Abstract:
A power steering waste heat recovery system for a vehicle and method of operating is disclosed. The system may include a power steering system and a waste heat absorption system. The power steering system may include a power steering pump, a liquid-to-liquid heat exchanger located downstream of the power steering pump and configured to allow power steering fluid flow therethrough, and a steering rack operatively engaging the heat exchanger to receive the power steering fluid therefrom. The waste heat absorption system may include an auxiliary heater loop configured to direct a liquid through the heat exchanger; and an automatically controllable heat control valve having an inlet, a first outlet for directing the liquid to bypass the auxiliary heater loop, and a second outlet for directing the liquid through the heat exchanger in the auxiliary heater loop.

Description:
BACKGROUND OF INVENTION 
     The present invention relates generally to waste heat recovery from a power steering system. 
     An ongoing concern with automotive vehicles is quick warm-up of the passenger cabin on cold winter days. For conventional gasoline powered automotive vehicles, when outside ambient temperatures are low and the vehicle has not been operated for a time, slow engine coolant warm-up results in a slow warm-up of the passenger cabin. In particular, with fuel economy becoming more of a concern, many automotive vehicles are employing smaller engines or diesel engines, which exacerbates the issue. Thus, some have resorted to add-on auxiliary heating systems, such as, for example, electric heaters, fuel fired heaters, engine driven viscous heaters, and hot gas heaters. All of these auxiliary heating systems, however, use extra fuel, or put extra load on the engine in order to produce the heat, which is counter to the original intended purpose of improving vehicle fuel economy. 
     In addition, for automotive vehicles with automatic transmissions, operation of the transmission when the transmission oil is cold can result in less than optimal transmission operation. Thus, this can lead to a reduction in fuel economy under cold operating conditions. 
     SUMMARY OF INVENTION 
     One or more embodiments may contemplate a power steering waste heat recovery system for a vehicle that may comprise a power steering system and a waste heat absorption system. The power steering system may include a power steering pump, a liquid-to-liquid heat exchanger located downstream of the power steering pump and configured to allow power steering fluid flow therethrough, and a steering rack operatively engaging the heat exchanger to receive the power steering fluid therefrom. The waste heat absorption system including an auxiliary heater loop configured to direct a liquid through the heat exchanger; and an automatically controllable heat control valve having an inlet, a first outlet for directing the liquid to bypass the auxiliary heater loop, and a second outlet for directing the liquid through the heat exchanger in the auxiliary heater loop. 
     An embodiment contemplates a method of warming a liquid using heat from power steering fluid of a power steering system, the method comprising the steps of: pumping the power steering fluid through a liquid-to-liquid heat exchanger, a power steering rack, and a liquid-to-air power steering cooler; determining if an ambient air temperature is below a predetermined ambient air temperature threshold; determining if a liquid temperature of a waste heat absorption system is below a predetermined liquid temperature threshold; and actuating a heat control valve to direct the liquid to bypass an auxiliary heater loop containing the liquid-to-liquid heat exchanger if the ambient air temperature is not below the predetermined ambient air temperature threshold or the liquid temperature is not below the predetermined liquid temperature threshold. 
     An advantage of an embodiment is the ability to recover the energy supplied to the power steering system that is otherwise rejected as waste heat by selectively transferring the waste heat to coolant passing through an auxiliary coolant heater loop. This enhances the heater performance of a heating, ventilation and air conditioning (HVAC) system, allowing for a faster warm-up of a passenger cabin. The faster warm-up is achieved without the need for the engine to provide extra energy. A restriction introduced by the auxiliary coolant heater loop may also help to reduce noise emanating from the power steering system. Moreover, such an auxiliary coolant heater loop may be employed with minimal packaging and weight impact since the power steering system in typical automotive vehicles is close to the vehicle&#39;s instrument panel. Hence, coolant hoses to the heater core can be easily plumbed, and the small sized liquid-to-liquid heat exchanger can be easily packaged in the vehicle. In addition, no new vehicle fluids need to be introduced, since the vehicles already employ coolant and power steering fluid. 
     An advantage of an embodiment is the ability to recover the energy supplied to the power steering system that is otherwise rejected as waste heat by selectively transferring the waste heat to transmission oil passing through an auxiliary transmission oil heater loop. This may enhance the operation of the automatic transmission (or transaxle) by minimizing the time at which the transmission is operating with cold transmission oil, which has a higher than desired viscosity. The enhanced transmission performance may improve fuel economy under this operating condition. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a schematic diagram of a power steering waste heat recovery system according to a first embodiment. 
