Abstract:
A speed-based system for controlling a pump displacement to control a pump flow rate of a hydraulic pump in a vehicle, such as a hybrid. The system includes a plurality of sensors, a controller, and a hydraulic pump. The controller is configured to receive data from the sensors, ascertain a speed of the vehicle, determine a target pump displacement, and transmit the target pump displacement. The target pump displacement is less than a predetermined maximum value when the speed of the vehicle is greater than a first predefined threshold, and equal to the predetermined maximum value when the speed of the vehicle is less than or equal to the first predefined threshold. The hydraulic pump is configured to ascertain an actual pump displacement, receive the target pump displacement from the controller, and alter the actual pump displacement to the target pump displacement.

Description:
RELATED APPLICATIONS 
     This application claims priority to U.S. Provisional Application No. 61/839,968, filed on Jun. 27, 2013 and titled “SPEED-BASED HYDRAULIC PUMP CONTROL SYSTEM AND METHOD FOR A HYBRID VEHICLE,” the entire contents of which is incorporated by reference. 
    
    
     BACKGROUND 
     The present invention relates to hydraulic hybrid vehicle systems. Hydraulic hybrid vehicle systems include four main components: a hydraulic fluid, a fluid reservoir, a hydraulic pump/motor (in parallel hybrid systems) or in-wheel motors and pumps (in series hybrid systems), and a fluid accumulator. The pump/motor extracts kinetic energy during braking to pump the working fluid from the fluid reservoir to the fluid accumulator. Working fluid is thus pressurized. When the vehicle accelerates, this pressurized working fluid provides energy to the pump/motor to power the vehicle. 
     As is known, hydraulic pumps generate a substantial amount of noise. Unavoidable design imperfections of the components used in hydraulic pumps result in uneven flow characteristics and pressures waves that produce unwanted system noise. In additional, these uneven flow characteristics and pressure waves make the components vibrate. This vibration of system components also generates unwanted system noise. Higher pump flow rates lead to an increase in uneven flow characteristics, pressure waves, and system component vibration. Accordingly, higher pump flow rates generate a significant amount of unwanted hydraulic system noise. 
     SUMMARY 
     In one embodiment, the invention provides a speed-based system for controlling a pump displacement to control a pump flow rate of a hydraulic pump in a vehicle, such as a hybrid. The system includes a plurality of sensors, a controller, and a hydraulic pump. The controller is configured to receive data from the sensors, ascertain a speed of the vehicle, determine a target pump displacement, and transmit the target pump displacement. The target pump displacement is less than a predetermined maximum value when the speed of the vehicle is greater than a first predefined threshold, and equal to the predetermined maximum value when the speed of the vehicle is less than or equal to the first predefined threshold. The hydraulic pump is configured to ascertain an actual pump displacement, receive the target pump displacement from the controller, and alter the actual pump displacement to the target pump displacement. 
     In another embodiment, the invention provides speed-based method for controlling a pump displacement and a flow rate of a hydraulic pump in a vehicle, such as a hybrid, to reduce system noise. A controller receives sensor data from a plurality of sensors, including a speed of the vehicle. The controller determines a target pump displacement. The target pump displacement is less than a predetermined maximum value when the speed of the vehicle is greater than a first predefined threshold, and equal to the predetermined maximum value when the speed of the vehicle is less than or equal to the first predefined threshold. The controller transmits the target pump displacement to the hydraulic pump. The hydraulic pump alters an actual pump displacement to the target pump displacement. 
     In yet another embodiment, the invention provides an electronically implemented speed-based system for controlling a pump displacement to control a pump flow rate of a hydraulic pump in a vehicle, such as a hybrid. In this embodiment, the hydraulic pump is a variable displacement pump. The controller controls the pump displacement by altering the pump angle of a swashplate inside the variable displacement pump. This embodiment does not require any additional mechanical hardware to be employed such as hydraulic noise suppressors, control valves, or pump control plates. 
     Other embodiments and aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an illustration of a hydraulic hybrid system and vehicle layout. 
         FIG. 2  is an illustration of a hydraulic displacement pump. 
         FIG. 3  is a schematic illustration of a hybrid hydraulic control system according to one embodiment. 
         FIG. 4  is a graphical representation of a braking event wherein a control system disclosed in the prior-art is implemented. 
