Method for improving driving dynamic stability of commercial vehicle having lift bridge

Abstract

The invention relates to a method (1) for improving the driving dynamic stability of a commercial vehicle (300), the commercial vehicle (300) having a lift bridge (314), the method (1) comprising: ascertaining (3) a current driving speed (V) of the commercial vehicle (300); ascertaining (5) a speed (Vcrit) of a critical instability of the commercial vehicle (300); comparing (7) the current driving speed (V) with the critical unstable speed (Vcirct); ascertaining (9) a lifting situation (Slift) of a lifting bridge (314) of the commercial vehicle (300); and lowering (11) the lift bridge (314) of the commercial vehicle (300) if the lift condition (Slift) represents that the lift bridge is in lift (Sup) and the current travel speed (V) is greater than or equal to a critical unstable speed (Vcrit). In addition, the invention also relates to a device for improving the driving dynamic stability of a commercial vehicle (300), a commercial vehicle (300) and a computer program product.

Description

Technical Field

[0001] The present invention relates to a method for improving the driving dynamic stability of commercial vehicles with lift axles. Background Art

[0002] A commercial vehicle is a motor vehicle that is configured and equipped for transporting people or goods and / or for towing trailers, but is not a passenger car or a motorcycle. Commercial vehicles are, for example, buses, trucks, towing machines or crane substructures. Within the scope of this disclosure, a commercial vehicle can be a simple commercial vehicle, which is commonly referred to in English as a rigid vehicle, or also a vehicle combination consisting of a towing vehicle and one or more trailer vehicles. A typical example of a vehicle combination includes a saddle tractor and a semi-trailer.

[0003] Commercial vehicles are mostly configured for transporting large loads and often have more than two axles in order to distribute the load evenly onto the ground and prevent individual axles from being overloaded. However, additional axles have the disadvantage that, when these additional axles are not necessary, they increase the operating costs of the commercial vehicle. Therefore, the fuel consumption and wear of commercial vehicles with additional axles are generally increased. In addition, additional axles often reduce the maneuverability of commercial vehicles, which can be disadvantageous especially in urban areas. Commercial vehicles often have liftable additional axles, which are also referred to as lift axles. Such an axle can be raised or lifted, where the lift axle is not placed on the roadway in the raised state. In the raised state, the wheels of the lift axle do not rotate along, which results in economic advantages in particular. Therefore, tire wear during cornering is reduced. In addition, fuel can be saved due to reduced bearing and tire friction, and toll expenses can be saved when paying tolls per axle. The turning radius of a commercial vehicle is generally smaller when the lift axle is raised than when the lift axle is lowered. For these reasons, the lift axle is mostly only lowered when the load to be transported by the commercial vehicle is so large that, in the case of the raised lift axle, it exceeds the permitted axle load of the non-raised axles, or when the vehicle with the raised lift axle exceeds the permitted axle load when crossing a bridge. When the lift axle is lowered, the load of the vehicle is distributed onto the additional axles and the axle load on each axle is reduced. However, the ability of a commercial vehicle to transport a larger load when the lift axle is lowered is accompanied by higher wear and higher costs for the aforementioned reasons.

[0004] Therefore, in the prior art, the lowering of a lifting bridge usually depends on the load. DE 20 2019 003 735 U1 discloses a device for automatically lowering and for load-dependent lifting of a lifting bridge, wherein the device for automatic lifting only lifts the lowered lifting bridge when the weight is below a predeterminable maximum on the loading surface.

[0005] DE 10 2019 007 532 A1 discloses a method for condition-dependent control of a lifting bridge of a commercial vehicle, in which the lifting bridge is lowered. In the disclosed method (by which a dangerous situation due to overheating of the brakes of the commercial vehicle should be prevented), after activation of the automatic parking function of the commercial vehicle, the lifting bridge is lowered to maximize the braking force. The lifting bridge is only lowered after activation of the automatic parking function when a predeterminable speed of the commercial vehicle is reached (or undershot), in order to ensure that the rotational speeds of the vehicle wheels and the wheels of the lifting bridge when it is lowered to the ground have as small a difference as possible, thereby preventing damage to the tires during braking. The method only lowers the lifting bridge after activation of the automatic parking function, i.e., only in an emergency situation and not during normal driving operation. Summary of the Invention

[0006] So far, the influence of the lifting bridge on the dynamic driving behavior of a commercial vehicle has not been taken into account. The object of the present invention is to describe a method by which the driving dynamic stability of a commercial vehicle with a lifting bridge can be improved.

[0007] In a first aspect, the present invention solves this object by a method for improving the driving dynamic stability of a commercial vehicle with a lifting bridge, the method having the following steps: ascertaining the current driving speed of the commercial vehicle; ascertaining the critical instability speed of the commercial vehicle; comparing the current driving speed with the critical instability speed; ascertaining the lifting state of the lifting bridge of the commercial vehicle; and if the lifting state represents that the lifting bridge is raised and the current driving speed is greater than or equal to the critical instability speed, then lowering the lifting bridge of the commercial vehicle. If the commercial vehicle is critically unstable when the lifting bridge is raised, then by this method the driving dynamic stability, in particular the yaw stability, of the commercial vehicle is increased via the lowering of the lifting bridge. The commercial vehicle is preferably a vehicle combination that includes a towing vehicle and at least one trailer vehicle. The stability of the vehicle combination can be increased in particular by lowering the lifting bridge, in particular because instability of the trailer vehicle caused by excessive yaw excitation of the towing vehicle can be prevented.

[0008] In order to judge whether a commercial vehicle exhibits critical instability behavior, the current driving speed of the commercial vehicle is compared with the critical instability speed of the commercial vehicle. The current driving speed is the speed at which the commercial vehicle continues to move forward under the current conditions, that is, the conditions in which the method is implemented. The critical instability speed is the speed from which the commercial vehicle will be critically unstable. A commercial vehicle is critically unstable when it becomes unstable due to common steering excitations. Common steering excitations are steering excitations that may occur during the driving operation of the commercial vehicle, and such steering excitations especially occur in emergency situations, such as during evasive maneuvers. Preferably, if the damping of the vehicle for the predetermined excitation is lower than the predetermined minimum and / or if the natural angular frequency of the vehicle is within the range of common excitation frequencies, the vehicle exhibits critical instability behavior. The critical instability damping amount is preferably 0.6 or less, preferably 0.5 or less, preferably 0.4, where a damping amount of 1 corresponds to the so-called aperiodic boundary case.

[0009] It should be understood that it is not necessarily the case that once a commercial vehicle continues to move forward at the critical instability speed, the commercial vehicle is unstable. Rather, if a destabilizing excitation is applied to the vehicle while it is traveling at the critical instability speed, then the commercial vehicle will become unstable in such a case. This may be the case, for example, when the commercial vehicle has to perform an evasive maneuver or drive through a curve with a very small radius of curvature.

[0010] In addition, the method further includes: obtaining the lifting condition of the lifting bridge of the commercial vehicle, where the lifting condition characterizes whether the lifting bridge of the commercial vehicle is lowered or raised. The lifting condition can at least represent a raised lifting bridge and a lowered lifting bridge, and thus can be a digital condition. However, it can also be set that the lifting condition represents the degree of lifting of the lifting bridge. The lifting condition can, for example, represent the percentage value of the absolute lift of the lifting bridge, where a value of 100% represents that the lifting bridge is fully raised, and a value of 0% represents that the lifting bridge is fully lowered.

[0011] In order to improve the driving dynamic stability of the commercial vehicle, the method further includes: if the lifting condition represents that the lifting bridge is raised and the current driving speed is greater than or equal to the critical instability speed, then lower the lifting bridge of the commercial vehicle. Therefore, when the lifting bridge is already lowered, it is meaningless or impossible to lower the lifting bridge. Therefore, preferably, the lowering is only performed when the lifting bridge was previously in a fully or partially raised state. In addition, according to the present invention, if the commercial vehicle continues to move forward at a current driving speed greater than the obtained critical instability speed, then lower the lifting bridge. Preferably, the lowering of the lifting bridge is performed regardless of wear or economic considerations.

[0012] Lowering the lift bridge of a vehicle bridge configured as a trailing bridge, i.e., arranged behind the drive axle in the driving direction, results in a reduction of the effective lever arm of the force acting on the trailer. In addition, lowering the lift bridge in principle also results in an increase in the potential lateral tractive force of the vehicle, thus preventing the commercial vehicle from fishtailing even in the case of a high steering frequency. Both of these effects improve driving stability and reduce the risk of commercial vehicle instability. By the method according to the invention, the influence of the lift bridge, in particular the lift bridge configured as a trailing bridge, on the driving stability of the commercial vehicle is taken into account.

[0013] Obtaining the current driving speed of the commercial vehicle and obtaining the critical instability speed of the commercial vehicle do not have to be performed in the order reproduced in the claims. These steps can preferably also be performed in reverse order or (partially) simultaneously. Obtaining the lift state can be performed before, after, completely simultaneously with, and / or partially simultaneously with obtaining the current driving speed, obtaining the critical instability speed, and / or comparing these speeds.

