GB2035500A - A wheel set for a rail bogie - Google Patents

Abstract

In a wheel set for a bogie for a rail or track vehicle, having profiled wheels (4) for rotation on a common axle (1) and connected together by way of a controllable frictional clutch (6), slippage of the clutch (6) is variable under the control of a regulator (8), which receives measured values of the vehicle speed, the rate of revolution (n1, n2) of both wheels (4) and an estimated value (R) of the respective effective track curve radius. <IMAGE>

Description

SPECIFICATION Wheel set for a rail bogie The invention relates to a wheel set for a rail bogie and in particular to the controlling of the tracking thereof.

In rail vehicles bogies are used which have wheel sets having severely-centering running surfaces which are guided laterally relatively rigidly in the bogie frame. Such sets have a tendency, especially at high speeds, to run unstably. When this happens, the bogie performs rapid and violent rotary motion about its vertical axis. Above a specific critical speed such a bogie can perform yawing oscillations caused by lateral sliding or transverse motions, which oscillations can, upon further speed increase build up to a dangerous level.The result is a striking of the wheel flanges against the rails and thus a great running unsteadiness as well as high wear of the wheel flanges, rails and permanent way. An appropriate increase in the turning resistance of such a bogie for example by means of restraint applied to its pivot on the vehicle frame does lead to a more stable running, but also lessens the cornering ability of the bogie. The latter fact cannot of course be completely precluded even by use of rotary restraints whose resistance decreases with increasing turning of the bogie. On the other hand, the cornering ability can indeed be improved as a result of mechanisms for controlling the bogie into a specific position with regard to the curvature of the track. However, on account of the positioning effect, the known mechanisms of this kind are not able to fulfil the aforesaid task of the stabilisation bogie travel.A suitable solution which prevents yawing oscillations as well as lateral sliding or transverse motions, can also not be seen in wheel sets having wheels which are mounted for rotation independently on the axle. Such "loose" wheel arrangement does indeed have, as compared with the conventional fixed wheel set the advantage that upon lateral shifting of the wheel set (more especially on a curve in the track) by virtue of the then different rolling radii of the wheels no longitudinal sliding between wheel and rail (with the result of destabilising forces) can arise. However, such sets have no self-centering properties in relation to the track and complicated and/or expensive steering or guiding mechanisms are necessary in order to be able to undertake, at any curve in the track, the correct positioning of the wheel set relative thereto.Moreover, as is well known, the loose wheel arrangement suffers from high wheel flange wear.

A reduction in the yawing motions and lateral sliding or transverse motions in the case of bogies having fixed wheel sets is possible by reducing the tread inclination of the wheels, because then the possible rolling radii difference and therewith also the longitudinal slippage of the wheels which is dependent thereon becomes less. From this there results, however, in turn a reduction in the yawing faces exerted on the bogie about its vertical axis and consequently a considerable worsening of the cornering ability, since these forces are a main constituent of the guidance forces exerted by the wheel set.Upon reduc ing of the tread inclination or conicity of the wheel profile, the stabilising effect of the wheel set and bogie travel is at the cost of the cornering ability, in contrast to wheel sets having a large tread inclination of the wheel profiles, which as is well known have good cornering ability and relatively poor running stability. Moreover, irrespective of the original profile of the wheel tyres when manufactured, sooner or later the tyre wears and the wheel takes up the so-called wear profile, with the result of that there is a large rolling radii difference between the wheels. Accordingly, basically destabilising states can arise.

Thus the object of the present invention is to provide a wheel set for a bogie wherein stabilisation of the wheel set and of bogie travel is achieved without impairing the cornering ability or the guidance behaviour of the wheel set irrespective of the state of wear of the tyres of the wheels. German Offenlegungsschrift No. 2,259,035 tries to solve these problems, but does not do so completely. In this specification the position of the axle centres with regard to a central plane of the track is influenced actively by a positional regulator, adjusting members of which act directly or indirectly on the wheel sets. Common to all three embodiments described in this specification is the fact that they are at best only able to improve the steering or controlling action of the wheels which is predetermined by virtue of the conicity of the tyres.In the first embodiment for a fixed or loose wheel set, this is achieved by a positioning procedure, that is by rotating the wheel set about its vertical axis with the result of a variation in the effective conicity of the treads and thus of the rolling radii of the wheels.

