EP4719867A2 - Steering assembly and method for controlling the same - Google Patents
Steering assembly and method for controlling the sameInfo
- Publication number
- EP4719867A2 EP4719867A2 EP24733263.8A EP24733263A EP4719867A2 EP 4719867 A2 EP4719867 A2 EP 4719867A2 EP 24733263 A EP24733263 A EP 24733263A EP 4719867 A2 EP4719867 A2 EP 4719867A2
- Authority
- EP
- European Patent Office
- Prior art keywords
- steering
- steering assembly
- wheels
- moveable
- wheel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D7/00—Steering linkage; Stub axles or their mountings
- B62D7/06—Steering linkage; Stub axles or their mountings for individually-pivoted wheels, e.g. on king-pins
- B62D7/14—Steering linkage; Stub axles or their mountings for individually-pivoted wheels, e.g. on king-pins the pivotal axes being situated in more than one plane transverse to the longitudinal centre line of the vehicle, e.g. all-wheel steering
- B62D7/142—Steering linkage; Stub axles or their mountings for individually-pivoted wheels, e.g. on king-pins the pivotal axes being situated in more than one plane transverse to the longitudinal centre line of the vehicle, e.g. all-wheel steering specially adapted for particular vehicles, e.g. tractors, carts, earth-moving vehicles, trucks
- B62D7/144—Steering linkage; Stub axles or their mountings for individually-pivoted wheels, e.g. on king-pins the pivotal axes being situated in more than one plane transverse to the longitudinal centre line of the vehicle, e.g. all-wheel steering specially adapted for particular vehicles, e.g. tractors, carts, earth-moving vehicles, trucks for vehicles with more than two axles
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D13/00—Steering specially adapted for trailers
- B62D13/04—Steering specially adapted for trailers for individually-pivoted wheels
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D7/00—Steering linkage; Stub axles or their mountings
- B62D7/22—Arrangements for reducing or eliminating reaction, e.g. vibration, from parts, e.g. wheels, of the steering system
- B62D7/228—Arrangements for reducing or eliminating reaction, e.g. vibration, from parts, e.g. wheels, of the steering system acting between the steering gear and the road wheels, e.g. on tie-rod
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B62—LAND VEHICLES FOR TRAVELLING OTHERWISE THAN ON RAILS
- B62D—MOTOR VEHICLES; TRAILERS
- B62D9/00—Steering deflectable wheels not otherwise provided for
- B62D9/002—Steering deflectable wheels not otherwise provided for combined with means for differentially distributing power on the deflectable wheels during cornering
Landscapes
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Transportation (AREA)
- Mechanical Engineering (AREA)
- Steering-Linkage Mechanisms And Four-Wheel Steering (AREA)
- Non-Deflectable Wheels, Steering Of Trailers, Or Other Steering (AREA)
Abstract
A steering assembly comprising a pair of wheels and a moveable steering linkage, the wheels being mounted at either end of the moveable steering linkage; wherein each wheel is provided with a brake, each brake independently actuatable such that a different braking torque may be selectively applied to each wheel so as to induce a yawing moment across the moveable steering linkage, thereby causing the wheels to steer.
Description
STEERING ASSEMBLY AND METHOD FOR CONTROLLING THE SAME FIELD OF THE INVENTION The present invention relates to a steering assembly and method for controlling the same. BACKGROUND Heavy Goods Vehicles (HGVs) are a significant source of carbon emissions, accounting for 19% of UK road transport emissions. Supporting the logistics sector to become sustainable and more efficient is crucial to the UK’s economic wellbeing and will deliver significant improvements to society. One solution that can implemented now is the use of higher-capacity vehicles. Provided that its capacity is fully utilised, as a vehicle’s length increases it becomes more productive and uses less energy per freight task. The downside is that longer HGVs become less manoeuvrable and more difficult to control. In countries such as the UK, such vehicles are not considered roadworthy since they fail to comply with the roundabout test requirements. To overcome the manoeuvrability limitations of longer vehicles, active steering systems can be installed on the trailer's axle group and unlock the adoption of longer vehicles for road freight distribution. Conventionally, active rear-steering is achieved using electro-hydraulic actuators. For example, in one conventional design for an active steering axle a double- ended hydraulic actuator is used to control the steering angle of both wheels on a steerable axle via a mechanical linkage similar to those used in rack-and-pinion steering. However, the mechanical components used in conventional designs such as this are prohibitively expensive and heavy, preventing widespread adoption of the active steering systems currently available. There is therefore a need for lighter and cheaper solutions. SUMMARY OF INVENTION According to a first aspect of the invention, a steering assembly is provided. The steering assembly comprises a pair of wheels and a moveable steering linkage,
the wheels being mounted at either end of the moveable steering linkage; wherein each wheel is provided with a brake, each brake independently actuatable such that a different braking torque may be selectively applied to each wheel so as to induce a yawing moment across the moveable steering linkage, thereby causing the wheels to steer. The application of a different braking torque to each wheel generates a different braking force on each wheel at the respective wheel-road interfaces. This force differential in turn leads to the induction of the yawing moment across the moveable steering linkage which in turn results in the two wheels to steer. The steering assembly therefore eliminates the need for additional steering actuators and associated hardware required (such as mechanical linkages or hydraulic pumps, accumulators, batteries etc.). The benefits of the steering assembly include significant reductions in mass, cost, and complexity of steering systems, thereby improving over conventional active steering systems and allowing safe manoeuvring of a wide range of vehicle types in confined spaces. A particular benefit is that the improved steering allows for the use of higher-capacity vehicles in the regions such as the UK, boosting productivity and reducing carbon emissions. The use of steered rear-axles will also significantly reduce tyre wear and enable low rolling resistance tyres to be used under all applications, reducing fuel consumption by 7-9%. According to a second aspect of the invention, a steering assembly is provided. The steering assembly comprises a pair of wheels and a moveable steering linkage, the wheels being mounted at either end of the moveable steering linkage; wherein the steering assembly comprises a driven axle connecting the wheels, the driven axle being configured to independently provide drive to each wheel independently such that a different driving torque may be selectively applied to each wheel so as to induce a yawing moment across the moveable steering linkage, thereby causing the wheels to steer. The second aspect of the invention provides the same advantages as the first aspect of the invention, and is particularly suitable for use in implementations
