GB2365398A

GB2365398A - Anti-jack-knife system

Info

Publication number: GB2365398A
Application number: GB0018995A
Authority: GB
Inventors: Richard William Cooke
Original assignee: Qinetiq Ltd; UK Secretary of State for Defence
Current assignee: Qinetiq Ltd; UK Secretary of State for Defence
Priority date: 2000-08-03
Filing date: 2000-08-03
Publication date: 2002-02-20
Also published as: GB0018995D0

Abstract

An anti-jack-knife system for an articulated vehicle has a rotary actuator (8) positioned between a tractor (2) and trailer (3) of the vehicle (1). A fluid control system is coupled to the actuator (8). A processor (22, see figure 5) monitors outputs from an angular position sensor, a braking sensor and a vehicle sensor and adjusts the fluid control system accordingly.

Description

<Desc/Clms Page number 1> ANTI -JACK-KNIFE SYSTEM FOR AN ARTICULATED VEHICLE This invention relates to an anti-jack-knife system for an articulated vehicle. Articulated vehicles under heavy braking conditions are prone to jack-knife.

This is the term used to describe the accidental folding of the tractor and trailer. Every year there are numerous road accidents involving articulated vehicles which skid, jack-knife and sometimes overturn. A significant amount of research has been conducted into which vehicle parameters contribute to the onset of a jack-knife. Yaw instability has been found to be contributory, and is affected both by the lateral acceleration of the tractor relative to the trailer, and the vehicle speed. It has been found that even at low lateral accelerations a jack-knife can occur if the vehicle is travelling at high speed, The effect is worsened if the tractor and trailer axles lock up at different times, which may occur on poor road conditions, i.e. on a loose surface or on ice. The most common cause of a jack-knife is as a result of an overrunning load. This is when the force exerted by the trailer on the tractor exceeds the maximum retarding force the tractor can exert on the trailer.

Several methods have been used to attempt to combat the problem of jackknifing. Anti-lock braking systems (ABS) and electronic braking systems (EBS) are widely used. The former modulates all the brakes of the vehicle simultaneously in response to the detection of wheel slippage, whilst the latter monitors and adjusts the braking of each wheel individually. Both systems can help to reduce the severity of a jack-knife, with EBS being the more effective. The main problem associated with these systems is that in order to be effective, matching equipment must be fitted to both the tractor and the trailer. In practice, an individual tractor may be required to tow many different trailers, each of which would need to be fitted with either an ABS or EBS system.

The great majority of articulated vehicles use a fifth wheel assembly to connect the tractor to the trailer. This is a substantial, fixed pivot point on the tractor onto which the trailer is fitted. It is the uncontrolled rotation of the trailer about this pivot point which gives rise to a jack-knife. Many prior art attempts to address the problem of jack-knifing involve some modifications to the fifth wheel assembly.

GB 2,266,506 describes a system whereby a standard drum brake is fitted to the fifth wheel. On application of the braking system for the road wheels of the vehicle, this fifth wheel brake is also applied in an attempt to limit the angle of articulation between the tractor and the trailer. Various other systems based on fifth wheel brakes are also known, however the forces transmitted to the fifth wheel during

a jack-knife incident are far in excess of those which standard vehicle brakes are designed to resist. The effectiveness of fifth wheel brakes is therefore limited.

US 4,281,846 describes an anti-jack-knife mechanism, This is an open loop, passive system which is designed to be operated by the driver. The system is normally deactivated when the vehicle is stationary or moving slowly. It works by limiting the angle of articulation between the tractor and the trailer to 260 either side of the straight ahead position. This system improves the driver's ability to control a jackknife incident and regain full steering control of the vehicle, but it does not prevent a jack-knife occurring in the first place.

In accordance with the present invention an anti-jack-knife system for an articulated vehicle comprises a rotary actuator positioned between a tractor and a trailer of the vehicle, a fluid control system coupled to the actuator, an angular position sensor to detect the articulation angle of the tractor relative to the trailer, a braking sensor, a vehicle speed sensor and a processor; wherein the processor monitors the output of the sensors, derives a risk level from the outputs, and adjusts the fluid control system, such that rotation of the rotary actuator is adapted to the prevailing risk level.