Since, of course, only extremely small rotations are necessary for influencing the guidance behaviour of the wheel set, the relevant mechanisms is very difficult to construct. The same applies to the proposed axial shifting of the wheels in accordance with the second embodiment. In this case there is posed, in addition to this, also the problem that upon a variation of the wheel/rail contact conditions as a result of tyre wear, the connection, assumed for the design of the system, between wheel transverse displacement and travel of the wheel contact point on the rail no longer exists. For an accurate effect of the system, therefore, the respective wheel bearing point would have to be measurable, which is of course not possible.Finally, the predetermining of a speed difference by means of a differential gearing in accordance with the third embdodiment, in which each wheel, driven individually, is seated on its own axle shaft and the two axle shafts per pair of wheels are coupled by way of the differential gearing, also contributes only to increasing the effective conicity. As soon as the wheels wear, and take up a profile which causes a great rolling radius difference, the effect thereof is further increased by the predetermined speed difference and thus the wheel set is necessarily destabilised. Common to all three embodiments is thus the fact that the desired effect is at most ensured only in the case of wheels having exactly conical treads.

As soon as a wear profile forms, the second and third embodiment are unusable. The first embodiment is usable only in the case of reduced cycle amplification of the regulating system. Then of course the effectiveness is very slight, i.e. the guidance and stability behaviour, resulting from wear of the wheel set dominates.

Moreover, a further known wheel set, (German Patent No. 950,011) has mutually-rotatable wheels between which is disposed a regulatable brake, the braking force or action of which is fixed upon manufacture, an improvement in travel on curves is merely achieved in that an adhering of the wheels of this loose wheel set to the rail is prevented.

In contrast thereto, however, finally in the case of a wheel set in accordance with German Offenlegungsschrift No. 26 14 166 fundamentally undesirable effects of wear of the tyres of the wheels on the stability can be avoided without impairing the guidance behaviour of the wheel set and accordingly the wear-favouring yawing conditions when the wheels are worn can be further utilised. In this case, namely with the recognition that in the case of loose wheels (only with respect to a common axle shaft) the destabilising slippage, resulting from large rolling radii differences, of the wheels relatively to the track is influencable in the aforementioned sense without difficulties, a clutch which connects the wheels is controlled, by a regulator, in the sense that the slippage of the clutch is increased with increasing vehicle speed and is reduced with decreasing vehicle speed.The basic effect of the clutch is in the modulation of the longitudinal slippage forces between the wheels and the track to improve the stability conditions afforded by a wear profile. The slippage in the clutch reduces the dynamically-effective conicity as well as the dynamically-effective wheel base and thus leads, in the case of a worn wheel set to good stability. A good guidance behaviour on tight curves in the track can be achieved in a simple manner by obviating the slippage in the clutch, i.e. the wheel set then fulfils the function of a fixed wheel set with the good guidance properties on small radius curves which are peculiar to it.

Of course in this wheel set it has to be accepted that the measured values of "frequency of wheel-set sinuous oscillations increasing in amplitude, lateral displacement of the wheel set as compared with the central plane of the track, transverse forces acting on the wheel", which are to be supplied to the regulator for it to fulfil its function, necessitate a considerable expenditure on measuring points on the wheel set or the relevant bogie, i.e. at such a point where more especially by virtue of atmospheric influences higher wear and, possibly, more frequent failures of the measuring equipment are likely.

In view therof, the object of the present invention can be restated to be the provision of a wheel set for a rail bogie wherein a clutch connecting the two wheels of the set is under the influence of cheaper and/or simpler control means.