where a steering assembly would be drive by and electric drive by configuring the drive to independently provide drive to each wheel. In particularly advantageous embodiments of the first aspect of the invention, the steering assembly further comprises a driven axle connecting the wheels, the driven axle being configured to independently provide drive to each wheel such that a different driving torque may be selectively applied to each wheel so as to induce a yawing moment across the moveable steering linkage, thereby causing the wheels to steer. The independent application of braking and/or driving torque can thereby be used to provide improved steering. For each particular design situation (i.e. a particular axle geometry for a particular application), the caster angle and kingpin inclination are preferably chosen so as to minimise the energy consumption of a vehicle to which the steering assembly is mounted and minimise the tracking error, while not exceeding the available friction in the tyre interface. Advantageously the caster angle is kept small so as to allow the steering assembly to steer in reverse. Each wheel is preferably mounted to the moveable steering linkage with a caster angle of -2º to 2º, preferably of -1º to 1º, more preferably of -0.5º to 0.5º, and still more preferably of substantially 0º. Each wheel is preferably mounted to the moveable steering linkage with a kingpin inclination of less than 5º, preferably of less than 3º, more preferably of less than 1º, and still more preferably of substantially 0º. The steering parameters affect the performance of the steering assembly by affecting the forces required to induce steering of the wheels. The caster angle and kingpin inclination are two particularly relevant parameters. Other relevant parameters include the caster trail and kingpin offset (also referred to as the scrub radius) which are influenced by the caster angle and kingpin inclination parameters as well as by other aspects of the steering assembly, such as tyre radius and tyre diameter. These parameters together influence the stability, required steering effort, and “returnability” (i.e. the inclination of the wheels to
return to a straight-ahead, unsteered orientation) and it has been found that low values of the caster angle and kingpin inclination are optimal for improving low speed cornering performance while reducing the braking and/or driving torque required to induce steering. These also allow for the wheels to be steered whichever direction they are traveling in. One particular measure of steering performance which is affected by the steering parameters is the steering angle error, which is a measure of the difference between a desired steering angle and that achieved when selectively applying different braking and/or driving torques to each wheel. Depending on the steering parameters chosen, the steering linkage may lead to the induced steering angle of the wheels being either greater or less than the desired steering angle, and the steering angle error is therefore preferably measured as the root mean square of the difference between the induced and desired steering angles. It has been found that there is typically a trade-off between minimising the steering error and minimising the energy required to induce steering of the wheels, and it is also advantageous to select the steering parameters such that the overall friction utilization during steering is reduced. Friction utilization is a measure of how much of the available friction from a road surface is used by the steering assembly, and reducing the friction utilization of the steering assembly allows for improved cornering performance on low friction surfaces. In order to optimize these various requirements, selection of the steering parameters is advantageously performed using a multi-objective performance optimization which aims to minimise at least two of the steering error, the energy required to induce steering of the wheels, and friction utilization. In order to maintain a suitable alignment of the wheels, the moveable steering linkage preferably comprises a track rod connecting the pair of wheels. More preferably, the steering assembly has an Ackermann geometry such that both wheels turn around a common turn centre. This helps to provide low side-slip angles during cornering and, as a result, provides benefits in terms of reduced tyre wear and energy consumption.
As will be appreciated, it is advantageous to configure the steering assembly so as to reduce the magnitude of the yawing moment required to cause the wheels to steer. In order to prevent this resulting in oscillations in the steering linkage, the steering assembly preferably comprises a steering damper connected to the moveable steering linkage so as to damp shimmy oscillations, which are oscillations in the steering angle of the wheels. In some implementations, the steering damper is telescopic with coaxial shafts and connected between the moveable steering linkage and a fixed point of the steering assembly. For example, the steering assembly may comprise an axle beam and the moveable steering linkage may comprise a track rod, in which case the telescopic steering damper may be attached to the axle beam at one end and a steering arm or the track rod at the other end. In other implementations, the steering damper may rotational and located at one or both steering kingpins, thereby restricting rotation of the steering arms relative to the axle. In order to ensure the steering damper damps oscillations without increasing the magnitude of the yawing moment required to cause the wheels to steer, the damping force of the steering damper is preferably substantially 0 at 0 velocity. Likewise, the steering damper preferably a linear force-velocity characteristic. It is also advantageous for the steering damper to provide the same damping characteristics in extension and compression. For example, a telescopic steering damper may be arranged such that it is in compression when the wheels are turned in one direction and in extension when the wheels are turned in the other direction. The steering assembly preferably comprises a centring system having an actuator configured to engage with the moveable steering linkage such that actuation of the actuator induces a centring force on the moveable steering linkage. The actuator may be an electric actuator or a pneumatic actuator.
