Steering system for a vehicle and motor vehicle equipped with it

Abstract

A steering system (10a, 10b) for a vehicle with two wheels individually steered by means of their own steering drives (12a, 12b) is characterized in that both steering drives (12a, 12b, 12c, 12d) each comprise a vehicle-side supported hydraulic element (20a, 20b), wherein the hydraulic elements (20a, 20b) can be hydraulically coupled to each other and a hydraulic coupling of the hydraulic elements (20a, 20b) results in a mechanical coupling of the two steering drives (12a, 12b).By integrating two interconnectable hydraulic elements into the respective steering drives (12a, 12b), it is possible either to functionally short-circuit the hydraulic elements (20a, 20b) and thus individually adjust the steering angles of both steered wheels, or to couple the hydraulic elements (20a, 20b) together and thus create a quasi-mechanical connection between the two steering drives (12a, 12b), thereby synchronizing the steering angles of the two steered wheels.

Description

The invention relates to a steering system for a vehicle having two wheels individually steered by means of respective dedicated steering drives, wherein the steering drives each have a steering kinematics connected to the respective wheel. The invention further relates to a motor vehicle equipped with such a steering system.DE 10 2005 030 259 A1 relates to a steering system according to the preamble of claim 1 and discloses a steering system for a vehicle having two individually steered wheels in each case, which steering system allows a fallback operation with mutually synchronized, steered wheels in the event of a system fault. By integrating two hydraulic elements that can be coupled to one another into the respective steering kinematics, it is possible either to short-circuit the hydraulic elements functionally and thereby render them ineffective and thus individually adjust the steering excursions of the two steered wheels, or to couple the hydraulic elements functionally to one another and thus to establish a quasi-mechanical connection between the two steering drives, as a result of which the steering excursions of the two steered wheels are synchronized with one another.DE 10 2016 006 088 A1 discloses a single-wheel steering system for a motor vehicle with two steering drives assigned to the two wheels, which drive systems act on associated steering rod halves. Between the rack halves a coupling is provided by which the rack halves can be rigidly connected.DE 10 2014 224 970 A1 discloses an individual wheel steering system for the steered wheels of a motor vehicle with two servo motors assigned to the wheels as steering drives.DE 198 38 490 A1 discloses a steering device for a motor vehicle having an electromotive main steering device and a hydraulic emergency steering device.DE 10 2013 016 757 A1 discloses an individual wheel steering system for a motor vehicle having a mechanical coupling device for the two wheels in an emergency operation.The object of the invention is to provide a steering system according to the preamble of claim 1 which provides a mechanical anti-theft protection for the vehicle.The invention results from the features of the independent claims. Advantageous refinements and refinements are the subject matter of the dependent claims.The object is achieved according to claim 1 in that the valve device has a blocking position in which at least one of the hydraulic elements and thus the steering kinematics coupled therewith is blocked. This anti-theft device, in addition to electronic anti-theft devices or anti-theft devices installed in the interior, functions in the manner of a steering lock of a motorcycle, in which the vehicle is only still movable in the direction of the steering wheel deflection.As in the prior art, by integrating two hydraulic elements that can be coupled to one another into the respective steering kinematics, it is possible either to short-circuit the hydraulic elements functionally and thereby render them ineffective and thus individually adjust the steering excursions of the two steered wheels, or to functionally couple the hydraulic elements to one another and thus to produce a quasi-mechanical connection between the two steering drives, as a result of which the steering excursions of the two steered wheels are synchronized with one another. The hydraulic elements are coupled to one another in opposite directions, in other words, a retraction of one of the hydraulic elements causes a retraction of the other hydraulic element, which has the result that the coupling acts functionally as if the actuating rods of the two hydraulic elements were rigidly connected to one another. The steering drives comprise steering elements acting on the steered wheels, which are each movable by electric servo motors and are mechanically connected to the respective hydraulic element. The steering elements can be designed as steering rods, preferably as spindle nuts, which are directly or indirectly articulated at one end to respective steering knuckles of the steered wheels and are connected at the other end to the hydraulic elements. In this case, the steering angle of a steering wheel of the vehicle (or a steering angle setpoint value from an autonomous control unit of the vehicle) is fed to a control unit which, on the basis of kinematic and kinetic requirements, preferably via a characteristic diagram, determines the parameters for the steering angles to be set of the two steered wheels and actuates the actuating motors accordingly.The hydraulic elements and the possibility of using flexible hydraulic lines for coupling the steering drives provide a very efficient and flexible connection between the steering drives, in particular under limited circumstances. The degrees of freedom of a steering angle adjustment can also be limited and thus protection against control errors can be provided. For example, a maximum steering angle difference between the two steering wheels can be defined, in the event of the steering wheels being exceeded, a forced coupling of the steering drives is effected.In this case, a valve device is arranged between the two hydraulic elements, which valve device is designed to hydraulically short-circuit or couple the hydraulic elements to one another. In the short-circuit position, both sides of each hydraulic element are hydraulically connected to one another, in order to switch the respective hydraulic element into