Patent Publication Number: US-9835243-B2

Title: Hydraulic circuit for the transmissions of industrial and agricultural vehicles

Description:
RELATED APPLICATIONS 
     The present application is a U.S. national phase application of International Application No. PCT/EP2014/058404 filed on Apr. 24, 2014, which claims the benefit of priority to Italian Patent Application Number PD2013A000112, filed on Apr. 24, 2014, the contents of which are incorporated in this application by reference. 
     TECHNICAL FIELD 
     This invention relates to a hydraulic circuit for the transmissions of industrial and agricultural vehicles of the type comprising an internal combustion engine connected to a transmission provided with a feed pump for the hydraulic circuit and an output shaft driven by the internal combustion engine which is capable of providing useful power to drive other working components. 
     BACKGROUND OF THE INVENTION 
     Typically earthmoving machines, such as for example backhoe loaders and excavators, but in general many vehicles for industrial and agricultural use, use a transmission to provide the motive power required to move them. 
     The hydraulic circuits used in these transmissions typically comprise a pump to raise the oil to the working pressure and deliver it to a lubrication circuit and the vehicle transmission components. The pump is driven by an internal combustion engine which is caused to work at variable speeds and powers depending upon the pressure/power required to move the vehicle. 
     The oil pressure in the hydraulic circuit is however maintained above a lower limit value because a certain throughput is required in order to lubricate the transmission even when the vehicle is stopped. In this type of vehicle provision is also made for a so-called power take-off, that is to say an output shaft, also known as a PTO shaft, coupled to the internal combustion engine, which drives the vehicle&#39;s auxiliary pump and which is used to transmit power from the internal combustion engine to the moving arm of the excavator, in the case of an earthmoving machine, or in general to other working components. 
     For example, again in the case of vehicles of this type, the power take-off is connected to the pump of another hydraulic circuit which brings about movement of the arm and other tools. 
     In general, two different working situations for the vehicle can be envisaged—a first situation in which the vehicle is moving and power may be requested for the vehicle&#39;s hydraulic system, and a second situation in which the power to the vehicle&#39;s hydraulic circuit is provided when it is stopped. In the first case power has to be provided to both the hydraulic circuits, while in the second case the working components have to be fed and only the minimum hydraulic flow for lubrication is provided to the transmission. 
     However in the latter case both the power provided to the working components and the pressure provided to the transmission depend on the rotation speed of the internal combustion engine and therefore in known vehicles it is not possible to provide high power to the working components and limit the pressure to the hydraulic circuit of the transmission to the minimum values necessary to ensure adequate lubrication at the same time. 
     In fact, in the example of a backhoe loader or an excavator, the transmission is not required to operate when it is engaged purely in excavation work with the vehicle stopped. 
     However the internal combustion engine is nevertheless made to work at a high rotation speed to deliver power to the hydraulic circuit of the working components, the pump for this circuit being driven by the power take-off shaft. 
     In this way, when purely excavation work is being carried out the hydraulic system of the transmission is also inevitably maintained at a high pressure, even though this is not required. 
     As the pump controlling the transmission has a fixed cylinder capacity there will be an expenditure of power to maintain pressure in the transmission&#39;s hydraulic system which will depend on the throughput delivered by the pump and the main pressure in the hydraulic circuit of the transmission. 
     This gives rise to consumption of power P from the internal combustion engine which is dissipated without being utilized, with a consequent inefficiency for the vehicle. 
     This is even more true when it is borne in mind that these vehicles are mainly used for purely excavation work during their lives. 
     It will therefore be desirable to avoid such energy wastage. 
     The technical problem which underlies this invention is therefore that of providing an industrial vehicle which makes it possible to overcome the abovementioned disadvantages with reference to the known art. 