In particularly preferred embodiments, the centring system comprises an inflatable airbag and a pair of lever arms, each lever arm being connected at one end to the air bag and being configured to engage with the moveable steering linkage at its other end. The inflatable airbag preferably comprises a pair of endplates, each connected to one of the lever arms. In order to ensure correct alignment of the endplates during steering, the endplates are preferably connected along a central axis of the airbag by a telescopic cylindrical bearing so as to maintain the alignment of the endplates. To the same end, the connection point of each lever arm with its respective endplate is preferably laterally offset from the central axis of the airbag. This produces a realigning moment and ensures correct alignment of the pair of end- plates during the steering movement. In some embodiments, the steering assembly comprises an axle beam connecting the wheels, the pivot point of each lever arm being connected to the axle beam. In embodiments where the actuator is a pneumatic actuator, the steering assembly preferably further comprises: a first pressure control valve configured to receive air from a compressed air source and to output air at a first pressure; a second pressure control valve arranged to receive air from the compressed air source and to output air at a second pressure, the second pressure being lower than the first pressure; an actuator valve configured to receive air output from the first and second pressure control valves and to selectively output air to the pneumatic actuator at the first or second pressure. In this way, air may be selectively output at a first pressure to actuate the pneumatic actuator and thereby induce a centring force on the moveable steering linkage or at a second pressure so as not to actuate the pneumatic actuator and thereby allow for movement of the moveable steering linkage with little or no resistance from the centring system so as to enable steering of the wheels. The steering assembly is particularly suitable for improving the steering characteristics of a vehicle at low speed. It may be desirable, however, to lock the
steering assembly at higher speeds (or, indeed, at lower speeds in some situations) and the steering assembly may therefore comprise a locking mechanism configured to engage with the moveable steering linkage so as to inhibit steering of the wheels. The steering assembly may comprise an axle beam and the locking mechanism may comprise: a first mounting plate attached to the moveable steering linkage; a second mounting plate attached to the axle beam; a locking pin configured to engage with the first and second mounting plates so as to inhibit steering of the wheels; and a locking pin actuator configured to move the locking pin out of engagement with one or both of the mounting plates so as to allow steering of the wheels. The locking pin actuator may be electrical or pneumatic. The steering assembly may also comprise end stops configured to limit the range of movement of the moveable steering linkage. This limits the steering of the wheels so as to prevent excessive steering. According to a third aspect of the invention, a vehicle is provided. The vehicle comprises a first steering assembly and a second steering assembly, the second steering assembly being provided according to embodiments of the first or second aspects of the invention and being provided further to the rear of the vehicle than the first steering assembly. Advantageously, the vehicle comprises a trailer and a tractor unit, the trailer being connected to the tractor unit at a mounting point, wherein the first steering assembly is mounted to the tractor unit and the second steering assembly is mounted to the trailer, the first and second steering assemblies each having an Ackermann geometry configured such that both wheels of a respective assembly turn around a common turn centre, the longitudinal position of the turn centre of the first steering assembly being at the mid-point between the mounting point of the trailer and the second steering assembly. The second steering assembly may advantageously be controlled such that the wheels of the first and second steering assemblies turn around a common turn
centre, said turn centre being located at a longitudinal position corresponding to the mid-point between the mounting point and the second assembly. According to a fourth aspect, a controller for a steering assembly or a vehicle is provided, the controller being configured to induce a yawing moment across the moveable steering linkage by applying a different braking torque to each wheel and/or by applying a different driving torque to each wheel so as to steer the wheels. The controller preferably comprises an outer loop controller and an inner loop controller, wherein: the outer loop controller is configured to determine a target torque differential based on a target steering angle of the wheels and a current steering angle of the wheels; and the inner loop controller is configured to determine a braking torque and/or a driving torque to apply to each wheel based on the target torque differential. The outer loop controller is preferably configured to determine the target torque differential based on one or more of: the current speed of a vehicle to which the steering assembly is mounted; the articulation angle between a tractor unit and a trailer to which the steering assembly is mounted; the output of one or more wheel sensors, which is used to estimate the speed of the vehicle and distance rolled; and the output of one or more inertial sensors configured to measure vehicle yaw. In embodiments where the controller is for steering a vehicle, the vehicle preferably has a steerable front axle and at least one further steerable front axle provide according to embodiments of the present invention. In such cases the controller is preferably configured to determine the path of a reference lead point at the front of the vehicle and the path of a follow point at the rear of the vehicle. In such embodiments, the target steering angle of the wheels used by the outer loop controller to determine a target torque differential is determined such that the deviation between the path of the reference lead point and the follow point is within a predetermined range whilst the vehicle is in motion. For example, the vehicle may comprise a trailer and a tractor unit, in which case the reference lead point is preferably the mounting point of the trailer to the tractor unit. Linear Quadratic
Regulator control may then be used to optimally balance minimising the deviation between the path of the reference lead point and the follow point and minimising the amount of braking torque required to induce steering.According to a fifth aspect of the invention, a method for controlling a steering assembly is provided, the method comprising steering the wheels by applying a different braking force to each wheel and/or by applying a different drive force to each wheel so as to induce a yawing torque across the moveable steering linkage. The method preferably further comprises: determining a target torque differential based on a target steering angle of the wheels and a current steering angle of the wheels; and determining a braking torque and/or a driving torque to apply to each wheel based on the target torque differential. According to a sixth aspect of the invention a computer program product is provided, the computer program product comprising instructions which, when performed by a processor, cause the method of firth aspect to be performed. BRIEF DESCRIPTION OF DRAWINGS Preferred embodiments of the invention will now be described with reference to the figures in which: Figure 1 shows a steering assembly according to embodiments of the present invention; Figure 2 shows another steering assembly according to embodiments of the present invention; Figure 3 shows a vehicle according to embodiments of the present invention; Figure 4 shows the steering angles achieved by the vehicle illustrated in Figure 3; Figure 5 shows a centring mechanism for use with embodiments of the present invention;
