Abstract:
A coaching system for drivers of vehicles monitors the power dissipation of a manual transmission clutch and, when the energy dissipated during an event is excessive, suggests modified driving technique. The system may monitor launch events, shift events, and steady state driving. The system may adjust the energy threshold at which a suggestion is provided based on vehicle weight or road gradient. The system may also adjust the energy threshold when an estimate of clutch temperature is elevated. The suggestion may be provided on a graphic display or may be provided verbally over a speaker. In some cases, the suggested may also be conveyed to a third party outside the vehicle.

Description:
TECHNICAL FIELD 
     This disclosure relates to the field of vehicle information systems. More particularly, the disclosure pertains to a system to provide information regarding manual transmission driving technique. 
     BACKGROUND 
     A typical manual powertrain is illustrated in  FIG. 1 . Solid lines represent mechanical power flow through rotating shafts. Dashed lines represent control connections, which may be implemented using mechanical linkages. Engine  10  generates power at crankshaft  12  by burning fuel. The engine responds to changes in the position of accelerator pedal  14  to generate more power when the pedal is depressed further by the driver. Transmission  16  transmits power from crankshaft  12  to driveshaft  18  which may rotate at a different speed than crankshaft  12 . Transmission  16  includes a friction clutch  20  and a gearbox  22  connected by input shaft  24 . Gearbox  22  is capable of establishing a variety of forward speed ratios and at least one reverse speed ratio in response to driver manipulation of shifter  26 . The driver controls the torque capacity of clutch  20  by manipulation of clutch pedal  28 . Differential  30  splits power from driveshaft  18  between a left axle  32  driving a left wheel  34  and a right axle  36  driving a right wheel  38  while permitting slight speed differences between the axles as the vehicle turns a corner. 
     For internal combustion engine  10  to generate power, crankshaft  12  must rotate at sufficient speed. However, when the vehicle is stationary with gearbox  22  establishing a speed ratio, input shaft  24  is also stationary. In order to start the vehicle moving, the driver controls the torque capacity of clutch  20  to transmit power from moving crankshaft  12  to stationary input shaft  24 . As the vehicle accelerates the speed of input shaft  24  gradually increases until it is equal to the speed of crankshaft  12 , at which point clutch  20  can be fully engaged. With clutch  20  fully engaged, the speed of crankshaft  12  is proportional to vehicle speed. As the vehicle accelerates in 1st gear, the speed of crankshaft  12  becomes excessive, necessitating a shift to 2nd gear. Gearbox  22  is not capable of changing ratios while transmitting power. Therefore, the driver shifts by disengaging clutch  20 , then manipulating shifter  26  to change the gearbox ratio, then re-engaging clutch  20 . Re-engagement of clutch  20  forces the crankshaft speed to become equal to input shaft speed, predominantly by changing the speed of the crankshaft. 
     Whenever clutch  20  transits torque between shafts rotating at different speeds, as during a vehicle launch event, some power must be dissipated. Power is the product of speed and torque. During a launch event, the torque exerted by the crankshaft and the torque exerted on the input shaft are both equal to the clutch torque capacity. The power flowing into the clutch is the torque capacity multiplied by the crankshaft speed. The power flowing out of the clutch mechanically is the torque capacity multiplied by the input shaft speed. The difference between the power inflow and the mechanical power outflow is dissipated by conversion into heat. Initially, the heat is absorbed into clutch components causing the temperature of those components to increase. Then, the heat is gradually transferred to the environment through convection, conduction, and radiation, gradually reducing the temperature of the clutch components. 
     The amount of energy dissipated by the clutch in a time interval is equal to the integral of the power dissipation over time. If an excessive amount of energy is dissipated in a short amount of time, the clutch temperature will rise excessively. When the clutch temperature is elevated, the rate of wear of the clutch facing material increased dramatically. At sufficiently high temperatures, the friction coefficient of the material decreases and the clutch may be incapable of achieving sufficient torque capacity. Driver technique in manipulating the accelerator pedal, clutch pedal, and shifter strongly influences energy dissipation. 
