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1. WO2003022656 - VEHICULE FERROVIAIRE A DIRECTION PROPRE

Note: Texte fondé sur des processus automatiques de reconnaissance optique de caractères. Seule la version PDF a une valeur juridique

[ EN ]

SELF STEERING RAIL VEHICLE

BACKGROUND OF THE INVENTION

This invention relates generally to a self steering rail vehicle and more particularly is concerned with a self steering railway bogie.

It is highly desirable for a wheel set of a rail vehicle to be able to travel over straight

(tangent) and curved track without contact or with minimal contact between flanges of the wheels and sides of the rails. By reducing or eliminating this type of contact rail and wheel wear are reduced and vehicle stability is enhanced.

Self steering bogies of which the applicant is aware make use of a sandwich-type primary suspension with an interconnecting linkage between wheelsets. It is however highly advantageous if it is possible to eliminate the linkage because space in the bogie, which such a linkage occupies, can readily be utilised for brake gear and other important structural components such as the bolster or main load carrying components of the bogie. The linkage requires an accurately manufactured sub-frame which is fairly substantial in mass and which is expensive. It follows therefore that without the linkage the unsprung mass of the vehicle or bogie is reduced considerably and this implies a reduction in the dynamic forces which act between the wheels and rails. Ancillary components are simplified and the overall mass compares very favourably with a conventional bogie of the same type eg. a three piece freight bogie with a bolster and two side frames encompassing two wheelsets, a secondary suspension (rubber or steel springs) and brake gear.

SUMMARY OF INVENTION

The invention provides a rail vehicle which has at least first and second wheelsets and wherein:
(a) the treads of the wheels are coned at an angle of between 4° and 9°,
(b) each wheelset is engaged with axle boxes,
(c) each axle box has an inclined chevron-type primary suspension, and
(d) no linkage connects the first wheelset to the second wheelset.

The wheel treads may be coned at an angle of from 5° to 8° but preferably are coned at an angle less than 7°. The cone angle is chosen to allow the wheelsets to self-steer around the sharpest curves on a rail track without material contact of the flanges of the wheels with the rails. With a higher or steeper cone angle the likelihood of flange contact is reduced but the critical speed at which instability can occur is also reduced.

The primary suspension may be of any appropriate type but preferably is of the type described in the specification of South African patent No. ZA97/4198 or ZA89/3711.

The rail vehicle may include an elongate underframe or chassis with the first and second wheelsets being located respectively towards opposed ends of the underframe or chassis.

On the other hand in a different form of the invention the rail vehicle includes at least one bogie and the first and second wheelsets form part of the bogie. With this form of the invention the rail vehicle will normally include at least two bogies at spaced positions to support an underframe or chassis.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is further described by way of example with reference to the accompanying drawings in which:
Figure 1 is a perspective view of a self steering bogie according to the invention wherein brake gear and certain ancillary equipment associated with the bogie have been omitted for clarity of illustration,
Figure 2 is schematic end view of portion of a wheel used in the bogie of Figure 1 , and
Figure 3 illustrates in plan two wheelsets of a rail vehicle with a longer wheel base than the bogie of Figure 1 , with preferred suspension assemblies, and
Figure 4 is a side view of a suspension arrangement used in the bogie of Figure 1.

DESCRIPTION OF PREFERRED EMBODIMENT

Figure 1 of the accompanying drawings illustrates in perspective a self steering bogie according to the invention. As has been indicated brake gear and other ancillary equipment associated with the bogie have been omitted for clarity of illustration.

Such gear and equipment play no role in an understanding of the invention.

The bogie 10 includes first and second wheelsets 12 and 14 respectively which are mounted in side frame members 16 and 18. A cross member 20 extends between the frame members 16 and 18 and, in use, is pivotally connected at a central point 22 to a chassis of a rail vehicle (not shown). Springs 24 or similar suspension elements support the cross member on the frame members. The springs 24 are preferably made from rubber laminations and may be circular cylindrical in shape. It has been found that rubber springs are highly suitable for they can function under overload conditions while retaining self-damping characteristics. The self-damping characteristics, in turn, eliminate friction wedges or similar devices which are used to provide a measure of friction damping when suspension elements, other than rubber springs, are used.

