GEAR TRAIN BACKLASH CONTROL

[0001] This technical disclosure concerns reduction of noise, vibration, and harshness (NVH) in an internal combustion engine. The specific example presented describes reduction of noise and vibration in the gear train of an opposed-piston engine.

BACKGROUND

[0002] Gear vibration and clash in an internal combustion engine can lead to intense whining, sharp impulse noise, or both.  These noises can cause extreme operator and passenger discomfort in a vehicle.  Engine whine and rattle also add to the constant cacophony that can make proximity to transportation routes unpleasant.  Because of this, performance standards and environmental regulations relating to vehicles increasingly include NVH limits.

[0003] Whenever gears interface with each other, there is side contact between the respective gear teeth. These teeth side contacts are classified as overrunning side contacts or driving side contacts.  Because of these contacts, there is usually a gap between the interfacing gear teeth.  As the gears rotate, these gaps are closed when the teeth make new contacts, which can result in gear rattle.  Backlash in the gear trains of opposed-piston engines during torque reversals will also produce gear rattle.

[0004] The gear train of an opposed-piston engine with dual crankshafts inherently experiences torque reversals and other events where gear teeth lose contact and then produce clatter and vibration.  In the case where a phase difference is provided between the crankshafts in order to differentiate port opening and closing times, the gear train is subjected to a torque reversal at least once every cycle of engine operation.  Even without an inter-crankshaft phase difference, momentary inter-gear torque reversals result from any of idler bounce, gear rotational distortion, shaft rotational distortion, or a combination thereof.  Torque reversals result in crank train rattle when gear backlash and powertrain gear teeth clearances are present.

[0005] Backlash control in an opposed-piston engine, particularly one with two crankshafts, can be a balance between noise control, minimization of friction loss, and the efficient transfer of torque in the gear train.  Conventional backlash controls include methods and apparatus that fix the backlash of an engine prior to operation of the engine, or perhaps additionally after operation and alteration of an engine, but dynamic backlash control is not a feature of these conventional controls.

SUMMARY

[0006] A system and method for dynamic control of backlash in an opposed-piston engine with one or more crankshafts are provided in the implementations described below.  The amount of backlash between an idler gear and at least one other gear in a gear train can be adjusted during operation of the engine.  During operation, adjustments to the backlash between each of the engine’s idler gears and one or more other gears adjacent to the idler gears can be initiated based upon at least one of following: the instantaneous engine speed, vehicle speed, engine or vehicle acceleration, engine temperature, and desired fuel economy.

[0007] Provided in some implementations is a backlash control system for use with an opposed-piston engine that includes a controller, a gear position actuator, and one or more engine status sensors.  The opposed-piston engine can be a two-stroke-cycle, internal combustion engine having at least one cylinder with longitudinally-separated exhaust and intake ports and a pair of pistons disposed in opposition to one another in a bore of the cylinder, each piston in the pair of pistons connected to a crankshaft, each crankshaft connected to a crank gear in a gear train, such that there is a first crank gear and a second crank gear in the gear train.  The following features can be present in some embodiments of the backlash control system in any reasonable combination.  The gear position actuator can include a moveable platform attached to an idler gear in the gear train, in which the idler gear is situated between first and second adjacent gears.  The gear position actuator can also include an actuator to move the moveable platform to alter backlash between the idler gear and the first and second adjacent gears. The first and second adjacent gears can be the first and second crank gears.  The one or more engine status sensors can include an engine speed sensor, a vehicle speed sensor, and/or an engine temperature sensor.  The controller can be configured to accept engine status data from the one or more engine status sensors, as well as determine when a change in backlash in the gear train is needed based on the engine status data.  The controller can also be configured to signal to the gear position actuator to move the moveable platform to affect the change in backlash when needed.

[0008] In a related aspect, an opposed-piston engine with a backlash control system that includes a controller, a gear position actuator, and one or more engine status sensors is provided in some of the implementations described herein.

[0009] In a further related aspect, a method of dynamic backlash control in the gear train of an opposed-piston engine with a controller, a gear position actuator, and one or more engine status sensors is provided in some implementations.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1A is a side elevation view of an arrangement of cylinders, pistons, and a gear train in an opposed-piston engine.  FIG. 1B shows a schematic of a system for dynamic backlash control in an engine.

[0011] FIG. 2 shows a schematic of an exemplary backlash varying mechanism for use in the system of FIG. 1B which includes a sliding idler gear mounting base, according to some implementations.

