Abstract:
A method for redistributing driving torque between front and rear driving wheels of a vehicle traveling at essentially the same speed. The method includes determining a vehicle condition corresponding to load, based upon at least one vehicle parameter, comparing the determined vehicle condition to a predetermined value, wherein if the determining vehicle condition exceeds the predetermined value, a high load condition exists, and redistributing the driving torque between the front and rear wheels, when the determining step determines that a high load condition exists. By controlling torque redistribution in accordance with one or more high load conditions on the driveline components, subsequent damage of the driveline system can be reduced or prevented.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a method of redistributing driving torque based on one or more load conditions in a 4-wheel drive (4WD) vehicle. More particularly, it relates to a method of redistributing driving torque among all wheels (e.g., between the front and rear wheels) of a 4WD vehicle based on one or more load conditions that can cause significant damage or wear and tear to driveline components such as CV joints and driveshaft. 
     2. Description of the Related Art 
     In 4WD vehicles, various systems are known for distributing driving torque between front and rear wheels. For instance, driving torque can be distributed by employing a limited slip center or inter-axle differential, or by employing a clutch of a hydraulic or electromagnetic type in a torque path for varying the driving torque transmitted there through. The above known driving torque redistribution systems can be used to, e.g., enhance the turning performance of 4WD vehicles. In particular, the driving torque is distributed or transferred based on a difference of speed between the front and rear wheels, engine output when the vehicle speed is less than a given value, or line pressure in a transfer clutch. 
     Furthermore, most 4WD vehicles are designed so that one pair of wheels (front or rear) is the primary driving wheels and the other pair is the auxiliary driving wheels. In other words, under normal driving conditions, the primary driving wheels receive most of the torque and the auxiliary driving wheels receive a smaller amount of torque (or none at all). In some 4WD vehicles, the primary driving wheels are the front wheels, and in other 4WD vehicles the primary driving wheels are the rear wheels. 
     When a 4WD vehicle encounters a high load condition caused by climbing a steep hill, towing a trailer, or other heavy load condition, the 4WD vehicle typically requires a large amount of driving torque in its driveline system to cope with the heavy load. Such heavy application of the driving torque to the driveline system inevitably causes wear and tear or even significant damage to various components of the driveline system. 
     None of the above known driving torque redistribution systems is able to distribute or transfer torque between front and rear wheels based on high load conditions. Accordingly, the above known driving torque redistribution systems cannot prevent wear and tear and damage of the components of the driveline systems when 4WD vehicles encounter one or more high load conditions. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is provided in order to increase the life cycle of driveline components by redistributing torque among different wheels in a 4WD vehicle based on one or more high load conditions. For example, in a 4WD vehicle where most (or all) of the driving toque is normally transmitted through the front wheels, when the vehicle encounters a high load condition, a great deal of wear and tear, or even damage, may occur to the drive train components of the front wheels. However, when such a high load condition is sensed, the instant invention transfers an additional amount of torque through the rear wheels, in order to reduce wear and tear or damage to the drive train of the front wheels. Of course, the instant invention also applies to a system where most of the driving torque is normally transmitted through the rear wheels. 
     Various methods are provided in the torque redistribution method of the present invention that would reduce the torque and the subsequent damage of certain components of the driveline system by controlling torque redistribution among different wheels of the vehicle based on one or more high load conditions on the components of the driveline system. 
     The load-based torque redistribution system of the instant invention ensures that the excessive torque due to the high load on the front or rear wheels, the primary driving wheels of a 4WD vehicle, is appropriately transferred or distributed to the auxiliary driving wheels so as to alleviate the load and reduce wear and tear. 
     In accordance with the present invention, a method of redistributing driving torque between front and rear driving wheels of a vehicle, when the front of a rear wheels are traveling at essentially the same speed, includes: determining a vehicle condition corresponding to load, based upon at least one vehicle parameter; comparing the determined vehicle condition to a predetermined value, wherein if the determining vehicle condition exceeds the predetermined value, a high load condition exists; and redistributing the driving torque between the front and rear wheels, when the determining step determines that a high load condition exists. 
