Abstract:
An active roll stabilization system of a vehicle having an axle with at least two wheels, wherein the axle is provided with a roll stabilizer that is actuated by means of a hydraulic device. The hydraulic device is actuated and controlled by at least one pressure control valve with a preselected pressure level by a pressure supply device, such as a pump. In order to reduce the costs for producing such an active roll stabilization system, the pressure control valve is pilot-operated by a pressure control pilot valve.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This is a continuation of International Application Serial No. PCT/DE2005/000006, with an international filing date of Jan. 7, 2005, and designating the United States, the entire contents of which is hereby incorporated by reference to the same extent as if fully rewritten. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to an apparatus for active roll stabilization of a vehicle, with at least one axle having at least two wheels, which axle is provided with a transverse stabilizer that is operable with the help of a hydraulic apparatus that can be subjected to a pre-selected pressure level, through at least one pressure limiting valve, by means of a pressure supply unit, such as a pump. 
   2. Description of the Related Art 
   Such roll stabilization devices are also referred to as anti-roll systems or roll stabilization systems. In conventional anti-roll systems, directly controlled pressure-limiting and directional valves are employed. 
   An object of the invention is to provide an apparatus for active roll stabilization of a vehicle, with at least one axle having at least two wheels, which axle is provided with a transverse stabilizer that is operable with the help of a hydraulic apparatus that can be subjected to a pre-selected pressure level through at least one pressure limiting valve, by means of a pressure supply unit such as a pump, which can be produced economically. 
   SUMMARY OF THE INVENTION 
   The object is achieved with an apparatus for active roll stabilization of a vehicle, with at least one axle having at least two wheels, which axle is provided with a transverse stabilizer that is operable with the help of a hydraulic apparatus that can be subjected to a pre-selected pressure level through at least one pressure limiting valve, by means of a pressure supply unit, such as a pump. The at least one pressure limiting valve is controlled by a pilot valve. In conjunction with the present invention, it was discovered that the magnet coils used for direct activation of the pressure limiting valves in conventional anti-roll systems cause a not-insignificant part of the cost. In comparison, the present invention offers the advantage that economical pilot valves that are available on the market can be used. 
   The object mentioned above is achieved with an apparatus for active roll stabilization of a vehicle, with at least two axles having at least two wheels, each axle of which is provided with a transverse stabilizer. The transverse stabilizers are operable with the help of hydraulic devices that can be subjected to various pressure levels by a pressure supply unit, such as a pump, through pressure limiting valves. The pressure limiting valves assigned to the hydraulic devices are pilot-controlled by at least two pressure limiting pilot valves connected in series. The series connection of the pressure limiting pilot valves provides the advantage that an additional inlet orifice which would otherwise be necessitated by the pilot circuit can be dispensed with. 
   A preferred exemplary embodiment of the roll stabilization apparatus is characterized in that a direction switching valve, for example a 7/2 directional valve that is used for direction-dependent switching of the hydraulic devices, is pilot-controlled by a direction switching pilot valve. That makes it possible to reduce the manufacturing costs further. 
   A further preferred exemplary embodiment of the roll stabilization apparatus is characterized in that a fail-safe valve, which is pilot-controlled by a fail-safe pilot valve, is connected between the direction switching valve and one of the hydraulic devices. That makes it possible to further reduce the manufacturing costs. 
   A further preferred exemplary embodiment of the roll stabilization apparatus is characterized in that a direction switching valve, for example a 7/2 directional valve that is used for direction-dependent switching of the hydraulic devices, and a fail-safe valve that is connected between the direction switching valve and one of the hydraulic devices, are pilot-controlled by a single on/off pilot valve. The advantage here consists partly in the elimination of an additional point of leakage in a pilot circuit, and partly in the elimination of an additional pilot valve. 
   A further preferred exemplary embodiment of the roll stabilization apparatus is characterized in that the on/off pilot valve has three switching positions. In the first state of the on/off pilot valve neither the direction switching valve nor the fail-safe valve is switched on. In the second state of the on/off pilot valve only the fail-safe valve is switched on, and in the third state of the on/off pilot valve both the fail-safe valve and the direction switching valve are switched on. The direction switching valve and the fail-safe valve are preferably spring-loaded directional valves with two switching positions. In the first state the on/off pilot valve can be electrically un-powered. Then both the direction switching valve and the fail-safe valve are in their home position, in which they are held, for example, by a pre-tensioned spring, as long as a directional valve used to operate the magnet is un-powered. In the second state, a medium voltage is applied to the on/off pilot valve so that the pilot pressure overcomes the pre-tensioning of the spring of the fail-safe valve, and the fail-safe valve switches from its home position to a second position. At the medium voltage the resulting pressure force on the direction switching valve is sufficient to overcome the latter&#39;s stronger pre-tensioning, so that the direction switching valve remains in its home position. When a higher voltage is applied to the direction switching valve, and hence to the higher pressure, the direction switching valve is also switched from its home position to a second position. The fail-safe valve remains in its second position. 
