Abstract:
Apparatus and methods are provided for modifying a torque differential between the road wheels of a non-driven axle. One apparatus includes, but is not limited to, two non-driven shafts and a torque transfer modulator coupling the two non-driven shafts. The torque transfer modulator is configured to modify the torque differential between the two non-driven shafts. A motor vehicle includes, but is not limited to, the apparatus coupling left and right road wheels, a sensor for detecting a left turn and/or right turn, and a controller. The controller is configured to transmit an actuating signal to the torque transfer modulator in response to the turn. One method includes, but is not limited to, detecting a driving condition in a motor vehicle, subtracting an amount of torque from a first non-driven road wheel, and adding the amount of torque to a second non-driven road wheel in response to detecting the driving condition.

Description:
TECHNICAL FIELD 
       [0001]    The present invention generally relates to motor vehicles, and more particularly relates to modifying the torque differential between the road wheels of a non-driven axle. 
       BACKGROUND OF THE INVENTION 
       [0002]    There are several compensation techniques for reducing the effects of a motor vehicle understeer. Some techniques are implemented by distributing input torque on a driven axle of the motor vehicle. That is, torque from the motor vehicle engine is distributed between the left and right road wheels according to the needs of a particular situation. 
         [0003]    For example, to reduce an understeer on a front-wheel drive motor vehicle, engine torque may be distributed between the left and right road wheels on the front axle. Similarly, to correct an understeer for a rear-wheel drive motor vehicle, engine torque may be distributed between the left and right road wheels on the rear axle. Likewise, distributing input torque between the left and right road wheels increases the performance and handling of the motor vehicle. While distribution of engine torque between the road wheels of an axle driven by the motor vehicle engine provides numerous benefits and improves the driving experience, other improvements in the driving experience are sought through modification of the torque differential between non-driven road wheels of the motor vehicle. 
         [0004]    For example, it has been found that some users of front-wheel drive motor vehicles prefer the driving experience of a rear-wheel drive vehicle, while also desiring the benefits of a front-wheel drive motor vehicle. Because previous torque modification techniques were implemented by distributing input torque from the motor vehicle engine (i.e., were implemented on the driven axle), users that desired the benefits of a front-wheel drive vehicle were unable to enjoy the driving experience of a rear-wheel drive vehicle and receive other benefits and improvements to the driving experience provided by a driven axle configuration. 
         [0005]    Accordingly, it is desirable to provide apparatus and methods for modifying the torque differential between road wheels of a non-driven axle. In addition, it is desirable to provide apparatus and methods for reducing the effects of an understeer situation in a front-wheel drive vehicle using the rear axle. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention. 
       BRIEF SUMMARY OF THE INVENTION 
       [0006]    Various embodiments of the invention provide apparatus for modifying the torque differential between the road wheels of a non-driven axle. One apparatus comprises a first non-driven shaft, a second non-driven shaft, and a torque transfer modulator coupling the first non-driven shaft and the second non-driven shaft. The torque transfer modulator is configured to modify a torque differential between the first non-driven shaft and the second non-driven shaft. 
         [0007]    Other embodiments of the invention provide a motor vehicle capable of modifying the torque differential between the road wheels of a non-driven axle. One motor vehicle comprises a left road wheel, a right road wheel, and a non-driven axle comprising a first torque transfer modulator coupling the left road wheel and the right road wheel. The first torque transfer modulator is configured to modify torque between the left road wheel and the right road wheel void of engine torque. One or more sensors configured to detect a left-turn understeer and/or a right-turn understeer is/are also included. The motor vehicle also comprises a controller in communication with the sensor and the first torque transfer modulator. The controller is configured to transmit an actuating signal to the first torque transfer modulator in response to left-turn or right-turn understeer, and the first torque transfer modulator is configured to distribute torque between the left road wheel and the right road wheel in response to receiving the actuating signal. 