     Additionally, a system for redistributing driving torque distributed between front and rear wheels of a vehicle, when the front and rear wheels are traveling at essentially the same speed, includes: a front driveline for driving the front wheels; a rear driveline for driving the rear wheels; a torque transfer unit connecting the front and rear drivelines for distributing torque, from a power source, between the front and rear drivelines; at least one vehicle sensor; and a controller, coupled to the sensor and the differential, for controlling torque split of the differential in response to the sensor. 
    
    
     Related aspects and advantages of the invention will become apparent and more readily appreciated from of the following detailed description of the invention, taken in conjunction with the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flow diagram for explaining the basic operation of the torque redistribution method according to a preferred embodiment of the present invention; 
     FIG. 2 is a flow diagram for explaining the torque redistribution method of the present invention; 
     FIG. 3 is a detailed flow diagram of FIG. 2; 
     FIG. 4 is a flow diagram showing total torque distribution according to the preferred embodiment of the present invention; 
     FIG. 5 is a torque frequency comparison chart for 4-wheel and 2-wheel drive modes; 
     FIG. 6 is a flow diagram showing a second embodiment of the present invention; 
     FIG. 7 is a design torque limitation map for the flow diagram of FIG. 6; 
     FIG. 8 is a flow diagram showing a third embodiment of the present invention; 
     FIG. 9 is a chart showing gear and throttle positions for the flow diagram of FIG. 8; 
     FIG. 10 is a flow diagram showing a fourth embodiment of the present invention; and 
     FIG. 11 is a flow diagram showing 4-wheel driveline systems. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention will now be described by way of preferred embodiments with reference to the accompanying drawings. 
     FIG. 1 shows a basic operation of the torque redistribution method according to the present invention. A signal sensed from a vehicle sensor in the sensor step S 10  is processed a controller in the 4WD ECU step S 20  that includes the system check step S 21 , 4WD calculation&#39;software step S 22 , predetermined design torque limitation step S 23 , rear torque contribution step S 24 , and clutch control step S 25 . A comparator in the 4WD ECU step S 20  compares the sensed vehicle parameter from the vehicle sensor corresponding to a vehicle, with a predetermined value to determine if parameters exist to safely redistribute or transfer the torque from the front driveline for driving front wheels to the rear driveline for driving rear wheels so as to ease the load on the front driveline components during a high load condition. If the system check step S 21  determines that the signals from the sensor step S 10  are valid, then signals are processed by the 4WD calculation software step S 22 . Otherwise, the signals are processed by another calculation software in step S 26 . By comparing detected values from the system check step S 21  with the predetermined values from the predetermined design torque limitation step S 23 , the 4WD calculation software step S 22  allows the rear torque contribution step S 24  to determine the amount of rear torque contribution to be executed. For this system, the torque is varied using an electromagnetic clutch system. The clutch control step S 25  controls current in the torque application step S 30 , which shows various components of a 4WD vehicle with front wheels as primary driving wheels, including a 4WD clutch unit  1 , a transfer case  2 , a differential  3 , a transmission  4 , an engine  5 , front wheels  6 , and rear wheels  7 . In particular, the clutch control step S 25  regulates the electric current supplied to the 4WD clutch unit  1  so that the split of torque to front and rear wheels can be controlled based on the determined high load condition. 
     Moreover, a power source such as the engine  5  transfers power through the transmission  4 , transfer case  2 , and 4WD clutch control  1 , and is supported by one or more current operated clutches in the 4WD clutch unit  1  for changing the torque split between the front and rear wheels in response to one or more vehicle sensor in the sensor step S 10 , which is coupled to the differential  3  via the controller in the 4WD ECU step S 20  for controlling the torque split. The 4WD clutch unit  1  has a torque transfer unit that includes the ability to transfer varying amounts of torque such as a hydraulic wet clutch or electromagnetic clutch. This system must enable clutch slip or some other speed sensitive compensating method or device to counteract the differential speeds between the front and rear wheels during redistribution of the driving torque. 
     Since the rotational speed of the front and rear wheels is not in a one to one ratio (1:1), the 4WD clutch unit  1  as shown in FIG. 1 cannot remain in a full-lock condition for an extended period of time. Accordingly, some slips are required to transfer partial torque (i.e., 50% or less of the total) and equalize the speed difference. 
