Abstract:
A variable displacement pump is provided. A pump body has an outer ring defining an inner cavity, where the inner cavity further defines a pump suction path and a pump discharge path in fluid communication with the inner cavity. A cam ring is pivotably supported in the inner cavity by a pivot pin formed on a portion of an inner diameter of the adapter ring. An actuated cam is formed on the cam ring. An actuator is linked through the actuated cam to the cam ring for moving the cam ring in a pivotable motion. A control module is linked to the actuator.

Description:
This application is a continuation in part of U.S. patent application Ser. No. 09/826,268, entitled “Auxiliary Solenoid Controlled Variable Displacement Power Steering Pump,” filed on Apr. 3, 2001 now U.S. Pat. No. 6,470,992, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates generally to the field of pumps, in particular variable displacement pumps utilized in automotive vehicles. These pumps are designed to improve the fuel efficiency of automotive vehicles. 
     BACKGROUND OF THE INVENTION 
     In a power steering system of a vehicle, a variable displacement pump is a hydraulic pump that responds to the needs of the power steering system, as well as to changes in revolutions per minute (RPM) of the engine, by supplying fluid to the power steering system. Variable displacement pumps reduce the input torque requirements on the front-end accessory drive (FEAD) of the driving engine. In this displacement pump, the discharge flow rate increases or decreases in accordance with the speed of the engine. As the shaft speed, which is controlled by a drive belt from an engine of the vehicle, increases, the pump pressure and output flow of the pump also increases. When the pump reaches a desired shaft speed, a spool valve, and a spring allow pressure to be exposed on one side of a cam ring structure in a variable displacement pump. This pressure decreases eccentricity of the cam ring to the pump shaft center by providing a force to swing the cam ring. The decrease in eccentricity decreases the pump displacement by moving the cam ring center point towards the shaft center. 
     In order to control the flow rate of fluid through the variable displacement pump, various techniques have been developed. One such technique is described in U.S. Pat. No. 5,562,432, which discloses a conventional variable displacement pump having a cam ring that is moved by the pressures of the first and second fluid pressure chambers and the biasing force of the compression coil spring is formed in the second fluid pressure chamber. The movement of the cam ring occurs in accordance with an increase or decrease of the supply flow rate of the fluid accompanying a change in rotational speed of the pump, thereby controlling the pump volume to a required value. However, a problem exists in appropriately controlling the swing motion of the cam ring. 
     SUMMARY OF THE INVENTION 
     The present invention provides, in one embodiment, a variable displacement pump. A pump body has an outer ring defining an inner cavity, where the inner cavity further defines a pump suction path and a pump discharge path in fluid communication with the inner cavity. A cam ring is pivotably supported in the inner cavity by a pivot pin formed on a portion of an inner diameter of the outer ring. An actuated cam is formed on the cam ring. An actuator is linked through the actuated cam to the cam ring for moving the cam ring in a pivotable motion. A control module is linked to the actuator. 
     In a further embodiment of the invention a variable displacement pump is provided. A pump body has an outer ring defining an inner cavity, where the inner cavity further defines a pump suction path and a pump discharge path in fluid communication with the inner cavity. A cam ring is pivotably supported in the inner cavity by a pivot pin formed on a portion of an inner diameter of the outer ring. An actuator is linked through a screw arm to the cam ring for moving the cam ring in a pivotable motion. A control module is linked to the actuator. 
     In another embodiment of the invention a device is provided for adjusting the amount of fluid flowing through a variable displacement pump. A control module is configured to receive measurements of pressure from a power steering system and measurements of an engine speed from an engine of a vehicle, the module is configured to produce pump control signals. A cam ring is disposed in the variable displacement pump, the ring being actuatable in response to the signals from the control module. 
     In another embodiment of the invention a method for adjusting the amount of fluid flowing in a variable displacement pump is disclosed. The method includes providing a cam ring pivotably supported in an inner cavity of a pump body by a pivot pin formed on a portion of an inner diameter of the pump body and a portion of an outer diameter of the cam ring. An actuator is provided as a link to the cam ring. The control module receives measurements from an engine and measurements from a power steering system of a vehicle. The measurements are transmitted from the control module to the actuator. The cam ring is adjusted via the actuator in response to the measurements. 
