Patent Publication Number: US-2005142006-A1

Title: Device for pressure regulation of hydraulic pumps

Description:
FIELD OF THE INVENTION  
      The invention relates to devices for pressure regulation of hydraulic pumps, in particular for oil pumps, having a delivery-quantity-regulating device for supplying lubricating oil to internal combustion engines, having a regulating piston and a regulating spring for controlling the delivery-quantity-regulating device, and having an activating device for the regulating piston. Regulating devices of this type have the object of adapting the delivery capacity of the hydraulic pump, and in particular of an oil pump, to changing requirements, for example of the lubricating system of an internal combustion engine with respect to oil pressure and oil quantity. This avoids unnecessarily high oil pressures, and also enables the driving power of the lubricating-oil pump to be kept low for good efficiency of the internal combustion engine.  
     BACKGROUND OF THE INVENTION  
      Known oil pumps having delivery-quantity regulation, in which the oil delivery quantity is matched in accordance with the configuration of the oil pumps to the requirements of the internal combustion engine to be supplied, have a lower oil-pump-driving power than oil pumps having short-circuit regulation. The delivery quantities are regulated essentially by the oil pressure, with corresponding delivery-quantity reductions taking place in particular at higher engine speeds and also at low operating temperatures.  
      In simple oil-pump constructions having delivery-quantity regulation, the oil pressure is determined directly by a regulating spring. However, this embodiment has the disadvantage that the spring has to be configured in accordance with the maximum oil-pressure requirement at the maximum engine speed of the internal combustion engine, this then having the consequence of unnecessarily high oil pressures with correspondingly high driving powers in the lower speed range. Furthermore, a delivery-quantity regulation exclusively by means of a regulating spring, as proposed, for example, in DE 3028573 and DE 3528651, results, because of the rising spring force of the regulating spring as its travel increases, in an additional increase in oil pressure, and so the driving-power advantage which is sought by reducing the delivery quantity is at least partially offset again as a consequence of the unnecessary rise in oil pressure.  
      The external-gear oil pump which is proposed in DE 10043842 A1 and has axial displacement of the gearwheel largely avoids the undesirable rise in oil pressure upon reduction of the delivery quantity by means of a throttle regulation which stabilizes the oil-pressure level. However, its oil pressure pulsates during the regulating mode because of a slight, constant variation, caused by the regulation, in the axial engagement overlap of the two delivery gearwheels. Frictional forces opposing the axial displacement of the gearwheels reinforces this effect. To further minimize the delivery quantity and oil pressure, in particular in accordance with the lower oil-pressure requirement at low engine speeds, this throttle regulation additionally requires electric control components.  
      DE 19915737 A1 discloses a method for regulating the lubrication of an internal combustion engine, in which the regulation of the oil pump is controlled via a characteristic diagram as a function of the operating state of the internal combustion engine, the characteristic variables being taken from the engine controller. An actuator (not described specifically) of the oil pump converts the electric activations into changes in the delivery capacity of the oil pump.  
      DE-C-753580 describes an oil pump having a speed-variable delivery quantity, in which the centrifugal regulator of an injection pump changes the delivery quantity of the oil pump via a mechanical coupling. Other configurations of oil pumps which can be regulated are to be found in DE-A-37 26 800 and U.S. Pat. No. 4,828,462.  
     SUMMARY OF THE INVENTION  
      Starting from this prior art, it is the object of the invention to provide a regulating device for oil pumps having a delivery-quantity-regulating device which, as a function of predefined operating values, for example the operating speed of an internal combustion engine, reliably minimizes the oil pressure and also the oil-delivery quantity largely in accordance with the hydraulic supply requirements, and therefore reduces the driving power of the oil pump.  
