Abstract:
The invention relates to a vehicle seat or a vehicle cab with a suspension system comprising an upper closing part and a lower closing part which is deflectable in relation to the upper closing part, which closing parts are connected to each other in a resilient manner by means of a suspension element, and with a damping system for damping vibrations acting on at least one of the two closing parts, wherein the damping system and a distance levelling system for adjusting a distance between the upper closing part and the lower closing part have a common fluid actuator element controlled by compression and tension stages.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a national stage application under 35 U.S.C. 371 and claims the benefit of PCT Application No. PCT/EP2014/070305 having an international filing date of 24 Sep. 2014, which designated the United States, which PCT application claimed the benefit of German Patent Application No. 10 2013 110 926.8 filed 1 Oct. 2013, the disclosures of each of which are incorporated herein by reference in their entirety. 
     FIELD 
     The invention relates to a vehicle seat or a vehicle cab, having a suspension device comprising an upper end part and a lower end part that is deflectable relative to the upper end part, which parts are resiliently interconnected by means of a suspension element, and comprising a damping device for damping vibrations acting between the end parts. 
     Furthermore, the invention relates to a utility motor vehicle comprising a vehicle seat and comprising a vehicle cab. 
     BACKGROUND 
     Generic vehicle seats or vehicle cabs by means of which the ride comfort in particular of utility motor vehicles can be considerably improved are well known from the prior art. 
     SUMMARY 
     The object of the present invention is to support generic vehicle seats or vehicle cabs respectively in a structurally simpler manner relative to a vehicle body while providing improved seating comfort and ride comfort respectively. 
     The object of the invention is solved by a vehicle seat or a vehicle cab having the features indicated in claim  1 . 
     The invention expands on the generic prior art in that the damping device and a distance-adjusting device for adjusting a distance between the upper end part and the lower end part comprise a common actuator fluid element controlled by pressure stages and tension stages, as a result of which a suspension system can be provided which is constructed in a correspondingly simple manner. 
     Advantageously, at least parts of the damping device and the distance-adjusting device are implemented in a structurally simple manner by means of the common actuator fluid element controlled by pressure stages and tension stages, and therefore these devices can be constructed using much fewer components in conjunction with a fluid-conveying system. 
     Within the meaning of the invention, the present distance-adjusting device is a height-adjusting device that operates in the vertical direction, and therefore the upper end part can be moved relative to the lower end part in a vertical deflection direction by means of the common actuator fluid element controlled by pressure stages and tension stages. 
     According to the invention, the actuator fluid element controlled by pressure stages and tension stages is arranged between the two end parts such that it can act on the upper of the two end parts in the vertical direction of the vehicle in both a vibration-isolating manner and a height-regulating manner. 
     As a result, a hydraulically acting damping and height-adjusting unit for a suspension system, in terms of a damping device together with height adjustment, and thus the entire substructure of the vehicle seat or the vehicle cab respectively can be implemented in an extremely structurally simple manner, in order to bring about corresponding vibration isolation and/or height adjustment exclusively or in an auxiliary manner. 
     Therefore, adjustment forces acting in the vertical direction of the vehicle can be generated in a structurally simple manner, as is explained in the following in greater detail, still by way of example. 
     In addition, this hydraulically acting damping and height-adjusting unit or the common actuator fluid element controlled by pressure stages and tension stages respectively can produce a linearly rising force characteristic curve or spring characteristic curve respectively over the entirety of the available suspension travel. 
     At this point, it is noted that the common actuator fluid element controlled by pressure stages and tension stages and the hydraulically acting damping and height-adjusting unit respectively can be constructed in a structurally very simple manner if the actuator fluid element comprises a hydraulic shock absorber element. 
     The object of the invention is furthermore solved by a utility motor vehicle having the features indicated in claim  11 . 