     In yet another embodiment of the invention a system is provided for adjusting the amount of fluid flowing in a variable displacement pump in a vehicle. A power steering system includes a variable displacement pump having a pumping chamber and a pivotably mounted cam ring inside the pumping chamber. An engine is mounted in the vehicle. A control module is configured to receive measurements of pressure from the power steering system and measurements of an engine speed from the engine to move the cam ring and adjust pressure in the variable displacement pump. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other advantages of the present invention will become more fully apparent as the following description is read in conjunction with the accompanying drawings, wherein: 
     FIG. 1 depicts a sectional view of the main part of a variable displacement pump according to the preferred embodiment of the invention; 
     FIG. 2 depicts a flow chart according to the preferred embodiment of the invention; 
     FIG. 3A depicts one view of the main part of the variable displacement pump according to the preferred embodiment of the invention; 
     FIG. 3B depicts another view of the main part of the variable displacement pump according to the preferred embodiment of the invention; 
     FIG. 4 depicts a representation of the main part of the variable displacement pump controlled by a power steering system and engine speed according to the preferred embodiment of the invention; 
     FIG. 5 is a graphical depiction of the relationship between pump flow versus shaft speed (in rpm) at various pressures without forced displacement adjustment according to the preferred embodiment of the invention; and 
     FIG. 6 is a graphical depiction of the relationship between pump flow versus shaft speed (in rpm) at varying pressures with forced displacement adjustment according to the preferred embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the figures, FIG. 1 is a representation of a variable displacement pump  101 , which includes an outer ring  103  and a cam ring  105 . The cam ring  105  is free to swing in an inner cavity  107 , formed in the outer ring  103  of the pump body  101 . A spring means  109  or coil spring  109  biases the cam ring  105  to the left, as shown in this view. 
     A rotor  111  is accommodated in the cam ring  105  to be eccentric on one side to form a pump chamber  113  on the other side. When the rotor  111  is rotatably driven by an external drive source, vanes  111   a  held to be movable forward or backward in the radial direction are projected and refracted. Reference numeral  111   b  denotes a driving shaft of the rotor  111 . The rotor  111  is driven by the rotating shaft  111   b  to rotate in a direction indicated by an arrow in FIG.  1 . Under vane ports (not shown) provide hydraulic pressure behind the vanes  111   a  to force the vane tips to ride along the cam ring  105  profile. This creates a sealed chamber between vanes  111   a , allowing the pump  101  to do work on the fluid. 
     In the following description, the pump chamber  113  is a space formed in the cam ring  105  on one side of the rotor  111  and extends from a suction opening  115  to a discharge opening  117 . 
     A fluid pressure chamber  119  is formed on two sides around an outer surface of the cam ring  105  in the inner cavity  107  of an inner surface on the outer ring  103  set in the pump body  101 . Path  119   a  is an opening to the fluid pressure chamber  119 , through a spool valve (not shown), to guide the fluid and control the pressure to swing the cam ring  105 . 
     The pump suction opening  115  and pump discharge opening  117  are formed in at least corresponding ones of a pressure plate and a side plate (not shown) serving as stationary wall portions for holding other pump constituent elements such as the rotor  111  and cam ring  105 , by sandwiching them between these plates. 
     The cam ring  105  is biased by the compression coil spring  109  from the fluid pressure chamber  119  and is urged in a direction to keep the volume (pump volume) in the pump chamber  113  maximized. A seal member  121  is preferably placed in the outer surface portion of the cam ring  105  to define the fluid pressure chamber  119 , together with a pivot pin  123 , on the right and left sides. 
     FIG. 2 depicts a flow chart of the process of adjusting the amount of fluid flowing in a variable displacement pump of a vehicle. As previously described, fluid is transferred through the variable displacement pump to the power steering system as a response to the fluid needs of the power steering system. In this flow chart, the process for adjusting the amount of fluid starts at  201 . At  203 , measurements are taken by at least one sensor connected to an engine for measuring the engine speed. The other measurement is taken from at least one sensor from the steering hoses that is able to obtain a steering pressure of the power steering system. These sensors are able to read or sense measurements of an engine speed from the engine and pressure from the power steering system. These measurements may also be read from the vehicle&#39;s computer. Then, the sensors are able to send these measurements to a control module. The control module is able to detect the measurements  205  from these sensors. 
     The control module is preferably a microprocessor that utilizes one or more of the following parameters: system pressure, engine speed, steering wheel angle, pump flow and pump speed. The input parameters can be measured in various ways, including but not limited to sensors, transducers, flow meters and gauges. The control module is also programmed with a “look-up” table. The look-up table includes measurements for engine speeds and measurements of pressure for the power steering system and corresponding instructions given to the actuator to move the cam ring  105  a specific distance in the variable displacement pump. In addition, the control module may have an algorithm or matrix or any device or method that acts similar to the look-up table. 
     Once the control module is able to detect the measurements  205 , then these detected measurements are compared with measurements on the look-up table to determine where on the table the measurements fall. The determination of where the measurements fall corresponds with the movement of the actuator by the control module at  207  to move the cam ring  105 , as previously described, in the variable displacement pump. This movement of the cam ring  105  controls the amount of fluid the power steering system will receive from the variable displacement pump. 
