Patent Publication Number: US-2019193558-A1

Title: System for providing torque assist in a vehicle

Description:
TECHNICAL FIELD 
     The present disclosure relates to a wheeled vehicle, and more particularly, to a system and method for providing torque assist in a wheeled vehicle. 
     BACKGROUND 
     Many wheeled vehicles such as off-highway trucks may be used for commercial, work, or other similar applications. In some cases, a layout of a prime mover and a transmission included in these wheeled vehicles may be characteristic of a front-wheel drive (FWD) setup in which the prime mover e.g., an engine or an electric motor and the transmission are configured to provide torque to a set of front wheels alone. In other cases, these vehicles may be characteristic of a rear-wheel drive (RWD) vehicle in which the prime mover and the transmission are configured to provide torque to a set of rear wheels alone. In a vehicle having a FWD or a RWD setup, the vehicle may rely on torque provided to either of the front wheels or the rear wheels alone to propel the vehicle. 
     When poor traction conditions are present or when such vehicles encounter gradients in their path of travel, it may become difficult to propel these vehicles considering that the torque is available only at the front wheels or the rear wheels alone. Some previously known strategies have been developed to overcome the aforementioned shortcoming by providing an all-wheel drive system to the vehicle. For instance, U.S. Pat. No. 6,508,328 (hereinafter referred to as “the &#39;328 patent”) relates to a hydrostatic transmission that is used as part of an all-wheel drive (AWD) system of a motor grader. The &#39;328 patent discloses that each front wheel of the motor grader includes its own drive system comprising a pump, a hydraulic motor, and a bypass valve that is provided to protect the hydraulic motor from cavitation conditions. The bypass valve also facilitates the hydrostatic transmission to avoid occurrences of “hydrostatic braking” and therefore, avoid wastage of otherwise usable power. 
     The hydrostatic transmission of the &#39;328 patent has been disclosed in conjunction with a motor grader for rendering the motor grader as an AWD vehicle. Although the hydrostatic transmission of the &#39;328 patent, when operational, can render a motor grade as an AWD vehicle, it will be acknowledged that a motor grader would typically encounter working conditions different from those that are likely to be experienced by other types of FWD or RWD vehicles, such as off-highway trucks. Therefore, it may be helpful to provide a system to such other types of FWD or RWD vehicles so that such other types of FWD or RWD vehicles can operatively mimic an AWD vehicle when poor traction conditions are present or when such other types of FWD or RWD vehicles encounter gradients in their path of travel. 
     SUMMARY OF THE DISCLOSURE 
     In one aspect of the present disclosure, a system for providing torque assist in a vehicle having a first set of wheels and a second set of wheels includes a hydrostatic transmission, multiple speed sensors, and a controller. The hydrostatic transmission includes a pair of pumps in which each of the pumps is configured to output pressurized fluid therefrom. The hydrostatic transmission also includes a pair of hydraulic motors that are fluidly coupled to the pair of pumps and the first set of wheels such that each hydraulic motor is configured to be driven by pressurized fluid output from a corresponding one of the pumps. 
     The speed sensors are associated with the first and second sets of wheels. Each speed sensor is configured to output a wheel speed associated with a corresponding one of the first and second sets of wheels. The controller is disposed in communication with each speed sensor and each pump from the pair of pumps. The controller is configured to compute an aggression factor for the first set of wheels from a ratio between an average of the wheel speeds for the second set of wheels and an average of the wheel speeds for the first set of wheels, determine if the aggression factor is greater than a first predefined limit, and selectively actuate operation of the pair of pumps to drive the pair of hydraulic motors so that corresponding ones of the planetary gear sets are rotatively driven to provide torque to corresponding ones of the first set of wheels. 
     In an additional aspect of the present disclosure, these pumps are variable displacement bi-directional pumps. Also, in a further aspect of the present disclosure, the controller is configured to independently operate each pump from the pair of pumps until the aggression factor is less than the first predefined limit. 
