Abstract:
A work machine having a mechanical transmission in combination with a hydrostatic ground drive including a primary drive and a secondary drive engageable for providing additional propulsion torque in a power assist mode, the hydrostatic drive automatically providing an increased torque capability when the transmission is engaged in a high speed range, thereby allowing the work machine to accelerate from a complete stop to a high speed range with the transmission in a high speed range without the need to stop to shift the mechanical transmission to accommodate an increased propulsion torque requirement.

Description:
TECHNICAL FIELD 
       [0001]    This invention relates generally to a work machine having a hydrostatic ground drive and a clutchless mechanical transmission, and more particularly, to providing increased propulsion torque availability when the transmission is in a high gear thereby allowing the work machine to accelerate from a complete stop with the transmission engaged in a high speed range without downshifting to meet an increased propulsion torque requirement. 
       BACKGROUND ART 
       [0002]    It is well known to provide hydrostatic ground drives for work machines such as agricultural combines and the like. Such drives typically include one or more fluid pumps operable for supplying a flow of pressurized fluid to a primary drive including at least one fluid motor for operating a set of primary movers, typically the front movers, of the machine. Additionally, it is known to provide such drives in combination with multiple speed mechanical transmissions in driven relation to the at least one fluid motor and connected in driving relation directly with the primary movers. These clutchless transmission systems require the work machine to come to a complete stop prior to shifting between speed ranges. The multiple speed ranges or gears of the mechanical transmission include at least one low speed range suitable for performing work functions in a field and at least one high speed range suitable for travel over public roads. In addition, when the transmission is engaged in a low speed range and the machine is experiencing high propulsion torque requirements, a power assist mode may be engaged to divert a portion of the flow of pressurized fluid to a secondary drive including one or more fluid motors in driving relation to a set of secondary movers, typically the rear movers, of the machine. In other words, additional propulsion torque is provided by the secondary movers when a portion of the flow of pressurized fluid is divided between the primary fluid drive and the secondary fluid drive. For example, the power assist mode is typically employed to provide additional torque from the rear axle drive of a combine in muddy conditions during field operations and for improved steering on side hills. 
         [0003]    Problems and shortcomings of work machines having clutchless mechanical transmission systems in combination with presently known hydrostatic ground drives include the inability to provide additional propulsion torque when the transmission is engaged in a high speed range. For example, when the work machine is performing an operation in which it will be driven at high speed, the transmission is necessarily engaged in a high speed range. However, if the machine encounters muddy or hilly conditions during the operation, the propulsion torque required by these conditions may exceed the propulsion torque available from the primary drive alone, resulting in extremely poor operating efficiency, excessive hydraulic fluid heat, hydraulic component wear, slow acceleration, or even stalling. In this situation, the machine must be stopped, and the mechanical transmission shifted into a low speed range so the power assist mode can engage to provide additional propulsion torque from the secondary drive. Once out of the mud or at the crest of the hill, the machine must again be stopped and the mechanical transmission shifted into a high speed range to continue the high speed operation. 
         [0004]    Another example in which these problems and shortcomings have been observed is in connection with transporting a work machine over the road. When climbing out of a field, the work machine experiences a high propulsion torque requirement, a situation in which additional propulsion torque from the secondary drive may be required, so the transmission must be engaged in a low speed range. When traveling over the road, however, the transmission is preferably engaged in a high speed range in order for the work machine to reach road speeds. Using presently known systems, the work machine must pull out of the field onto the road with the transmission in a low speed range so additional propulsion torque is available from then secondary drive to propel the machine up the hill. Once on the road, the machine must come to a complete stop in order to shift the transmission into a high speed range for traveling at road speeds. 
         [0005]    It would be advantageous for the work machine to have additional propulsion torque to be able to pull out of the field onto the road and accelerate to road speeds without the need to stop on the road to shift the transmission from a low gear to a high gear. Using presently known systems, however, the choices include driving at road speeds with the transmission in a low speed range which causes excessive hydraulic system wear, or climbing out of the field with the transmission in a high speed range and risk experiencing propulsion torque requirements that can not be met by the primary drive. 