Figure 6 shows examples of the forces developed on one wheel of a steering assembly provided according to embodiments of the present invention; Figure 7 shows the values for the longitudinal and lateral forces acting on a wheel of a steering assembly provided according to embodiments of the present invention; Figure 8 shows the performance of different designs of an airbag for use in a centring system provided according to embodiments of the present invention; Figure 9 shows an example of a lever arm for use in a centring system provided according to embodiments of the present invention; Figure 10 shows a force-height diagram of an example air spring at different pressures; Figure 11 shows a centring system comprising an airbag provided according to embodiments of the invention as the pressure in the airbag is varied; Figure 12 shows solutions for improving the alignment of the endplates of an airbag according to embodiments of the invention; Figure 13 shows the steering damper and locking mechanism of a steering assembly provided according to embodiments of the invention in more detail; Figure 14 shows a force-velocity diagram for a preferred example of a steering damper; Figure 15 shows an example of a pneumatic locking mechanism provided according to embodiments of the invention; Figure 16 shows another example of a pneumatic locking mechanism provided according to embodiments of the invention; Figure 17 shows a preferred pneumatic circuit used to control the centring and locking mechanisms; and
Figure 18 shows an example of a control system provided according to embodiments of the invention. DETAILED DESCRIPTION An overview of a steering assembly 100 provided according to embodiments of the present invention is shown in plan-view in Figure 1. The steering assembly 100 comprises a pair of wheels 101 mounted at either end of a moveable steering linkage 102, with each wheel 101 being provided by a brake 103. The wheels 101 are mounted on respective steering arms 104, each of which is rotatable around a respective kingpin 105, the two kingpins 105 being connected by an axle 106. The axle 106 may be driven or undriven. The two steering arms 104 are connected to each other by means of a track rod 107 such that there is a direct relationship between the orientation of each wheel 101. As will be discussed in detail below, the steering assembly 100 advantageously has an Ackermann steering geometry to ensure the wheels 101 turn about a common turn centre. Each brake 103 can be individually controlled by a controller 108 such that a different braking torque may be selectively applied to each wheel 101 so as to produce a different braking force 110 at the road-tyre interface, also referred to herein as the road-wheel interface, of each wheel. This difference in the force 110 on each wheel 101 induces a yawing moment across the steering linkage 102, thereby causing the wheels 101 to steer. Additionally or as an alternative, in embodiments with a driven axle106 , it is advantageous for the driven axle 106 to be configured to independently provide drive to each wheel 101. Similar to the application of a different braking torque to each wheel 101, the application of a different driving torque induces a yawing moment across the moveable steering linkage 102. It is preferable for the kingpins 105 to be oriented vertically, i.e. with a kingpin inclination of substantially 0º, and for the caster angle of the wheels to be substantially 0º. This allows the system to operate when a vehicle is traveling in
both the forward and reverse directions. However, the system could also be implemented with other values of the caster angle and kingpin inclination. For each particular design situation (i.e. a particular axle geometry for a particular application), the caster angle and kingpin inclination are preferably chosen so as to minimise the energy consumption of the vehicle and minimise the tracking error, while not exceeding the available friction in the tyre interface. As has been explained above, the steering parameters affect the performance of the steering assembly 100 by affecting the forces 110 required to induce steering of the wheels 101. The caster angle and kingpin inclination are two particularly relevant parameters. Other relevant parameters include the caster trail and kingpin offset which are influenced by the caster angle and kingpin inclination parameters as well as by other aspects of the steering assembly 100, such as tyre radius and tyre diameter. These parameters together influence the stability, required steering effort, and “returnability” (i.e. the inclination of the wheels to return to a straight-ahead, unsteered orientation) and it has been found that low values of the caster angle and kingpin inclination are optimal for improving low speed cornering performance while reducing the braking and/or driving torque required to induce steering. These also allow for the wheels 101 to be steered whichever direction they are traveling in. One particular measure of steering performance which is affected by the steering parameters is the steering angle error, which is a measure of the difference between a desired steering angle and that achieved when selectively applying different braking and/or driving torques to each wheel 101. Depending on the steering parameters chosen, the steering linkage 102 may lead to the induced steering angle of the wheels 101 being either greater or less than the desired steering angle, and the steering angle error is therefore preferably measured as the root mean square of the difference between the induced and desired steering angles. It has been found that there is typically a trade-off between minimising the steering error and minimising the energy required to induce steering of the wheels 101, and it is also advantageous to select the steering parameters such that the overall
friction utilization during steering is reduced. Friction utilization is a measure of how much of the available friction from a road surface is used by the steering assembly 100, and reducing the friction utilization of the steering assembly 100 allows for improved cornering performance on low friction surfaces. In order to optimize these various requirements, selection of the steering parameters is advantageously performed using a multi-objective performance optimization which aims to minimise at least two of the steering error, the energy required to induce steering of the wheels 101, and friction utilization. In this way, it is possible to actively steer the wheels 101 of the steering assembly 100 without the need for a mechanical linkage to act on the steering linkage 100. As a result, the steering assemblies 100 provided according to embodiments of the present invention allow for reduced complexity and cost. A particularly preferred embodiment of the embodiment of Figure 1 is shown in Figure 2. As with Figure 1, the steering assembly 200 in this embodiment comprises an axle beam 201 with a steering arm 202 mounted at each end on a respective kingpin 203 and the steering arms 202 are connected by a track rod 204. The wheels and brakes are not shown, but as with Figure 1 these are each provided with an independently actuatable brake. The steering linkage 200 formed by the axle beam 201, track rod 204, and steering arms 202 is advantageously arranged in a conventional trapezoidal or Ackermann geometry, which provides low side-slip angles during cornering and, as a result, benefits in terms of reduced tyre wear and energy consumption. The steering kingpins 203 are oriented substantially vertically, i.e. with substantially zero kingpin inclination and the stub axles on which the wheels are to be mounted are advantageously arranged so as provide substantially zero caster angle. For each particular design situation (i.e. a particular axle geometry for a particular application), the caster angle and kingpin inclination are preferably chosen so as to minimise the energy consumption of the vehicle and minimise the tracking error, while not exceeding the available friction in the tyre interface.
