Abstract:
A system and method for detecting that a four-wheel drive manual transmission vehicle is being operated in a manner that could cause a clutch over-speed problem. Upon detecting that the vehicle is being operated in the manner that could cause the clutch over-speed problem, the system and method activate a braking countermeasure to remove the potential problem. In addition, a fault code may be stored for subsequent diagnostic measures and/or a fault indicator may be used to alert the driver of the problem.

Description:
FIELD 
       [0001]    The present disclosure relates to clutch over-speed protection for vehicles with manual transmission, particularly four wheel drive vehicles with a low range mode of operation. 
       BACKGROUND 
       [0002]    Four-wheel drive (4WD) vehicles are four-wheeled vehicles with a drivetrain that may be controlled to allow all four wheels to receive torque from the engine at the same time. Four-wheel drive vehicles are typically placed from a two-wheel drive mode, where torque is only applied to two of the wheels, to the four-wheel drive mode by the driver when more traction is desired. Currently, the term all-wheel drive (AWD) is used to refer to a vehicle that operates in a four-wheel drive mode “full time” without the need for the driver to activate the four-wheel drive mode. Four-wheel drive vehicles are also known or advertised as four-by-four (4×4) vehicles. 
         [0003]    When switched into four-wheel drive mode, the vehicle&#39;s transfer case will lock the front-axle driveshaft to the rear-axle driveshaft, forcing the wheels to spin at the same speed. Some transfer cases also contain an additional set of gears providing the vehicle with a low range four-wheel drive mode (4-LO). The low range gear ratio gives the vehicle extra torque and a slow output speed, which allows drivers to slowly and smoothly crawl up very steep hills and dunes, or drive over rocky terrain. 
         [0004]    The low range mode works well for climbing and descending hills and dunes. Problems may arise for manual four-wheel drive vehicles, however, if the driver decides to coast down the hill or dune while depressing the clutch pedal when the vehicle is in the low range mode and still in gear. This situation will lead to excessive spinning of the clutch disk (e.g., almost two-times its specified rate), often referred to as over-speeding the clutch, which could cause the clutch to burst. Compounding the issue is the fact that the clutch over-speed condition may occur at low speeds and often times the driver may not even be aware of the potential problem. Repairing or replacing a burst clutch can be expensive and could cause the vehicle manufacturer to lose goodwill with the driver (even though it is the driver&#39;s actions that necessitated the repairs). 
         [0005]    Accordingly, there is a need and desire to detect when driving and operating conditions are detrimental to the vehicle&#39;s clutch in a four-wheel drive manual transmission vehicle and to implement countermeasures to avoid damage to the clutch. 
       SUMMARY 
       [0006]    In one form, the present disclosure provides a method of detecting and modifying an operating condition associated with a clutch over-speed condition in a four-wheel drive vehicle. The method comprises determining that a current vehicle speed is greater than a last known vehicle speed, the vehicle is in a low range operating mode, the vehicle clutch is being depressed, and the vehicle is not in neutral; and applying the vehicle&#39;s brakes if it is determined that the current vehicle speed is greater than the last known vehicle speed, the vehicle is in the low range operating mode while the vehicle clutch is being depressed, and the vehicle is not in neutral. 
         [0007]    The present disclosure also provides a clutch over-speed detection and protection apparatus for a four-wheel drive vehicle. The apparatus comprises an engine controller adapted to determine that the current vehicle speed is greater than a last known vehicle speed, the vehicle is in a low range operating mode, the vehicle clutch is being depressed, and the vehicle is not in neutral; and apply the vehicle&#39;s brakes if it is determined that the current vehicle speed is greater than the last known vehicle speed, the vehicle is in the low range operating mode while the vehicle clutch is being depressed, and the vehicle is not in neutral. 
         [0008]    In one form, the brakes are applied to maintain the vehicle&#39;s speed within a predetermined speed limit of the last known vehicle speed. The predetermined speed limit may be based on the vehicle&#39;s current gear ratio. The predetermined speed limit is about three to five miles per hour when the vehicle is in a first gear ratio. 
         [0009]    In another form, the last known vehicle speed is a last known speed when the vehicle clutch was engaged and the vehicle was not in neutral. 
