Abstract:
Method for adapting an automated mechanical transmission based upon a PTO load. The method includes setting the transmission gears so that no torque is being transmitted to the output shaft of the transmission. With the PTO load engaged, engine torque is measured by the engine control unit. This torque is compared to the expected engine torque. Using the difference from the expected value and the measured value, the transmission control unit adjusts the shifting of the transmission because the PTO will cause the engine to lose some of its available torque. Based on the PTO load, the transmission control unit will select the appropriate start gear, upshift gears, and downshift gears.

Description:
[0001]    The present application claims the benefit of U.S. Provisional Application No. 60/596,212 filed Sep. 8, 2005. Said application is expressly incorporated herein by reference in its entirety. 
     
    
     BACKGROUND AND SUMMARY 
       [0002]    The present disclosure relates to determining the magnitude of a power take off unit and adapting an automated transmission of a heavy commercial vehicle based on the presence of an additional load of the power take off unit. 
         [0003]    Heavy commercial vehicles such as overland trucks and buses are known to employ automatic mechanical transmissions (AMT) that are based on preprogrammed routines. One example of an automatic mechanical transmission is the multi-stage gearbox. A multi-stage gearbox is usually made up of an input shaft, an intermediate shaft, which has at least one gearwheel in engagement with a gearwheel on the input shaft, and a main shaft with gearwheels which engage with gearwheels on the intermediate shaft. The main shaft is also connected to an output shaft coupled to the driving wheels via, for example, a drive shaft. Each pair of gearwheels has a different ratio compared with another pair of gearwheels in the gearbox. Different gears are obtained by virtue of different pairs of gearwheels transmitting the torque from the engine to the driving wheels. 
         [0004]    One of the problems in controlling an AMT, however, is attributable to the power consumption by a power take off (PTO). A PTO can generally be classified as a PTO upstream or downstream of the master clutch. In general, a PTO that is upstream of the master clutch can take power from, the vehicle&#39;s engine regardless of the state of engagement of the transmission via the master clutch. A PTO that is located downstream of the master clutch is typically used when the vehicle is stationary. A downstream PTO often involves placing the gearbox in neutral so that the vehicle wheels are not drivingly engaged to the transmission. However, there are cases when a transmission mounted PTO is used while the vehicle is in motion. PTO&#39;s are known to impose significant load on Ihe vehicle&#39;s engine. Exemplary PTOs use engine power to drive hydraulic pumps that can be activated for such things as mixing applications (concrete trucks) or causing motion of a bed on the truck such as in the case of dump trucks and flat-bed haulers. 
         [0005]    Similarly, PTOs may be used to power spreaders such as those used to broadcast salt or sand on icy roads, or to power associated trailer components such as compartment refrigeration units. While these examples are not exhaustive, they do serve to exemplify PTO loads of significant magnitude which can appreciably compromise the driving power available from the engine of the vehicle for the drive wheels, and which often causes undesirable disturbances to automated transmission programs that do not take then-intermittent influences into account. For purposes of comparison, these significant PTO loads can be compared to less influential engine loads imposed by such power consumers as cooling fans and air conditioning compressors. As an example of the potential drag that a PTO can impose on the vehicle&#39;s engine, it is not uncommon for PTOs to siphon off engine torque on the order of 5 to 3000 Nm. An example of a PTO that requires on the order of 3000 Nm is a fire truck that operates a water pump, and an example of a PTO that requires on the order of 5 Nm is a PTO for a small refrigerator device. 
         [0006]    The present invention appreciates the fact that transmission control routines that do not take into consideration whether or not a significant PTO load is imposed on the vehicle&#39;s engine will experience degradation in performance when the PTOs are operational. For example, if the PTO loads are of such magnitude that the engine can not compensate therefore by increased engine speed, there will be an effective reduction in power available for driving the vehicle. The strategy must, however, appreciate that the behavior of the PTO-loaded engine is not that of a smaller engine, but is in fact a unique behavior of the particular engine whose power is divided between a PTO of significant load and the drivetrain. 
         [0007]    Still further, it has been appreciated that it can be difficult to detect a PTO&#39;s influence on an engine if it is also connected to a loaded drivetrain; therefore, one of the aspects of the present invention has as a goal to provide a solution wherein drivetrain loads do not conflict with PTO detection procedures. 