     The vehicle seat according to the invention or the vehicle cab according to the invention respectively can be advantageously used in particular in conjunction with utility motor vehicles, since the vehicle driver is better protected against premature fatigue owing to the considerably improved seating comfort and ride comfort respectively. Furthermore, in terms of utility motor vehicles, there is also great interest in solutions for corresponding suspension systems that are structurally simple and thus less susceptible to faults. This also applies in particular with regard to agricultural utility motor vehicles. 
     The suspension system which is provided in the vehicle seat or the vehicle cab respectively therefore comprises the suspension device and the damping device, and in the present case a height-adjusting device is also implied. 
     The suspension device may comprise one or more suspension elements, which may for example be designed as a mechanical suspension element and/or preferably as a pneumatic suspension element. 
     The upper end part of the suspension device may for example be attached to the underside of a seat part of the vehicle seat or to the underside of the vehicle cab, or may be formed directly from this respective underside. 
     In this respect, the lower end part of the suspension device may for example be fastened to a component of a vehicle body or may be formed directly by said body. 
     In any case, the upper end part is mounted on a substructure of the vehicle seat or the vehicle cab respectively relative to the lower end part such that said upper end part can be deflected relative to the lower end part in the vertical deflection direction, i.e. in the vertical direction of a vehicle, in particular a utility motor vehicle, in particular if external vibrations are acting on the vehicle seat or vehicle cab respectively. 
     In this respect, the upper end part is a component of the suspension device that vibrates substantially vertically, the main vibration direction of which is oriented in the vertical direction of the vehicle, i.e. is vertical. 
     For this purpose, the suspension device is in particular equipped with a vertical suspension element which can act in the vertical direction of the vehicle in a resilient manner. 
     A deflection mechanism for deflecting the upper end part relative to the lower end part can be achieved very simply for example by means of a scissors type frame. However, it does not necessarily have to comprise a scissors type frame of this type. 
     In structural terms, it is however advantageous for the upper end part and the lower end part to be operatively interconnected by means of a scissors type frame. As a result, the upper end part is also guided in the vertical direction in a defined manner. 
     A preferred variant of the embodiment provides that the actuator fluid element is operatively connected to a controllable fluid-conveying device, which is in fluid connection with both the pressure-stage chamber and the tension-stage chamber of the actuator fluid element such that various height adjustments of the upper end part can be carried out by controlling the power of the controllable fluid-conveying device. 
     As a result of this fluid connection, the upper end part can be actively raised or lowered relative to the lower end part by the fluid-conveying device or by a fluid-conveying flow generated thereby respectively, in particular depending on in which conveying direction the fluid-conveying device conveys the fluid. As a result, the fluid-conveying system can be advantageously further developed. 
     In this respect, it is also particularly advantageous for the fluid-conveying device to be reversible in terms of its conveying direction. 
     Alternatively, two fluid-conveying devices having opposite conveying directions could also be integrated into a correspondingly designed fluid-conveying system. 
     In particular in this context, it is advantageous for the actuator fluid element to be operatively connected to a controllable fluid-conveying device which is in fluid connection with both the pressure-stage chamber and the tension-stage chamber of the actuator fluid element such that the fluid can be conveyed out of either the pressure-stage chamber or the tension-stage chamber of the actuator fluid element depending on the conveying direction of the fluid-conveying device and/or out of another fluid reservoir of the fluid-conveying system into either the pressure-stage chamber or the tension-stage chamber. As a result, the upper end part can be actively moved, in particular raised or lowered, relative to the lower end part very precisely in two opposite directions. 
     A particularly preferred variant of the embodiment provides that the actuator fluid element is operatively connected to a flow-control valve element, which is in fluid connection with the actuator fluid element and a controllable fluid-conveying device such that the power of the pressure stage or the tension stage can be additionally modulated by means of this flow-control valve element. As a result of this too, the fluid-conveying system can again be simplified in terms of structure. 
     Here, the flow-control valve element is a device for modulating damper performance at both the pressure stage and the tension stage of the actuator fluid element. 