         [0008]    Various embodiments of the invention also provide methods for modifying the torque differential between the road wheels of a non-driven axle. One method comprises the steps of detecting a driving condition, subtracting an amount of torque from the first non-driven road wheel, and adding the amount of torque to the second non-driven road wheel in response to detecting the driving condition. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements, and 
           [0010]      FIG. 1  is a block diagram of a non-driven axle in accordance with an exemplary embodiment; 
           [0011]      FIG. 2  is a schematic diagram of a torque transfer modulator (TTM) of  FIG. 1  in accordance with an exemplary embodiment; 
           [0012]      FIG. 3  is a diagram illustrating a configuration of the TTM of  FIG. 2  when utilized to reduce an unstable condition in accordance with one exemplary embodiment; 
           [0013]      FIG. 4  is a diagram illustrating a configuration of the TTM of  FIG. 2  when utilized to reduce another unstable condition in accordance with an exemplary embodiment; 
           [0014]      FIG. 5  is a diagram of one exemplary embodiment of a motor vehicle comprising the non-driven axle of  FIG. 2 ; and 
           [0015]      FIG. 6  is a flow diagram representing one exemplary embodiment of a method for modifying the torque differential between the road wheels of a non-driven axle. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0016]    The following detailed description of the invention is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding background of the invention or the following detailed description of the invention. 
         [0017]      FIG. 1  is a block diagram of a non-driven axle  100  that does not receive input torque from a motor vehicle engine (herein after referred to as a non-driven axle) in accordance with one exemplary embodiment. Non-driven axle  100  comprises a torque transfer modulator (TTM)  105  coupling a left axle portion  107  and a right axle portion  109 . Axle portions  107  and  109  couple non-driven axle  100  to road wheel mounts  130  and  140 , respectively. 
         [0018]    TTM  105  may be any device, structure, or mechanism capable of transferring/distributing torque from road wheel mount  130  to road wheel mount  140 , or vice-versa, without torque input from, for example, an engine. That is, TTM  105  is anything capable of taking torque from (i.e., applying a negative torque to) road wheel mount  130  or road wheel mount  140  and distributing the torque (i.e., applying an equal and opposite (positive) amount of torque) to the other respective road wheel mount void of engine torque. For example, TTM  105  may be a mechanical system (e.g., wave gear, planetary gear set, lay shafts, etc.), a hydraulic system (e.g., servo-drive pump, hydraulic motor, etc.), an electrical system (e.g., an electric motor, etc.), and the like. 
         [0019]    As one skilled in the art will appreciate, there are numerous techniques and devices capable of transferring torque between road wheel mount  130  and road wheel mount  140  without using engine torque, and the present invention contemplates each of these techniques. Therefore, the discussion below is not intended to limit the scope of the invention, but rather, is intended to disclose one of many devices and techniques capable of transferring torque between road wheel mount  130  and road wheel mount  140  void of engine torque. 
         [0020]      FIG. 2  is a schematic diagram of one exemplary embodiment of TTM  105 . As illustrated, TTM  105  comprises an axle system  110  coupled to road wheel mount  140  via axle portion  109  and an axle system  120  coupled to road wheel mount  130  via axle portion  107 . 
         [0021]    In accordance with one exemplary embodiment, axle system  110  comprises a torque transferring device (TTD)  110  coupled to axle portion  107 . TTD  110  may be, for example, a multi-plate wet clutch (e.g., magnetically actuated or hydraulic), a magneto-rheological (MR) fluid clutch, a motor-generator (e.g., hydraulic or electrical), or other torque transferring device capable of being engaged and disengaged. TTD  1110  is also coupled to a lay shaft  1120  via a gear  1125 , and lay shaft  1120  is coupled to road wheel mount  140  via a gear  1135  and axle portion  109 . Lay shaft  1120  and gears  1125 ,  1135  are well known in the art and are not discussed in detail herein. When engaged (released), TTD  1110  is configured to apply a negative torque to (i.e., take torque away from) road wheel mount  130  and apply a positive torque to (i.e., distribute an equal and opposite torque to) road wheel mount  140  via gear  1125 , lay shaft  1120 , and gear  1135 . 