         [0006]    What is sought therefore is a work machine having a clutchless mechanical transmission in combination with a hydrostatic ground drive which automatically provides increased propulsion torque availability when the transmission is engaged in a high speed range, and which overcomes one or more of the problems and shortcomings set forth above. 
       SUMMARY OF THE INVENTION 
       [0007]    What is disclosed is a work machine having a clutchless mechanical transmission in combination with a hydrostatic ground drive which automatically provides increased propulsion torque availability when the transmission is engaged in a high speed range, and which overcomes one or more of the problems and shortcomings set forth above. 
         [0008]    According to the present invention, the work machine includes a set of primary movers which support a portion of the machine and are operable for propelling the machine over the ground at a ground speed. A set of secondary movers which support another portion of the machine and are operable by at least one secondary fluid motor connected in driving relation thereto for driving the secondary movers assist the primary movers. A mechanical transmission, connected in driving relation directly to the set of primary movers, is selectably engageable in a plurality of speed ranges, and is configured and operable for transitioning between the ranges only at a zero ground speed. In particular, the plurality of speed ranges include at least one road speed range for propelling the work machine between the zero ground speed and a predetermined high ground speed suitable for travel over public roads, and at least one low speed range within the road speed range for propelling the work machine between the zero ground speed and a predetermined low ground speed suitable for performing work functions in agricultural fields and slower than the predetermined high ground speed. The work machine also includes a hydrostatic drive including a pump connected in a fluid loop with a primary fluid motor. The drive is operable for directing a flow of pressurized fluid through the loop at a fluid pressure to the primary fluid motor for controllably driving the primary fluid motor which is connected in driving relation to the mechanical transmission. A valve, connected to the fluid loop and to the at least one secondary fluid motor, is selectably operable in a power assist mode for diverting a portion of the flow of fluid in the loop to the at least one secondary motor for controllably driving the at least one secondary fluid motor. The work machine also includes a controller which is connected in operative control of the valve, and is configured and operable for monitoring the speed range of the transmission, the fluid pressure in the loop, and the ground speed of the machine. The controller is programmed for automatically operating the valve in the power assist mode when the transmission is engaged in the at least one road speed range and the ground speed below a predetermined transition speed slower than the predetermined high ground speed. 
         [0009]    According to a preferred aspect of the invention, the controller is preferably programmed for smooth transitions when engaging or disengaging the power assist mode by operating the valve to produce gradual changes in the fluid pressure in the loop. 
         [0010]    As another preferred aspect of the invention, the mechanical transmission provides four forward speed ranges. A low or first speed range between the zero ground speed and a predetermined first ground speed suitable for performing work or harvesting functions in the field. A high or fourth speed range between the zero ground speed and a predetermined fourth ground speed suitable for travel between fields or on public roads. A second and third speed range between the zero ground speed and a predetermined second and third ground speed, respectively, are midranges between the low and high speed ranges. According to this aspect, the controller is programmed for automatically operating the valve in the power assist mode when the mechanical transmission is engaged in the third or fourth speed range and the ground speed is below the predetermined transition speed slower then the predetermined third ground speed. 
         [0011]    According to a feature of the invention, the power assist mode includes a first sub mode for diverting a first portion of the flow of fluid in the loop from the primary motor to the at least one secondary motor and a second sub mode for diverting a second smaller portion of the flow of fluid in the loop from the primary motor to the at least one secondary motor. When the transmission is in the road speed, or the high speed range, the controller is further programmed for automatically operating the valve in the first sub mode when the ground speed is below a predetermined first transition speed and operating the valve in the second sub mode when the ground speed is between the predetermined first transition speed and a predetermined second, higher transition speed. 
