Arrangement and method for determining a steering angle of a steerable rear axle

Abstract

Method for determining a steering angle (ϕ1) of a steerable rear axle (1) of a means of transport (10), comprising the steps: - determining (100) a driving dynamics signal based on a steering angle (ϕ2) of a front axle (2) of the means of transport (10), - Determining (200) a first signal of an index sensor (7) coupled to the rear axle (1), and - Determining (500) the steering angle (ϕ1) of the rear axle on the basis of the driving dynamics signal and the first signal of the index sensor (7).

Description

Prior ArtThe present invention relates to a means of transportation, an arrangement and a method for determining a steering angle of a steerable rear axle of a means of transportation. In particular, the present invention relates to a cost-effective arrangement and to the use of already present information in the vehicle for determining the steering angle.Currently, there are various variants and embodiments of mechatronic actuators for steering the rear axle of vehicles on the market. By means of these actuators, a steering angle can be set at the rear axle, which steering angle, together with the front axle steering, exerts a significant influence on the transverse dynamics of the vehicle. The rear wheels can be turned in opposite directions to the front wheels in order to reduce the turning radius. The wheels are steered in the same direction in order to reduce the yaw rate, for example, during lane changes or high speeds. In addition, the steering system can be controlled in rapidly driven turns in such a way that the slip angle at the wheel is reduced. The lateral force potential and thus the achievable curve speed can thus be increased.DE 10 2006 020 041 A1 and DE 10 2011 006 998 A1 disclose steerable rear axle arrangements for means of transport. It is partially proposed to set the rear axle steering angle as a function of a signal of a driving dynamics control system.DE 10 2011 085 607 A1 discloses a steering device for a rear wheel steering system for the exact and cost-effective determination of an actual steering angle. A motor angle sensor for determining the rotor position of an actuator of the rear axle and two counting units are used together for this purpose, wherein the counting units remain switched on even during a switched-off ignition of the motor vehicle and the counters of the counting units increment or decrement depending on the change in the steering angle of the steerable rear wheels depending on the direction of rotation of the rotor of the electric motor. The motor angle sensor is designed as an AMR, GMR, Hall sensor or as a resolver. In the event of the loss of the current rotor position of the electric motor, a new zero point calibration takes place.DE 10 2007 000 974 A1 discloses a superposition steering system in which a front axle is monitored with respect to its steering angle by means of an index pulse and on the basis of pulses of two wheel rotational speed sensors.An important factor for a particularly efficient, accurate and highly performance implementation of the requirements mentioned at the beginning by control algorithms is an accurate provision of the current actuator position. A simple solution according to the prior art consists in using a displacement sensor which measures the relative position of the parts of the actuator which move with respect to one another during a rear-axle steering operation. However, this solution is comparatively complicated and thus cost-intensive. A calculation of the actuator position from the current angle of the electric motor is indeed possible in principle. However, the motor does not have a defined starting position, so that at least when starting up the steering system, another determination of a predefined reference position is necessary.It is therefore an object of the present invention to provide a cost-effective possibility for exact determination of the steering angle.Disclosure of the InventionThe object identified above is achieved according to the invention by a method for determining a steering angle of a steerable rear axle of a means of transport having the features of claim 1, by an arrangement for determining a steering angle of a steerable rear axle having the features of claim 7 and by a means of transport having the features of claim 10.The dependent claims show preferred developments of the invention.The means of transport can be, for example, a car, a transporter or a truck. In a first step, a driving dynamics signal of the means of transportation is ascertained on the basis of a steering angle of the means of transportation. This can be done, for example, by an electronic stability control system (ABS, ESP or the like). For example, a rough calculation of the current steering angle ("reference position") can be carried out from a comparison of the wheel rotational speeds of the rear axle. The current yaw rate, the steering angle of the front axle and the vehicle speed can also be used for the steering angle estimation. All the aforementioned signals are usually available in means of transportation via a bus system. In a second step, a first signal of an indexer coupled to the rear axle is determined. The indexer differs from a displacement sensor mentioned at the beginning in particular in that it only has individual positions (for example one to ten positions) in which it outputs a signal. In this case, the signals do not necessarily have to differ from position to position, so that the construction and the signal generator unit can be very simple and cost-effective. The current steering angle of the rear axle is then determined from the driving dynamics signal and the first signal of the indexer. While the driving dynamics signal can only give a rough / inaccurate orientation with respect to the steering angle of the rear axle, in conjunction with the signal of the indexer, which is output in one position or a few positions of the indexer, the steering angle can be unambiguously determined. For this purpose, an adapted vehicle model can be used, which is calculated on a control device (or another evaluation unit) assigned to the rear axle steering system. A relatively rough position of the actuator (servomotor for setting a desired rear axle steering angle) or of the rear axle can thus be determined. On the basis of this first, comparatively inaccurate reference position, the actuator can already be actuated. According to the invention, in a second step, a drastic reduction of the tolerance of the previously determined steering angle position is carried out. For this purpose, an index generator which is significantly less expensive than an angle sensor is