     In yet an additional aspect of the present disclosure, the hydrostatic transmission further includes a pair of planetary gear sets that are disposed between and coupled to corresponding ones of the pair of hydraulic motors and the first set of wheels. Each planetary gear set includes a sun gear that is configured to remain stationary, multiple planet gears that are disposed in mesh with the sun gear, and a planet carrier that is rigidly coupled to the plurality of planet gears and an output shaft of a corresponding one of the hydraulic motors. Additionally, each planetary gear set further comprises a ring gear that is disposed in mesh with the planet gears and coupled to a corresponding one of the first set of wheels. 
     In yet an additional aspect of this disclosure, each of the hydraulic motors is a radial piston motor having a casing, a cam ring that is defined on an inner surface of the casing, and a block that is rotatably disposed within the casing. The block is configured to define multiple cylinders radially arranged therein. Also, this block would be coupled to the planet carrier of a corresponding planetary gear set. The radial piston motor further includes pistons that are slidably disposed in corresponding ones of the cylinders defined in the block. These pistons are biased against the cam ring and rotatively drive the block in response to a receipt of pressurized fluid serially in the cylinders of the block from a corresponding one of the pumps via a distribution valve. 
     In another aspect of this disclosure, the hydrostatic transmission includes at least one electronically controlled valve disposed in communication with the controller. The at least one electronically controlled valve is configured to selectively allow flow from each of the pumps to corresponding ones of the hydraulic motors. 
     In a further aspect of the present disclosure, the system also includes a pair of pressure sensors that are disposed in communication with the controller. Each pressure sensor would be configured to output a value that is indicative of pressure between each pump and a corresponding one of the hydraulic motors. In response to a receipt of pressure values from the pair of pressure sensors, the controller could be configured to determine a difference in pressure values between the pair of pressure sensors, determine whether a difference in torque between the first set of wheels, obtained from a correlation of the difference in pressure values, is larger than a second predefined limit, and selectively vary an amount of displacement associated with at least one of the pumps until the wheel speed associated with each wheel from the first set of wheels is equal. 
     Further, aspects of this disclosure are also directed to a vehicle having a first set of wheels, a second set of wheels, and employing the system disclosed herein to provide torque assist to the first set of wheels. Furthermore, aspects of this disclosure have also been directed to a method for providing torque assist in a vehicle. 
     Other features and aspects of this disclosure will be apparent from the following description and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a bottom perspective view of an exemplary vehicle showing a frame and wheels rotatably supported on the frame; 
         FIG. 2  is a schematic illustration of a system for providing torque assist in the exemplary vehicle, according to an embodiment of the present disclosure; 
         FIG. 3  is a diagrammatic illustration of a portion of a hydrostatic transmission associated with the system of  FIG. 2  and located adjacent to the wheel of the exemplary vehicle, according to embodiments of the present disclosure; and 
         FIG. 4  is a flowchart of a method depicting steps to provide torque assist in the exemplary vehicle, according to an embodiment of the present disclosure; and 
         FIG. 5  is a schematic illustration of a system for providing torque assist in the exemplary vehicle, according to an alternative embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     Reference will now be made in detail to specific aspects or features, examples of which are illustrated in the accompanying drawings. Wherever possible, corresponding or similar reference numbers will be used throughout the drawings to refer to the same or corresponding parts. 
       FIG. 1  illustrates an exemplary vehicle  100 . The vehicle  100  may be a mobile machine that performs some type of operation associated with an industry such as mining, construction, farming, transportation or any other industry known in the art. In an example as shown in  FIG. 1 , the vehicle  100  is embodied in the form of an off-highway truck. 
     Although the vehicle  100  shown in  FIG. 1  is embodied in the form of an off-highway truck, in other embodiments, the vehicle  100  may include a dozer, a loader, a backhoe, an excavator, a motor grader, or any other earth moving machine known to persons skilled in the art. Moreover, the vehicle  100  may also include other operation-performing work machines such as a truck having a generator set mounted thereon, or a truck having one or more rig pumps mounted thereon. In fact, the vehicle  100  may optionally include other types of machines including passenger cars, but is not limited thereto. It will be acknowledged that a type of vehicle used for implementing embodiments disclosed herein is non-limiting of this disclosure. Rather, it will be appreciated by persons skilled in the art that aspects of the present disclosure may be applied to any type of vehicle having a frame and wheels as will be evident from the following disclosure. 
