Abstract:
A system is specified for the automatic adjustment of a gap between a tractor vehicle and an attached trailer, with a length-adjustable hitch with a tension tube, at the end of which is arranged a tension lug, while the tension lug can travel in the vehicle&#39;s lengthwise axis relative to the tension tube by an actuator along a predetermined travel path, as well as a control unit. The basic problem of the invention was to provide a system with which the gap between tractor vehicle and trailer can be changed automatically in driving operation and depending on the speed, both for articulated and unarticulated trailers. The problem is solved according to the invention with a system in which the control unit is an electronic controller, which is hooked up to a speed pickup for the processing of a speed signal and connected to the actuator.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention concerns a system for the automatic adjustment of a gap between a tractor vehicle and an attached trailer, comprising a length-adjustable, especially a telescoping hitch with a tension tube, at the end of which is arranged a tension lug, while the tension lug can travel in the vehicle&#39;s lengthwise axis relative to the tension tube by means of an actuator along a predetermined travel path, as well as a control unit. 
       BACKGROUND OF THE INVENTION 
       [0002]    The tractor vehicle and the trailer in the coupled-together condition form a load train or articulated train, wherein both the tractor vehicle and the trailer are configured with a boxlike, high-rising cargo space to maximize their transport volume. Especially when driving fast on a straight road, considerable vortices and turbulence occur around the gap between tractor vehicle and trailer, having a negative impact on the fuel consumption and the exhaust emissions. However, it is only possible to reduce the gap on a straight roadway, since on curved roadways there is a risk of the trailer colliding with the tractor vehicle. Accordingly, after reducing the gap during road travel it is absolutely necessary to restore a sufficiently large gap once again in event of a panic braking or an avoidance maneuver, while the term “automatic” means an adjustment of the gap internal to the system, that is, without human intervention. 
         [0003]    In the past, efforts have already been made to reduce the gap during straight travel of the articulated train and to increase it when traveling on a curve in order to prevent a bumping of the opposite corners of the cargo space of the tractor vehicle and trailer. One generic prior art is formed by DE 33 33 231 A1 with a hitch that can be adjusted by means of a hydraulic slave cylinder, where the slave cylinder is fed from a master cylinder arranged underneath the rim bearing. As soon as the front axle of the trailer turns, the piston of the master cylinder is retracted or extended and it forces hydraulic fluid out from the master cylinder and into the slave cylinder, which in turn moves the tension lug in the axial direction of the hitch. The major drawback of this known hitch is that it only works with trailers having an articulated front axle and cannot be installed on trailers with rigid hitch. Another drawback is the exclusively angle-dependent control of the length-adjustable hitch, not taking into account the travel speed of the articulated train. Furthermore, this known type of constrained control generally works well as long as the geometrical relations of tractor vehicle and trailer do not change, that is, the trailer is always pulled by the same tractor vehicle. But if the trailer is pulled .by different tractor vehicles with a chassis or cargo space contour differing from each other, there is a heightened risk of a collision of the trailer with the tractor vehicle upon sideways movement along a curve, due to too small a gap achieved between tractor vehicle and trailer. 
         [0004]    A similar technical solution of a so-called short coupling system, which also enables the hauling of trailers with rigid hitch, is proposed by DE 41 36 334 C1, but here the slave cylinder located on the trailer is operated from a master cylinder arranged on the tractor vehicle, which in turn is activated by a mechanical gearing depending on the buckling angle between the tractor vehicle and the trailer. 
         [0005]    It has become known from DE 195 07 034 A1 how to avoid damage to the forked draw-bar or mounted equipment of a tractor vehicle during backward movement of a truck with trailer. For this, a trailer coupling is provided with a coupling mouth, mounted so that it can swivel or be suspended on the cross beam of the chassis, and forced to swivel along with the forked draw-bar when the vehicle is steered accordingly. To detect the movement of the coupling mouth, sensors are arranged on either side of the opening of the coupling mouth. The sensors trigger an engine stop just before the forked draw-bar knocks against the chassis or other mounted equipment, so that the truck driver must first take other steps in order to operate his vehicle once again. The known truck draw-bar safety feature only works during slow maneuvering during backward movement and causes an engine shutdown when a given buckling between tractor vehicle and trailer is exceeded. This is a massive safety risk during fast highway driving and therefore it is not acceptable. 
