Abstract:
An apparatus for controlling a sequential transmission of a vehicle is provided comprising a control motor that drives a selector drum for shifting gears wherein the apparatus measures torque applied to or position of the selector drum and controls the control motor to engage the gears, to accommodate for wear and transient gear interference or jamming.

Description:
FIELD OF THE INVENTION 
     The present invention relates to an apparatus and system for controlling a sequential transmission using a control motor and sensors to shift gears. 
     BACKGROUND OF THE INVENTION 
     A transmission is used to transmit power from an engine to a drive mechanism. The transmission uses the principle of mechanical advantage to convert the rotational speed, direction, and torque of a driving element into a different rotational speed, direction, and torque of a driven element. Most transmissions use a combination of gears in differing ratios to achieve this speed-torque conversion. 
     Vehicle transmissions often include more than one set of gear ratios (typically called “gears”) to allow the vehicle to operate in a variety of conditions. When the vehicle is at rest or travelling at a low speed, a gear ratio may be selected to deliver relatively high torque from the engine to the driveline. When the vehicle is travelling at higher speeds, a different ratio may be used to deliver higher rotational speeds at lower torque to the driveline. Gear ratio may be selected to optimize the delivery of power to the driveline having regard to the characteristics of the engine, and in particular, to the engine&#39;s delivery of power as a function of the engine&#39;s rotational speed. Changing the gear ratio of a transmission is commonly known as shifting or changing gears, and typically requires a brief decoupling of the engine from the driveline using a clutch arrangement. 
     A typical vehicle transmission as exemplified in  FIG. 1  may include an input shaft  101  which is driven by the engine through a clutching arrangement, and an output shaft  102  which may drive the driveline when a gear is selected. The input shaft  101  typically passes through a number of input gears  110 . The output shaft  102  in this arrangement may pass through a number of corresponding output gears  109  which mesh with the input gears  110 , each pair of meshed gears being a gear set. In each gear set, one of the gears is not directly affixed to the input or output shaft, and may spin independently of the shaft when not engaged, and the other is affixed to the input or output shaft. Adjacent to the each free spinning gear  111 , a sliding gear  108  may be mounted on the shaft passing through that free spinning gear  111 . Each sliding gear  108  may slide along the length of the shaft, but otherwise engage the shaft so that it rotates along with the shaft. Each free spinning gear  111  may have dog teeth which engage with the adjacent sliding gear  108  when the sliding gear  108  is slid along the shaft. The sliding gear  108  engages and rotates the free spinning gear  111  with the corresponding shaft, thereby selecting a gear. Once engaged, the output shaft  102  is driven by the input shaft  101  in a ratio determined by the selected gear. 
     Although this is a common implementation of a vehicle transmission, there are many variations which achieve the same function in a similar manner. 
     Some vehicles use a sequential transmission, which is a transmission having at least two sets of gears which must be selected in a predetermined order during shifting. If a vehicle has three gears, the sequential transmission cannot be shifted from any one gear set to any other gear set. It must be shifted in an order which is determined by the configuration of the gear changing mechanism. 
     In a sequential transmission implemented on the typical vehicle transmission described above as exemplified in  FIG. 1 , the sliding gears  108 , are moved by selector forks  106  that slidably engage a selector fork shaft  107  which is aligned parallel to a selector drum  104 . Typically, there are grooves  105 , wedges or ridges on a selector drum  104  which engage the selector forks  106  and convert the rotation of the selector drum  104  into lateral movement of the selector forks  106  along the selector fork shaft  107  in a direction parallel to the input shaft  101  and output shaft  102 , thereby moving the sliding gears  108  along the input shaft  101  or output shaft  102 . The use of a selector drum  104  to select gears in this arrangement forces the operator to shift gears in order. Gear dog teeth  112  located on the side of sliding gears  108  are used to engage gear dog windows  113  located on the common side of the free spinning gear  111 . This engagement effectively locks the free spinning gear  111  to the shaft running through its hub and permits torque to be transmitted from the input shaft  101  to the output shaft  102  through the free spinning gear  111  and its meshing gear  119 . 
     Sequential transmissions are preferred in certain applications over other types of transmissions because of the relative simplicity of the apparatus. A typical sequential transmission has fewer moving parts and is generally more reliable than a comparable fully manual non-sequential transmission. They can often be made smaller and lighter than other comparable designs, and can be faster to complete gear shifts. They are often employed in automotive racing and motorcycle applications for these reasons. 