      To achieve this object, a device for pressure regulation of hydraulic pumps having the features mentioned at the beginning is proposed, the device being distinguished by the fact that the regulating piston has an active surface for oil pressure which is always produced, and furthermore can be subjected to an additional force by the activating device. This has the effect that the oil pressure is set at least in two regulating-pressure stages. For this purpose, the regulating piston, which can be subjected to a variable force by an activating device, brings about the associated setting of the delivery-quantity-regulating device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The invention will be explained in greater detail with respect to function and variant possibilities with reference to the following drawings:  
       FIG. 1  shows an external gear pump which can be regulated in its delivery quantity with an electromagnetically variable action of force upon its regulating piston;  
       FIG. 2  shows an external gear pump which can be regulated in its delivery quantity with variable action of force upon its regulating piston by means of a stepping motor;  
       FIG. 3  shows an external gear pump which can be regulated in its delivery quantity with variable, hydraulic action of force upon a stepped regulating piston by means of a centrifugally actuated switching piston;  
       FIG. 4  shows an external gear pump which can be regulated in its delivery quantity with variable action of force upon its regulating piston by means of an electrovalve and/or by means of a speed-dependent action upon the oil pressure;  
       FIG. 5  shows a further exemplary embodiment, as a variant for  FIG. 3 ;  
       FIG. 6  shows an alternative to  FIG. 2 ; and  
       FIG. 7  shows a preferred exemplary embodiment of a regulating unit. 
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS  
       FIG. 1  shows a first exemplary embodiment of the pressure-regulating device according to the invention for an external-gear oil pump with delivery-quantity regulation. This oil pump comprises an oil-pump housing  1  in which a driving gearwheel  3 , which is fixed on a drive shaft  2 , is arranged. The drive shaft  2  is mounted in a cover piston  5  belonging to a closure cover  4 . During a regulation of the delivery quantity, a displacement gearwheel  6  which is in meshing engagement with the driving gearwheel  3  is displaced axially in a known manner relative to said driving gearwheel  3 , so that then the oil-delivery quantity is correspondingly changed by the changed width of engagement of the teeth.  
      The displacement gearwheel  6  is mounted on a nonrotating bolt  7  which bears a displacement piston  8  on the right-hand side and a spring piston  9  on the left-hand side. This composite which is formed is referred to as the displacement unit  10 . The displacement unit  10  is continuously subjected to oil pressure on its displacement piston  8  while, in a manner opposed to this on the spring piston  9 , a piston spring  11  and also a control pressure which can be regulated and acts in the spring chamber  12  undertake the regulation of the delivery quantity.  
      The regulation of the control pressure acting in the spring chamber  12  is undertaken via a control bore  13  by a regulating piston  14  which is subjected continuously to oil pressure on its active surface  15  via a connection  16 . As a counterforce to this, a regulating spring  17  acts on the left-hand side of the regulating piston  14 . In the shown regulating position of the regulating piston  14 , its regulating pin  18  is situated lying directly opposite the control bore  13 . The regulating pin  18  is bounded on the left-hand side by a pressure groove  19  and on the right-hand side by a relief groove  20 .  
      Since the regulating pin  18  is slightly narrower than the diameter of the control bore  13 , in the regulating position which is shown a control pressure is set in the spring chamber  12 , it being possible for the control pressure to lie between the oil pressure produced in the pressure groove  19  via a further connection  21  and a complete relief from pressure, which can be fed in via the relief groove  20 . The relief groove  20  is connected to the surroundings via a diagonal bore  22  in the regulating piston  14 .  
      As soon as the oil pressure produced at the active surface  15  exceeds the level of the maximum operating oil pressure required of, for example, 5 bar for the associated internal combustion engine, the regulating piston  14  is displaced counter to the force of the regulating spring  17  with the effect of reducing the control pressure in the spring chamber  12 . By this means, the displacement unit  10  is displaced, for the purpose of reducing the delivery quantity, to the left until the oil pressure reaches the desired value of, for example, 5 bar. Conversely, a dropping of the pressure below the desired oil pressure of 5 bar leads to a displacement of the regulating piston  14  by the regulating spring  17  to the right, this triggering, by means of an increase in the control pressure in the spring chamber  12 , a corresponding increase in the delivery quantity with a resultant rise in the oil pressure.  
      The activating device of the regulating piston  14 , which device is required for the reduction according to the invention of the oil pressure, comprises a magnet coil  23  which, upon appropriate activation by means of a controller of the internal combustion engine, exerts via its armature  24  a magnetic additional force on the regulating piston  14 . A change in the magnetic positional force can be undertaken by the controller either continuously or in a stepwise manner orientated to requirements, which has a corresponding effect on the regulation of the oil pressure and delivery quantity of the oil pump.  