The steering assembly also comprises a centring system formed by an airbag 205 and two lever arms 206, a locking mechanism 207 comprising a locking actuator, and a steering damper 208 arranged to damp oscillations in the movement of the track rod 204. The functions of these elements will be described below. The steering assembly 200 is actively steered using the brakes in the manner described above, with the wheels steering freely around the kingpins 203, which is to say that in the absence of additional forces, such as from the actuation of the centring system, the yawing moment induced by applying a different braking torque to each wheel is sufficient to cause the steering arms 202 to rotate about the kingpins 203. This is different from, for example, so-called skid steering systems in which the wheels, which are not mounted on rotatable steering arms, do not rotate. It also differs from systems in which a track rod is actively moved by a mechanical steering linkage. The steering assembly 200 is particularly suited to use as a steered axle in the trailer of a tractor-trailer arrangement 300, as shown in Figure 3. The tractor unit 301 has a conventionally steered front axle and an unsteered rear axle, while the trailer 302 has at least one steering assembly 303 provided according to embodiments of the present invention. The trailer 302 is mounted to the tractor unit 301 at a mounting point 304, also referred to as a 5th wheel, and the geometry of the steered axis of the tractor unit 301 is arranged so such that it has a turn centre the longitudinal position of which is at a mid-point between of the 5th wheel 304 and the steered axis 303 of the trailer 302. The distance between the 5th wheel 304 and the steered axis 303 of the trailer 302 (specifically, the axle beam of the steered axis 303 of the trailer 302) is labelled f in Figure 3. The line from the turn centre running perpendicular to the axle beam of the steered axis 303 of the trailer 302 is a distance le from the 5th wheel 304, where le=2f. The steered axle 303 of the trailer 302 can be controlled such that the wheels also turn around substantially the same turning centre as the steered axis of the tractor unit 301. For steering assemblies arranged having an Ackermann steering geometry, the ideal inner- and outer-wheel steering angles can be calculated as follows:
where le is the trailer’s effective wheelbase (measured from the 5th wheel), f is the distance between the fifth wheel and the steered axle, T is the track width of the axle, and δ is the average axle steer angle. For steering assemblies arranged having a trapezoidal steering geometry, the inner- and outer-wheel steering angles can be calculated as follows:
where λ is the ratio between the distance between the axle kingpins and the length of the steering radius arms, and γ is the steering arm fixed angle, as shown in Figure 3. Advantageously, the steering arm fixed angle is determined according to the following formula:
where l1 is the distance between the axle kingpins. The control of the steered axle 303 of the trailer 302 is advantageously performed by first determining target steering angles of the wheels according to these formulae and determining a target torque differential to apply to the wheels based on these target steering angles. An appropriate braking torque is then applied based on this target torque differential. Figure 4(a) compares the achieved steering angles for a trailer having a steered axle arranged having a trapezoidal geometry to the ideal Ackermann steering angles and to the ideal trapezoidal steering angles. The errors relative to ideal
Ackermann steering are shown in Figure 4b. It can be seen that the steered axle achieved near-Ackermann geometry, with a maximum Ackermann steering error of 0.6°. A steering assembly provided according to the embodiments of the present invention may advantageously comprise a centring system, as is shown in Figure 2. An example of this centring system is shown in more detail in Figures 5a and 5b. The centring system is configured to return the steered wheels to their straight- ahead, unsteered positions, for example in case of an emergency. The centring assembly system advantageously comprises a horizontally mounted airbag and a pair of lever arms. The airbag is inflatable and comprises a pair of endplates, with the lever arms each being attached to a respective endplate at one end. The other end of each lever arm is in contact with a track rod clamping bracket, with each lever arm being mounted at a fulcrum point to the axle beam via a concentric bushing. When the airbag is inflated, as shown in Figure 5a, the two arms press the track-rod clamping plate (2) into line with a fixed plate (1) which is attached to the vehicle or to the axle beam. This action centres the track-rod and enables a locking pin to drop into holes in places (1) and (2), locking them together. When the airbag is not inflated, the track rod may move freely, as shown in Figure 5b. The centring system is preferably configured to provide a sufficient centring force to counteract extreme loads on the track rod, such as in the case of one wheel locking up or during excessive steering. The tyre forces and directions for two such “worst case” scenarios are illustrated in Figures 6a and 6b. Figure 6a shows the tyre forces developed on wheel for a vehicle driven along a straight-line in the event of a full wheel-lock up, e.g. due to a brake failure on one side of the vehicle. The longitudinal force creates a moment around the kingpin due to the kingpin offset. Figure 6b shows the tyre forces developed on wheel for the case of a severe braking during a turn. For such a manoeuvre, the tyre is subjected to both
longitudinal forces acting at a distance d (kingpin offset) from the kingpin, and lateral forces developed at an offset t (pneumatic trail) from the wheel centre. Resolving the moments about the kingpin for each case, the relationship between the tyre forces and that acting at the track-rod level can be calculated as follows:
where X and Y are the longitudinal and lateral tyre forces developed at the wheel, l2 is the steering radius arm length. The force Ft at the track rod required to counteract the forces on the wheels in order to centre the wheel can therefore be calculated as:
Figure 7 illustrates values for the longitudinal and lateral forces, X/µZ and Y/µZ in the case of combined braking and cornering, where Z is the vertical tyre force, for a fully laden vehicle in which 4 tonnes acts on each wheel and on which the friction coefficient µ of the surface on which the vehicle is driven is 0.9. Factoring in these forces and the forces experienced in the case of a full wheel lock up, it is advantageous for the centring system to be configured to provide a load of 35kN on the track rod. The design of the centring system also affects the maximum steering angles that can be achieved by the steering assembly. It is therefore desirable to provide an arrangement of the elements of the centring system which allows for high forces to be applied to the track rod which does not limit the steering angles that can be achieved by the steering assembly.
The implementation of the centring system may be configured to provide the desired centring forces by one or both of: (i) Suitable selection of the parameters of the airbag, such as its diameter; (ii) Positioning of the fulcrum point of the lever arms to achieve an acceptable lever ratio. In selecting the airbag parameters, the diameter is an important design variable as this affects both the force developed by the airbag, which is proportional to the cross-sectional area, and the geometric constraints of the surrounding components. The effective airbag area varies throughout the compression and extension strokes. Air spring manufacturers provide a characteristic plot of how the effective cross-sectional area, Ae (mm2), changes with the air spring deflection. The volume of the air spring is also provided for any given effective diameter. Maximum forces are achieved at the maximum compression, which corresponds to the minimum height and maximum effective area of the airbag. As shown in Figures 5a and 5b, the airbag is advantageously located behind the axle beam, towards the rear of the vehicle. A convoluted air spring design is preferable for the airbag as it has a large effective diameter at maximum compression. The specific shape also allows it to withstand high loads with less air pressure, in contrast to other types of air bags (e.g. sleeve style air springs). In particular, double-convoluted air springs have been found to ensure a sufficient travel for maximum steering angles. The mechanical advantage of the centring-system lever arms is defined as the ratio of the distances from the fulcrum to where the air-spring force and the track- rod force are applied. This is denoted as ξr and defined according to the following equation:
where la and lt are the distances from the fulcrum point to the air spring and track rod respectively. The air spring force, Fa, and travel, Sa, may be computed by assuming a simple proportional relationship to the corresponding track rod quantities as follows:
The parameters of three candidate double-convoluted air springs, each with a different value of effective area, are shown in Table 1 below. Table 1 Airspring parameters used for analysis
Figures 8a to 8d show the performance of each of these designs for a range of pivot positions ahead and behind the axle beam centreline, as illustrated in Figure 5, based on a fixed length of the lever arm. Figures 8a and 8c show the forces developed at the track-rod and air spring respectively, plotted with their required values for each considered air spring.