     Many sequential transmissions are driven manually by the operator using hand or foot levers that may rotate the selector drum  104  through a ratcheting arrangement  114 . This allows the operator to rotate the selector drum  104  enough to cause the shift, but helps prevent the operator from rotating the selector shaft too far. When implemented on a motorcycle, the sequential transmission may include an indexer arrangement, such as a cam indexer  116 . The indexing arrangement may include a cam sprocket  115  connected to the selector drum  104  in combination with a pawl or cam follower  118  that engages depressions in the cam sprocket  115  as the selector drum  104  is rotated. The cam follower  118  may have a wheel  117  at one end which may roll along the cam sprocket  115 , and may be biased so that the wheel  117  maintains contact with the cam sprocket  115 . When the cam follower  118  is seated in a depression, the selector drum  104  has been rotated to a position where a gear is engaged. By applying force to a shift lever attached to the ratcheting arrangement  114 , the operator may rotate the selector drum  104  if the force is sufficient to unseat the cam follower  118  from the depression and overcome friction forces. As the selector drum  104  rotates, the cam follower  118  will move into an adjacent depression on the cam sprocket  115 . 
     Automatic and Semiautomatic Configurations 
     Any sequential transmission systems known in the art may be operated by automatic or semi-automatic control means. These automatic or semi-automatic controllers typically include an electrical or electronic control system that may be programmable, and a control mechanism which may include buttons, levers or switches that may be operated by the vehicle operator. In a fully automatic configuration the shifting of the transmission is performed entirely by the controller in response to external conditions, engine speed, current gear in which the transmission is operating and other factors such as whether the operator is braking or accelerating. Such an automatic transmission will shift up and down through the gears as the operator attempts to accelerate or decelerate the vehicle. 
     There are a number of transmission systems for sequential controllers that include a control motor or other drive means directly connected to the selector drum allowing the controller to drive the selector shaft and thereby shift the transmission from one gear set to another gear set in response to its programming. Many configurations for such control motor driven sequential transmissions have been disclosed in the prior art. Some describe a motor coupled to a sequential transmission using a set of gears to increase the electrical motor torque and reduce the speed. Some prior art configurations show a selector shaft gear system being implemented as a worm gear arrangement. 
     Semi-automatic and automatic transmission systems may use one or a number of sensors in order to determine the status of the transmission, such as what gear it is in, the position of the control motor and/or the position of the selector drum. The control system for such systems initiates a shift or prevents a shift from occurring under certain circumstances in response to the sensory inputs. For example, a control system could be aware of the current gear of the transmission and how far and how long it needs to operate the control motor to shift the system into an adjacent gear. 
     One problem with such systems is that the system must be calibrated when assembled to pre-select the particular positions for each gear relative to the motor. Once the pre-selected gear positions are programmed into the system, the system will typically drive the control motor to the pre-selected gear position. This can pose difficulties in operation because the transmission wears over time and may expand or contract as a result of external temperature changes, and so the exact position to shift the transmission into an adjacent gear may change over time and with such external conditions. 
     Some existing sequential transmission systems incorporate mechanical means (such as springs or biasing means) to accommodate variances in shift position due to wear and temperature changes. The incorporation of a control motor and control system in such systems typically leads to further losses in precision as the motor system may load these dynamic elements while attempting to perform the shift, which may prevent the shift from completing or interfere with sensing when a shift has been completed. 
     Another difficulty with electronically controlled motor driven transmission systems is that such systems typically perform poorly when detecting and responding to interference between the gear dogs during shifting. Commonly known as gear jam, the problem occurs when the leading edge of a gear dog belonging to a sliding gear is brought against the leading edge of the gear dog belonging to the corresponding free spinning gear. Under these conditions the gears may not fully engage or may resist engaging and the shift attempt will fail. Many modern transmissions incorporate a synchronizer mechanism, commonly known as a synchromesh device, to enable gear engagement, however these devices add to the size, weight, and cost of the transmission. In the absence of a synchromesh device, if the control system does not sense such interference conditions, it will continue to drive the motor generating excessive strain on the elements of the system. Under those circumstances the transmission, the control motor, or both may be damaged. Since a shift of a sequential transmission may occur in a short period of time (e.g. less than one hundredth of a second), any control system would have to be equipped with sensors that detect interference conditions quickly and accurately. 
     There is a need for a semi-automatic or automatic sequential shift system that detects the in-gear position of the selector shaft and calibrates the controller to adjust for short term changes in temperature and long term changes due to wear and tear. There is a need for control systems for motor controlled sequential transmissions that can quickly detect gear jams and accurately react to permit gear engagement without risking damage to the engine. 
