Patent Publication Number: US-8123492-B2

Title: Speed-related control mechanism for a pump and control method

Description:
FIELD OF THE INVENTION 
     The present invention relates to fixed or variable capacity pumps. More specifically, the present invention relates to a speed-related control mechanism to control the output of a fixed or variable capacity pump. 
     BACKGROUND OF THE INVENTION 
     Pumps for incompressible fluids, such as oil, are often gear, vane or piston pumps. In environments such as engine lubricating systems, gear pumps are often employed as they are reliable and relatively inexpensive to manufacture. 
     Gear pumps suffer from a disadvantage in that they are a constant displacement volume (capacity) pump (i.e.—they pump substantially the same volume of fluid for each revolution of the pump and thus deliver more fluid at higher operating speeds than at lower speeds). In environments such as automotive engine lubrication systems, wherein the pump speed will change while the required amount of fluid to be provided by the pump will remain substantially constant, the pump capacity is sized to provide the necessary volume of fluid at the expected lower operating speeds and thus, at higher operating speeds, the gear pump will oversupply the fluid. 
     To control the oversupply, and the resulting over pressure which would otherwise damage engine components, gear pumps in such environments are typically provided with a pressure relief valve which allows the undesired portion of the oversupplied fluid to return to a sump, tank or back to the inlet of the pump so that only the desired volume of fluid is supplied to the engine. 
     While equipping gear pumps with such pressure relief valves does manage the problems of oversupply at higher operating speeds, there are disadvantages with such systems. For example, the pump still consumes input energy to pump the oversupply of fluid, even though the pressure relief valve prevents delivery of the undesired portion of the oversupplied fluid, and thus the pump consumes more engine power than is necessary. 
     An alternative to gear pumps, in such environments, is the variable capacity vane pump. Such pumps include a moveable ring known as a slide ring, which allows the eccentricity of the pump to be altered to vary the capacity of the pump. Typically a control piston, connected to the slide ring, or alternatively, a pressurized chamber formed between the slide ring and the pump housing, is supplied with pressurized oil, directly or indirectly, from the output of the pump and, when the force created by the pressure of the supplied oil acting either on the control piston or directly on the slide ring is sufficient to overcome the force of a return spring, the slide ring is moved to reduce the capacity of the pump and thus lower the volume of the pumped oil to a desired level. If the supplied pressurized oil is at a pressure less than the desired level, then the force generated at the control piston or on the slide ring is less than that generated by the return spring and the return spring will move the slide ring to increase the capacity of the pump. In this manner, the output volume of the pump can be adjusted to maintain a selected value of pressure. 
     A disadvantage of both fixed and variable capacity pumps when controlled in the ways previously described is that, when operating above a threshold value of speed, the control pressure is constant according to the balance of forces between the spring and the pressurized area of the piston or slide ring. The threshold speed is the speed below which the pressure is insufficient to move the slide ring or open the relief valve. The value chosen for the control pressure depends on the worst case operating condition, which is typically at maximum speed, whereas the engine is likely to spend most operational time at lower speeds, when a lower control pressure would be satisfactory. 
     It is desirable in these circumstances to vary the output pressure of these pumps relative to the speed of the engine. Effective pressure control of the pump, based at least partially on the operating speed of the engine, can result in an improvement in engine efficiency and/or fuel consumption. 
     While such speed-related control can be achieved by a combination of electronic speed sensors, computer controllers and solenoid actuators, to date no effective and reliable mechanical means to accomplish such speed-related control has been available. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a novel system and method of controlling the pressure of a fixed or variable capacity pump which obviates or mitigates at least one disadvantage of the prior art. 
     According to a first aspect of the present invention, there is provided a speed-related control mechanism for a fixed or variable capacity pump having a regulating mechanism for regulating output pressure; and a pressure generator to supply pressurized fluid to the regulating mechanism, the pressure of the supplied fluid being proportional to the operating speed of the pump. 
