Patent Publication Number: US-2006003861-A1

Title: Continuously variable hydro-mechanical transmission

Description:
CROSS-REFERENCE TO RELATED PATENT APPLICATIONS  
      This application is a continuation of U.S. patent application Ser. No. 10/345,578 filed on Jan. 16, 2003, which is a divisional application of U.S. patent application Ser. No. 09/740,469 filed on Dec. 19, 2000, now U.S. Pat. No. 6,565,471. 
    
    
     FIELD OF THE INVENTION  
      The present invention relates to an improved transmission of the type including a combination of hydrostatic (fluid) and mechanical devices.  
     BACKGROUND OF THE INVENTION  
      Both hydrostatic transmissions and geared transmissions are used in agricultural and construction equipment to transmit power from power sources, such as internal combustion engines to equipment for accomplishing a desired task. For example, transmissions are used to properly transmit power to the wheels of a vehicle, or to a vehicle implement. Two important considerations in selecting transmissions are their efficiency and range of input and output speed variability. In general, hydrostatic transmissions provide extremely high-speed variability between the input and output, but are less efficient than geared transmissions. Unlike construction equipment applications, the agricultural applications require prolonged operation at full power in the “tillage” or “working” speed range. Under these conditions, optimum efficiency is required. Further, “on road” haulage performance requirements similar to that of a truck is desired for operating the work vehicle on the highway. In certain instances, it is required that the work vehicle has the capability of maintaining a road speed of 50 km per hour.  
      In an agricultural equipment application, such as on a tractor, power to drive an implement is typically obtained from a power take-off (PTO) device that is coupled to the tractor&#39;s primary power source or engine. When the tractor is using the PTO, the engine speed must be held constant to maximize the efficient use of the implement. With a conventional transmission, such situation cannot be maintained if the tractor speed changes since that will affect the PTO&#39;s rpm and therefore affect the implement&#39;s efficiency.  
      Thus there is a need for a transmission for use with agricultural equipment that will provide a constant horsepower with the ability to change speed and torque in a seamless manner, in other words, “continuously variable”. There is also a need for a continuously variable hydro-mechanical transmission that provides a “working range” for tillage and heavy draw bar applications and a “roading range” for haulage and transport on the highway.  
     SUMMARY OF THE INVENTION  
      According to one aspect of the present invention, a transmission for use with a power source and a load includes a primary sun gear adapted to be coupled to the power source, a hydrostatic power unit including a pump coupled to a motor, a ring gear driven by the motor, a secondary sun gear coupled to a first output shaft, a compound planetary gear carrier coupled to a second output shaft and a compound planetary gear carried by the compound planetary gear carrier and in engagement with the ring gear and the secondary sun gear. The first output shaft and the second output shaft are adapted to be selectively coupled to the load.  
      According to another aspect of the present invention, a work vehicle includes a power source and a transmission. The transmission includes a primary sun gear coupled to the power source, a hydrostatic power unit including a pump coupled to a motor, a ring gear driven by the motor, a secondary sun gear coupled to a first output shaft, a compound planetary gear carrier coupled to a second output shaft and a compound planetary gear carried by the compound planetary gear carrier and in engagement with the ring gear and the secondary sun gear. The first output shaft and the second output shaft are selectively coupled to the load.  
      According to another aspect of the present invention, a transmission includes a hydrostatic power unit including a pump coupled to a motor, a primary sun gear adapted to be coupled to a power source, a secondary sun gear selectively coupled to the motor, a ring gear selectively coupled to the motor in synchronization with the secondary sun gear, a compound planetary gear carrier coupled to an output shaft and a compound planetary gear cluster carried by the compound planetary gear carrier and in engagement with the ring gear and the secondary sun gear. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is an exemplary embodiment of a work vehicle with the present continuously variable hydro-mechanical transmission configured with four input shafts and one output shaft and further providing for two different hydrostatic inputs, whereby the hydro-mechanical transmission can provide a pure mechanical power flow or a combined hydro-mechanical power flow from the vehicle power source.  
       FIG. 2  is a partial sectional view of an exemplary embodiment of a compound planetary gear unit illustrated in  FIG. 1 .  
       FIG. 3  is an exemplary embodiment of a work vehicle with the present continuously variable hydro-mechanical transmission configured with three input shafts and two output shafts, whereby the hydro-mechanical transmission can provide a pure hydrostatic power flow or a combined hydro-mechanical power flow from the vehicle power source.  
       FIG. 4  is a partial sectional view of an exemplary embodiment of a compound planetary gear unit illustrated in  FIG. 3 .  