         FIG. 5  is a graphical representation of the relationship between pump angle and vehicle speed implemented by the controller according to one embodiment. 
         FIG. 6  is a graphical representation of a braking event wherein a control system according to one embodiment is implemented. 
     
    
    
     DETAILED DESCRIPTION 
     Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. 
     Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of “including,” “comprising” or “having” and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. The terms “mounted,” “connected” and “coupled” are used broadly and encompass both direct and indirect mounting, connecting and coupling. Further, “connected” and “coupled” are not restricted to physical or mechanical connections or couplings, and can include electrical connections or couplings, whether direct or indirect. Also, electronic communications and notifications may be performed using other known means including direct connections, wireless connections, etc. 
     It should also be noted that a plurality of hardware and software based devices, as well as a plurality of different structural components may be utilized to implement the invention. Furthermore, and as described in subsequent paragraphs, the specific configurations illustrated in the drawings are intended to exemplify embodiments of the invention. Alternative configurations are possible. 
       FIG. 1  illustrates a vehicle  100 . The vehicle  100  includes two front wheels  110  and  112 , and two rear wheels  114  and  116 . The vehicle  100  includes other components including a controller  120 , a hydraulic pump  130 , a fluid reservoir  150 , a fluid accumulator  155 , an engine  160 , a transmission  165 , a hybrid gearbox  170 , and a transaxle  175 . When the engine  160  stops supplying power and the vehicle  100  is moving, the vehicle  100  will slow down. As the vehicle  100  slows down, the rear wheels  114  and  116  rotate. The rear wheels  114  and  116  are connected to the transaxle  175  and the transaxle  175  also rotates. The transaxle  175  is connected to the hybrid gearbox  170 . The hybrid gearbox  170  translates the rotating motion of the transaxle  175  to the hydraulic pump  130 . In turn, the hydraulic pump  130  uses the rotating motion to pump fluid from the fluid reservoir  150  to the fluid accumulator  155 . The controller  120  regulates the operation of the hydraulic pump  130 . 
       FIG. 2  illustrates a hydraulic pump  130  according to one embodiment of the invention, wherein the hydraulic pump  130  is a variable displacement pump. In the embodiment illustrated, the hydraulic pump  130  includes a swashplate  232 , a plurality of pistons  234 , a shaft  236 , a rotary valve  238 , and a cylinder block  240 . The cylinder block  240 , represented in  FIG. 2  by the dark areas, includes a plurality of cylinders  242  that are arranged in parallel to the plurality of pistons  234 . The cylinder block  240  is connected to the shaft  236  such that the cylinder block  240  and the plurality of cylinders  242  will rotate when the shaft  236  rotates. The swashplate  232  does not rotate. Therefore, as the plurality of pistons  234  rotate, the angle of the swashplate  232  causes the pistons  234  to move in and out of the plurality of cylinders  242 . The rotary valve  238  alternately connects each of the plurality of cylinders  242  from the fluid supply line  244  and a fluid delivery line  246 . 
     In one embodiment, each cylinder  242  is filled with low pressure fluid from the fluid reservoir  150  when it is attached to the fluid supply line  244 . Each cylinder  242  expels high pressure fluid to the fluid accumulator  155  when it is attached to the fluid delivery line  246 . A pump angle  250  is the angle between the swashplate  232  and an axis  248 . By varying the pump angle  250 , the stroke of the plurality of pistons  234  can be varied. If the swashplate  232  is perpendicular to the axis of rotation of the shaft  236  (i.e., pump angle  250  is zero degrees), no fluid will flow. On the other hand, if the swashplate  232  is at a sharp angle (i.e., pump angle  250  is 15 degrees), a large volume of fluid will flow. 
     A pump flow rate is the volume of fluid pumped through the system by a hydraulic pump  130  per unit time. In the variable displacement pump used in certain embodiments of the invention, the pump flow rate is determined by a pump speed and a pump displacement. Pump speed is the common rate of rotation of the shaft  236 , the cylinder block  240 , the plurality of cylinders  242 , and the plurality of pistons  234 . The pump speed is linearly related to the speed of the vehicle  100 . Pump displacement, or the volume of fluid pumped per revolution of the shaft  236 , is determined by pump angle  250 . The larger the pump angle  250 , the larger the pump displacement. Therefore, varying the pump angle  250  and/or the vehicle speed will affect the pump flow rate. 
