Method for improving a vehicle-dynamics-related stability of a utility vehicle having a lift axle

Abstract

The invention relates to a method (1) for improving a vehicle-dynamics-related stability of a utility vehicle (300), wherein the utility vehicle (300) has a lift axle (314), the method (1) comprising: determining (3) a current ground speed (V) of the utility vehicle (300); determining (5) a stability-critical speed (Vcrit) of the utility vehicle (300); comparing (7) the current ground speed (V) with the stability-critical speed (Vcrit); determining (9) a lift status (Slift) of the lift axle (314) of the utility vehicle (300); and lowering (11) the lift axle (314) of the utility vehicle (300) if the lift status (Slift) represents a raised lift axle (Sup) and the current ground speed (V) is greater than or equal to the stability-critical speed (Vcrit). The invention further relates to a device for improving a vehicle-dynamics-related stability of a utility vehicle (300), to a utility vehicle (300) and to a computer program product.

Description

[0001] Method for improving the driving dynamic stability of a commercial vehicle with a lifting axle

[0002] The invention relates to a method for improving the driving dynamic stability of a commercial vehicle having a lifting axle.

[0003] A commercial vehicle is a motor vehicle which, by its design and equipment, is intended for the transport of people or goods and / or for towing trailers, but is not a passenger car or motorcycle. A commercial vehicle is, for example, a bus, a truck, a tractor unit, or a crane truck. For the purposes of the present disclosure, the commercial vehicle can be a simple commercial vehicle, often referred to as a rigid vehicle, or a vehicle combination consisting of a tractor unit and one or more trailers. A typical example of a vehicle combination includes a tractor unit and a semitrailer.

[0004] Commercial vehicles are usually designed to transport heavy loads and often have more than two axles to distribute the load evenly across the ground and avoid placing excessive strain on individual axles. However, additional axles have the disadvantage that they increase the operating costs of the commercial vehicle when the additional axles are not needed. For example, fuel consumption and wear and tear on the commercial vehicle with additional axles are generally higher. Furthermore, additional axles often reduce the maneuverability of the commercial vehicle, which can be particularly disadvantageous in urban areas. Commercial vehicles often have a liftable additional axle, also known as a lifting axle. Such an axle can be raised or lifted, although the lifting axle does not rest on the road surface when raised. When raised, the wheels of the lifting axle do not rotate, which offers particular economic advantages.This reduces tire wear, especially when cornering. Furthermore, fuel savings are possible due to reduced bearing and tire friction, and tolls can be saved with tariffs that are paid per axle. The turning circle of a commercial vehicle is generally smaller with a raised lifting axle than with a lowered lifting axle. For these reasons, lifting axles are usually only lowered when the load to be transported by the commercial vehicle is so great that the permissible axle load of the non-raised axles is exceeded with the lifting axle raised, or when the vehicle with the lifting axle raised exceeds the permissible axle load for driving over a bridge. With a lowered lifting axle, the vehicle load is distributed across an additional axle and the axle load of the individual axles is reduced.However, the ability of the commercial vehicle to transport larger loads with the lift axle lowered is associated with greater wear and tear and higher costs for the reasons stated above.

[0005] Therefore, in the prior art, the lowering of the lifting axle is generally dependent on the load. DE 20 2019 003 735 U1 discloses a device for automatically lowering and raising a lifting axle in a load-dependent manner. Devices for automatically raising a lowered lifting axle only raise the lowered lifting axle when the load falls below a predefined maximum weight on a loading area.

[0006] DE 10 2019 007 532 A1 discloses a method for the situation-dependent control of a lifting axle of a commercial vehicle, in which the lifting axle is lowered. In the disclosed method, which is intended to prevent a hazardous situation caused by overheated brakes of the commercial vehicle, the lifting axle is lowered to maximize braking force after an automatic stop function of the commercial vehicle is activated. After the automatic stop function is activated, the lifting axle is only lowered when the commercial vehicle reaches (or falls below) a predetermined speed to ensure that the difference in speed between the vehicle wheels and the wheels of the lifting axle is as small as possible when lowered to the ground, thus preventing tire damage during braking. The method lowers the lifting axle only when an automatic stop function is activated, i.e., only in emergency situations and not during regular ferry operation.

[0007] The influence of the lifting axle on the dynamic handling of the commercial vehicle has not been considered to date. The invention is based on the object of providing a method by which the dynamic handling stability of a commercial vehicle with a lifting axle can be improved.

[0008] In a first aspect, the present invention solves the problem by a method for improving the driving dynamics stability of a commercial vehicle having a lifting axle, the method comprising the steps of: determining a current driving speed of the commercial vehicle; determining a stability-critical speed of the commercial vehicle; comparing the current driving speed with the stability-critical speed; determining a lift status of the lifting axle of the commercial vehicle; and lowering the lifting axle of the commercial vehicle if the lift status represents a raised lifting axle and the current driving speed is greater than or equal to the stability-critical speed. The method increases the driving dynamics stability, in particular the yaw stability of the commercial vehicle, by lowering the lifting axle if the commercial vehicle would be stability-critical with a raised lifting axle.The commercial vehicle is preferably a vehicle combination comprising a towing vehicle and at least one trailer. Lowering the lifting axle can also increase the stability of a vehicle combination, particularly since instabilities of a trailer resulting from excessive yaw excitations of the towing vehicle can be prevented.

[0009] To assess whether the commercial vehicle's behavior is critical to stability, the commercial vehicle's current driving speed is compared with a stability-critical speed. The current driving speed is the speed at which the commercial vehicle is moving in the current situation, i.e., the situation in which the procedure is being carried out. The stability-critical speed is the speed above which the commercial vehicle's stability is critical. The commercial vehicle is considered to be stability-critical if it becomes unstable as a result of normal steering inputs. Normal steering inputs are steering inputs that can occur during the operation of a commercial vehicle, particularly those that occur in emergency situations, for example, during an evasive maneuver.Preferably, the vehicle exhibits stability-critical behavior if a predetermined minimum damping factor for predefined excitations is undershot and / or if the vehicle's natural angular frequencies are within the range of typical excitation frequencies. The stability-critical damping factor is preferably 0.6 or less, preferably 0.5 or less, preferably 0.4, with a damping factor of 1 corresponding to the so-called aperiodic limit.

[0010] It should be understood that the commercial vehicle is not necessarily unstable as soon as it travels at the stability-critical speed. Rather, the commercial vehicle can become unstable if a destabilizing stimulus is applied to the vehicle while traveling at the stability-critical speed. This can be the case, for example, if the commercial vehicle must perform an evasive maneuver or negotiate a curve with a tight radius.

[0011] The method further includes determining a lift status of the commercial vehicle's lift axle, which indicates whether the commercial vehicle's lift axle is lowered or raised. The lift status can represent at least one raised lift axle and one lowered lift axle, thus can be a digital status. However, it can also be provided that the lift status represents a measure of the lifting of the lift axle. For example, the lift status can represent a percentage value of an absolute lift of the lift axle, wherein preferably a value of 100% represents a fully raised lift axle, while a value of 0% represents a fully lowered lift axle.

[0012] To improve the dynamic driving stability of the commercial vehicle, the method further comprises lowering the lifting axle of the commercial vehicle if the lift status represents a raised lifting axle and the current driving speed is greater than or equal to the stability-critical speed. Lowering the lifting axle is therefore not advisable or possible if it is already lowered. Lowering is therefore preferably only carried out if the lifting axle has previously been fully or partially raised. Furthermore, according to the invention, lowering the lifting axle occurs when the commercial vehicle is moving at a current driving speed that is greater than the determined stability-critical speed. The lowering of the lifting axle preferably occurs independently of wear or cost-effectiveness considerations.

[0013] Lowering a lift axle designed as a trailing axle, i.e., an axle arranged downstream of a drive axle in the direction of travel, reduces the effective lever arm for the forces acting on a trailer. Furthermore, lowering the lift axle generally increases the vehicle's potential lateral guidance forces, preventing the commercial vehicle from skidding even at high steering frequencies. Both effects increase driving stability and reduce the risk of commercial vehicle instability. The method according to the invention takes into account the influence of a lift axle, in particular a lift axle designed as a trailing axle, on the driving stability of the commercial vehicle. Determining a current driving speed of the commercial vehicle and determining a stability-critical speed of the commercial vehicle do not have to be carried out in the order specified in the claim.The steps can preferably also be performed in reverse order or (partially) simultaneously. Determining the lift status can be performed before, after, completely simultaneously, and / or partially simultaneously with determining the current travel speed, determining the stability-critical speed, and / or comparing the speeds.