[0012] FIG. 3 shows a schematic of an exemplary backlash varying mechanism for use in the system of FIG. 1B which includes an eccentric idler gear shaft with a lever arm, according to some implementations.

[0013] FIG. 4 shows a flow diagram of an exemplary method for dynamic adjustment of backlash according to some implementations.

DETAILED DESCRIPTION

[0014] A system and method for dynamic control of backlash in an opposed-piston engine are described.  The amount of backlash between an idler gear and at least one other gear in a gear train can be adjusted dynamically, during operation of the engine.  During operation, adjustments to the backlash between the engine’s idler gear and one or more other gears can be initiated based upon at least one of following: instantaneous engine speed, engine temperature, vehicle speed, and desired fuel economy.

[0015] FIG. 1A illustrates an arrangement of cylinders, pistons, and crankshafts in an opposed-piston engine with an associated gear train that can include a backlash reducing gear. The figure shows a three-cylinder arrangement, although this is not intended to be limiting; in fact, the basic architecture portrayed in FIG. 1A is applicable to opposed-piston engines with fewer, or more, cylinders. The opposed-piston engine 10 includes cylinders 12, each including exhaust and intake ports 14 and 16. Preferably, the cylinders comprise liners (also called “sleeves”) that are fixedly mounted in tunnels formed in an engine frame or block 18. A pair of pistons (unseen in this figure) is disposed for opposing reciprocal movement in the bore of each cylinder 12. The opposed-piston engine 10 includes an interlinked crankshaft system comprising two rotatably-mounted crankshafts 21 and 22 and a crankshaft gear train 30 linking the crankshafts and coupling them to a power take-off shaft (”PTO shaft”). The crankshafts 21 and 22 are mounted to the engine by main bearing arrangements (not shown), one at the bottom of the engine block 18 and the other at the top. The crankshaft gear train 30 is supported in one end of the engine block 18 and is contained in a compartment 31 therein that is accessed through a removable cover 32.

[0016] As per FIG. 1A, one piston of each piston pair is coupled to a respective crank journal 23 of the crankshaft 21 by a connecting rod assembly 27; the other piston is coupled to a respective crank journal 25 of the crankshaft 22 by a connecting rod assembly 29. The crankshafts 21 and 22 are disposed with their longitudinal axes in a spaced-apart, parallel arrangement. The crankshaft gear train 30 includes a plurality of gears, including two input gears 36a and 36b, which are fixed to respective ends of the crankshafts 21 and 22 for rotation therewith. An output gear 37 is mounted for rotation on a shaft or post. The output gear 37 drives a power take-off shaft 38 about an output axis of rotation A. In this configuration, two idler gears 39a and 39b are provided, each mounted for rotation on a fixed shaft or post 40. The idler gear 39a meshes with the input gear 36a and the output gear 37; the idler gear 39b meshes with the input gear 36b and the output gear 37. As a result of the configuration of the crankshaft gear train 30, the crankshafts 21 and 22 are co-rotating, that is to say, they rotate in the same direction. However, this is not meant to so limit the scope of this disclosure. In fact, a gear train construction according to this specification may have fewer, or more, gears, and may have counter-rotating crankshafts. Thus, although five gears are shown for the crankshaft gear train 30, the numbers and types of gears for any particular crankshaft gear train are dictated only by the engine design. For example, the crankshaft gear train 30 may comprise one idler gear for counter-rotation, or two idler gears (as shown) for co-rotation.

[0017] FIG. 1B shows a schematic of a system for dynamic backlash control in an engine 100 that includes a controller 110, a gear position actuator 120, a gear pressure and/or resistance sensor 130, a gear position and/or translation sensor 140, an engine speed sensor 150, an temperature sensor 160, a fuel consumption sensor 170, and a user interface 180.  During operation of the engine 100, the engine speed sensor 150, vehicle speed sensor 155, temperature sensor 160, acceleration sensor 165, engine load sensor/indicator 170, and user interface 180 can send information about the engine’s status to the controller 110.  The controller 110 can use this information to determine whether or not the backlash of the engine 100 needs to be adjusted.  Alternatively, or additionally, the controller can determine the location and degree of adjustment to backlash needed based on sensor information.  When the controller 110 determines that backlash needs to be adjusted, the controller 110 can send instructions to the gear position actuator 120 to move one or more gear in the gear train.  The gear position actuator 120 can be connected to one or more gear sensors, such a gear pressure/force sensor 130 and/or a gear position or translation sensor 140, which provide position, translation, pressure, or friction (i.e., force) feedback to the actuator 120.  The feedback provided by the gear sensor or sensors 130, 140 can verify that the backlash has been adjusted appropriately, and the gear position actuator 120 can continue to move one or more gears until the gear sensor or sensors 130, 140 indicate the desired backlash has been achieved.