     Preferably, the pressure generator comprises: a disc defining an interior volume containing a fluid; at least one inlet port to supply working fluid to the volume; at least one outlet port to supply working fluid from the disc to the chamber of the pump, the disc being rotated at a speed related to the operating speed of the pump to create a forced vortex in the working fluid to pressurize the working fluid at the at least one outlet port proportionally to the square of the rotational speed of the disc. 
     According to a second aspect of the present invention, there is provided a variable capacity pump system, comprising: a variable capacity pump having a moveable capacity adjusting element; an equilibrium pressure control comprising a first chamber connected to the moveable capacity adjusting element and supplied with pressurized fluid from the outlet of the pump and a return spring connected to the moveable capacity adjusting element and acting against the force generated by pressurized fluid in the first chamber; and a speed-related control comprising: a pressure generator to supply pressurized fluid, the pressure of the supplied fluid being proportional to the operating speed of the pump; and a second chamber connected to the moveable capacity adjusting element and acting with the return spring, the second chamber being supplied with pressurized fluid from the pressure generator. 
     According to a third aspect of the present invention, there is provided a fixed capacity pump system, comprising: a fixed capacity pump; an equilibrium pressure control comprising a valve plunger whose first end is supplied with pressurized fluid from the outlet of the pump, a valve bore with an opening leading to a low pressure space such as the pump inlet, the valve plunger being disposed in the valve bore such that the position of the valve plunger determines whether the opening is blocked or connected to the pump outlet, a return spring acting against the valve plunger such as to close off the opening; and a speed-related control comprising: a pressure generator to supply pressurized fluid, the pressure of the supplied fluid being proportional to the operating speed of the pump; the pressurized fluid being supplied to a second end of the valve plunger, such that the force generated acts with the return spring to close off the opening. 
     According to a fourth aspect of the present invention, there is provided a pressure generator to provide a working fluid pressurized whose pressure is proportional to the square of the speed at which a device is rotated, comprising: a disc defining a volume to contain a fluid; at least one inlet port to supply working fluid to the volume; at least one outlet port to supply working fluid from the disc, the disc being rotated at a speed related to the speed at which the device is rotating to create a forced vortex in the working fluid to pressurize the working fluid at the at least one outlet port proportionally to the rotational speed of the device. 
     According to yet another aspect of the present invention, there is provided a method for the speed responsive control of a variable capacity pump, comprising the steps of: (i) providing a piston supplied with working fluid from the output of the pump, the piston moving a capacity altering member of the pump to decrease the capacity of the pump; (ii) providing a return spring acting against the piston to move the capacity altering member of the pump to increase the capacity of the pump; and (iii) providing a second piston supplied with working fluid from a pressure generator, the piston acting with the return spring to move the capacity altering member of the pump to increase the capacity of the pump, the pressure generator pressurizing the working fluid proportionally to the operating speed of the pump. 
     According to yet another aspect of the present invention, there is provided a method for the speed responsive control of a fixed capacity pump, comprising the steps of: (i) providing a valve plunger whose first end is supplied with working fluid from the outlet of the pump, which when allowed to move past an opening in the valve bore, allows fluid to pass from the pump outlet to a low pressure space such as the pump inlet and thereby reduces the outlet flow of the pump system; (ii) providing a return spring acting against the valve plunger in a direction opposed to that of the force generated by the working fluid pressure thereby tending to close the valve; and (iii) providing a chamber at the second end of the valve plunger supplied with working fluid from a pressure generator, the force thereby generated acting with the return spring and also tending to close the valve, the pressure generator pressurizing the working fluid proportionally to the operating speed of the pump. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred embodiments of the present invention will now be described, by way of example only, with reference to the attached Figures, wherein: 
         FIG. 1  shows a schematic representation of a system including variable capacity pump and a speed-related control mechanism in accordance with the present invention; 
         FIG. 2  shows a front view of the body of a pressure generator utilized in the system of  FIG. 1 ; 
         FIG. 3  shows a perspective view of a section, taken through line  3 - 3 , of the body of  FIG. 2 ; 
         FIG. 4  shows a front view of a system including a fixed capacity pump and a speed related control mechanism in accordance with the present invention; and 
         FIG. 5  shows a section view taken through the line  5 - 5 , of the system of  FIG. 4 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A pump system including a speed-related control mechanism and variable capacity pump in accordance with an embodiment of the present invention is indicated generally at  20  in  FIG. 1 . System  20  includes a capacity adjusting mechanism  24 , which in this embodiment is the moveable ring of the vane pump, and a speed-related control mechanism  28  for operating the capacity adjusting mechanism  24 . 