   A further preferred exemplary embodiment of the roll stabilization apparatus is characterized by a pressure reducing valve, which sets the pilot pressure level to, for example, 5 bar. The total pilot pressure valve is operated parallel to the pressure limiting valves for the actuators. 
   A further preferred exemplary embodiment of the roll stabilization apparatus is characterized in that the total pilot pressure reducing valve is subjected to the pressure from a tank from which the pressure supply unit is supplied. The intentional returning of the tank pressure to the spring chamber of the total pilot pressure reducing valve causes the total pilot pressure to be raised by the amount of the tank pressure level, so that a regulating differential pressure of, for example, 5 bar is available. That enables the influence of the tank pressure level on the pilot circuit to be eliminated. 
   A further preferred exemplary embodiment of the roll stabilization apparatus is characterized in that the pressure limiting valves and/or the direction switching valve and/or the fail-safe valve are subjected to the pressure from a tank from which the pressure supply unit is supplied. The intentional returning of the tank pressure to the spring chamber of the pressure limiting valve, the direction switching valve, and/or the fail-safe valve, causes the total pilot pressure to be raised by the amount of the tank pressure level, so that a regulating differential pressure of, for example, 5 bar is available. 
   A further preferred exemplary embodiment of the roll stabilization apparatus is characterized in that all of the valves include valve pistons that are guided in a cast valve block in which channels are cast for supplying hydraulic medium and/or conducting it away. Conventional valves for motor vehicle use are constructed using so-called plug-in construction. There the valve piston is guided in a valve sleeve which is firmly connected to a magnet. The valve sleeve, in turn, is inserted into a valve block against which it is sealed with the help of O-rings. By guiding the valve piston directly in the valve block, both the valve sleeve and the O-rings can be dispensed with. 
   A further preferred exemplary embodiment of the roll stabilization apparatus is characterized in that various valves are connected with each other through cast channels. That has the advantage that complex and expensive reworking can be eliminated. 
   A further preferred exemplary embodiment of the roll stabilization apparatus is characterized in that valve actuator elements, control elements, sensor elements, hydraulic elements, and/or electronic elements, of a plurality of valves are combined in one unit and are shielded against the surroundings by one protective cover, in particular a protective pan. The protective cover offers the advantage that complicated and cost-intensive individual protection of the magnets and sensors can be eliminated. The protective cover shields the control elements from the outside, and at the same time ensures that no hydraulic medium escapes into the environment. 
   A further preferred exemplary embodiment of the roll stabilization apparatus is characterized in that the individual control elements, sensor elements, hydraulic elements, and/or electronic elements, are directly connected with each other electrically. By eliminating a cable tree with its multiplicity of plug-in connections, not only are the manufacturing costs reduced but the system reliability is also significantly increased. Internal cabling in the controller is not necessary, thanks to direct contacting of magnets, sensors, and the connector plug with the electronics. The sensors, for example pressure and displacement sensors, do not need housings, amplifiers, and evaluation units of their own. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional advantages, characteristics, and details of the invention are evident from the following description, in which various embodiments are described in detail with reference to the drawings. The characteristics mentioned in the claims and in the description can be essential to the invention individually or in any combination. The figures show the following: 
       FIG. 1 : a hydraulic circuit diagram of a conventional roll stabilization apparatus; 
       FIG. 2 : a hydraulic circuit diagram of a roll stabilization apparatus according to the invention, with valves controlled by pilot valves; 
       FIG. 3 : a hydraulic circuit diagram of a roll stabilization apparatus according to the invention, with two pressure limiting pilot valves connected in series; 
       FIG. 4 : a hydraulic circuit diagram of a roll stabilization apparatus according to the invention, with intentional returning of tank pressure; 
       FIG. 5 : a longitudinal section through a valve housing with a valve piston guided in it; and 