Accordingly the invention provides a wheel set, for a bogie for a rail or track vehicle, whose wheels, which have profiled running surfaces, are mounted, for rotation on a common axle and are connected to one another by way of a controllable frictional clutch, in which the slippage can be varied during travel in accordance with restrictions from a regulator which receives measured values of the vehicle speed, the slippage of the clutch being increased with increasing speed of the vehicle and reduced with decreasing speed of the vehicle, wherein measured values of the rates of revolution n1, n2 of both wheels as well as an estimated value of the respective effective track curve radius are supplied to the regulator and wherein by virtue of these input values the regulator, in controlling the slippage of the clutch, differentiates between a stabilising clutch moment component, which is proportional to the differential speed (n2-n1) and inversely proportional to the vehicle speed, and a guiding clutch moment component which is inversely proportional to the effective track curve radius.

The invention will be described further, by way of example, with reference to the accompanying drawings, wherein the single figure is a transverse cross-sectional view through a preferred wheel set of the invention.

A preferred wheel set of the invention has an axle 1 is arranged in frame or longitudinal supports 2 of a bogie, for example by way of a suspension 3 which is preferably soft in the lateral and vertical directions, but hard in the longitudinal direction. The wheels 4 are mounts for rotation on the axle 1. The wheel bearing 5, which are indicated only symbolically, may be roller bearings. In this wheel set the wheels 4 are not so-called "loose wheels", i.e. wheels seated loosely with re gard to one another on the axle 1. This is because the wheels 4 are connected to one another by way of a clutch 6 (also only indicated schematically), in which respect there are connecting means, arranged for rotation about the axle 1, between the wheels 4 and can consequently revolve with them.The clutch 6 is a controllable electromagnetic friction clutch in which the frictional action of a magnetisable iron powder 6.1 is utilised to transfer torque and slippage is adjustable even in travel by varying the electric current supplied thereto.

The clutch 6 has the function, upon travel along the track 7, in the event of a difference in rolling radii of the wheels 4, of permitting a differential which speed to stabilise the set.

That is the clutch 6 reduces the longitudinal slipping of the wheels relative to the track.

This applies mainly when the wheels have worn to have a so-called wear profile. In this condition the conventional fixed wheel set has a good guidance behaviour, but as a result of the wear profile the stability conditions are poor by virtue of a large rolling radius difference and therewith a large longitudinal slippage of the wheels relative to the track. In the afore-described arrangement of the wheels 4 and clutch 6 by appropriate changing of the clutch current the slippage merely needs to be adjusted in order to reduce the longitudinal slippage of the wheels 4 with regard to the track 7.The clutch 6 is accordingly a suitable adjusting member by means of which the entire slippage, resulting from the rolling radius difference of the wheels 4, can be split up into, on the one hand, longitudinal slippage of the wheels with regard to the track 7 and, on the other hand, slippage in the clutch. Thus, the wheel set is dynamic irrespective of the wheel profile. As regards the guidance behaviour of the wheel set on tight curves in the track, then also by way of the clutch 6 a rigid connection between the two wheels 4 needs to be re-established, with the result that the wheel set acts as a fixed wheel set. In the case of curves in the track having a fairly large radius, which can be traversed at high speed, an increase in the moment transmitted by the clutch 6 brings about an improvement in the cornering.