     Preferably, the flow-control valve element is implemented as an electrically operable throttle valve in the form of a proportional flow control valve, since the flow-control valve element can be actuated very rapidly by this means, as a result of which corresponding pressure changes in the pressure-stage or tension-stage chamber respectively of the flow-control valve element can in turn be achieved very rapidly. It is clear that as an alternative, flow-control valve elements that are operable in different ways may also be used. 
     If the flow-control valve element is in fluid connection with the actuator fluid element and the controllable fluid-conveying device such that the power of the pressure stage and the tension stage can be additionally modulated by means of this flow-control valve element while not affecting the power of the fluid-conveying device, the response behaviour of the actuator fluid element can be improved further. 
     In the present case, vibrations can be very effectively isolated if the flow-control valve element is in fluid connection with the actuator fluid element and the controllable fluid-conveying device such that vibrations of one of the end parts can be isolated by means of the flow-control valve element. 
     If a low-pressure connection of the fluid-conveying device is in fluid connection with the tension-stage chamber by means of a low-pressure line and a high-pressure connection of the fluid-conveying device is in fluid connection with the tension-stage chamber by means of a high-pressure line, or vice versa, the low-pressure line and the high-pressure line being fluidically interconnected by means of an electrically operable proportional flow control valve, as well as an active height adjustment, vibration isolation can also be carried out in a manner which is particularly simple structurally and in terms of process. 
     In this case, the low-pressure side and high-pressure side switch depending on the conveying direction of the fluid-conveying device. 
     Here, the type and intensity of the control of the common actuator fluid element controlled by pressure stages and tension stages can be influenced by means of a control algorithm of a corresponding open-loop and/or closed-loop control device. 
     In this respect, it is advantageous for there to be an open-loop and/or closed-loop control device for adjusting a fluid-conveying device and/or a flow-control valve element depending on a load acting on the upper end part. 
     Specifically, adjusting the fluid-conveying device and/or the flow-control valve element depending on the type and intensity of the external forces acting on the actuator fluid element makes it possible to significantly increase the seating comfort. 
     The common actuator fluid element controlled by pressure stages and tension stages may operate particularly efficiently if the open-loop and/or closed-loop control device comprises an acceleration-measuring sensor which is arranged on the face of the lower end part and is intended for detecting accelerations acting on the lower end part. 
     Yet more precise open-loop or closed-loop control of the common actuator fluid element controlled by pressure stages and tension stages can be achieved if the open-loop and/or closed-loop control device comprises a position-measuring sensor for detecting a distance and/or a distance variation between the upper and the lower end part. 
     The present invention provides an actively controlled suspension system using very simple means, which suspension system additionally has the common actuator fluid element controlled by pressure stages and tension stages, which can temporarily adjust a set height level, in particular a set height of a vehicle seat. On the other hand, it can also be actively involved in isolating vibrations. In this respect, this means that the hydraulic damping and height-adjusting unit is also produced to be particularly simple in structure. 
     Here, a conventional air suspension element or the like may be used as basic suspension, while the common actuator fluid element controlled by pressure stages and tension stages can act in the vertical suspension direction in an auxiliary manner as an additional active component or additional active assembly. 
     The controllable fluid-conveying device is preferably in the form of a high-pressure pump which is driven by an electric motor and has a variable rotational speed and ideally a rotational direction reversal. It has, for example, a defined fluid discharge rate in cm 3 /revolution, which introduces a specific conveyed fluid quantity produced thereby into the pressure-stage chamber or pressure-stage side respectively or into the tension-stage chamber or tension-stage side of the actuator fluid element at a corresponding rotational speed respectively, as a result of which an extension force (pressure-stage side) or retraction force (tension-stage side) acting on the upper end part is generated in accordance with the flow resistance inherent in the pressure-stage side or tension-stage side respectively. 
     When stopped, i.e. 0.0 l conveying capacity of the controllable fluid-conveying device, the actuator fluid element acts as a passive shock absorber, which in its basic design contains characteristic data for the tension-stage and pressure-stage power, as is also used in passive, commercially available vehicle seats. 