      The hydraulic connections  16 ,  21  and  26  to the displacement piston  8  and the regulating piston  14 , which connections do not branch off until behind the oil filter  25 , have two advantages. Firstly, the oil pressure behind the oil filter  25  is set to the desired pressure level by the pressure regulation of the oil pump, so that a reliable oil pressure for the lubrication of the internal combustion engine is ensured irrespective of variable pressure losses from the oil filter  25  caused by soiling. Secondly, all of the parts of the regulating device and also all bearings of the oil pump, for example the mounting of the drive shaft  2  in the cover piston  5 , are supplied with filtered oil from displacement chamber  28  via an oil bore  27 , so that the operational reliability and also the service life of the oil pump are increased.  
       FIG. 2  shows a further exemplary embodiment of the invention with continuously variable regulation of the oil pressure. For the reduction according to the invention of the oil pressure, instead of the magnet coil  23  from  FIG. 1 , here a stepping motor  29  having an adjustable spring system  30  for the regulating spring  17  of the regulating piston  14  (now illustrated without being cut away) is used. The basic position of the spring system  30  of regulating spring  17 , which is set automatically without electric activation of the stepping motor  29 , ensures the maximum operating oil pressure required of, for example, 5 bar, by the appropriate prestressing of the regulating spring  17 . A correspondingly programmed controller of the internal combustion engine enables the oil pressure to be reduced in a manner matching requirements or, in special applications, even to be increased further.  
       FIG. 3  shows a preferred exemplary embodiment of the oil-pressure and delivery-quantity regulation according to the invention using the example of an external-gear oil pump, in which the activating device of the regulating piston takes place exclusively as a function of centrifugal force in two speed-regulating-pressure stages. The regulating piston, which is now formed as a step piston  51 , is derived from the regulating piston  14  of  FIGS. 1 and 2 . It has a regulating spring  52  on the left-hand side and, on the right-hand side, a first active surfaces  53  which is continuously subjected to oil pressure. At low operating speeds of the internal combustion engine, a second active surface  54  on the right-hand side of the step piston  51  is likewise subjected to oil pressure, so that an oil-pressure regulation at, for example, 2.5 bar of the first regulating-pressure stage takes place by the action of the oil pressure on the two active surfaces  53  and  54  and on the correspondingly configured regulating spring  52 . The increase in oil pressure, which is required by the engine at high speeds, to an oil-pressure level of, for example, 5 bar of the second regulating-pressure stage requires a complete relieving of the second active surface  54  from pressure for the corresponding regulating function of the step piston  51 . In this exemplary embodiment, the activating device for changing between the two regulating-pressure stages by the action of oil pressure on the second active surface  54  of the step piston  51  or relief thereof from pressure comprises a centrifugal valve which is arranged in the driving gearwheel  55  and acts as a function of the speed.  
       FIG. 4 , which belongs to  FIG. 3 , shows the compact centrifugal valve on an enlarged scale. It comprises a switching piston  56  and a switching-piston spring  57 . For spatial reasons, the switching piston  56  is orientated obliquely with respect to the radial direction of centrifugal force, but could, in certain cases, also be orientated radially, i.e. its orientation has to have at least one radial component. The stepped receiving bore of the switching piston  56  and switching-piston spring  57  may even, for space reasons, protrude partially into a tooth of the driving gearwheel  55 . The position which is shown for the switching piston  56  with relaxed switching-piston spring  57  corresponds to low operation speeds with little centrifugal-force action. A guide pin  59  situated on the switching piston  56  ensures the radial guidance of the switching-piston spring  57  and prevents deflections thereof caused by centrifugal force.  
      The oil pressure produced on the switching piston  56  via the oil bore  27  and the associated circumferential bevel of the cover piston  5  also acts continuously via its central bore  60  in the chamber of the switching-piston spring  57 . At low operating speeds, the oil pressure is conducted, as a consequence of the position of the switching piston  56  that is shown in  FIG. 4 , via an oblique bore  61  of the driving gearwheel  55  and via a connecting bore  62  of the oil-pump housing  63  onto the second active surface  54  of the step piston  51  in order thereby to activate the first regulating-pressure stage with oil pressure, for example of 2.5 bar.  