     SUMMARY OF THE DISCLOSURE 
     A method of coaching a driver of a vehicle with a manual transmission includes monitoring sensor values, estimating the power dissipation, and suggesting a driving technique change when the power dissipation is excessive. In one embodiment, the method determines that the energy dissipation is excessive by integrating the power dissipation over an event and comparing the integrated power to an energy threshold. The event may be a vehicle launch, a shift, or steady state driving with the clutch slipping for more than a threshold amount of time. In another embodiment, the energy dissipation is considered excessive if the power dissipation exceeds a power threshold for longer than a duration threshold. The method may employ multiple power thresholds each associated with corresponding duration thresholds for different types of events. The thresholds that define excessive power dissipation may be adjusted based on vehicle weight, road gradient, or estimated clutch temperature. Suggestions may be conveyed to the driver by, for example, a graphic display or a speaker. In some circumstances, the suggestion may be conveyed to a third party not in the vehicle via a communications interface. 
     For a launch event, the suggestion may be, for example, utilizing lower clutch torque capacity, utilizing lower engine speed, or reducing the frequency of launch events by waiting for more space between vehicles. For a shift event, the suggestion may be, for example, utilizing a lower engine speed or lower engine torque while re-engaging the clutch. For a steady state cruise with the clutch slipping, the suggestion may be to fully engage the clutch. When the clutch temperature is elevated 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is schematic illustration of a vehicle powertrain having a manual transmission. 
         FIG. 2  is a schematic illustration of a vehicle powertrain having a manual; transmission supplemented with a driver coaching system. 
         FIG. 3  is a flow chart for a method of providing driving technique suggestions following vehicle launch events. 
         FIG. 4  is a flow chart for a method of adjusting a threshold used in the method of  FIG. 3  based on vehicle weight and road gradient. 
         FIG. 5  is a flow chart for a method of adjusting a threshold based on an estimate of clutch temperature. 
         FIG. 6  is a flow chart for a second method of providing driving technique suggestions. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations. 
     In preparation for launching a vehicle from a stationary position, the driver uses shift lever  26  to select an appropriate gear ratio. Reverse is selected if the driver intends to move backwards and 1st gear is selected if the driver intends to move forward. During the launch event, the driver manipulates accelerator pedal  14  to control the amount of torque generated by engine  10  and manipulates the clutch pedal  28  to control the torque capacity of clutch  20 . These actions must be carefully coordinated. The torque actually produced by the engine depends on both the accelerator pedal position and the crankshaft speed, generally increasing as crankshaft speed increases. If the clutch torque capacity exceeds the engine torque, then the crankshaft speed decreases. If the crankshaft speed decreases excessively, an engine stall occurs. On the other hand, if the engine torque exceeds the clutch torque capacity, then the crankshaft speed increases. 
     When the vehicle is on level ground the amount of energy dissipation is primarily determined by the crankshaft speed maintained during the launch event. A higher crankshaft speed increases the energy dissipation in two ways. First, at a given input shaft speed and clutch torque capacity, a higher crankshaft speed increases the power dissipation. Second, the launch event will continue until the input shaft speed is equal to the crankshaft speed. Increasing crankshaft speed increases the duration of the launch event. The average clutch torque capacity during the launch event has little overall direct impact on the energy dissipated. Although a higher clutch torque capacity increases the power dissipation, it also shortens the event duration. The consequence of launching the vehicle more aggressively is indirect. Launching more aggressively may require maintaining a higher crankshaft speed during the event to avoid engine stall. 
     When the energy dissipation associated with a launch is excessive, a driver coaching system, as illustrated in  FIG. 2 , can assist the driver in manipulating clutch pedal  28  and accelerator pedal  14  to reduce energy dissipation on future events. Controller  40  monitors crankshaft speed sensor  42  and input shaft speed sensor  44  to determine the slip speed across clutch  20 . Controller  40  also monitors torque sensor  46  which, in conjunction with information about the gearbox ratio, indicates clutch torque capacity during a launch event. Alternatively, torque could be measured at the crankshaft or input shaft or could be estimated based on an estimate of engine torque. When the controller determines that the energy dissipation was excessive, the controller suggest modified technique via either speaker  48  or display device  50 . These devices may be capable of providing the suggestions with varying levels of urgency. For example, the display may use a different color or an audible suggestion may be accompanied by a warning horn. In some circumstances, a third party outside the vehicle, such as a parent or a dispatcher, may wish to be informed of excessive energy launches. If such as request has been registered with the controller, the controller may also send the suggestion via communications interface  52 . Communication interface  52  may be, for example, an interface with a cell phone. 