     When the controllable conveying device is activated, in accordance with its rotational speed and its conveying direction, a defined conveyed quantity is transferred from the tension-stage side to the pressure-stage side, or vice versa, by pumping. The flow resistance produced depending on conveyed quantity at the valve holes in the pressure stage brings about an extension force or vertically acting supporting force respectively on the piston-rod side of the actuator fluid element. This means that the upper end part of the suspension device to which a load is applied is raised by a value resulting therefrom. The flow resistance produced depending on conveyed quantity at the tension stage brings about an retraction force on the opposite piston-rod side, as a result of which the upper end part can be lowered quickly relative to the lower end part or brought closer to the lower end part respectively. 
     This active force or extension or retraction force respectively is used on the one hand for height adjustment and on the other hand as a control variable for influencing the vibration isolation and also to increase or decrease the damper performance of the actuator fluid element. 
     As an additional feature, in the present case the flow-control valve element is provided, which additionally influences the isolation of the introduction of vibrations. Here, the damper performance of the actuator fluid element, which is defined as hard in the passive state, is set to be softer. This means that the flow resistance between the pressure stage and tension stage of the actuator fluid element is reduced by means of the flow-control valve element. 
     Further advantages, aims and properties of the present invention are explained with reference to the drawings and the following description, in which a vehicle seat substructure of a utility motor vehicle seat comprising a common actuator fluid element, controlled by tension stages and pressure stages, of a damping device and of a distance-adjusting device is shown and described by way of example. In the drawings: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic perspective view of vehicle seat substructure comprising a common actuator fluid element, controlled by tension stages and pressure stages, of a damping device and of a distance-adjusting device, the actuator fluid element being arranged between two end parts of a suspension device such that it acts on one of the two end parts in the vertical direction of the vehicle in both a vibration-isolating manner and a height-adjusting manner, 
         FIG. 2  schematically shows a first fluid circuit diagram of a first possible fluid-conveying system of the actuator fluid element from  FIG. 1 ; 
         FIG. 3  schematically shows a further fluid circuit diagram of a further possible fluid-conveying system of the actuator fluid element from  FIG. 1 , and 
         FIG. 4  schematically shows a graph having different spring characteristic curves of the suspension device from  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION 
     The vehicle seat substructure  1 , shown in  FIG. 1 , of a vehicle seat (not shown here in greater detail) comprises a suspension device  2 , which is characterized by an upper end part  3  and a lower end part  4  which, in this embodiment, are both coupled to one another by a scissors type frame  5  in a height-adjustable manner. 
     The scissors type frame  5  substantially consists of two pairs of scissor arms  6  and  7 , which in turn each comprise a first scissor arm  8  and  9  respectively and a second scissor arm  10  and  11 . 
     The first scissor arms  8  and  9  respectively are on the one hand rotationally mounted on the lower end part  4  by means of a common lower fixed-bearing device  12 . On the other hand, they are mounted on the upper end part  3  in a linearly movable manner by means of a common upper movable-bearing device  13 . 
     The second scissor arms  10  and  11  behave similarly, and are rotationally mounted on the upper end part  3  by means of a common upper fixed-bearing device  14  and are mounted on the lower end part  4  in a linearly movable manner by means of a common lower movable-bearing device  15 . 
     The first and second scissor arms  8 ,  10  and  9 ,  11  respectively of the respective pairs of scissor arms  6  and  7  respectively are rotationally interconnected by means of pivotal points  16  (only explicitly provided with a reference numeral at this point). 
     Furthermore, the suspension device  2  also comprises a suspension element  19 , by means of which the two end parts  3  and  4  are resiliently interconnected. In this embodiment, the suspension element  19  is provided by a pneumatic-spring element. 
