed in claim 1 or 2, in which the coupling member is tiltable about a transverse pivot axis, the piston-and-cylinder device being connected to the coupling member at a position spaced from the pivot axis.
4. A tractor unit as claimed in claim 3, in which the said position is in front of the pivot axis.
5. A tractor unit as claimed in claim 3 or 4, including a driven axle to the rear of the pivot axis.
6. A tractor unit as claimed in any preceding claim, in which the piston-andcylinder device has a cylinder with first and second ports in opposite end portions of the cylinder, the tractor unit including valve apparatus having an inlet for receiving a working fluid under pressure and a drain or exhaust outlet, the valve apparatus being operable to connect one of the first and second ports to the inlet and the other port to the outlet.
7. A tractor unit as claimed in claim 6, in which the valve apparatus is also operable to connect the said other port to the inlet and the said one port to the outlet.
8. A tractor unit as claimed in claim 6 or 7, in which the valve apparatus is also operable to connect the first and second ports to each other.
9. A tractor unit as claimed in any of claims 6 to 8, including a flow restrictor between at least one of the first and second ports and the valve apparatus.
10. A tractor unit as claimed in any of claims 6 to 9, in which the valve apparatus comprises a spool valve.
11. A tractor unit as claimed in any of claims 6 to 10, including a positive displacement machine for supplying the working fluid under pressure.
12. A tractor unit as claimed in any of claims 6 to 11, in which the working fluid is hydraulic fluid.
13. A tractor unit as claimed in any of claims 6 to 11, in which the working fluid is a gas.
14. An articulated vehicle comprising a tractor unit and a trailer unit, the trailer unit being in accordance with any preceding claim.
15. A tractor unit substantially as described with reference to, and as shown in, the accompanying drawing.

15. An articulated vehicle as claimed in claim 14, in which the at least one pistonand-cylinder device is selectively forcibly extensible and forcibly retractable so as to vary the weight applied to at least one axle of the tractor unit.

16. A tractor unit substantially as described with reference to, and as shown in, the accompanying drawing. Amendments to the claims have been filed as follows 1. A tractor unit for an articulated vehicle, the tractor unit having a chassis and a coupling member which is connectable to a counter member on the underside of a trailer unit so as to allow turning of the tractor unit relative to the trailer unit, the coupling member being mounted on the chassis so as to be tiltable in a fore-and-aft direction, at least one piston-and-cylinder device capable of functioning as a damper being connected at one end to the coupling member and at the other end to the chassis.

2. A tractor unit as claimed in claim 1, in which the coupling member is tiltable about a transverse pivot axis, the piston-and-cylinder device being connected to the coupling member at a position spaced from the pivot axis.

3. A tractor unit as claimed in claim 2, in which the said position is in front of the pivot axis.

4. A tractor unit as claimed in claim 2 or 3, including a driven axle to the rear of the pivot axis.

5. A tractor unit as claimed in any preceding claim, in which the piston-andcylinder device has a cylinder with first and second ports in opposite end portions of the cylinder, the tractor unit including valve apparatus operable to connect the first and second ports to each other.

6. A tractor unit as claimed in any of claims 5 to 8, including a flow restrictor between at least one of the first and second ports and the valve apparatus.

7. A tractor unit as claimed in claim 5 or 6, in which the valve apparatus has an inlet for receiving a working fluid under pressure and a drain or exhaust outlet, the valve apparatus being operable to connect one of the first and second ports to the inlet and the other port to the outlet.

8. A tractor unit as claimed in claim 7, in which the valve apparatus is also operable to connect the said other port to the inlet and the said one port to the outlet.

9. A tractor unit as claimed in any of claims 5 to 8, in which the valve apparatus comprises a spool valve.

10. A tractor unit as claimed in any of claims 5 to 9, including a positive displacement machine for supplying the working fluid under pressure.

11. A tractor unit as claimed in any of claims 5 to 10, in which the working fluid is hydraulic fluid.

12. A tractor unit as claimed in any of claims 5 to 10, in which the working fluid is a gas.

13. An articulated vehicle comprising a tractor unit and a trailer unit, the trailer unit being in accordance with any preceding claim.

14. An articulated vehicle as claimed in claim 13, in which the at least one pistonand-cylinder device is selectively forcibly extensible and forcibly retractable so as to vary the weight applied to at least one axle of the tractor unit.