     Referring to FIGS. 2 and 3, the torque redistribution method of the present invention includes a load detection step S 40  that uses various vehicle sensors such as engine FI electronic control unit (ECU) sensors  10 , anti-lock braking system (ABS) sensors  30 , transmission sensors  20 , and transmission AT ECU sensors  40  to detect one or more load conditions of the 4WD vehicle. In particular, the engine FH ECU sensors  10  can be used to detect the manifold pressure  11 , throttle angle  12 , AC clutch gear  13 , engine retard  14 , vehicle speed  15 , air temperature  16 , and water temperature  17  while the transmission AT ECU sensors  40  can be used to detect transmission range  42 , gear range  43 , and torque converter slip (ratio)  44 . Additionally, signals from the FI ECU sensors  10  and transmission sensors  20  can be used to calculate the total driveshaft torque in the load calculation step S 50 . If the total driveshaft torque is determined to be above a certain predetermined torque value in the load calculation step S 50 , the current of a current control clutch  54  is controlled by a current regulator  56  in the current regulation step S 60 , and the front driveshaft torque  57  is redistributed to the rear drive shaft torque  58  in the torque redistribution step S 70 . In other words, if a load calculation software  51  of the load calculation step S 50  determines that the load (e.g., the driveshaft torque) is above a predetermined design torque limitation or value  52 , then the torque redistribution between front and rear wheels will be executed to reduce or prevent damage to the driveline components. 
     After determining in the load calculation step S 50  that torque redistribution is required, the current controlled clutch  54  is activated in the current regulation step S 60  according to the current regulator  56  to redistribute torque from, e.g., the front wheels of the front driven 4WD vehicle to the rear wheels. 
     Alternatively, input signals from a vehicle speed sensor  15 , throttle angle sensor  12 , and gear range sensor  4  detected in the load detection step S 40  may be used in the load calculation step S 50  to calculate the actual acceleration of the vehicle at a given throttle. In the load calculation step S 50 , the actual acceleration is compared with the stored acceleration data, which contain information on the acceleration of the vehicle on level ground with only the vehicle and passenger weight in order to determine whether the torque redistribution in the torque redistribution S 70  is necessary. 
     Still further, signals from the transmission sensors, including signals from one or more pressure switches in the transmission, can be used to calculate the increase in the line pressure due to a reactor arm and pressure regulators in the transmission. The increase in the line pressure is used to determine whether torque redistribution in S 70  is necessary. 
     As illustrated in FIG. 4, the total torque  60  required during towing or high load conditions can be divided into front driveshaft torque  62  and rear driveshaft torque  64 . A torque frequency (S-N) graph shown in FIG.S illustrates the number of rotations of the driveline components for a given load condition (e.g., towing). By redistributing the torque between the front and rear wheels, the S-N graph indicates that the high load cycles, which is capable of causing significant damage, can be reduced by redistributing the remaining needed torque to the rear driving wheels of the front driving 4WD vehicle. The increase in the number of rotational cycles of the front torque is equivalent to the torque cycles distributed to the rear wheels. This increases the lower torque cycles for the primary driving components but these smaller torque levels cause significantly less damage to components. 
     FIG. 6 shows another embodiment of the present invention which uses software control based on the calculated torque. More specifically, if the vehicle is moving (i.e., Vspd&gt;0 mph), then (1) signals from a first sensor group  72  of the engine FI ECU sensors  10  regarding water temperature, air temperature, AC clutch, and retard are processed by the engine torque reduction factor step S 121  in 4WD ECU step S 120 ; and (2) signals regarding the transmission range  42  and torque converter slip derived from the AT ECU sensors  40  are processed by the transmission effect factor step S 123  in 4WD ECU step S 120 . Thereafter, factors from steps S 121  and S 123 , along with signals from a second sensor group  74  regarding the manifold pressure and throttle angle, and signals from a third sensor group  76  regarding the vehicle speed are processed in order to calculate front and rear driveshaft torques in step S 122 . A comparison step S 124  compares the actual driveshaft torque received from step S 122  and the stored torque map received from the designed torque limitation map step S 123  to determine whether the load factor is equal to the difference between the actual torque and the stored torque in the map. If the load factor is less than or equal to zero, then the 4WD ECU step S 120  is proceeded to other 4WD calculation step  126 . If the load factor is greater than zero, then the 4WD ECU step S 120  is proceeded to the select proper current for load factor step S 127 . The front or rear current from S 127  is then used by the 4WD electronic current control step S 128  to control amperage. The control amperage from the 4WD ECU step S 120  is received by the current controlled 4WD clutch step S 132 , and applied by the torque transferred to rear wheel step S 134 . 