       FIG. 3  illustrates the method in the form of a flow chart. The method begins at  60  with the vehicle stationary, reverse of 1st gear engaged, and the clutch disengaged. The energy for the event is initially zero. During the launch event, the method loops to compute the energy dissipated. At  62 , the controller measures or estimates crankshaft speed, input shafts speed, and clutch torque. At  64 , the controller computes the power dissipated by subtracting the input shaft speed from the crankshaft speed and multiplying the result by the clutch torque. At  66 , the controller updates the energy by multiplying the power by the controller time step and adding the result to the previous value. The end of the launch event is determined at  68  if the crankshaft speed and the input shaft speed are equal. When the event is complete, the controller moves to  70  and determines if the energy is greater than a threshold. If not, then the method terminates at  72  without making any suggestion. If the energy exceeds the threshold, then at  74  the controller computes the crankshaft speed that would be required to provide a margin above engine stall at the clutch torque that the driver utilized. For example, this can be determined based on the engine maximum torque versus speed curve by finding the minimum speed at which the engine could produce 50% more torque than the torque capacity. At  76 , the controller determines whether the actual crankshaft speed exceeded the recommended value. If so, at  78  the controller suggest to the driver that engine speed be maintained at a lower value for future launches. If not, at  80  the controller the controller suggests reducing clutch torque to enable reducing engine speed. 
     The energy dissipated during a launch event also depends upon the way the vehicle is loaded and the gradient of the road. When a vehicle is heavily loaded or going uphill, the acceleration rate is lower for a particular clutch torque capacity. Consequently, a launch at that torque capacity requires longer. Because the power dissipation is unchanged, a launch event of longer duration results in increased energy dissipation. 
     Because a launch requires more energy dissipation when the weight or road gradient are increased, even with excellent driving technique, the controller may increase the threshold at which driving advice is given. In addition to the advice discussed above, the controller may advise the driver to consider unloading cargo. When the vehicle is on an uphill grade, launching at higher torque capacity may decrease energy dissipation. Any increase in power dissipation associated with higher required engine speed may, in some circumstances, be outweighed by reduced launch duration. After determining that the energy is higher than the revised threshold, the controller may calculate the energy that would have been dissipated at a higher torque capacity and, if that reduces energy dissipation, may suggest to the driver that future launches on a comparable grade be performed at a higher torque capacity. 
     The controller can determine the current vehicle weight and road gradient by various methods. A suitable method to perform this computation is described in detail in U.S. patent application Ser. No. 14/215,812, filed Mar. 17, 2014, which is incorporated by reference herein. Another suitable method is illustrated in  FIG. 4 . At  90 , the controller reads an accelerometer that is oriented along the longitudinal axis of the vehicle. An accelerometer so oriented registers an acceleration when the vehicle is increasing in speed and also when the vehicle is going uphill at constant speed. At  92 , the controller numerically differentiates a reading from a vehicle speed sensor or another suitable measure of vehicle speed. By comparing these two values and  94 , the controller can determine what portion of the accelerometer reading is caused by road gradient and then calculates the road gradient. While the vehicle is launching, the controller measures the clutch torque at  96 . Combining the clutch torque with information about gear ratio and tire size, the controller calculates tire tractive force at  98 . Based on the tractive force, road gradient, and derivative of vehicle speed, the controller can estimate vehicle mass at  100 . Finally, the controller adjust the energy threshold at  102 . Specifically, the controller increases the threshold for above heavy weights and for uphill road gradients. The controller may also decrease the threshold from the nominal threshold for lighter weights and downhill road gradients. 