[0014] Preferably, the method comprises, before determining a stability-critical speed of the commercial vehicle: determining whether the commercial vehicle is a vehicle combination comprising a towing vehicle and at least one trailer vehicle. The determination of whether the commercial vehicle is a vehicle combination comprising a towing vehicle and at least one trailer vehicle is preferably carried out using signals provided on a trailer network of the commercial vehicle. Alternatively or in addition to detecting whether the commercial vehicle is a vehicle combination, which is carried out using signals provided on a trailer network of the commercial vehicle, the detection can also be carried out by determining using a total train mass of the commercial vehicle and a towing vehicle mass of the towing vehicle.

[0015] Preferably, the lift axle is a lift axle of the towing vehicle of a vehicle combination. However, the stability advantages mentioned also apply to lift axles of a trailer, so the lift axle can preferably also be a lift axle of a trailer vehicle. Furthermore, it should be understood that the commercial vehicle can also have multiple lift axles, whereby to increase yaw stability, preferably several, particularly preferably all, lift axles of the commercial vehicle are lowered.

[0016] Determining the lift status can also be omitted, and the lift axle can be lowered whenever the current travel speed reaches or exceeds the stability-critical speed. For example, a lowering request can be sent to a lift unit of the lift axle intended for lowering the lift axle whenever the current travel speed reaches or exceeds the stability-critical speed. If the lift axle is already lowered in this case, the lowering request is ignored and / or produces no result.

[0017] In a first preferred embodiment of the method, determining the lift status of the lift axle of the commercial vehicle comprises: determining a lift axle wheel speed of at least one wheel of the lift axle; determining a reference wheel speed of at least one reference wheel of a reference axle of the commercial vehicle; and comparing the lift axle wheel speed with the reference speed, wherein the lift status represents a raised lift axle when the lift axle wheel speed falls below the reference wheel speed by a wheel speed tolerance value, and represents a lowered lift axle when the lift axle wheel speed is within a wheel speed tolerance range around the reference wheel speed.The wheel speed tolerance value, which can also be referred to as wheel speed tolerance, is preferably provided to compensate for small speed differences that result, for example, from different wheel diameters of the wheels on the lifting axle and the reference axle or from wheel slip. The wheel speed tolerance range is a range whose boundary values ​​are determined by the reference wheel speed less the wheel speed tolerance value and by the reference wheel speed plus the wheel speed tolerance value. When the lifting axle is lowered, the wheels of the lifting axle roll on the road surface. The rolling speed of the tire circumferential surface of the wheels on the lifting axle is essentially identical to the rolling speed of the wheels on the other axles of the commercial vehicle or on a reference axle. The invention makes use of this knowledge. In this way, a lowered lifting axle can then be detected orcan be determined when the wheels of the lifting axle rotate at essentially the same wheel speed as the wheels of the reference axle, since the wheels of a commercial vehicle generally have the same diameter. If the lifting axle wheel speed is within the wheel speed tolerance range, then the lifting axle is lowered. If, on the other hand, the lifting axle is raised, its wheels generally do not rotate or only rotate very slowly. In this case, the lifting axle wheel speed deviates from the reference wheel speed by more than the wheel speed tolerance value. By examining the lifting axle wheel speed and the reference wheel speed, the lift status can be determined particularly easily. The reference wheel is preferably a driven wheel of the commercial vehicle.

[0018] Preferably, determining the lift status of the lift axle of the commercial vehicle comprises: determining lift status signals provided on a vehicle network, preferably a bus network, particularly a CAN bus, of the commercial vehicle; and determining the lift status from the network data. Thus, the method can preferably utilize a lift status already known in a vehicle system, for example, a driving stability system such as an ABS or ESC system.

[0019] According to a preferred development, the method further comprises: determining a locking status of a steerable additional axle of the commercial vehicle; and locking the steerable additional axle of the commercial vehicle if the locking status represents a currently steerable additional axle and the current driving speed of the commercial vehicle is greater than or equal to the stability-critical speed. The steerable additional axle is an additional axle of the vehicle that is steerable. Furthermore, the steerable additional axle can also be locked in its orientation or steerability. By locking, the steerable additional axle is fixed in straight-ahead travel 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-ahead travel, i.e., in an orientation that the steerable additional axle assumes when the vehicle is traveling straight.Locking the steerable auxiliary axle generally shifts the handling of commercial vehicles toward understeering, improving vehicle stability. This prevents the steerable auxiliary axle from fluttering or swinging when locked.

[0020] Preferably, the method further comprises: raising the lifting axle if the current driving speed of the commercial vehicle reaches or falls below a stable speed, wherein the stable speed corresponds to the stability-critical speed less a speed buffer. The stable speed is a speed at which the commercial vehicle remains in a stable driving state even with the lifting axle raised, if a sudden stimulus (in particular steering stimulus) occurs. If the vehicle is moving at the stable speed, an evasive maneuver can be performed even with the lifting axle raised without the commercial vehicle becoming unstable. In this case, raising the lifting axle is advisable in order to avoid the disadvantages of a lowered lifting axle described above (increased wear, increased fuel consumption, increased toll fees, reduced maneuverability, etc.).The speed buffer ensures that the lifting axle is not immediately raised when the vehicle speed falls below the stability-critical speed. This ensures that the vehicle is moved within a stable speed range for an extended period before the lifting axle is raised. Alternatively, it can also be provided that the stable speed essentially corresponds to the stability-critical speed, or that the speed buffer tends towards 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. This means that the lifting axle can be raised, for example, even if the vehicle is moving at 15 km / h, even if the stability-critical speed is less than 15 km / h.

[0021] The speed buffer is preferably in a range from 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 key values ​​of the claimed range are also preferred. The speed buffer can therefore preferably also be 1 km / h. Raising preferably only occurs when the current driving speed reaches or falls below the stable speed for a predetermined period of time. This avoids raising the lifting axle in cases where the vehicle only briefly falls below the stability-critical speed, for example as a result of a brief braking maneuver. The predetermined period of time can, for example, be 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 commercial vehicle's lift axle is lowered only when the lift status represents a raised lift axle, the current driving speed is greater than or equal to the stability-critical speed, and the driving speed reaches a minimum speed. The minimum speed is preferably 15 km / h or more, 20 km / h or more, 25 km / h or more, and particularly preferably 30 km / h. This prevents the lift axle from lowering at low driving speeds, which generally pose only a low risk even under unfavorable vehicle, road, and / or weather conditions.In one variant, determining a stability-critical speed of the commercial vehicle comprises: predicting a lateral dynamic stability behavior of the commercial vehicle based on a current vehicle configuration of the commercial vehicle and defining the stability-critical speed based on the predicted lateral dynamic stability behavior of the commercial vehicle. Preferably, the prediction of the lateral dynamic stability behavior of the commercial vehicle is based at least partially on geometric characteristics of a trailer vehicle and / or load characteristics of the trailer vehicle if the commercial vehicle is a vehicle combination. The geometric characteristics and load characteristics represent at least partially a current vehicle configuration of the commercial vehicle, which 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 geometric dimensions, the geometric characteristics can preferably also contain quantitative information (e.g., the number of vehicle axles). Geometric characteristics are or include, in particular, geometric variables that define the driving dynamics of the vehicle, such as a wheelbase of the vehicle, axle spacing between vehicle axles, a track width of the vehicle, a distance between a rear axle of the vehicle and a coupling point of a trailer, or a design of a trailer vehicle (e.g., drawbar trailer or center-axle trailer). The load characteristics represent loads acting on the vehicle, which can result from the vehicle's own weight and from a vehicle load. Thus, a current vehicle configuration of an unloaded vehicle is different from a current vehicle configuration of the same vehicle in a loaded state.A load characteristic can preferably be or include a wheel load, an axle load, a total vehicle mass, a mass of a vehicle part and / or a center of gravity of the vehicle or a vehicle part.

[0023] Within the framework of the procedure, the determined geometric characteristics and load characteristics are taken into account when predicting the lateral dynamic behavior. By defining the stability-critical speed based on the predicted lateral dynamic stability behavior of the commercial vehicle, the determined characteristics also influence the definition of the stability-critical speed. The stability-critical speed is at least partially tailored to the current vehicle configuration. The time for lowering the lifting axle can be determined with particular precision. This allows the risk of instability resulting from unfavorable vehicle loading to be identified and taken into account when defining the stability-critical speed.

[0024] By predicting the lateral dynamic stability behavior, the behavior of the vehicle can be predicted. The lateral dynamic stability behavior preferably includes the yaw behavior of the towing vehicle, the buckling behavior of the trailer vehicle(s), the natural angular frequencies of the vehicle, and / or the damping measures of the vehicle or of the dynamic system formed by the vehicle. The prediction of the lateral dynamic stability behavior of the current vehicle configuration is preferably model-based. For this purpose, a basic vehicle model can preferably be customized using the geometric characteristics and the load characteristics, and the lateral dynamic stability behavior of the vehicle can be determined using the customized vehicle model.