[0014] Preferably, before obtaining the critical instability speed of the commercial vehicle, the method includes: obtaining whether the commercial vehicle is a vehicle combination composed of a towing vehicle and at least one trailer vehicle. Obtaining whether the commercial vehicle is a vehicle combination composed of a towing vehicle and at least one trailer vehicle is preferably performed using the signals provided on the trailer network of the commercial vehicle. As an alternative or supplement to identifying whether the commercial vehicle is a vehicle combination using the signals provided on the trailer network of the commercial vehicle, it can also be identified by obtaining in the case of using the total vehicle combination mass of the commercial vehicle and the towing vehicle mass of the towing vehicle.

[0015] Preferably, the lift bridge is the lift bridge of the towing vehicle of the vehicle combination. However, the described stability advantages also apply to the lift bridge of the trailer, so that the lift bridge can preferably also be the lift bridge of the trailer vehicle. In addition, it should also be understood that the commercial vehicle may also have multiple lift bridges, and in order to improve yaw stability, preferably multiple, particularly preferably all, lift bridges of the commercial vehicle can also be lowered.

[0016] If the current driving speed has reached or exceeded the critical instability speed, the obtaining of the lift state can also be cancelled and the lift bridge can always be lowered. Therefore, once the current driving speed reaches or exceeds the critical instability speed, for example, a lowering request can always be provided to the lift unit of the lift bridge that is set to lower the lift bridge. If the lift bridge has already been lowered in this case, the lowering request is ignored and / or no result is caused.

[0017] In a first preferred embodiment of the method, ascertaining the lifting state of the lifting bridge of a commercial vehicle comprises: ascertaining the rotational speed of the lifting bridge wheels of at least one wheel of the lifting bridge; ascertaining the rotational speed of the reference wheels of at least one reference wheel of the reference bridge of the commercial vehicle; comparing the rotational speed of the lifting bridge wheels with a reference rotational speed, wherein when the rotational speed of the lifting bridge wheels is lower than the reference rotational speed by a wheel rotational speed tolerance value, the lifting state represents that the lifting bridge is being lifted, and when the rotational speed of the lifting bridge wheels is within the wheel rotational speed tolerance range around the reference rotational speed, the lifting state represents that the lifting bridge is being lowered. The wheel rotational speed tolerance value, which can also be referred to as the wheel speed tolerance, is preferably set to balance small rotational speed differences caused, for example, by different wheel diameters of the wheels of the lifting bridge and the reference bridge or by wheel slip. The wheel rotational speed tolerance range is the following range: the boundary values of the range are determined by subtracting the wheel rotational speed tolerance value from the reference rotational speed and by adding the wheel rotational speed tolerance value to the reference rotational speed. When the lifting bridge is being lowered, the wheels of the lifting bridge roll on the carriageway surface. The rolling speed of the tire circumferential surface of the wheels of the lifting bridge is basically the same as the rolling speed of the wheels of the remaining axles of the commercial vehicle or of the reference bridge. The present invention makes use of this knowledge. Thus, when the wheels of the lifting bridge rotate basically at the same wheel rotational speed as the wheels of the reference bridge (since the wheels of a commercial vehicle usually have the same diameter), it can be recognized or ascertained that the lifting bridge is being lowered. When the rotational speed of the lifting bridge wheels is within the wheel rotational speed tolerance range, the lifting bridge is being lowered. Conversely, when the lifting bridge is being lifted, its wheels usually do not rotate or rotate only extremely slowly. In this case, the rotational speed of the lifting bridge wheels deviates from the reference rotational speed by more than the wheel rotational speed tolerance value. The lifting state can be ascertained particularly simply by observing the rotational speed of the lifting bridge wheels and the reference rotational speed. The reference wheels are preferably the driven wheels of the commercial vehicle.

[0018] Preferably, ascertaining the lifting state of the lifting bridge of a commercial vehicle comprises: ascertaining a lifting state signal provided on the vehicle network of the commercial vehicle, preferably on a bus network, in particular on a CAN bus; and ascertaining the lifting state from the network data. Thus, the lifting state already known in vehicle systems, such as driving stability systems like an ABS system or an ESC system, can preferably be used in the method.

[0019] According to a preferred improvement, the method further includes: learning the locking status of the steerable additional axle of the commercial vehicle; and if the locking status indicates that the additional axle can currently be steered and the current driving speed of the commercial vehicle is greater than or equal to the critical instability speed, locking the steerable additional axle of the commercial vehicle. The steerable additional axle is the steerable additional axle of the vehicle. In addition, the steerable additional axle can also be locked in terms of its orientation or its steerability. By locking, the steerable additional axle is fixed in straight running or its steerability is locked. In the locked state, the steerable additional axle acts as a rigid axle. Preferably, the steerable additional axle is locked in straight running, that is, locked in the orientation occupied by the steerable additional axle during the straight running of the vehicle. The driving behavior of the commercial vehicle generally shifts towards understeering behavior due to the locking of the steerable additional axle, so the stability of the vehicle is improved. Therefore, the steerable additional axle will not shimmy or sway in the locked state.

[0020] Preferably, the method further includes: if the current driving speed of the commercial vehicle reaches or is lower than the stable speed, raising the lifting axle, where the stable speed is equivalent to the critical instability speed minus the speed buffer. The stable speed is the speed at which, when a sudden excitation occurs, the commercial vehicle remains in a stable driving state even if the lifting axle is raised. When the vehicle moves at the stable speed, even if the lifting axle is raised, evasive maneuvers can still be performed without making the commercial vehicle unstable. In this case, raising the lifting axle is meaningful to avoid the disadvantages of the lowered lifting axle described at the beginning of this article (increased wear, increased fuel consumption, increased toll expenditure, reduced dispatchability, etc.). The speed buffer ensures that the lifting axle is not immediately raised when the vehicle speed is lower than the critical instability speed. Therefore, it is ensured that the vehicle moves within the stable speed range for a long time before the lifting axle is raised. However, alternatively, it can also be set that the stable speed is basically equivalent to the critical instability speed, or the speed buffer tends to zero. Alternatively or additionally, the stable speed can also have a fixed value. The fixed value of the stable speed is preferably 15 km / h, 20 km / h or 25 km / h. Therefore, when the vehicle continues to move forward at 15 km / h, even if the critical instability speed is less than 15 km / h, the lifting axle can still be raised, for example.

[0021] Preferably, the speed buffer is preferably in the range of 1 km / h to 25 km / h, preferably 5 km / h to 25 km / h, preferably 5 km / h to 20 km / h, preferably 10 km / h to 20 km / h. The boundary values of the claimed scope are likewise preferred. Accordingly, the speed buffer can preferably also be 1 km / h. Preferably, the lifting is only carried out when the current driving speed reaches or falls below the stable speed and lasts for a predetermined period of time. Thus, lifting is avoided in the case where the vehicle is only briefly below the critical instability speed, for example due to a short braking maneuver. The predetermined period of time can, for example, include 1 s (second) or more, preferably 2 s or more, preferably 3 s or more, preferably 4 s or more, preferably 5 s or more.

[0022] Preferably, the lifting bridge of the commercial vehicle is only lowered when the lifting condition represents that the lifting bridge is in the lifted state, the current driving speed is greater than or equal to the critical instability speed, and the driving speed reaches the minimum speed. The minimum speed preferably has a value of 15 km / h or higher, 20 km / h or higher, 25 km / h or higher, particularly preferably 30 km / h. Thus, lowering of the lifting bridge can be prevented at low driving speeds that generally pose only a small potential danger even under adverse vehicle characteristics, lane characteristics, and / or weather characteristics.

[0023] In a variant, ascertaining the critical instability speed of the commercial vehicle includes: predicting the stable behavior of the lateral dynamics of the commercial vehicle based on the current vehicle configuration of the commercial vehicle, and defining the critical instability speed based on the predicted stable behavior of the lateral dynamics of the commercial vehicle. Preferably, if the commercial vehicle is a vehicle combination, the prediction of the stable behavior of the lateral dynamics of the commercial vehicle is at least partially based on the geometric characteristics and / or the load characteristics of the trailer vehicle. The geometric characteristics and the load characteristics at least partially represent the current vehicle configuration of the commercial vehicle, and the current vehicle configuration relates to both vehicle-specific aspects and load-specific aspects. The geometric characteristics represent the geometry of the commercial vehicle. In addition to or instead of the geometric dimensions, the geometric characteristics preferably can also include numerical specifications (such as the number of axles of the vehicle). The geometric characteristics are in particular or include geometric parameters that define the driving dynamics of the vehicle, such as the wheelbase of the vehicle, the axle spacing between the axles of the vehicle, the track width of the vehicle, the spacing between the rear axle of the vehicle and the coupling point of the trailer, or the design form of the trailer vehicle (such as a full trailer or a mid-axle trailer). The load characteristics represent the load acting on the vehicle, and this load can be caused by the vehicle's own weight and the vehicle's load. Accordingly, the current vehicle configuration of an unloaded vehicle is different from the current vehicle configuration of the same vehicle in the loaded state. The load characteristics can preferably be or include wheel loads, axle loads, gross vehicle mass, mass of vehicle parts, and / or the center of gravity position of the vehicle or vehicle parts.

