GB2374329A

GB2374329A - Articulated vehicle with steering accumulator

Info

Publication number: GB2374329A
Application number: GB0109268A
Authority: GB
Inventors: David John Bowes Brown
Original assignee: Multidrive Ltd
Current assignee: Multidrive Ltd
Priority date: 2001-04-12
Filing date: 2001-04-12
Publication date: 2002-10-16
Anticipated expiration: 2021-04-12
Also published as: GB2374329B; GB0109268D0

Abstract

An articulated vehicle has an energy generation and storage system responsive to angular changes during steering. The vehicle's trailer unit 2 has an upper main chassis 3 pivotally connected to a lower bogey chassis 4. During steering, increases in the angle between the trailer and bogey cause hydraulic pressure to be generated by a hydraulic ram 22 and stored in an accumulator. The hydraulic pressure results in a resistance force through the ram which can reduce over-steer. A signal from a load detector controls a pressure relief valve. During the release of accumulator pressure, the hydraulic ram assists the decrease in angle, thus reducing under-steer when turning out of lock.

Description

Regenerative Steering System This invention relates to an articulated vehicle having a tractor unit and a trailer unit. In particular it relates to the steering of such a vehicle.

A trailer unit with two or more axles will always tend to travel along a straight line normal to the axles. Accordingly, when the tractor unit is steered away from the straight line (turning into lock), the effect of the trailer unit will be to cause over-steer, and, conversely, when the tractor unit is steered back to the straight line (turning out of lock), the effect of the trailer unit will be to resist this, causing under-steer. The heavier the load, the greater the over-steer into lock and the under-steer out of lock, since a greater weight is acting on the tyres.

The present invention provides a system which accumulates energy when turning into lock, thereby reducing over-steer, and releases energy when turning out of lock, thereby reducing under-steer.

In general terms the invention provides an articulated vehicle comprising a trailer unit pivotably connected to a steerable tractor unit, and an energy generation and storage system responsive to changes in angle between centre-lines of the units such that, as the angle increases, energy is generated and stored and the angular increase is resisted, and, as the angle decreases, stored energy is released and the angular decrease is assisted.

In a preferred embodiment the trailer unit has an upper chassis pivotably connected to a lower chassis, each chassis having being pivotably connected to the tractor unit at different positions along its centre-line. In this case the energy generation and storage system can be made responsive to changes in angle between centre-lines of the upper and lower chassis, this angle being a function of the first-mentioned angle.

This provides the advantage that the system can be provided entirely on the trailer unit.

The system preferably stores energy by building up a pressure. In a preferred embodiment, a hydraulic positive displacement device is connected to an accumulator.

Preferably, a valve assembly is provided to control the hydraulic pressure. The valve assembly may be arranged to connect the device to a hydraulic reservoir when the trailer unit is unladen and/or when the vehicle is reversing.

The invention will be described further, by way of example only, with reference to the accompanying drawings, in which: Figure 1 is a side view of an articulated vehicle ; Figure 2 is an enlarged detail of Figure 1 ; Figure 3 is a plan view of the vehicle, partly in phantom; and Figure 4 is a diagram of a hydraulic circuit.

The vehicle illustrated is of the type having a tractor unit 1 and a trailer unit 2, which has an upper chassis 3 (main chassis) and a lower chassis 4 (bogey chassis) connected by a vertical pivot axis 6. The tractor unit 1 has an engine (not shown) driving front and rear wheels 7,8 through a suitable power train including a gearbox.

The front wheels 7 are steerable. The upper chassis 3 of the trailer unit is connected to

the tractor unit 1 by a pivotal connection (a so-called"fifth wheel") having a vertical pivot axis 9. The lower chassis 4 is connected to the tractor unit 1 by a linkage 11 having a vertical pivot axis 12. The pivot axes 9 and 12 are at different locations along the centre-line 13 of the tractor unit 1. The lower chassis 4 mounts front and rear wheels 14,16 with fixed axles driven via cardan shafts 17 from the tractor unit.

Vehicles of this type are described in EP-A-0 112712, EP-A-0 229 756, and EP-A- 0440651.

When the front wheels 7 are turned so that the tractor unit 1 is steered away from the straight line, the centre-line 13 of the tractor unit 1 makes an angle a with the centre-line 18 of the upper chassis 3, which consequently makes an angle ss with the centre-line 19 of the lower chassis 4, the angle ss being a function of the angle a. The relationship between a and ss depends on the length of a rod 21, one end of which is

connected to the upper chassis 3 and the other end of which is connected to a part of the linkage 11 movable along the centre-line 19 of the lower chassis 4.

A closed hydraulic ram 22 has one end 22a connected to the upper chassis 3 by a pivotal connection 23 with a vertical pivot axis 24 and has its other end 22b connected to the lower chassis 4 by a pivotal connection 26 with a vertical pivot axis 27. The axes 24 and 27 lie on the respective centre-lines 18 and 19. As seen in Figure 4, the ram 22 comprises a cylinder 28, a rod 29, and a piston 31 carried by the rod 29 and dividing the interior of the cylinder 28 into two chambers 28a, 28b which communicate with a valve block 32 (mounted on the lower chassis 4) via respective hydraulic lines 33,34. The valve block 32 has a conduit 36 which is connected to an hydraulic reservoir 37 (mounted on the upper chassis 3) and to which the chamber 28b is connected. The valve block 32 also has a conduit 38 which is connected to an accumulator 39 (mounted on the lower chassis 4) containing a gas such as nitrogen.