     FIG. 7 is a chart showing a design torque limitation map in terms of vehicle speed and driveshaft torque for the flow diagram of FIG. 6 
     FIG. 8 shows still another embodiment of the present invention which uses software control based on gear and throttle positions. More specifically, if the vehicle is moving (i.e., Vspd&gt;0 mph), then (1) signals from a first sensor group  82  of the engine FI ECU sensors  10  regarding vehicle speed; (2) signals from a second sensor group  84  of the engine FI ECU sensors  10  regarding throttle angle; (3) signals regarding the transmission range  45  from the AT ECU sensors  40  are received by the 4WD ECU step S 220 . A comparing step S 224  in the 4WD ECU step S 220  compares the gear position and throttle data to the stored data from the storing step S 225  (gear position versus throttle stored data). In step S 226 , one of the three load types, i.e., light, medium, or heavy is selected, and a corresponding load factor  90  is processed by the 4WD electronic current control step S 228  (PID F/B). One of the control amperages  92 ,  94 , and  96  (i.e., heavy, medium or light) from the 4WD ECU step S 220  is received by the current controlled 4WD clutch step S 132 , and applied by the torque transferred to rear wheel step S 134 . 
     FIG. 9 is a chart showing gear and throttle positions during heavy, medium, and low loads for the flow diagram of FIG.  8 . 
     FIG. 10 shows yet another embodiment of the present invention which uses software control based on acceleration. More specifically, if the vehicle is towing or going uphill during cruise condition, then (1) signals from the engine FI ECU sensors  10  regarding vehicle speed  15 , manifold pressure  11 , throttle angle  12 , retard  14  and AC clutch  13  are processed by the calculate actual acceleration step S 321  in 4WD ECU step S 320 . Thereafter, (1) signals regarding the transmission range  42  and transmission converter slip  45  derived from the AT ECU sensors  40 ; (2) the calculated actual acceleration from step S 321 ; and (3) stored acceleration from step S 323  (stored acceleration versus throttle data for normal condition) are processed by step S 322  to compare actual acceleration with measure acceleration in the 4WD ECU. The compared factor is proceeded then to step S 327  in which a load factor is selected (i.e., select load factor (actual/stored acceleration * factor)). The current controlled by step S 328  in the 4WD ECU step S 320  is then processed by the current controlled 4WD clutch step S 32 , and applied by the torque transferred to rear wheel step S 34 . 
     The torque redistribution method of the present invention is applicable to any front or rear wheel drive 4WD vehicle having front and rear wheels connected or engaged there between by an electromagentic, hydraulic or similar type of clutch system. Additionally, the torque redistribution method of the present invention is operable when the 4WD vehicle is moving and when all the wheels of the vehicle are moving at the same speed. In order to counteract the differential speeds between the front and rear wheels when transferring torque, the 4WD vehicle incorporates a clutch system capable of compensating the speed differences between the front and rear axles. The compensating device can also be incorporated in the transfer case, clutch system, or rear differential. 
     Since any damage to the driveline components from the high load condition would be a powered function of the torque applied to the components according to the damage theories such as the Mirev&#39;s theory, the torque redistribution method of the present invention would allow the driveline components to be manufactured at a lower tolerance or strength and yet achieve the same or increased life cycle. Examples of the driveline components in the 4WD vehicle include CV joints, bearings, final drive differential gear, driveshaft, and other rotating components between the wheels and transfer case. 
     FIG. 11 shows different 4-wheel driveline systems, including a front wheel drive system with 4WD and 2-clutch, a rear wheel drive system with 4WD, and a front wheel drive with 4WD and 1-clutch. In the various 4-wheel driveline systems as shown in FIG. 11, the optional driving wheels are operated using a controllable clutch system with a wet clutch system. However, Gerotor type clutches or hydraulic clutches can also be used for the same purpose. 
     Although a specific form of embodiment of the present invention has been described above and illustrated in the accompanying drawings in order to be more clearly understood, the above description is made by way of example and not as a limitation to the scope of the present invention. It is believed that various modifications apparent to one of ordinary skill in the art could be made without departing from the scope of the present invention.