     SUMMARY OF THE INVENTION 
     The present invention relates to an apparatus for controlling a sequential transmission of a vehicle, the transmission comprising an input shaft, an output shaft, at least two sets of gears which are selectively engageable, and a selector drum that when rotated selects a set of gears which engage to drive the output shaft from the input shaft, the apparatus comprising a control motor which is mechanically connected to the selector drum to rotate the selector drum when actuated, a torque sensor which senses the torque applied to the selector drum by the control motor, and a controller which controls the motor based on signals received from the torque sensor. 
     The apparatus may also include the feature wherein the torque sensor comprises a current sensor that monitors the current drawn by the control motor, and the controller detects a change in the current draw of the control motor during operation of the control motor as an indication of gear jam and adjusts the control motor in response to the change in the current draw. 
     The apparatus may include a plurality of selector drums, each independently actuated by a control motor to selectively engage sets of gears. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the invention will be described by way of example and with reference to the drawings in which: 
         FIG. 1  is a top sectional view of a prior art sequential transmission for a motorcycle. 
         FIG. 2  is a top view of an embodiment of the invention depicting a control motor driving the selector drum through a geartrain. 
         FIG. 3A  is a side view of an indexing means slightly out of ideal position according to an embodiment of the invention. 
         FIG. 3B  is a side view of an indexing means in a settled position according to an embodiment of the invention. 
         FIG. 4  is a schematic view of the system depicting the controller and its connection to other elements according to an embodiment of the invention. 
         FIG. 5  is a schematic view of a DC brushed motor, its driving circuits, and current sensing circuit according to an embodiment of the invention. 
         FIG. 6   a  is a diagram showing gear dogs prior to engagement. 
         FIG. 6   b  is a diagram showing gear dogs in an interference state. 
         FIG. 6   c  is a diagram showing gear dogs in an engaged state. 
         FIG. 7  is a flowchart showing controller logic according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 2  shows one embodiment of the invention comprising a control motor  201  driving the selector drum  104 . A cam indexer  116  having a series of impressions therein biases the selector drum  104  into a fixed number of gear positions using a biased pawl  118 . The control motor  201  may drive the selector shaft  203  through a series of selector shaft gears  202 . The control motor  201  may incorporate a position sensor, such as a Hall effect sensor, to determine the position of the control motor  201 . 
     The selector shaft gears  202  may include spur gears, bevel gears, helical gears and hypoid gears. In a preferred embodiment the selector shaft gears  202  would not include a worm drive arrangement, as worm gear arrangements are typically poor mechanical transmitters of reverse torque, and therefore may not provide good feedback to a torque sensor. Worm gears are helical gears having a helix angle that does not exceed 50 degrees. 
     The invention may also comprise a position sensor  206  in addition to or instead of the position sensor in the control motor  201 , which may incorporate a Hall effect sensor or other current sensing means that encompasses or encircles or is immediately adjacent to the selector shaft  203  or selector drum  104 . The position sensor  206  may be used to detect the position of the selector shaft  203  relative to a fixed point such as the motor mounting  204  or relative to the housing of the transmission  205 . The position sensor  206  may operate by use of a potentiometer, in which case the selector shaft  203  rotates relative to the potentiometer changing the current flow through the potentiometer. In the case of a Hall effect sensor, the selector shaft  203  may have mounted upon it permanent magnets or may comprise a portion which has been magnetized so that it generates a magnetic field which is detected by the Hall effect sensor. Changes in the magnetic field may be outputted by the Hall effect sensor as a digital signal or as an analog voltage. 
     The position sensor  206  may also be used to determine the torque experienced by the selector shaft  203 , when positioned on a portion of the selector shaft  203  that is subject to mechanical strain caused by torque. In one embodiment, the position sensor  206  is located between the driving gears and the selector drum, which is subject to mechanical strain caused by torque. 
     When the position sensing means are used in conjunction with mechanical biasing means of the system, it is possible for the system to adapt over time to account for wear, and also to adapt on the fly to address transient dangerous gear jam conditions. In an embodiment which includes a biasing means for mechanically biasing the selector drum  104  into one of a number of gear positions, when the controller has actuated the control motor  201  and driven the selector drum  104  into one of those desired positions, as perceived by the controller in accordance with a set of pre-programmed control positions, the control motor  201  has completed its actuation into the next shift position. If the pre-programmed control position is out of calibration, the cam indexer  116  will apply a correcting torque to the selector drum  104  bringing it to the mechanically correct position. By monitoring the position of the selector drum  104  via the position sensor  206  the controller can detect when the pre-programmed control positions have fallen out of calibration. The control system can therefore alter the stored motor control positions to approach the settled values of the mechanical system. It may accomplish this by calculating the difference between the motor position coordinates following a gear change and the stored motor position coordinates corresponding with that gear, and modifies the stored motor position coordinates if the difference is greater than a predefined threshold. 