[0018] The gear position actuator 120 can connect to one or more idler gears in the gear train.  By moving the one or more idler gears, the gear position actuator 120 can cause more or less distance between the idler gear(s) and adjacent gears (e.g., crank gears, a crank gear and a take-off gear), thus increasing or decreasing backlash.  A moveable platform can support the idler gear(s), and the gear position actuator 120 can translate the moveable platform to adjust the backlash between the idler gear(s) and adjacent gears.  The actuator can be any suitable type of actuator that can change, and optionally maintain, the position of the idler gear.  Types of actuator that can be used in the gear position actuator 120 include one or more of the following: hydraulic, pneumatic, electric, thermal, and magnetic actuators. Specifically, the gear position actuator 120 can include any of the following: a servo motor; a linear electric motor; a rotary electric motor; a piezoelectric transducer; a hydraulic cylinder; a cam; a solenoid; and the like.   The maximum amount of force applied by the actuator on the moveable platform of the idler gear can be a function of the properties, such as the stiffness, of the gear position actuator 120.

[0019] Additionally, or alternately, a constant load can be applied to the idler gear(s), such as to the moveable platform to which the idler gear or gears are mounted, to maintain a constant pressure between the idler gear(s) and one or more adjacent gears.  This constant load can be applied by a spring, weight, tensioning belt, or tensioning chain.  Further, the constant load can be applied while the gear position actuator can make small adjustments to the position of the idler gear(s) to refine the backlash between the idler gear(s) and adjacent gears.

[0020] FIG. 2 shows a schematic 200 of an exemplary backlash varying mechanism 220 which includes a sliding idler gear mounting base.  The schematic 200 shows an idler gear 205, a first crank gear 215, a second crank gear 216, and a rotary actuator with screw mechanism 220.  As the screw mechanism in the rotary actuator 220 turns, the idler gear 205 can translate in a linear fashion, right to left in FIG. 2.  In the schematic 200, as the idler gear 205 translates to the right, less pressure is exerted on the first and second crank gears 215, 216, increasing the backlash between these three gears. As the idler gear 205 translates to the left, the backlash between these three gears decreases as the gap between the gear teeth reduces, and eventually the contact between the gear teeth will create friction between the gears, leading to resistance and pressure.  Additionally, a secondary actuator can lock the backlash varying mechanism into a position.

[0021] Sensors on the idler gear mounting base can detect the translation of the gear or the resistance and pressure on gears in the gear train that result from a reduction of backlash.  The sensors can include at least one of a gear pressure and/or resistance sensor 130 and a gear position and/or translation sensor 140. The gear pressure and/or resistance sensor 130 can include a pressure gauge on one or both of the crank gears 215, 216. The gear position and/or translation sensor 140 can include a distance sensor, such as an infrared distance sensor, a laser displacement or position sensor, an optical comparator, a strain gauge, a linear variable differential transformer, and the like, which can determine the distance between the center of the idler gear 205 and a fixed location in the engine, or the distance between the center of the idler gear 205 and the center of one or both of the crank gears 215, 216.

[0022] FIG. 3 shows a schematic 300 of an exemplary backlash varying mechanism 320 that includes an eccentric idler gear shaft with a lever arm.  The schematic 300 shows an idler gear 205, a first crank gear 215, a second crank gear 216, and a linear actuator 320 connected to an eccentric shaft 321. As in the schematic 200 shown in FIG. 2, the idler gear 205 is mounted on a moveable platform.  As the linear actuator translates, right to left in FIG. 3, the center of the idler gear 205 is also translated.  Additionally, a secondary actuator can lock the backlash varying mechanism into a position. The sensors described with respect to backlash varying mechanism shown in FIG. 2 can be used to confirm the backlash adjustment made by the backlash varying mechanism 320 shown in FIG. 3.

[0023] In an engine, such as that shown in FIGS. 1A-3, various sensors and user input (reference numbers 150, 155, 160, 165, 170, 180 in FIG. 1B) can signal a controller 110, and in turn the controller 110 causes a gear position actuator 120 to move an idler gear.  The gear position actuator 120 can include, or communicate with, sensors to determine when the amount of backlash has been adjusted appropriately in response to the signal received by the controller.  The sensors associated with monitoring the movement of the idler gear or the adjustment of backlash affected by the gear position actuator 120 can include a gear pressure and/or resistance sensor 130, a gear position/translation sensor 140, or both a gear pressure/resistance sensor 130 and a gear position/translation sensor 140.  One or more of these sensors, including more than one of each type of sensor, can be associated with just the idler gear, just one crank gear, both crank gears, one crank gear and the idler gear, or with all of the gears in the gear train.