     When installed, the upper end part  3  is integrated in the vehicle seat on the seat-part side and the lower end part  4  is integrated in the vehicle seat on the vehicle-body side such that the upper end part  3  can rebound and deflect respectively relative to the lower end part  4  in the vertical direction  21  of the vehicle, i.e. vertically, when a corresponding external stimulus acts on the vehicle seat or on the vehicle respectively. 
     In order for it to be possible to at least partially isolate the vibrations of the upper end part  3 , the vehicle seat substructure  1  further comprises a damping device  25  comprising a hydraulic shock absorber element  26 . 
     The hydraulic shock absorber element  26  is attached by its cylinder part  27  to a cross bar  28  of the common lower movable-bearing device  15  and by a piston part  29  (see  FIG. 2 ) to the first scissor arm  9  of the second pair of scissor arms  7 . 
     In this embodiment, the hydraulic shock absorber element  26  forms the basis for the claimed actuator fluid element  31  controlled by pressure stages  30  and tension stages  30 A, by means of which element active vibration isolation can additionally be achieved, and furthermore height adjustment of the upper end part  3  relative to the lower end part  4  can also be achieved. 
     For this purpose, the actuator fluid element  31  controlled by pressure stages  30  and tension stages  30 A is arranged between the two end parts  3 ,  4  such that it can act on the upper end part  3  in the vertical direction  21  of the vehicle in an actively vibration-isolating manner and also in a height-adjusting manner. 
     In this respect, the vehicle seat substructure  1  not only comprises a simple damping device  25  but also a distance-adjusting device (not specifically provided with a reference numeral here) for adjusting the distance  32  between the upper end part  3  and the lower end part  4 , the damping device  25  and the distance-adjusting device together comprising the actuator fluid element  31  controlled by pressure stages  30  and tension stages  30 A. This means that the vehicle seat substructure  1  is extremely compact, despite its functionality being considerably enhanced. 
     Furthermore, a controllable fluid-conveying device  33  for conveying a fluid, this being a hydraulic fluid  46  as in the present embodiment, and a flow-control valve element  34  are also provided in the vehicle seat substructure  1 . 
     The fluid-conveying device  33  consists of a hydraulic pump  35 , which is continuously driven by an electric motor  36 , the fluid-conveying device  33  having two opposite conveying directions  59  and  59 A (see drawings,  59 ,  59 A), as will be explained in more detail below. 
     In this case, the flow-control valve element  34  is designed as an electrically operable throttle valve in the form of a proportional flow control valve  37 . 
     The controllable fluid-conveying device  33 , the flow-control valve element  34  and the actuator fluid element  31  controlled by pressure stages  30  and tension stages  30 A respectively are fluidically interconnected by means of a corresponding fluid pipeline system  38  (only provided with a reference numeral in  FIG. 1  by way of example). 
     In the arrangement of the first fluid-conveying system  39  shown in  FIG. 2  according to the first flow diagram  39 A, the actuator fluid element  31  controlled by pressure stages  30  and tension stages  30 A is arranged on the left. To the right thereof, there is the flow-control valve element  34 , and the controllable fluid-conveying device  33  is arranged further to the right and has two opposite conveying directions  59  and  59 A respectively. 
     The actuator fluid element  31  controlled by pressure stages  30  has an external housing  42  which forms a hydraulic-fluid tank  41  and also defines the actual working cylinder  43  in which the piston part  29  consisting of the piston head  44  and the piston rod  45  moves. 
     Some of the hydraulic fluid  46  is stored in the hydraulic-fluid tank  41 . Furthermore, the hydraulic-fluid tank  41  also provides a gas-volume compensation space  47 . 
     The working cylinder  43  comprises a pressure-stage chamber  48 , by means of which the pressure stage  30  of the actuator fluid element  31  is implemented. The corresponding tension stage  30 A is produced inter alia by means of a tension-stage chamber  49  of the working cylinder  43 . 
     Furthermore, the actuator fluid element  31  also comprises a rising pipe  50  comprising a pressure-compensation valve  51  for pressure compensation within the tension-stage chamber  49 , in particular when the pressure stage  30  is activated, it then being possible for hydraulic fluid  46  to flow out of the hydraulic-fluid tank  41  into the tension-stage chamber  49  through this rising pipe  50 . 