     After activating the actuator at  207 , the control module must decide if it should complete controlling the movement of the cam ring  105  at  209  in the variable displacement pump. If the control module decides to continue sensing and adjusting the cam ring  105 , then the process continues at start  201 . If the control module decides not to continue sensing and adjusting the cam ring  105 , because it is no longer necessary to control the movement of the cam ring  105  then the process ends  211 . 
     FIG. 3A depicts one view of the main part of the variable displacement pump. One view  300  includes the outer ring  103 , the cam ring  105  and the pivot pin  123 , as previously described, a cam pivot  301 , an actuated cam  303 , an actuated arm  305  and an electronic actuator  307 . The actuator  307  includes a motor and mechanism that causes the cam ring  105  to be adjusted or moved in the variable displacement pump. The actuator  307  is capable of moving the cam ring  105  in a pivotable motion over the pivot pin  123 . The actuator  307  may also be referred to as an electronic leveraging device. 
     The actuated cam  303 , is preferably a lopsided linking piece in this mechanical linkage that links the actuated arm  305  to the cam ring  105 . However, the actuated cam  305  can have any shape associated with a linking piece that acts as a mechanical linkage between the actuated arm  305  and the cam ring  105 . The actuator arm  305  is a mechanical arm that moves the cam ring  105  in the variable displacement pump. The actuated arm  305  may also be a lever, a direct connection, a push spring or any device or method that is able to control the movements of the actuated cam  303 . The actuator arm  305  is given instructions by the actuator  307  to move the cam ring  105  a specific distance in a pivotable motion over the pivot pin  123 . 
     The actuated cam  303  and the cam pivot  301  are formed on an inner portion of outer ring  103  and an outer portion of cam ring  105 . There may also be another pin (not shown) on the actuated arm  305 , which assists the actuated arm  305  in moving the cam ring  105 . One side of the actuated arm  305  is connected to the actuator  307  and the other side of the actuated arm  305  extends through a portion of the outer ring  103  to the cam ring  105 . Thus, the actuator  307  is linked to the cam ring  105 . 
     As described above, when the electronic actuator  307  receives instructions from the control module, then the electronic actuator  307  through the actuated arm  305 , the actuated cam  303  and the cam pivot  301  moves the cam ring  105  in a pivotable motion over the pivot pin  123 . For example, responsive to the measurements received by the control module, the electronic actuator  307  may: not move the cam ring  105  over the pivot pin  123 , move the cam ring  105  over the pivot pin  123  slightly to the left of the outer ring  103 , or move the cam ring  105  over the pivot pin  123  all the way to the left of outer ring  103 , as shown in FIG.  3 . The aforementioned example does not limit the ability of the actuator  307  to move the cam ring  105  in any direction. 
     FIG. 3B depicts another view of the main part of the variable displacement pump. A second view  302  includes the outer ring  103 , the cam ring  105 , the pivot pin  123 , a screw arm  309  and the electronic actuator  307 . The screw arm  309  is a threaded mechanical arm. The screw arm  309  is also a mechanical arm that moves the cam ring  105  in the variable displacement pump. Further, the screw arm  309  is given instructions by the actuator  307  to move the cam ring  105  a specific distance in a pivotable motion over the pivot pin  123 . 
     The screw arm  309  has two sides, one side is connected to the electronic actuator  307  and the other extends through the outer ring  103  to the cam ring  105 . As described above, when the electronic actuator  307  receives instructions from the control module, then the electronic actuator  307 , through the screw arm  309 , moves the cam ring  105  in a pivotable motion over the pivot pin  123 . For example, responsive to the measurements received by the control module the electronic actuator  307  may: not move the cam ring  105  over the pivot pin  123 , move the cam ring  105  over the pivot pin  123  slightly to the left of the outer ring  103 , or move the cam ring  105  over the pivot pin all the way to the left of the outer ring  103 , as shown in FIG.  3 . The aforementioned example does not limit the ability of the actuator  307  to move the cam ring  105  in any direction. 
     FIG. 4 depicts a representation of the main portion of the variable displacement pump that is controlled by a power steering system and engine speed. The actuator is preferably an electronic actuator. In this figure, there is a system that includes: a power steering system  401 , an engine  403 , a control module  405 , the electronic actuator  307 , the actuated arm  305 , the outer ring  103 , the cam ring  105  and the rotor  111 . Power steering system  401  includes at least one sensor  401   a  that provides measurements of pressure to the control module  405 . The engine  403  also includes at least one sensor  403   a  that provides measurements of engine speed to the control module  405 . 