used and which outputs a signal when passing over a defined path point (e.g. by the actuator / motor of the steering system). Since the position of the indexer is mechanically exactly fixed, the actuator position can subsequently be determined very exactly. By the joint use of two steering angle information items which are not particularly meaningful independently in each case, according to the invention, a cost-effective and exact determination of a steering angle of a steerable rear axle can be carried out.A change in the steering angle can preferably subsequently be determined on the basis of a rotor angle signal of an electric motor for steering the rear axle. In other words, the relative angle (change) information of the electric motor can be used to update the further change in the steering angle on the basis of the steering angle information determined according to the invention. Since the rotor angle signal of the electric motor is already advantageous for regulating the same, the invention also makes use of predominantly known or present information and hardware in this embodiment.Preferably, a second signal of the indexer can also be determined, which is generated by the indexer in a position that differs from the position in which the indexer generates the first signal. Accordingly, it can be recognized that the second signal of the indexer is assigned to a different steering angle than the first signal of the indexer. This can be detected, for example, on the basis of the driving dynamics signals of the means of transportation. For example, the first signal can be output during a left turn and the second signal can be output during a right turn, so that it is possible to determine on the basis of a sign of respective wheel rotational speed differences which position the indexer currently has to have. Accordingly, the steering angle of the rear axle can be determined on the basis of a previously known condition under which the indexer outputs the first signal or the second signal. Due to the mechanically fixed distance of the positions of the indexer from one another, in which the first signal or the second signal is emitted, the need for an exact positioning of the indexer during production / assembly is superfluous, since the use of both the first signal and the second signal eliminates the influence of an exact positioning in the means of transport.The driving dynamics signal of the vehicle can be read out, for example, as a bus message via a CAN bus. Accordingly, a bus subscriber is to be provided for the evaluation unit, which carries out the method according to the invention for determining the steering angle of the rear axle. An additional determination unit or even separate sensors and connecting lines can therefore be dispensed with.The driving dynamics signal can be ascertained, for example, on the basis of a comparison of wheel speeds of the rear axle and / or of the front axle. Alternatively or additionally, the yaw rate and / or the travel speed of the means of transportation may be ascertained as a driving dynamics signal.The different information proposed according to the invention, which can be used to determine the steering angle, also allows plausibility checking of the information with respect to one another. For example, a steering angle of the rear axle determined by means of the driving dynamics signal and the rotor angle signal can be compared with a steering angle of the rear axle determined by means of the driving dynamics signal and the indexer. Such a comparison can be made permanently or repetitively. Each time the index position is crossed, it can now be checked whether the current actuator position corresponds to the fixed index position. Furthermore, it can be checked whether the current actuator position corresponds to the position calculated from the driving dynamics signal. Tolerances can be provided for both plausibility checking mechanisms. If an implausible state for the steering angle of the rear axle is detected via one of the two methods, different measures can be initiated. If, for example, the actuator position is determined as implausible only with respect to an index position, but not with respect to the position calculated from the driving dynamics signals, the comparison can be carried out again via the index positions. If implausible states occur more frequently within a predefined period of time, the actuator or actuators can be moved into a center position and deactivated with a signal calculated on the basis of the last plausible state. Information can be provided in a fault memory of a control signal assigned to the rear axle steering system (or to another evaluation unit). The method can be applied to a centrally located actuator for both rear wheels. The method can likewise be used in a system consisting of two wheel-specific actuators. Furthermore, in a two-actuator system, it is possible to plausibilize the travel signal of the one actuator by the travel signal of the second actuator using vehicle signals.According to a second aspect of the present invention, an arrangement for determining a steering angle of a steerable rear axle is proposed. The rear axle can be assigned to a vehicle (a car, a transporter, a truck, or the like), for example. The arrangement comprises a driving dynamics control system which is set up to ascertain a driving dynamics signal of the means of transportation. The driving dynamics signals can describe, in particular, a vehicle speed, a steering angle of the front axle, wheel speeds and wheel speed differences, and a yaw rate of the means of transport. In addition, an indexer is provided, which is configured to ascertain a first signal of an indexer coupled to the rear axle. The indexer of the present invention can be mechanically coupled to the rear steering angle, for example, via the actuator (electric motor for producing a desired rear steering angle). In particular, the indexer can be arranged on a shaft of the actuator and be configured to acknowledge a single-digit number of different positions with respective signals. Finally, an evaluation unit is provided which is configured to determine the steering angle of the rear axle on the basis of the driving dynamics signal and the signal of the indexer. For this purpose, the evaluation unit can be connected via signal lines to the driving dynamics control system and the indexer in terms of information technology.The indexer can preferably have at least two positions dependent on the steering angle of the rear axle, wherein it is configured to output a first signal in the first position and a second signal in the second position. A particularly simple and cost-effective indexer acknowledges the position with