    
    
     DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS  
       FIG. 1  is a schematic diagram of a work vehicle, such as an agricultural tractor designated by the reference numeral  2 . Vehicle  2  includes a power source for such as an internal combustion engine mechanically coupled to a continuously variable hydro-mechanical transmission  10 . A hydro-mechanical transmission  10  drives the hydrostatic power unit  12  and a compound planetary gear unit  30  which are coupled to a range gear set  58  mounted within the transmission housing  11  and coupled to a load L which can be the wheels of the vehicle. It should be understood that the vehicle can also be operated with tracks supported by the wheels and that the work vehicle may be articulated with appropriate coupling and power transmission equipment between the articulated parts.  
      Continuously variable hydro-mechanical transmission  10  is supported in the work vehicle  2  by a housing or support frame  11 . The hydro-mechanical transmission  10  comprises a transmission housing  11  with a hydrostatic power unit  12  associated with the housing  11  and including a pump  16  coupled to a motor  18  with the hydrostatic power unit  12  coupled to a first input shaft  14  and a first output shaft  20 . The hydrostatic power unit  12  is coupled to a synchronous lockup clutch  24  by the first output shaft  20 . Depending upon the desired speed of work vehicle  2  or the desired rpm of the load L, an electronic controller actuates clutch  24  to couple drive gears  26 ,  28  to input shafts  36  and  40 , respectively, to select an appropriate hydrostatic input gear range. At the same time, the electronic controller also adjusts the angle of a swash plate of motor  18 . The motor  18  of the hydrostatic power unit  12  is connected to the pump  16  by appropriate hydraulic conduits  17  and appropriate fluid filters and storage tanks (not shown) as required. The pump  16  and motor  18  are operated in a closed circuit. An exemplary embodiment of the hydrostatic power unit  12  is provided with a variable displacement hydraulic pump and a fixed displacement hydraulic motor, preferably with an electronically controlled variable displacement hydraulic pump. A hydrostatic power unit driving gear  7  coupled to the input shaft  6  from the power source  4  with the hydrostatic power unit driving gear  7  engaging a hydrostatic power unit driven gear  8  that is coupled to the first input shaft  14  drives the hydrostatic power unit  12 .  
      The hydro-mechanical transmission  10  also includes a compound planetary gear unit  30  mounted in the housing and coupled to the power source  4  with a second input shaft  32  and the input shaft  6  from the power source. The compound planetary gear unit  30  also includes a third input shaft  36 , a fourth input shaft  40  and a second output shaft  44 . The second input shaft  32 , the third input shaft  36 , the fourth input shaft  40  and the second output shaft  44  are all coaxial with the second input shaft  32  inside the hollow third input shaft  36  which in turn is within the fourth input shaft  40  as shown in  FIGS. 1 and 2 . The compound planetary gear unit  30  is selectively coupled to the load L selectively coupled to the hydrostatic power unit  12  and coupled to the power source  4  utilizing various clutches as will be described below. The hydro-mechanical transmission  10  also includes a load shaft  60  which is coupled to the load L and mounted for rotation in the housing  11 . An intermediate shaft  56  rotatably mounted in the housing  11  supports a range gear set  58  mounted for rotation in the housing  11  and selectively coupled to the compound planetary gear unit  30  and the load shaft  60 .  
      The compound planetary gear unit  30  comprises a primary sun gear  34  coupled to the second input shaft  32 , which is directly coupled to the power source via input shaft  6  from the power source  4 . A secondary sun gear  38  is coupled to the third input shaft  36  with the third input shaft  36  selectively coupled to the first output shaft  20  by a synchronous lockup clutch  24 . A ring gear  42  is coupled to the fourth input shaft  40 , which is selectively coupled to the first output shaft  20  also with the synchronous lockup clutch  24 . A compound planetary gear cluster  46  mounted on a compound planetary gear carrier  48  engages with the primary sun gear  34 , the secondary sun gear  38  and the ring gear  42 . The compound planetary gear carrier  48  is coupled to the second output shaft  32  of the compound planetary gear unit  30 . A compound planetary gear carrier  48  supports three compound planetary gears  47  which make up the compound planetary gear cluster  46 .  