[0024] Within the scope of the method, the geometric characteristics and load characteristics known are taken into account when predicting the lateral dynamic behavior. Since the determination of the critical instability speed is based on the predicted stable behavior of the lateral dynamics of the commercial vehicle, the known characteristics also influence the determination of the critical instability speed. The critical instability speed is at least partially coordinated with the current vehicle configuration. The time point for lowering the drawbridge can be determined particularly precisely. Thus, the instability risk caused by improper loading of the vehicle is recognized and taken into account when determining the critical instability speed.

[0025] By predicting the stable behavior of the lateral dynamics, the behavior of the vehicle can be predicted in advance. The stable behavior of the lateral dynamics preferably includes the yaw behavior of the towing vehicle, the folding behavior of a trailer vehicle or multiple trailer vehicles, the natural angular frequency of the vehicle, and / or the damping amount of the vehicle or the dynamic system formed by the vehicle. The prediction of the stable behavior of the lateral dynamics of the current vehicle configuration is preferably carried out based on a model. For this purpose, the vehicle basic model can be individualized preferably in the case of using geometric characteristics and load characteristics, and the stable behavior of the lateral dynamics of the vehicle can be known in the case of using the individualized vehicle model.

[0026] Preferably, the step of predicting the stable behavior of the lateral dynamics of a commercial vehicle based on the current vehicle configuration of the commercial vehicle includes: knowing two or more geometric characteristics and two or more load characteristics of the current vehicle configuration; generating an individualized vehicle model of the current vehicle configuration in the case of using geometric characteristics and load characteristics; and predicting the dynamic characteristics of the current vehicle configuration in the case of using the individualized vehicle model. Preferably, generating the individualized vehicle model of the current vehicle configuration includes: approximately calculating the mass distribution of the current vehicle configuration along at least one vehicle longitudinal direction in the case of using geometric characteristics and load characteristics; and generating the individualized vehicle model of the current vehicle configuration from the vehicle basic model of the commercial vehicle in the case of using geometric characteristics and the approximately calculated mass distribution.

[0027] In a preferred embodiment, determining the critical instability speed of a commercial vehicle is or includes: selecting a pre-stored critical instability speed from a memory in which at least one critical instability speed is pre-stored. The pre-stored critical instability speed of the commercial vehicle is preferably stored in the memory of the control unit. Preferably, the pre-stored critical instability speed has a fixed value. Additionally, determining the critical instability speed of a commercial vehicle can also be: selecting one pre-stored critical instability speed from a plurality of pre-stored critical instability speeds. The selection is preferably made taking into account the current vehicle configuration. Thus, if the commercial vehicle does not include a trailer vehicle, for example, the first pre-stored critical instability speed can be selected, and if the commercial vehicle is a vehicle combination, the second pre-stored critical instability speed can be selected. The selection can also be based on the loading state. Thus, all other things being equal, a different critical instability speed can be selected for a fully loaded commercial vehicle than for an empty or partially loaded commercial vehicle. Additionally, the selection is preferably made taking into account the current road situation, wherein the method preferably includes determining the current vehicle situation.

[0028] Preferably, the pre-stored critical instability speed is in the range of 20 km / h to 100 km / h, preferably 20 km / h to 90 km / h, preferably 20 km / h to 80 km / h, preferably 30 km / h to 80 km / h, preferably 30 km / h to 70 km / h, preferably 30 km / h to 60 km / h, preferably 30 km / h to 55 km / h, preferably 40 km / h to 55 km / h, particularly preferably 45 km / h to 55 km / h. Preferably, when selecting the pre-stored critical instability speed from the memory, if the commercial vehicle is on a road in a closed residential area, then a critical instability speed in the range of 45 km / h to 55 km / h is selected, if the commercial vehicle is traveling on a suburban road, then a critical instability speed in the range of 56 km / h to 70 km / h is selected, and / or if the vehicle is traveling on a highway, then a critical instability speed in the range greater than 70 km / h is selected.

[0029] According to a preferred improvement, obtaining the critical instability speed of a commercial vehicle includes: approximately calculating the current friction coefficient for the commercial vehicle; wherein, the critical instability speed of the commercial vehicle is obtained using the approximately calculated friction coefficient. There will be a certain error in obtaining the current friction coefficient, so the obtained friction coefficient is only close to the actually existing friction coefficient. The obtained current friction coefficient may thus preferably also deviate from the actual friction coefficient between the commercial vehicle and the lane traveled by the commercial vehicle. In a preferred design of the method, the pre-stored critical instability speed is selected depending on the approximately calculated friction coefficient. Thus, for a high friction value, a speed of 50 km / h may be critical instability, for example, while for a low friction value, a speed of 30 km / h may already be critical instability. However, the friction value can also be considered alternatively or additionally within the scope of predicting the lateral dynamic behavior.

[0030] Preferably, the method further includes: obtaining dynamic route alignment data, wherein the critical instability speed of the commercial vehicle is obtained using the dynamic route alignment data. Thus, the critical instability speed, for example, has a greater value when the route alignment is straight than when the route alignment is multi-curved or includes a large slope. It is also possible to lower the drawbridge only when the route alignment data characterizes a specific road type. Thus, the knowledge of the route improves the targeted use of the method or the targeted lowering of the drawbridge. For example, it may be possible to prevent the drawbridge from being continuously lowered during straight driving on a highway, thereby reducing the economic efficiency of commercial vehicle operation. However, it can also be set that the drawbridge is lowered regardless of the road type. Thus, it can be set that the method can also be executed during highway driving, or the drawbridge is lowered when the dynamic route alignment data characterizes a dangerous situation, such as an oil-slick road surface or a slippery lane ahead. When the critical instability speed of the commercial vehicle is obtained using the dynamic route alignment data, it is preferably possible to first obtain the critical instability speed of the driving dynamics, for example, based on a customized vehicle model, and then adaptively adjust the critical instability speed of the driving dynamics to the critical instability speed using the dynamic route alignment data. Thus, for example, the critical instability speed of the driving dynamics of 60 km / h when the route ahead is multi-curved can be reduced to the critical instability speed of 50 km / h.

[0031] Preferably, even when the drawbridge is lifted without exceeding the maximum allowable axle load of the commercial vehicle, the drawbridge of the commercial vehicle is lowered. Then, the method will be executed contrary to economic considerations.

[0032] In a second aspect, the present invention solves the task mentioned at the beginning herein by means of a device for improving the driving dynamic stability of a commercial vehicle, which device is configured to carry out the method according to the first aspect of the present invention. Preferably, the device for improving the driving dynamic stability of a commercial vehicle has a control unit and an interface, wherein the control unit is configured to provide a lowering request for the lift bridge actuator at the interface if the lift condition represents that the lift bridge is raised and the current driving speed is greater than or equal to the critical instability speed.

[0033] In a third aspect, the present invention solves the task mentioned at the beginning herein by means of a device for improving the driving dynamic stability of a commercial vehicle, wherein the commercial vehicle has a lift bridge, and wherein the device has an interface and a control unit, wherein the control unit can be connected to at least one network of the commercial vehicle for receiving signals and is configured to: determine the current driving speed of the commercial vehicle using the signals; determine the critical instability speed of the commercial vehicle; compare the current driving speed of the commercial vehicle with the critical instability speed of the commercial vehicle; determine the lift condition of the lift bridge using the signals, and if the lift condition represents that the lift bridge is raised and the current driving speed of the commercial vehicle is greater than or equal to the critical instability speed, provide a lowering request at the interface to cause the lift bridge of the commercial vehicle to lower.

[0034] In a preferred refinement, the control unit can be connected to the vehicle network of the vehicle for receiving a wheel speed signal representing the rotational speed of at least one wheel of a reference wheel of the commercial vehicle, wherein the control unit is configured to determine the current driving speed of the commercial vehicle based on the wheel speed signal.

[0035] In a fourth aspect, the task mentioned at the beginning herein is solved by means of a commercial vehicle which has a lift bridge and the device according to the second aspect of the present invention and / or the device according to the third aspect of the present invention. The commercial vehicle preferably also includes a front axle and a rear axle. The lift bridge is preferably a trailing axle of the commercial vehicle.

[0036] According to a fifth aspect, the present invention solves the task mentioned at the beginning herein by means of a computer program product having a program code medium stored on a computer-readable data carrier, such that when the program product is implemented on a computing unit of a commercial vehicle having a lift bridge, the method according to the first aspect of the present invention is implemented. The commercial vehicle is preferably the commercial vehicle according to the fourth aspect of the present invention.

[0037] It should be understood that the device for improving the driving dynamic stability of a commercial vehicle according to the second and / or third aspects of the present invention, the commercial vehicle according to the fourth aspect of the present invention, and the computer program product according to the fifth aspect of the present invention may have the same and similar sub-aspects as those recorded especially in the dependent claims for the method according to the first aspect of the present invention.