     As shown in  FIG. 1 , the vehicle  100  may include a frame  102 , and a plurality of wheels  104  rotatably supported on the frame  102 . The wheels  104  may include a set of powered wheels  104   a - 104   d  disposed at an aft portion of the vehicle  100 . These powered wheels  104   a - 104   d  may be “mechanically driven” by a prime mover  106 . The prime mover  106  may include, but is not limited to, an engine, an electric motor, or any other type of prime mover known to persons skilled in the art for propelling the vehicle  100  on a ground surface. Referring to a schematic illustration of the vehicle  100  in  FIG. 2 , the vehicle  100  may include a transmission system and a differential system that mechanically transmit drive power from the prime mover  106  to the set of powered wheels  104   a - 104   d.    
     Referring to  FIGS. 1-2 , the wheels  104  also include a pair of steering wheels  104   e ,  104   f  disposed at a fore of the vehicle  100 . It may be noted that a number of steering wheels disclosed herein is merely exemplary in nature and hence, non-limiting of this disclosure. Rather, a number of steering wheels used in a vehicle may depend on a type of vehicle used and hence, may vary from one type of a vehicle to another. In operation, the set of steering wheels  104   e ,  104   f  allows an operator of the vehicle  100  to steer the vehicle  100  on a desired path of travel. As shown in  FIG. 1 , each of the steering wheels  104   e ,  104   f  is capable of operatively executing a swiveling movement shown by way of directional arrows AA′. 
     The present disclosure relates to a system  200  for providing torque assist in the vehicle  100 . For sake of the present disclosure, the pair of steering wheels  104   e  and  104   f  will hereinafter be referred to as “the first set of wheels” and denoted by identical alpha-numerals “ 104   e ” and “ 104   f ”. Moreover, when references are made to the first set of wheels  104   e .  104   f  in the singular, the first set of wheels  104   e ,  104   f  may be regarded as having a front right (FR) wheel and a front left (FL) wheel each of which are denoted with identical alpha-numerals “ 104   e ” and “ 104   f ” respectively. 
     Similarly, the set of powered wheels  104   a - 104   d  will hereinafter be referred to as “the second set of wheels” and denoted by identical alpha-numerals “ 104   a - 104   d ”. Moreover, the second set of wheels  104   a - 104   d  may be regarded as being inclusive of a right set of second wheels  104   a - 104   b , and a left set of second wheels  104   c - 104   d.    
     As shown in  FIG. 2 , the system  200  includes a hydrostatic transmission  202 , multiple speed sensors  204 , and a controller  206 . The hydrostatic transmission  202  includes a pair of pumps  208  in which each of the pumps  208  is configured to output pressurized fluid therefrom. As shown in the illustrated embodiment of  FIG. 2 , each of the pumps  208  is embodied, for instance, in the form of a variable displacement bi-directional pump whose displacement can be varied based on, amongst other things, a steering movement of the first set of wheels  104   e ,  104   f  or an amount of payload associated with the vehicle  100  that manifests itself as a resistance to the movement of the first set of wheels  104   e ,  104   f  as the vehicle  100  is in operation. It may be noted that the pumps  208 , employed for use in powering the first set of wheels  104   e ,  104   f  may also be used to power other hydraulic systems that could be present on the vehicle  100 . 
     The hydrostatic transmission  202  also includes a pair of hydraulic motors  210  that are associated with the first set of wheels  104   e - 104   f  and each hydraulic motor  210   e - 210   f  is configured to be driven by pressurized fluid output from a corresponding one of the pumps  208   e - 208   f . As shown, these hydraulic motors  210   e - 210   f  are fluidly coupled to the pair of pumps  208   e - 208   f  in a closed loop fashion using a first fluid line  212   e  and a second fluid line  212   f  respectively. 