[0025] Preferably, the step of predicting a transverse dynamic stability behavior of the commercial vehicle based on a current vehicle configuration of the commercial vehicle comprises: determining 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 using the geometric characteristics and the load characteristics; and predicting dynamic properties of the current vehicle configuration using the individualized vehicle model.Preferably, generating an individualized vehicle model of the current vehicle configuration comprises: approximating a mass distribution of the current vehicle configuration in at least one vehicle longitudinal direction using the geometric characteristics and the load characteristics; and generating an individualized vehicle model of the current vehicle configuration from a basic vehicle model of the commercial vehicle using the geometric characteristics and the approximated mass distribution.

[0026] In a preferred embodiment, determining a stability-critical speed of the commercial vehicle is or includes selecting a pre-stored stability-critical speed from a memory in which at least one stability-critical speed is pre-stored. The pre-stored stability-critical speed of the commercial vehicle is preferably stored in a memory of a control unit. Preferably, the pre-stored stability-critical speed has a fixed value. Furthermore, determining a stability-critical speed of the commercial vehicle can also be selecting a pre-stored stability-critical speed from a plurality of pre-stored stability-critical speeds. The selection is preferably made taking into account a current vehicle configuration.For example, a first pre-stored stability-critical speed can be selected if the commercial vehicle does not include a trailer, and a second pre-stored stability-critical speed can be selected if the commercial vehicle is a vehicle combination. The selection can also be made based on a loading condition. Thus, under otherwise identical conditions, a different stability-critical speed can be selected for a fully loaded commercial vehicle than for an empty or partially loaded commercial vehicle. Furthermore, the selection is preferably made taking current road conditions into account, wherein the method preferably comprises determining current vehicle conditions.

[0027] The pre-stored stability-critical speed is preferably in a range from 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 a pre-stored stability-critical speed from a memory, a stability-critical speed in a range of 45 km / h to 55 km / h is selected if the commercial vehicle is located on a road within a built-up area, a stability-critical speed in a range of 56 km / h to 70 km / h is selected if the commercial vehicle is traveling on a country road, and / or a stability-critical speed in a range of greater than 70 km / h is selected if the vehicle is traveling on a motorway.

[0028] According to a preferred development, determining a stability-critical speed of the commercial vehicle comprises: approximating a current friction coefficient for the commercial vehicle; wherein the stability-critical speed of the commercial vehicle is determined using the approximated friction coefficient. The determination of the current friction coefficient may be subject to errors, so that the determined friction coefficient only approximates a real prevailing friction coefficient. The determined current friction coefficient may therefore preferably also deviate from the actual friction coefficient between the commercial vehicle and a roadway traveled by the commercial vehicle. In a preferred embodiment of the method, a pre-stored stability-critical speed is selected as a function of the approximated friction coefficient.For example, for a high friction coefficient, a speed of 50 km / h could be stability-critical, while for a low friction coefficient, a speed of 30 km / h is already stability-critical. However, the friction coefficient can also be considered alternatively or additionally when predicting lateral dynamic behavior.

[0029] The method preferably further comprises: determining dynamic route progression data, wherein the stability-critical speed of the commercial vehicle is determined using the dynamic route progression data. For example, the stability-critical speed can have a higher value on a straight route than on a winding route or a route that includes a steep gradient. The lowering of the lifting axle can also only occur if the route progression data indicate a specific road type. Route knowledge thus improves the targeted use of the method or the targeted lowering of the lifting axle. For example, it is possible to prevent a lifting axle from being permanently lowered when driving straight ahead on the motorway, which would reduce the economic efficiency of the commercial vehicle operation.However, it can also be provided that the lowering of the lifting axle occurs independently of the road type. For example, it can be provided that the method is also carried out during motorway travel, or that the lifting axle is lowered if the dynamic route data indicate a hazardous situation, such as an oil slick ahead or a slippery road surface. If the stability-critical speed of the commercial vehicle is determined using the dynamic route data, it is preferable to first determine a speed that is critical to driving dynamics, for example, based on the customized vehicle model, and then adjust this speed to the stability-critical speed using the dynamic route data.For example, a speed of 60 km / h, which is critical for driving dynamics and stability, can be reduced to a speed of 50 km / h, which is critical for stability, when a winding road lies ahead.

[0030] Preferably, the commercial vehicle's lifting axle is lowered even if the maximum permissible axle load of the commercial vehicle is not met with the lifting axle raised. In such cases, the procedure is carried out contrary to economic considerations.

[0031] In a second aspect, the invention achieves the aforementioned object with a device for improving the dynamic driving stability of a commercial vehicle, which device is configured to carry out a method according to the first aspect of the invention. Preferably, the device for improving the dynamic driving stability of a commercial vehicle comprises a control unit and an interface, wherein the control unit is configured to provide a lowering request for a lift axle actuator at the interface if the lift status represents a raised lift axle and the current driving speed is greater than or equal to the stability-critical speed.

[0032] In a third aspect, the invention solves the problem mentioned above by means of a device for improving the driving dynamics stability of a commercial vehicle, wherein the commercial vehicle has a lifting axle, wherein the device has an interface and a control unit, wherein the control unit is connectable to at least one network of the commercial vehicle for receiving signals and is designed to determine a current driving speed of the commercial vehicle using the signals, determine a stability-critical speed of the commercial vehicle, compare the current driving speed of the commercial vehicle with the stability-critical speed of the commercial vehicle, determine a lifting status of the lifting axle using the signals, provide a lowering request at the interface to cause the lifting axle of the commercial vehicle to be lowered,if the lift status represents a raised lift axle and the current driving speed of the commercial vehicle is greater than or equal to the stability-critical speed. In a preferred development, the control unit is connectable to a vehicle network of the vehicle for receiving wheel speed signals representing at least one wheel speed 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 signals.

[0033] In a fourth aspect, the object mentioned above is achieved with a commercial vehicle having a lifting axle and a device according to the second aspect of the invention and / or a device according to the third aspect of the invention. Preferably, the commercial vehicle further comprises a front axle and a rear axle. The lifting axle is preferably a trailing axle of the commercial vehicle.

[0034] According to a fifth aspect, the invention achieves the aforementioned object with a computer program product having program code means stored on a computer-readable data carrier for executing the method according to the first aspect of the invention when the program product is executed on a computing unit of a commercial vehicle having a lifting axle. The commercial vehicle is preferably a commercial vehicle according to the fourth aspect of the invention.

[0035] It should be understood that the devices for improving the driving dynamics stability of a commercial vehicle according to the second and / or third aspect of the invention, the commercial vehicle according to the fourth aspect of the invention and the computer program product according to the fifth aspect of the invention may have the same and similar sub-aspects as are set out in particular in the dependent claims for the method according to the first aspect of the invention.

[0036] In a sixth aspect, the invention is achieved by a method for improving the driving dynamics stability of a commercial vehicle, wherein the commercial vehicle has a steerable additional axle, the method comprising: determining a current driving speed of the commercial vehicle; determining a stability-critical speed of the commercial vehicle; comparing the current driving speed with the stability-critical speed; determining a locking status of the steerable additional axle; and locking the steerable additional axle of the commercial vehicle in straight-ahead travel if the locking status represents a currently steerable additional axle and the current driving speed of the commercial vehicle is greater than or equal to the stability-critical speed.As already explained with reference to a preferred development of the first aspect of the invention, the dynamic driving stability of a commercial vehicle can be improved by locking a steerable additional axle. For this purpose, the steerable additional axle can also be locked independently of lowering a lifting axle, in particular even if the commercial vehicle does not have a lifting axle. The finding underlying the invention, that stabilizing measures can advantageously be carried out depending on a stability-critical speed, also applies to the sixth aspect of the invention or the locking of a steerable additional axle independently of a lifting axle. When the steerable additional axle of the commercial vehicle is locked when traveling straight ahead, the steerable additional axle is locked in an orientation that it has when the commercial vehicle is traveling straight ahead.The method according to the sixth aspect of the invention can be designed with regard to preferred developments essentially analogously to preferred developments of the first aspect of the invention, which are set out in particular in the dependent claims.