       SUMMARY OF THE INVENTION 
       [0006]    Therefore, the basic problem of the invention is to provide a system with which the gap between tractor vehicle and trailer can be changed automatically in driving operation and depending on the speed, both for articulated and unarticulated trailers. 
         [0007]    The problem is solved according to the invention with a system in which the control unit is an electronic controller, which is hooked up to a speed pickup for the processing of a speed signal and connected to the actuator. Accordingly, the controller receives a metered value of the currently driven speed as its input quantity and puts out a corresponding signal to the actuator as its output quantity. The actuator thereupon adjusts the gap between the tractor vehicle and the trailer in dependence on the speed of travel. For this, a characteristic curve can be stored in the controller, plotting a constant functional setting of the gap as a function of the current speed of travel. 
         [0008]    Basically, a larger gap is advantageous in the low speed range, since the aerodynamic disadvantages are of little effect and the articulated train is generally traveling on a stretch with many curves, which means large deflections about a vertical pivot axis between tractor vehicle and trailer. On the other hand, when traveling on the highway, the speed of travel increases and so do the aerodynamic effects of a large gap. The curves to be negotiated at high speed are generally gentle, so that only slight relative movements occur between the tractor vehicle and the trailer, and there is no chance of the trailer knocking against the chassis of the tractor vehicle. 
         [0009]    According to a first preferred embodiment, the speed pickup is a speed sensor cooperating with the vehicle&#39;s transmission. This embodiment involves a modification of the tractor vehicle and it provides to the system of the invention an especially exact and near-simultaneous signal regardless of the rest of the electronic configuration. 
         [0010]    Advantageously, the speed pickup can also be a speed sensor cooperating with an axle of a trailer. This embodiment has the advantage that all system components are installed on the trailer, the trailer can be picked up by various tractor vehicles and still the benefits of the invention are achieved. Alternatively, the speed sensor can also work as a wheel sensor or otherwise convert a rotary movement per unit of time into a speed signal. 
         [0011]    According to another embodiment, the speed pickup can be formed from the Antilock-System (ABS) of the trailer. The ABS system constantly generates a speed signal, so that no further sensors need to mounted and hooked up. 
         [0012]    Depending on the technical outfitting of the tractor vehicle, the CAN-bus if present can also serve as a speed pickup, since a speed signal is also generally available from it. 
         [0013]    Preferably, the tension lug can be mechanically locked relative to the tension tube in predetermined positions. In this way, one can achieve a form-fitting locking at discrete distances, which relieves the burden on the actuator. The locking can be realized in particular in the form of one or more radially extending locking means, which engage on the tension tube or tension lug and fit into corresponding detent openings in the other mating part. For an adjustment of the draw bar, the locking means can be taken out of engagement with the mating detent opening by a servomotor, e.g., in the form of a pneumatic cylinder, so that a relative movement between the tension lug and the tension tube is possible. After reaching the changed position, the locking means are again set in place and they fix the tension lug and the tension tube in form-fitting manner. Since the movement of the locking means must be near-simultaneous in an emergency situation, the servomotor should likewise be operated by the same electronic controller as the actuator. A manual activation would be too slow and therefore not acceptable for safety reasons. 
         [0014]    Preferably, a force measuring element is applied to the tension lug and/or the tension tube, providing a load-dependent signal to the electronic controller. This can be advisable, since a loaded trailer in event of a panic braking or a fast avoidance maneuver has a tendency to substantial load-shifting reactions. These anticipated load-shifting reactions can be taken into account by allowing for the load-dependent signal when adjusting the automatic gap by the electronic controller. Strain gage strips or piezoelectric sensors can be used as the force measuring element, for example. 
         [0015]    Advisedly, the actuator has hydraulic, electromechanical or pneumatic operation. It is preferable to use a hydraulic pressure cylinder. By an electromechanical actuator is meant a spindle driven by a motor, on which a spindle nut runs and is prevented from rotating. 
         [0016]    The tension tube on the adjustable draw-bar can be configured as a first pipe segment and the tension lug can comprise a second pipe segment, the two pipe segments being concentrically overlapping. If an electromechanical drive is used, it is preferable to use a nonround cross section, especially a square or a polygon profile. These embodiments, thanks to the geometry of the pipe segments, provide protection against rotation of the spindle nut. A configuration of the pipe segments at least partly as a closed hollow profile furthermore allows the components of the system according to the invention to be protected inside one or both hollow profiles. Thus, preferably the actuator can be arranged inside one or both pipe segments. 