     In operation, the control motor  201  drives the selector shaft gears  202  which in turn drive the selector shaft  203  to one of the pre-programmed positions, overcoming the resistance of friction and the indexer biasing means to shift the system into an adjacent gear. 
       FIGS. 3   a  &amp;  3   b  depict a mechanical biasing means comprising a cam sprocket  115  having a series of indentations and a cam follower  118  hinged at one end and having a wheel or cam follower  117  at the other end and a spring  301  for biasing the cam follower  118  against the cam sprocket  115 . When in gear, the cam follower  118  will settle into one of the indentations. As previously mentioned, a control system can detect if it has driven the selector drum  104  into a position where the cam follower  118  is not quite settled into one of the impressions because the selector drum  104  will experience torque caused by the biased cam follower  118  against the surface of the cam sprocket  115  to settle it into position. This permits the system to continually calibrate itself relative to the mechanical environment, which is necessary because, as mentioned, the system may over time become imprecise as wear and sensor degradation occurs. 
       FIG. 4  depicts a schematic of the system showing a controller  401  interfaced with a number of elements. The controller  401  controls a motor  402 , preferably a brushless DC motor, the motor  402  may be a three phase motor permitting AC control of the motor  402  and may also in such an environment include a motor position sensor  412 , which may be inherent in the design of the motor  402 , or separate. The system may also comprise a gear position sensor  403 , separate and independent from any sensing capabilities in the motor  402 , the gear position sensor  403  will sense the position of the selector drum and measure the position of the selector drum directly. The system may also comprise a gear position display  405  to display the current gear based on inputs from the gear position sensor  403  or the motor  402  and is determined by the gear controller  401 . 
     The controller may comprise hardware, electronic or electrical circuitry and/or a processor and storage for executing software. Software is executable statements and instructions stored in a memory for execution by a processor. A memory may include any static, transient or dynamic memory or storage medium, including without limitation read-only memory (ROM) or programmable ROM, random access registers memory (RAM), transient storage in registers or electrical, magnetic, quantum, optical or electronic storage media. A processor includes any device or set of devices, howsoever embodied, whether distributed or operating in a single location, that is designed to or has the effect of carrying out a set of instructions, but excludes an individual or person. A system implemented in accordance with the present invention may comprise a computer system having memory and a processor to execute the software. 
     The system may also comprise some sort of user interface, such as a shift button array  404  in a semi-automatic embodiment, and it may also be used in conjunction with other controls known in the art. 
     The controller  401  may control an automatic or semi-automatic clutch  409  in conjunction with the system in a preferred embodiment. A semi-automatic or automatic clutch system  409  may be directly controlled by the gear controller  401  such that the controller  401  both actuates the clutch and shifts the gears in response to a single input from a rider or in response to an automatic control strategy programmed into the controller  401 , or other electronic control units (ECUs)  410  located on the vehicle. 
     The controller  401  may be directly connected with the vehicle&#39;s sensors, or may communicate with ECUs  410  or an onboard computer system through direct connection or a bus. A commonly used standard for vehicle communication is a bus implementing the CAN multi-master broadcast serial bus standard, but any electronic or electrical communication means may be used. Though such communication means, or directly using a separate bus or buses  411 , the controller  401  may access and use any of the information produced by the vehicle&#39;s sensors, including wheel speed, throttle position, ignition timing, etc. This information may be used to control the transmission to optimize shifting speed and timing, and to prevent damage. 
     For example, the controller  401  may sense the current wheel speed via a wheel speed sensor which permits it to control which gears may be shifted into by the rider, to prevent errors by the rider which may damage the transmission or engine. 
     The controller  401  may also receive inputs from the ignition system through the wiring harness, such as the position of the stop switch, the position of the throttle and the speed of the engine. 
     The system may also be adapted to connect to other control systems on the vehicle such as any existing control systems that deal with engine control, braking, traction control or similar automated or semi-automated systems to coordinate shifting with those systems. This coordination would have the benefit of preventing shifts that could lead to unsafe conditions. 
     In the preferred embodiment, if the shift attempt causes the gears to interfere or clash, the shift would not initially proceed. In such a circumstance, the torque sensor, in this case two Hall effect current sensors  408  placed adjacent to the motor power lines  413 , would measure significant torque, by way of increased current flow, and the controller  401  could change the speed, target position, or applied torque of the control motor  402  to allow the transient condition to clear so that the selector drum could proceed into the desired position. This mechanism allows detection of transient gear interference conditions and prevention of damage to the control motor  402  and/or the transmission that may be otherwise caused by driving the transmission into a position where it mechanically cannot go. 
