Abstract:
In order to minimize shift shocks during R→N and D→N manual shifts, in a manual valve of a hydraulic control system of a continuously variable transmission including a valve body having one input port and two output ports and a valve spool having a first land and a second land connecting the input port with one of the two output ports or completely blocking the input port from the two output ports, each land includes slots configured such that inner ends of the slots can be connected to the output ports in a neutral state.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims priority to and the benefit of Korean Patent Application No. 10-2005-0123199 filed in the Korean Intellectual Property Office on Dec. 14, 2005, the entire contents of which are incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     (a) Field of the Invention  
         [0003]     The present invention relates to a manual valve of a hydraulic control system of a continuously variable transmission for vehicles. More particularly, the present invention relates to a manual valve of a hydraulic control system of a continuously variable transmission that minimizes shift shock by controlling release pressure in D→N and R→N shifts.  
         [0004]     (b) Description of the Related Art  
         [0005]     A continuously variable transmission includes a fixed pulley and a moving pulley. The moving pulley provides thrust force on a side surface of a metal belt to a degree suitable for driving torque by hydraulic pressure in a hydraulic pressure chamber at a rear portion of the moving pulley. Continuous shifting occurs as a result of changes in diameter of the pulleys.  
         [0006]     A continuously variable transmission also includes a planetary gear set with three operational elements connected by a forward clutch and a reverse clutch such that two of the three operational elements always operate as an input and an output element, and the third selectively acts as an input element or a fixed element.  
         [0007]     Since the operating pressure supplied to the forward clutch and the reverse brake is exhausted only through an exhaust port formed in a manual valve, active control of exhaust hydraulic pressure is impossible.  
         [0008]     However, viscosity of transmission fluid changes depending on temperature. Exhaust time is thus shorter at room temperature, and longer at lower temperatures because of an increase of viscosity of the transmission fluid. Exhaust time is traditionally not controlled in response to temperature, so shift shock occurs in D→N and R→N shifts.  
         [0009]     The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.  
       SUMMARY OF THE INVENTION  
       [0010]     An exemplary embodiment of the present invention provides a manual valve of a hydraulic control system of a continuously variable transmission including a valve body having one input port and two output ports, and a valve spool, having a first land and a second land, that connects the input port with one of the two output ports or completely blocks the input port from the two output ports. Each land has slots on its outer surfaces at each end, and inner ends of the slots connect to the output ports in a neutral state.  
         [0011]     The slots may be tapered such that the outer end of each slot is deeper than the inner end.  
         [0012]     Each land may have three slots: one at each end on the side opposite the input port, and one at the outer end on the side adjacent the input port.  
         [0013]     The valve spool may further have a third land at one end, and an exhaust hydraulic line formed by an exhaust hole and an exhaust indentation therein may be formed in the third land such that exhaust pressure can be exhausted through an output port controlled by the second land.  
         [0014]     The third land may open and close a bypass port communicating with the output port controlled by the first land in a parking P range.  
         [0015]     In another embodiment of the present invention, a manual valve of a hydraulic control system of a continuously variable transmission includes a valve body including an input port through which hydraulic pressure is supplied from a pressure control valve; a reverse range port and a forward range port selectively supplying the hydraulic pressure supplied through the input port to a reverse brake and a forward clutch; and a valve spool including a first land and a second land disposed apart from each other at one side of a connecting member connected to a selector lever so as to selectively connect the input port to the reverse range port and the forward range port; and a third land having an exhaust hydraulic line therein so as to exhaust transmission fluid through the forward range port together with the second land. Lengths of the first and second lands may be longer than widths of respective circumferential grooves that form each output port. Slots may be formed on both ends of the first land and the second land such that inner ends of the slots can be connected to the output ports in a neutral state.  
         [0016]     The slots may be tapered such that their outer ends are deeper than their inner ends.  
         [0017]     Each land may have three slots: one at each end on the side opposite the input port, and one at the outer end on the side adjacent the input port.  