         [0012]    According to another preferred aspect of the invention, the controller is further programmed for automatically operating the valve in the power assist mode when the mechanical transmission is engaged in the at least one road speed range and the fluid pressure exceeds a predetermined maximum fluid pressure and remains greater than a predetermined lower, transition fluid pressure. Similarly, the controller is further programmed for automatically operating the valve in the second sub mode when the transmission is engaged in the at least one road speed range and the fluid pressure exceeds a predetermined second maximum fluid pressure and remains greater than a second predetermined transition fluid pressure lower than the second maximum fluid pressure and operating the valve in the first sub mode when the transmission is engaged in the at least one road speed range and the fluid pressure exceeds a first maximum pressure higher than the second maximum pressure and remains greater than a predetermined first transition fluid pressure. 
         [0013]    According to another feature of the invention, the higher speed ranges include the lower speed ranges, and the transition speeds are typically within the lower speed ranges. For example, when the road speed range is from zero to twenty miles per hour, the low speed range is from zero to five or ten miles per hour, and the transition speed is about five miles per hour. As another, non-limiting example, when the first ground speed range is from zero to five miles per hour, the second speed range is from zero to ten miles per hour, the third speed range is from zero to fifteen miles per hour, and the fourth speed range is from zero to twenty miles per hour, the transition speed is about five miles per hour. Also, when operating in the power assist sub modes, exemplary speed for the first transition speed and the second transition speed are five and ten miles per hour, respectively. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  is a simplified side view of a representative work machine, which is an agricultural combine, including a hydrostatic ground drive having a power assist mode in combination with a mechanical transmission; 
           [0015]      FIG. 2  is a simplified top view of the representative work machine including a schematic of a preferred embodiment of the invention; 
           [0016]      FIG. 3  is a graphical representation of a power assist mode status versus ground speed according to the invention; 
           [0017]      FIG. 4  is a graphical representation of a power assist sub mode status versus ground speed according to the invention; 
           [0018]      FIG. 5  is another graphical representation of the power assist mode status versus ground speed according to the invention; 
           [0019]      FIG. 6  is another graphical representation of the power assist sub mode status versus ground speed according to the invention; 
           [0020]      FIG. 7  is a simplified side view of the combine situated for operation in a representative level field; 
           [0021]      FIG. 8  is a simplified side view of the combine situated near a road; 
           [0022]      FIG. 9  is a simplified side view of the combine climbing a hill towards the road; and 
           [0023]      FIG. 10  is a simplified side view of the combine situated for operation on the road at road speeds in a high speed range. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    Referring to  FIG. 1 , a representative self-propelled work machine, which is an agricultural combine  20 , is shown, including a set of primary movers, represented by front wheels  22 , supporting a portion of the machine and a set of secondary movers, represented as a pair of rear wheels  24 , supporting another portion of the machine. Front wheels  22  are operable by a primary fluid motor  28  for propelling the machine over the ground, and rear wheels  24  are operable by at least one secondary fluid motor  30  connected in driving relation thereto for assisting front wheels  22  for propelling the machine at a ground speed. 
         [0025]    Turning also to  FIG. 2 , a simplified schematic of combine  20  shows a mechanical transmission  32  connected in driven relation to primary fluid motor  28  and in driving relation directly to front wheels  22 . Because the combine uses a clutchless system, transmission  32  is configured and operable for shifting between a plurality of speed ranges only when the machine is stationary or at a zero ground speed. Combine  20  includes a hydrostatic drive  26  including a pump  34  connected in a fluid loop, represented by fluid paths  36 , with primary fluid motor  28 . Hydrostatic drive  26  is operable for directing a flow of pressurized fluid through the loop at a fluid pressure to primary fluid motor  28  for controllably driving primary fluid motor  28 . The fluid loop also includes a valve  46  connected to secondary fluid motors  30  which is selectably operable, in a power assist mode, for diverting a portion of the flow of fluid in the loop from primary fluid motor  28  to secondary motors  30  for controllably driving secondary fluid motors  30 . 
         [0026]    The speed ranges in which transmission  32  may be selectably engaged are illustrated in  FIGS. 3 and 4 , and include at least one road speed range  50  for propelling the work machine between a zero ground speed and a predetermined high ground speed HS suitable for travel over public roads, typically at least 15 miles per hour, and at least one low speed range  52  within road speed range  50  for propelling the work machine between the zero ground speed and a predetermined low ground speed LS suitable for performing work functions in agricultural fields, typically less than 10 miles per hour. 