         [0017]    The actuator can also be driven by a subassembly arranged on or inside one or both pipe segments. Advantageously, the electronic controller is also accommodated on or inside one or both pipe segments. 
         [0018]    Preferably the electronic controller is hooked up to at least one additional signal generator for the processing of a vehicle condition signal. In this way, the primary speed-dependent adjustment of the gap while the articulated train is moving along a curve can be further refined, wherein the following embodiments take into account the actually occurring distance of the tractor vehicle from the trailer as additional parameter. This distance between tractor vehicle and trailer can be found either directly by a distance measurement or indirectly by an angle measurement. 
         [0019]    If a distance sensor is used, this senses a change in the distance from the trailer to a tractor vehicle located in front of it. It has proven to be especially favorable for the distance sensor to be arranged at the front side of the trailer. From this position, the chassis of the tractor vehicle can be measured especially effectively as it occasionally collides with the trailer. Furthermore, the sensors are located along with the other system components on the trailer and allow the system to operate independently of the outfitting of the tractor vehicle. Alternatively, the distance sensors can also be arranged at the rear of the tractor vehicle or its cargo space. 
         [0020]    Advisedly, the distance sensor is arranged spaced apart to the side of the lengthwise axis of the trailer. The actually occurring gap is measured in the region of the outer vehicle corners, since these regions are also the first to collide with the trailer when the articulated train is moving on a curve. 
         [0021]    According to an alternative embodiment, the signal generator can also be an angle sensor, which is arranged at the side of the trailer, for example, in the region of a bearing rim, and which detects the change in its angle of rotation. 
         [0022]    Advantageously, the angle sensor is a steering sensor, which can be arranged in the area of a steering wheel, steering linkage or steering transmission and which detects a change in the steering angle of the steering wheel, steering linkage, or parts of the steering transmission. Any travel on a curve is initiated by a change in position of these parts of the steering system, so that an especially near-simultaneous signal can be detected before the articulated train begins its actual travel on the curve. This, in turn, makes possible a timely expanding of the hitch and minimizes the risk of a collision between tractor vehicle and trailer. 
         [0023]    Another alternative embodiment is to provide the angle sensor as a steering angle sensor, which can be arranged in the area of a front wheel of the tractor vehicle and which detects a change in the steering angle of this front wheel from the position during straight travel. 
         [0024]    In another alternative embodiment, the signal generator is the brake system of an attached tractor vehicle or that of the trailer, which in the case of a heavy braking produces a corresponding brake signal. This brake signal can be used within the electronic controller to expand the hitch and adjust a larger gap between tractor vehicle and trailer, since a full braking is often related to a following avoidance maneuver. 
         [0025]    For regular driving operation, control programs are advantageously stored in the electronic controller, by which the position of the tension lug relative to the hitch is determined in dependence on the driving speed and the momentary distance or angle as measured by the signal generator. 
         [0026]    In the event of a panic braking of the articulated train with concomitant load-shift reactions or a sudden avoidance maneuver, the controller can determine a distance or angle gradient from the change in distance or angle per unit of time and set the actuator in operation in dependence on a distance or angle gradient stored in the controller, which increases or decreases the gap between the tractor vehicle and the trailer. 
         [0027]    It has proven to be especially positive to arrange at least one load sensor on the axle or axles of the tractor vehicle and/or the trailer, which measures the axle load and provides the measured value to the electronic controller. This load sensor can be provided in addition or alternatively to the force measuring element arranged on the hitch. It should also be possible to identify a full-cargo or empty trailer in this way and take into account the anticipated driving behavior when adjusting the gap. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0028]    For a better understanding, the invention will now be discussed more closely by means of seven figures. There are shown 
           [0029]      FIG. 1 , a side view of an articulated train with variously adjusted gap; 
           [0030]      FIG. 2 , a side view of a telescopic hitch according to a first embodiment; 
           [0031]      FIG. 3 , a side view of a telescopic hitch according to a second embodiment; 
           [0032]      FIG. 4 , a schematic top view of an articulated train with another signal generator in the form of a distance sensor; 
           [0033]      FIG. 5 , a schematic top view of an articulated train with another signal generator in the form of an angle sensor in the area of the bearing rim; 
           [0034]      FIG. 6 , a schematic top view of an articulated train with another signal generator in the form of a steering sensor; and 
           [0035]      FIG. 7 , a schematic top view of an articulated train with another signal generator in the form of a steering angle sensor. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0036]      FIG. 1  shows in a side view an articulated train, consisting of a tractor vehicle  2  and an attached trailer  3 . Both the tractor vehicle  2  and the trailer  3  have a cargo space  42 ,  43 , which is used for the transport of goods. Usually the tractor vehicle  2  has steerable front wheels  30   a  and motor-powered rear wheels  30   b.    