         [0018]     The third land may be configured to open and close a bypass port communicating with the output port controlled by the first land in a parking P range. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a hydraulic circuit diagram of a hydraulic control system to which a manual valve according to an exemplary embodiment of the present invention is applied;  
         [0020]      FIG. 2  is a perspective view of a valve spool of a manual valve according to an exemplary embodiment of the present invention;  
         [0021]      FIG. 3  is a schematic diagram of a manual valve according to an exemplary embodiment of the present invention; and  
         [0022]      FIG. 4  is a drawing showing effects of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]     An exemplary embodiment of the present invention will hereinafter be described in detail with reference to the accompanying drawings.  
         [0024]     Referring to  FIG. 1 , a hydraulic control system for operating a belt-type continuously variable transmission is configured such that three-stage relief of hydraulic pressure generated by a hydraulic pump  2  is performed by a line regulator valve  4 , a second regulator valve  6 , and a torque converter feed valve  8 .  
         [0025]     The hydraulic pressure regulated by the line regulator valve  4  is simultaneously supplied directly to a secondary pulley  10 ; to a first solenoid valve S 1  and a second solenoid valve S 2  via a solenoid control valve  12 ; and to a primary pulley  16 , as an operating pressure thereof, and a fail-safe valve  18 , as a control pressure thereof, via a speed ratio control valve  14 .  
         [0026]     In addition, a control pressure of the first solenoid valve S 1  is supplied to the speed ratio control valve  14  as a control pressure thereof, and a control pressure of the second solenoid valve S 2  is supplied to the line regulator valve  4  and the second regulator valve  6  as control pressures thereof.  
         [0027]     In addition, a portion of the hydraulic pressure of the line regulator valve  4  is supplied to the second regulator valve  6  and is then secondly regulated. The regulated hydraulic pressure is supplied to a pressure control valve  20 , a damper clutch control valve  22  as a torque converter supply pressure, and a reducing valve  24 .  
         [0028]     The hydraulic pressure supplied to the reducing valve  24  is reduced and is then supplied to the third solenoid valve S 3  and the fourth solenoid valve S 4  as control pressures thereof. The hydraulic pressure supplied to the pressure control valve  20  is controlled by the third solenoid valve S 3  and is then supplied to the manual valve  26 , then selectively supplied to the forward clutch C or the reverse brake B depending on range conversion of the manual valve  26 . The hydraulic pressure supplied to the damper clutch control valve  22  acts as a torque converter supply pressure according to a control of the fourth solenoid valve S 4 .  
         [0029]     In addition, a torque converter feed valve  8  communicates with a fail-safe valve  18  and a release line of the damper clutch control valve  22 , and controls torque converter release pressure.  
         [0030]     The first solenoid valve S 1 , the second solenoid valve S 2 , the third solenoid valve S 3 , and the fourth solenoid valve S 4  may be a 3-way valve. An orifice  28  and a check valve CV 1  are disposed in parallel in a line connecting the manual valve  26  and the forward clutch C, and an orifice  30  and a check valve CV 2  are disposed in parallel in a line connecting the manual valve  26  and the reverse brake B. Accordingly, engaging pressure supplied to the forward clutch C and the reverse clutch B is controlled by the orifices  28  and  30 , and during disengagement, hydraulic pressure is rapidly exhausted by the check valves CV 1  and CV 2 .  
         [0031]     In addition, an exhaust valve  34  is connected to the fail-safe valve  18  such that release pressure of the primary pulley  16  can be controlled, a line downstream of the line regulator valve  4  is connected to a torque converter supply pressure line  36  of the second regulator valve  6  by an orifice  38  disposed therebetween, and the torque converter supply pressure line  36  is connected to a torque converter release pressure line  40  by an orifice  42  disposed therebetween. These are configured so as to stably control pressure released from a high hydraulic pressure.  
         [0032]     In addition, a line relief valve  44 , which is supplied with reduced pressure of the reducing valve  12  as a control pressure thereof, is disposed between the hydraulic pump  2  and the line regulator valve  4  to relieve excessive line pressure.  