      After the changeover speed for activating the second regulation-pressure stage is exceeded, for example at 2500/min, the switching piston  58  is caused by centrifugal force to be displaced counter to the switching-piston spring  57  into its outer end position. By this means, in order to raise the oil pressure to the second regulating-pressure stage of 5 bar, the step piston  51  is relieved from pressure on its second active surface  54  by a connection being produced via the oblique bore  61  and a circumferential groove  64  of the switching piston  56  and via further cross sections to the central bore  65  of the drive shaft  58 , which is open at the right-hand end.  
      With reference to  FIG. 3 ,  FIG. 5  shows an exemplary embodiment in which the step piston  51  can be subjected to oil pressure on its second active surface  54  by two further, independent activating devices (illustrated in  FIG. 5 ). The two activating devices may, as shown in  FIG. 5 , enter into operation in combination with each other, but may also each operate independently with the other activating device being omitted.  
      The first activating device, has, on the drive shaft  74 , a spiral groove  73  which is bounded on both sides by the circumferential grooves  75  and  76 . It has a relatively small groove depth and, during rotation of the drive shaft  74 , produces a speed-dependent drop of pressure over its length by means of oil-shearing forces which occur. The circumferential groove  75  on the left-hand side is subjected to oil pressure via the oil bore  27 . The direction of inclination of the spiral groove  73  is selected in such a manner that, when the drive shaft  74  rotates, the drop in pressure acting in the spiral groove  73  causes a reduction in pressure in the circumferential groove  76  on the right-hand side. The speed-variable pressure in the circumferential groove  76  is conducted via a longitudinal bore in the drive shaft  74  and via a connecting bore  79 , which is situated in the housing  78 , onto the second active surface  54  of the step piston  51 .  
      At maximum speed, the oil pressure of, for example, 5 bar which is produced in the circumferential groove  75  is reduced by a relatively high drop in pressure produced by the spiral groove  73  to virtually 0 bar in the circumferential groove  76 , so that the second active surface  54  of the step piston  51  is effectively relieved from pressure at 5 bar for the desired pressure regulation of the oil pressure. With decreasing speed, the drop in pressure in the spiral groove  73  is reduced continuously, so that pressure on the second active surface  54  of the step piston  51  correspondingly rises and the oil pressure is regulated at a pressure level which can vary as a function of speed.  
      The second activating device for the step piston  51 , which device can be fitted on its own or together with the first activating device, comprises an electrovalve  71  which, upon electrical activation, switches the oil pressure onto the second active surface  54  of the step piston in order to reduce the oil pressure of the oil pump. Both active surfaces  53  and  54  are therefore loaded by oil pressure, so that the step piston  51 , even at an oil pressure of, for example, 2.5 bar for the first regulating-pressure stage, exerts its regulating function counter to the force of the regulating spring  52  and provides the corresponding control pressure for regulating the delivery quantity.  
      When the electrovalve  71  is not energized, the supply of oil pressure is interrupted and a pressure relief or loading of the second active surface  54  is caused via a relief connector  72  on the electrovalve  71 . The oil pressure, which is now only produced on the first active surface  53  of the step piston  51 , then shifts the start of the regulating operation to a higher value, for example 5 bar, of the second regulating-pressure stage. The second regulating-pressure stage is ensured as a safety oil pressure for all operating conditions of the internal combustion engine if there is an interruption, caused by a defect, in the electrical connections of the electrovalve  71 .  
      In the combined function (for example) of the two activating devices that are shown in  FIG. 5 , a continuously speed-variable regulation of the oil pressure can be carried out by the spiral groove  73  when the internal combustion engine is operationally warm, but the electrovalve  71  then has to keep its connection to the step piston  51  closed by means of an additional function. The electrovalve  71  then enters into operation during cold operation when the spiral groove  73  is effectively unusable because of viscous oil. Its two-stage oil-pressure regulation by means of pressurization or pressure release of the second active surface  54  of the step piston  51  then takes place in a known manner.  