         [0037]    The trailer  3  has a so-called tandem axle with front wheels  34   a  and rear wheels  34   b  arranged close to each other in the driving direction. Neither wheel pair  34   a,    34   b  is steerable in the driving direction. The mechanical connection of the trailer  3  to the tractor vehicle  2  is realized by a hitch  4 , which comprises a tension tube  5 , at whose front end is formed a tension lug  6 . The tension lug  6  prior to the start of the drive is introduced into a bolt coupling  33  arranged permanently on the tractor vehicle  2  and held in form-fit by a coupling bolt, not shown. The hitch  4  rigidly engages the trailer  3 . For this, a mounting bracket  38  can be provided on the hitch  4 , which in turn is screwed to the trailer chassis. 
         [0038]    A gap  1  is present between the tractor vehicle  2  and the trailer  3 , which in the top drawing is formed with a maximum distance xmax and in the bottom drawing with a minimum distance xmin. The large distance xmax enables a maneuvering and driving on narrow curves, when the corner of the cargo space  42  facing the trailer  3  and the corner of the cargo space  43  facing the tractor vehicle can approach each other on the inside of the curve, or even bump each other and cause damage. When the articulated train is moving fast on a straight stretch, no sharp curves are possible, so that the distance x between tractor vehicle  2  and trailer  3  and thus the gap  1  can be. shortened. This results in better air flow across the gap  1  and less turbulence, so that the fuel consumption and pollution emissions of the articulated train are reduced. 
         [0039]    The detecting of the current speed of travel is done internally to the system by means of a speed pickup  9  located on the trailer  3 . The speed pickup  9  in the embodiment of  FIG. 1  is arranged as a speed sensor  11  on one of the axles  10  of the trailer  3 . The actual speed of the trailer  3  is determined from the number of revolutions of the axle  10  per unit of time and processed in an electronic controller  8  (see  FIGS. 2 and 3 ) into a signal for adjusting the distance x. 
         [0040]    Reducing of the distance x occurs by a telescoping of the hitch  4 . The tension tube  5  permanently engaging the trailer  3  forms a first pipe segment  15 , in which a second pipe segment  16  that can be adjusted in the lengthwise direction of the vehicle is movably held. The tension lug  6  is an integral part of the second pipe segment  16 . 
         [0041]    The particular distance x that is set is detected by a distance sensor  19  arranged on the back side of the tractor vehicle  2  and used in adjusting the intended gap  1 . 
         [0042]      FIG. 2  shows in a side view a first embodiment of the telescoping hitch  4 . The hitch  4  comprises a smaller-diameter first pipe segment  15  with a preferably round cross section, which is permanently joined to the mounting bracket  38 . The mounting bracket  38 , in turn, has several boreholes  39  in its top section for a fastening of the hitch  4  to the trailer  3 . 
         [0043]    Onto the first pipe segment  15  is shoved coaxially a larger-diameter second pipe segment  16  and movably held in the axial direction by means of an actuator  7 . The actuator  7  comprises a pressurized fluid cylinder  35  and is located at least partly inside the contour of the first pipe segment  15 . The pressurized fluid cylinder  35  is held permanently inside the first pipe segment  15  by its first end, facing the trailer  3 . The opposite, second end of the pressurized fluid cylinder  35  is constantly located inside the contour of the second pipe segment  16  and is permanently fastened to this. The second pipe segment  16 , furthermore, carries the tension lug  6  for a detachable fastening of the hitch  4  to a bolt coupling  33  of a tractor vehicle  2  (see  FIG. 1 ). By activating the pressurized fluid cylinder  35 , the second pipe segment  16  with the tension lug  6  formed on it can move in linear fashion relative to the first pipe segment  16 . 