       FIG. 3  is a schematic illustration of a hydraulic pump system  300  according to one embodiment of the invention. The system  300  includes a controller  120 , a hydraulic pump  130 , and a plurality of sensors  310 . In this embodiment, the hydraulic pump  130  is a variable displacement pump. In general terms, the controller  120  alters the pump displacement of the hydraulic pump  120  by controlling the pump angle  250 . The controller  120  includes an electronic processing unit  322 , a memory  324 , and an input/output interface  326 . The input/output interface  326  connects the controller  120  to external devices such as sensors. In one embodiment, the input/output interface  120  is connected to a controller area network (“CAN”) bus  340 . A CAN bus is a known vehicle network through which various vehicle systems can transmit and receive information. The controller  120  receives signals from the plurality of sensors  310 . Also, the controller  120  receives and sends signals from the hydraulic pump  130 . In one embodiment, communications between the controller  120 , the sensors  310 , and the hydraulic pump  130  occur over the CAN bus  340 . However, it is possible to connect the sensors  310  and the hydraulic pump  130  (via wired or wireless connection) directly to the controller  120 . 
     In this embodiment, the plurality of sensors  310  include: a vehicle speed sensor  350  and a pump angle sensor  355 . The vehicle speed sensor  350  ascertains the current velocity of the vehicle  100 . The pump angle sensor  355  measures the pump angle  250  of the swashplate. 
       FIG. 4  illustrates a braking event wherein controller logic is similar to that of prior-art technology (normal) is implemented. In  FIG. 4 , an exemplary braking event  405  occurs at a speed of approximately 40 kilometers per hour (“KPH”). With prior-art technology, the pump angle  250  changes rapidly from a low or zero value to a high value  410 . Once the high value  410  is reached, the pump angle  250  remains relatively steady until the end of the braking event  405 . Between approximately 40 KPH and 20 KPH the values of the pump flow rate are high. These high values of pump flow rate generate unwanted hydraulic system noise. 
       FIG. 5  graphically illustrates one embodiment of logic implemented by the controller  120  with regard to pump angle  250  and vehicle speed. When the speed of the vehicle  100  is greater than a first predetermined threshold  505  (e.g., 25 miles per hour), the controller  120  commands the hydraulic pump  130  to set the pump angle  250  to a minimum value. When the speed of the vehicle  100  is equal to the first predetermined threshold  505 , the controller  120  commands the hydraulic pump  130  to change the pump angle  250  to an offset value  515 . When the speed of the vehicle  100  is less than the first predetermined threshold  505  as well as greater than a second predetermined threshold  520  (e.g., 15 miles per hour), the pump angle  250  increases from the offset value  515  in a linear fashion. When the speed of the vehicle  100  is less than or equal to the second predetermined threshold  520 , the controller  120  commands the hydraulic pump  130  to set the pump angle  250  to a maximum value  525 . It is to be understood that pump angle  250  can be replaced with pump displacement. 
       FIG. 6  illustrates a braking event, similar to  FIG. 4 , wherein controller logic similar to that in  FIG. 5  is implemented. In  FIG. 6 , an exemplary braking event  605  occurs at a speed of approximately 40 KPH. Using the control techniques of embodiments of the invention, the pump angle  250  changes from a low or near zero value to about 7 degrees. As the speed of the vehicle  100  continues to decrease, the pump angle  250  increases in a linear fashion. When the speed of the vehicle  100  is approximately 20 KPH, the pump angle  250  remains steady at a high value  610 . Finally, when the speed of the vehicle  100  approaches zero (i.e., end of the braking event  605 ), the pump angle  250  changes to a low or near zero value. By controlling the pump angle  250  throughout the braking event  605 , the controller  120  limits the pump flow rate. Limiting the pump flow rate minimizes the generation of unwanted hydraulic system noise by the hydraulic pump  130 . 
     It is to be understood that the logic implemented by the controller can also be used for acceleration events even though the above examples are braking events. 
     Thus, the invention provides, among other things, a speed-based control system for controlling hydraulic pump displacement to limit unwanted system noise. Various features and advantages of the invention are set forth in the following claims.