Abstract:
Hydraulic systems generally comprise expansion hose lines and other damping elements which are provided with one or several serially connected hose chambers according to the generated pressure pulsation. The damping measures of the inventive hydraulic system are initiated according to the prevailing pressure during operation thereof. The aim of the invention is to keep the loss of pressure low and save a significant amount of energy during continuous operations. Said aim is achieved by a direct line connection between the source of pressure and the user, which bypasses the dampers. Said bypass line is blocked by a valve when the pressure in the system increases.

Description:
RELATED APPLICATIONS 
   This application claims priority to international patent application numbers PCT/DE03/01455, filed on May 7, 2003; and DE 102 21 276.7, filed on May 14, 2002, the disclosure of which is incorporated by reference herein in its entirety. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a pressurized fluid power transmission system such as, for example, a hydraulic system and its damping device. 
   2. Description of the Related Art 
   In power transmission systems which use a compressible or incompressible pressurized fluid for power transmission, i.e., in pneumatic systems or hydraulic systems, pulsation dampers are frequently interposed between the pressure source and the load, said dampers damping pulsations due to the pressure source or the user. Such pulsation dampers are, for example, expansion hoses which, in addition, may contain installed in them, for example, resonator pipes or reflectors for the generation of pressure wave interferences to extinguish such pressure waves. Such damping devices are interposed between the pressure source and the user. 
   Pressurized fluid power transmission systems are frequently used in situations in which the load varies, i.e., is not constant in terms of time. Likewise, the pumping rate of the pressure source may fluctuate as a function of the speed of the engine, for example. 
   Damping devices exhibit a specific resistance to flow which may lead to energy losses in the power transmission system. These losses are of consequence from the viewpoint of economic efficiency. On the other hand, damping devices cannot just be omitted. 
   In addition, damping devices frequently are effective only for a more or less wide band of pressure pulsations. If all pressure pulsations occurring in every conceivable state of operation are to be eliminated by the damping device, a complex damping device with correspondingly high resistance to flow is the result. 
   Considering this, the problem to be solved by the invention is to provide a pressurized fluid power transmission system, which works very efficiently and reduces pressure pulsations to a tolerable minimum. 
   This problem has been solved with the power transmission system using a pressurized fluid as disclosed by Claim  1 : 
   SUMMARY OF THE INVENTION 
   A power transmission system using a pressurized fluid is provided. In an embodiment, the inventive pressurized fluid power transmission system is configured as a hydraulic system. This system comprises a pressure source and a load, between which a damping device is arranged. This device comprises at least two channels which are arranged parallel with respect to each other and exhibit different damping properties. For example, one of the channels comprises one or more pulsation dampers while the other channel comprises differently tuned pulsation dampers, or may even be configured as a bypass channel which does not comprise any pulsation dampers or other dampers. The channels are associated with a valve means which effects the pressure distribution to the channels as a function of the pressure applied to one selected point of the damping device. As a result, at least one of the channels is activated in a pressure-dependent manner, i.e., opened or closed, or even more or less opened. Consequently, the properties of the damping device vary, depending on the pressure at a selected site of the power transmission system. As a result, it is possible to work on the one hand with a greater damping effect in certain states of operation of the power transmission system and on the other hand with a lesser damping effect in certain other states of operation. In conjunction with the change of the damping effect, there usually is a change of the flow resistance provided by the damping device, consequently, it is possible, in accordance with the inventive power transmission system, to adapt the flow resistance provided by the damping device to the states of operation of the power transmission systems, i.e., in particular, to the load ratios. For example, the power transmission system may be used as a hydraulic system in motor vehicles. In straight-line driving mode, which does not require any steering assistance, a channel provided in the damping device and acting as a bypass may be opened. The power transmission system is in recirculating mode, so that in this instance damping is not important. However, the reduced flow resistance in the bypass channel in this operating state requires only little power in order to maintain the recirculating mode, so that only a small load is applied by the hydraulic pump (pressure source) to the engine of the motor vehicle. 
   When a steering action is initiated, the flow resistance of the hydraulic actuator device—which is used for steering assistance—increases. Corresponding thereto, the pressure in or at the damping device increases. This pressure causes the valve means to switch preferably suddenly or, if needed, also in a sliding manner, so that the bypass channel or another channel with low flow resistance used during recirculating mode is now increasingly throttled. Now, increasingly, fluid is forced to flow through the parallel channel which contains at least one pulsation damper. In doing so, pulsations, pressure shocks, and vibrations, which could be caused by the pressure source, are kept away from the load. Conversely, pulsations, vibrations, and pressure shocks which can originate from the load, are kept away from the pressure source. Consequently, any power losses which could occur at the dampers of the damping devices are largely restricted to briefly occurring steering actions. A hydraulic level control may occur in a similar manner. 