     SUMMARY OF THE INVENTION 
     This problem is resolved by the hydraulic circuit for industrial vehicles summarized as follows, and by vehicles comprising it. The hydraulic circuit is for the transmissions of industrial and agricultural vehicles of the type comprising an internal combustion engine, a hydraulic transmission connected to the hydraulic circuit, a hydraulically operated auxiliary unit, and an output shaft driven by the internal combustion engine which is capable of providing a useful power to drive other working components. The circuit includes (a) a feed pump operating on a working fluid of the hydraulic circuit and connected to the internal combustion engine of the vehicle in order to be driven; (b) a delivery section connected to a hydraulic transmission of the vehicle, the transmission having a lubrication circuit and/or a torque converter of the vehicle; (c) an auxiliary uses section connected to the hydraulically operated auxiliary unit for providing the working fluid at a working pressure to the hydraulically operated auxiliary unit; (d) a main pressure regulator adapted to bring about a first variation in pressure in an operating fluid in the circuit through an inlet section connected to the pump and an outlet section connected to the delivery section; (e) a first regulating section connecting the main pressure regulator to a switching device and to which a first regulating pressure is associated, the switching device adapted to alternately open or close a connecting branch to the regulating section in such a way as to modify the first regulating pressure and regulate a first pressure variation; (f) a maximum pressure regulator connected to the delivery section which can bring about a second pressure variation in the operating fluid between the outlet section and a discharge section, wherein the auxiliary uses section and the delivery section are positioned respectively upstream and downstream of the main pressure regulator. 
     This invention has a number of significant advantages. A main advantage lies in the fact that it can reduce the energy wastage which takes place during the stage when an earthmoving machine is purely excavating and in general when industrial vehicles are only engaged in working. In addition to this the hydraulic circuit according to this invention is simple from the point of view of construction and has a minimum effect on the overall cost of the vehicle. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary, but are not restrictive, of the invention. Other advantages, characteristics and methods of use of this invention will be apparent from the following detailed description of some embodiments provided by way of example and without limitation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
       The invention is best understood from the following detailed description when read in connection with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Reference will be made to the figures in the appended drawing in which: 
         FIG. 1  is a diagrammatical illustration of the hydraulic circuit according to an exemplary embodiment of this invention; 
         FIG. 2  is a diagrammatical illustration of a second embodiment of the hydraulic circuit according to this invention; 
         FIGS. 3A and 3B  are two cross-sectional views of a switching device and a corresponding drive unit, details of the circuit in  FIG. 2 , according to a first operating condition in which the circuit operates at a first pressure level; 
         FIGS. 4A and 4B  are two cross-sectional views of the switching device and the corresponding drive unit in  FIGS. 3A and 3B  according to a second operating condition in which the circuit operates at a second pressure level which is lower than the former; 
         FIG. 5  is a diagrammatical illustration of the hydraulic circuit according to this invention according to a further embodiment; 
         FIG. 6  is a diagrammatical illustration of the hydraulic circuit in  FIG. 5  in accordance with a first operating condition in which the circuit operates at a first pressure level; and 
         FIG. 7  is a diagrammatical illustration of the hydraulic circuit in  FIG. 5  according to a second operating condition in which the circuit operates at a second pressure level which is lower than the former. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference initially to  FIG. 1 , a hydraulic circuit for the transmissions of industrial and agricultural vehicles, such as for example an earthmoving machine, is indicated as a whole by reference number  100 . 
     As will be more apparent below, this hydraulic circuit  100  is intended to be used in vehicles of the type comprising an internal combustion engine  101  connected to the hydraulic circuit  100  and an output shaft  102  driven by the internal combustion engine  101  forming a power take-off (PTO) to provide working power to working components of the vehicle, which are not shown in the figure. 
     These working components may be represented by a moving arm on which excavation mechanisms are supported or by other working mechanisms or services which receive power from output shaft  102 . 
     Hydraulic circuit  100  comprises a feed pump  1  which operates on a working fluid for the circuit, typically oil, in order to raise it to a main working pressure p 1 . 