[0037] Embodiments of the invention will now be described below with reference to the drawings. These are not necessarily intended to represent the embodiments to scale; rather, the drawings are schematic and / or slightly distorted where this is useful for explanation. With regard to additions to the teachings immediately apparent from the drawings, reference is made to the relevant prior art. It should be noted that numerous modifications and changes to the form and detail of an embodiment can be made without deviating from the general idea of ​​the invention. The features of the invention disclosed in the description, in the drawings and in the claims can be essential for the further development of the invention, both individually and in any combination.Furthermore, all combinations of at least two of the features disclosed in the description, the drawings and / or the claims fall within the scope of the invention. The general idea of ​​the invention is not limited to the exact form or detail of the preferred embodiments shown and described below, or limited to an object that would be more limited than the object claimed in the claims. For specified dimensioning ranges, values ​​within the stated limits are also intended to be disclosed as limit values ​​and to be used and claimed as desired. For the sake of simplicity, the same reference numerals are used below for identical or similar parts or parts with identical or similar functions.

[0038] Further advantages, features and details of the invention will become apparent from the following description of the preferred embodiments and from the drawings, which show:

[0039] Fig. 1 a commercial vehicle with a lifting axle;

[0040] Fig. 2 shows a first embodiment of the method;

[0041] Fig. 3 is a diagram showing the course of a yaw reaction and a buckling course for an evasive maneuver for a commercial vehicle with a raised lifting axle and for an otherwise identical commercial vehicle with a lowered lifting axle;

[0042] Fig. 4 shows a second embodiment of the method.

[0043] Method 1 is illustrated using the example of a commercial vehicle 300 configured as a vehicle combination 302. The vehicle combination 302 shown in Fig. 1 comprises a three-axle towing vehicle 304 that pulls a two-axle trailer 306 configured as a drawbar trailer 308. The towing vehicle 304 comprises a front axle 310, a first rear axle 312, and a lift axle 314. The lift axle 314 is arranged as a trailing axle behind the first rear axle 312 in a vehicle longitudinal direction R1.

[0044] A loading situation frequently encountered in vehicle trains 302 is characterized by the fact that the towing vehicle 304 is driven empty while the trailer vehicle 306 is loaded. This loading situation is chosen for economic reasons, particularly when the trailer vehicle 306 has been leased while the towing vehicle 304 is owned by the operator. Thus, in the loading situation described, the trailer vehicle 306 in particular is subject to wear. Wear on the towing vehicle 304 is minimized due to the lack of cargo. A disadvantage, however, is that the stability of the commercial vehicle 300 may be impaired due to the unfavorable load distribution.

[0045] To accommodate cargo 320, the towing vehicle 304 has a first loading area 322. For the same purpose, the trailer vehicle 306 includes a second loading area 324. The first loading area 322 is empty, while a load 320 is arranged on the second loading area 322. Arrows 325 in Fig. 1 illustrate that a load on the trailer vehicle 306 is approximately twice as great as a load on the towing vehicle 304 resulting from the dead weight of the towing vehicle 304. This load distribution is unfavorable for the dynamic driving stability of the commercial vehicle 300. A drawbar 316 of the trailer vehicle 306 does not transfer any vertical loads to the towing vehicle 304, so that axle loads in the towing vehicle 304 do not deviate from its empty loads. For economic reasons, the lifting axle 314 of the towing vehicle 304 is usually raised in this configuration, which further impairs the driving dynamics stability of the commercial vehicle 300.

[0046] The method 1 according to the invention is intended to improve the driving dynamic stability of the commercial vehicle 300 and in particular of the trailer vehicle 306, in particular by lowering the lifting axle 314 depending on the situation.

[0047] However, it should be understood that method 1 can be used not only for the illustrated vehicle combination 302 with towing vehicle 304 pulling a drawbar trailer 308, but also for commercial vehicles 300 without a trailer 306 and for commercial vehicles 300 with a central axle trailer. The distance between a first rear axle 312 of the towing vehicle 304 and a coupling point 318 is significantly longer for a drawbar trailer 308 than for a low-coupling system. A stability gain achieved by lowering the lift axle 314, as described later, is therefore generally greater for a commercial vehicle 300 with a drawbar trailer 308 than for commercial vehicles 300 with a central axle trailer. This increase in stability is particularly advantageous for commercial vehicles 300 with drawbar trailers 308, since a drawbar trailer 308 usually has multiple articulated joints (not shown in Fig. 1) and is therefore generally more sensitive to excitations than a center-axle trailer. The system shown in Fig.The commercial vehicle 300 shown in Fig. 1 is characterized by a current vehicle configuration 326. This current vehicle configuration 326 includes both geometric characteristics 328 and load characteristics 330. For clarity, the characteristics 328, 330 of the current vehicle configuration 326 of the commercial vehicle 300 are illustrated in Fig. 1 only using a few geometric characteristics 328 and load characteristics 330. An axle distance L11 between the front axle 310 and the first rear axle 312 of the towing vehicle 304 is shown as an example of the geometric characteristics 328. Further geometric characteristics 328 shown in Fig. 1 are a coupling distance L13 between the first rear axle 312 and the coupling point 318 of the towing vehicle 304 and a lift axle distance L12 between the first rear axle 312 and the lift axle 314 of the towing vehicle 304.The geometric characteristics 328 of the current vehicle configuration 326 further include a lift status S of the lift axle 314. The lift status S can represent a lowered lift axle 314 (lift status Sdown) and a raised lift axle 314 (lift status Sup). With the lift axle 314 lowered, the dynamically effective wheelbase of the towing vehicle 304 changes from the axle distance L11 shown in Fig. 1 to a sum of the axle distance L11 and half the lift axle distance L12 (L11 + L12 / 2).

[0048] The lateral dynamic stability behavior of the commercial vehicle 300 is influenced by the wheelbase, with the lift status S of the lift axle 314 being a geometric characteristic 328 that directly characterizes this influence. Further geometric characteristics 328 of the commercial vehicle 300 shown are a drawbar length of the drawbar 316 of the drawbar trailer 308 or a wheelbase of the trailer vehicle 306, which, however, are not explicitly marked in Fig. 1 for illustrative reasons.

[0049] The load characteristics 330 indicate the loads acting on the commercial vehicle 300 in the current vehicle configuration 326, which here result from the dead weight of the commercial vehicle 300 and from the load 320. The load characteristics 330 are illustrated in Figure 1 in a simplified manner as loads acting on the first rear axle 312 of the towing vehicle 304 and a front axle 332 of the trailer vehicle 306. As already explained, the trailer vehicle 306 is loaded while the towing vehicle 304 is empty, so that the load acting on the first rear axle 312 of the towing vehicle 304 is lower than the load acting on the front axle 332 of the trailer vehicle 306. This is illustrated by the length of the arrows representing the load characteristics 330.

[0050] Here, the load characteristic 330 acting on the first rear axle 312 of the towing vehicle 304 is an axle load of the first rear axle 312. This axle load is determined by an electronically controllable air suspension of the commercial vehicle 300. As a further load characteristic 330, the electronically controllable air suspension determines the axle load acting on the front axle 332 of the trailer vehicle 306. In the present exemplary embodiment, in addition to the determined axle load on the first rear axle 312 of the towing vehicle 304, a total mass of the towing vehicle 304 and the lift status S of the lift axle 314 are also known, so that an axle load on a front axle 310 of the towing vehicle 304 can be mathematically determined by calculating the load distribution. Furthermore, based on the axle load of the front axle 332 of the trailer vehicle 306 and a known total mass of the trailer vehicle 306, an axle load on a rear axle of the trailer vehicle 306 can also be determined.In the present embodiment, the load characteristics 330 can therefore be recorded directly by measurement on the one hand and determined indirectly by calculation on the other.

[0051] The current vehicle configuration 326 can vary for the same commercial vehicle 300 depending on the geometric characteristics 328 and the load characteristics 330. Thus, a current vehicle configuration 326 of the commercial vehicle 300 would be different from the current vehicle configuration 326 shown in Fig. 1 if the lift axle 314 of the commercial vehicle 300 were lowered (i.e., the lift status S would be different) or if the load 320 were arranged on the first loading area 322 and not on the second loading area 324. Fig. 1 is intended to clarify that the current vehicle configuration 326 is situation-dependent and represents a current state of the commercial vehicle 300.

[0052] Another factor that can be included in the current vehicle configuration 326 is a current friction coefficient p between the commercial vehicle 300 and a roadway 336 indicated by a dashed line in Fig. 1. Even with an identical geometric configuration of the commercial vehicle 300 and an identical load situation, the current vehicle configuration 326 of the commercial vehicle 300 can vary due to different roadway conditions or due to a different friction coefficient p. In particular, based on the friction coefficient p, it becomes immediately understandable that the current vehicle configuration 326 of the commercial vehicle 300 can also change during operation of the commercial vehicle 300. For example, the friction coefficient p can decrease during a journey of the commercial vehicle 300 when it starts to rain.