[0038] In a sixth aspect, the present invention is solved by a method for improving the driving dynamic stability of a commercial vehicle, wherein the commercial vehicle has a steerable additional axle, and the method includes: obtaining the current driving speed of the commercial vehicle; obtaining the critical instability speed of the commercial vehicle; comparing the current driving speed with the critical instability speed; obtaining the locking status of the steerable additional axle; and if the locking status represents that the additional axle can currently be steered and the current driving speed of the commercial vehicle is greater than or equal to the critical instability speed, locking the steerable additional axle of the commercial vehicle in straight running. As already explained with reference to the preferred improvements for the first aspect of the present invention, the driving dynamic stability of a commercial vehicle can be improved by locking the steerable additional axle. For this purpose, the steerable additional axle can also be locked regardless of the lowering of the lifting axle, especially even when the commercial vehicle does not have a lifting axle. The recognition on which the present invention is based, that is, the stabilization measures that can be advantageously carried out depending on the critical instability speed, also applies to the sixth aspect of the present invention or to locking the steerable additional axle regardless of the lifting axle. When locking the steerable additional axle of the commercial vehicle in straight running, the steerable additional axle is locked in the orientation it has when the commercial vehicle is running straight. The method according to the sixth aspect of the present invention can be configured substantially similarly to the preferred improvements of the first aspect of the present invention, especially as recorded in the dependent claims.

[0039] Now, the embodiments of the present invention will be described with reference to the accompanying drawings. These drawings do not necessarily show the embodiments to scale. Instead, the drawings for illustration are implemented in a schematic and / or slightly distorted form. For supplementary content regarding the teachings directly obtained from the drawings, refer to the relevant prior art. It is to be considered that, without departing from the general concept of the present invention, various modifications and alterations can be made to the form and details of the embodiments. The features disclosed in the description, the drawings, and the claims, either individually or in any combination, are of great significance for the improvement of the present invention. In addition, all combinations of at least two features disclosed in the description, the drawings, and / or the claims fall within the scope of the present invention. The general concept of the present invention is not limited to the exact form or details of the preferred embodiments shown and described below, nor is it limited to the subject matter restricted compared to the subject matter claimed in the claims. Regarding the set measurement range, the values within the mentioned boundary ranges should also be disclosed as boundary values and can be used arbitrarily and are protected by rights. For the sake of clarity, the same reference numerals are used hereinafter for consistent or similar parts or parts having consistent or similar functions. Description of the Drawings

[0040] Further advantages, features, and details of the present invention result from the following description of the preferred embodiments and from the drawings; in the figures:

[0041] Figure 1 A commercial vehicle with a lifting bridge is shown;

[0042] Figure 2 A first embodiment of the method is shown;

[0043] Figure 3 A diagram showing the curves of the yaw response and the folding direction during an avoidance maneuver of a commercial vehicle with a raised lifting bridge and a commercial vehicle with a lowered lifting bridge that is otherwise identical;

[0044] Figure 4 A second embodiment of the method is shown. Detailed Description of the Embodiments

[0045] Method 1 is explained using the commercial vehicle 300 as an example, and the commercial vehicle is configured as a vehicle combination 302. In Figure 1 The vehicle combination 302 shown includes a three-axle tractor vehicle 304 that towes a two-axle trailer vehicle 306 configured as a full trailer 308. The tractor vehicle 304 includes a front axle 310, a first rear axle 312, and a lifting bridge 314. The lifting bridge 314 is arranged as a trailing axle behind the first rear axle 312 in the longitudinal direction R1 of the vehicle.

[0046] The loading condition that is often adjusted in the vehicle combination 302 is characterized in that the towing vehicle 304 travels unloaded, while the trailer vehicle 306 is loaded. When the trailer vehicle 306 is leased and the towing vehicle 304 is owned by the operator, this loading condition will be particularly selected for economic reasons. Therefore, in the described loading condition, the trailer vehicle 306 particularly suffers wear. The wear at the towing vehicle 304 is minimized due to the lack of load. However, disadvantageously, due to the unfavorable load distribution, the stability of the commercial vehicle 300 may be impaired.

[0047] To accommodate the load 320, the towing vehicle 304 has a first loading surface 322. For the same purpose, the trailer vehicle 306 includes a second loading surface 324. The first loading surface 322 is empty, while the load 320 is arranged on the second loading surface 322. Figure 1 It should be shown by an arrow 325 that the load on the trailer vehicle 306 is approximately twice as large as the load on the towing vehicle 304 caused by the dead weight of the towing vehicle 304. This load distribution is unfavorable for the driving dynamic stability of the commercial vehicle 300. The drawbar 316 of the trailer vehicle 306 does not transfer any vertical load to the towing vehicle 304, thus preventing the axle load in the towing vehicle 304 from deviating from its unloaded load. For economic reasons, in this configuration, the lift axle 314 of the towing vehicle 304 is usually raised, thereby further impairing the driving dynamic stability of the commercial vehicle 300.

[0048] The method 1 according to the invention is set up to improve the driving dynamic stability of the commercial vehicle 300 and especially the trailer vehicle 304, in particular by lowering the lift axle 314 depending on the situation.

[0049] However, it should be understood that the method 1 can also be used in the commercial vehicle 300 without a trailer vehicle 306 and in the commercial vehicle 300 with a mid - axle trailer, in addition to the vehicle combination 302 with the towing vehicle 304 towing the full - trailer 308 shown. In the case of the full - trailer 308, the distance from the first rear axle 312 of the towing vehicle 304 to the coupling point 318 is significantly longer than in the case of a low - coupling system. Therefore, the stability gain achieved by lowering the lift axle 314 described later is usually greater in the commercial vehicle 300 with a full - trailer 308 than in the commercial vehicle 300 with a mid - axle trailer. This stability gain is particularly advantageous in the commercial vehicle 300 with a full - trailer 308 because full - trailers 308 mostly have multiple folding joints (not shown in Figure 1 and are therefore usually more sensitive to excitation than mid - axle trailers.

[0050] In Figure 1The commercial vehicle 300 shown is characterized by the current vehicle configuration 326. This current vehicle configuration 326 includes geometric features 328 and load characteristics 330. The features 328, 330 of the current vehicle configuration 326 of the commercial vehicle 300 are illustrated in Figure 1 only by means of some geometric features 328 and load characteristics 330 for better overview. As an example of the geometric feature 328, the axle spacing L11 between the front axle 310 and the first rear axle 312 of the towing vehicle 304 is shown. In Figure 1 The other geometric features 328 shown are the coupling spacing L13 between the first rear axle 312 and the coupling point 318 of the towing vehicle 304 and the lift bridge spacing L12 between the first rear axle 312 and the lift bridge 314 of the towing vehicle 304. In addition, the geometric feature 328 of the current vehicle configuration 326 also includes the lift condition S of the lift bridge 314. The lift condition S can represent here that the lift bridge 314 is in the lowered state (lift condition Sdown) and the lift bridge 314 is in the raised state (lift condition Sup). When the lift bridge 314 is in the lowered state, the effective wheelbase of the driving dynamics of the towing vehicle 304 will become and more precisely from Figure 1 the shown axle spacing L11 to the sum of the axle spacing L11 and half of the lift bridge spacing L12 (L11 + L12 / 2).

[0051] The stable behavior of the lateral dynamics of the commercial vehicle 300 is affected by the wheelbase, where the lift condition S of the lift bridge 314 is a geometric feature 328 that directly characterizes this influence. In addition, the other geometric features 328 of the shown commercial vehicle 300 are the drawbar length of the drawbar 316 of the full trailer 308 or the wheelbase of the trailer vehicle 306, but these are not explicitly marked in Figure 1 for clarity.

[0052] The load characteristic 330 characterizes the load acting on the commercial vehicle 300 in the current vehicle configuration 326, which is caused here by the self-weight of the commercial vehicle 300 and the load 320. The load characteristic 330 is illustrated in Figure 1 simplified as the load acting on the first rear axle 312 of the towing vehicle 304 and the front axle 332 of the trailer vehicle 306. As already explained, the trailer vehicle 306 is loaded while the towing vehicle 304 is unloaded, so that the load acting on the first rear axle 312 of the towing vehicle 304 is smaller than the load acting on the front axle 332 of the trailer vehicle 306. This is illustrated by the length of the arrow representing the load characteristic 330.

[0053] Here, the load characteristic 330 acting on the first rear axle 312 of the towing vehicle 304 is the axle load borne by the first rear axle 312. This axle load is known from the electronically controllable air suspension of the commercial vehicle 300. As a further load characteristic 330, the electronically controllable air suspension knows the axle load acting on the front axle 332 of the trailer vehicle 306. In the current embodiment, in addition to the known axle load acting on the first rear axle 312 of the towing vehicle 304, the total mass of the towing vehicle 304 and the lifting state S of the lifting axle 314 are also known, so that the axle load acting on the front axle 310 of the towing vehicle 304 can be known in a calculated manner by calculating the load distribution. In addition, based on the axle load borne by the front axle 332 of the trailer vehicle 306 and the known total mass of the trailer vehicle 306, the axle load acting on the rear axle of the trailer vehicle 306 can also be known. The load characteristic 330 can thus be detected directly by measurement technology on the one hand and indirectly by calculation on the other hand in the current embodiment.