     After the control module  405  receives these measurements, the module  405  compares the measurements, by utilizing a processor, with a look-up table that includes measurements of engine speed and measurements of pressure from a power steering system of the vehicle to determine where on the look-up table the measurements from at least one sensor  403   a  of engine speed and measurements from at least one sensor  401   a  of pressure from the power steering system fall. When the control module  405  determines where on the look-up table the measurements from at least one sensor  401   a  of engine speed and measurements from at least one sensor  403   a  of pressure from the power steering system fall, the control module  405  instructs the electronic actuator  307  to move the cam ring  105  in a pivotable motion. The electronic actuator  307  utilizes the actuated arm  305  or screw arm  309  to move the cam ring  105  in a pivotable motion over the pivot pin  123 . 
     FIG. 5 is a flow curve depicting an initial pump function of flow versus shaft speed. This flow curve shows that pump shaft speed (in rpm) is related to pump flow (in GPM) for a variable displacement pump of the preferred embodiment. Regardless of system pressure, increase of shaft speed from approximately 400 rpm to about 800 rpm led to an increase in fluid movement in the pump of from less than about 0.5 GPM to about 2.5 GPM. Further increases in shaft speed had little impact on the fluid movement, as at higher rpm, the cam ring is pivoted to a position that results in lower displacement of fluid movement in the pump. Note that a minimum flow in steering gear is required to obtain power assist. Generally, steering input changes back pressure, and causes the cam to shift for higher displacement to get higher flow. 
     FIG. 6 is a flow curve depicting the utilization of an electronic leverage device and its effect on a variable displacement pump. This flow curve shows pump shaft speed is related to pump flow for a variable displacement pump constructed in accordance with the views  300  and  302  illustrated in FIG.  3 . FIG. 6 demonstrates in graphical form the dramatic difference in flow at shaft speeds ranging from about 400 rpm to about 3000 rpm at three different pressures when the cam is forced to a position of minimum displacement. When the shaft speed reaches a point where the “naturally” occurring displacement equals or approximates that obtained with forced displacement of the cam by the piston, the actuator  307  can be turned off or deactivated. Naturally occurring displacement refers to the displacement that results from operation of the variable displacement pump in variable displacement mode, wherein the displacement is reduced in response to higher pump shaft speed. Above a certain pump shaft speed, the displacement of the pump will be reduced below or approximate the displacement that would be caused by activation of the actuator  307 . 
     The actuator  307  can be deactivated at lower shaft speeds in response to steering maneuvers. The reduction in flow when the cam is forced into a minimum displacement position and when the actuator  307  of the present invention is not present or is not activated corresponds to the greatly increased efficiency of pumps and hydraulic systems constructed and utilized in accordance with the present invention. 
     In an embodiment of an automotive power steering system, the gear piston must always be charged. The minimum displacement required to maintain the gear piston charge is calculated as the minimum displacement to overcome the internal leakages in the pump and gear assemblies. For example, if the internal leakage in the pump and gear were 0.3 and 0.2 gallons per minute respectively, the minimum displacement would have to be 3.06 cc per rev. In other words, the cam ring cannot be forced into a position wherein the displacement of the pump is not sufficient to keep the gear piston charged. 
     The combined internal leakage value for a particular power steering system can be calculated, and either the actuator  307  programmed or adjusted to maintain the minimum displacement, or a mechanical stop used to maintain the minimum displacement. This would prevent the pump from producing a flow lower then the combined internal leakage and consequently would keep the gear piston charged. A factor of safety could easily be added in the actuator  307 . However, the actuator  307  controlled displacement cannot be held throughout the rpm range, as at higher rpm, the actuator  307  controlled minimum displacement becomes higher than the “naturally” occurring displacement in the pump, as shown in FIG.  5 . At the point where the forced displacement becomes less than the “naturally” occurring displacement, the actuator  307  would be switched off, so that the actuator controlled variable displacement pump functions like a standard variable displacement pump. 
     EXAMPLE 1 
     The improved efficiency of an actuator controlled variable displacement pump was tested using a computer simulation. The change in fuel economy for the actuator controlled variable displacement pump versus a standard variable displacement pump was evaluated. The pumps were modeled in a standard sport-utility vehicle. A vehicle stimulation program model was used that measures fuel economy for highway and city driving. The results are equivalent to the advertised sticker fuel economy placed on the vehicles before sale. Using the vehicle simulation program model, the actuator  307  pump saved an additional 0.01-mile per gallon (mpg) in a metro-highway scenario. 
     The improved pumps of the present invention are useful in all modes of self-propelled vehicles, such as but not limited cars, buses, and trucks, and may also be useful in other applications. 
     While a new actuator controlled variable displacement power steering pump has been disclosed as an example, there could be a wide range of changes made to this pump and hydraulic systems incorporating the same without departing from the present invention. 
     Thus it is intended that the foregoing detailed description be regarded as illustrative rather than limiting and that it be understood that it is the following claims, including all equivalents, which are intended to define the scope of the invention.