[0053] In the following, preferred embodiments of the method 1 according to the invention for improving the driving dynamics stability of the commercial vehicle 300 are explained essentially with reference to Fig. 2 to Fig. 4. If necessary, individual aspects relating in particular to the commercial vehicle 300 can also be explained with reference to Fig. 1.

[0054] Fig. 2 schematically shows a first embodiment of method 1, within the scope of which a current driving speed V of the commercial vehicle 300 is first determined (determination 3 in Fig. 2). The determination 3 of the current driving speed V can be carried out, for example, based on signals provided by a speedometer, a speed sensor, and / or a control unit of the commercial vehicle 300. Preferably, the determination 3 of the current driving speed V is carried out continuously or is repeated cyclically.

[0055] In the first exemplary embodiment, a stability-critical speed Vcrit of the commercial vehicle 300 is determined 5 simultaneously with the determination 3 of the current driving speed V. The simultaneous determination 3, 5 of the current driving speed V and the stability-critical speed Vcrit offers the advantage that the method 1 is streamlined and errors are reduced. However, it can also be provided that the determination 3 of the current driving speed V takes place before or after the determination 5 of the stability-critical speed Vcrit, or that the steps of the determination 3, 5 are partially carried out simultaneously. Thus, the determination 5 of the stability-critical speed Vcrit can preferably also be carried out upon vehicle activation, which occurs, for example, by actuating the ignition or a drive switch of a commercial vehicle 300.

[0056] Following the determination 3, 5, in the illustrated embodiment, a comparison 7 of the current driving speed V with the stability-critical speed Vcrit takes place. The comparison 7 here shows that the current driving speed V is greater than or equal to the stability-critical speed Vcrit (V > Vcrit). If the comparison 7 shows that the driving speed V is less than the stability-critical speed Vcrit (V < Vcrit), method 1 is terminated and restarted if the driving speed V or an influencing factor underlying the determination 5 changes. However, it can also be provided that method 1 is restarted after a certain waiting time has elapsed.However, it can also be provided that one or more of the steps of method 1 described below are also carried out if the comparison 7 shows that the driving speed V is less than the stability-critical speed Vcrit (V < Vcrit).

[0057] Simultaneously with the comparison 7 of the current driving speed V with the stability-critical speed Vcrit, the lift status S of the lift axle 314 is determined (determination 9 in Fig. 2). Here, this determination 9 results in the lift status S being a lift status Sup, which represents a raised lift axle 314. However, it can also be provided that the determination 9 of the lift status S occurs before, after, or simultaneously with the comparison 7 of the speeds V, Vcrit. Preferably, the lift status S is determined upon vehicle activation.

[0058] In the exemplary embodiment shown in Fig. 2, the current vehicle speed V is greater than the stability-critical speed Vcrit, and the lift axle 314 of the commercial vehicle 300 is raised (S = Sup). For this reason, in a further step, the lift axle 314 of the commercial vehicle 300 is lowered 11.

[0059] As already explained at the beginning, the wheelbase of the commercial vehicle relevant for driving dynamics is extended from the axle distance L11 to the sum of the axle distance L11 and half the lift axle distance L12. This increases the driving stability of the towing vehicle 304. By increasing the wheelbase of the commercial vehicle relevant for driving dynamics from L11 to L11 + L12 / 2, the ability of the towing vehicle 304 to follow changes in direction is reduced, whereby the towing vehicle 304 achieves lower yaw rates and is stabilized. Furthermore, the distance between the coupling point 318 and a dynamically effective contact point of the towing vehicle 304 at the rear is reduced from the coupling distance L13 to the difference between the coupling distance L13 and half the lift axle distance L12 (L13-L12 / 2). This reduces the lever arm for forces transmitted from the trailer vehicle 306 or the drawbar 316 to the towing vehicle 304.This results in a kinematic towing curve of the coupling point 318 describing a larger curve radius when cornering if the lift axle 314, designed as a trailing axle, is lowered in the commercial vehicle 300. This results in a reduced deflection of the drawbar trailer 308, thereby reducing the risk of the trailer vehicle 306 swerving in a dangerous situation. An evasive maneuver (lane or double lane change) in which a yaw reaction of the commercial vehicle 300 is generated with high steering angle amplitudes and steering angle velocities is an example of such a dangerous situation.

[0060] Fig. 3 shows a yaw response and a kink angle curve along the path for a vehicle combination 302 with a raised lift axle 314 (the vehicle combination 302 is shown only in a simplified manner in Fig. 3) executing an evasive maneuver that is a double lane change maneuver. Similarly, Fig. 3 illustrates the curve of the yaw rate V and the kink angle Y along the path for an otherwise identical vehicle combination 302 with a raised lift axle 314, which executes the identical evasive maneuver. In short, Fig. 3 shows a comparison of the yaw response and the kink angle curve for a vehicle combination 302 with a lowered lift axle 314 and a vehicle combination 302 with a raised lift axle 314.

[0061] The articulation angle profile describes the temporal progression of the articulation angle y formed between the towing vehicle 304 and the trailer vehicle 306. For a trailer vehicle 306 traveling exactly straight behind the towing vehicle 304, the articulation angle Y has a value of 0°. When cornering or performing an evasive maneuver, the articulation angle Y decreases or increases accordingly. The yaw reaction relates to the progression of the yaw rate V of the commercial vehicle 300 along a path traveled by the commercial vehicle 300. In Fig. 3, line 47a (solid line) indicates the course of the yaw rate V with the lift axle 314 lowered, and line 47b (coarse dashed line) indicates the course of the yaw rate V with the lift axle 314 raised. Line 49a (dash-dot line) similarly indicates the articulation angle course with the lift axle 314 lowered, and line 49b (fine dashed line) indicates the articulation angle course with the lift axle 314 raised.

[0062] Fig. 3 illustrates that the yaw rate V with the lift axle 314 lowered in curve 47a for an otherwise identical evasive maneuver 51 reaches both a flatter gradient and a lower maximum than the curve 47b of the yaw rate V for the vehicle combination 302 with the lift axle 314 raised. This is due to an earlier onset of understeering behavior of the commercial vehicle 300. In addition, the articulation angle Y between the trailer vehicle 306 or drawbar 316 and the towing vehicle 304 decreases when the lift axle 314 is lowered. Yaw damping of the commercial vehicle 300 is increased, so that an excitation of the vehicle combination 302 caused by the trailer vehicle 306 is better damped with the lift axle 314 lowered (line 49a) than with the lift axle 314 raised (line 49b).The increased driving stability of the commercial vehicle 300 is particularly evident in the small articulation angle Y between the towing vehicle 304 and the trailer vehicle 306 during the re-steering 53 into an exit lane 55 and the subsequent straight course of the route. In particular, in commercial vehicles 300 configured as a vehicle combination 302, driving stability is significantly increased by lowering the lifting axle 314. However, driving stability can also be improved in commercial vehicles 300 without a trailer vehicle 306, particularly when the wheelbase of such a commercial vehicle 300 is short and / or the commercial vehicle 300 is loaded with a rear-heavy load.

[0063] In the embodiment according to Fig. 2, the determination 5 of the stability-critical speed Vcrit is carried out by predicting 13 a transverse dynamic stability behavior of the commercial vehicle 300 and defining 15 the stability-critical speed Vcrit based on the predicted transverse dynamic stability behavior of the commercial vehicle 300.

[0064] In a first step of prediction 13, two or more geometric characteristics 328 and two or more load characteristics 330 are determined 17. The determined geometric characteristics 328 include, among others, the axle distance L11, the lift axle distance L12, the coupling distance L13, and the lift status S. The coupling distance L13 can be determined, for example, via an axle formula of the commercial vehicle 300 using a type of trailer 306 (center-axle trailer or drawbar trailer 308). The type of trailer 306 can be determined, for example, based on signals from a trailer network (not shown in the figures), which can in particular be an ISO 11992 CAN. Simultaneously with determining the geometric characteristics 328, two or more load characteristics 300, which are only partially illustrated in Fig. 2 for reasons of clarity, are determined.In the present exemplary embodiment, the load characteristics 330 include axle loads acting on the front axle 310 and the first rear axle 312 of the towing vehicle 304. Furthermore, the load characteristics 330 include axle loads acting on axles 338 of the trailer vehicle 306, of which only the axle load acting on the front axle 332 of the trailer vehicle 306 is illustrated as load characteristic 330 in Fig. 1. Preferably, however, the load characteristics 330 also include only a total towing vehicle mass of the towing vehicle 304 and a total trailer vehicle mass of the trailer vehicle 306, and / or a mass distribution of the commercial vehicle 300, wherein the mass distribution is a ratio formed from the total towing vehicle mass and the total trailer vehicle mass.