     Feed pump  1  is driven by internal combustion engine  101  and is in particular connected, for example through a key, to a transmission shaft  103  of a transmission unit, which is not shown in the figure, which is in turn connected to engine  101 . As a consequence, a change in the rotation speed of the engine will result in a change in the power transmitted to both pump  1  and the working components via the power take-off. 
     The hydraulic circuit  100  may also comprise an inlet filter  11  and a delivery filter  12 , illustrated in  FIG. 5 , upstream and downstream from pump  1 , respectively. 
     With reference again to  FIG. 1 , the working fluid leaving pump  1  is intended to provide operative fluid at working pressure p 1  to a hydraulically operated auxiliary unit  6 , such as the arm of a backhoe, via an auxiliary uses section  36 . The working fluid provides the lubrication necessary for the transmission components via a delivery section  21  which delivers fluid to a heat exchanger  7  and a lubricating circuit  8 , and which may also be intended for a torque converter  2 , which is only illustrated in connection with the embodiment of  FIGS. 5 to 7 . More generally, the delivery section  21  is connected to a hydraulic transmission providing power to the wheels or tracks of the vehicle for moving it. 
     The throughput of the working fluid delivered to lubricating circuit  8  and, if present, to torque converter  2  may have a pre-set pressure, indicated below as the secondary working pressure p 2 , and as a consequence the pressure between the output of the pump  1  and the input to the torque converter  2  must be regulated. 
     For this purpose the hydraulic circuit  100  according to this invention comprises a main pressure regulator  3  in correspondence of which a first change in pressure Δp 1  in the working fluid occurs. 
     The working fluid delivered by pump  1  to main pressure regulator  3  through an inlet section  31  at a main working pressure p 1  is delivered by main pressure regulator  3  to lubricating circuit  8  and/or torque converter  2  through an outlet section  32  at the working pressure p 2  of torque converter  2  which is lower than pressure p 1 . 
     For this purpose, main pressure regulator  3 , which is illustrated diagrammatically in the figures, comprises a valve body  30  within which there is housed a moving plug which moves in an axial direction depending upon the pressure of the working fluid, opposed by a resilient member  302 . 
     In other words, ignoring load losses, pressure p 1  will be regulated by resilient member  302 . 
     It should be also noted that the working fluid operated by the pump  1  is also delivered at a working pressure to the hydraulically operated auxiliary unit  6  via auxiliary uses section  36  which is positioned upstream from main pressure regulator  3  and, in the present embodiment, connected to the inlet section  31 . 
     By contrast, delivery section  21  is positioned downstream from main pressure regulator  3 . 
     Hydraulic circuit  100  according to this invention further comprises a second pressure regulator  4  connected to outlet section  32  in order to regulate the pressure p 2  fed to torque converter  2  and/or lubricating circuit  8 . This second pressure regulator  4  preferably has characteristics similar to main pressure regulator  3  and is connected to a discharge branch  42  in such a way as to regulate pressure p 2  on the basis of a corresponding resilient member  402 . The change in pressure Δp 1  between pressure p 1  and pressure p 2  is therefore defined on the basis of the pressure regulation brought about by resilient members  302  and  402 . 
     In order to change the manner in which the hydraulic circuit  100  operates, the circuit according to this invention makes it possible to regulate the pressure change Δp 1  between inlet and outlet sections  31  and  32 . 
     In particular, in this embodiment, regulation of pressure change Δp 1  takes place by bypassing main pressure regulator  3 . 
     For this purpose a flow of working fluid is intercepted by a regulating or by-pass section  33  which transmits the working fluid originating from pump  1  to a switching device  5  through a connecting branch  33   a.    
     According to a first embodiment, switching device  5  takes the form of a switching valve  50  and comprises a moving slide  51 , movement of which in a corresponding valve body and in connection with a resilient member  51   a  switches operation of switching valve  50  between a first and a second operating condition. Movement of slide  51  is brought about by a suitable operating valve  56  which in this embodiment takes the form of a solenoid system of the ON/OFF type. 