         [0027]    As shown in  FIG. 2 , a controller  40 , constructed and operable according to the present invention, is connected in operative control of valve  46  via conductive path  42 . Controller  40  is configured and operable for monitoring the speed range of transmission  32  the fluid pressure in the loop, and the ground speed of combine  20 . Fluid pressure can be measured with representative pressure sensors  44  and ground speed can be determined by a ground speed sensor (not shown), for example. Further, controller  40  is programmed for automatically operating valve  46  in the power assist mode when transmission  32  is engaged in the at least one road speed range  50  and the ground speed is below a predetermined transition speed TS which is slower than predetermined high ground speed HS as illustrated in  FIG. 3 . Predetermined transition speed TS is selected to provide additional propulsion torque required for low speed, high torque operations, such as climbing out of a field, when transmission  32  is in road speed range  50 . Depending on the application, transition speed TS may be slower than, as shown in  FIG. 3 , faster than, or equal to predetermined low speed LS. 
         [0028]      FIGS. 4 and 5  illustrate an aspect of the invention wherein the plurality of speed ranges includes a first speed range  54  for propelling the machine between the zero ground speed and a predetermined first ground speed  1 ST, a second speed range  56  including first speed range  54  for propelling the machine between the zero ground speed and a predetermined second ground speed  2 ND, a third speed range  58  including second speed range  56  for propelling the machine between the zero ground speed and a predetermined third ground speed  3 RD, and a fourth speed range  60  including third speed range  58  for propelling the machine between the zero ground speed and a predetermined fourth ground speed  4 TH. Controller  40  is programmed for automatically operating valve  46  in the power assist mode when mechanical transmission  32  is engaged in third speed range  58  or fourth speed range  60  and the ground speed is below predetermined transition speed TS which is slower then predetermined third ground speed  3 RD as illustrated in  FIG. 5 . Again transition speed TS is selected to provide additional propulsion torque required for low speed, high torque operations, when transmission  32  is in third speed range  58  or fourth speed range  60 . Depending on the application, transition speed TS may be slower, faster, as shown in  FIG. 5 , or equal to predetermined first ground speed  1 ST. 
         [0029]    Turning now to  FIGS. 4 and 6  which illustrate another aspect of the invention wherein the power assist mode includes a first sub mode for diverting a first portion of the flow of fluid in the loop from primary motor  28  to secondary motors  30  and a second sub mode for diverting a second smaller portion of the flow of fluid in the loop from primary motor  28  to secondary motors  30 . According to this aspect, controller  40  is programmed for automatically operating valve  46  in the first sub mode when transmission  32  is engaged in the at least one road speed range  50  ( FIG. 4 ) (or third speed range  58  or fourth speed range  60  ( FIG. 6 )) and the ground speed is below a predetermined first transition speed T 1 . Further controller  40  is programmed for operating valve  46  in the second sub mode when transmission  32  is engaged in the at least one road speed range  50  ( FIG. 4 ) (or third speed range  58  or fourth speed range  60  ( FIG. 6 )) and the ground speed is between predetermined first transition speed T 1  and a predetermined second transition speed T 2 . Predetermined second transition speed T 2  is chosen between predetermined first transition speed T 1  and predetermined high ground speed HS ( FIG. 4 ) or predetermined third ground speed range  3 RD ( FIG. 6 ). Transition speeds T 1  and T 2  are selected to provide more additional propulsion torque at very low speeds and less additional propulsion torque as the machine accelerates to road speed. Transition speeds T 1  and T 2  may be chosen to be slower, faster, or equal to predetermined low speed LS ( FIG. 4 ) or predetermined first or second ground speeds  1 ST or  2 ND ( FIG. 6 ). 