[0065] The determination 17 of the geometric characteristics 328 and the load characteristics 330 is performed for the first time upon vehicle activation of the commercial vehicle 300. A vehicle type of the commercial vehicle 300 and geometric characteristics 328 (number of axles 310, 312, 314, 338, axle distance L11) are already known upon activation of the ignition of the commercial vehicle 300. Furthermore, further properties of the axles 310, 312, 314, 338 are available. These are stored here as geometric characteristics 328 in an ESC control unit 340 of the commercial vehicle 300, which intervenes in the driving operation in the event of instability, for example, by braking an outside wheel of an oversteering commercial vehicle 300. In the present case, the trailer vehicle 306 has an electronic braking system (EBS). The trailer vehicle 306 is connected via a trailer interface (in Fig.1 not shown), which can be designed as an ISO11992 interface, is connected to the towing vehicle 304. The trailer vehicle 306 provides signals for the towing vehicle 304 on the trailer interface, which are used to determine the geometric characteristics 328 of the trailer vehicle 306. The geometric characteristics 328 of the trailer vehicle 306 include a model type of the trailer vehicle 306, a number of axles 338 of the trailer vehicle 306, and their distances from the coupling point 318. These geometric characteristics 328 of the trailer vehicle 306 are provided here directly at the ISO11992 interface, so that determining the characteristics 328, 330 of the trailer vehicle 306 involves receiving the corresponding signals. In addition, the EBS trailer vehicle 306 has sensors (not shown in Fig. 1) assigned to the axles 338.These sensors determine the axle loads present on the sensed axles 338 and provide corresponding signals to the trailer interface. From these signals, the axle loads of the trailer vehicle 306 are in turn determined as load characteristics 330. Furthermore, the determination 17 here includes calculating an axle load on the front axle 310 of the towing vehicle 304.

[0066] Following the determination 17 of the geometric characteristics 328 and load characteristics 330, in a next step of method 1, an individualized vehicle model of the current vehicle configuration 3 is generated from a basic vehicle model of the commercial vehicle 300 (generation 19 in Fig. 2). The individualized vehicle model can be a single-track model of the commercial vehicle 300, which, as a simplified model of the commercial vehicle 300, maps the towing vehicle 304 and the trailer vehicle 306 from Fig. 1 in their minimum coordinates, wherein the vehicle width approaches zero and lifting, rolling, or pitching movements of the commercial vehicle 300 can be neglected.

[0067] The generation 19 of the individualized vehicle model is carried out using the geometric characteristics 328 and the load characteristics 330. For this purpose, a mass distribution of the current vehicle configuration 326 in the vehicle longitudinal direction R1 is approximated. Subsequently, during the generation 19 of the individualized vehicle model, a parameterized basic vehicle model of the commercial vehicle 300 is preferably individualized by applying the geometric characteristics 328 and the load characteristics 330, wherein the determined characteristics 328, 330 and the mass distribution are inserted into the basic vehicle model as parameter values.

[0068] Using the customized vehicle model, dynamic properties, in particular lateral dynamic properties, of the current vehicle configuration 326 are then predicted (prediction 21 in Fig. 2). In the present exemplary embodiment, the dynamic properties determined as part of prediction 21 are natural angular frequencies and damping measures for eigenvalues ​​of the customized vehicle model. In Fig. 1, the commercial vehicle 300 is traveling straight ahead in a stationary manner and is stable. However, due to the rear-heavy load, the commercial vehicle 300 is susceptible to instabilities in the event of a sudden evasive maneuver 51 (cf. Fig. 3), which is characterized by a high steering angle frequency. Depending on the current driving speed V, the trailer vehicle 306 may not be sufficiently damped against an excitation of the commercial vehicle 300 caused by the evasive maneuver and may swerve.A control unit 202 of the commercial vehicle 300 is configured to determine, based on the determined dynamic properties, the current driving speed V at which the commercial vehicle 300 becomes unstable for a typical steering input of an evasive maneuver 51. The control unit 202 defines this speed as the stability-critical speed Vcrit. The control unit 202 is also configured to predict 21 the dynamic properties, to determine the characteristics 328, 330, and to generate 19 the individualized vehicle model.

[0069] In the exemplary embodiments of method 1, an approximation 33 of a current friction coefficient p for the commercial vehicle 300 is further provided. In the exemplary embodiment according to Fig. 2, the determination 5 of the stability-critical speed Vcrit of the commercial vehicle 300 takes place using the approximated friction coefficient p. The friction coefficient p is taken into account when predicting 21 the dynamic properties of the commercial vehicle 300 by using the friction coefficient p as a parameter value of the model when generating 19 the individualized vehicle model. By determining 33 the current friction coefficient p for the commercial vehicle 300, the quality of the prediction 21 of the dynamic properties of the current vehicle configuration 326 is further improved. In reality, fluctuations in the current friction coefficient p frequently occur.For example, the friction coefficient p prevailing between commercial vehicle 300 and roadway 336 may be reduced in wet or icy conditions compared to dry conditions. This results in a significant influence on the dynamic properties of commercial vehicle 300. If the current friction coefficient p is taken into account when predicting 21 the dynamic properties, this may affect the determined stability-critical speed Vcrit, and the safety of operating commercial vehicle 300 is increased. However, the dynamic properties of commercial vehicle 300 can also be predicted without taking the current friction coefficient p into account, in which case the predicted dynamic properties may then be subject to errors. For safety reasons, a low friction coefficient p can then be assumed during prediction 21, so that the stability-critical speed Vcrit may be lower than necessary.

[0070] Furthermore, in method 1 according to Fig. 2, when defining 15 the stability-critical speed Vcrit, dynamic route data Droute are also taken into account, which were determined in a previous step (determination 35 in Fig. 2).

[0071] Thus, a stability-critical speed Vcrit derived from the predicted dynamic properties of the current vehicle configuration 326 can be reduced here using the route data Droute if the route data Droute represents a winding route. The route data Droute is determined 35 by a navigation system 344 of the towing vehicle 304, which provides the route data Droute to the control unit 202.

[0072] After the lowering 11 of the lifting axle 314, the commercial vehicle 300 continues to perform a driving task, for example, a journey from a point A to a point B. During the course of the driving task, the driving speed V of the commercial vehicle 300 can vary, so that it can sometimes be greater and sometimes less than the critical speed Vcrit. If the commercial vehicle 300 is moving at a current driving speed V that is less than the stability-critical speed Vcrit, the lifting axle 314 does not necessarily have to be lowered to stabilize the commercial vehicle 300. In the first exemplary embodiment (Fig. 2), the lifting axle 314 is therefore raised 31 if the current driving speed V of the commercial vehicle 300 reaches or falls below a stable speed Vstab (V < Vstab).

[0073] The driving speed V, the stable speed Vstab, and the stability-critical speed Vcrit are illustrated in Fig. 1. The stable speed Vstab corresponds to the stability-critical speed Vcrit minus a speed buffer AV (Vstab = Vcrit - AV). The speed buffer AV ensures that the lifting axle 314 is not raised immediately when the speed falls below the stability-critical speed Vcrit. This prevents the lifting axle 314 from being raised (and lowered) by the stability-critical speed Vcrit even with slight fluctuations in the current driving speed V. Furthermore, the speed buffer AV ensures that the lifting axle 314 is only raised when the commercial vehicle 300 is safely moving within a stable speed range.The risk of instabilities occurring decreases the lower the current driving speed V is, so that the provision of the speed buffer AV further increases the added safety provided by method 1. Furthermore, errors, in particular measurement errors, when determining 3 the current driving speed V can be compensated. Furthermore, it can be provided that the raising 31 of the lifting axle 314 only occurs when the current driving speed V falls below the stable speed Vstab for a predetermined period of time Δt. This prevents, for example, the lifting axle 314 from being raised when the commercial vehicle 300 brakes briefly, for example in order to increase the distance to another vehicle merging into the lane in front of the commercial vehicle 300.

[0074] To achieve a further improvement in the lateral dynamic stability of the commercial vehicle 300, method 1 comprises locking 45 a steerable additional axle 344. In the exemplary embodiment shown in Fig. 1, the first rear axle 312 of the towing vehicle 304 is the steerable additional axle 344. This steerable additional axle 344 can be locked, wherein the locking 45 increases the driving dynamic stability of the towing vehicle 304 and thus of the entire vehicle combination 302. In method 1, the locking 45 of the steerable additional axle 344 only occurs if the current driving speed V is greater than or equal to the stability-critical speed Vcrit and if a locking status LS indicates that the steerable additional axle 344 is unlocked or open. If, however, the steerable additional axle 344 is already locked, which is represented by a locking status LSIock, the locking 45 can be omitted.