     Under such conditions, the controller  401  may respond in a number of different ways to resolve the gear interference. The controller  401  may adopt a position control, speed control, or torque control strategy to overcome the interference. 
     In one embodiment, shown in  FIG. 5 , the means used to sense torque involves detecting current in the motor power lines  503 . The torque sensor in controller  501  may comprise an in-line resistor  504  or one or more Hall effect sensors to detect changes in current on the transmission lines  503  as consumed or generated by the control motor  502 . Current sensing can be used to detect power and torque as experienced by the control motor  502  when the voltage applied to the control motor  502  is known, as it is in the case of an electrically controlled system. A controller  501 , upon measuring the changes in current as compared to the input voltage, can calculate the torque experienced by the control motor  502  and can adjust it appropriately to prevent damage to the transmission. In this embodiment, the control motor  502  is controlled by the controller  501  though a set of switches  505  implemented using MOSFET circuitry. Other current sensing means may also be used, such as a dynamic transformer affixed to either the control motor or the selector shaft. The control motor  502  control means may also include a power conditioning unit  506  for conditioning the electrical power delivered to the control motor  502  for voltage, polarity, reverse polarity protection, and switching noise suppression, and delivers the power within the optimum parameters for the control motor  502 . The torque sensing means may also comprise a control signal conditioning unit  507  for filtering control signal noise, and providing amplification or attenuation of the control signals to drive the control motor  502   
     As shown in  FIGS. 6   a - 6   c , gear interference, or jams, typically arise when the sliding gear  601  is slid towards the free spinning gear  602 . If outward surfaces  605  of the dog teeth of the sliding gear  603  impact the outward surfaces  606  of the dog teeth of the free spinning gear  604  when slid together, the dog teeth  603   604  will not engage, causing a jam. This gear dog interference causes the lateral force being applied by the shift forks to quickly increase, which is converted to torque seen at the selector drum based on the cam profile of the grooves cut into the selector drum. Once the jam is cleared or under normal operation, the dog teeth  603   604  engage, driving the free spinning gear together with the sliding gear. 
     There is typically a specific set of selector drum positions where jams can occur. These positions are particular to the shape of the selector drum and transmission, and are typically where the drum is moving the dog teeth of the gears together but not overlapping or engaging. Outside of these particular set of drum positions, high current readings may be measured, but are associated with other transient loads that are not related to jamming, such as loads caused by starting up the vehicle and braking. 
     In  FIG. 7 , an embodiment of the invention is shown depicting the logic of the controller during a shift to detect a jam event. The process starts by detecting whether the selector drum has entered one of the positions where a jam is possible (a “jam zone”)  701 . The system may detect whether the selector drum has entered a jam zone by using a position sensor. The position sensor may be coupled directly to the selector drum, or may be integrated into the control motor. In the latter case, the position of the selector drum may be inferred from the number of revolutions that the control motor has made since the shift started. The system may also deem the selector drum to be in a jam zone after a predetermined delay from the initiation of the shift. 
     If the gear selector is in a jam zone, the process measures whether the control motor is drawing current in excess of a predefined threshold  702 . The value of the predefined threshold  702  will depend on the system, and the current typically drawn by the control motor during a jam event, as determined by modeling or experimentation, or based on previous jam events recorded by the controller. The process sets a jam event flag  703  should the current threshold be exceeded at any time while the drum is in a jam zone  702   704 . Should the process detect that the jam event flag is on, the process may adopt a position control, speed control, or torque control strategy to resolve the interference dynamically during the shift. These control strategies are designed to shepherd the transmission out of the jam zone, either into the desired gear, or back out into the starting gear. A jam event flag status check  706  ensures the event is only flagged once. Once the drum has exited the jam zone, the process can set a gear engaged flag  705  to indicate that the gear is expected to engage successfully. Should the process detect that the gear engaged flag  705  is on the process may trigger external events such as clutch control or engine control. If the jam event flag  703  is set at the end of the process, the process may run a diagnostic routine to identify the cause of the jam, or adopting a position control, speed control, or torque control strategy to resolve the interference should it remain (for example, because the shift has failed entirely, and the drum has reverted to its starting position). 
     It will be appreciated that the above description relates to the preferred embodiments by way of example only. Many variations on the system and method for delivering the invention without departing from the spirit of same will be clear to those knowledgeable in the field, and such variations are within the scope of the invention as described and claimed, whether or not expressly described.