[0054] For the same commercial vehicle 300, the current vehicle configuration 326 can change depending on the geometric characteristic 328 and the load characteristic 330. Thus, when the lifting axle 314 of the commercial vehicle 300 is in the lowered position (i.e., the lifting state S is different) or when the load 320 is arranged on the first loading surface 322 instead of on the second loading surface 324, the current vehicle configuration 326 of the commercial vehicle 300 will be different from Figure 1 the current vehicle configuration 326 shown in Figure 1 It should be clarified that the current vehicle configuration 326 is condition-dependent and represents the current state of the commercial vehicle 300.

[0055] Another factor that can be included in the current vehicle configuration 326 is the current coefficient of friction μ between the commercial vehicle 300 and Figure 1 the carriageway 336 shown by the dashed line in

[0056] Next, a preferred design of the method 1 for improving the driving dynamic stability of the commercial vehicle 300 according to the invention will be explained essentially with reference to Figures 2 to 4 and, if necessary, also with reference to Figure 1Explain various aspects particularly related to the commercial vehicle 300.

[0057] Figure 2 Schematically shows a first embodiment of method 1, within the scope of this method, first obtain the current driving speed V of the commercial vehicle 300 ( Figure 2 the obtaining 3 in ). The obtaining 3 of the current driving speed V can be carried out, for example, based on signals provided by a speedometer, a rotational speed sensor and / or a control unit of the commercial vehicle 300. Preferably, the obtaining 3 of the current driving speed V is continuously or cyclically repeated.

[0058] In the first embodiment, simultaneously with the obtaining 3 of the current driving speed V, also obtain 5 the critical instability speed Vcrit of the commercial vehicle 300. The advantage of simultaneously carrying out the obtaining 3 and 5 of the current driving speed V and the critical instability speed Vcrit is that method 1 is streamlined and the error is reduced. However, it can also be arranged that the obtaining 3 of the current driving speed V is carried out before or after the obtaining 5 of the critical instability speed Vcrit in terms of time or the steps of obtaining 3 and 5 are partially carried out simultaneously. Therefore, preferably, the obtaining 5 of the critical instability speed Vcrit can also be carried out, for example, when the vehicle is activated by operating the ignition system or the driving switch of the commercial vehicle 300.

[0059] In the shown embodiment, immediately after the obtaining 3 and 5, compare 7 the current driving speed V with the critical instability speed Vcrit. The comparison 7 results in that the current driving speed V is greater than or equal to the critical instability speed Vcrit (V ≥ Vcrit). For the case where the comparison 7 results in the driving speed V being less than the critical instability speed Vcrit (V < Vcrit), method 1 is ended, and when the driving speed V or the influencing factors on which the obtaining 5 is based change, method 1 is restarted. However, it can also be arranged that after a certain waiting time, method 1 is restarted. However, it can also be arranged that even when the comparison 7 results in the speed V being less than the critical instability speed Vcrit (V < Vcrit), one or more of the following steps of method 1 are still carried out.

[0060] Simultaneously with the comparison 7 of the current driving speed V with the critical instability speed Vcrit, obtain 9 the lifting state S of the lifting bridge 314 ( Figure 2 the obtaining 9 in ). Here, the obtaining 9 results in the lifting state S being the lifting state Sup, which represents that the lifting bridge 314 is in the lifted state. However, it can also be arranged that the obtaining 9 of the lifting state S is carried out before, after or simultaneously with the comparison 7 of the speeds V and Vcrit in terms of time. Preferably, the lifting state S is obtained when the vehicle is activated.

[0061] In accordance with Figure 2In the embodiment, the current driving speed V is greater than the critical instability speed Vcrit and the lift bridge 314 of the commercial vehicle 300 is in the raised position (S = Sup). For this reason, in a further step, the lift bridge 314 of the commercial vehicle 300 will be lowered 11.

[0062] As already explained at the beginning of this text, the important wheelbase of the driving dynamics of the commercial vehicle is extended from the axle spacing L11 to the sum of the axle spacing L11 and half of the lift bridge spacing L12. Thereby, the driving stability of the towing vehicle 304 is improved. Since the effective wheelbase of the driving dynamics of the commercial vehicle is increased from L11 to L11 + L12 / 2, the ability of the towing vehicle 304 to change the following direction is reduced, so that the towing vehicle 304 achieves a smaller yaw rate and is stabilized.

[0063] In addition, the distance between the coupling point 318 and the effective support point of the driving dynamics at the rear of the towing vehicle 304 is reduced from the coupling distance L13 to the difference (L13 - L12 / 2) composed of the coupling distance L13 and half of the lift bridge spacing L12. Therefore, the lever arm for the force transmitted from the towing vehicle 306 or the drawbar 316 to the towing vehicle 304 is shortened. This results in that when the lift bridge 314, which is configured as a trailing axle in the commercial vehicle 300, is lowered, the kinematic drag curve of the coupling point 318 during cornering will describe a larger turning radius. Thereby, the deflection of the full trailer 308 is reduced, so that the risk of the trailer vehicle 306 fishtailing in a dangerous situation is reduced. An avoidance maneuver (lane change or two-lane change) that builds up the yaw response of the commercial vehicle 300 with a high steering angle amplitude and steering angular velocity is an example for this dangerous situation.

[0064] Figure 3 Shows the yaw response and the folding angle change curve of the path taken when performing an avoidance maneuver as a two-lane change maneuver along the vehicle combination 302 with a raised lift bridge 314 (the vehicle combination 302 is only shown simplified in Figure 3 ). Similarly, Figure 3 also shows the yaw rate and the change curve of the folding angle γ of the path taken when performing the same avoidance maneuver along the vehicle combination 302 with a raised lift bridge 314 that is otherwise identical. In short, Figure 3 shows a comparison of the yaw response and the folding angle change curve of the vehicle combination 302 with a lowered lift bridge 314 and the vehicle combination 302 with a raised lift bridge 314.

[0065] The folding angle variation curve describes the temporal variation curve of the folding angle γ formed between the towing vehicle 304 and the trailer vehicle 306. For the trailer vehicle 306 driving strictly straight behind the towing vehicle 304, the folding angle γ has a value of 0°. When driving in a curve or performing an avoidance maneuver, the folding angle γ decreases or increases accordingly. The yaw response relates to the yaw rate of the commercial vehicle 300 along the path traversed by the commercial vehicle 300. of the variation curve. In Figure 3 , line 47a (solid line) characterizes the variation curve of the yaw rate when the lifting bridge 314 is lowered, and line 47b (sparse short-dashed line) characterizes the variation curve of the yaw rate when the lifting bridge 314 is raised. Line 49a (dotted line) similarly characterizes the folding angle variation curve when the lifting bridge 314 is lowered, and line 49b (dense short-dashed line) characterizes the folding angle variation curve when the lifting bridge 314 is raised.

[0066] Figure 3 Illustrates that, compared with the variation curve 47b of the yaw rate of the vehicle combination 302 when the lifting bridge 314 is raised, for an otherwise identical avoidance maneuver 51, the yaw rate in the variation curve 47a when the lifting bridge 314 is lowered reaches a flatter gradient and a smaller maximum value. This is attributed to the earlier use of the understeering driving behavior of the commercial vehicle 300. In addition, when the lifting bridge 314 is lowered, the folding angle γ between the trailer vehicle 306 or the drawbar 316 and the towing vehicle 304 is reduced. The yaw damping of the commercial vehicle 300 is increased, such that when the lifting bridge 314 is lowered (line 49a), the excitation of the vehicle combination 302 by the trailer vehicle 306 is damped better than when the lifting bridge 314 is raised (line 49b). The improved driving stability of the commercial vehicle 300 is demonstrated in particular by the very small folding angle γ between the towing vehicle 304 and the trailer vehicle 306 when returning to the initial lane 55 during the steering return 53 and during the subsequent straight route. In particular, in the commercial vehicle 300 configured as the vehicle combination 302, the driving stability is significantly improved by lowering the lifting bridge 314. However, the driving stability can also be improved better in a commercial vehicle 300 without a trailer vehicle 306, especially when the wheelbase of such a commercial vehicle 300 is very short and / or the commercial vehicle 300 is loaded with a heavy load at the rear.

[0067] In accordance with Figure 2In an embodiment, the critical instability speed Vcrit is obtained by predicting the stable behavior of the lateral dynamics of the commercial vehicle 300 and defining the critical instability speed Vcrit based on the predicted stable behavior of the lateral dynamics of the commercial vehicle 300.

[0068] In a first step of the prediction 13, it is carried out here to obtain 17 two or more geometric features 328 and two or more load features 330. The geometric features 328 obtained are in particular the axle spacing L11, the lift axle spacing L12, the coupling spacing L13 and the lift condition S. The coupling spacing L13 can be obtained, for example, by the axle formula of the commercial vehicle 300 in the case of using the type of the trailer vehicle 306 (mid-axle trailer or full trailer 308). The type of the trailer vehicle 306 can be obtained, for example, based on the signal of the trailer network (not shown in the figure), and the trailer network can in particular be ISO 11992 CAN. Simultaneously with the obtaining of the geometric features 328, two or more load features 300 are obtained, and the load features are only partially indicated in Figure 2 for the sake of overview. The load features 330 in the current embodiment include the axle loads acting on the front axle 310 and the first rear axle 312 of the towing vehicle 304. In addition, the load features 330 also include the axle loads acting on the axles 338 of the trailer vehicle 306, where, in Figure 1 only the axle load acting on the front axle 332 of the trailer vehicle 306 is shown as the load feature 330. Preferably, however, the load features 330 also include only one total towing vehicle mass of the towing vehicle 304 and the total trailer vehicle mass of the trailer vehicle 306, and / or the mass distribution of the commercial vehicle 300, where the mass distribution is the ratio formed by the total towing vehicle mass and the total trailer vehicle mass.