         [0033]     In a hydraulic control system of a continuously variable transmission according to an embodiment of the present invention, as shown in  FIG. 2  and  FIG. 3 , a valve spool  50  of the manual valve  26  has a connecting member  52  at one end, and a first land  54 , a second land  56 , and a third land  58 . The first and second lands  54  and  56  are disposed at positions such that the input port  60  can selectively communicate with the reverse range port  62  and the forward range port  64 .  
         [0034]     Lengths L and L′ of the first and second lands  54  and  56  are longer than widths of circumferential grooves  66  and  68 , respectively, which form the reverse range and forward range ports  62  and  64 . Slots  70 ,  72 ,  74 , and  76  are formed on each end of the first and second lands  54  and  56 . The slots  70 ,  72 ,  74 , and  76  are configured such that inner ends thereof can be connected to the reverse range and forward range ports  62  and  64  in a neutral state.  
         [0035]     Referring to  FIG. 3 , the slots  70 ,  72 ,  74 , and  76  are deeper at their outer ends, and the depths decrease toward their inner ends.  
         [0036]     Each land may have three slots: two at their outer ends  70 , 76 , but only one  72 ,  74 , at their inner ends. Slots  72  and  74  are disposed at the side of the land  54 ,  56  that faces away from input port  60 .  
         [0037]     These are formed such that hydraulic pressure of the input port  60  can be connected to the reverse range and forward range ports  62  and  64  in a neutral N range.  
         [0038]     In addition, an exhaust indentation  78 , one side of which is open along an axial direction, is formed within the third land  58 , and an exhaust hole  80  connected to the exhaust indentation  78  is disposed between the second land  56  and the third land  58  in a direction perpendicular to the exhaust indentation  78 .  
         [0039]     Further, the third land  58  is configured to open and close a bypass port  84  communicating with the reverse range pressure line  82  in a parking P range.  
         [0040]     In a manual valve  26  according to an embodiment of the present invention, the reverse range port  62  and the forward range port  64  are connected to the exhaust port EX through slots  70  and  76  in a neutral position, so that the hydraulic pressure that has been supplied to the reverse brake B and the forward clutch C is exhausted.  
         [0041]     In such an exhaust state, if the temperature of the transmission fluid is high, the viscosity of the transmission fluid is low and exhaust time is short, and if the temperature of the transmission fluid is low, the viscosity of transmission fluid is high and exhaust time is long. The exhaust time is controlled by controlling the third solenoid valve S 3 .  
         [0042]     That is, when the transmission fluid is hot, the third solenoid valve S 3  controls the pressure control valve  20  such that high control pressure is supplied to the manual valve  26 .  
         [0043]     Then, during R→N shift, the control pressure joins the reverse range exhaust pressure through slots  70  and  72 , and during D→N shift, the control pressure joins the forward range exhaust pressure through slots  74  and  76 . Accordingly, exhaust of the reverse range exhaust pressure or the forward range exhaust pressure is hindered by an increase of amount of hydraulic fluid, so exhaust pressure is controlled.  
         [0044]     On the other hand, when the transmission fluid is cold, the control pressure of the pressure control valve  20  is lowered so that the reverse range exhaust pressure and the forward range exhaust pressure are exhausted through the exhaust port EX of the pressure control valve  20  as well as through the exhaust port EX. Therefore, exhaust time is shortened.  
         [0045]     As shown in  FIG. 4 , from the result of simulations for R→N shift, the exhaust time is higher when the control pressure of the pressure control valve  20  is 6 bar than when the control pressure of the pressure control valve  20  is 0 bar.  
         [0046]     In a manual valve according to the present invention, the control pressure of the pressure control valve is lowered when the viscosity of transmission fluid is high because of a low temperature of transmission fluid, thereby shortening exhaust time, and on the other hand, the control pressure is increased when the viscosity of transmission fluid is low because of a high temperature of transmission fluid, thereby increasing exhaust time. Accordingly, shift shocks can be minimized during R→N and D→N manual shifts.  
         [0047]     While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.