     As shown in the illustrated embodiment of  FIG. 3 , each of the hydraulic motors  210  is a radial piston motor having a casing  302 , a cam ring  304  that is defined on an inner surface  306  of the casing  302 , and a block  308  that is rotatably disposed within the casing  302 . The block  308  is configured to define multiple cylinders  310  radially arranged therein. Also, this block  308  would be coupled to a planet carrier  224  of a corresponding planetary gear set  214 . The radial piston motor  210  further includes pistons  312  that are slidably disposed in corresponding ones of the cylinders  310  defined in the block  308 . These pistons  312  are biased against the cam ring  304  and rotatively drive the block  308  in response to a receipt of pressurized fluid serially in the cylinders  310  of the block  308  from a corresponding one of the pumps  208  via a distribution valve  314 . 
     As shown in  FIG. 2 , the hydrostatic transmission  202  further includes a pair of planetary gear sets  214   e - 214   f  coupled to the pair of hydraulic motors  210   e - 210   f  and the first set of wheels  104   e - 104   f . In the illustrated embodiment of  FIGS. 2-3 , each of these planetary gear sets  214  is embodied as an epicyclic planetary gear set. However, in other embodiments, other configurations of planetary gear sets including, but not limited to, a Simpson planetary gear set, or a Ravigneaux planetary gear set may be used in lieu of the epicyclic planetary gear set disclosed herein depending on specific requirements of an application. 
     With reference to the illustrated embodiment of  FIGS. 2-3 , each planetary gear set  214  includes a sun gear  216  that is configured to remain stationary. The sun gear  216  may be rigidly disposed on a fixed spindle  218  about which a hub  220  of an associated wheel  104   e  or  104   f  rotates. Further each planetary gear set  214  also includes multiple planet gears  222  that are disposed in mesh with the sun gear  216 , and a planet carrier  224  that is rigidly coupled to the plurality of planet gears  222 . The planet carrier  224  is also coupled to an output shaft  226  of a corresponding one of the hydraulic motors  210 . As best shown in  FIG. 2 , the planet carrier  224   e  from the planetary gear set  214   e  associated with the FR wheel  104   e  is rigidly coupled to the output shaft  226   e  associated with the hydraulic motor  210   e  while the planet carrier  224   f  from the planetary gear set  214   f  associated with the FL wheel  104   f  is rigidly coupled to the output shaft  226   f  associated with the hydraulic motor  210   f.    
     Additionally, as shown in  FIG. 2 , each of the planetary gear sets  214  further comprises a ring gear  228  that is disposed in mesh with the planet gears  222  and coupled to a corresponding one of the first set of wheels  104   e  or  104   f . Referring to the illustrated embodiment of  FIG. 3 , the ring gear  228  from each planetary gear set  214  could be rigidly coupled to the hub  220  of a corresponding one of the first set of wheels i.e., the FR wheel  104   e  or the FL wheel  104   f.    
     Moreover, as shown in  FIG. 2 , the speed sensors  204  are associated with the first and second sets of wheels  104   a - 104   f . For instance, the speed sensor  104   c  is associated with a left rear axle  230   a  disposed between the differential system  110  and the left set of second wheels  104   c - 104   d . Similarly, the speed sensor  104   d  is associated with a right rear axle  230   b  disposed between the differential system  110  and the right set of second wheels  104   a - 104   b . Each speed sensor  204  is configured to output a wheel speed associated with a corresponding one of the first and second sets of wheels  104 . The system  200  also includes a controller  206  that is disposed in communication with each speed sensor  204  and each pump  208  from the pair of pumps  208   e - 208   f.    