[0069] The obtaining 17 of the geometric features 328 and the load features 330 is carried out for the first time when the commercial vehicle 300 is activated. When the ignition system of the commercial vehicle 300 is activated, the vehicle type of the commercial vehicle 300 and the geometric features 328 (the number of axles 310, 312, 314, 338, the axle spacing L11) are already known. In addition, other characteristics of the axles 310, 312, 314, 338 can also be provided. These characteristics are stored as geometric features 328 in the ESC controller 340 of the commercial vehicle 300, and in the case of instability, the ESC controller intervenes in the driving operation in a regulated manner, for example, by initiating braking of the wheels on the outer side of the bend of the oversteering commercial vehicle 300. In the current case, the trailer vehicle 306 has an electronic braking system (EBS). The trailer vehicle 306 is connected via a trailer interface that can be configured as an ISO11992 interface (in Figure 1is not shown) is connected to the towing vehicle 304. The trailer vehicle 306 provides, at the trailer interface, signals for the towing vehicle 304 that are used to determine the geometric characteristics 328 of the trailer vehicle 306. The geometric characteristics 328 of the trailer vehicle 306 include: the type of trailer vehicle 306, the number of axles 338 of the trailer vehicle 306, and the spacing thereof from the coupling point 318. These geometric characteristics 328 of the trailer vehicle 306 are provided directly at the ISO 11992 interface here, so that determining the characteristics 328, 330 of the trailer vehicle 306 is to receive the corresponding signals. In addition, the EBS type trailer vehicle 306 has sensors assigned to the axles 338 (not shown in Figure 1 . These sensors determine the axle loads present at the sensed axles 338 and provide corresponding signals at the trailer interface. From these signals, the axle loads of the trailer vehicle 306 are determined as load characteristics 330. In addition, determining 17 here also includes: calculating the axle load acting on the front axle 310 of the towing vehicle 304.

[0070] In the next step of method 1, immediately following the determination 17 of the geometric characteristics 328 and the load characteristics 330, a customized vehicle model of the current vehicle configuration 3 is generated from the vehicle base model of the commercial vehicle 300 (the generation 19 in Figure 2 ). The customized vehicle model can be a single-track model of the commercial vehicle 300, and the single-track model depicts the towing vehicle 304 and the trailer vehicle 306 of Figure 1 in their minimum coordinates, where the vehicle width tends to zero, and the lifting, rolling, or pitching motions occurring in the commercial vehicle 300 can be ignored.

[0071] The generation 19 of the customized vehicle model is carried out using the geometric characteristics 328 and the load characteristics 330. For this purpose, the mass distribution of the current vehicle configuration 326 along the vehicle longitudinal direction R1 is approximately calculated. Immediately following this, when generating 19 the customized vehicle model, the parameterized vehicle base model of the commercial vehicle 300 is preferably customized by using the geometric characteristics 328 and the load characteristics 330, where the determined characteristics 328, 330, and the mass distribution are used as parameter values in the vehicle base model.

[0072] In the case of using the customized vehicle model, immediately following this, the dynamic characteristics of the current vehicle configuration 326, especially the lateral dynamic characteristics (the prediction 21 in Figure 2 ), are predicted. The dynamic characteristics determined within the scope of the prediction 21 are, in the current embodiment, the natural angular frequency and damping of the eigenvalues of the customized vehicle model. In Figure 1In this case, the commercial vehicle 300d is moving straight ahead in a steady state and is stable. However, due to the load on the rear, the commercial vehicle 300 is prone to instability in the case of a sudden avoidance maneuver 51 characterized by a high steering angle frequency (see Figure 3 ). Depending on the current driving speed V, the trailer vehicle 306 may not sufficiently damp the excitation caused by the avoidance maneuver of the commercial vehicle 300 and a fishtail may occur. The control unit 202 of the commercial vehicle 300 is configured to determine, based on the known dynamic characteristics, from which current driving speed V the typical steering excitation of the commercial vehicle 300 for the avoidance maneuver 51 becomes unstable. The control unit 202 defines this speed as the critical instability speed Vcrit. In addition, the control unit 202 is also configured here to: predict 21 the dynamic characteristics; determine the characteristics 328, 330; and generate 19 a customized vehicle model.

[0073] In these embodiments of method 1, an approximate calculation 33 of the current friction coefficient μ for the commercial vehicle 300 is also provided. In accordance with Figure 2 In the embodiment, the critical instability speed Vcrit of the commercial vehicle 300 is determined 5 using the approximately calculated friction coefficient μ. The friction coefficient μ is taken into account when predicting 21 the dynamic characteristics of the commercial vehicle 300 by using the friction coefficient μ as a parameter value of the model when generating 19 the customized vehicle model. By determining 33 the current friction coefficient μ for the commercial vehicle 300, the quality of the prediction 21 of the dynamic characteristics of the current vehicle configuration 326 is further improved. In reality, the current friction coefficient μ often fluctuates. Therefore, the friction coefficient μ between the commercial vehicle 300 and the roadway 336 is reduced when it is wet or icy compared to dry conditions. This thus has a significant impact on the dynamic characteristics of the commercial vehicle 300. When the current friction coefficient μ is taken into account when predicting 21 the dynamic characteristics, this has an impact on the determined critical instability speed Vcrit and increases the safety during operation of the commercial vehicle 300. However, the dynamic characteristics of the commercial vehicle 300 can also be predicted without taking into account the current friction coefficient μ, where the predicted dynamic characteristics may also be incorrect. Thus, for safety reasons, a small friction coefficient μ can also be assumed during the prediction 21, such that the critical instability speed Vcrit may be smaller than required.

[0074] In addition, in method 1 in accordance with Figure 2 the dynamic route data Droute is also taken into account when defining 15 the critical instability speed Vctit, the dynamic route data having been determined in the previous step (in Figure 2The knowledge in 35). Thus, when the route direction data Droute represents a multi-curved route, the critical instability speed Vcrit derived from the predicted dynamic characteristics of the current vehicle configuration 326 may be reduced here when using the route direction data Droute. The knowledge of the route direction data Droute is carried out by the navigation system 344 of the towing vehicle 304, and the navigation system provides the route direction data Droute to the control unit 202.

[0075] After the lifting bridge 314 has been lowered by 11, the commercial vehicle 300 continues to perform its driving task, such as driving from point A to point B. During the driving task, the driving speed V of the commercial vehicle 300 may change, so that the speed may sometimes be greater than and sometimes less than the critical speed Vcrit. When the commercial vehicle 300 moves at the current driving speed V that is less than the critical instability speed Vcrit, the lifting bridge 314 does not have to be lowered to stabilize the commercial vehicle 300. Therefore, in the first embodiment ( Figure 2 ), if the current driving speed V of the commercial vehicle 300 reaches or is lower than the stable speed Vstab (V ≤ Vstab), then the lifting bridge 314 is lifted.

[0076] In Figure 1 the driving speed V, the stable speed Vstab and the critical instability speed Vcrit are indicated. The stable speed Vstab is equivalent to the critical instability speed Vcrit minus the speed buffer ΔV (Vstab = Vcrit - ΔV). The speed buffer ΔV ensures that the lifting bridge 314 is not lifted immediately when the speed is lower than the critical instability speed Vcrit. Thus, it is prevented that the lifting bridge 314 is already lifted (and lowered) when the current driving speed V fluctuates slightly around the critical instability speed Vcrit. In addition, the speed buffer ΔV also ensures that the lifting bridge 314 is only lifted when the commercial vehicle 300 is safely moving within the stable speed range.

[0077] The smaller the current driving speed V, the smaller the risk of instability, so that setting the speed buffer ΔV further increases the safety gain provided by method 1. In addition, errors in knowing the current driving speed V, especially measurement errors, can be compensated. It can also be set that the lifting bridge 314 is only lifted when the current driving speed V is lower than the stable speed Vstab and lasts for a predetermined time period Δt. This prevents, for example, the lifting bridge 314 from being lifted when the commercial vehicle 300 brakes temporarily, for example, to increase the distance from another vehicle that has driven into the driving lane in front of the commercial vehicle 300.

[0078] For a further improvement of the lateral dynamic stability of the commercial vehicle 300, method 1 includes: locking 45 the steerable additional axle 344. In Figure 1 the illustrated embodiment, the first rear axle 312 of the towing vehicle 304 is the steerable additional axle 344. The steerable additional axle 344 can be locked, wherein the driving dynamic stability of the towing vehicle 304 and thus of the entire vehicle combination 302 is increased by the locking 45. In method 1, the steerable additional axle 344 is locked 45 only when the current driving speed V is greater than or equal to the critical instability speed Vcrit and if the locking status LS indicates that the steerable additional axle 344 is not locked or is open. Conversely, if the steerable additional axle 344 is already locked, which is represented by the locking status LSlock, then the locking 45 can be canceled.