the same signal in each case, regardless of the respective position, which is unproblematic according to the invention. Instead, according to the invention, the positions are distinguished by means of the information of the driving dynamics signal.Due to the aforementioned configuration of the arrangement, it is configured to execute a method according to the first aspect of the invention. The features, combinations of features and the advantages resulting from these therefore correspond to the method according to the invention in such a way that reference is made to the above explanations in order to avoid repetitions.According to a third aspect of the present invention, a means of transport (a passenger car, a transporter, a truck, or the like) is proposed, which has a steerable rear axle. The steerable rear axle can be moved, for example, by an actuator (e.g. an electric motor) into a position with a desired steering angle. In order to determine the actually set steering angle, an arrangement according to the second-mentioned aspect of the invention is provided. With respect to the means of transport according to the invention, the features, combinations of features and the advantages resulting therefrom are also obtained according to the first aspect of the invention mentioned above and therefore reference is made to the above explanations in order to avoid repetitions.Brief Description of the DrawingsHereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings. In the drawings, there is: FIG. 1 shows a schematic plan view of components of an exemplary embodiment of a means of transport according to the invention; FIG. 2 shows a schematic illustration of components of an exemplary embodiment of an arrangement according to the invention; and FIG. 3 shows a flow chart illustrating steps of an exemplary embodiment of a method according to the invention for determining a steering angle of a steerable rear axle of a means of transport.Embodiments of the InventionFIG. 1 shows a passenger car 10 as a means of transport, the wheels 3 of which are arranged on a steerable front axle 2 or on a steerable rear axle 1. For the front axle 2, a steering angle φ 2, for the steerable rear axle 1 can be set to a steering angle φ 1, independent thereof. Wheel speed sensors, not shown, supply their signals to a driving dynamics control system 4, which is connected via a CAN bus to an evaluation unit 5 of a control device assigned to the rear axle steering system. The evaluation unit 5 is connected with an indexer 7 with information technology, which reports a signal to the evaluation unit 5 as a function of the steering angle φ 1. In the example, four different positions of the indexer 7 are reported by respective (identical) signals. An electric motor 6 is connected in terms of information technology as an actuator for setting a desired rear axle steering angle φ 1 to the evaluation unit 5 and mechanically to the steerable rear axle 1. The components of the electric motor 6 are presented in more detail in connection with FIG. 2.FIG. 2 shows an arrangement 9 for determining a steering angle φ 1, as it has been presented in overview form and in combination with a steering system in FIG. 1. The electric motor 6 has a rotor angle sensor 8, which, although outputting a comparatively finely resolved feedback as a function of its rotational position, does not have a predefined starting or reference position. The rotor angle sensor 8 is connected to the evaluation unit 5 by information technology. Furthermore, an index generator 7 is provided on the shaft 12 and is likewise connected to the evaluation unit 5 by information technology. The evaluation unit can adapt the actual position of the steerable rear axle via a control line 11 by instructing the electric motor 6 accordingly via a control line 11. Driving dynamics signals of a driving dynamics control system (not shown) are provided to evaluation unit 5 via a CAN bus.FIG. 3 shows steps of a method for determining a steering angle of a steerable rear axle of a means of transport. In step 100, a driving dynamics signal of the means of transportation is ascertained for this purpose by means of a driving dynamics control system. In step 200, a first signal of an indexer coupled to the rear axle is ascertained. In step 300, a corresponding second signal of the indexer is determined and in step 400 it is recognized that the second signal of the indexer is assigned to a different steering angle than the first signal of the indexer. For the detection, the driving dynamics signal of the means of transportation ascertained in step 100 is used, which enables at least a differentiation of the different positions of the indexer acknowledged by signals. In step 500, the steering angle of the rear axle is determined on the basis of the driving dynamics signal and the first signal of the indexer. In this case, the fact is used that only a few positions are acknowledged by the indexer by means of the first signal, which positions can be clearly distinguished from one another on the basis of the driving dynamics signal of the means of transportation. In step 600, a change in the steering angle is ascertained on the basis of a rotor angle signal of an electric motor for steering the rear axle. On the basis of the determination of the steering angle carried out according to the invention, a change in the steering angle is thus tracked by the rotor angle signals. To check a proper function, a comparison is claimed in step 700, in which a steering angle of the rear axle determined by means of the driving dynamics signal and the rotor angle signal is compared with a steering angle of the rear axle determined by means of the driving dynamics signal and the indexer. Depending on a result of the comparison, different measures (such as, for example, the deactivation of the steering function for the rear axle) can be taken.Although the aspects and advantageous embodiments according to the invention have been described in detail on the basis of the exemplary embodiments explained in conjunction with the appended drawing figures, modifications and combinations of features of the illustrated exemplary embodiments are possible for the person skilled in the art without departing from the scope of the present invention, the scope of protection of which is defined by the appended claims.List of reference characters1 Rear axle 2 Front axle 3 Wheels 4 Driving dynamics control system 5 Evaluation unit 6 Electric motor 7 Indexer 8 Rotor angle sensor 9 Arrangement for determining the steering angle 10 Car 11 Control line 12 Shaft 100- 700 Method steps CAN Controller Area Network (bus) φ 1 Steering angle of the rear axle φ 2 Steering angle of the front axle

