Abstract:
A hydraulic system for propelling a vehicle, and with the system arranged with a pump and vehicle drive motors and valves and pilot lines. The operator can select an all-wheel drive or a lesser number of wheel drives. Also, there is a system automatic response to certain conditions of vehicle drive, whereupon the system activates to alter the drive to the various vehicle wheels, including changing from a four-wheel drive mode to a two-wheel drive mode. Further, the operator can override the system&#39;s own activation and thereby establish the two-wheel drive mode desired.

Description:
This invention relates to a hydraulic system for propelling a vehicle, and, more particularly, it relates to a hydraulic system which is both manually and automatically controllable for directing hydraulic fluid to the motors which drive the vehicle wheels. 
     BACKGROUND OF THE INVENTION 
     Hydraulic systems for directing hydraulic fluid to motors for driving vehicle wheels have already been established in tractor propulsion, for example. Such prior art is commonly dependent upon manual manipulation of hydraulic valves for directing the hydraulic fluid to the particular motor and in particular conditions of timing and fluid pressure. Those systems utilize hydraulic components which permit forward and reverse drive of the vehicle and which also permit selectivity between driving all of the wheels and also driving only some of the vehicle wheels. In those arrangements, the requirement is that a manually operative valve be employed for the various desired settings to enable the wheel drive selectivity mentioned. 
     The present invention improves upon the prior art by providing a hydraulic system which is arranged to have both manual and automatic control of the fluid flow in the system for the purpose of forward and reverse propulsion of the vehicle and also for driving all of the wheels and thus controlling movement of the vehicle. In these arrangements, consideration is given to the propelling of the tractor on level ground, and up a hill, and also down a hill, and with all of those three conditions also entailing a forward and reverse drive and in two-wheel and four-wheel drive modes. Under some of those conditions, it is desirable to have the vehicle shift from a four-wheel drive mode to a two-wheel drive mode. Also, it is desirable to have some of the vehicle wheels in a non-powered mode, such as with regard to the rear wheels when the vehicle is moving forwardly down a hill. Again, the prior systems commonly necessitate the inclusion of a manually operated hydraulic valve to disengage the four-wheel drive system in order to achieve the desired mode. 
     Also, the present invention provides the hydraulic system wherein the manually operated selector valve can be only a two-way and two-position valve, rather than say a three-way and two-position valve heretofore utilized. 
     The hydraulic system of this invention also has the feature of hydraulically engaging and disengaging the drive to the vehicle rear wheels, and to do so both manually and automatically, as desired. In one refinement of this invention, that is achieved by sensing both hydraulic flow and pressure and this invention thereby determines the proper condition to shift from the four-wheel drive to the two-wheel drive. The system arrangements of this invention are arranged to provide for either manual or automatic selectivity within the system to cause the system to alter from a four-wheel drive mode to a two-wheel drive mode. In the automatic mode, there is no requirement for manual, or even electrical, dis-engagement of the four-wheel drive selector valve, such as by means of a reverse switch on the vehicle traction pedal. In the hydraulic flow controlled system, when traveling forward down a slope, the vehicle rear wheels can actually slip and momentarily spin slightly backwards. This system will sense that reverse flow and automatically shift to the two-wheel drive mode. In these arrangements, the system can actually be adjusted to selective hydraulic pressures which can be slightly lower than the pressure required to cause the rear wheels to start to slip and, as such, it is a system which senses the rear motor hydraulic pressure and rear wheel slip. 
     The hydraulic system of this invention provides for eight different conditions of operation, namely, the four systems of two-wheel drive traveling forward both up and down a grade and traveling in reverse both up and down a grade; and the four systems of four-wheel drive traveling forward in both the up and down grade and traveling in reverse in both the up and down grade. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a hydraulic schematic view of an arrangement of this invention. 
     FIG. 2 is a hydraulic schematic view of an arrangement of this invention and is a variation of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a hydraulic system which includes a suitably powered hydraulic pump  10 , two vehicle front-wheel drive hydraulic motors  11 , a manually controllable hydraulic selector valve  12 , two vehicle rear wheel drive hydraulic motors  13 , and the hydraulic flow lines shown connecting the aforesaid elements. 
     It will be understood by one skilled in the art that the hydraulic pump  10  is arranged to be suitably powered by a prime mover on the vehicle, such as an engine, and it is conventionally shown to be a reversible hydraulic pump. A hydraulic fluid flow line  14  extends from one side of the pump  10  and is connected to the selector valve  12 . Another hydraulic fluid flow control line  17  is connected to the pump  10  on another side thereof, as shown, and it extends to a check valve  18  in the line  17 . It will also be understood by one skilled in the art that the hydraulic motors  11  are suitably connected with the vehicle front wheels, such as represented by the wheel  19 . 
