Abstract:
A variable flow orifice for a hydraulic control system in a transmission includes a shape memory alloy that selectively increases and decreases the size of an orifice. The deformation of the shape memory alloy, and therefore the size of the orifice, is a function of the temperature of the transmission. During cold conditions the orifice size is increased and during normal operating conditions the size of the orifice is decreased.

Description:
CROSS-REFERENCE 
     This application claims the benefit of U.S. Provisional Application No. 61/507,433, filed Jul. 13, 2011. The entire contents of the above application are incorporated herein by reference. 
    
    
     FIELD 
     The present disclosure relates to hydraulic control systems in transmissions for motor vehicles and more particularly to a hydraulic fluid orifice in the hydraulic control system having temperature dependent variable fluid flow. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art. 
     Current transmissions in motor vehicles are expected to have consistent, responsive shifting performance at all times and in all operating conditions. This means that a transmission must have sufficient clutch actuation response times even during cold start or cold operating conditions. In automatic transmissions, hydraulic fluid is used to actuate clutches in order to select or maintain gear ratios. However, in cold conditions where the transmission has not achieved nominal operating temperatures, the hydraulic fluid in the valve body has an increased viscosity. The increased viscosity of the hydraulic fluid can lead to additional hydraulic flow restrictions due to hydraulic circuit dimensions and fixed diameter orifices within the circuit. Restrictions can in turn lead to sluggish or non-responsive shift times and clutch actuation. 
     One solution is to increase the pressure of the hydraulic fluid at low temperatures to overcome orifice restrictions. However, increased pump size can be undesirable due to added cost, increased packaging size, and decreased fuel efficiency. Therefore, there is a need in the art to improve the performance of automatic transmissions in cold start conditions while minimizing costs and packaging requirements. 
     SUMMARY 
     A variable flow orifice for a hydraulic control system in a transmission is provided. The variable flow orifice includes a shape memory alloy that selectively increases and decreases the size of an orifice. The deformation of the shape memory alloy, and therefore the size of the orifice, is a function of the temperature of the transmission. During cold conditions the orifice size is increased and during normal operating conditions the size of the orifice is decreased. 
     In one aspect, the shape memory alloy is disposed in a recess of a transmission component. 
     In another aspect, the shape memory alloy is disposed between two gaskets. 
     Further aspects, advantages and areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  is a top view of an exemplary valve body spacer plate having a variable flow orifice according to the principles of the present invention; 
         FIG. 2  is an enlarged, top view of a portion of the exemplary valve body spacer plate having a variable flow orifice; 
         FIG. 3  is an exploded view of the exemplary valve body spacer plate and variable flow orifice shown in  FIG. 2 ; 
         FIG. 4A  is an enlarged, top view of a portion of the exemplary valve body spacer plate having a variable flow orifice in a first condition; 
         FIG. 4B  is an enlarged, top view of a portion of the exemplary valve body spacer plate having a variable flow orifice in a second condition; 
         FIG. 5  is a top view of a gasket having a variable flow orifice according to the principles of the present invention; and 
         FIG. 6  is an exploded view of the gasket having a variable flow orifice shown in  FIG. 5 . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
     With reference to  FIG. 1 , a component of a hydraulic control system in a transmission is generally indicated by reference number  10 . In the example provided, the component  10  is illustrated as an exemplary valve body spacer plate. The spacer plate  10  includes various bores, openings, flanges and features that receive, locate, support and protect the valve body halves, valves, and solenoids of the valve body. For example, the spacer plate  10  includes a variable flow orifice  12  that communicates hydraulic fluid from a first side  14  of the spacer plate  10  to a second side  16  of the spacer plate  10 . The orifice  12  may hydraulically connect any number of components in the hydraulic control system together. For example, the orifice  12  may connect a pump outlet with a supply line in the valve body, or connect an accumulator with a pump or supply line, etc. However, it should be appreciated that the variable flow orifice may be located in various other transmission components, such as the valve body, without departing from the scope of the present invention. 