         [0010]    In another form, the method and apparatus store a fault code indicative of a clutch over-speed condition. In yet another form, the method and apparatus output, to a driver of the vehicle, an indicator indicative of a clutch over-speed condition. In another alternative, the method and apparatus determine whether the vehicle is, or is not, in neutral based on a signal from a transmission neutral sensor. 
         [0011]    Further areas of applicability of the present disclosure will become apparent from the detailed description and claims provided hereinafter. It should be understood that the detailed description, including disclosed embodiments and drawings, are merely exemplary in nature intended for purposes of illustration only and are not intended to limit the scope of the invention, its application or use. Thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIG. 1  is a flowchart of a method in accordance with an embodiment disclosed herein that detects a driving and operating condition that could lead to a clutch over-speed problem and automatically corrects the condition to avoid the problem; and 
           [0013]      FIG. 2  is an illustration of a vehicle constructed in accordance with an embodiment disclosed herein that is adapted to implement the method of  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The technology disclosed herein is preferably applied to a four-wheel drive vehicle having a manual transmission and a transfer case providing a low range operating mode. Non-limiting examples of such a vehicle include various models of the Jeep® Wrangler, Jeep® Wrangler Unlimited, Jeep® Grand Cherokee, Jeep® Liberty, Jeep® Compass, Jeep® Patriot and the Dodge® RAM.  FIG. 1  illustrates a method  100  of detecting a driving and operating condition that could lead to a clutch over-speed problem and automatically modifying the driving condition to minimize or prevent the problem. In a desired embodiment, the method  100  is implemented in software, stored in a computer readable medium (e.g., memory  222  illustrated in  FIG. 2 , which could be a random access memory (RAM) device, non-volatile random access memory (NVRAM) device, or a read-only memory (ROM) device) and executed by a processor such as the engine controller  220  illustrated in  FIG. 2 . The method  100  can be executed periodically, at a predetermined rate deemed suitable for success, as part of the engine controller&#39;s  220  normal operating processing or background diagnostic processing. 
         [0015]    As will become apparent, the method  100  contains steps (e.g., steps  102 - 114 ) for monitoring certain driving and operating conditions that could lead to the clutch over-speed problem mentioned above. The method  100  also contains a step (e.g., step  120 ) for modifying the driving conditions to avoid the clutch over-speed problem and a step (e.g., step  124 ) for storing a fault code so that a diagnostic program can detect that the vehicle was being operated in a manner that could lead to the clutch over-speed problem. Optionally, the method can also provide an indication to the driver that the vehicle&#39;s transmission may need to be serviced (e.g., step  122 ). 
         [0016]    The method  100  determines: whether the vehicle is operating in the low range mode (step  102 ), whether the clutch pedal is depressed (step  104 ), whether the vehicle speed is greater than the last known vehicle speed when the clutch was engaged and the transmission was not in neutral (step  106 ) and whether the transmission is currently not in neutral (step  108 ). As is discussed below in more detail, determining whether the transmission is in neutral or not will be accomplished using a transmission neutral sensor or similar device. It should be appreciated that while  FIG. 1  illustrates these steps in a particular order, the disclosed embodiments are not limited to the exact order illustrated. 
         [0017]    At step  110 , the method  100  determines if all of the conditions have been met. That is, step  110  will determine if the vehicle is operating in the low range mode with the clutch pedal depressed while the transmission is currently not in neutral and that the vehicle speed is greater than the last known vehicle speed (when the clutch was engaged and the transmission was not in neutral). If all of these conditions are true at step  110 , the method  100  will continue at step  120  where the engine controller  220  causes the brakes to be applied. The brakes are applied to slow down and hold the vehicle&#39;s speed within a predetermined speed limit over the last known vehicle speed (when the clutch was engaged and the transmission was not in neutral). In one example embodiment, when the transmission is in first gear, the predetermined speed limit is about 3 to 5 miles per hour (mph) over the last known speed. It should be appreciated that this predetermined speed limit hysteresis is gear dependent. As such, a table of predetermined speed limits, one limit for each available gear ratio, can be created and stored in a memory (e.g., memory  222 ) or hardware and used at step  120 . 