         [0044]    The pressurized fluid cylinder  35  is permanently connected to a subassembly  17  in the form of an electrically operated pump, especially a hydraulic pump. The subassembly  17  is put in operation automatically by an electronic controller  8 . Both the subassembly  17  and the electronic controller  8  are advantageously accommodated inside the first and/or second pipe segment  15 ,  16 , with a pipe segment  15 ,  16  that is fixed in place relative to the trailer  3  being especially suitable—the first pipe segment  15  in the present case. 
         [0045]    The, electronic controller  8  is joined by data lines at least to the speed sensor  11 . Furthermore, as further input quantities, data from another signal generator  18  and a force measuring element  14  arranged on the hitch  4  can be processed by the electronic controller  8 . 
         [0046]    In order to relieve the actuator  7  of load when a quasi-stationary operating state is attained, locking means  40  are arranged on opposite sides in the circumferential wall of the movable, second, pipe segment  16 , which in the descended position engage by form fitting with complementary detent openings  41  of the first pipe segment  15 . A plurality of detent openings  41  staggered in the axial direction enables a locking in different positions. 
         [0047]    During the adjusting of the hitch  4 , the actuator  7  pushes forward the second pipe segment  16  under control by the electronic controller  8  at discrete intervals, so that the locking means  40  can descend into the next detent opening  41 . The raising and lowering of the locking means  40  occurs by servomotors  44 , which are preferably operated by compressed air. The servomotors  44  are likewise connected directly to the electronic controller  8 . 
         [0048]      FIG. 3  shows an alternative embodiment of the telescoping hitch  4 , in which instead of a pressurized fluid cylinder  35  an electromechanical drive with a spindle  36  driven by a subassembly  17  and a spindle nut  37  running thereupon is used as the actuator  7 . The spindle  36  here is fixed in its axial direction but can rotate on the first pipe segment  15 . The spindle nut  36  is fixed without rotation on the second pipe segment  16  and pushes this in or out of the first pipe segment  15 , depending on the direction of rotation of the spindle  35 . 
         [0049]    According to the embodiment shown in  FIG. 3 , the first pipe segment  15  permanently arranged on the trailer  3  is of larger diameter and the second pipe segment  16  smaller in diameter, so that the first pipe segment  15  at least partly receives the second pipe segment  16  coaxially. A rotation of the spindle nut  37  or the second pipe segment  16  relative to the first pipe segment  15  can be accomplished in particular by not having a round cross section for the pipe. Instead, square or polygon or elliptical cross sections are especially suitable. If the second pipe segment  16  is to be given a round cross section, axially running rails can also be used to brace the pipe wall against rotation. 
         [0050]      FIG. 4  shows a schematic top view of an articulated train formed from tractor vehicle  2  and trailer  3 . The tractor vehicle  2  and the trailer  3  are outfitted with an ABS  12 , in which a speed signal can be picked off at any time. The ABS  12  here serves as a speed pickup  9  for the electronic controller  8 . This embodiment is advantageous in that the trailer  3  does not need its own speed sensor  11  to detect the actual speed of travel. 
         [0051]    As further input quantities, the electronic controller  8  obtains data from another signal generator  18  in the form of two distance sensors  19  located on the front end  20  of the trailer  3 . The distance sensors  19  are each pointed in the direction of travel of the trailer  3  and detect the shortest distance x (see  FIG. 1 ) from the back side  21  of the tractor vehicle  2  on opposite sides of the hitch  4 . 
         [0052]    As soon as one of the distance sensors  19  recognizes a drop below the predetermined minimum distance, the electronic controller  8  places the actuator  17  in motion (see  FIGS. 2 and 3 ), which increases the length of the hitch  4  and thus the gap  1  by moving apart the first and second pipe segments  15 ,  16 . To prevent trailer  3  and tractor vehicle  2  from bumping together, a telescoping of the hitch  4  should occur when the minimum distance is passed, regardless of the detected speed of travel of the articulated train. 