         [0022]    As opposed to conventional torque distributing techniques, TTD  1110  distributes the torque from road wheel mount  130  to road wheel mount  140  without input torque (e.g., torque from an engine), while TTD  1210  (discussed below) is open. That is, TTD  1110  does not distribute engine torque between road wheel mounts  130  and  140 , but rather, takes (or subtracts) torque from road wheel mount  130  and applies the taken (or subtracted) torque to road wheel mount  140 . 
         [0023]    Similarly, axle system  120  includes a TTD  1210  (similar to TTD  1110 ) coupled to axle portion  109 . TTD  1210  is also coupled to a lay shaft  1220  via a gear  1225 , and lay shaft  1220  is coupled to road wheel mount  140  via a gear  1235  and axle portion  107 . When engaged (released), TTD  1210  is configured to apply a negative torque to (i.e., take torque away from) road wheel mount  140  and apply a positive torque to (i.e., distribute an equal and opposite torque to) road wheel mount  130  via gear  1225 , lay shaft  1220 , and gear  1235 . 
         [0024]    Similar to TTD  1110 , TTD  1210  distributes the torque from road wheel mount  140  to road wheel mount  130  without input torque (e.g., torque from an engine), while TTD  1110  is open. That is, TTD  1210  does not distribute engine torque between road wheel mounts  130  and  140 , but rather, takes (or subtracts) torque from road wheel mount  140  and applies the taken (or subtracted) torque to road wheel mount  130 . 
         [0025]      FIG. 3  is a diagram of non-driven axle  100  when utilized to reduce an unstable condition (e.g., a left-turn understeer, a non-linear range solution, etc.) and/or increase the performance envelop of the motor vehicle in accordance with one embodiment. Here, TTD  1110  has been engaged such that TTD  1110  applies a negative torque to a road wheel  1310  coupled to road wheel mount  130 , and applies a positive torque to a road wheel  1410  coupled to road wheel mount  140  via gear  1125 , lay shaft  1120 , and gear  1135  (as indicated by the dashed lines surrounding TTD  110 , gear  1125 , lay shaft  1120 , and gear  1135 ). One result of TTD  1110  applying a negative torque to road wheel  1310  and a positive torque to road wheel  1410  is to increase the torque differential between road wheels  1310  and  1410 . 
         [0026]    Note that TTD  1110  does not distribute engine torque between road wheels  1310  and  1410 , but rather, is a speed-based system on a non-driven axle. That is, TTD  1110  takes an amount of torque from road wheel  1310  (i.e., brakes road wheel  1310 ) and applies an equal and opposite amount of torque to road wheel  1410  (i.e., accelerates road wheel  1410 ). 
         [0027]    The amount of torque taken from road wheel  1310  and applied to road  1410  may be a fixed ratio (e.g., 0-30%) of the torque on road wheel  1310 . For example, if road wheel  1310  is rotating at 1000 revolutions-per-minute (RPMs), TTD  1110  may be configured to subtract (or slow road wheel  1310  by) 250 RPMs (i.e., a fixed ratio of 25%) from road wheel  1310  and add (or accelerate road wheel  1410  by) 250 RPMs to road wheel  1410 . Moreover, the amount of torque taken from road wheel  1310  and applied to road  1410  may be a variable ratio depending on the speed at which the motor vehicle is traveling. 
         [0028]      FIG. 4  is a diagram of non-driven axle  100  when utilized to reduce another unstable condition (e.g., a right-turn understeer, non-linear range solution, etc.) and/or increase the performance envelop of the motor vehicle in accordance with one embodiment. Here, TTD  1210  has been engaged such that TTD  1210  applies a negative torque to a road wheel  1410  coupled to road wheel mount  140 , and applies a positive torque to a road wheel  1310  coupled to road wheel mount  130  via gear  1225 , lay shaft  1220 , and gear  1235  (as indicated by the dashed lines surrounding TTD  1210 , gear  1225 , lay shaft  1220 , and gear  1235 ). One result of TTD  1210  applying a negative torque to road wheel  1410  and a positive torque to road wheel  1310  is to increase the torque differential between road wheels  1310  and  1410 . 