       FIG. 6 : a schematic depiction of a roll stabilization control apparatus according to the invention, in sectional view. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows the actual state of a standard system. The pressure supply unit is a suction-restricted radial piston pump  21  that supplies two different pressure levels through a cascade connection by means of two proportional pressure limiting valves  22  and  28 , which are connected as pressure differential valves. The pressure levels are monitored by pressure sensors  23  and  27 . For a turning motor  37  on the stabilizer on the front axle these pressure ranges are designated as  35  for the right side and  34  for the left side respectively; for a turning motor  36  on the stabilizer on the rear axle they are designated accordingly as  33  and  32 . The pressure on the rear axle must always be lower than the pressure on the front axle. These two pressure levels are switched when rounding curves, to the right or left depending on the direction, by means of a 7/2 directional valve  24 , which is also referred to as a direction switching valve, so that with synchronization the pressure in the turning motors is increased or reduced on either the right or the left side of the vehicle. The operation of direction switching valve  24  is monitored with the help of a switching position detection sensor  26 . In addition, in the front axle hydraulic line there is a fail-safe valve  25  whose function is to block the turning motor  37  of the front axle and switch the turning motor  36  of the rear axle to zero pressure in a fail-safe case if a valve jams or if the electric power fails. In addition, two feeder valves  29  and  30  are installed, which can connect pressure regions  35  and  34  of turning motor  37  on the front axle with the tank line and tank  31  in such a way that restricted free turning of turning motor  37  can occur via the leakage points in the turning motor itself through feeding of the volumetric and without cavitation problems. 
   Proportional pressure limiting valves  22  and  28  and 7/2 and 3/2 directional valves  24  and  25  are directly controlled valves. A not insignificant part of the costs is caused by the magnet coils used for control. To ensure the requisite actuating power for the valves, quite large and expensive magnet coils are utilized. For that reason, in conjunction with the present invention consideration was given to replacing the direct control of the valves with pilot control. The great advantage is the availability of economical pilot valves. 
   In the exemplary embodiment illustrated in  FIG. 2  the direct magnets were replaced with pilot valves  42 . In addition, a pressure reducing valve  41  was connected after pump  21  to provide the total pilot pressure. The hydraulic circuit diagrams shown in  FIGS. 1 through 4  are similar. The same reference numerals are used to designate the same parts. To avoid repetitions, reference should be made to the preceding description of  FIG. 1 . In the following description only the differences between the individual embodiments will be described. 
   In  FIG. 2  a pressure limiting pilot valve  44  and an inlet orifice  45  are connected ahead of pressure limiting valve  22 . A pressure limiting pilot valve  48  and an inlet orifice  49  are connected ahead of pressure limiting valve  28 . A direction switching pilot valve  51  is connected ahead of direction switching valve  24 . A fail-safe pilot valve  52  is connected ahead of fail-safe valve  25 . Along with the availability of economical pilot valves, the exemplary embodiment illustrated in  FIG. 2  offers the advantage that higher actuating forces may be able to operate on the main valves, which increases the reliability of operation. In addition, the pilot valves can be activated by smaller magnets, which because of their lower power consumption do not place such a heavy load on the on-board network as do the direct magnets traditionally used. However, investigations conducted in conjunction with the present invention on the roll stabilization apparatus illustrated in  FIG. 2  found elevated system leakage, which has a detrimental effect on the overall efficiency and/or the dynamics of the system. Furthermore, the tank pressure, which can be as much as 15 bar at low temperatures, can influence the functioning of the pilot circuit significantly. These problems were eliminated by the exemplary embodiments depicted in  FIGS. 3   
   In  FIG. 3  one can see within an ellipse  42  that pressure limiting pilot valves  44  and  48  are connected in series, in a departure from the exemplary embodiment depicted in  FIG. 2 . That has the advantage that in the pilot circuit a parallel oil stream via the supply orifice  49  ( FIG. 2 ), which represents a “point of leakage” due to the pilot circuit, can be dispensed with. Within an ellipse  60  a single on/off pilot valve  61  is shown, which replaces the two pilot valves  51  and  52  of  FIG. 2 . 