     In addition to energy dissipation during launch events, the clutch also dissipates energy during shift events. After engaging the new gear ratio, the driver must re-engage the clutch. If the engine is below the speed required for the vehicle speed and new gear ratio, engaging the clutch will increase the engine speed. In this circumstance, the output torque will be negative while the engine speed is increasing. Since negative torque is generally unpleasant, it is more common to err on the side of maintaining the engine speed somewhat higher than required for the vehicle speed and new gear ratio. As the clutch is re-engaged, the clutch torque tends to decrease the engine speed to the required value. However, if the driver is simultaneously commanding engine torque, the engine speed will not decrease as quickly, extending the re-engagement and increasing the amount of energy dissipated by the clutch. Following a shift event, the controller can calculate the amount of energy dissipated based on the speed difference and torque capacity. If the energy dissipated is above a threshold, the controller suggests that the driver either set the engine speed lower before re-engaging the clutch or delay commanding engine torque. The method for shift events is analogous to the method for launch events as illustrated in  FIG. 3  except that the vehicle is not stationary in the initial condition and the method is initiated by a change in gearbox ratio. The energy threshold for shift events is not necessarily the same as the threshold energy for launch events. 
     The adverse impact of excessive clutch energy dissipation are most severe if multiple events occur in a short period of time because there is little opportunity for the clutch to dissipate the energy as heat. In this circumstance, the clutch temperature increases. A given energy dissipation causes more clutch wear when the clutch is hot than if the clutch is cool. If the clutch is too hot, the friction coefficient decreases, decreasing the maximum torque capacity. In extreme cases, the decreased maximum torque capacity may cause the clutch to slip during normal driving. 
     The controller can estimate the clutch temperature based on the calculated energy input and a model of the heat dissipation rate. When the clutch temperature is higher, the controller may decrease the threshold at which suggestions are given. Additionally, the controller may suggest that the driver pull over and wait for the clutch to cool down. If a number of launch events occur within a predetermined amount of time, the controller may suggest that the driver wait to launch the vehicle until there is enough space between the vehicle and the vehicle ahead for the driver to stay in gear for longer. 
     The method for adjusting the thresholds based on clutch temperature is illustrated in  FIG. 5 . At  110  and  112 , the controller measures clutch torque and speed difference and computes the power dissipation in the same way as it does at  62  and  64  in  FIG. 3 . The power dissipation causes the clutch temperature to increase. At  114 , the controller estimates the heat dissipation rate based on the current clutch temperature and a thermal model of the clutch. The thermal model may include the effects of other parameters such as the clutch speeds. Heat dissipation causes the clutch temperature to decrease. At  116 , the controller adjusts the current temperature estimate based on the power dissipation, the heat dissipation, and the clutch thermal capacity. At  118 , the thresholds for both launch events and shift events are adjusted. This process is repeated at regular intervals both during clutch events and during non-events. 
     When the vehicle is cruising in a fixed gear ratio, there is no need for the clutch to dissipate energy. In fact, this is the condition in which the clutch cools down by dissipating the accumulated heat. However, sometimes a driver accidentally rests a foot on the clutch pedal allowing some degree of clutch slip. The controller may detect this condition based on power dissipation exceeding a threshold level for a threshold amount of time while the clutch output speed exceeds the minimum speed at which the engine could generate the clutch torque. In response, the controller may suggest that the driver fully engage the clutch. 
     An alternate method of providing driving suggestions in illustrated in  FIG. 6 . In this method, the suggestion is triggered by a power dissipation exceeded a power threshold for a continuous period of time exceeding a time threshold. By using a variety of different power and time thresholds, this method is suitable for launch events, shift events, and inappropriate use of the clutch during cruising. An advantage of this method is that the suggestion may be provided before the event is completed. Each of these thresholds could be adjusted dynamically based on road gradient, vehicle weight, and clutch temperature as discussed above. At  130  and  132 , the dissipated power is calculated as described for  62  and  64  in  FIG. 3 . At  134 , the dissipated power is compared to a power threshold. If the dissipated power is low, control remains in the loop on the left. If the dissipated power is high, a countdown timer is started at  136  and control transitions to the loop on the right. At  140  and  142 , the dissipated power is calculated as described for  62  and  64  in  FIG. 3 . At  144 , if the dissipated power is below the threshold, control reverts to the loop on the left. If the dissipated power is still above the threshold and the timer has expired at  146 , then a suggestion is provided at  148 . 
     While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.