[0075] The locking status LS is determined in a previous step (determination 43 in Fig. 2). The determination 43 of the locking status LS is performed by determining locking signals provided on a vehicle network 334 of the commercial vehicle 300 and by determining the locking status LS using the locking signals. In the illustrated embodiment, the ESC control unit 340 provides the locking status LS to a vehicle network 334, which here is an ISO 11992 CAN bus. The control unit 202 receives the locking signals and determines the locking status LS therefrom.

[0076] In the first exemplary embodiment of method 1 (cf. Fig. 2), the lifting status S of the lifting axle 314 is determined 9 based on wheel speeds n_wheel, n_ref of the lifting axle 314 and a reference axle 346 of the commercial vehicle 300. The reference axle 346 is preferably a driven axle of the commercial vehicle 300. In the present case, the front axle 310 of the commercial vehicle 300 forms the reference axle 346. The determination 9 of the lifting status comprises determining 37 a lifting axle wheel speed n_wheel of wheels 348 of the lifting axle 314 and determining 39 a reference wheel speed n_ref of reference wheels 222, which here are front wheels of the commercial vehicle 300. After determining 37 the lift axle wheel speed n_wheel and determining 39 the reference wheel speed n_ref, a comparison 41 of these two wheel speeds n_wheel, n_ref is performed. In Fig.2, the comparison 41 shows that the lift axle wheel speed n_wheel is less than or equal to the reference speed n_ref less a wheel speed tolerance value An (n_wheel < n_ref - An).

[0077] While the commercial vehicle 300 moves at the driving speed V, the reference wheels 350 roll on the roadway 336, with a tire rolling speed of the reference wheels 350 approximately corresponding to the driving speed V. The reference wheel speed n_wheel corresponds to the tire rolling speed of the reference wheels 350 and is significantly greater than zero at higher driving speeds V. If the lift axle 314 is raised, its wheels 348 are not on the roadway 336, so that the lift axle wheel speed n_wheel in this case has a value of zero or slightly greater than zero. A large difference between the reference wheel speed n_ref and the lift axle wheel speed n_wheel therefore corresponds to a raised lift axle 314 or a lift status Sup, which represents a raised lift axle 314.

[0078] If, however, the lifting axle 314 is lowered, its wheels 348 also rest on the roadway 336 and roll along it. The tire rolling speed of the reference wheels 350 and the wheels 348 of the lifting axle 314 is essentially identical if all wheels 348, 350 have the same circumference. Therefore, a lowered lifting axle 314 or a lift status Sdown representing a lowered lifting axle 314 can be determined if a lifting axle wheel speed n_wheel of the wheels 348 of the lifting axle 314 lies within a wheel speed tolerance range ± An around the reference wheel speed n_ref of the reference wheels 350. The wheel speed tolerance value An is provided in the illustrated embodiment of method 1 to compensate for inaccuracies or errors in the determination 37, 39 of the wheel speeds n_wheel, n_ref. Such inaccuracies may, for example, result from minor deviations in the diameter of nominally equal-sized wheels 348, 350.Preferably, the wheel speed tolerance range ± Δn has a width of 100 rpm or less, preferably 50 rpm or less, particularly preferably 15 rpm or less. Preferably, the determination 9 can also only be performed when the lift axle wheel speed n_wheel is constant for a predetermined period of time, for example, a period of two seconds.

[0079] The lift axle 314 of the commercial vehicle 300 shown in Fig. 1 is raised, so that the lift axle wheel speed n_wheel is significantly lower than the reference speed n_ref of the reference wheels 350 on the front axle 310 of the commercial vehicle 300 (n_ref - n_wheel > An) and the determination 9 of the lift status S of the lift axle 314 results in a lift status Sup that represents a raised lift axle 314.

[0080] Fig. 4 illustrates a second embodiment of method 1, wherein identical steps are identified by identical reference numerals. Method 1 according to the second embodiment differs from method 1 according to Fig. 2 essentially in determining 5 the stability-critical speed 5 and in determining 9 the lift status S.

[0081] In method 1 according to the second exemplary embodiment, the determination 5 of the stability-critical speed Vcrit comprises a selection 27 of a pre-stored stability-critical speed vcrit_pre from a memory 204. The selection 27 is performed here by the control unit 202, wherein the memory 204 is a memory 204 of the control unit 202. Analogous to the first exemplary embodiment, the method 1 according to the second exemplary embodiment also approximates 33 the friction coefficient p and determines 35 dynamic route data Droute. The selection 27 of the pre-stored stability-critical speed Vcrit_pre is a parameter-based selection of a pre-stored stability-critical speed Vcrit_pre from a plurality of stability-critical speeds Vcrit_pre pre-stored in the memory 204.It can also be provided that selection 27 is a map-based selection in which relevant characteristic values ​​(type of trailer vehicle 306, mass distribution of the commercial vehicle 300, towing vehicle mass, trailer vehicle mass, axle loads, geometric characteristics 328, etc.) are represented. Within the scope of selection 27, in addition to the route data Droute and the friction coefficient p, geometric characteristics 328 and load characteristics 330 of the current vehicle configuration 330 are also taken into account. Thus, in selection 27, a pre-stored stability-critical speed Vcrit_pre corresponding to the geometric characteristics 328 and the load characteristics 330 is selected and then adapted to the route data Droute and the current friction coefficient p.

[0082] With reference to the commercial vehicle 300 shown in Fig. 1, a pre-stored stability-critical speed Vcrit_pre is selected, which is stored for a vehicle combination 202 comprising an unloaded towing vehicle 304 and a loaded trailer vehicle 306. If the determined friction coefficient p has a low value, i.e., adhesion between the commercial vehicle 300 and the road surface 336 is low, then this pre-stored stability-critical speed Vcrit_pre can be reduced in accordance with the determined current friction coefficient p. Thus, for the vehicle 300 shown in Fig. 1, a pre-stored stability-critical speed Vcrit_pre of 65 km / h can be selected and reduced to a stability-critical speed Vcrit of 50 km / h when the friction coefficient p is low (i.e., on a slippery road surface).Analogously, the pre-stored stability-critical speed Vcrit_pre can be reduced if the route data Droute represents a winding route.

[0083] Alternatively, it can be provided that the route data Droute and / or the current friction coefficient p are part of the parameter combination, and the stability-critical speeds vcrit_pre prestored in memory 204 are stored to match these parameter combinations. Preferably, the prestored stability-critical speed vcrit_pre that most closely matches the parameter combination is selected. For example, the selection 27 can include interpolation and / or averaging of several prestored stability-critical speeds vcrit_pre.

[0084] In the second exemplary embodiment (cf. Fig. 4), the lift status S is not determined directly by determining wheel speeds n_ref, n_wheel (cf. the first exemplary embodiment according to Fig. 2), but rather by determining lift status signals 23 that are provided on the vehicle network 334, which is designed as an ISO 11992 CAN bus. Based on the determined lift status signals, the lift status S can then be determined. Here, the ESC control unit 340 provides the lift status signals on the vehicle network 334. The ESC control unit 340 can provide the lift status signals, for example, based on axle load sensor data that represent an axle load on the lift axle 314, or based on data from a distance measuring sensor and / or limit switch assigned to the lift axle 314.

[0085] The control unit 202 and the memory 204 are part of a device 200 for improving the driving dynamics stability of a commercial vehicle 300, which is designed to carry out method 1. The device 200 further comprises an interface 206, which is designed here on the control unit 202. By means of the interface 206, the control unit 202 can provide a lowering request. In the commercial vehicle 300 according to Fig. 1, the interface 206 is connected to the vehicle network 334, so that the control unit 202 provides the lowering request for lowering the lifting axle 314 on the vehicle network 334. The vehicle network 334 is connected to the lifting axle 314 or to a lifting unit (not shown) of the lifting axle 314, which receives the lowering request. In response to receiving the lowering request provided by the device 200, the lift unit lowers the lift axle 314.In an analogous manner, the lift unit lifts the lift axle 314 when it receives a lift request provided on the vehicle network 334.