     For pressure compensation in the pressure-stage chamber  48  when the tension stage  30 A is activated, a foot valve  52  is provided through which hydraulic fluid  46  can flow out of the hydraulic-fluid tank  41  into the pressure-stage chamber  48 , but not in the other direction. 
     A pressure-stage/tension-stage valve  53  of the actuator fluid element  31  is also integrated in the piston head  44 , by means of which valve a basic tension stage/pressure stage is inherent in the actuator fluid element  31  as a passively acting hydraulic shock absorber element. 
     As already mentioned above, the actuator fluid element  31  is connected, by its cylinder part  27 , to the cross bar  28  and thus also to the lower end part  4  by means of a lower connecting point  53 , while said element is connected, by its piston part  29 , to the first scissor arm  9  of the second pair of scissor arms  7  and thus also to the upper end part  3  by means of an upper connecting point  54 . 
     The actuator fluid element  31  comprises, at its tension-stage chamber  49 , a tension-stage chamber connection  56 , with which a first fluid pipeline  57  is in fluid connection. This first fluid pipeline  57  represents a fluid connection between the tension-stage chamber  49  and a first connection  58  of the hydraulic pump  35 , and therefore the hydraulic fluid  46  can be conveyed out of the tension-stage chamber  49  by means of the controllable fluid-conveying device  33  in the conveying direction  59  of the hydraulic pump  35 . In this case, the first fluid pipeline  57  is a low-pressure line and the first connection  58  is a low-pressure connection. 
     A further fluid pipeline  61  leads from a further connection  60  of the hydraulic pump  35  to a pressure-stage chamber connection  62 , and therefore the hydraulic fluid  46  conveyed out of the tension-stage chamber  49  can be further conveyed into the pressure-stage chamber  48 , as a result of which the piston part  29  is accordingly pushed out of the cylinder part  27 . As a result, the upper end part  3  is raised in the vertical direction  21  of the vehicle and is thus moved further away from the lower end part  4 . In this case, the further fluid pipeline  61  is a high-pressure line and the further connection  60  is a high-pressure connection. 
     It is precisely the reverse case if the hydraulic fluid  46  is conveyed in the conveying direction  59 A, which is opposite the first conveying direction  59 . In this further case, the first fluid pipeline  57  becomes a high-pressure line and the further fluid pipeline  61  becomes a low-pressure line. 
     A connecting line  63  is also connected between the first fluid pipeline  57  and the further fluid pipeline  61 , by means of which connecting line the flow-control valve element  34  is in fluid connection between the actuator fluid element  31  and the controllable fluid-conveying device  33 . More precisely, the flow-control valve element  34  is connected in parallel with the controllable fluid-conveying device  33  with respect to the actuator fluid element  31 . Therefore, the flow resistance at the actuator fluid element  31  can be changed by means of the flow-control valve element  34 , independently of the conveying direction  59  or  59 A respectively of the fluid-conveying device  33 , as a result of which an influence on the vibration-isolating capacity of the actuator fluid element  31  can be achieved. 
     An overflow fluid line  64  is also provided between the hydraulic pump  35  and the hydraulic-fluid tank  41 . 
     A feed line  65  comprising a non-return valve  66  is also arranged between the first fluid pipeline  57  and the hydraulic-fluid tank  41 ; likewise, a further feed line  67  comprising a further non-return valve  68  is provided between the further fluid pipeline  61  and the hydraulic tank  41 . As a result, if necessary, hydraulic fluid  46  can be directly conveyed out of the hydraulic-fluid tank  41  into the pressure-stage chamber  48  or into the tension-stage chamber  49  by means of the hydraulic pump  35 . 