         [0029]    Note that TTD  1210  does not distribute engine torque between road wheels  1310  and  1410 , but rather, is a speed-based system on a non-driven axle. That is, TTD  1210  takes an amount of torque from road wheel  1410  (i.e., brakes road wheel  1410 ) and applies an equal and opposite amount of that torque to road wheel  1310  (i.e., accelerates road wheel  1310 ). 
         [0030]    The amount of torque taken from road wheel  1410  and applied to road  1310  may be a fixed ratio (e.g., 0-30%) of the torque on road wheel  1410 . Moreover, the amount of torque taken from road wheel  1410  and applied to road  1310  may be a variable ratio depending on the speed at which the motor vehicle is traveling. For example, when the motor vehicle is traveling less than 25 miles-per-hour (mph), TTD  1210  may be configured to subtract (or slow road wheel  1410  by) 30% of the torque from road wheel  1410  and add (or accelerate road wheel  1310  by) that 30% to road wheel  1310 . Furthermore, TTD  1210  may be configured to subtract (or slow road wheel  1410 ) 20% of the torque from road wheel  1410  and add (or accelerate road wheel  1310  by) the 20% of torque to road wheel  1310  when the motor vehicle is traveling between 25 mph and 50 mph. Furthermore, TTD  1210  may be configured to subtract (or slow road wheel  1410 ) 10% of the torque from road wheel  1410  and add (or accelerate road wheel  1310  by) the 10% to road wheel  1310  when the motor vehicle is traveling greater than 50 mph. 
         [0031]      FIG. 5  is a diagram of one exemplary embodiment of a motor vehicle (e.g., an automobile, truck, etc.)  500  comprising non-driven axle  100 . Motor vehicle  500  comprises a driven axle  510  (i.e., an axle that receives input or engine torque) coupled to and configured to provide engine torque to road wheels  512  and  514  via respective road wheel mounts (not shown). Driven axle  510  is coupled to, and driven by, a power plant (e.g., an electric engine, combustion engine, a hybrid engine, and the like)  520 . Notably, power plant  520  does not drive non-driven axle  100 . 
         [0032]    In one embodiment, motor vehicle  500  is a front-wheel drive automobile such that driven axle  510  is located toward a front  504  and non-driven axle  100  is located toward a rear  508  of motor vehicle  500 . In another embodiment (not shown), motor vehicle  500  is a rear-wheel drive automobile such that non-driven axle  100  is located toward front  504  and driven axle  510  is located toward rear  508  of motor vehicle  500 . 
         [0033]    Motor vehicle  500  suitably includes at least one sensor  530  coupled to road wheel  512  and/or road wheel  514  of driven axle  510 , and in communication with a controller  550  via a bus  540  (e.g., an electrical bus, optical bus, and the like). Sensor(s)  530  are configured to detect an unstable condition (e.g., a right-turn understeer, a left-turn understeer situation, non-linear range solution, etc.) and transmit a message to controller  550  via bus  540  indicating the type of unstable condition or a stable condition. Sensor(s)  530  may be located anywhere on motor vehicle  500  that would enable sensor(s)  530  to detect a right-turn understeer and/or a left-turn understeer situation. 
         [0034]    Controller  550  is coupled to each of TTD  1110  and TTD  1210  via bus  540 . Controller  550  is configured to receive messages from sensor(s)  530  and engage TTD  1110  or TTD  1210  depending upon whether the unstable condition is, for example, a left-turn or right-turn understeer situation. That is, controller  550  is configured to engage TTD  1110  or TTD  1210  to increase the torque differential between road wheels  1310  and  1410  (i.e., apply a negative torque to one of road wheels  1310  and  1410  and apply an equal amount of positive torque to the other respective road wheel). 