         [0030]    According to another preferred aspect of the invention, controller  40  is further programmed for automatically operating valve  46  in the power assist mode when mechanical transmission  32  is engaged in the at least one road speed range  50  ( FIG. 4 ) (or third speed range  58  or fourth speed range  60  ( FIG. 6 )) and the fluid pressure exceeds a predetermined maximum fluid pressure and remains greater than a predetermined lower, transition fluid pressure. Similarly controller  40  is further programmed for automatically operating valve  46  in the second sub mode when transmission  32  is engaged in the at least one road speed range  50  ( FIG. 4 ) (or third speed range  58  or fourth speed range  60  ( FIG. 6 )) and the fluid pressure exceeds a predetermined second maximum fluid pressure and remains greater than a second predetermined transition fluid pressure lower than the second maximum fluid pressure. If engaging the second sub mode does not provide enough additional propulsion torque, controller  40  is programmed for automatically operating valve  46  in the first sub mode when the transmission  32  is engaged in the at least one road speed range  50  ( FIG. 4 ) (or third speed range  58  or fourth speed range  60  ( FIG. 6 )) and the fluid pressure exceeds a first maximum pressure higher than the second maximum pressure and remains greater than a predetermined first transition fluid pressure. 
         [0031]    Operationally, it is important that transition into and out of the power assist mode and sub modes is smooth and seamless. Rapid changes in the flow of fluid in the loop may result in delays or jerky transitions. According to a feature of the invention, controller  40  is programmed for automatically operating valve  46  to produce gradual changes in the fluid pressure in the fluid loop. Controller  40  may use a modulated or ramped command to valve  46 , or another suitable method, to avoid abrupt changes of flow in the loop. 
         [0032]      FIGS. 7-10  will be used to illustrate the important operational aspects of combine  20  when pulling out of a field onto a road.  FIG. 7  is depicts combine  20  performing work functions in a field. Ground speeds for this type of operation are typically below five to ten miles per hour and are performed with transmission  32  in a relatively low speed range. Representative, non-limiting low speed ranges for transmission  32  during field operations include zero to five miles per hour, and zero to ten miles per hour. Because transmission  32  is in a lower speed range, high torque requirements will be provided by traditional power assist modes. 
         [0033]    Some field operations, however, may be performed at higher speeds, with transmission  32  engaged in one of the higher speed ranges  50 ,  58 , or  60 . In these situations, if combine  20  encounters muddy or hilly conditions, the propulsion torque requirement increases increasing the fluid pressure in the fluid loop. When the fluid pressure reaches the predetermined maximum fluid pressure, controller  40  automatically operates valve  46  in the power assist mode until the fluid pressure falls below the transition fluid pressure. Combine  20  can continue to operate with transmission  32  engaged in one of the higher speed ranges  50 ,  58 , or  60  and receive additional propulsion torque when required without stopping to shift transmission  32  to a lower speed range. 
         [0034]      FIG. 8  depicts combine  20  situated near a road preparing to climb out of the field to a public road, possibly in traffic. Road speeds are typically greater than ten miles per hour and are driven with transmission in a relatively high speed range. Representative, non-limiting high speed ranges for transmission  32  during road operation include zero to fifteen miles per hour and zero to twenty miles per hour. 
         [0035]    To pull out of the field onto the road, transmission  32  is engaged in one of the high speed ranges  50 ,  58 , or  60 , and controller  40  automatically operates valve  46  in the power assist mode. When combine  20  begins to accelerate to climb a hill to the road as shown in  FIG. 9 , additional propulsion torque is automatically supplied by rear wheels  24 . Once combine  20  reaches the road as shown in  FIG. 10  transmission  32  is already in on of the high speed ranges  50 ,  58 , or  60 , and the operator can proceed to road speeds without stopping combine  20  to shift transmission  32 . Controller  40  will cease operation of valve  46  in the power assist mode or transition from low speed sub mode to high speed sub mode prior to ceasing operation of valve  46  in the power assist mode as combine  20  accelerates through transition speeds TS, T 1 , and T 2  as shown in  FIGS. 3-6 . Representative, non-limiting transition speeds TS, T 1 , and T 2  include ground speeds in the low speed ranges such as five and ten miles per hour. 
         [0036]    While the embodiments of the invention disclosed herein are presently considered to be preferred, various changes and modifications can be made without departing from the spirit and scope of the invention. The scope of the invention is indicated in the appended claims, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.