     In the further arrangement of the first fluid-conveying system  40  shown in  FIG. 3  according to the first flow diagram  40 A, the flow-control valve element  34  is missing (see in particular FIG.  2 ). Otherwise, the set-up of the arrangement from  FIG. 2  is identical to the set-up of the further arrangement shown in  FIG. 3 . In this respect, the further arrangement is not explained again, in order to avoid repetitions. The function of the flow-control valve element  34  (not present) is achieved at least in part by way of the reversal of the conveying direction  59  or  59 A respectively. 
     The arrangements shown in the flow diagrams  39 A and  40 A each represent a first advantageous damping and height-adjusting unit  90  of the invention. In this respect, this hydraulically acting damping and height-adjusting unit  90  can not only be considered to be an additional functional assembly of the damping device  25 , but at the same time is also the height-adjusting and distance-adjusting device respectively (not explicitly provided with a reference numeral here) for adjusting the distance  32  with respect to the upper end part  3  and the lower end part  4  in the vertical direction  21  of the vehicle. 
     It is also advantageous for linearly rising force characteristic curves  75  and  79  to be provided over the entirety of the available suspension travel s, as is also shown by the graph  70  shown in  FIG. 4 . 
     In the graph  70 , the existing suspension travel s is plotted in millimeters on the abscissa  71 , a desired average vertical height level  72  being at 90 mm, so that the upper end part  3  can ideally cover both a vertically downwardly available negative suspension travel and a vertically upwardly available positive suspension travel of 90 mm in each case. 
     The force F counteracting a load on the upper end part  3  is plotted on the ordinate  73  of the graph  70  in Newtons. 
     The central spring characteristic curve  74  plotted on this graph  70  is that of the suspension element  19  which extends through the point of intersection  76  of the line  77  produced by the load of 1000 N and the further line  78  produced by the vertical height level  72  and which progresses logarithmically at the start of the suspension travel s and exponentially at the end of the suspension travel s; in between, the central spring characteristic curve  74  of the suspension element  19  rises linearly. 
     The force characteristic curve  75  extending above the central spring characteristic curve  74  contains the effect of activating the pressure stage  30  of the actuator fluid element  31  controlled by pressure stages  30  and tension stages  30 A, this upper force characteristic curve  75  extending completely linearly over the entirety of the suspension travel s. 
     The upper force characteristic curve  75  therefore shows the upper target values for the forces generated by the damping and height-adjusting unit  90  in the vertical direction  21  of the vehicle. 
     The lower force characteristic curve  79  extending below the central spring characteristic curve  74  describes the forces generated by the damping and height-adjusting unit  90  in the vertical direction  21  of the vehicle with respect to lower target values. The lower force characteristic curve  79  contains the effect of activating the tension stage  30 A of the actuator fluid element  31  controlled by pressure stages  30  and tension stages  30 A, this lower force characteristic curve  79  also extending completely linearly over the entirety of the suspension travel s. 
     It can be clearly seen from the graph  70  that in particular the suspension element  19  serves as a basis for receiving a basic load which acts on the suspension as a mass. The maximum possible spring force is in particular specified by the dimension of the damping and height-adjusting unit  90 , which is 200 N in the vertical direction  21  of the vehicle in the graph  70  shown. In the event of temporary level variations which may occur for example by the drivers weight shifting when driving uphill, downhill or at an angle, depending on the direction and intensity of the variation, the forces generated by the damping and height-adjusting unit  90  can be increased or decreased. In the present damping and height-adjusting unit  90 , the forces generated thereby are actively utilised to influence external introductions of force that are fed into the suspension system. The damping and height-adjusting unit  90  may on the one hand work with the introduction of force, i.e. a retraction force is caused or a supporting force respectively for carrying the mass is reduced, as a result of which the upper end part  3  is actively lowered relative to the lower end part  4 . On the other hand it may also work against the introduction of force, the supporting force being accordingly increased, as a result of which the upper end part  3  is actively raised relative to the lower end part  4 . 