         [0035]    For example, when motor vehicle  500  is experiencing a right-turn understeer, sensor(s)  530  detects that motor vehicle  500  is experiencing the right-turn understeer and communicates such to controller  550 . Controller  550  then engages TTD  1210 , which results in torque being taken from (i.e., a negative torque applied to) road wheel  1410  (i.e., the inside road wheel) and an equal amount of torque being applied (i.e., positive torque) to road wheel  1310  (i.e., the outside road wheel). The opposite is the situation when motor vehicle  500  is experiencing a left-turn understeer—controller  550  engages TTD  1110 , which results in torque being taken from (i.e., a negative torque applied to) road wheel  1310  (i.e., the inside road wheel) and an equal amount of torque being applied (i.e., positive torque) to road wheel  1410  (i.e., the outside road wheel). 
         [0036]      FIG. 6  is a flow diagram representing an exemplary method  600  for modifying the torque differential between the road wheels of a non-driven axle (e.g., non-driven axle  100 ). Method  600  begins when at least one sensor (e.g., sensor  530 ) detects a driving condition (e.g., a right turn, a left turn, right-turn understeer, or a left-turn understeer) (step  610 ), and communicates such to a controller (e.g., controller  550 ) (step  620 ). 
         [0037]    Controller  550  then actuates a TTM (e.g., TTM  105 ) on non-driven axle  100  (step  630 ). When actuated, TTM  105  transfers torque between the left and right road wheels (e.g., roadwheel  1310  and  1410 , respectively) (step  640 ). 
         [0038]    The amount of torque transferred between road wheels  1310  and  1410  may be either a fixed ratio (e.g., 0-30%) or a variable ratio depending upon the speed of the motor vehicle and/or the severity of the driving condition (e.g., an understeer) as discussed above with reference to  FIGS. 3 and 4 , respectively. The severity of, for example, an understeer may be determined by the angle of the steering wheel in relation to the angle the motor vehicle is traveling and/or by comparing the actual yaw rate to a pre-determined/model yaw rate for the motor vehicle. 
         [0039]    When a turn is detected, whether TTM  105  transfers torque from road wheel  1310  to road wheel  1410  or from road wheel  1410  to road wheel  1310  depends on if a left turn or a right turn is detected (step  650 ). In either situation, TTM  105  distributes non-input torque from the inside road wheel to the outside road wheel (i.e., reacts the left and right road wheels against one another). That is, non-engine torque is transferred from the left road wheel (i.e., road wheel  1310 ) to the right road wheel (i.e., road wheel  1410 ) for left turns (step  654 ), and non-engine torque is transferred from the right road wheel (i.e., road wheel  1410 ) to the left road wheel (i.e., road wheel  1310 ) for right turns (step  658 ). For example, torque is shifted from the left road wheel to the right road wheel to correct a left-turn understeer and/or to increase the performance of the motor vehicle when turning left, and torque is shifted from the right road wheel to the left road wheel to correct a right-turn understeer and/or to increase the performance of the motor vehicle when turning right. 
         [0040]    In one exemplary embodiment, TTM  105  uses a TTD (e.g., TTD  1110  or TTD  1210 ) to correct a right-turn or left-turn understeer, and/or to increase performance when the motor vehicle is turning left or right. For example, TTD  1110  is actuated to correct a left-turn understeer and/or increase left-turn performance by transferring torque from road wheel  1310  (i.e., the inside road wheel) to road wheel  1410  (i.e., the outside road wheel), and TTD  1210  is actuated to correct a right-turn understeer and/or increase right-turn performance by transferring torque from road wheel  1410  to road wheel  1310 . That is, an understeer may be corrected or performance may be increased by braking (i.e., applying a negative torque, slowing down rotation, holding against rotation, etc.) the inside wheel and transferring the torque (i.e., applying a positive torque, speeding up rotation, releasing rotation, etc.) to the outside wheel (in an equal amount) void of input/engine torque. Other embodiments of the invention contemplate the use of other devices and/or techniques for transferring non-input torque between road wheels  1310  and  1410 . 
         [0041]    While at least one exemplary embodiment has been presented in the foregoing detailed description of the invention, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration of the invention in any way. Rather, the foregoing detailed description will provide those skilled in the art with a convenient road map for implementing an exemplary embodiment of the invention, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope of the invention as set forth in the appended claims and their legal equivalents.