   Consequently, the inventive power transmission system activates its dampers only when a power transmission actually occurs between the pressure source and the load In idling mode (recirculating mode), i.e., when no appreciable power is transmitted from the pressure source to the load, the dampers—which inevitably involve energy losses—are at least partially deactivated. 
   Furthermore, the inventive power transmission system permits the use of the pulsation dampers, mainly when pulsations actually do occur. This is a function of load, for example. In addition, the frequency spectrum of the pulsations may change in response to the load. Also, in this case, the inventive power transmission system offers the option of activating or deactivating the pulsation damper adapted for specific pulsations as a function of the operating state of the power transmission system. 
   The damping device may have two or more channels arranged parallel to each other. They may be connected with each other on their respective input sides and switched on their output sides, or they may be connected with each other on their output sides and switched on their input sides. This switching operation may be performed by bypass valves. However, in preferred embodiments, the channel to be deactivated only contains a shut-off valve which closes when the pressure increases, for example. This shut-off valve is preferably arranged in that one of the two channels which exhibits the lower flow resistance. This channel may be considered as the bypass channel which, for example, is gradually blocked as the pressure of the system is increased. 
   For example, as mentioned, it is basically possible to activate or deactivate the channels in a surge-like manner. This, however, may result in a noticeable change of the behavior of the overall system. For example, considering a motor vehicle steering system using hydraulic assistance, the degree of steering assistance would change suddenly. In those cases, a smooth transition between activated and deactivated channel is preferred. This sliding mode of operation allows the fading-over or switching between channels, preferably in a manner that is substantially free of hysteresis effects. In contrast, when a sliding transition is used, it is advantageous if a certain switching hysteresis exists in order to avoid vibration conditions, i.e., in order to avoid a constant hunting of the valve means certain states. 
   In order to switch the valve means, the valve actuating pressure is preferably drawn from the damping device or another point of the power transmission system. By means of a suitable pressure-activated driving arrangement, the pressure may be used for moving the valve means. Preferably, the actuation arrangement comprises a spring means which generates a counter-force. In many cases, it is sufficient if the spring means exhibits a linear force-versus-path characteristic. In individual cases, it may be useful if a nonlinear force-versus-path characteristic is provided. This allows compensation of a non-linear valve characteristic. In other cases, it may even be desirable to employ a non-linear characteristic for switching between the two channels. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Additional details of advantageous embodiments of the invention are obvious from the drawings, the specification or the subclaims. 
       FIG. 1  is a schematic illustration of an invention pressurized fluid power transmission system and 
       FIGS. 2–5  are schematic illustrations of modified forms of embodiments of inventive power transmission systems. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1  shows a hydraulic system  1  which uses an incompressible fluid, such as for example hydraulic oil, as a pressurized fluid. This means is used for the transmission of the mechanical output of a pressure source  2  to a user  3 . Consequently, hydraulic system  1  is a pressurized fluid power transmission system comprising. Pressure source  2 , for example, is a hydraulic pump provided on a motor vehicle. Load  3 , for example, is a steering gear, a valve block or another actuator to be driven by pressure source  2 . A damping device  4  is interposed between pressure source  2  and load  3 . Input  5  of this damping device is connected with one output  6  of pressure source  2 . Its output  7  is connected with one input  8  of load  3 . A recirculating line from the load to pressure source  2  is provided, however not illustrated. (This applies to  FIGS. 1 through 5 .) 
   Damping device  4  contains at least two channels  9 ,  11 , which are arranged parallel to each other. To achieve this, the input sides  12 ,  13  of channels  9 ,  11 , as well as their output sides  14 ,  15 , are connected with each other. Channel  9  is configured as a bypass channel and, in this form of embodiment, does not contain any damping devices or the like; however, it does contain a shut-off valve  16  which acts as a valve means for dividing the hydraulic fluid between channels  9 ,  11 . Shut-off valve  16 , located in the bypass channel (channel  9 ), has a first state I, in which it is fully open and enables channel  9 , and a second state II, in which it blocks channel  9 . Furthermore, said valve may adopt any states in between, in which it more or less throttles channel  9 . Shut-off valve  16  is activated by the pressurized fluid. Said valve comprises a pressurized fluid drive  17  which, when pressure is applied, actuates shut-off valve  16  in closing direction against the force of a pressure spring  18 . Pressurized fluid drive  17  is connected with input  12  of channel  9  by means of a line  19 , for example. If desired, e.g., to avoid any switching hysteresis, line  19  may also be connected with the valve output. 