         [0053]    The brake system  31  regulated by the ABS  12  can likewise function as an additional signal generator  18 . As soon as the driver activates the brake system  31 , the electronic controller  8  also receives a corresponding signal, which can be used to increase the distance x between tractor vehicle  2  and trailer  3  by a telescoping of the hitch  4 . When a sharp braking is initiated, the brake system  31  is the first in time to be involved in the process, so that a signal is available very early to the electronic controller  8  to increase the distance x regardless of the actually measured speed of the articulated train. 
         [0054]      FIG. 5  shows an alternative embodiment of the system of the invention, in which the minimum distance between trailer  3  and tractor vehicle  2  is determined indirectly by a change in the relative angle between trailer  3  and tractor vehicle  2 . 
         [0055]    If the trailer is an articulated trailer  3 , it will have a bearing rim  23  beneath its cargo space  43 . A change in the angle of rotation α 1  of the bearing rim  23  relative to straight travel is measured by the angle sensor  22  and relayed to the electronic controller  8 , located inside the hitch  4 . When a given maximum angle of rotation α 1  is exceeded, an extension of the hitch  4  occurs thanks to the electronic controller  8 . On the other hand, the hitch  4  can be shortened upon passing below the maximum angle of rotation α 1 . 
         [0056]    In the embodiment of  FIG. 5 , the CAN bus  13  serves as the speed pickup  9  for the electronic controller  8 . 
         [0057]    In  FIG. 6 , an angle measurement by means of an angle sensor  22  in the form of a steering sensor  24  likewise takes place. In this case, however, due to the hitch  4  rigidly engaging with the trailer  3 , the angle sensor  22  is arranged not on the trailer  3 , but instead on the tractor vehicle  2 , and it measures the steering angle α 2 . The steering angle α 2  can be picked off in particular from the steering wheel  25 , the steering linkage  26 , or parts of the steering transmission  27 , especially transmission gears. The measured value found in this way is transmitted wirelessly or by data cable from the tractor vehicle  2  to the electronic controller  8  arranged on the trailer  3 . 
         [0058]    A load sensor  32  arranged on the trailer  3  detects the cargo condition and provides a corresponding measured value to the electronic controller  8 . Under full cargo load, the electronic controller  8  can adjust a correspondingly larger distance x in the context of given limit values and thereby compensate for load-shift reactions of the trailer  3 . The load sensor  32  is preferably arranged between one of the axles  10  and the cargo space  43 . 
         [0059]      FIG. 7  shows another alternative embodiment of the invention, in which the steering angle α 3  is detected directly by a steering angle sensor  29  arranged in the area of the steerable front wheels  30   a  of the tractor vehicle  2 . By the steering angle α 3  is meant the lateral position of the front wheels  30   a  relative to straight travel. The measured value determined at the tractor vehicle  2  is transmitted to the trailer  3  by means of data cable or wirelessly and provided to the electronic controller  8 . 
       LIST OF REFERENCE SYMBOLS 
       [0000]    
       
           1  gap 
           2  tractor vehicle 
           3  trailer 
           4  hitch 
           5  tension tube 
           6  tension lug 
           7  actuator 
           8  electronic controller 
           9  speed pickup 
           10  axle, trailer 
           11  speed sensor 
           12  ABS 
           13  CAN bus 
           14  force measuring element 
           15  first pipe segment 
           16  second pipe segment 
           17  subassembly 
           18  signal generator 
           19  distance sensor 
           20  front side, trailer 
           21  back side, tractor vehicle 
           22  angle sensor 
           23  bearing rim 
           24  steering sensor 
           25  steering wheel 
           26  steering linkage 
           27  steering transmission 
           28  part of steering transmission 
           29  steering angle sensor 
           30   a  front wheel, tractor vehicle 
           30   b  rear wheel, tractor vehicle 
           31  brake system 
           32  load sensor 
           33  bolt coupling 
           34   a  front wheel, trailer 
           34   b  rear wheel, trailer 
           35  pressurized fluid cylinder 
           36  spindle 
           37  spindle nut 
           38  mounting bracket 
           39  boreholes 
           40  locking means 
           41  detent openings 
           42  cargo space, tractor vehicle 
           43  cargo space, trailer 
           44  servomotor 
         x distance tractor vehicle/trailer 
         α 1  angle of rotation, bearing rim 
         α 2  steering angle 
         α 3  steer angle