     While the following discussion relates to a variable capacity vane pump, the present invention can be employed with other fixed or variable capacity pumps as will be apparent to those of skill in the art. Variable capacity vane pumps are typically provided with a pressure control piston  32  and a return spring  36  to provide pressure-relief type control. The working fluid  38  from the outlet side of the pump, such as oil from a reservoir or gallery in an engine, is supplied to pressure control piston  32  and, when the pressure is sufficient to create enough force on pressure control piston  32  to overcome the force of return spring  36 , the pressure control piston will move the pump ring to reduce the capacity of the pump. If the pressure supplied to pressure control piston  32  is insufficient to overcome the force of return spring  36 , then return spring  36  moves the pump ring to increase the capacity of the pump. These pumps typically reach equilibrium at a constant value of pressure, provided that the pump ring is not abutting any limit stops, or the like, and the equilibrium pressure is determined by the piston area that the pressurized working fluid acts against and the return spring force. 
     In addition to the above-mentioned equilibrium pressure control mechanism, pump system  20  further includes speed-related control mechanism  28  which comprises a control piston  40 , a control pressure supply  44  and a pressure generator  48 . Control piston  40  is connected to control pressure supply  44  and, as the pressure of control pressure supply  44  increases, piston  40  applies force to adjustment mechanism  24  in addition to that of return spring  36  which tends to increase the capacity of the variable capacity pump. The increased capacity thus achieved increases the flow volume delivered by the pump with a commensurate increase in the pressure of the flow through the device supplied with the flow. 
     Control pressure supply  44  is not supplied with working fluid from the output side of the pump but is instead supplied with working fluid from pressure generator  48  which, as described below, varies the pressure of the supplied fluid with the square of the operating speed of the pump. Therefore, a pump system in accordance with the present invention reaches a steady state equilibrium at a range of discharge volumes (and associated pressures) which increase with rotational speed of the pump. 
     As best seen in  FIGS. 2 and 3 , pressure generator  48  comprises a disc  52  which defines an enclosed interior annular volume  56 . At least one inlet port  60  and one outlet port  64 , and in the illustrated embodiment a set of three inlet ports  60  and a set of three outlet ports  64 , extend into disc  52  to annular volume  56  and allow working fluid to enter and exit volume  56 . As illustrated, outlet ports  64  are adjacent to the outer periphery of disc  52  while inlet ports  60  are adjacent the axis of rotation of disc  52 . 
     As shown in  FIG. 1 , disc  52  is mounted on, and rotates with, drive shaft  68  which drives the impeller of the vane pump. A manifold  72  connects a working fluid supply  76  with inlet ports  60  and connects outlet ports  64  to control pressure supply  44 . Fluid supply  76  is connected to the inlet of the variable capacity pump and supplies fluid at zero gauge pressure to volume  56 . 