As noted above, it advantageous for the air springs to provide a force of at least 35kN on the track rod, while the force at the air springs are given according to the formula above. These are illustrated as dashed lines in Figures 8a and 8c. The maximum force developed by an air spring is proportional to the maximum pressure at full compression stroke of the air spring, Pmax, where the proportionality constant depends on the effective diameter De and Pmax was taken to be 6 bar.
The force generated by the air spring on the track rod is proportional to the force developed at the spring centre. From the force analysis it was found that, for the designs illustrated above, it is advantageous for the pivot location to be greater than zero. Figures 8b and 8d show the travel of the track-rod and air spring, respectively. It is preferable for the minimum stroke of the track-rod St to be 85 mm, while that of the spring, Sa, was found using the equation above. From the stroke analysis it was found that the pivot location is preferably no more than 12 mm behind the solid-axle centreline. Based on this analysis, air spring with a maximum effective diameter of approximately 276 mm was found to be most preferable, with a pivot location of between 0mm and 12mm. Particularly suitable lever arm dimensions are included in Table 2, with Figure 9 illustrating a particularly advantageous design of the lever arm. Table 2 Suitable designs for the steering axle lever arms. Positive value of pivot position correspond to its location moved from the axle beam centerline towards the trackrod.
It is also advantageous for the selected air spring, when not actuated, to provide little resistance to steering operations. Hence, an air spring that provides a low force at low pressure, such as 1 kN at 0.3 bar, is preferable as this minimises the torque differential required to induce steering of the wheels. A force-height diagram of an example air spring at different pressures is shown in Figure 10. While a double-convoluted airbag design allows for a larger stroke, by installing a double-convoluted airbag with pivots at both ends, instability may be experienced in the system during the airbag compression stroke. Specifically, the endplates of the airbag are preferably substantially parallel but may become misaligned under pressure. This is shown in Figures 11a to 11c, which show a centring system as the pressure in the airbag is varied. In this example, a significant angular misalignment (exceeding 16°) occurs at the airbag endplates at high (Figure 8b). This can be resolved by tightening the bolts at the lever arm end-attachment, as shown in Figure 11, which ensures the endplates remain aligned during compression. However, locking the pivots may cause the combined lever arms and airbag endplates to move as a rigid body. Two improved solutions have therefore been developed that maintains the alignment of the endplates. These improved solutions are illustrated in Figures 12a and 12b.
The first of these solutions comprises an internal guidance design in which a telescopic cylindrical bearing 1201 with high bending stiffness is fitted inside the airbag 205 at its mid-axis and attached to the end-plates 1202. This removes the additional degree of freedom caused by the central convolution of the airbag 1200, ensuring that the pivot-ends adopt a linear piston type movement. Consequently, the end-plates remain aligned. A cross-section of this design is shown in Figure 12a. The second of these solutions comprises a revised design of the lever arms 206. In this design, the two end-plate mounting pivot-ends are still free to rotate but act at an offset with respect to the centre axis of the airbag 205 (preferably approximately 5% of the effective diameter of the airbag). This creates a restoring moment causing the end-plates 1202 to rotate inwards (opposite to the direction of instability) until making contact with flat buffer stops added to the lever arms. This is shown in Figure 12b. Embodiments of the present invention may therefore advantageously comprise one or both of these solutions. As noted above, the steering assembly preferably includes a steering damper 208. This is used to ensure yaw stability of the axle, specifically by damping the shimmy mode. As shown in Figure 13, in the embodiment of Figure 2 one end of the steering damper 208 is attached to the axle 201 and the other end is attached to the steering track-rod 204. The damper 208 is preferably mounted to have 50% extension at the central position (δ = 0°). Depending on the angle of rotation of the steering wheel-hub assembly, the damper 208 is either compressed or extended. As such, it is preferable for the steering damper 208 to have the same damping properties in extension and compression. It is also preferable for the steering damper 208 to provide substantially zero damping force at zero velocity so as to reduce torque differential required to cause the wheels to steer.
A force-velocity diagram for a preferred steering damper, manufactured by Koni Ltd, is shown in Figure 14. An alternative design of a steering damper comprises a rotational damper. A rotational damper may be coupled to at least one of the kingpins such that rotations in the steering arm are damped, thereby damping shimmy oscillations in the track rod. The present invention advantageously provides improved steering at low speeds. However, at higher speeds it is preferable for the steering assembly to be locked in the straight-ahead, unsteered position so as to improve vehicle stability. To this end, the embodiment of Figure 2 includes a locking mechanism 207. This can be seen in Figure 13, while Figures 15 and 16 show examples of a pneumatic locking mechanism 207 comprising a first mounting plate 1501 attached to the moveable steering linkage, a second mounting plate 1502 attached to the axle beam, a locking pin 1503 configured to engage with the first 1501 and second 1502 mounting plates so as to inhibit steering of the wheels, and a pneumatic locking pin actuator 1504 configured to move the locking pin 1503 out of engagement with one or both of the mounting plates 1501, 1502 so as to allow steering of the wheels. When the locking pin is moved into engagement with the two mounting plates, the track rod is locked in position and steering of the wheels is inhibited. The second mounting plate 1502 is preferably U-shaped, while the first mounting plate 1501 preferably provides a corresponding slotted hole 1505 for the locking pin 1503. In preferred embodiments, the locking pin 1503 is spring loaded. When it is unpressurised, the spring forces the pin 1503 through an opening in the locking plate, locking the axle. To unlock the axle, compressed air may be provided to the pneumatic actuator to retract the pin and allow the track rod to freely move laterally for normal steering operations.