     For that much of the mentioned system, the output of the pump  10  is connected to the line  14  and will cause pressurized fluid to flow through the motors  11  for rotation of the wheels, such as the one shown wheel  19 , and that flow will return to the pump  10  through the line  17 . 
     Hydraulic lines  21  are connected between the line  14  and the motors  11 , and hydraulic lines  22  are connected between the hydraulic line  17  and the motors  11 , as shown. 
     It can be considered that fluid flow into the line  14  and the lines  21  and through the motors  11  and the lines  22  and back to the pump  10  through the line  17  will produce a forward drive of the vehicle. Conversely, flow from the pump  10  and into the line  17  and the lines  22  and into the motors  11  and into the lines  21  and back to the pump  10  through the line  14  can produce reverse movement of the vehicle. Likewise, and throughout the hydraulic system shown, there are forward drive lines and reverse drive lines, and the letters “F” and “R” indicate those directional modes. 
     The selector valve  12  is manually controllable, and it has a check valve  23  therein and a flow passageway  24 . Therefore, in the FIG. 1 shown position, hydraulic fluid will not flow beyond the valve  12  because it is shown to be in the closed position. When the valve  12  is shifted to where the passageway  24  receives flow from the line  14 , that flow is conducted to a line  26  which is connected to the valve  12 , and the line  26  extends to a line  27  and to a line  28  which is shown connected with the one rear hydraulic motor  13 . 
     Also, there is a crossover hydraulic line  29  which is connected with the line  26  and extends to connect to a line  31  which is connected with the check valve  18 . In turn, line  31  connects with a line  32  which also connects with the motor  13 , as do the ends of lines  27  and  31  which connect with the other motor  13  which is shown to be in driving relationship with a vehicle rear-driven wheel  33  of which there would of course be two wheels driven by the respective motors  13 , just as with the two front wheels  19 . 
     The crossover lines  29  and  35  have a check valve  34  therebetween. There is a hydraulic pilot line  36  connected to both the main line  27  and the check valve  18 . There is a pilot line  37  connected with the main line  17  and with the check valve  34 . 
     In the system shown, it will be seen that the motors  11  and  13  are in parallel connection with the main line as described which form in essence an endless loop, and the parallelism of the rear motors  13  is established by the shown crossover lines at the motors  13 . Further, the selector valve  12  is described as being in series connection with the main line which has its extended branches  14 ,  26 , and  27  on that side of the loop, and it has a pump operatively inlet side on the left thereof and a pump operatively outlet side on the right side thereof, as viewed in FIG.  1 . 
     In that system, the line  14  is considered to be the forward drive direction line for the front wheels  19 , and the line  17  is considered to be the reverse drive direction line for the front wheels  19 . 
     As mentioned, with this system, there are eight modes of operation. 
     First, when traveling forward up a grade in two-wheel drive, the pump  10  pressurizes the forward drive line  14  where pressure meets the closed port  23  of valve  12 . Consequently, flow can only be through the two front-wheel drive motors  11  while the rear-wheel drive motors  13  push the oil through the check valve  34  in a hydraulic loop formed with the motors  13 . 
     Second, when traveling forward down a grade in two-wheel drive, oil is again flowing in the forward direction but the front motors  11  are forcing oil into the pump  10  and that pressurizes the reverse leg  17  of the circuit. That pressure meets the check valve  18  and terminates there. The rear motors  13  continue to function as mentioned. 
     Third, when traveling in reverse and up a grade in two-wheel drive, the pump pushes oil into the reverse line  17  and again that oil meets the check valve  18  and is stopped there so it flows only through the front motors  11 . However, pressure in line  17  is effective on the check valve  34  through the connecting pilot line  37 , and that causes the oil to loop through the connecting lines relative to the rear-wheel drive motors  13  so there is no vehicle drive resistance from the motors  13 . 
     Fourth, when traveling downgrade in reverse in two-wheel drive, the oil is again flowing in the reverse direction and in line  17  but the front motors  11  are forcing oil into the pump pressurizing the line  14  and that hydraulic pressure meets the closed port or check  23 , and therefore the flow can only return to the pump  10  for the reverse drive desired. The rear motors  13  tend to suck oil from the reverse leg  31  and thus cause a pressure reduction at the check  18 . That leaves a greater pressure in the line  17  and that pressure is presented to the check valve  34  through the connecting pilot line  37 . That pressure opens the check valve  34  and allows the oil to loop through the rear motors  13 . 
     Fifth, in the four-wheel drive mode, the selector valve  12  is positioned so that the through passageway  24  connects the lines  14  and  26 . Thus, when traveling forward upgrade in that four-wheel drive mode, the pump pushes the oil in the forward direction through the line  14  where it flows through the passageway  24  and into the lines  26  and  27 , and flow continues through the rear motors  13  and the line  31  and the check valve  18  and back to the pump  10 . That circuit of oil flow meets the closed valve  34  and does not pass therethrough. 