   Channel  11  contains at least one damper; however, in this instance it contains two dampers  21 ,  22 , which are arranged in series. Both dampers  21 ,  22  are pulsation dampers, for example, each comprising an expansion hose and a tuner pipe  23 ,  24  located in said expansion hose. Each damper  21 ,  22  is adjusted to a specific pulsation frequency or a frequency band. 
   The two paralleling channels  9 ,  11  may be preceded by a joint damper  25  which connects the input of damping device  4  with the inputs  12 ,  13  of channels  9 ,  11 . Damper  25  may be a pulsation damper adjusted for narrow or wide bands. 
   The so far described hydraulic system  1  operates as follows: 
   During operation, pressure source  2  constantly transports hydraulic fluid. If load  3  does not tap any power, it allows the fluid arriving at its input  8  to pass unimpeded and flow back to pressure source  2  through a not illustrated recirculating line. The hydraulic system operates in recirculating mode. In this state, the pressure tapped by line  19  is low in damping device  4 . Consequently, shut-off valve  16  is in its state I, i.e., it allows unimpeded passage into channel  9 . Consequently, the hydraulic fluid takes its path through damper  25  and then through channel  9  which is switched as the bypass to user  3 . The flow through channel  11 , which is also open, is comparatively lower because of this channel&#39;s greater flow resistance. Therefore, in order to maintain the hydraulic circulatory system, pressure source  2  requires only low power. 
   As explained above, user  3 , for example, is a hydraulic actuator which assists the steering motion of a motor vehicle. If this user is activated by a steering motion, it offers increasing resistance to the hydraulic fluid which passes through. In doing so, the pressure in the damping device increases noticeably, specifically at input  12  of channel  9 . In turn, this pressure triggers the initial closing operation of shut-off valve  16  by means of pressurized fluid drive  17 . Therefore, channel  9  is throttled increasingly, thereby forcing increasingly more fluid to take the path through channel  11  and thus over dampers  21 ,  22 . As a result, it is ensured that the increasing transmission of power causes the concurrent damping of pulsations between pressure source  2  and user  3 . If, at maximum counter-pressure, shut-off valve  16  is closed completely, channel  9  is shut off. 
   Then, only channel  11  is active. Operation takes place with full pulsation damping. The connection between-the pressure tapped at line  19  and the fluid distribution to channels  9 ,  11 , can be adjusted by selecting an appropriate force-versus-path characteristic for pressure spring  18 . 
   If load  3  is deactivated, for example, by resetting the steering to straight-line mode of operation, the hydraulic fluid may again flow unimpeded through load  3 . Hence, the pressure tapped by line  19  drops, and channel  9  is cleared as the pressure drops. Consequently, the system returns to recirculating operation with low pulsation damping. This is a low-loss operation and, hence, is maintained until load  3  becomes active again. 
   As an alternative, line  19  may lead to output  7  in order to exclude or reduce positive feedback effects. However, this also avoids any hysteresis which would be desirable to avoid vibrations in some cases. 
     FIG. 2  shows a modified embodiment of hydraulic system  1 . This embodiment is different from the above-described embodiment in that damper  25  was omitted. This results in an undamped but still extremely loss-free recirculating operation when channel  9  acting as bypass is left fully open, i.e., when there is no power decrease to load  3 . In as much as these embodiments are otherwise completely identical, reference is made hereinafter to the above description and the application of the same reference numbers. For example, the number of dampers in channel  11  may vary as needed. Valve  16  may be located in or in front of channel  9 . 
   Another potential modification of hydraulic system  1  of  FIG. 1  is sown by  FIG. 3 . Again, full reference is made to the description of the example of embodiment of  FIG. 1 . The same reference numbers apply. Different from the example of embodiment of  FIG. 1 , hydraulic system  1  of  FIG. 3  comprises only one pulsation damper  21  in channel  11 . Its flow resistance is considerably greater than that of open channel  9 , so that this channel causes a substantially greater pressure drop. Therefore, when channel  9  is open (recirculating operation), only the combined total of the flow resistance of damper  25  and the substantially lower flow resistance of channel  9  is effective. Consequently, the pressure drop between pressure source  2  and load  3  is substantially determined by the pressure drop on damper  25 . However, if load  3  removes power, channel  9  is closed more and more, so that damper  21  becomes active. Now the pressure drop of damping device  4  is added to the pressure drop of damper  21 , so that there is an increased pressure drop, but also increased pulsation damping. 