   Pilot valve  61  has three discrete switch positions. When no power is applied the two directional valves  24  and  25  are not switched. When a medium voltage is applied to on/off pilot valve  61 , the pilot pressure overcomes the pre-tensioning of a spring  65  on fail-safe valve  25 , so that fail-safe valve  25  switches to its second position (not shown in  FIG. 3 ). At this medium voltage the resulting pressure force on direction switching valve  24  is not yet sufficient to overcome the stronger pre-tensioning of a spring  66 . Consequently, direction switching valve  24  remains unswitched, i.e., in the position shown in  FIG. 3 . When a higher voltage is applied to on/off pilot valve  61  the higher pre-tensioning force of spring  66  is overcome by the higher pilot pressure, and direction switching valve  24  switches to its second switch position (not shown in  FIG. 3 ). At the same time, fail-safe valve  25  remains in its second position. 
   In  FIG. 3 , arrows  63  and the associated dashed lines also indicate that the tank pressure is conducted back into the spring chambers of pressure reducing valve  41  and directional valves  24 ,  25 . The returning of the tank pressure to the spring chamber of pressure reducing valve  41  ensures that the total pilot pressure is always raised by the level of the tank pressure, so that a regulating differential pressure of, for example, 5 bar is available. The same is true of the two directional valves  24 ,  25 . 
   In  FIG. 4 , arrows  67  and the associated dashed lines indicate that the tank pressure is fed back not only to pressure reducing valve  41  and directional valves  24 ,  25 , but also to pressure limiting valves  22 ,  28 . 
     FIG. 5  shows a cross-sectional view of a die cast aluminum housing  70 . A blind bore  72  is recessed in aluminum die cast housing  70 , in which a valve piston  73  is received so that it can move back and forth. Blind bore  72  is closed with the help of a plug  74 , which is held in blind bore  72  by a holding plate  75 . On the side of holding plate  75  facing away from valve piston  73  there is a receiving space  76  for a magnet (not shown). Holding plate  75  and/or plug  74  can also be formed by the magnet. Furthermore, plug  74  and holding plate  75  can be integrated into the magnet. Valve piston  73  is held by the biasing force of a helical compression spring  77  against a stop surface  78  that forms the inner end of blind bore  72 . 
   Four passageways  81 ,  82 ,  83 ,  84  that run transversely to the longitudinal axis of valve piston  73  are recessed in aluminum die cast housing  70 , which is also referred to as the valve housing. Passageway  81  serves to recycle leakage. Passageway  82  forms a connecting conduit to a pump (element  21  in  FIGS. 1 through 4 ). Passageway  83  forms a drainage conduit, for example to a pressure limiting valve (elements  22 ,  28  in  FIGS. 1 through 4 ). Passageway  84  represents, for example, a connecting conduit to an additional pilot valve. 
   The valve shown in  FIG. 5  can be, for example, a pressure limiting pilot valve, as shown in  FIGS. 2 through 4  and designated as elements  22  and  28 . The pilot pressure is applied to valve piston  73  via passageway  81 . In the position of valve piston  73  shown in  FIG. 5 , the hydraulic medium, under the pilot pressure, passes via passageway  82  and an indentation  86  that is formed on valve piston  73 , into drainage passageway  83 , which is connected to one of the pressure limiting valves (elements  22 ,  28  in  FIGS. 2 through 4 ). If the pilot pressure in passageway  81  overcomes the biasing force of spring  77 , or if valve piston  73  is moved away from stop surface  78  with the help of a magnet, then the connection between passageways  82  and  83  is interrupted. The so-called labyrinth solution of the several flow conduits shown in  FIG. 5  gives the advantage that valve piston  73  runs directly into valve housing  70 . A plurality of valves are connected with each other through cast conduits. 
   In  FIG. 6  a vehicle boundary surface is designated as  90 . Electronic elements  91  of a roll stabilization control apparatus are installed directly on the vehicle boundary surface. Sensor elements  92  are installed directly on the electronic elements  91 . A connector plug  93  is connected directly to the electronic elements  91 . A first control plate  94 , which is formed in the labyrinthine manner of the flow conduits of an aluminum die cast housing part, contains conduits and connections, in particular hydraulic connections  95  for the valves. A second control plate  99  is separated from first control plate  94  by an intermediate plate  98 . Second control plate  99  contains actuators and magnets  100  of the valves. The electronic elements, sensor elements, and control plates are shielded against the outside by a protective plate  104 , which is also referred to as a protective pan. That offers the advantage that the respective components do not have to be encased individually. Protective pan  104  shields the control elements against the outside, and at the same time it ensures that no oil escapes into the environment. The direct contacting of the individual elements with each other offers the advantage that a complex cable tree with a multitude of plug connections can be eliminated. That not only reduces the costs, but also significantly increases the reliability of the system.