Each wheelset 12, 14 includes an axle 26 and wheels 28. The wheels roll on rails

30.

Figure 2 is an end view of a portion of an axle 26 and a wheel 28. The wheel has a flange 32 and a track-engaging portion or tread 34. The tread portion is coned in the sense that it presents a conical surface, ie. a surface which is inclined to a line 36 which is parallel to the axle 26. In accordance with a preferred feature of the invention the wheel tread is coned at an angle 38 which lies in the range of from 4° to 9°, typically in the range of from 5° to 7°. The cone angle is chosen to limit flange contact with the rail, taking into account the maximum rail curvature. The wheel tread has a width 40 which should be as wide as possible and the flange 32 is relatively thin to ensure maximum tread contact with the top of an associated rail 30.

It is pointed out that the wheel flange 32 should only contact a side of the rail 30 under unusual conditions eg. very poor track and or very sharp radius curves. In other words the wheel flange is a safety feature which comes into play under extreme conditions.

Figure 3 depicts in plan the wheelsets 12 and 14 of a relatively long vehicle, on the rails 30. Each axle 26 is mounted to axle boxes which have a primary suspension consisting of inclined elastromeric chevron-type suspensions designated 44A, 44B, 44C and 44D respectively, in the manner described in the specification of South African patent No. 97/4198 or 89/3711. The disclosures in these specifications are to be deemed to be incorporated in this specification.

The inclined chevron-type primary suspensions referred to act like springs and provide a very low yaw restraint, some vertical deflection under load and a high lateral spring rate to ensure stability and a high critical speed for "hunting" ie. the yaw oscillation of the rail vehicle about its own centre of gravity.

Figure 4 is a side view of the chevron-type suspensions 44 referred to in connection with Figure 3. The chevrons on the left side of the drawing are illustrated partly sectioned, to show their construction. The axle 26 extends through an axle box 50 and is mounted on bearings which are located in the axle box. The axle is directly connected to a pair of wheels 28.

The axle box has two inclined support surfaces 52 and 54 respectively each of which has an upstanding respective spigot 56 for correctly positioning the axle box with respect to chevrons 58 and 60, on opposed sides of the axle box. Other means of locating the chevrons correctly could be used in place of the spigots.

Each of the chevrons 58 and 60 includes angled members, in this case steel plates 62, which are bonded to intermediate elements 64 of rubber or an equivalent elastomeric material.

The lowermost plate of each chevron, designated 66, has a bridging plate 68 in which is formed a hole, not shown, and the corresponding spigot 56 is engaged with the hole when the chevron is placed on the inclined surface 52 or 54 of the axle box. The plate 66 is essentially parallel to the plates 62.

An upper plate 70 is fixed to the body of the rail vehicle. Stops 72 or similar devices locate the upper plates 58 and 60 correctly.

Viewed in plan the chevrons 58 and 60 are inclined to the longitudinal axis of the axle and, viewed from the side, the chevrons are inclined to the vertical.

The aforementioned type of suspension locates the wheel set correctly and keeps the wheel set geometry in a desired configuration.

No linkages extend between the wheel sets. The linkages are omitted and this step can be taken since stability in yaw is achieved by selecting the correct chevron angle and hence the most suitable lateral spring rate.

Figure 3 illustrates the concept of focalising. This concept is fully described in the specification of patent No. ZA97/4198. In the bogie of the invention if the wheel base is relatively short in comparison with the track gauge and minimum curvature then focalising is not usually required. On the other hand if the wheel base is relatively large compared to the track gauge and the curves are sharp then focalising would normally be required. Focalising can however readily be incorporated when chevrons with a small chevron angle are required. These chevrons can increase the yaw restraint substantially in sharp curves unless they are focalised.