The present invention addresses the problem of jack-knifing by providing a system which acts to prevent a jack-knife from occurring. This is in contrast to the prior art systems described above which aim to control a jack-knife situation once it is in progress, assisting the operator to regain control of the vehicle.

Preferably, the rotary actuator is operated by a hydraulic system. This may comprise a system which uses a pump to supply the required hydraulic pressure, but is preferably a closed system with no external pressure supply. In this case, the rotation of the trailer relative to the tractor, and in turn the rotation of the actuator provides the required hydraulic pressure. An advantage of a closed hydraulic system is that there is no need for an external pump system. This leads to a simpler design which reduces weight and cost. The maintenance requirements of a closed system are also less.

Preferably, the control system alters the flow of hydraulic fluid in the hydraulic system by the use of variable orifices. Alternatively, the flow of hydraulic fluid may be altered by using servo-valves.

Preferably, the variable orifices or servo-valves are controlled independently. This allows the flow of fluid in the system, and hence rotation of the rotary actuator, to be restricted in one direction only.

Preferably, the hydraulic system further comprises a pressure release mechanism. This prevents damage to the system under extreme loading conditions.

Alternatively, the rotary actuator may comprise an electro-viscous or magneto-viscous fluid operated rotary actuator.

In this case, preferably, the fluid control system applies an electric or magnetic field to the fluid of the rotary actuator. This causes an increase in the viscosity of the fluid which provides resistance to the rotation of the actuator.

Preferably, the rotary actuator is incorporated into the fifth wheel of an articulated vehicle. This allows the actuator to be sited at the point where the forces generated during a jack-knife are transmitted. It also allows the system to be sited on the tractor of the vehicle with few, if any, modifications needed to the trailer. This leads to significant cost advantages.

Preferably, the braking sensor comprises a linear displacement transducer attached to the brake pedal of the vehicle. Alternatively, the braking sensor may be a pneumatic pressure sensor incorporated into the vehicle braking system.

Preferably, the angular position sensor is incorporated into the rotary actuator, however any sensor capable of determining the angular position of the tractor relative to the trailer would also be suitable.

The invention will now be described by way of example only with reference to the following drawings in which: Figures 1 a-c show representations of an articulated vehicle in three modes of travel; Figure 2 shows an example of an anti-jack-knife system according to the present invention using a hydraulic rotary actuator; Figure 3 shows an example of an anti-jack-knife system according to the present invention using an electro- or magneto-viscous fluid operated rotary actuator; Figures 4a and 4b show two examples of vane designs suitable for an electro- or magneto-viscous fluid operated rotary actuator; Figure 5 shows a diagrammatic representation of a processor for use in the present invention; Figures 6a and 6b illustrate the risk of a jack-knife as it is related to vehicle speed and articulation angle and vehicle speed and braking level respectively; and, Figure 7 shows a rotary actuator incorporated into the fifth wheel of an articulated vehicle, An articulated vehicle 1 is shown in Fig. 1 a travelling with the tractor 2 and trailer 3 in line with each other. The direction of travel is indicated by the arrow 6. The

tractor and trailer are connected at a pivot point 4. In this configuration there is a low risk of a jack-knife, even if the speed of travel is high.

Fig. 1 b shows the vehicle cornering at low speed in the direction shown by arrow 7. The angle 5 as the trailer 2 rotates about the pivot point 4 is the articulation angle. This is also a low risk situation.

A jack-knife situation is illustrated in Fig. 1 c. The articulation angle 5 is large as in Fig. 1 b, however the vehicle is travelling in the straight ahead direction of Fig. 1 a, as indicated by the arrow 6. This type of situation can rapidly lead to the driver losing control of the vehicle. It may occur in circumstances where heavy braking is applied whilst the vehicle is moving at high speed, especially if the road surface is slippery, or if abrupt steering is needed, for example in order to avoid an unexpected obstacle.