Claims

Method for determining a steering angle (φ 1) of a steerable rear axle (1) of a means of transport (10), comprising the steps: - determining (100) a driving dynamics signal on the basis of a steering angle (φ 2) of a front axle (2) of the means of transport (10), - determining (200) a first signal of an indexer (7) coupled to the rear axle (1), and - determining (500) the steering angle (φ 1) of the rear axle on the basis of the driving dynamics signal and the first signal of the indexer (7).Method according to Claim 1, further comprising - determining (600) a change in the steering angle (φ 1) on the basis of a rotor angle signal of an electric motor (6) for steering the rear axle (1).Method according to Claim 1 or 2, further comprising - determining (300) a second signal of the indexer (7), - detecting (400) that the second signal of the indexer (7) is associated with a different steering angle than the first signal of the indexer (7), and - determining the steering angle (φ 1) of the rear axle (1) on the basis of a previously known condition under which the indexer (7) outputs the first signal and the second signal.Method according to one of the preceding claims, wherein the determination of the driving dynamics signal of the means of transportation (10) comprises a reading out of a bus message.Method according to one of the preceding claims, wherein the driving dynamics signal is additionally determined on the basis of - a comparison of wheel speeds of a right and a left wheel (3) of the steerable rear axle (1) and / or - a yaw rate of the means of transport (10) and / or - a travel speed of the means of transport (10).Method according to one of the preceding claims, further comprising - comparing (700) - a steering angle (φ 1) of the rear axle (1) determined by means of the driving dynamics signal and the rotor angle signal with - a steering angle (φ 1) of the rear axle determined by means of the driving dynamics signal and the first signal of the indexer (7).Arrangement for determining a steering angle (φ 1) of a steerable rear axle (1), comprising: - a driving dynamics control system (4) which is set up to determine a driving dynamics signal on the basis of a steering angle (φ 2) of a front axle (2) of the means of transportation (10), - an indexer (7) which is set up to determine a first signal of an indexer (7) coupled to the rear axle, and - an evaluation unit (5) which is set up to determine the steering angle (φ 1) of the rear axle (1) on the basis of the driving dynamics signal and the signal of the indexer (7).Arrangement according to Claim 7, wherein the indexer (7) has at least two positions dependent on the steering angle (φ 1) of the rear axle (1), wherein it is configured to output a first signal in the first position and a second signal in the second position.Arrangement according to claim 7 or 8, wherein the arrangement (9) is configured to carry out a method according to any one of the preceding claims 1 to 6.Means of transport comprising - a steerable rear axle (1) and - an arrangement (9) according to one of Claims 7 to 9.

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