no effect. In the coupling position, the hydraulic elements are hydraulically coupled in opposite directions.According to an advantageous development of the invention, the valve device is designed to couple the hydraulic elements in the electrically deenergized state. In this way, in the event of a functional failure, in particular a voltage failure, it is ensured that the two steered wheels are rigidly coupled to one another, as is conventional, as with a continuous track rod, and thus have the same steering angle.According to an advantageous development of the invention, the valve device can be connected to a compensation reservoir. This makes it possible to achieve a compensation in the fluid system, in particular if the two steering drives set different steering angles. The compensation reservoir preferably has a spring system on the rear side in order to ensure a harmonic movement of the hydraulic elements and thus of the entire steering system.According to an advantageous development, the steering drives each have electric servo motors coupled via a freewheel, so that in the event of failure of one of the servo motors in the coupling position, both steering drives can be driven by means of the other, intact servo motor. In this way, both steered wheels can be actuated jointly by means of an intact servomotor, so that the failure of one servomotor can be compensated.According to an advantageous further development of the invention, the hydraulic elements are designed as hydraulic cylinders, the working volumes of which can be connected hydraulically effectively. These hydraulic cylinders are hydraulically coupled to one another in such a way that the respective two working spaces of the hydraulic cylinders can be connected to the same working spaces of the other hydraulic cylinder with the valve device being interposed. Both working spaces of each of the hydraulic cylinders are directly connected to one another in a decoupling position of the valve device, which causes a hydraulic short circuit of the hydraulic cylinder.According to an advantageous development of the invention, the steering system comprises a steering angle control unit which preferably uses a characteristic diagram to determine the parameters for the steering angles of the steered wheels to be set and to actuate the steering drives accordingly. In this case, further parameters such as the vehicle speed, the longitudinal and transverse acceleration are preferably also taken into account.According to an advantageous development of the invention, the steering angle control unit only controls the steering drive of a wheel on the outside of the curve, while the hydraulic elements are controlled for hydraulic coupling. In this embodiment, two motor-controlled steering drives are provided, but only the wheel on the outside of the curve is actively increased in order to save energy, wherein the valve device is in the coupling position, so that the two steering drives are virtually mechanically coupled and thus the wheel on the inside of the curve is pulled along via the servomotor of the wheel on the outside of the curve. This is expedient since only the wheel on the outside of the curve has to support large lateral forces.According to an alternative embodiment of the invention, the vehicle steering wheel is mechanically coupled to one of the two steered wheels and the steering angle of the other steered wheel is adjustable by means of a steering drive. In this embodiment, one of the steering drives therefore does not have a servomotor, but the steering deflection of the vehicle steering wheel is mechanically passed on directly to the respective steered wheel. The steering angle of the other steered wheel is determined by the steering angle control unit. The steering angle control unit thus controls the servomotor of the second wheel accordingly. The two hydraulic elements are both short-circuited in the normal operating state, so that the steering rods of the two steering drives are movable completely independently of one another. In this embodiment, emergency or fallback operation in the event of failure of the steering drive can be achieved by hydraulically coupling the hydraulic elements to one another, because the two steering rods are thereby virtually mechanically coupled and the defective steering drive is also actuated by means of the directly driven steering drive.According to an advantageous development of the invention, the steered wheels are front wheels and / or rear wheels of a motor vehicle.According to an advantageous embodiment of the invention, the steered wheels are those of a steered trailer, for example a passenger trailer for a bus train.The object according to the invention is also achieved by a vehicle, in particular a motor vehicle, which is provided with a steering system according to one of the embodiments described above.Further advantages, features and details are evident from the following description, in which--possibly with reference to the drawing--at least one exemplary embodiment is described in detail. Identical, similar and / or functionally identical parts are provided with the same reference numerals. The invention is also applicable to steered wheels of a trailer.The following are shown: FIG. 1 : shows a schematic illustration of a steering system in a first operating position; FIG. 2 : shows the steering system of FIG. 1 in a second operating position; FIG. 3 : shows a second embodiment of a steering system.FIG. 1 shows a schematic illustration of a steering system 10 afor a land vehicle, in particular a motor vehicle, which is not illustrated. The steering system 10 aincludes two steering drives 12 a, 12 bfor adjusting the steering of two steered wheels, not shown. The steering drives 12 a, 12 beach comprise a steering rod 14 a, 14 b, one end of each of which ends in a ball head 16 a, 16 bwhich is in each case connected in an articulated manner to a steering knuckle, not shown. The steerable wheels are in turn attached to the pivotable steering knuckles. At the respective other ends of the link rods 14a, 14b, they are coupled to piston rods 18a, 18b of hydraulic cylinders 20a, 20b. Two hydraulic pistons 22 a, 22 bpart the interior of the hydraulic cylinders 20 a, 20 binto two working volumes 24 a, 24 b, 26 a, 26 b, respectively. The working volumes 24 a, 24 bcan be connected to one another by means of first hydraulic lines 28 aand by means of a valve device 30. The working volumes 26 a, 26 bcan