         [0018]    The method  100  may perform the optional step of flashing a “Check Transmission” indicator on the vehicle&#39;s dashboard if it is equipped with a mechanism for displaying/outputting the indicator (e.g., an output device  206  as shown in  FIG. 2 ). The indicator can be flashed while the clutch over-speed conditions exist or can remain lit until the driver has the vehicle serviced. The same indicator, or another indicator, can also be used to alert the driver to manually brake the vehicle. At step  124 , an “Over-Speed” fault code is stored in a memory (e.g., memory  222 ) or hardware registers. The stored fault code can than be retrieved by the dealer&#39;s service department to determine if the clutch has been damaged by an over-speed condition. 
         [0019]    After step  124 , or if step  110  determines that one or more of the conditions in steps  102 - 108  are not met, the method  100  continues at step  112  where the last known gear is calculated based on the ratio of vehicle engine speed to road speed (N/V). The calculated last known gear is stored e.g., in a memory  222  or a register for subsequent use (in e.g., step  120 ). At step  114 , the method  100  calculates and stores the last known vehicle speed. If the clutch is engaged and the transmission is not in neutral, the last known vehicle speed will also be stored as the last known vehicle speed with clutch engaged and transmission not in neutral. The method  100  is complete and can be executed again at the predetermined rate. 
         [0020]      FIG. 2  illustrates a vehicle  200  constructed in accordance with an embodiment disclosed herein. As was discussed above, the vehicle  200 , particularly its engine controller  220 , is adapted to execute the method  100  of  FIG. 1 . The engine controller  220 , which may be a programmed processor, is connected to receive engine speed  202  and vehicle speed  204 . The controller  220  is also connected to an output device  206 , a transmission neutral sensor  208 , brake controls  210 , a transfer case  214  and a clutch switch  216 . The transmission neutral sensor  208  is connected to the transmission (not shown). The controller  220  may be coupled to a memory device  222  used to store vehicle and operating data, calculated data for steps  112 ,  114 , the speed limit hysteresis table used in step  120 , diagnostics information, programs and other data or source code needed to implement the method  100 . Although shown as a separate component, the memory device  222  may also be part of the engine controller  220 . The engine controller  220  may also include internal RAM, NVRAM and ROM memory devices. The transmission neutral sensor  208  may be a sensor or switch and should not be limited to any particular type of device. 
         [0021]    The controller  220  can input engine speed  202  from the engine and vehicle speed  204  from a vehicle sensor. The controller  220  can send a signal to the output device  206  when it is time to flash/output the “Check Transmission” indicator (e.g., at step  122 ). The controller  220  can input a neutral indication signal from the neutral sensor  208 . One value of the neutral indication signal will indicate that the transmission is in neutral and a second value will indicate that the transmission is not in neutral. The neutral indication signal is used in step  108  to determine if the transmission is in neutral or not. The neutral sensor  208  can be a switch similar to the ones currently used for vehicles in Europe for assisting with Start/Stop technology. 
         [0022]    The controller  220  also inputs a low range mode signal from the transfer case  214  indicating whether or not the transfer case  214  has been put in low range. One value of the low range mode signal will indicate that the vehicle is in the low range mode and a second value will indicate that the vehicle is in another mode. The low range mode signal is used in step  102  to determine if the is in low range mode or not. 
         [0023]    The controller  220  also inputs a clutch depressed indication signal from the clutch switch  216  indicating whether or not the clutch pedal is currently being depressed or not. One value of the clutch depressed indication signal will indicate that the clutch is being depressed and a second value will indicate that the clutch is not being depressed. The clutch depressed indication signal is used in step  104  to determine if the clutch is being depressed or not. 
         [0024]    As can be seen, the method and vehicle system described herein provide a technique for automatically preventing a driver from damaging a clutch due to clutch over-speed caused by an improper combination of driving and operating conditions. Although the disclosed embodiments have been described with use with four-wheel drive vehicles, it should be appreciated that the embodiments could also be used with all-wheel drive and other types of manual transmission vehicles implementing a low range mode of operation, if desired.