     FIG. 4  shows another modified form of embodiment of hydraulic system  1 . In this form of embodiment, both dampers  25 ,  21  are bridged by a bypass channel which is open as long as the system operates in recirculating mode. Dampers  21 ,  25 , which are actuated only when load  3  requires mechanical power, may be designed for high pulsation damping effects. Concomitant pressure losses only occur during—as a rule—brief phases of the power drop, so that these phases are negligible regarding the energy balance of the system. In contrast, these phases are of no effect in recirculating mode. 
   Specifically, damper  21  is part of channel  11 . Regarding this channel&#39;s description and function, reference is made to the description in conjunction with  FIG. 3 . The same applies to channel  9 . Different therefrom, damper  25  forms a channel  11   a  which is associated with channel  9   a . Input  13   a  of channel  11   a  is connected with input  12   a  of channel  9   a . Both are located at output  6   a  of pressure source  2 . While output  15   a  of channel  11   a  is connected with inputs  12 ,  13  of channels  9 ,  13 , output  7   a  of channel  9   a  is connected with output  7  of channel  9 . Consequently, channel  9   a  forms a bypass which bridges damping device  4  as a whole. This bypass is controlled by valve  16   a  which is connected with the output of pressure source  2  via a pressure line  19   a.    
   This hydraulic system  1  is designed in such a manner that both shut-off valves  16 ,  16   a  are open in recirculating state. A low pressure drop exists. Pulsation damping does not occur. If load  3  decreases as a result of a corresponding control of power, a counter-pressure is created in hydraulic system  1 , whereby this pressure initially causes valve  16   a  to close. As a result, damper  25  is activated increasingly. As the counter-pressure rises, valve  16  is also closed, which now also causes damper  21  to be activated. Thus, as power drops more and more, pulsation damping increases correspondingly. In doing so, shut-off valves  16 ,  16   a  may be dimensioned—by appropriately dimensioning pressure springs  18 ,  18   a —in such a manner that they successively exert their blocking action or that they fix an overlap range in which shut-off valve  16  begins to close, while shut-off valve  16   a  more and more approaches its completely closed state II. 
   Also, in this system which permits extremely high pulsation damping, such damping is prompted only during phases of power transmission. Consequently, damping losses that occur will be limited to these brief phases. 
   An even further modified embodiment of hydraulic system  1  is shown by  FIG. 5 . Regarding this, reference is made to the same reference numbers and the description of the hydraulic system of  FIG. 1 . The difference described hereinafter consists in the arrangement and configuration of the valve means. As such, a switching valve  26  is provided which, alternately, connects the outputs of channels  9 ,  11  with load  3 . In addition, channel  9  is not purely a bypass channel but contains damping element  25 . It may be omitted, if required. If required, pressure line  19  may be connected with input  5  of damping device  4  or with another point of hydraulic system  1 . 
   Hydraulic systems  1 , as a rule, contain expansion hose lines and other damping elements  21 ,  22 , which, depending on the generated pressure pulsation, are provided with one or more serially connected hose chambers. These chambers represent the flow resistance, as well as the resilience and inertia features of the system, which result in the damping of input pressure signals. Frequently, the pulsation of the pump increases with static pressure, i.e., for example, with the degree and intensity of the steering operations or with the degree of assistance of a hydraulically active assistance system. Pulsations may be minimized by damping measures, as a result of which the pressure loss increases and, hence, the energy loss increases. This situation is remedied by the invention in that, during the operation of a hydraulic circulatory system, the damping measures are activated as a function of pressure. As a result of this, a minimal pressure loss and considerable energy savings are possible in recirculating mode. This is achieved by a direct line connection which is provided between pressure source  2  and user  3 , and which bridges the dampers. This short-circuit line is blocked by a valve when a pressure increase occurs in the system. Inasmuch as the pressure loss occurring on the damper occurs only very briefly, damping elements featuring a strong damping effect and a high pressure loss and having an extremely strong damping effect on pressure fluctuations can be used during these brief periods of time. Still, considering the mean time of activation, an improved energy balance can be achieved.