likewise be connected to one another by means of second hydraulic lines 28 bvia the valve device 30.The valve device 30 can furthermore connect the second hydraulic lines 28 bto a spring-loaded compensation reservoir 32 via a third hydraulic line 28 c.The link rods 14 a, 14 bare each in engagement with a ball screw 34 a, 34 bwith freewheel, which in turn is coupled via a reduction gear 36 a, 36 bto a servomotor 38 a, 38 b. The steering angles of the two steered wheels are thus individually adjusted by means of the servomotors 38 a, 38 bin normal operation.A steering angle control unit 40 controls the servomotors 38 a, 38 band the valve device 30. The steering angle control unit 40 receives a desired steering angle setpoint value from a steering wheel sensor, not shown, or from an autonomous control system of the vehicle, and uses this to determine the steering angles to be set for both wheels, which steering angles are then commanded to the servomotors 38 a, 38 b. Of course, the steering angle control unit 40 is connected to sensors, not shown, which feed back the actually applied steering angle of the wheels for regulation.FIG. 1 shows the steering system 10 ain a first operating position of the valve device 30, which is referred to here as decoupling position, because the two hydraulic cylinders 20 a, 20 bare decoupled by the hydraulic lines 28 aand 28 cof the hydraulic cylinder 20 aon the left in the drawing being hydraulically connected to one another, so that the hydraulic cylinder 20 ais hydraulically short-circuited, since hydraulic fluid exiting from the working volume 24 awhen the steering rod 14 ais actuated flows back via the hydraulic lines 28 aand 28 cto the other side of the hydraulic piston 22 ainto the working volume 26 a. The same occurs on the right side in the steering drive 12 b, analogously, through the connection of the hydraulic lines 28 band 28 d. As a result, the two steering drives 12 a, 12 bare independent of one another, the two steering rods 14 a, 14 bcan be moved independently of one another, so that the steering angles of the two linked wheels can be individually determined by the steering angle control unit 40 and adjusted by means of the two servo motors 38 a, 38 b. In this decoupling position, the compensation reservoir 32 is also incorporated into the hydraulic circuits via the hydraulic line 28 e, since the working volumes 24 a, 24 bhave a smaller volume than the second working volumes 26 a, 26 b, which are opposite with respect to the hydraulic pistons 22 a, 22 b, on account of the piston rods 18 a, 18 blocated therein, and therefore hydraulic fluid has to be removed from or supplied to the circuits.FIG. 2 shows the same steering system 10 ain a second operating position, which is referred to here as the coupling position of the valve device 30, because the two steering drives 12 a, 12 bare coupled to one another. In this coupling position of the valve device 30, the hydraulic lines 28 aand 28 bare hydraulically coupled to one another and the hydraulic lines 28 cand 28 dare likewise. In this coupling position, the hydraulic cylinders 20 a, 20 bare thus hydraulically coupled to one another in a manner which acts like a mechanical connection of the two link rods 14 a, 14 b. The steering drives 12 a, 12 bare thus positively connected. The coupling position thus acts as a fall-back plane in the event of failure of components in one of the steering drives 12 a, 12 b.FIG. 3 shows an alternative embodiment of a steering system 10 b, in which the steering drive 12 ccauses a direct mechanical coupling of a vehicle steering wheel via a steering rod 42 and a steering gear 44 to the steering rod 14 acoupled at the steered edge. The steering drive 12 dshown on the right-hand side in FIG. 3, on the other hand, corresponds to the steering drive 12 aand 12 bfrom the embodiment according to FIGS. 1 and 2 In this steering system 10 b, the steering drive 12 cillustrated on the left in the figure and thus the wheel coupled thereto is moved directly mechanically via the vehicle steering wheel, while the second wheel is actuated via the right-hand steering drive 12 d. The valve device 30 is in the decoupling position shown in FIG. 1, so that the guide rods 14 aand 14 bare moved independently of one another.If the electrically driven right steering drive 12d suffers a component failure, for example of the servomotor 38b, the valve device 30 is brought into the coupling position shown in FIG. 2, so that the two hydraulic cylinders 20a, 20b are positively coupled and the steering rod 14b of the right steering drive 12d is actuated as it were mechanically by the steering rod 42.In both steering systems 10 a, 10 b, the valve device 30 can assume a third operating position in which some or all of the hydraulic lines 28 a, 28 b, 28 c, 28 dare blocked, such that one or both hydraulic cylinders 20 a, 20 bare not movable and thus anti-theft protection is provided because the steering impacts of the wheels are blocked.Although the invention has been illustrated and explained in more detail by preferred exemplary embodiments, the invention is not restricted by the disclosed examples and other variations can be derived therefrom by the person skilled in the art without departing from the scope of protection of the invention. It is therefore clear that a large number of possible variations exist. It is also clear that embodiments mentioned by way of example represent only examples which are not to be understood in any way as limiting, for example, the scope of protection, the possible applications or the configuration of the invention. Rather, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete terms, wherein the person skilled in the art, knowing the disclosed inventive concept, can make various changes, for example with regard to the function or the arrangement of individual elements mentioned in an exemplary embodiment, without departing from the scope of protection defined by the claims and their legal equivalents, such as further explanations in the description.List of reference characters10 a,b Lenksystem system 12 a,b,c,d Lenk drive 14 a,b Lenker rod 16 a,b Kugel head 18 a,b Kolbenstange rod 20 a,bYdraulikzylinder cylinder 22 a,b Hydraulik piston 24 a,b Arbeits volumes 26 a,b Arbeits volumes 28a,b,c,d,e Hydraulic lines 30 Valve device 32 Compensation reservoir 34 a,b Kugelgewinde screw 36 a,b Reduzier gear 38 a,b Stellmotor motor 40 Steering angle control unit 42 Lenkstange rod 44 Lenker gear