         FIG. 2  is a schematic diagram of a power steering waste heat recovery system according to a second embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a waste heat recovery system  20  for a vehicle is shown. The waste heat recovery system  20  encompasses portions of a power steering system  22  and a heating, ventilation and air conditioning (HVAC) system  24 . 
     The power steering system  22  includes a hydraulic system  26  having a high pressure line  28  and low pressure line  30 . The arrowheads on the lines between illustrated components in  FIGS. 1 and 2  represent fluid lines, with the arrows indicating the direction of fluid flow in the particular line when there is flow in that line. A power steering pump  32 , which may be driven by a pulley (not shown) coupled to the engine, draws power steering fluid  96  from a power steering reservoir  34  and directs it to a power steering control valve  36 . The control valve  36  directs the power steering fluid  96  either through a first outlet  38  back to the intake side of the pump  32  or forwards it through a second outlet  40  into the high pressure line  28  on the high pressure side of the hydraulic system  26 . The power steering fluid  96  is directed through a viscous heater with a liquid-to-liquid heat exchanger  42  before being directed into the steering rack  44 . The fluid pressure applied to the steering rack is used to provide assistance to the steering process, which is accomplished in a conventional manner. The power steering fluid  96  exits the power steering rack  44  into the low pressure line  30  on the low pressure side of the hydraulic system  26 , where it is directed through a power steering cooler  46  in order to allow for air cooling of the fluid  96 . The power steering fluid  96  is then directed back into the power steering reservoir  34 . 
     The portion of the HVAC system  24  shown is the heating portion of the system, and uses engine coolant  95  as its system fluid. An engine  50  includes a first coolant outlet  52  to a radiator cooling loop  54 , within which is a radiator  56 . A second coolant outlet  58  directs coolant  95  into an engine coolant bypass loop  60 . A third coolant outlet  62  directs coolant  95  into a heater core coolant loop  64 , within which is located a heat control valve  66  and a heater core  68 . Each of the coolant loops  54 ,  60 ,  64  directs the coolant  95  back to a thermostat and water pump  70  (shown with a single symbol in  FIG. 1 ). The thermostat and water pump may operate a conventional manner, as is known to those skilled in the art. While three engine coolant outlets  52 ,  58 ,  62  are schematically shown and discussed, this may be a single opening from the engine  50 , with hoses that split into the three loops  54 ,  60 ,  64 . 
     The heater core  68 , heat control valve  66  and viscous heater  42  also form a portion of an auxiliary coolant heater loop  74 . The heat control valve  66  includes an inlet  76  from the third coolant outlet  62  and two outlets—a heater core outlet  78  directing coolant  95  to the heater core  68 , and a viscous heater outlet  80  directing coolant  95  to the viscous heater  42 . Coolant  95  directed into the heat exchanger  42  is then directed to the heater core  68  to complete the auxiliary coolant heater loop  74 . A controller  82  controls the heat control valve  66 , which controls to which outlet  78  or  80  the coolant  95  is directed. Dashed lines in  FIGS. 1 and 2  represent control or communication lines, such as electrical wires. The controller  82  may be a stand alone controller or may be incorporated into another vehicle controller, such as a HVAC controller, if so desired. An ambient air temperature sensor  84  and a coolant temperature sensor  86  may be in communication with the controller  82 . The sensors  84 ,  86  may be located as desired on the vehicle in order to get the desired ambient air and coolant temperature readings. 
     The operation of the waste heat recovery system  20  as it interacts with the power steering system  22  and HVAC system  24  will now be discussed. When the vehicle is operating, the power steering system  22  essentially operates the same as conventional power steering systems with the exception that the power steering fluid  96  now flows through the heat exchanger  42 . The operation of the power steering system  22  causes the power steering fluid  96  to heat up as part of the normal operation of the system. Also, with the heat control valve  66  set to direct the coolant  95  through the heater core outlet  78  to the heater core  68 , the HVAC system and engine cooling essentially operate the same as with a conventional system. 