     As will be apparent to those of skill in the art, as disc  52  rotates with drive shaft  68 , a forced vortex is created in volume  56 , i.e.—the volume of fluid within volume  56  rotates with disc  52  with little or no relative movement of the particles of the fluid. In such a forced vortex, the pressure of the fluid within volume  56  increases with the radial distance of the fluid from the axis of rotation. Thus, the pressure of the working fluid at inlet ports  60  will be less than the pressure of the fluid at outlet ports  64  and the difference between the pressures is dependent upon the square of the rotational speed of drive shaft  68 . Specifically, the difference in pressure of the fluid between outlet ports  64 , and inlet ports  60 , is given by 
                 p   o     -     p   i       =         ρ   ·     ω   2       2     ·     (       r   o   2     -     r   i   2       )             
where p o  is the pressure at the outlet ports  64  in Pascals, p i  is the pressure at the inlet ports  60  in Pascals, ρ is the density of the fluid in kg/m 3 , ω is the speed of drive shaft  68  in rad/sec, r i  is the distance in meters of the inlet ports  60  from the rotational center of disc  52  and r o  is the distance in meters of the outlet ports  64  from the rotational center of disc  52 .
 
     As will now be apparent, the fluid in volume  56  is thus pressurized proportionally to the square of the speed of drive shaft  68 . Thus, in this particular embodiment, control pressure supply  44  varies with the square of the speed of drive shaft  68  and speed-related control mechanism  28  operates capacity adjusting mechanism  24  responsive to the square of the speed of drive shaft  68 . 
     As the speed of the engine, and thus drive shaft  68 , increases, the pressure of control pressure supply  44  on control piston  40  is increased, adding to the force of return spring  36  and speed-related control mechanism  28  moves capacity adjusting mechanism  24  to increase the capacity of the pump. Conversely, as the speed of the engine, and thus drive shaft  68 , decreases, the pressure of control pressure supply  44  on piston  40  is decreased, decreasing the total of the force exerted by piston  40  and return spring  36  on capacity adjusting mechanism  24 , so that capacity adjusting mechanism  24  moves to decrease the capacity of the pump. Thus, speed-related control mechanism  28  provides pump system  20  with a speed responsive control of the capacity of the pump. 
     A pump system including a fixed displacement pump and a speed related pressure control mechanism is generally indicated at  80  in  FIGS. 4 and 5 . The fixed displacement pump shown in this embodiment is a gear pump and comprises inner rotor  84 , outer rotor  88 , shaft  92 , housing  108  and cover  112 . As the shaft  92  and rotors  84  and  88  rotate, low pressure fluid is drawn into the pump through inlet connection  132  into inlet ports  120  where it enters the rotors. High pressure fluid is expelled from the rotors into discharge ports  124  and then out of the pump through discharge connection  128 . This type of fixed displacement pump is well known prior art, and may include but is not limited to gerotor pumps, other types of internal gear pump, external gear pumps and crescent gear pumps. Other types of pump altogether, such as axial piston pumps and radial piston pumps may also be employed. 
     A speed related pressure generator  52  is mounted on shaft  92  and housed within housing  116  and cover  112 . On initial start-up of the pump, fluid fills internal space  56  via priming orifice  148  which is connected to high pressure port  124  in the pump. Once internal space  56  is full, the fluid rotates substantially as a solid body with pressure generator  52 , and according to the physics of a forced vortex described previously, a higher pressure exists at outer port  64  than at inner port  60 . Inner port  60  is connected to inlet port  120  of the pump via passageway  76 , thus the pressure at inner port  60  is effectively maintained at zero gauge pressure at all times. The pressure at outer port  64  will therefore be higher than zero gauge pressure by an amount depending on the rotational speed of the shaft  92 . 
     Priming orifice  148  will continue to allow a small flow of fluid to enter internal space  56 , which will then pass through to pump inlet ports  120  via inner port  60  and passage  76 . If the orifice size is small enough, this flow will have a negligible effect on the operation of the pressure generator, and will only marginally affect the volumetric efficiency of the pump. Such orifices are currently deployed in some engine applications for the lubrication of camshaft drive chains with fine jets of oil. 
     A conventional relief valve plunger  96  and spring  100  are disposed within a valve bore in housing  108 , and are secured in place by plug  104 . The function of the valve system is to allow fluid to escape from the pump discharge back to pump inlet ports  120  via passage  144 , at the condition where the net pressure forces on the valve plunger  96  are high enough to sufficiently compress spring  100 . 