     The available force, for example 200 N, may be defined by the dimension of the hydraulic pump  35  with the following parameters: pressure (bar) and conveyed quantity (cm 3 /rev). The dynamics or control force respectively of the adjustment is mainly dependent on the hydraulic fluid volume introduced into the actuator fluid element  31  via the fluid-conveying device  33 , which volume is conveyed from the tension-stage chamber  49  into the pressure-stage chamber  48 , or vice versa. 
     The type and intensity of the control is taken as a basis in a control algorithm of a correspondingly designed open-loop and/or closed-loop control device (not explicitly shown here). 
     By means of the open-loop and/or closed-loop control device, the damping and height-adjusting unit  90  may be accordingly adjusted depending on a load acting on the upper end part  3 . 
     For this purpose, the open-loop and/or closed loop control device on the one hand comprises an acceleration-measuring sensor  96  which is arranged on the face  95  of the lower end part  4  and is intended for detecting accelerations acting on the lower end part  4  and on the other hand comprises a position-measuring sensor  97  for detecting the current distance  32  and/or a corresponding distance variation between the upper and the lower end part  3 ,  4  (see  FIG. 1 ). 
     It will be understood that the embodiments described above are only first configurations of the invention. The configuration of the invention is therefore not limited to these embodiments. 
     At this point, reference is explicitly therefore once again made to the fact that the above-described vehicle seat substructure  1  may alternatively also be used as a vehicle cab substructure, provided that it is dimensioned accordingly. 
     All of the features disclosed in the application documents are claimed as being essential to the invention provided that they are novel over the prior art either individually or in combination. 
     LIST OF REFERENCE NUMERALS 
     
         
           1  vehicle seat substructure 
           2  suspension device 
           3  upper end part 
           4  lower end part 
           5  scissors type frame 
           6  first pair of scissor arms 
           7  second pair of scissor arms 
           8  first scissor arm of the first pair of scissor arms 
           9  first scissor arm of the second pair of scissor arms 
           10  second scissor arm of the first pair of scissor arms 
           11  second scissor arm of the second pair of scissor arms 
           12  common lower fixed-bearing device 
           13  common upper movable-bearing device 
           14  common upper fixed-bearing device 
           15  common lower movable-bearing device 
           16  pivotal points 
           19  suspension element 
           21  vertical direction of the vehicle 
           25  damping device 
           26  hydraulic shock absorber element 
           27  cylinder part 
           28  cross bar 
           29  piston part 
           30  pressure stage 
           30 A tension stage 
           31  actuator fluid element 
           32  distance 
           33  fluid-conveying device 
           34  flow-control valve element 
           35  hydraulic pump 
           36  electric motor 
           37  proportional flow control valve 
           38  fluid pipeline system 
           39  first fluid-conveying system 
           39  first flow diagram 
           40  further fluid-conveying system 
           40 A further flow diagram 
           41  hydraulic-fluid tank 
           42  external housing 
           43  working cylinder 
           44  piston head 
           45  piston rod 
           46  hydraulic fluid 
           47  gas-volume compensation space 
           48  pressure-stage chamber 
           49  tension-stage chamber 
           50  rising pipe 
           51  pressure-compensation valve 
           52  foot valve 
           53  pressure-stage/tension-stage valve 
           54  lower connecting point 
           55  upper connecting point 
           56  tension-stage chamber connection 
           57  first fluid pipeline 
           58  first connection 
           59  first conveying direction 
           59 A second conveying direction 
           60  further connection 
           61  further fluid pipeline 
           62  pressure-stage chamber connection 
           63  connecting line 
           64  overflow fluid line 
           65  feed line 
           66  non-return valve 
           67  further feed line 
           68  further non-return valve 
           70  graph 
           71  abscissa 
           72  height level 
           73  ordinate 
           74  central spring characteristic curve 
           75  upper force characteristic curve 
           76  point of intersection 
           77  line produced 
           78  further line produced 
           79  lower force characteristic curve 
           90  damping and height-adjusting unit 
           95  face 
           96  acceleration-measuring sensor 
           97  travel-measuring sensor