     During operation of the vehicle  100 , the controller  206  is configured to compute an aggression factor for the first set of wheels  104   e - 104   f  from a ratio between an average of the wheel speeds for the second set of wheels  104   a - 104   d  and an average of the wheel speeds for the first set of wheels  104   e - 104   f . The controller  206  then determines if the aggression factor is greater than a first predefined limit, and selectively actuates operation of the pair of pumps  208   e - 208   f  to drive the pair of hydraulic motors  210   e - 210   f  so that corresponding ones of the planetary gear sets  214   e - 214   f  are rotatively driven to provide torque to corresponding ones of the first set of wheels  104   e - 104   f . Also, the controller  206  disclosed herein would be configured to independently and selectively operate each pump  208   e - 208   f  from the pair of pumps  208  until the aggression factor is less than the first predefined limit. 
     In yet another aspect of this disclosure as shown in  FIG. 2 , the hydrostatic transmission  202  includes at least one electronically controlled valve  232  that would be disposed in communication with the controller. The electronically controlled valve  232  is configured to selectively allow flow from each of the pumps  208   e - 208   f  to corresponding ones of the hydraulic motors  210   e - 210   f . With regards to a configuration of the electronically controlled valve  232 , it is hereby contemplated that the electronically controlled valve  232  may be embodied in the form of an electromagnetically operated relief valve or any other suitable type of valve configuration known to persons skilled in the art. Therefore, it must be noted that a type of valve configuration used to form the electronically controlled valve  232  disclosed herein is non-limiting of this disclosure. Rather, any type of valve configuration known to persons skilled in the art may be used to form the electronically controlled valve  232  disclosed herein such that the electronically controlled valve  232  is configured to perform functions that are consistent with the present disclosure. 
     In a further aspect of the present disclosure as shown in  FIG. 2 , the system  200  also includes a pair of pressure sensors  234   e - 234   f  that are disposed in communication with the controller  206 . Each pressure sensor  234   e - 234   f  would be configured to output a value that is indicative of pressure between each pump  208   e - 208   f  and a corresponding one of the hydraulic motors  20   e - 210   f . In response to a receipt of pressure values from the pair of pressure sensors  234   e - 234   f , the controller  206  could be configured to determine a difference in pressure values between the pair of pressure sensors  234   e - 234   f . The controller  206  may then co-relate the difference in pressure values to obtain a difference in torque between the first set of wheels  104   e  and  104   f . Thereafter, the controller  206  may determine if the torque difference between the first set of wheels  104   e  and  104   f  is larger than a second predefined limit. If so, the controller  206  would be configured to vary an amount of displacement associated with at least one of the pumps  208   e  and/or  208   f  until the wheel speed associated with each wheel  104  from the first set of wheels  104   e  and  104   f  is equal. 
     It may be noted that in embodiments of the present disclosure, the controller  206  is configured with suitable algorithms, programs, circuitry such as, but not limited to, power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, alarm driving circuitry, and the like for executing functionality consistent with the present disclosure. Moreover, algorithms and programs associated with the controller  206  can reside on one or more devices known to persons skilled in the art. Some examples of such devices may include, but is not limited to, read only memory (ROM), random access memory (RAM), floppy disks, compact disks, portable hard disks, and the like. Such devices may be contemplated and suitably implemented by one skilled in the art, in conjunction with the controller  206  to execute functions that are consistent with the present disclosure. 
       FIG. 4  illustrates a flowchart depicting a method  400  for providing torque assist in the vehicle  100  having a first set of wheels  104   e - 104   f  and a second set of wheels  104   a - 104   d . As shown in  FIG. 4 , at step  402 , the method  400  includes providing a hydrostatic transmission  202  between a prime mover  106  of the vehicle  100  and the first set of wheels  104   e - 104   f  in which the hydrostatic transmission  202  comprises a pair of pumps  208   e - 208   f , a pair of hydraulic motors  210   e - 210   f  in fluid communication with the pair of pumps  208   e - 208   f , and a pair of planetary gear sets  214   e - 214   f  coupled to the pair of hydraulic motors  210   e - 210   f  and the first set of wheels  104   e - 104   f . At step  404 , the method  400  includes measuring wheel speed associated with each wheel  104  from the first and second sets of wheels  104   a - 104   f  using the plurality of speed sensors  204   c - 204   f . At step  406 , the method  400  then includes computing an aggression factor for the first set of wheels  104   e - 104   f  from a ratio between an average of the wheel speeds for the second set of wheels  104   a - 104   d  and an average of the wheel speeds for the first set of wheels  104   e - 104   f.    