     However, when the temperature sensors  84 ,  86  detect that the ambient temperature is below a predetermined ambient temperature threshold and the coolant temperature is below a predetermined coolant temperature threshold, and the HVAC system  24  is in a heater mode, then the controller  82  will actuate the heat control valve  66  to cause the coolant  95  to flow through the viscous heater outlet  80 . The coolant  95 , then, flows through the heat exchanger  42  where it absorbs heat from the power steering fluid  96 . Thus, waste heat from the power steering system  22  is transferred to the HVAC system  24 . This warmed coolant  95  then flows through the auxiliary coolant heater loop  74  to the heater core  68  and back to the engine  50 . The extra heat absorption by the coolant  95  in the heat exchanger  42  will provide additional heat sooner to the heater core  68 . Thus, the time to heat the vehicle passenger cabin on cold days when the coolant  95  starts out near ambient temperature is reduced. Once the coolant  95  warms up due to engine operation, the controller  82  will then actuate the heat control valve  66  to direct the coolant  95  through the heater core outlet  78 . 
       FIG. 2  illustrates a second embodiment. Since this embodiment is similar to the first, similar element numbers will be used for similar elements, but employing 100-series numbers. The power steering system  122 , including the hydraulic system  126 , power steering pump  132 , power steering reservoir  134 , power steering control valve  136 , the viscous heater with liquid-to-liquid heat exchanger  142 , power steering rack  144  and power steering cooler  146 , may remain essentially unchanged from the first embodiment. 
     In this embodiment, the heat exchanger  142  is coupled to an auxiliary transmission oil heater loop  174  of a transmission oil cooling system  190 , which incorporates part of the wasted heat recovery system  120 . The auxiliary transmission oil heater loop  174  includes a heat control valve  166  that has an inlet  176  from an oil outlet  162  of a transmission (or transaxle)  150 , a transmission oil cooler outlet  178  and a viscous heater outlet  180 . The viscous heater outlet  180  directs transmission oil  197  to the heat exchanger  142 , which then directs the transmission oil  197  back to the transmission  150  to complete the auxiliary transmission oil heater loop  174 . The transmission oil cooler outlet  178  directs the transmission oil  197  to a transmission oil cooler  168 , which then directs the transmission oil  197  back to the transmission  150  to complete a transmission oil cooling loop  154 . 
     A controller  182  controls the heat control valve  166 , which controls to which outlet  178  or  180  the transmission oil  197  is directed. The controller  182  may be a stand alone controller or may be incorporated into another vehicle controller, such as a transmission (or transaxle) controller, if so desired. An ambient air temperature sensor  184 , a coolant temperature sensor  186  and transmission oil temperature sensor  192  may be in communication with the controller  182 . The sensors  184 ,  186 ,  192  may be located as desired on the vehicle in order to get the desired temperature readings. 
     The operation of the waste heat recovery system  120  as it interacts with the power steering system  122  and transmission oil cooling system  124  will now be discussed. When the vehicle is operating, the power steering system  122  essentially operates the same as convention power steering systems with the exception that the power steering fluid  196  now flows through the heat exchanger  142 . The operation of the power steering system  122  causes the power steering fluid  196  to heat up as part of the normal operation of the system. Also, with the heat control valve  166  set to direct the transmission oil  197  through the transmission oil cooler outlet  178  to the transmission oil cooler  168 , the transmission oil cooling system  124  essentially operates the same as with a conventional system. 
     However, when the temperature sensors  184 ,  186 ,  192  detect that the ambient temperature is below a predetermined ambient temperature threshold, the coolant temperature is below a predetermined coolant temperature threshold, and the transmission oil temperature is below a predetermined transmission oil temperature threshold, then the controller  182  will actuate the heat control valve  166  to cause the transmission oil  197  to flow through the viscous heater outlet  180 . The transmission oil  197 , then, flows through the heat exchanger  142  where it absorbs heat from the power steering fluid  196 . This warmed transmission oil  197  then flows through the auxiliary transmission oil heater loop  174  and back to the transmission  150 . One will note that, in this mode, the transmission oil  197  does not flow through the transmission oil cooler  168 . The extra heat absorption by the transmission oil  197  in the heat exchanger  142  will provide additional heat sooner, thus reducing the time to optimal transmission operation on cold days when the transmission oil  197  starts out near ambient temperature. Once the transmission oil  197  warms up due to vehicle operation, the controller  182  will then actuate the heat control valve  166  to direct the transmission oil  197  through the transmission oil cooler outlet  178 . 
     While certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.