[0079] The locking status LS is obtained in the previous step ( Figure 2 the obtaining 43 in). The obtaining of the locking status LS is carried out by obtaining the locking signal provided on the vehicle network 334 of the commercial vehicle 300, and thus the locking status LS is obtained 43 using the locking signal. In the illustrated embodiment, the ESC controller 340 provides the locking status LS on the vehicle network 334, which is the ISO 11992 CAN bus here. The control unit 202 receives the locking signal and thus obtains the locking status LS.

[0080] In a first embodiment of method 1 (see Figure 2 ), the lifting status S of the lifting axle 314 of the commercial vehicle 300 is obtained 9 based on the wheel speeds n_wheel, n_ref of the lifting axle 314 and the reference axle 346. The reference axle 346 is preferably the driven axle of the commercial vehicle 300. Currently, the front axle 310 of the commercial vehicle 300 is the reference axle 346. The obtaining 9 of the lifting status includes obtaining 37 the lifting axle wheel speed n_wheel of the wheel 348 of the lifting axle 314 and obtaining 39 the reference wheel speed n_ref of the reference wheel 222, which is the front wheel of the commercial vehicle 300 here. After obtaining 37 the lifting axle wheel speed n_wheel and obtaining 39 the reference wheel speed n_ref, these two wheel speeds n_wheel, n_ref are compared 41. In Figure 2 it, the comparison 41 results in the lifting axle wheel speed n_wheel being less than or equal to the reference speed n_ref minus the wheel speed tolerance value Δn (n_wheel ≤ n_ref - Δn).

[0081] During continued forward movement of the commercial vehicle 300 at the driving speed V, the reference wheel 350 rolls on the carriageway 336, wherein the tyre rolling speed of the reference wheel 350 corresponds approximately to the driving speed V. The reference wheel rotational speed n_wheel corresponds to the tyre rolling speed of the reference wheel 350 and is significantly greater than zero when the driving speed V is high. When the lifting bridge 314 is lifted, then its wheels 348 are not placed on the carriageway 336, such that the lifting bridge wheel rotational speed n_wheel has a value equal to or slightly greater than zero in this case. Thus, the large difference between the reference wheel rotational speed n_ref and the lifting bridge wheel rotational speed n_wheel corresponds to the lifted lifting bridge 314 or represents that the lifting bridge 314 is in the lifted lifting state Sup.

[0082] Conversely, when the lifting bridge 314 is in the lowered position, then its wheels 348 are also placed on the carriageway 336 and roll on the carriageway. When all the wheels 348, 450 have the same circumference, the tyre rolling speeds of the reference wheel 350 and the wheels 348 of the lifting bridge 314 are substantially identical. Thus, when the lifting bridge wheel rotational speed n_wheel of the wheels 348 of the lifting bridge 314 lies within the wheel rotational speed tolerance range ±Δn around the reference wheel rotational speed n_ref of the reference wheel 350, it can be ascertained that the lifting bridge 314 is in the lowered position or represents that the lifting bridge 314 is in the lowered lifting state Sdown. The wheel rotational speed tolerance value Δn is set in the illustrated embodiment of method 1 to compensate for inaccuracies or errors in ascertaining the wheel rotational speeds n_wheel, n_ref. These inaccuracies can be caused, for example, by slight deviations in the diameters of the nominally equally large wheels 348, 350. Preferably, the wheel rotational speed tolerance range ±Δn has a width of 100 revolutions per minute or less, preferably 50 revolutions per minute or less, particularly preferably 15 revolutions per minute or less. Preferably, the ascertaining 9 can also be carried out only when the lifting bridge wheel rotational speed n_wheel is constant and persists for a pre-determined period of time, for example a period of two seconds.

[0083] In Figure 1 the lifting bridge 314 of the commercial vehicle 300 shown in is in the lifted position, such that the lifting bridge wheel rotational speed n_wheel is significantly less than the reference rotational speed n_ref of the reference wheel 350 at the front axle 310 of the commercial vehicle 300 (n_ref - n_wheel > Δn) and the ascertaining 9 of the lifting state S of the lifting bridge 314 results in the lifting state Sup representing that the lifting bridge 314 is in the lifted position.

[0084] Figure 4 illustrates a second embodiment of the method, wherein the same steps are labelled with the same reference signs. The method 1 according to the second embodiment and according to Figure 2The difference from Method 1 basically lies in the speed of detecting the critical instability 6 and the ascending / descending condition S of detecting 9.

[0085] In Method 1 according to the second embodiment, detecting the speed Vcrit of critical instability includes: selecting 27 the pre-stored speed Vcrit_pre of critical instability from the memory 204. Here, the selection 27 is performed by the control unit 202, where the memory 204 is the memory 204 of the control unit 202. Similar to the first embodiment, in Method 1 according to the second embodiment, an approximate calculation 33 of the friction coefficient μ is also performed and the acquisition 35 of the dynamic route data Droute is also carried out. The selected 27 pre-stored speed Vcrit_pre of critical instability is parameter-based to select one pre-stored speed Vcrit_pre of critical instability from multiple pre-stored speeds Vcrit_pre of critical instability stored in the memory 204. It can also be set that the selection 27 is based on the selection of a comprehensive characteristic curve, in which relevant characteristic values (type of the trailer vehicle 306, mass distribution of the commercial vehicle 300, mass of the towing vehicle, mass of the trailer vehicle, axle load, geometric characteristics 328, etc.) are represented. Within the scope of the selection 27, in addition to the route data Droute and the friction coefficient μ, the geometric characteristics 328 and load characteristics 330 of the current vehicle configuration 330 are also taken into account. Therefore, a pre-stored speed Vcrit_pre of critical instability corresponding to the geometric characteristics 328 and load characteristics 330 is selected during the selection 27, and then the pre-stored speed Vcrit_pre of critical instability is adaptively adjusted according to the route data Droute and the current friction coefficient μ.

[0086] Reference Figure 1 to the commercial vehicle 300 shown in Figure 1 Therefore, the pre-stored speed Vcrit_pre of critical instability stored for the vehicle combination 202 with an unloaded towing vehicle 304 and a loaded trailer vehicle 306 is selected. When the detected friction coefficient μ has a very small value, that is, the adhesion between the commercial vehicle 300 and the lane 336 is very small, then the pre-stored speed Vcrit_pre of critical instability can be reduced according to the detected current friction coefficient μ. Therefore, for

[0087] Alternatively, it can be provided that the route alignment data Droute and / or the current coefficient of friction μ are part of a parameter combination and the critical instability speed Vcrit_pre pre-stored in the memory 204 is stored in association with these parameter combinations. Preferably, the pre-stored critical instability speed Vcrit_pre closest to the parameter combination is selected. The selection 27 can include, for example: interpolation and / or averaging of a plurality of pre-stored critical instability speeds Vcrit_pre.

[0088] In a second embodiment (see Figure 4 ), the lift condition S is not obtained directly by obtaining the wheel speeds n_wheel, n_ref (see the first embodiment according to Figure 2 ), but by obtaining the lift condition signal provided on the vehicle network 334 configured as an ISO 11992 CAN bus. Then, the lift condition S can be obtained based on the obtained lift condition signal. Here, the ESC controller 340 provides the lift condition signal on the vehicle network 334. The ESC controller 340 can provide the lift condition signal, for example, based on the axle load sensor data representative of the axle load acting on the lift axle 314 or based on the data of the travel measurement sensor and / or limit switch assigned to the lift axle 314.

[0089] The control unit 202 and the memory 204 are here part of a device 200 for improving the driving dynamic stability of the commercial vehicle 300, the device being configured to implement the method 1. The device 200 also includes an interface 206, which is here configured at the control unit 202. The control unit 202 can provide a lowering request via the interface 206. In the commercial vehicle 300 according to Figure 1 the interface 206 is connected to the vehicle network 334 such that the control unit 202 provides a lowering request for lowering the lift axle 314 on the vehicle network 334. The vehicle network 334 is connected to the lift axle 314 or to the lifting unit (not shown) of the lift axle 314, and the lifting unit receives the lowering request. In response to receiving the lowering request provided by the device 200, the lifting unit lowers the lift axle 314. In a similar manner, when the lifting unit receives a lifting request provided on the vehicle network 334, the lifting unit raises the lift axle 314.