     In the first working condition connecting branch  33   a  is closed and as a consequence the flow of working fluid coming from pump  31  all passes through main pressure regulator  3 . This operating condition, illustrated in  FIGS. 1 and 2 , will be referred to below as a closed operating condition, and switching valve  50  will be indicated in the closed position. 
     In the closed operating condition pressure p 1  is regulated by main pressure regulator  3  and in particular by the calibration of resilient member  302 , while pressure p 2  is regulated through second pressure regulator  4  through the calibration of corresponding resilient member  402 . 
     Again with reference to  FIG. 1 , switching valve  50  is also connected to a second regulating section  43  connected to outlet section  32  and a third regulating section  93 , which is connected to a pressure limiting valve  9 , constructed in such a way as to open when fed by a flow of fluid which respectively meets a pre-set pressure p 9  which is less than the main regulating pressure of main pressure regulator  3 . Limiting valve  9  is also constructed in such a way that once open after the aforesaid pressure has been exceeded it will discharge fluid through a further discharge section. 
     Thus, in the open position, regulating sections  33 ,  43 , and  93  are in communication via slide  51 . 
     In particular the bore of connecting branch  33   a  will make it possible to reduce the pressure difference between p 1  and p 2 , in this case making it substantially equal to zero, and as a consequence it will be possible to maintain a sufficiently high pressure p 2  for lubricating circuit  8  with a low working pressure for pump  1 . 
     As a consequence the power P at which pump  1  operates can advantageously be regulated independently of the rotation speed of the engine  101 , and therefore of the throughput delivered by the pump  1 . 
     This regulation will however be independent of the regulation of pressure p 2  in such a way that it is possible to maintain the minimum pressure required to lubricate the transmission even when the vehicle is stopped. 
     Regulation of pressure difference Δp 1  is in fact associated with the value of the pressure p 3  in regulating section  33 , which varies according to the position of switching valve  50 . 
     According to a preferred embodiment illustrated in  FIG. 2 , the drive unit comprises a three-way and two-position operating valve  56 ′ activated by a solenoid. 
     Operating valve  56 ′ may selectively deliver a flow of working fluid taken from inlet section  31  towards slide  51  of switching valve  50  in such a way as to make use of hydraulic circuit  100  itself to move slide  51  and achieve the open operating condition. 
     The flow of operating fluid is delivered to operating valve  56  through a feed section  35  connected to regulating section  33  which is closed in the closed operating position. 
     When the solenoid is excited operating valve  56  places feed section  35  in connection with slide  51  via section  58  opening switching valve  50 . Operating valve  56  is in connection with, and when open discharges fluid through, a discharge section  57 . 
     Switching valve  50  and operating valve  56  are shown in the first operating condition in  FIGS. 3A and 3B  and in the second operating condition in  FIGS. 4A and 4B . 
     It should be noted that this embodiment, although structurally more complex and bulky than the previous, makes it possible to use two cheaper components, advantageously making use of the pressure of pump  1  to operate switching valve  50 . 
     With reference now to  FIG. 5 , this illustrates a further embodiment of hydraulic circuit  100  for the transmissions of industrial and agricultural vehicles according to this invention. 
     Again in this embodiment, as illustrated in detail in  FIGS. 2 and 3 , a main pressure regulator  3 ′ comprises a valve body  30  within which there is housed moving plug  301  which moves in an axial direction according to the pressure of the operating fluid, opposed by resilient member  302 . 
     In this case, however, valve body  30  also comprises an outlet opening  303  which is open when the pressure acting on plug  301  reaches a predetermined level. In addition, provision is also made for an overflow channel  304  which makes it possible also to provide a flow of fluid to the opposite face of plug  301  with respect to that on which the main pressure acts. This flow of fluid will give rise to pressure p 3  which opposes movement of plug  301  together with resilient member  302  and therefore the pressure at which outlet opening  303  will open, and consequently the pressure at which fluid will flow out from main pressure regulator  3 ′ will also be determined by the pressure p 4  which is therefore referred to as the first regulating pressure. 