[0086] Reference symbol (part of the description)

[0087] Proceedings

[0088] Determine the current driving speed

[0089] Determining a stability-critical speed

[0090] Comparing the current driving speed with the stability-critical speed

[0091] Determine the lift status of the lift axle

[0092] Lowering the lift axle

[0093] Predicting a transverse dynamic stability behavior of the

[0094] commercial vehicle

[0095] Defining the stability-critical speed

[0096] Determination of geometric characteristics and load characteristics

[0097] Generating an individualized vehicle model

[0098] Predicting dynamic properties

[0099] Determining lift status signals

[0100] Selection of a pre-stored stability-critical speed

[0101] Raising the lift axle

[0102] Approximating a current friction coefficient

[0103] Determining dynamic route data

[0104] Determining a lift axle wheel speed;

[0105] Determining a reference wheel speed

[0106] Comparing the lift axle wheel speed with the reference speed

[0107] Determining a blocking status

[0108] Locking the steerable additional axle a Yaw rate curve with lowered lifting axle b Yaw rate curve with raised lifting axle a Articulation angle curve with lowered lifting axle b Articulation angle curve with raised lifting axle

[0109] evasive maneuvers

[0110] Steering back

[0111] Exit lane 200 Device for improving driving dynamic stability

[0112] 202 Control unit

[0113] 204 memory

[0114] 206 Interface

[0115] 300 commercial vehicles

[0116] 302 vehicle train

[0117] 304 towing vehicle

[0118] 306 trailer vehicle

[0119] 308 drawbar trailer

[0120] 310 front axle

[0121] 312 first rear axle

[0122] 314 Lift axle

[0123] 316 drawbar

[0124] 318 coupling point

[0125] 320 load

[0126] 322 first loading area

[0127] 324 second loading area

[0128] 325 arrows

[0129] 326 current vehicle configuration

[0130] 328 geometric characteristics

[0131] 330 Load characteristics

[0132] 332 Front axle of the trailer vehicle

[0133] 334 vehicle network

[0134] 336 roadway

[0135] 338 axles of the trailer vehicle

[0136] 340 ESC control unit

[0137] 344 steerable additional axle

[0138] 346 Reference axis

[0139] 348 wheels of the lift axle

[0140] 350 reference wheels

[0141] Droute route data

[0142] L1 1 axle distance

[0143] L12 Lift axle distance

[0144] L13 Coupling distance n_ref Reference wheel speed n_wheel Lift axle wheel speed

[0145] R1 Vehicle longitudinal direction

[0146] S Lift status

[0147] Sdown Lift status, which represents a lowered lift axle

[0148] LS lock status

[0149] LSIock Lock status representing a locked steerable additional axle

[0150] LSopen Lock status representing an unlocked steerable additional axle

[0151] Sup Lift status, which represents a raised lift axle

[0152] V current driving speed

[0153] Vcrit stability-critical speed

[0154] Vcrit_pre pre-stored stability-critical speed

[0155] Vstab stable speed

[0156] To wheel speed tolerance value

[0157] ± An wheel speed tolerance range

[0158] AV speed buffer

[0159] V articulation angle p current friction coefficient

[0160] V Yaw rate

Claims

Patent claims 1 . Method (1 ) for improving the driving dynamic stability of a commercial vehicle (300), wherein the commercial vehicle (300) has a lifting axle (314), the method (1 ) comprising: Determining (3) a current driving speed (V) of the commercial vehicle (300); Determining (5) a stability-critical speed (Vcrit) of the commercial vehicle (300); Comparing (7) the current driving speed (V) with the stability-critical speed (Vcrit); Determining (9) a lift status (Slift) of the lift axle (314) of the commercial vehicle (300); and Lowering (11) the lift axle (314) of the commercial vehicle (300) if the lift status (Slift) represents a raised lift axle (Sup) and the current driving speed (V) is greater than or equal to the stability-critical speed (Vcrit).

2. Method (1) according to claim 1, wherein determining (9) the lift status (Slift) of the lift axle (314) of the commercial vehicle (300) comprises: Determining (37) a lift axle wheel speed (n_wheel) of at least one wheel (348) of the lift axle (314); Determining (39) a reference wheel speed (n_ref) of at least one reference wheel (350) of a reference axle (346) of the commercial vehicle (300); and Comparing (41) the lift axle wheel speed (n_wheel) with the reference speed (n_ref), wherein the lift status (Sup) represents a raised lift axle (314) when the lift axle wheel speed (n_wheel) falls below the reference wheel speed (n_ref) by a wheel speed tolerance value (An), and represents a lowered lift axle (Sdown) when the lift axle wheel speed (n_wheel) is within a wheel speed tolerance range (± An) around the reference speed (n_ref).

3. Method (1) according to claim 1 or 2, further comprising: Determining (43) a locking status (LS) of a steerable additional axle (344) of the commercial vehicle (300); and Locking (45) the steerable additional axle (344) of the commercial vehicle (300) if the locking status (LSopen) represents a movable, currently steerable additional axle (344) and the current driving speed (V) of the commercial vehicle (300) is greater than or equal to the stability-critical speed (Vcrit).

4. Method (1) according to one of claims 1 to 3, further comprising: Raising (31) the lifting axle (314) if the current driving speed (V) of the commercial vehicle (300) reaches or falls below a stable speed (Vstab), wherein the stable speed (Vstab) corresponds to the stability-critical speed (Vcrit) less a speed buffer (AV).

5. Method (1) according to claim 4, wherein the speed buffer (AV) is in a range from 1 km / h to 25 km / h, preferably 10 km / h to 20 km / h.

6. Method (1) according to one of claims 1 to 5, wherein the determination (5) of a stability-critical speed (Vcrit) of the commercial vehicle (300) comprises: Predicting (13) a transverse dynamic stability behavior of the commercial vehicle (300) based on a current vehicle configuration (326) of the commercial vehicle (300); Defining (15) the stability-critical speed (Vcrit) based on the predicted lateral dynamic stability behavior of the commercial vehicle (300).

7. The method (1) according to claim 6, wherein the prediction (13) of a transverse dynamic stability behavior of the commercial vehicle (300) based on a current vehicle configuration (326) of the commercial vehicle (300) comprises: Determining (17) two or more geometric characteristics (328) and two or more load characteristics (330) of the current vehicle configuration (326); Generating (19) an individualized vehicle model of the current vehicle configuration (326) using the geometric characteristics (328) and the load characteristics (330); and Predicting (21 ) dynamic properties of the current vehicle configuration (326) using the individualized vehicle model.

8. Method (1) according to one of claims 1 to 5, wherein the determination (5) of a stability-critical speed (vcrit) of the commercial vehicle (300) is a selection (27) of a pre-stored stability-critical speed (Vcrit_pre) from a memory (204) in which at least one stability-critical speed (Vcrit_pre) is pre-stored.

9. Method (1) according to claim 8, wherein the pre-stored stability-critical speed (Vcrit_pre) is in a range from 20 km / h to 100 km / h, preferably 30 km / h to 60 km / h, particularly preferably 45 km / h to 55 km / h.

10. Method (1) according to one of claims 1 to 9, wherein the determination (5) of a stability-critical speed (Vcrit) of the commercial vehicle (300) comprises: Approximating (33) a current friction coefficient (p) for the commercial vehicle (300); wherein the determination (5) of the stability-critical speed (Vcrit) of the commercial vehicle (300) is carried out using the approximated friction coefficient (p).

11. Method (1) according to one of claims 1 to 10, further comprising: determining (35) dynamic route data (Droute), wherein the determination (5) of the stability-critical speed (Vcrit) of the commercial vehicle (300) is carried out using the dynamic route data (Droute).

12. Method (1) according to one of claims 1 to 11, wherein the lowering (11) of the lifting axle (314) of the commercial vehicle (300) also takes place when a maximum permissible axle load of the commercial vehicle (300) is undershot when the lifting axle (314) is raised.

13. Device (13) for improving the driving dynamic stability of a commercial vehicle (300), which is designed to carry out a method (1) according to one of claims 1 to 12.

14. A commercial vehicle (300) comprising a lifting axle (314) and a device (100) according to claim 13.

15. Computer program product with program code means stored on a computer-readable data carrier for carrying out the method (1) according to one of claims 1 to 12 when the program product is executed on a computing unit (104) of a commercial vehicle (300) having a lifting axle (314).

16. A method for improving the driving dynamics stability of a commercial vehicle (300), wherein the commercial vehicle (300) has a steerable additional axle (344), the method comprising: Determining (3) a current driving speed (V) of the commercial vehicle; Determining (5) a stability-critical speed (Vcrit) of the commercial vehicle; comparing (7) the current driving speed (V) with the stability-critical speed (Vcrit); Determining (43) a locking status (LSIock) of the steerable additional axle (344); and locking (45) the steerable additional axle (344) of the commercial vehicle (300) in straight-ahead travel if the locking status (LSopen) represents a movable, currently steerable additional axle (334) and the current travel speed (V) of the commercial vehicle (300) is greater than or equal to the stability-critical speed (Vcrit).

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