      The synchronous lockup clutch  24  selectively engages driving gears  26  and  28  which engage a third input shaft  36  and fourth input shaft  40 , respectively. When driving gear  26  is driven by the hydrostatic power unit  12 , it drives the secondary sun gear  38 . When driving gear  28  is driven by the hydrostatic power unit  12 , it drives the fourth input shaft  40 , which in turn drives the ring gear  42  within the compound planetary gear unit  30 . The above described power transmissions occur in the upstream side of the compound planetary gear unit  30  of the hydro-mechanical transmission  10 . On the down stream side of the compound planetary gear unit  30  a single output shaft, designated as the second output shaft  44  is coupled within the compound planetary gear unit  30  with the compound planetary gear carrier  48 . The second output shaft  44  is coupled to the directional clutch  50 , which has a forward component  54  and a reverse component  52  which respectively drive gears  55  and  53  to control the forward or reverse directions of the work vehicle  2 .  
      An intermediate shaft  56  is rotatably mounted in the housing  11  and supports a road range input gear  62 , which in turn engages a road range output gear  64  mounted on the load shaft  60 . A work range input gear  66  coupled to the intermediate shaft  56  engages a work range output gear  68  also mounted on the load shaft  60 . A reverse gear  70  is coupled to the intermediate shaft  56  and engages an idler reverse gear  72  mounted on the load shaft  60 . A range selector  74  is coupled to the load shaft and is used by the operator of the vehicle  2  to select either the road range speeds or the work range speeds. In an exemplary embodiment of the hydro-mechanical transmission, the range selector  74  is a sliding collar or synchronizer  76 .  
      The hydro-mechanical transmission described above can be operated in a pure mechanical configuration in which the compound planetary gear unit  30  is driven only by the power source  4  via input shaft  6  and second input shaft  32 . In the pure mechanical configuration, the hydrostatic power unit  12  is disconnected by hydrostatic disconnect clutch  22  coupled to the first output shaft  20 . In the pure mechanical configuration, synchronous lockup clutch  24  is actuated into engagement with both driving gears  26  and  28 . The hydro-mechanical transmission  10  can also be configured to operate with both the mechanical input directly from the power source  4  via the second input shaft  32  and input from the hydrostatic power unit  12  via driving gears  26  and  28  engaging, selectively, the third input shaft  36  and the fourth input shaft  40  of the compound planetary gear unit  30 .  
      Once the operator selects between the working range and road range speeds by manipulating the range selector  74 , controlling the pump swash plate angle in the hydrostatic power unit  12  and the selection of one of the drive gears  26  or  28  coupled to the first output shaft  20  achieve speed control. In low speeds, the hydrostatic drive is driven through ring gear  42 , which is coupled to the fourth input shaft  40  and is driven by driving gear  28 . The gear ratios in the compound planetary gear unit  30  are designed so that a synchronous condition occurs at the most desirable speed within a given working range. With the vehicle  2  starting from rest, the swash plate angle of the hydraulic motor  18  is increased in order to increase vehicle or rpm speed until a synchronous speed is reached (i.e., the two sun gears,  34  and  38 , the ring gear  42  and the planet carrier  48 , supporting the compound planetary gear cluster  46  all rotate at the same speed). At that same speed, the synchronous lockup clutch  24  can disengage driving gear  28  and engage driving gear  26  to drive the secondary sun gear  38 . With such change occurring at a synchronous speed it is “seamless” with little or no energy dissipation. With the hydrostatic drive being delivered through the secondary sun gear  38 , the swash plate angle is reduced to increase speed of the compound planetary gear carrier  48  until a maximum speed of the vehicle  2  is reached. It is also possible for the operator to engage both drive gears  26  and  28  with the synchronous lockup clutch  24  and with disconnect clutch  22  disconnecting output shaft  20  in which all gears of the compound planetary gear unit  30  will be transmitting power and thereby providing a very high efficiency through the hydro-mechanical transmission  10 . It has been determined that the optimal speed range for such operation is between 7 and 9 km per hour. As stated above, it is also possible to completely disengage the hydrostatic power unit  12  from the compound planetary gear unit  30  through the hydrostatic disconnect clutch  22 . In such instance, only direct mechanical power from the power source  4  is provided to the compound planetary gear unit driving only the primary sun gear  34  which in turn drives the compound planetary gear cluster  46  and the second output shaft  44 .  
      It is also possible for a full shuttle reverse in either the work range or road range by means of the directional clutch  50 . Since the directional change occurs downstream of the compound planetary gear unit  30 , it is not necessary to change the swash plate position of the pump  16  in the hydrostatic power unit  12  if the same forward to reverse ratio is retained.  