As moreover emerges from the drawing, for the aforesaid purpose the clutch 6 is controlled by a regulator 8, for example a state regulator, which calculates a desired value M n of the clutch moment. For this purpose a measured value (e.g. obtained by way of a tachogenerator) of the vehicle speed v, and measured values of the rates of revolution n1, n2 of both wheels 4 are supplied to the regulator 8. The speed measurement can by effected by speed counters 1 3 mounted on the two hollow shaft parts 6.4 or 6.5 which are associated with the clutch halves 6.2, 6.3. On the other hand there is fed to the regulator 8 an estimated value R of the respective effective track curve radius, which is ascertained at least from the measured values of vehicle speed vand free transverse assceleration a active at the bogey.Depending on accuracy requirements the track superelevation A h can be measured. The regulator 8 receives this effective track curve radius value R e.g. from a microprocessor 14, to which the respective free transverse acceleration a can be imparted by an accelerometer mounted at the centre of the bogie and track superelevation A h can be measured by way of an inclination measuring apparatus which is for example also present on the bogie. By virtue of these input vlaues, vehicle speed v, rates of revolution n1, n2 and track curve radius R, the regulator 8 decides on the operating conditions and varies Mnv accordingly thus varying the slippage of the clutch 6 according to conditions. The clutch 6 has higher slip with increasing vehicle speed and lower slip with decreasing vehicle speed.The regulator 8 distinguishes between a stabilising clutch moment component and a guiding clutch moment component. In this respect, the stabilising moment component is proportional to the differential speed n2-n1 and inversely proportional to the vehicle speed v. The guiding moment component is proportional to the respective effective track curve radius R. Thus, on a straight away only the stabilising moment component is crucial which decreases with increasing vehicle speed. As has been said, the increasing slippage of the clutch reduces the dynamically-effective conicity of the wheels as well as the dynamicallyeffective wheel base and thus leads to good stability behaviour. The good guidance behaviour of the wheel set is, in contrast, ensured by increasing the guiding clutch moment component, i.e. by reducing the slippage of the clutch when a track curve is encountered.

By virtue of the aforedescribed control of the clutch 6, this wheel set has, on the one hand, a small dynamically-effective conicity with respect to the stability of its motion about the respective working point of "contact point wheel/rail" and thus a high critical speed. On the other hand, the working-point migration, characterised by the guiding deviation, is so limited by the guiding clutch moment component that only the available track play is utilised and the reaction to free lateral forces, as occur on curves, is improved.

Depending on necessity, the afore-described regulator 8, which thus calculates the desired value Mnv for the clutch moment Mn and applies same as voltage to the clutch 6, may also contain networks for correcting the dynamic behaviour and non-linearities ( such as hysteresis) of the clutch. The clutch 6 is operated in moment-controlled manner (open-loop operation). Alternatively, the clutch 6 may however also be operated in moment-regulated manner (closed-loop operation), for which pur pose then in accordance with the drawing a feedback of the measured clutch moment Mn can be provided. In this case, the measuring of the clutch moment Mn can take place in conventional manner by means of a wire strain gauge 1 2 on one of the two hollow shaft parts 6.4 or 6.5.

Finally, it remains to be commented that it is possible, in the case of rail vehicles having driving bogies, to provide the described clutch in combination with a differential gearing which fulfils in engagement with the drive of the driving bogie the function of a driving means which equalises the driving forces.

Claims (6)

1. A wheel set, for a bogie for a rail or track vehicle, whose wheels, which have profiled running surfaces, are mounted, for the active setting of a differential speed, for rotation on a common axle and are connected to one another by way of a controllable frictional clutch, in which the slippage can be varied during travel in accordance with restrictions from a regulator which receives measured values of the vehicle speed, the slippage of the clutch being increased with increasing speed of the vehicle and reduced with decreasing speed of the vehicle, wherein measured values of the rates of revolution n1, n2 of both wheels as well as an estimated value of the respective effective track curve radius are supplied to the regulator and wherein by virtue of these input values the regulator, in controlling the slippage of the clutch, differentiates between a stabilising clutch moment component, which is proportional to the differential speed (n2-n,) and inversely proportional to the vehicle speed, and a guiding clutch moment component which is inversely proportional to the effective track curve radius.

2. A wheel set as claimed in claim 1, wherein the track curve radius value is ascertained at least from the measured values of vehicle speed and free transverse acceleration which is effective at the bogie.

3. A wheel set as claimed in claim 2, wherein additionally the track superelevation (ash) is measured for determining the track curve radius value.

4. A wheel set as claimed in claim 1, wherein measured values of the clutch moment are supplied to the regulator.

5. A wheel set substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

6. A railway vehicle bogie comprising a pair of wheel sets as claimed in any preceding claim.