The valve block 32 includes a main control valve 41 with two states, viz. , state A, in which the line 33 from the cylinder chamber 28a is connected to the line 34 from the chamber 28b via the conduit 36, and state B, in which the line 33 is connected to the accumulator 39 via the conduit 38. The valve 41 is controlled in accordance with signals from an ignition switch and a gear lever in the tractor unit 1. The valve block 32 also includes a subsidiary control valve 42 which has two states, viz. , a state C, in which the conduit 38 is connected to the conduit 36 via a pressure relief valve 43 set to a relatively low pressure Pi (e. g. 4 MPa), and a state D, in which the conduit 38 is cut off from the pressure relief valve 43 by a one-way valve 42a. The conduit 38 is also permanently connected to the conduit 36 via a pressure relief valve 44 set to a relatively high pressure P2 (e. g. 12 MPa), and the conduit 36 is permanently connected to the conduit 38 via a one-way valve 46. The subsidiary control valve 41 is controlled in accordance with a signal from a load-detector such as an air bag mounted on the rear axle of the tractor unit 1 or on an axle of the trailer unit 2.

The ram 22, valve block 32, and accumulator 39 constitute an energy generation and storage system. When the ignition switch is off or the gear lever is in the neutral or reverse position, the main control valve 41 is in state A and the system is therefore inoperative. When the ignition switch is on and the gear lever is set to a forward gear, the valve 41 is in state B. As the vehicle turns into lock, the angles a and ss increase from zero and the ram 22 is extended, displacing hydraulic fluid under pressure from the chamber 28a via the valve 41 and the conduit 38 into the gas-filled accumulator 39, thereby increasing the pressure in the accumulator 39. The increased fluid pressure in the chamber 28a resists the increases in the angle a and ss. The pressure relief valve 44 sets an upper limit to the resistance provided by the ram 22. If the trailer unit 2 is laden, this is detected by the above-mentioned load detector and the subsidiary control valve 42 is set to state D. If the trailer unit 2 is only lightly laden or unladen, the valve 42 is set to state C so that the pressure relief valve 43 sets a lower upper limit to the resistance provided by the ram 22.

As the vehicle subsequently turns out of lock, the angles a and ss decrease and the ram 22 is retracted. The pressure stored in the accumulator 39 acts on the hydraulic fluid in the chamber 28a, thereby assisting the decreases in the angles a and ss. The level of assistance decreases as the angles a and ss decrease.

Claims

CLAIMS:

1. An articulated vehicle comprising a trailer unit pivotably connected to a steerable tractor unit, and an energy generation and storage system responsive to changes in angle between centre-lines of the units such that, as the angle increases, energy is generated and stored and the angular increase is resisted, and, as the angle decreases, stored energy is released and the angular decrease is assisted.

2. A vehicle as claimed in claim 1, in which the trailer unit has an upper chassis pivotably connected to a lower chassis, each chassis being pivotably connected to the tractor unit at different positions along the centre-line of the tractor unit.

3. A vehicle as claimed in claim 2, in which the energy generation and storage system is responsive to changes in angle between centre-lines of the upper and lower chassis.

4. A vehicle as claimed in any preceding claim, in which the energy generation and storage system stores energy by building up pressure.

5. A vehicle as claimed in claim 4, in which the said system includes a hydraulic positive displacement device connected to an accumulator.

6. A vehicle as claimed in claim 5, in which the said system includes a valve assembly arranged to control the hydraulic pressure.

7. A vehicle as claimed in claim 6, in which the valve assembly is arranged to connect the hydraulic positive displacement device to a hydraulic reservoir to prevent pressure build-up when the vehicle is reversing.

8. A vehicle as claimed in claim 6, in which the valve assembly includes a pressure relief valve.

9. A vehicle as claimed in claim 8, in which the valve assembly includes a second pressure relief valve set to a lower pressure, and a subsidiary control valve which is responsive to a signal from a load-detector so as to connect the hydraulic positive displacement device to the second pressure relief valve when the load on the trailer unit is below a given value.

10. An articulated vehicle substantially as described with reference to, and as shown in, the accompanying drawings.

Amendments to the claims have been filed as follows

1. An articulated vehicle comprising a trailer unit pivotably connected to a steerable tractor unit, the trailer unit having an upper chassis pivotably connected to a lower chassis, each chassis being pivotably connected to the tractor unit at different positions along the centre-line of the tractor unit, and an energy generation and storage system responsive to changes in angle between centre-lines of the units such that, as the angle increases, energy is generated and stored and the angular increase is resisted, and, as the angle decreases, stored energy is released and the angular decrease is assisted.

2. A vehicle as claimed in claim 1, in which the energy generation and storage system is responsive to changes in angle between centre-lines of the upper and lower chassis.

3. An articulated vehicle comprising a steerable tractor unit; a trailer unit pivotably connected to the tractor unit, the trailer unit having an upper chassis pivotably connected to a lower chassis, each chassis being pivotably connected to the tractor unit at different positions along the centre-line of the tractor unit, the lower chassis having drivable wheels and having fixed front and rear axles; and an energy generation and storage system responsive to changes in angle between centre-lines of the upper and lower chassis such that, as the angle increases, energy is generated and stored and the angular increase is resisted, and, as the angle decreases, stored energy is released and the angular decrease is assisted.