         [0008]    In at least one embodiment, the present invention takes the form of a method of sensing the magnitude of a PTO load. The method comprises (includes, but is not necessarily limited to) measuring the PTO load while the engine is operating at a substantially constant engine speed and the driveline is disengaged. The disengagement of the driveline, preferably disengages the drivewheels from receiving torque. Then, the reduction of available torque is sensed as compared to an engine without a PTO load. This reduction in torque results in less available engine torque for transmission to the drivewheels. 
         [0009]    In another embodiment, a semi-automatic transmission is adjusted based upon the magnitude of the additional load placed on the engine by a PTO. The transmission controller is adjusted to account for the loss of torque to the PTO. Transmission control can be classified by two different types of control, namely gear shifting and gear selection. Gear shifting describes the actual engagement of the mechanical elements of the transmission. For example, gear shifting is the process of actually moving the mechanical parts of the transmission in the proper order to engage or disengage a gear or otherwise manipulate the transmission in response to a given request or instruction. Gear selection is the process of selecting the desired gear or decision to maintain the current gear state. Furthermore, gear selection can consider various parameters in order to determine the proper gear to engage. In an automated transmission, transmission control is carried out by having a gear selection strategy used to determine what gear should be engaged, then implementing a gear shifting strategy that actually carries out the requested shift in the transmission. 
         [0010]    In a preferred embodiment, the transmission is placed into a neutral gear state to estimate the PTO load on the engine. 
         [0011]    In yet another embodiment, the PTO unit load is determined by operating a prime mover at a substantially constant speed and disengaging the driveline so that substantially no torque is supplied to the drivewheels of the heavy vehicle. Furthermore, it determines the torque magnitude indicative of a power take off unit&#39;s torque consumption. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The present disclosure will now be more fully described, by way of example, with reference to the accompanying drawings in which: 
           [0013]      FIG. 1  is a flow diagram illustrating one method for determining the magnitude of the PTO torque load; and 
           [0014]      FIG. 2  is a schematic diagram of a power train of a heavy vehicle and controls associated therewith. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    One preferred embodiment relates to detecting a PTO load while the engine speed is substantially constant and the driveline disengaged. Another embodiment adapts vehicle systems in response to the determined torque magnitude (torque draw) of the PTO load, including making adjustments to the shifting strategies of an automatic mechanical transmission. Other vehicle systems include the engine brake, prime mover, and service brakes. 
         [0016]      FIG. 2  illustrates a block diagram showing the typical interconnections in an automated mechanical transmission system between engine controller  102 , transmission controller  112 , shifting lever  150 , and accelerator pedal  140 . Although not required, when the prime mover  100 , typically an internal combustion engine  100 , and the transmission  110  are both controlled through electronic controllers  102 ,  112 . Information can be shared between these controllers  102 ,  112 . This can lead to efficient exchange of engine information to the transmission  110  and transmission information to the engine  100 . Even though the transmission controller  112  and engine controller  102  are shown separately, it is contemplated that the controllers can be combined in a single unit. Alternatively, the engine controller  102  and transmission controller  112  can be made of sub-controllers, for example the transmission controller  112  might have controllers specifically designed to control the gear shifting and gear selection for the transmission  110 . 
         [0017]    The gear selector/lever  150  enables the driver to select an appropriate driving mode. The driving modes include but are not limited to automatic, manual, and low. Furthermore, in manual mode the driver can request specific shifting of gears using the gear selector  150 , preferably through the use of buttons to increase or decrease the gear ratio. As described above, a PTO can be a PTO  130  located upstream of the master clutch  105  or a PTO  135  located downstream of the master clutch  105 . The master clutch  105  transfers energy to the transmission  110 , which further transfers the energy to the driveshaft  160 . Then, a rear gear or differential  182 , transfers energy to the drivewheels  170 . 
         [0018]    A PTO  130 ,  135 , when operationing, constitutes a prime mover power consumer that should be considered in order to make automated transmission shifting more comfortable, efficient, faster, and to appropriate gear ratios. In order to take into account the additional load of the PTO  130 ,  135 , it is necessary to calculate or otherwise quantify the load. This can be performed either using conventional sensors onboard a given vehicle or through specifically designed sensors. Some of the standard sensors include the input shaft speed sensor, engine speed sensor, and output shaft speed sensor. The prime mover control unit  102  preferably produces or calculates a value of the prime mover&#39;s  100  generated torque. Alternatively, the torque that is being produced by the prime mover  100  is calculated by the prime mover control unit  102 . While there are many ways of calculating this prime mover  100  generated value or measured torque magnitude, a few examples involve using the dwell angle of injection into a diesel engine and using current readings in an electric motor where the prime mover is a diesel engine or electric motor, respectively. The prime mover  100  can be any device designed to provide power to the drivetrain of the heavy vehicle. The prime mover  100  can be one of a diesel engine, gasoline engine, other internal combustion engine, an electric motor, or a hybrid engine. 