     Sixth, when traveling forward down a grade in four-wheel drive, oil is still flowing in the forward direction, but the front motors  11  are forcing oil into the pump  10  and thereby pressurizing the reverse line  17  of the circuit. This pressure meets check valves  18  and  34  causing a reversal of flow and closing the check valve  18  while allowing the oil to flow through the check valve  34  and loop through the rear motors  13 . 
     Seventh, while traveling in reverse up a grade and in four-wheel drive, the pump  10  pushes oil in the reverse direction in line  17  and again this oil meets check valve  18  and is stopped there so it flows through the front motors  11 . This pressure also acts on pilot line  37  to open check valve  34  and thus allow the oil to loop through the rear motors  31 . 
     Eighth, when traveling in reverse down a grade and in four-wheel drive, oil is still flowing in the reverse direction, but the front motors  11  are forcing oil into the pump  10 , pressurizing the forward leg  14  of the circuit. This pressure passes through the open selector valve  12  and is effective on the pilot line  36  to open the check valve  18 . The same pressure causes the valve  34  to close, allowing all of the motors to add traction effort to hold the tractor vehicle on the grade or slope. 
     The variation shown in FIG. 2 with its additional elements which are added to FIG. 1, includes the elements of FIG. 1, and thus the same reference numerals are employed. However, FIG. 2 has some additional hydraulic components, and that arrangement provides for both pressure and flow sensing for the automatic hydraulic system modes described herein. 
     In place of the valve  34  of FIG. 1, there is a valve  41  which has a closure portion  42  and a passageway  43 , and the valve  41  is connected with the pilot line  37 , as indicated. Also, there is another four-wheel drive selector valve  44  which is connected to the valve  41  through the lines  35 ,  46  and  47 , as shown, and is also connected to the line  31 . The selector valve  44  has a passageway  48  for connecting lines  46  and  47  and  31 , when shifted leftwards, and it also has a passageway  49  for connecting the lines  46  and a line  51  which connects with a tank  52 , if desired. Again, the valves  18  and  41  sense reverse hydraulic fluid flow, and thus there is the automatic shifting from the four-wheel drive back to the two-wheel drive mode, and that is when the valve  41  has shifted rightward and thereby connect lines  31  and  27 . That condition exists when the tractor is moving forward down a grade and until the rear wheels  33  slip and momentarily spins backwards, and then there is the sensing by the valves  18  and  41  of the reverse oil flow and thus there is shifting to the two-wheel drive mode until the tractor is substantially on level ground. 
     There may also be a relief valve  53  in cross connections  54  and  59  between the lines  27  and  31 , and valve  53  has a passageway  56  to communicate line  31  to line  27 . Pilot lines  57  and  58  also connect with the crossover lines  54  and  59  and the valve  53 . 
     With the use of the valve  56  which can be set to a hydraulic pressure slightly lower than the pressure required to cause the rear wheel  33  to slip, the valves  18  and  41  sense the reverse flow before the wheels start to slip, and thus there is the automatic shift to two-wheel drive. If the turf conditions are very slick, the system will also act as the flow or rear-wheel slip sensing type, as previously described. 
     The selector valves  12  and  44  are used to manually shift into a constant two-wheel drive mode. Also, an additional check valve  61  and a flow restriction  62  could be incorporated into the pilot line  36  to tailor the shifting between the two-wheel drive mode and the four-wheel drive mode. 
     Because of the incorporation of the valves  18  and  41 , the system has the feature of allowing the rear wheels  33  to supply traction force while backing down a slope, and it does not require the manual or electric disengagement of the four-wheel selector drive valve  12 , such as by means of a reverse switch on the traction pedal. 
     Throughout this description, the method of operating and controlling the hydraulic system is inherent herein. 
     With regard to the variation shown in FIG. 2, just as with FIG. 1, there eight modes of operation. 
     The first mode is considered as when the vehicle is traveling forward up a grade and in two-wheel drive. The pump  10  pushes the oil in the forward direction line  14 , and it meets the closed port  23  of the manual selector valve  12 . Therefore, pressured oil can flow only through the front-wheel drive motors  11 . The passageway  43  of valve  41  is in the open position relative to line  29 , and that is due to the static charge pressure that is typical in the closed loop traction circuit of this type. Therefore, oil circulates in the loop having the motors  13  therein, and thus the motors  13  are not being driven for traction drive. 
     Second, when traveling forward in two-wheel drive and down a grade, the oil is still flowing in the forward direction but the front motors  11  are forcing oil into the pump  10 , and that pressurizes the circuit reverse line  17 . That pressure is contained by the check valve  18 , and the rear motors  13  continue to function as mentioned above. 