      The configuration of the hydro-mechanical transmission, described above provides that the synchronized ratio change gear speeds takes place on the input side (upstream side) of the compound planetary gear unit  30  in the hydrostatic power unit  12  with only one output shaft  44  from the compound planetary gear unit  30 . It is contemplated, that the control of the various clutches and the swash plate angle of the pump  16  in the hydrostatic power unit  12  can be controlled by an electronic control circuit operated from the cab of work vehicle  2  and utilizing appropriate sensors located at appropriate locations in the work vehicle  2 .  
      In another embodiment, a hydro-mechanical transmission  10  there is no operator preselected work range or road range of speeds per se. However, seamless speed changes from zero to a maximum speed, such as 50 km per hour can be obtained through four gear ranges defined as range “A”, “B”, “C”, and “D” with synchronized shift points between each range to obtain the seamless speed changing. In this embodiment, the synchronized ratio changing takes place on the output side (downstream side) of the compound planetary gear unit  30  which has two coaxial output shafts  44  and  45  and will be discussed more fully below.  
       FIG. 3  is a schematic diagram of a work vehicle  2  such as an agricultural tractor. Work vehicle  2  includes a power source  4  mechanically coupled to a continuously variable hydro-mechanical transmission  10 . The hydro-mechanical transmission  10  selectively drives a hydrostatic power unit  12  and a compound planetary gear unit  30 , which in turn drives a plurality of range gear sets  58  which are coupled to a load L. The load can be the wheels of the work vehicle  2 .  
      The hydro-mechanical transmission  10  is supported in the work vehicle by housing or support frame  11 . The hydro-mechanical transmission  10  comprises the transmission housing  11 , which supports the hydrostatic power unit  12 , which is associated with the housing  11 . The hydrostatic power unit  12  as shown in  FIG. 3  is contained within the hydro-mechanical transmission housing  11  but it may also be external to the housing  11  and accessed with appropriate couplings. The hydrostatic power unit  12  includes a pump  16  coupled to a motor  18  with the hydrostatic power unit  12  coupled to a first input shaft  14  and a first output shaft  20 . The power to the hydrostatic power unit  12  is provided by a driven gear  8  mounted on the first input shaft  14  and engaged with a hydrostatic power unit driving gear  7  mounted on the input shaft  6  of the power shaft  4 . The pump  16  is in fluid communication with the motor  18  by appropriate conduits  17 . The first output shaft  20  rotably supports a gear for engaging a third input shaft of the compound planetary gear unit  30  as described below.  
      A hydro-mechanical transmission  10  also includes a compound planetary gear unit  30  mounted in the housing. The compound planetary gear unit  30  includes a second input shaft  32 , a third input shaft  36 , a second output shaft  44  and a third output shaft  45 . (See  FIG. 4 ) The compound planetary gear unit  30  is selectively coupled to the load L, coupled to the hydrostatic power unit  12  and selectively coupled to the power source  4 . The compound planetary gear unit  30  can be connected to a plurality of range gear sets  58  as will be described below. The second input shaft  32 , the third input shaft  36 , the second output shaft  44 , and the third output shaft  45  are coaxial with the third input shaft being hollow and the second input shaft,  32  being supported within the third input shaft  36 . The second output shaft  44  is hollow and third output shaft  44  is supported within the hollow second output shaft  44  as shown in  FIG. 3 . The hydro-mechanical transmission  10  also includes a load shaft  60  coupled to the load L and mounted for rotation in the housing. An intermediate shaft  56  supporting a plurality of range gear sets  58  is mounted for rotation in the housing and selectively coupled to the compound planetary gear unit  30  and the load shaft  60 .  
      The compound planetary gear unit  30  of the hydro-mechanical transmission  10  comprises a primary sun gear  34 , which is coupled to the second input shaft  32 . A ring gear  42  is coupled to the third input shaft  36  and coupled to the first output shaft  20  with the hydrostatic power unit with the gear  26  engaging the third input shaft  36 . A compound planetary gear cluster  46  mounted on a compound planetary gear carrier  48  and engaged with the secondary sun gear  30  and the ring gear  42  is mounted within the compound planetary gear unit  30 . A compound planetary gear carrier  48  is coupled to the second output shaft  44 . The compound planetary gear cluster  46  includes three compound planetary gears  47 .  
      In operation, the continuously variable hydro-mechanical transmission  10  can be configured to have a combined hydrostatic and mechanical power flow by engaging the reverse clutch  52  or forward clutch  54  which respectively drive a reverse drive gear  53  and a forward drive gear  55  which in turn drives the first input shaft  20  and the second input shaft  32 . It is also possible to configure the hydrostatic mechanical transmission for a pure hydrostatic power flow by disengaging both clutches  52  and  54  in which case the second input shaft  32  is not directly driven by the power source  4 . In the pure hydrostatic configuration, one range gear is coupled to carrier  48  and another range gear  58  is connected to the secondary sun gear  38  simultaneously.  