In Fig. 2, a hydraulic rotary actuator 8 is positioned at the pivot point 4 between the tractor 2 and trailer 3 of an articulated vehicle 1. A fluid control system is provided. In this example, the actuator 8 is filled with a hydraulic fluid 9 and has a vane 10 which rotates with the trailer around the pivot point 4 as shown by the arrows 11, 12. A hydraulic system 13, comprising an accumulator 14 and two variable orifices 15,16 is coupled to the actuator. In a low risk situation, for example as shown in Figs. 1 a and 1 b, both variable orifices 15,16 are open. As the trailer 3 rotates relative to the tractor 2 the vane 10 rotates. This forces hydraulic fluid 9 through the hydraulic system 13 via one of the orifices 15,16, dependent on the direction of rotation, to the accumulator 14. There is little or no resistance to rotation.

If the vehicle is travelling at speed in a straight ahead position and heavy breaking is applied, the orifices 15,16 are narrowed or closed completely. The flow of fluid to the accumulator is thus restricted or prevented. This in turn prevents the vane 10 and the trailer 3 from rotating.

In a high risk situation, for example Fig. 1 c, the articulation angle of the vehicle may be such that the vane 10 is rotated in the direction of arrow 12. In this case, only orifice 16 is narrowed or closed. This restricts or blocks the flow of fluid to the accumulator 14, via orifice 16, but allows flow via orifice 15. Further rotation of the vane 10 in the direction of arrow 12, which would lead to a worsening of the jackknife, is prevented. Rotation in the direction of arrow 11 is not restricted, allowing the vehicle to re-adopt a safe, straight ahead configuration. If the jack-knife is in the opposite direction or the trailer overswings past the straight ahead configuration, the control of the orifices is reversed.

The system adapts to the prevailing conditions. In a low risk situation, the fluid control system allows the rotary actuator to rotate freely. Conversely, when there is a high risk of a jack-knife, for example, when heavy braking is applied whilst the vehicle is travelling at high speed, the fluid control system acts to restrict the rotation of the rotary actuator. It is not always desirable simply to restrict the rotation of the rotary actuator. If the articulation angle is or becomes large when heavy breaking is applied then there is again a high risk of a jack-knife. In this case, if the fluid control system were to prevent any rotation of the actuator the articulation angle may remain large. To counter this, the angular position sensor is adapted to determine the angular direction of the trailer relative to the tractor. The fluid control system is adapted to only restrict rotation of the actuator in the direction which would increase the magnitude of the articulation angle. Substantially free rotation in the direction which reduces the magnitude of the articulation angle is allowed. If the trailer subsequently swings past the straight ahead position and starts to jack-knife in the opposite direction, the fluid control system adapts to restrict rotation in the new direction only.

In place of a hydraulic actuator, one using an electro- or magneto-viscous fluid may be used. This is shown in Fig. 3. An actuator 17 comprises a vane 10 and a fluid 18 whose viscosity can be altered by the application of an electric or magnetic field. The field is supplied via a circuit 19. In a low risk situation the field is switched off, allowing substantially free rotation of the vane 10 and hence the trailer 3 about the pivot point 4. As there is no accumulator, the vane 10 allows fluid to flow past or through it. This can be achieved by employing a perforated vane or one which is smaller than the axial dimension of the actuator housing. This is shown in Figs. 4a and 4b, where the arrows represent the flow of fluid. In a high risk situation, a field is applied, increasing the viscosity of the fluid. This provides resistance to the rotation of the vane 10. As with the hydraulic system described above, rotation can be restricted in one direction only in order to allow the vehicle to regain a straight ahead position.