In other words with a bogie of the type shown in Figure 1 it would not normally be necessary to focalise the suspensions. On the other hand if a first wheelset is positioned at one end of an elongate chassis and a second wheelset is positioned at an opposing end of the chassis it will normally be appropriate to focalise the chevrons.

It has been found that by utilising the principles described herein ie. by coning the wheel treads at an angle of from 4° to 9°, depending on the rail conditions, and by making use of inclined elastromeric chevron-type primary suspensions that the requirement for a linkage, to achieve a self-steering capability, is dispensed with. In operation of the bogie of the invention each wheelset follows its own path when travelling on straight (tangent) or curved track. This ensures that the coned wheel treads roll on the track at all times through track irregularities and curves with a very substantial reduction in rolling resistance. By way of contrast if the wheelsets are linked to each other they influence the motion of each other. They then tend to behave like a conventional rigid wheel base bogie.

With the self-steer bogie of the invention derailments are reduced because the coned wheels with low yaw restraint steer themselves away from a track irregularity. If a wheel flange 32 does contact the rail 30 the point of contact is behind the centre of the vertical force on the rail and this generates a vertical friction force downwardly which increases the adhesion of the wheel on the rail instead of generating an unwanted vertical flange force ahead of the wheel which can lift that wheel over the rail and so result in a derailment.

Clearly it is preferred that the wheelsets of the bogie of the invention are correctly aligned. Nonetheless a degree of misalignment can be tolerated as there is no interconnecting linkage between the wheelsets to generate incorrect tracking of one or both wheelsets.

The principles of the invention can be incorporated into a bogie, as is shown in Figure 1 , wherein two of the bogies are attached at spaced positions to an underframe of a rail vehicle. Alternatively wheelsets of the kind used in the bogie are directly attached to an underframe of a rail vehicle.

In designing the primary suspension for the bogie the spring characteristics of the secondary suspension must be considered, together with the leading dimensions of the bogie such as wheel diameter, track gauge and wheel base, and the superstructure and load, including parameters such as the bogie centre spacing, and the width and height above the rail. Empty and loaded vehicles have natural frequencies of vibration about their principal axes and synchronous/critical conditions arise when any one of these frequencies is the same as any of the input frequencies eg. hunting frequencies (lateral movement across the track) or frequencies induced by rail joints (in the longitudinal direction of the track) or the like. Coned wheels generate a sinusoidal motion across the track depending upon cone angle, wheel diameter and track gauge with a wavelength which is very nearly constant. When the speed along the track and the wavelength of yaw oscillation of the wheelsets generate a frequency which is synchronous with any one of the natural frequencies of the vehicle mass, then a critical condition is reached at which the oscillation cannot be damped and either the speed must be changed or a derailment will occur. This condition must be avoided by the correct design of the suspension of the bogies to suit the application to the wagon under which they will operate. It is preferable to have the critical speeds higher than the maximum operating speed of the rail vehicle.

This is generally not difficult to achieve when proper consideration is given to all the parameters.

It is advisable to incorporate the lowest wheel tread conicity consistent with the minimum radius of curve in order to have the longest wavelength sinusoidal hunting oscillation of each wheelset consistent with the other parameters.

Under unusual conditions there may be a very low critical speed and the vehicle may be accelerated through this critical condition. This arrangement is however not recommended because operating conditions could arise under which the critical speed is commonly encountered.

Since the wheels roll and do not slide on the rails the wheel treads tend to harden resulting in very little wear. When wear does occur, usually from brake block action, then it is even and very little "hollow wear" is experienced.

The bogie of the invention is simple in design, effective in operation, substantially maintenance free and easy to access should service be required after unusual occurrences such as accidents or derailments. Expensive accurately made linkages are an undesirable feature of self-steered and steered bogies and, as stated, such linkages are avoided in the invention by making use of inclined chevron-type primary suspensions which provide lateral stability as well as reducing high frequency vibrations.