      As described above, a preferred exemplary embodiment of the hydro-mechanical transmission  10  provides a variable displacement hydraulic pump  16  and a fixed displacement hydraulic motor  18 . It is contemplated that the operator from the cab of the work vehicle can control the swash plate angle of the pump  16  preferably by electronic controls. The plurality of arranged gear sets  58  comprise an A-range output gear  80  coupled to the intermediate shaft  56  and engaged with an A-range input gear  82  mounted on the second output shaft  44 . A B-range output gear  84  is coupled to the intermediate shaft  56  and engaged with a B-range input gear  86  mounted on the third output shaft  45 . A C-range output gear  88  coupled to the intermediate shaft  56  and engaged with a C-range input gear  90  is mounted on the second output shaft  44 . A D-range output gear  92  is coupled to the intermediate shaft  56  and engaged with D-range input gear  94  mounted on the third output shaft  45 . A plurality of range selectors  74  is coupled to the intermediate shaft to provide the selection of range gear sets. A typical range selector  74  in this exemplary embodiment is a clutch  77  associated with the respective range gear sets. A main input drive gear  96  is coupled to the intermediate shaft  56  and engaged with a main output drive gear  98 , which is mounted on the load shaft  60 .  
      As stated above in this embodiment, there is no selection for a work range or road range per se. However, the four ranges (A-D) provide a seamless transition between ranges similar to the work/road configuration previously described. Speed change from zero to maximum speed is achieved in a smooth and continuous manner by changing the swash plate angle of the pump  16 , preferably by appropriate electronic controls. For high efficiency, the first stall point of the motor  18  in the hydrostatic power unit  12  (i.e., ring gear  42  is a relative zero speed point) is selected in the 7-9 km per hour optimum speed range in order to transmit 100% of the power from the power source  4 . A full shuttle reverse is also available through the clutches  52  and  54  since the directional change occurs on the input side (upstream side) of the compound planetary gear unit  30 . Since directional changes occur on the input side of compound planetary unit gear  30 , it may be necessary to adjust the position of the swash plate in motor  18  depending upon the desired forward to reverse speed change ratio. In the low speed pure hydrostatic power flow regenerative heat is kept under control during prolonged creep operation of the work vehicle  2 . Also, in the pure hydrostatic power flow mode, different creep speed ranges can be achieved by engaging different combinations of the range clutches. For example, range gear set A,  80 ,  82  and B range set  84 ,  86  can be simultaneously engaged through their respective range selectors  74 . Similarly, range set  80  can be combined with C or D to obtain a different creep speed range as selected by the operator of the work vehicle  2 . With this embodiment, it is also possible to shuttle between forward and reverse in either the combined hydro-mechanical mode or the pure hydrostatic mode. Further, in this embodiment, the vehicle speed can be controlled independent of engine speed enabling constant output speed from the PTO during implement operation.  
      Thus, there is provided a continuously variable hydro-mechanical transmission which provides seamless speed changes within ranges selected by the operator. One embodiment of the continuously variable hydro-mechanical transmission provides for a synchronized change in speed ranges in the hydrostatic power unit on the input side of the compound planetary gear unit. This enables the continuously variable hydro-mechanical transmission to run at an optimum speed with the compound planetary gear unit locked up and all power being transmitted mechanically by the power source. Such arrangement facilitates a peak efficiency point and low speed creeper ranges which reduces regenetative heat in the transmission. A single output shaft from the compound planetary gear unit assists in achieving a full forward to reverse capability without changing the hydraulic pump swashplate angle in the hydrostatic power unit. In another embodiment, the compound planetary gear unit is configured to have two input shafts and two output shafts which facilitate a pure hydrostatic operation feature in this embodiment of the continuously variable hydro-mechanical transmission. In the pure hydrostatic mode of operation, three different creep speed ranges can be achieved by engaging different combinations of the four range gear sets located downstream of the compound planetary gear unit within the transmission housing. This embodiment of the continuously variable hydro-mechanical transmission allows a work vehicle speed to be controlled independent of the engine speed of the work vehicle and enabling a constant output speed from the power unit  12  coupled to the present transmission.  
      It will be understood that the foregoing descriptions are for preferred embodiments of this invention and that the invention is not limited to the specific forms shown. Other modifications may be made in the design and arrangement of other elements without departing from the scope of the invention as expressed in the appended claims.