     Chamber  140  at the spring end of plunger  96  is connected to pressure from outer port  64  of pressure generator  52  via passage  44 . Chamber  136  at the other end of valve plunger  96  is connected to pump discharge pressure. The net hydraulic force on valve plunger  96  thus depends on the difference between these two pressures, unlike a conventional pressure relief valve where the net hydraulic force depends on the pump discharge pressure alone. 
     At low speed, the pressure in chamber  140  is low and the pressure in chamber  136  creates a force on valve plunger  96  which is opposed only by the spring force. Thus the valve will open at relatively low pump discharge pressure. At high speed the pressure in chamber  140  is higher and augments the spring force. The pressure in chamber  136  must therefore also be higher in order to create the same net force required for the valve to open. Thus, the valve will open at a range of pressures according to the pump speed; the higher the speed, the higher the pressure. 
     As will be apparent to those of skill in the art, various known mechanisms can be employed, if desired, to alter the operation of speed-related capacity mechanism  28  such that capacity adjusting mechanism  24 , or the like, is varied with the speed of drive shaft  68  or  92 , rather than with the square of the speed of drive shaft  68  or  92  or proportionally to other speeds. For example, one or more orifices can be formed in disc  52 , or any other body forming the containment chamber for the pressurized fluid, to allow working fluid to exit disc  52 . Without such orifices, fluid  56  contained within disc  52  is unable to escape and tends to take up the same rotational speed as disc  52 , each particle of fluid describing a circle, according to the accepted definition of a forced vortex. With such orifices introduced, the fluid  56  contained within disc  52  is able to flow through disc  52 , thereby inducing relative motion between the fluid and the disc. The particles of fluid  56  move in outward spirals, and the effective rotational speed component of fluid  56  is reduced to less than that of disc  52 , thus reducing the pressure of the working fluid at outlet ports  64 . As will be apparent, the escaped working fluid can be returned via the orifices to the inlet side of the pump. 
     By allowing some of the working fluid to escape through such orifices, especially if the orifices are sized appropriately with respect to the viscosity of the working fluid such that a given flow will occur at given pressures, the pressure versus speed performance of pressure generator  48  can be altered to be proportional to a quantity somewhat less than the square of the rotation speed. 
     By employing a forced vortex of fluid, pressure generator  48  advantageously provides a mechanical means of providing a supply of pressurized fluid whose pressure is proportional to the square of a rotation speed. While in the examples above, pressure generator  48  is driven from the drive of the pump, it is contemplated that the pressure generator can be driven by any other convenient rotating member which rotates at a speed related to the speed of the pump, allowing pressure generator  48  to be located conveniently within an engine casting or elsewhere. It is also contemplated that pressure generator  48  can be employed in a variety of applications in addition to the pump capacity control applications described herein wherein a speed-related pressure is required for a control purpose and such other applications are within the contemplated scope of the present invention. 
     In the embodiment shown in  FIG. 1 , control piston  40  acts with return spring  36  against pressure control piston  32 . In the embodiment shown in  FIG. 5  speed related pressure acts on valve plunger  96  with return spring  100  in opposition to the pump discharge pressure. However, as will be apparent to those of skill in the art, the present invention is not so limited and merely requires that the speed related pressure be applied to a controlling member of a pump system against suitable biasing means. Such biasing means can be additional return springs, other control mechanisms and/or pistons, etc. 
     As described above, control pressure supply  44  is applied to a second piston, namely control piston  40 , to move capacity adjusting mechanism  24 . However, as will be apparent to those of skill in the art, control pressure supply  44  can instead be provided to a second chamber of a double acting piston if desired. In this manner, only a single piston, albeit a double acting one, is required. 
     The above-described embodiments of the invention are intended to be examples of the present invention and alterations and modifications may be effected thereto, by those of skill in the art, without departing from the scope of the invention which is defined solely by the claims appended hereto.