In particularly preferred embodiments, both the centring and locking mechanisms are pneumatic, with Figure 17 illustrating a preferred pneumatic circuit used to control these mechanisms. In the top part of the diagram, compressed air from the reservoir (1) passes through both a solenoid-operated (2) and a manually-operated (3) ‘3-2’ valve before entering the locking actuator (5) via a double-check valve (4). When locking is desired, solenoid (2) is energised. Air pressurizes the type-12 braking chamber, which causes the locking pin to be lifted. The manual valve (3) is added to control the locking operations in the event of electrical faults. In the bottom part of the diagram, compressed air passes through two pressure limiting valves, (6) and (7), which prevent over pressurization of the system and set values of the low-feed and high-feed pressure lines, respectively. A ‘5-2’ valve (8) with an external pilot is used to control which of the two feed-lines is connected to the air-spring (11). When normal steering operations are required, the low-feed line pressure is activated, whereas the air flowing in the high-feed line is dumped to the atmosphere. A double-check valve (9) compares the pressures values downstream of the ‘5-2’ valve, allowing the one with the highest value to enter the air-spring. When emergency centring is desired, the high-feed line is activated with the low-feed line vented to the atmosphere. Hence, the airbag can be inflated at the maximum pressure set by (7), which enables centring of the axle. A pressure transducer (10) is used to monitor the airbag pressure. This signal is fed to the global controller for use by the centring control-logic and fault detection in the system. To guarantee fail-safe operations for the emergency centring system, the high-feed pressure line is connected to the ‘5-2’ valve port, which is active when the solenoid is de- energised. This means that in case of power failure, the axle will self-centre. As noted above, the control of a steering assembly is advantageously performed by first determining target steering angles of the wheels according to these formulae and determining a target torque differential to apply to the wheels based on these target steering angles, with an appropriate braking torque then applied
based on this target torque differential. Figure 18 illustrates an exemplary control system for providing this control of the steering assembly. The control system comprises an outer loop and an inner loop in which: (i) The outer loop takes the error in steering angle between the target angle and the measured angle as inputs, for example received sensors mounted at the kingpins, and outputs a target torque differential. (ii) The inner loop takes the target torque differential (which has been output by outer loop) as an input and regulates the measured differential braking and/or driving torque. It advantageously uses a closed-loop feedback strategy for each brake actuator, using pressure sensors inside the brake actuators and estimators of the brake chamber pressures. The controller advantageously further comprises an upper control layer. This layer is configured to determine an optimal path for the steering assembly to follow, for example as part of the optimal path to be followed by a tractor-trailer in which the steering assembly is installed, which is then used to determine the target steering angle for the steering assembly.
Claims
CLAIMS 1. A steering assembly comprising a pair of wheels and a moveable steering linkage, the wheels being mounted at either end of the moveable steering linkage; wherein each wheel is provided with a brake, each brake independently actuatable such that a different braking torque may be selectively applied to each wheel so as to induce a yawing moment across the moveable steering linkage, thereby causing the wheels to steer.
2. A steering assembly comprising a pair of wheels and a moveable steering linkage, the wheels being mounted at either end of the moveable steering linkage; wherein the steering assembly comprises a driven axle connecting the wheels, the driven axle being configured to independently provide drive to each wheel such that a different driving torque may be selectively applied to each wheel so as to induce a yawing moment across the moveable steering linkage, thereby causing the wheels to steer.
3. A steering assembly according to claim 1 or claim 2, wherein for each particular design situation the caster angle and kingpin inclination of the wheels are chosen so as to minimise the energy consumption and minimise tracking error, while not exceeding the available friction in the road-tyre interface.
4. A steering assembly according to any of the preceding claims, the moveable steering linkage comprising a track rod connecting the pair of wheels.
5. A steering assembly according to claim 4, the steering assembly having an Ackermann geometry such that both wheels turn around a common turn centre.
6. A steering assembly according to any of the preceding claims, the steering assembly comprising a steering damper connected to the moveable steering linkage so as to damp shimmy oscillations.
7. A steering assembly according to claim 6, the damping force of the steering damper being substantially 0 at 0 velocity.
8. A steering assembly according to claim 6 or claim 7, the steering damper providing the same damping characteristics in extension and compression.
9. A steering assembly according to any of claims 6 to 8, the steering damper having a linear force-velocity characteristic.
10. A steering assembly according to any of the preceding claims, the steering assembly comprising a centring system having an actuator configured to engage with the moveable steering linkage such that actuation of the actuator induces a centring force on the moveable steering linkage.
11. A steering assembly according to claim 10, the centring system comprising an inflatable airbag and a pair of lever arms, each lever arm being connected at one end to the air bag and being configured to engage with the moveable steering linkage at its other end.
12. A steering assembly according to claim 11, the inflatable airbag comprising a pair of endplates, each connected to one of the lever arms.
13. A steering assembly according to claim 12, the endplates being connected along a central axis of the airbag by a telescopic cylindrical bearing so as to maintain the alignment of the endplates.
14. A steering assembly according to claim 12 or claim 13, the connection point of each lever arm with its respective endplate being laterally offset from the central axis of the airbag.
15. A steering assembly according to any of claims 10 to 14, the actuator being a pneumatic actuator and the steering assembly further comprising: a first pressure control valve configured to receive air from a compressed air source and to output air at a first pressure; a second pressure control valve arranged to receive air from the compressed air source and to output air at a second pressure, the second pressure being lower than the first pressure;
an actuator valve configured to receive air output from the first and second pressure control valves and to selectively output air to the pneumatic actuator at the first or second pressure.
16. A steering assembly according to any of the preceding claims, the steering assembly comprising a locking mechanism configured to engage with the moveable steering linkage so as to inhibit steering of the wheels.
17. A steering assembly according to claim 16, the steering assembly comprising an axle beam and the locking mechanism comprising: a first mounting plate attached to the moveable steering linkage; a second mounting plate attached to the axle beam; a locking pin configured to engage with the first and second mounting plates so as to inhibit steering of the wheels; and a locking pin actuator configured to move the locking pin out of engagement with one or both of the mounting plates so as to allow steering of the wheels.
18. A steering assembly according to any of the preceding claims, the steering assembly comprising end stops configured to limit the range of movement of the moveable steering linkage.
19. A vehicle comprising a first steering assembly and a second steering assembly, the second steering assembly being provided according to any of the preceding claims and being positioned further to the rear of the vehicle than the first steering assembly.
20. A vehicle according to claim 19, the vehicle comprising a trailer and a tractor unit, the trailer being connected to the tractor unit at a mounting point, wherein the first steering assembly is mounted to the tractor unit and the second steering assembly is mounted to the trailer, the first and second steering assemblies each having an Ackermann geometry configured such that both wheels of a respective assembly turn around a common turn centre, the longitudinal position of the turn centre of the first steering assembly being at the
mid-point between the mounting point of the trailer and the second steering assembly.