[0090] List of reference numerals (part of the description)

[0091] 1 Method

[0092] 3 Obtaining the current driving speed

[0093] 5 Obtaining the critical instability speed

[0094] 7 Compare the current driving speed with the speed at critical instability

[0095] 9 Obtain the lifting status of the lifting bridge

[0096] 11 Lower the lifting bridge

[0097] 13 Predict the stable behavior of the lateral dynamics of a commercial vehicle

[0098] 15 Define the speed at critical instability

[0099] 17 Obtain the geometric and load characteristics

[0100] 19 Generate a personalized vehicle model

[0101] 21 Predict the dynamic characteristics

[0102] 23 Obtain the lifting status signal

[0103] 27 Select the pre-stored speed at critical instability

[0104] 31 Raise the lifting bridge

[0105] 33 Approximately calculate the current friction coefficient

[0106] 35 Obtain the dynamic route direction data

[0107] 37 Obtain the rotational speed of the lifting bridge wheels;

[0108] 39 Obtain the reference rotational speed of the wheels

[0109] 41 Compare the rotational speed of the lifting bridge wheels with the reference rotational speed

[0110] 43 Obtain the locking status

[0111] 45 Lock the additional bridge that can be steered

[0112] 47a Curve of the change in yaw rate when the lifting bridge is lowered

[0113] 47b Curve of the change in yaw rate when the lifting bridge is raised

[0114] 49a Curve of the change in folding angle when the lifting bridge is lowered

[0115] 49b Curve of the change in folding angle when the lifting bridge is raised

[0116] 51 Avoidance maneuver

[0117] 53 Return the steering wheel

[0118] 55 Initial lane

[0119] Device for improving driving dynamic stability

[0120] 202 Control unit

[0121] 204 Memory

[0122] 206 Interface

[0123] 300 Commercial vehicle

[0124] 302 Vehicle combination

[0125] 304 Tractor vehicle

[0126] 306 Trailer vehicle

[0127] 308 Full trailer

[0128] 310 Front axle

[0129] 312 First rear axle

[0130] 314 Lift axle

[0131] 316 Drawbar

[0132] 318 Coupling point

[0133] 320 Load

[0134] 322 First loading surface

[0135] 324 Second loading surface

[0136] 325 Arrow

[0137] 326 Current vehicle configuration

[0138] 328 Geometric feature

[0139] 330 Load characteristic

[0140] 332 Front axle of trailer vehicle

[0141] 334 Vehicle network

[0142] 336 Lane

[0143] 338 Axles of trailer vehicle

[0144] 340 ESC controller

[0145] 344 Steerable additional axle

[0146] 346 Reference axle

[0147] 348 Wheels of lift axle

[0148] 350 Reference wheel

[0149] Droute Route alignment data

[0150] L11 Axle spacing

[0151] L12 Lift bridge spacing

[0152] L13 Coupling spacing

[0153] n_ref Reference wheel speed

[0154] n_wheel Lift bridge wheel speed

[0155] R1 Vehicle longitudinal direction

[0156] S Lift condition

[0157] Sdown Represents the lift condition where the lift bridge is in the lowered position

[0158] LS Locking condition

[0159] LSlock Represents the locking condition of the steerable additional bridge when it is locked

[0160] LSopen Represents the locking condition of the steerable additional bridge when it is unlocked

[0161] Sup Represents the lift condition where the lift bridge is in the raised position

[0162] V Current driving speed

[0163] Vcrit Critical instability speed

[0164] Vcrit_pre Pre-stored critical instability speed

[0165] Vstab Stable speed

[0166] Δn Wheel speed tolerance value

[0167] ±Δn Wheel speed tolerance range

[0168] ΔV Speed buffer

[0169] γ Folding angle

[0170] μ Current friction coefficient

[0171] Yaw rate

Claims

1. A method (1) for improving the driving dynamic stability of a commercial vehicle (300), wherein, The commercial vehicle (300) has a lift bridge (314), and the method (1) includes: - obtaining (3) the current driving speed (V) of the commercial vehicle (300); - obtaining (5) the critical instability speed (Vcrit) of the commercial vehicle (300); - comparing (7) the current driving speed (V) with the critical instability speed (Vcirt); - obtaining (9) the lifting condition (Slift) of the lift bridge (314) of the commercial vehicle (300); and - if the lifting condition (Slift) indicates that the lift bridge is in the raised state (Sup) and the current driving speed (V) is greater than or equal to the critical instability speed (Vcrit), lowering (11) the lift bridge (314) of the commercial vehicle (300).

2. The method (1) according to claim 1, wherein Obtaining (9) the lifting condition (Slift) of the lift bridge (314) of the commercial vehicle (300) includes: - obtaining (37) the lift bridge wheel speed (n_wheel) of at least one wheel (348) of the lift bridge (314); - obtaining (39) the reference wheel speed (n_ref) of at least one reference wheel (350) of the reference bridge (346) of the commercial vehicle (300); and - comparing (41) the lift bridge wheel speed (n_wheel) with the reference speed (n_ref), where when the lift bridge wheel speed (n_wheel) is lower than the reference wheel speed (n_ref) by the wheel speed tolerance value (Δn), the lifting condition (Sup) indicates that the lift bridge (314) is in the raised state, and when the lift bridge wheel speed (n_wheel) is within the wheel speed tolerance range (±Δn) around the reference wheel speed (n_ref), the lifting condition (Sdown) indicates that the lift bridge is in the lowered state.

3. The method (1) according to claim 1 or 2, the method further includes: - obtaining (43) the locking condition (LS) of the steerable additional bridge (344) of the commercial vehicle (300); and - if the locking condition (LSopen) indicates that the additional bridge (344) can move and is currently steerable and the current driving speed (V) of the commercial vehicle (300) is greater than or equal to the critical instability speed (Vcrit), locking (45) the steerable additional bridge (344) of the commercial vehicle (300).

4. The method (1) according to any one of claims 1 to 3, further includes: - if the current driving speed (V) of the commercial vehicle (300) reaches or is lower than the stable speed (Vstab), raising (31) the lift bridge (314), where the stable speed (Vstab) is equal to the critical instability speed (Vcrit) minus the speed buffer (ΔV).

5. The method (1) according to claim 4, wherein, The speed buffer (ΔV) is in the range of 1 km / h to 25 km / h, preferably 10 km / h to 20 km / h.

6. The method (1) according to any one of claims 1 to 5, wherein Obtaining (5) the critical instability speed (Vcrit) of the commercial vehicle (300) includes: - Predict (13) the stable behavior of the lateral dynamics of the commercial vehicle (300) based on the current vehicle configuration (326) of the commercial vehicle (300); - Define (15) the critical instability speed (Vcrit) based on the predicted stable behavior of the lateral dynamics of the commercial vehicle (300).

7. The method (1) according to claim 6, wherein Predicting (13) the stable behavior of the lateral dynamics of the commercial vehicle (300) based on the current vehicle configuration (326) of the commercial vehicle (300) includes: - Obtain (17) two or more geometric features (328) and two or more load features (330) of the current vehicle configuration (326); - Generate (19) a personalized vehicle model of the current vehicle configuration (326) using the geometric features (328) and the load features (330); and - Predict (21) the dynamic characteristics of the current vehicle configuration (326) using the personalized vehicle model.

8. The method (1) according to any one of claims 1 to 5, wherein Obtaining (5) the critical instability speed (Vcrit) of the commercial vehicle (300) is to select (27) the pre-stored critical instability speed (Vcrit_pre) from a memory (204) in which at least one critical instability speed (Vcrit_pre) is pre-stored.

9. The method (1) according to claim 8, wherein The pre-stored critical instability speed (Vcrit_pre) is in the range of 20 km / h to 100 km / h, preferably 30 km / h to 60 km / h, and particularly preferably 45 km / h to 55 km / h.

10. The method (1) according to any one of claims 1 to 9, wherein, Obtaining (5) the critical instability speed (Vcrit) of the commercial vehicle (300) includes: - Approximately calculate (33) the current friction coefficient (μ) for the commercial vehicle (300); wherein the critical instability speed (Vcrit) of the commercial vehicle (300) is obtained (5) using the approximately calculated friction coefficient (μ).

11. The method (1) according to any one of claims 1 to 10, the method further comprising: - Obtain (35) dynamic route alignment data (Droute), wherein the critical instability speed (Vcrit) of the commercial vehicle (300) is obtained (5) using the dynamic route alignment data (Droute).

12. The method (1) according to any one of claims 1 to 11, wherein When the maximum allowable axle load of the commercial vehicle (300) is not exceeded when the lifting bridge (314) is raised, also lower (11) the lifting bridge (314) of the commercial vehicle (300).

13. An apparatus (13) for improving the driving dynamic stability of a commercial vehicle (300), the apparatus being configured to implement the method (1) according to any one of claims 1 to 12.

14. A commercial vehicle (300) having a lifting bridge (314) and the apparatus (100) according to claim 13.

15. A computer program product having a program code medium stored on a computer-readable data carrier for implementing the method (1) according to any one of claims 1 to 12 when the program product is executed on a computing unit (104) of a commercial vehicle (300) having a drawbridge (314).

16. A method for improving the driving dynamic stability of a commercial vehicle (300), wherein, The commercial vehicle (300) has a steerable additional axle (344), and the method includes: - determining (3) the current driving speed (V) of the commercial vehicle; - determining (5) the critical instability speed (Vcrit) of the commercial vehicle; - comparing (7) the current driving speed (V) with the critical instability speed (Vcrit); - determining the locking state (LSlock) of the steerable additional axle (344); and - locking (45) the steerable additional axle (344) of the commercial vehicle (300) in a straight-ahead position if the locking state (LSopen) indicates that the additional axle (334) is movable and currently steerable and the current driving speed (V) of the commercial vehicle (300) is greater than or equal to the critical instability speed (Vcrit).

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