Claims

Steering system (10a, 10b) for a vehicle having two wheels individually steered by means of respective own steering drives (12a, 12b), wherein the steering drives (12a, 12b, 12d) each have a steering kinematics connected to the respective steered wheel, wherein both steering drives (12a, 12b, 12c, 12d) each comprise a hydraulic element (20a, 20b) supported on the vehicle side, wherein the hydraulic elements (20a, 20b) can be hydraulically coupled to one another and, in the case of a hydraulic coupling of the hydraulic elements (20a, 20b), a mechanical coupling of the two steering drives (12a, 12b) takes place and a valve device (30) is arranged between the two hydraulic elements (20a, 20b), which valve device is designed to couple the hydraulic elements (20a, 20b) together, 20b) for hydraulically short-circuiting or coupling them to one another and the valve device (30) hydraulically short-circuits both hydraulic elements (20a, 20b) in a decoupling position and thus both steering kinematics can be individually actuated, and hydraulically couples both hydraulic elements (20a, 20b) in a coupling position and thus brings about the mechanical coupling of the two steering kinematics, characterized in that the valve device (30) has a blocking position in which at least one of the hydraulic elements (20a, 20b) and thus the steering kinematics coupled therewith is blocked.Steering system (10a, 10b) according to Claim 1, characterized in that the valve device (30) is designed to couple the hydraulic elements (20a, 20b) in the electrically deenergized state.Steering system (10a, 10b) according to Claim 1, characterized in that the valve device (30) can be connected to a compensation reservoir (32).Steering system (10a, 10b) according to Claim 3, characterized in that the compensation reservoir (32) has a rear-side spring suspension.Steering system (10a, 10b) according to Claim 4, characterized in that the steering drives (12a, 12b, 12d) each have electric servo motors (38a, 38b) coupled via a freewheel, with the result that, in the event of failure of one of the servo motors (38a, 38b), both steering drives (12a, 12b, 12c, 12d) can be driven by means of the other servo motor (38b, 38a) in the coupling position.Steering system (10a, 10b) according to one of the preceding claims, characterized in that the hydraulic elements (20a, 20b) are designed as hydraulic cylinders, the working volumes of which can be connected hydraulically effectively.Steering system according to Claim 1, characterized in that it comprises a steering angle control unit (40) which uses a characteristic diagram to determine the parameters for the steering angles of the steered wheels to be set and actuates the steering drives (12a, 12b, 12d) accordingly.Steering system according to Claim 7, characterized in that the steering angle control unit (40) actuates only the steering drive (12a, 12b) of a wheel on the outside of the curve and the hydraulic elements (20a, 20b) for hydraulic coupling.Steering system (10b) according to Claim 7, characterized in that a vehicle steering wheel is mechanically coupled to one of the two steered wheels and the steering angle of the other steered wheel can be adjusted by the steering angle control unit (40) via the associated steering drive (12d).Steering system according to Claim 1, characterized in that the steered wheels are front wheels and / or rear wheels of a motor vehicle.Steering system according to claim 1, characterized in that the steered wheels are those of a steered trailer.A vehicle comprising a steering system according to any preceding claim.

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