     In other words, ignoring load losses, pressure p 1  will be equal to the sum of the pressure determined by resilient member  302  and regulating pressure p 3 . 
     With reference again to  FIG. 5 , in order to regulate pressure p 2 , hydraulic circuit  100  according to this embodiment will comprise a maximum pressure regulator  4 ′. 
     Maximum pressure regulator  4 ′ has characteristics similar to pressure regulator  3 ′ and therefore also comprises a valve body  40  in which a movable closure member or moving plug  401  can move in an axial direction in order to open an outlet opening  403 . Again, in this case movement of plug  401  is opposed by resilient member  402  and regulating pressure p 4  of an overflow flow provided by a channel  404 . 
     In regulator  4 ′ plug  401  will be operated through pressure p 2  via a section  41  of hydraulic circuit  100  connected to outlet section  32  of regulator  3 ′, while outlet opening  403  is connected to discharge branch  42 , preferably at constant pressure. 
     In this way it will be possible to regulate pressure p 2  on the basis of a second pressure change which can therefore be regulated via regulating pressure p 4 . 
     In fact, in a similar way to regulator  3 ′, pressure p 2  will be defined as the sum of the pressure determined by resilient member  402  and regulating pressure p 4 . 
     In this embodiment, a switching device  5 ′ is advantageously able to regulate regulating pressures p 3  and p 4 . 
     It must in fact be noted that on the basis of the configuration described above regulation of pressures p 3  and p 4  makes it possible to regulate pressures p 2  and p 1  depending upon the working condition required. 
     In particular, by lowering pressures p 3  and p 4  it is possible to obtain a consequent respective reduction in pressure p 2  and pressure p 1 . 
     Switching device  5 ′ is connected by corresponding regulating sections  33 ′,  43 ′ to pressure regulators  3  and  4 , and they comprise pilot valves  53 ,  54 . 
     Pilot valves  53  and  54  are such that they open when they are provided with a flow of fluid which meets pressures p 3  and p 4 , respectively, and once open discharge fluid through a further discharge section  55 . 
     Regulating sections  33 ′ and  43 ′ are also connected to a switching valve  50 ′, preferably of the solenoid On/Off type, with characteristics similar to switching valve  50  previously described. 
     In a first position illustrated in  FIG. 6 , switching valve  50 ′ closes off connecting branches  33   a  and  43   a  from regulating sections  33 ′ and  43 ′ through the action of moving slide  51  in such a way that the flow of working fluid which is drawn off in pressure regulators  3 ′ and  4 ′ is wholly delivered to pilot valves  53  and  54 . 
     In the second position illustrated in  FIG. 7 , moving slide  51  is arranged in such a way that it allows working fluid to pass into branches  33   a  and  43   a  as far as discharge section  55  in such a way that regulating pressures p 3  and p 4  are equal to the discharge pressure, neglecting load losses, specifically equal to ambient pressure. 
     Thus pressures p 1  and p 2  will be defined by the opposing action of resilient members  302  and  402 . As a consequence the power P at which pump  1  operates may advantageously be regulated independently of the rotation speed of engine  101 , and therefore the flow delivered by pump  1 . 
     This regulation will however be independent of the regulation of pressure p 2 , in such a way that it is possible to maintain the minimum pressure required for lubricating the transmission even when the vehicle is stopped. 
     Therefore, hydraulic circuit  100  as described makes it possible to overcome the problems identified with reference to this invention, thanks to the possibility of operating at two different pressure levels. 
     In this way it will in fact be possible to reduce the power wasted when the vehicle is stopped and in general when there is no need to drive the hydraulic transmission. 
     Furthermore hydraulic circuit  100  uses particularly economical components and will not give rise to high costs in comparison with known circuits.