21. A controller for a steering assembly according to any of claims 1 to 18 or for the second steering assembly of a vehicle according to claim 19 or claim 20, the controller being configured to induce a yawing moment across the moveable steering linkage by applying a different braking torque to each wheel and/or by applying a different driving torque to each wheel so as to steer the wheels.
22. A controller according to claim 21, the controller comprising an outer loop controller and an inner loop controller, wherein: the outer loop controller is configured to determine a target torque differential based on a target steering angle of the wheels and a current steering angle of the wheels; and the inner loop controller is configured to determine a braking torque and/or a driving torque to apply to each wheel based on the target torque differential.
23. A method for controlling a steering assembly according to any of claims 1 to 18 or for the second steering assembly of a vehicle according to claim 19 or claim 20, the method comprising steering the wheels by applying a different braking force to each wheel and/or by applying a different drive force to each wheel so as to induce a yawing torque across the moveable steering linkage.
24. A method according to claim 23, the method further comprising: determining a target torque differential based on a target steering angle of the wheels and a current steering angle of the wheels; and determining a braking torque and/or a driving torque to apply to each wheel based on the target torque differential 25. A computer program product comprising instructions which, when performed by a processor, cause the method of claim 23 to be performed.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GBGB2308305.8A GB202308305D0 (en) | 2023-06-02 | 2023-06-02 | Steering assembly and method for controlling the same |
| PCT/GB2024/051411 WO2024246539A2 (en) | 2023-06-02 | 2024-05-31 | Steering assembly and method for controlling the same |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| EP4719867A2 true EP4719867A2 (en) | 2026-04-08 |
Family
ID=87156802
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| EP24733263.8A Pending EP4719867A2 (en) | 2023-06-02 | 2024-05-31 | Steering assembly and method for controlling the same |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP4719867A2 (en) |
| GB (1) | GB202308305D0 (en) |
| WO (1) | WO2024246539A2 (en) |
Families Citing this family (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| SE545455C2 (en) * | 2021-04-08 | 2023-09-19 | Scania Cv Ab | Control device and method for controlling a tag axle steering system |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4449727A (en) * | 1982-08-30 | 1984-05-22 | Bertil Roos | Skid control car |
| DE3736627A1 (en) * | 1987-10-29 | 1989-05-18 | Bergische Achsen Kotz Soehne | STEERING AXLE |
| IT1285451B1 (en) * | 1996-01-24 | 1998-06-08 | R C D S R L | IMPROVEMENT OF A SERVO-ASSISTED STEERING SYSTEM OF THE STEERING WHEELS OF ONE OR MORE REAR AXLES OF A VEHICLE SUCH AS |
| GB2360499B (en) * | 2000-03-21 | 2002-12-31 | Carlton John Davis | Control apparatus and method for a steerable axle |
| DE102020101587A1 (en) * | 2020-01-23 | 2021-07-29 | Thyssenkrupp Ag | Method for controlling a motor vehicle at slow speeds by means of differential drive torque on the rear axle |
-
2023
- 2023-06-02 GB GBGB2308305.8A patent/GB202308305D0/en not_active Ceased
-
2024
- 2024-05-31 WO PCT/GB2024/051411 patent/WO2024246539A2/en not_active Ceased
- 2024-05-31 EP EP24733263.8A patent/EP4719867A2/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| GB202308305D0 (en) | 2023-07-19 |
| WO2024246539A2 (en) | 2024-12-05 |
| WO2024246539A3 (en) | 2025-05-01 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| CN114502448B (en) | Method and system arrangement for vehicle steering and vehicle having such a system | |
| US7748724B2 (en) | Self-steering axle suspension system having a rotary stabilizer | |
| US8781684B2 (en) | Steering and control systems for a three-wheeled vehicle | |
| US5246242A (en) | Passively steered tandem axle group | |
| EP2517948B1 (en) | Rear-wheel toe-angle control device for a vehicle | |
| US6418856B2 (en) | Passive steering assembly for a guided vehicle | |
| US20110266774A1 (en) | Self-steering dolly for long load heavy haul | |
| US7766349B2 (en) | Self-steering axle suspension system having a rotary stabilizer mounted at a pivot joint associated with a tie rod | |
| JPH02144205A (en) | Rear wheel suspension device for rear wheel steering vehicle | |
| AU2021223601B2 (en) | Automated compensator for fifth-wheel couplings | |
| US20070029748A1 (en) | Steering system | |
| EP4719867A2 (en) | Steering assembly and method for controlling the same | |
| AU2017339976B2 (en) | Steering centering/damping mechanism for a steerable heavy-duty vehicle axle/suspension system | |
| WO2020164861A1 (en) | Vehicle having a tilting frame and spring-damper system | |
| CA2214813C (en) | Main landing gear having tilting of main gear pivot pins | |
| KR102126253B1 (en) | Hydraulic Auxiliary Steering Control System | |
| KR101349530B1 (en) | Rear Wheel Steer Suspension Apparatus | |
| EP4063238B1 (en) | A steerable wheel axle arrangement and a method of controlling a steerable wheel axle arrangement | |
| JPH0525353Y2 (en) | ||
| Duysinx | THE STEERING SYSTEM | |
| JPH052553B2 (en) | ||
| JPH06107221A (en) | Vehicle steering system | |
| JPH0237078A (en) | Rear wheel steering device for vehicle |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| STAA | Information on the status of an ep patent application or granted ep patent |
Free format text: STATUS: UNKNOWN |
|
| STAA | Information on the status of an ep patent application or granted ep patent |
Free format text: STATUS: THE INTERNATIONAL PUBLICATION HAS BEEN MADE |
|
| PUAI | Public reference made under article 153(3) epc to a published international application that has entered the european phase |
Free format text: ORIGINAL CODE: 0009012 |
|
| STAA | Information on the status of an ep patent application or granted ep patent |
Free format text: STATUS: REQUEST FOR EXAMINATION WAS MADE |
|
| 17P | Request for examination filed |
Effective date: 20251218 |
|
| AK | Designated contracting states |
Kind code of ref document: A2 Designated state(s): AL AT BE BG CH CY CZ DE DK EE ES FI FR GB GR HR HU IE IS IT LI LT LU LV MC ME MK MT NL NO PL PT RO RS SE SI SK SM TR |