         [0019]    The measurement of PTO load involves placing the transmission  110  in a configuration in which no torque is being transmitted to the output shaft of the transmission  110 . It should be appreciated that the torque transmitted to the output shaft may not be exactly zero, but the amount transferred during measurement should be so small as to be negligible. There are several configurations for assuring that no torque is transmitted to the output shaft of the transmission  110  (to the drive or propeller shaft). One way is to have the clutch  105  disengaged so that no torque is transmitted to the input shaft of the transmission  110 . Another method involves placing the transmission  110  in neutral so that no torque is transmitted to the output shaft of the transmission  110 . Alternatively, the main shaft may be disengaged preventing torque from being transferred to the output shaft despite engagement of the countershaft. In order to measure a PTO load located downstream of the clutch  105 , an appropriate procedure must be selected from above to allow the PTO  135  to remain engaged, but supply substantially no torque to the drivewheels  170 . Furthermore, if the PTO  130 ,  135  is equipped with a specially designed switch and the load of the attached PTO  130 ,  135  is known, the activation of the switch can be used to determine the magnitude of the PTO&#39;s  130 ,  135  torque consumption. 
         [0020]    The measurement of the PTO load further involves having the prime mover  100  maintain a substantially constant speed. This speed hi a preferred embodiment is the idling speed of the prime mover  100 . Other points at which speed is substantially constant are possible as well and remain within the scope of this disclosure. For instance, while the driveline is disengaged the vehicle operator depresses the accelerator pedal  140  to provide additional torque to the PTO  130 ,  135  so that the PTO  130 ,  135  will operate more efficiently. During this process, the vehicle operator may maintain the prime mover  100  at a substantially constant, but elevated speed. In yet another embodiment, the prime mover  100  is maintained at a constant speed, when the driveline is disengaged while rolling down a grade such that the vehicle freewheels. In a still further embodiment, the prime mover  100  is operated at a speed greater than idle speed to properly power an additional PTO  130 ,  135  such as an air compressor or hydraulic pump. While these examples have been provided, they are intended to describe types of additional loads that require the prime mover  100  to be operated at a substantially higher speed than idle speed. The measurement of PTO load further requires that the driveline be disengaged in a fashion as described above. Similarly, the driver may maintain the prime mover  100  at or near constant speed while the PTO load is being quantified. 
         [0021]    Assessment of the PTO load is important because it is used when configuring shifts as the vehicle is driven; in this manner, the transmission  110  is permitted to appropriately compensate for the loss of prime mover  100  torque due to the PTO load. The sensitive driving conditions of the vehicle include take off, reversing, slow movement, road speeds, and highway speeds. These conditions exist anytime a gear of the vehicle is selected and motion is caused through the transmission  110 . Furthermore, the transmission controller  112  is adjusted to account for the loss of torque to the PTO  130 ,  135 . Transmission control can be classified by two different types of control, namely gear shifting and gear selection. Gear shifting describes the actual engagement of the mechanical elements of the transmission  110 . For example, gear shifting is the process of actually moving the mechanical parts of the transmission  110  in the proper order to engage or disengage a gear or otherwise manipulate the transmission  110  in response to a given request or instruction. Gear selection is the process of selecting the desired gear or decision to maintain the current gear state. Furthermore, gear selection can consider various parameters in order to determine the proper gear selection. In an automated transmission  110 , transmission control is carried out by having a gear selection strategy used to determine what the gear should be, then implementing a gear shifting strategy that actually carries out the requested shift in the transmission  100 . 
         [0022]    While preferred embodiments of the presently disclosed solutions have been shown and described herein, it will be obvious that such embodiments are provided by way of example only. Numerous variations, changes and substitutions will occur to those skilled in the art without departing from the disclosure herein. Accordingly, it is intended that the embodiments claimed be limited only by the spirit and scope of the claims.