The risk of a jack-knife is derived by a processor 22 illustrated in Fig. 5 which collects the inputs of a vehicle speed sensor 23, a braking sensor 24 and an angular position sensor 25. In Fig. 5 identification numerals for parts previously described have been preserved. The vehicle is represented by a torque input 26. The processor has three ways of progressively activating the system. Inputs from the sensors are fed to two control blocks 28, 29. Each of these control blocks can individually activate the system to restrict rotation of the rotary actuator or they can act together to the same end. The control blocks 28, 29 contain a matrix which outputs the danger of a

jack-knife depending on its inputs. The outputs in this example are on a scale of 1 to 10, where 10 represents the greatest danger of a jack-knife.

Fig. 6a shows a graphical representation of the matrix for the first control block 28. When the articulation angle is zero, which corresponds to the vehicle travelling in a straight ahead position, the risk is low and rises only slowly with increasing vehicle speed. As the articulation angle increases the effect of vehicle speed becomes greater. As can be seen from Fig. 6a the greatest risk of a jack-knife occurs when the vehicle is travelling at high speed and has a large articulation angle.

The matrix for the second control block 29 is shown in Fig. 6b. At low vehicle speeds, relatively heavy breaking can be applied with a low risk of a jack-knife. Similarly, there is a low risk at high speed as long as the braking level is low. The greatest risk occurs under heavy braking whilst the vehicle is travelling rapidly.

The net effect of the first and second control blocks 28, 29 is the activation of the system to a degree determined by the overall risk of a jack-knife. Physical control of the system is via two further control blocks 30, 31 which control the variable orifices 15, 16 dependent on the outputs of the first and second control blocks 28, 29. In a hydraulic system, when the direction of swing reverses, fluid flows though a one way valve on the side with a restricted variable orifice and through an unrestricted variable orifice on the other side. Similar principles can be used in a system employing an electro- or magneto viscous rotary actuator system.

An example of how a rotary actuator may be incorporated into the fifth wheel assembly of an articulated vehicle is shown in Fig. 7. The actuator 8 is contained within a housing 33 which is attached to the struts 34 of the tractor. The tractor and trailer of the vehicle are connected using a standard arrangement which comprises a fifth wheel plate 35 and a fifth wheel 36. The trailer rotates about a pivot 4 which is fixedly attached to the rotary actuator with a coupling 37. In this way the rotation of the trailer relative to the tractor is under the control of the rotary actuator. The arrangement described in Fig. 7 is convenient as it involves only minor modifications to the standard coupling arrangement found on the great majority of articulated vehicles. It will be clear that alternative arrangements may be readily devised without departing from the scope of the present invention.

Claims

CLAIMS I . An anti-jack-knife system for an articulated vehicle, the system comprising a rotary actuator positioned between a tractor and a trailer of the vehicle, a fluid control system coupled to the actuator, an angular position sensor to detect the articulation angle of the tractor relative to the trailer, a braking sensor, a vehicle speed sensor and a processor; wherein the processor monitors the output of the sensors, derives a risk level from the outputs, and adjusts the fluid control system, such that rotation of the rotary actuator is adapted to the prevailing risk level.
2. A system according to claim 1, wherein the rotary actuator is operated by a hydraulic system.
3. A system according to claim 2, wherein the fluid control system alters the flow of hydraulic fluid in the hydraulic system by the use of variable orifices or servo- valves.
4. A system according to claim 3, wherein the variable orifices or servo-valves are independently controlled.
5. A system according to any of claims 2 to 4, wherein the hydraulic system further comprises a pressure release mechanism to prevent damage to the system under extreme loading conditions.
6. A system according to claim 1, wherein the rotary actuator comprises an electro-viscous or magneto-viscous fluid operated rotary actuator.
7. A system according to claim 6, wherein the fluid control system applies an electric or magnetic field to the fluid of the rotary actuator.
8. A system according to any preceding claim, wherein the rotary actuator is incorporated into the fifth wheel assembly of an articulated vehicle.
9. A system according to any preceding claim, wherein the braking sensor comprises a linear displacement transducer attached to the brake pedal of the vehicle.

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10. A system according to any preceding claim, wherein the angular position sensor is incorporated into the rotary actuator.
11. An anti-jack-knife system for an articulated vehicle as hereinbefore described with reference to the accompanying drawings.