     Turning to  FIGS. 2 and 3 , the variable flow orifice  12  is shown in detail. The variable flow orifice  12  includes a bore  18  that extends through the spacer plate  10 . A recess  20  is formed around the bore  18  on the first surface  14 . The recess  20  extends into the spacer plate  10  a predefined depth but does not extend through the spacer plate  10 . A shape memory alloy (SMA) insert  22  is disposed within the recess  20 . The SMA, also known as a smart metal, memory metal, memory alloy, muscle wire, and smart alloy, undergoes a transformation from one crystal phase to another over a particular temperature range. Above this range, the material exists as austenite. Austenite has a rigid crystal structure. The shape of a component while in the austenite phase is termed the memory shape. The low temperature phase, martensite, is soft and can be deformed about 6% from its original shape without causing any permanent deformation. Once deformed, martensitic material will remain in this deformed shape indefinitely. When heated later, the material transforms to the high temperature phase and returns to its memory shape. Exemplary SMA&#39;s include copper-zinc-aluminum-nickel, copper-aluminum-nickel, and nickel-titanium (NiTi) alloys. For example, the SMA insert  22  may be made from a NiTi alloy from Intrinsic Devices Incorporated, San Francisco, Calif., under the designation UNILOK. 
     The SMA insert  22  is a semi-circular plate having a circular outer side  24  and a straight outer side  26 . The circular outer side  24  has a radius that approximately matches a radius of the recess  20 . The SMA insert  22  partially covers or obstructs the bore  18  in both the memory shape and the deformed shape, as seen in  FIGS. 4A and 4B . For example, in  FIG. 4A , the SMA insert  22  is in its shape memory state. In the shape memory state the SMA insert  22  has a surface area A 1  which covers a portion of the bore  18  and leaves an area B 1  of the bore  18  open to hydraulic fluid communication. In  FIG. 4B , the SMA insert  22  is in its deformed state. In the deformed state the SMA insert  22  has a surface area A 2  which covers a portion of the bore  18  and leaves an area B 2  of the bore  18  open to hydraulic fluid communication. The surface area A 1  of the SMA insert  22  in the shape memory state is less than the surface area A 2  of the SMA insert  22  in the deformed shape. Therefore, the size of the opening B 2  of the bore  18  when the SMA insert  22  is deformed is greater than the size of the opening B 1  of the bore  18  when the SMA insert  22  is not deformed. Accordingly, the orifice  12  provides a variably sized opening via SMA insert  22  overtop the bore  18  that is controlled by the transition temperature of the SMA insert  22 . Furthermore, since the opening of the bore  18  is controlled by the overlap between SMA insert  22  and bore  18 , the percentage change of the opening area B 1  to B 2  is larger than the strain rate of the SMA insert  22  itself, which is critical in making the difference between area B 1  and B 2  larger than the typical 6% deformation of SMA material. 
     The transition temperature of the SMA insert  22  is tuned to the operating conditions of the transmission and includes adjustments for hysteresis. For example, during normal operating conditions, the temperature of the hydraulic fluid, and therefore the SMA insert  22 , is at an elevated temperature. This temperature is greater than the transition temperature of the SMA insert  22 . Therefore, during normal transmission operating conditions, the SMA insert  22  is in the memory shape. However, during cold start conditions when the hydraulic fluid is cool and therefore has a higher viscosity, the SMA insert  22  is at a temperature below the transition temperature and the SMA insert  22  is in the deformed shape. This allows the orifice  12  to have a greater flow rate therethrough during cold start conditions. 
     With reference to  FIGS. 5 and 6 , an alternate embodiment of the variable restriction orifice is indicated by reference number  12 ′. The orifice  12 ′ is disposed over the bore  18  of the spacer plate  10 . The orifice  12 ′ includes a first gasket  50  having a hole  52  formed therethrough, the SMA insert  22  described above, and a second gasket  54  having a hole  56  formed therethrough. The SMA insert  22  is disposed between and sandwiched by the gaskets  50  and  52 . The SMA insert  22  is aligned with the bore  18  as described above. In the variable flow orifice  12 ′, the gaskets are held in place by compression between the spacer plate  10  and the valve body (not shown), and accordingly the recess  20  is not present. The variable flow orifice  12 ′ operates in a manner similar to the variable flow orifice  12 . 
     By using a variable flow orifice, the transmission response time during cold operating conditions is improved by increasing the flow rate of the relatively high viscous hydraulic fluid. In addition, the device is passive and does not require active control. Finally, the known transition temperature range of the SMA makes calibration of the variable flow orifice robust. 
     The description of the invention is merely exemplary in nature and variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.