      In principle, the regulation of the oil pressure that is undertaken by the step piston  51  can also be carried out in a number of stages with a correspondingly formed step piston. In this case, its partial active surfaces would then have to be subjected to oil pressure in a speed-offset manner, for example, by an activating device formed with multiple stages.  
      When electric components are used for the oil-pressure regulation of an internal combustion engine, an arrangement of the electric parts outside the crank space accommodating the oil pump is advantageous. While, on the one hand, the loading of temperature- and/or oil-sensitive electric parts is reduced as a result, the electric connections to the crank space are also omitted, on the other hand, with the accessibility to the electric parts, for example for repair purposes, being improved. The electric valve  71  which is shown in  FIG. 5  may be fitted, for example, on the outside of the crank case. The electrically switchable action of oil pressure on the second active surface  54  of the step piston  51  can then take place via oil bores through the flange face of the oil-pump fastening on the crank case. However, with the electrically produced action of an additional force on the regulating piston  14  according to  FIGS. 1 and 2 , an arrangement of the magnet coil  23  or stepping motor  29  external to the crank space also requires the regulating piston  14  to be shifted.  
      The exemplary embodiment in  FIG. 6  shows, as an alternative to  FIG. 2 , an arrangement in which the stepping motor  29  is combined with the regulating piston  80  in a common housing  81  to form a regulating unit  82 . The regulating unit  82 , which is fitted to the outside of the crank case  84 , ensures a reliable pressure regulation of the oil pump by means of an electric connection  83 , which is now problem-free, and via a control bore  87 , which passes through the flange face  85 , to the spring chamber  12  of the oil pump  86 .  
      To further increase the operational reliability, the regulating unit  82  is fed from an adjacent crank case main oil bore  88  with pressure oil cleaned in an oil filter  89 . This pressure oil acts continuously, in the manner relevant for regulation via corresponding connecting cross sections of the regulating unit  82 , on the end side on the active surface  90  of the regulating piston  80  and also via a line  91  in the displacement chamber  28  of the oil pump  86 . The necessary pressure relief of the spring side of the regulating piston  80  and also the conducting of oil out of the spring chamber  12  when reducing the delivery quantity takes place via corresponding connecting cross sections of the regulating unit  82  into the relief duct  92  which is open to the interior of the crank case  84 .  
       FIG. 7  illustrates an electrically activated regulating unit  100  which operates in two regulator stages, with an arrangement on the crank case. It comprises the step piston  51 , which has already been described with reference to  FIG. 5 , an associated housing  101  and an electrovalve  102 . As in the embodiment according to  FIG. 6 , in this two-stage pressure regulation too, the oil pump  103  is pressure-regulated only via the connecting control bore  87 . By this means, and also by means of an oil-pump-internal pressurization of the displacement chamber  28  with the delivery-oil pressure (omission of the line  91  from  FIG. 6 ), an advantageous simplification of the oil pump is also possible in a two-stage pressure regulation. Without an electric activation of the electrovalve  102 , the second active surface  54  of the step piston  51  is relieved from pressure via the relief duct  92 , which is on the left in  FIG. 7 , so that the step piston  51 , which is acted upon by oil pressure only via the first active surface  53 , then carries out with its regulating spring  52  the pressure regulation of the oil pump at a higher pressure-regulating level. By contrast, with the electric activation of the electrovalve  102 , the second active surface  54  of the step piston  51  is additionally also acted upon by the oil pressure, so that then the pressure regulation of the oil pump  103  takes place at a reduced pressure-regulating level.  
      The regulation according to the invention of the oil pressure is largely independent of the temperature-dependent viscosity of the delivery oil. Therefore, by means of the proposed pressure regulation for oil pumps of motor-vehicle internal combustion engines, effectively reduced fuel consumption by means of oil-pump driving powers which are not inconsiderably reduced can be obtained not only when the engine is operationally warm, but also, in particular, even in the daily cold operation with oil temperatures which are still low after the engine is started.  
      Numerous modifications are conceivable within the context of the invention; for example, individual features from various embodiments of the one described above can be combined with one another and/or with the prior art. It is also possible for, for example, the activating device to have a plurality of the above-mentioned components.