     The method  400  then proceeds from step  406  to step  408  in which the method  400  includes determining if the aggression factor is greater than a first predefined limit. If so, then the method  400  proceeds from step  408  to step  410  in which the method  400  includes actuating operation of the pair of pumps  208   e - 208   f , by means of the controller  206 , for driving the pair of hydraulic motors  210   e - 210   f  so that corresponding ones of the planetary gear sets  214   c - 214   f  are rotatively driven to provide torque to corresponding ones of the first set of wheels  104   e - 104   f.    
     However, if at step  408 , the controller  206  determines that the aggression factor is less than the first predefined limit, then the method  400  may be configured to loop from step  408  to step  404  in which the wheel speeds of the first and second sets of wheels  104   a - 104   f  are measured for subsequently performing steps  406 - 408  disclosed herein for realizing functions that are consistent with the present disclosure. 
     Although in the illustrated embodiment of  FIG. 2 , the planetary gear sets  214   e ,  214   f  have been disclosed as forming part of the system  200 , it may be noted an inclusion of the planetary gear sets  214   e ,  214   f  is not always necessary and therefore, a configuration of the system  200  could be construed as being non-limiting of this disclosure. In an alternative embodiment of the present disclosure, a system  500  having a hydrostatic transmission  502  for providing torque assist to the first set of wheels  104   e ,  104   f  is shown in the diagrammatic illustration of  FIG. 5 . In this embodiment, the pair of planetary gear sets  214   e ,  214   f  shown in  FIG. 2  may be omitted such that the output shafts  226   e ,  226   f  of the pair of hydraulic motors  210   e ,  201   f  are connected directly to the pair of hubs  220   e ,  220   f  from corresponding ones of the first set of wheels  104   e ,  104   f . Consequently, in this embodiment, torque may be transmitted directly from the output shafts  226   e ,  226   f  of the pair of hydraulic motors  210   e ,  201   f  into driving corresponding ones of the first set of wheels  104   e ,  104   f  via the pair of wheel hubs  220   e ,  220   f  respectively. 
     INDUSTRIAL APPLICABILITY 
     Embodiments of the present disclosure have applicability for use in providing torque assist in a wheeled vehicle. The system  200  of the present disclosure, when implemented in a vehicle having a conventionally known RWD or FWD setup can help such wheeled vehicles to mimic an all-wheel drive (AWD) setup and help improve use of an overall tractive effort for the wheeled vehicle when poor traction conditions exist in the path of travel for such wheeled vehicles or when such wheeled vehicles are required to travel uphill in which such wheeled vehicles would otherwise typically rely on torque that was previously provided to either of the front wheels or the rear wheels alone. 
     Implementation of the system  200  disclosed herein may also serve as a cost-effective alternative to installation of an otherwise expensive mechanical transmission setup such as a transmission and a differential system. Also, with use of a “hystat” radial base piston motor for each of the hydraulic motors  210  disclosed herein, it is envisioned that the hydraulic motors  210  are imparted with adequate robustness. As known to persons skilled in the art, these “hydrostat” radial base piston motors are generally capable of withstanding high loads and subsequently high fluid pressure to counteract the high amounts of load, typically experienced by wheeled vehicles including, but not limited to, off-highway trucks, dump trucks, and the like. Therefore, the hydraulic motors  210  disclosed herein may exhibit improved reliability in operation and require little to no maintenance even when subject to severe loading conditions or with use for a prolonged period of time. 
     While aspects of the present disclosure have been particularly shown and described with reference to the embodiments above, it will be understood by those skilled in the art that various additional embodiments may be contemplated by the modification of the disclosed vehicles, systems and methods without departing from the spirit and scope of what is disclosed. Such embodiments should be understood to fall within the scope of the present disclosure as determined based upon the claims and any equivalents thereof.