     Third, when traveling in reverse in two-wheel drive up a grade, the pump  10  pushes oil into the reverse line  17  and again it meets the check valve  18 , so hydraulic fluid or oil is flowing only through the front motors  11 , and again the rear motors continue to recycle as mentioned above. 
     Fourth, when traveling in reverse in two-wheel drive down a grade, oil is still flowing in the reverse direction in line  17 , but the front motors  11  are forcing oil into the pump  10  and thus pressurizing the forward direction line  14  of the circuit. This pressure meets the closed port  23  of valve  12  and therefore can only return to the pump  10  through the motors  11 , and the rear motors  13  continue to function as above. 
     Fifth, when traveling forward in four-wheel drive and up a grade, the pump is pushing oil in the forward line  14  and this oil meets the open port  24  of the valve  12  and flows to the rear motors  13  and to the check valve  18 . The pressure in the forward lines  14  and  26  meet the closure  42  of the valve  41  and is stopped there. Valve  41  is in that closed position because valve  44  has been shifted to where its passageway  48  is communicating pressure between the lines  47  and  46  and thus causing the valve  41  to be in the closed position. The forward pressure in line  54  also meets the relief valve  53  which is in the closed position shown in FIG. 2, so the oil is stopped there. 
     Sixth, when traveling forward in four-wheel drive and down a grade, oil is still flowing in the forward direction in lines  14  and  26 , but the front motors  11  are forcing oil into the pump  10  and thus pressurizing the reverse line of the circuit. That hydraulic pressure meets the check valve  18  and passes through, thereby allowing the rear motors  13  to force oil into the pump  10  also. Valve  41  is closed, as shown, because valve  44  is manually shifted leftward and thus there is equal pilot pressure on both sides of valve  41 . That condition prevails until the reverse pressure exceeds the pressure setting of relief valve  53 , or the rear wheels  33  slip and momentarily spin slightly backwards. In either case, the flow of oil reverses through check valve  18  and thus closes it. Hydraulic pressure is then greater on the left side of valve  18  than it is on the right side, as viewed in FIG.  2 . That pressure difference is sensed through the pilot line  37  and also by the valve  41  to place the valve  41  in the open position relative to the lines  29  and  35 . That condition allows the oil to loop through the rear motors  13 , and thus there is the shifting to the two-wheel drive. That condition or mode continues until the vehicle reaches the bottom of the slope or grade and the pressure across the check valve  18  equalizes and thus closes the valve  41 . 
     Seventh, when traveling in reverse in four-wheel drive up a grade, the pump  10  pushes the oil in the reverse direction, and that oil meets the check valve  18  and is stopped there so it flows through the front motors  11 . That pressure also acts on the pilot line  37  for the piloted operated valve  41  and thus opens the valve  41 . When valve  44  is manually shifted to the left, the oil can loop through the valve  41  and the rear motors  13 , and the valve  41  serves as a bypass relative to the pump  10  so that pressurized fluid from the pump  10  is not presented to the motors  13  for driving purposes. 
     Eighth, when traveling in reverse in four-wheel drive down a grade, the oil is still flowing in the reverse direction line, but the front motors  11  are forcing oil into the pump  10  and thereby pressurizing the forward direction line  14 . That pressure passes through the open valve  12  and is presented to the pilot line  36  of the check valve  18  and thus opens valve  18 . Valve  44  has been shifted to where its passageway  48  connects lines  47  and  46  and presents, along with hydraulic pressure through pilot line  37 , equal hydraulic pressure on the valve  41 , and thus the valve  41  inherently closes with that equal hydraulic pressure on both sides and under the influence of its spring  63 , in a conventional arrangement. That mode allows all of the motors  11  and  13  to exert traction effort to thereby hold the vehicle on the slope. The forward pressure also meets the relief valve  53 , but it is stopped there. 
     The restriction orifice  62  and the check valve  61  can be added to the system to thus tailor the shifting between the two-wheel drive and the four-wheel drive modes by further controlling flow through the pilot line  36 , as indicated. 
     In the system of FIG. 2, just as with FIG. 1, the valves  18  and  41  are the essential elements for the system for automatic shifting between the plurality of wheel drives, as provided for and as desired. While the other valves add features, as described herein, they are not essential for the automatic control functions described. 
     The lines  14 ,  26 ,  27 ,  31 , and  17  form the main hydraulic circuit and are disposed in an endless loop. The lines  14 ,  26 , and  27  are considered to be the vehicle forward drive lines and the lines  31  and  17  are considered to be the vehicle reverse drive lines. The pump  10  and the motors  11  and  13  are capable of rotation in both directions of rotation. Of course throughout this description, the lines referred to are conduits suitable for conducting the flow of hydraulic fuild therethrough from and to the conventionally shown connection points on the drawings. The check valve  18  is referred to as the first valve, and the valves  34  and  41  are referred to as the additional valve.