[0024] Though described for use with gear trains with one idler gear and three total gears, the backlash varying mechanisms and systems described herein can be used with a gear train with any number of gears, with one backlash varying mechanism for each idler gear in a gear train.  Additionally, though the gear trains are shown with the idler gear larger than its adjacent gears, the relative sizes of the gears in a gear train can be any necessary to provide the appropriate power and to fit the volume allotted to the engine.  The amount to backlash can be set and adjusted prior to starting the engine.  Sensors can indicate the amount of translation needed to suitably reduce starting lash, for example sensors that indicate pressure, distance, force, and the like. Adjusting the lash in this manner, prior to starting the engine, can allow for a quiet start to the engine’s operation.

[0025] FIG. 4 shows a flow diagram 400 of an exemplary method for dynamic adjustment of backlash.  This method could be used with an engine, such as that shown in FIG. 1B, with a controller, various engine sensors, and a gear position actuator to adjust the position of one or more idler gears, as shown in FIGS. 2 and 3.  The one or more engine sensors could detect conditions requiring adjustment, and the degree and location of changes needed, to backlash, as in 410.  The determination that a change in backlash is needed can be made by the engine sensors, in which case the sensor includes a processor and memory to compare current data with stored threshold values.  Alternatively, or additionally, the controller in the engine can make the determination that gear backlash needs to be changed based upon raw current status data provided by the engine sensors.  The types of data collected by the engine status sensors can include engine temperature, engine speed, vehicle speed, fuel consumption mode, engine load, acceleration, and the like.  The operator of the engine may indicate performance preferences that cause the controller to default to an increased or decreased backlash setting.  For example, when the user desires to operate the engine in a quieter mode, the controller can register that less backlash is desirable, or when the user desires more fuel efficiency, the controller can register that a certain amount of engine friction, and in turn backlash, is required to meet that user defined efficiency.  Also, when engine sensors detect that the engine is idling, operating with low loads, or at a low speed, the controller can determine that backlash between the gears should be low to allow for improved noise control.

[0026] In the method shown in FIG. 4, the controller can verify the current status of gear train backlash and determine whether or not the relative position of the gears should be adjusted based on the data from the engine status sensors, as in 410.  When a change is needed in the backlash, the controller can indicate this to the gear position actuator, as in 420.  In response, the gear position actuator can move the idler gear, or if there is more than one idler gear, more than one gear can be moved, as in 430.  As mentioned above, a gear position/translation sensor, a gear pressure/resistance sensor, or both a pear position/translation sensor and a gear pressure/resistance sensor can be associated with the gear position actuator to help determine that the idler gear has been moved sufficiently to affect the change in backlash desired by the controller, as in 440.  The one or more engine sensors can monitor the engine status in an on-going manner, continuously or periodically, so that the engine controller can be signaled when the engine status changes and adjustments to backlash are needed over the course of engine operation.

[0027] Example 1

[0028] A vehicle includes an opposed-piston, two-stroke-cycle engine with two crankshafts.  The gear train of this vehicle’s engine includes one crank gear connected to each crankshaft, for a total of two crank gears in the gear train, and an idler gear between the crank gears.  The idler gear in this engine is mounted on a movable platform controlled by an actuator.  Sensors in the vehicle collect data about the vehicle’s engine status including the engine temperature, engine speed (RPM), engine load, vehicle speed, user set noise threshold, and/or user set fuel consumption.

[0029] The vehicle’s operator starts the engine.  At this point, the load is light, as the vehicle is idling or travelling slowly, but there is no road noise to mask any engine noise.  With this status indicated by the engine sensors to the vehicle’s engine controller, the controller can determine the status of the idler gear in the gear train.  Because of the conditions when the vehicle was last operated, the idler gear is currently in a position where there is a large backlash between it and either or both of the crank gears.  The controller signals the actuator to move the idler gear closer to the crank gears, thus reducing the backlash.

[0030] The vehicle’s operator accelerates the vehicle and drives it onto a major thoroughfare where it reaches a speed of about 45 MPH (about 72 kilometers per hour).  The engine sensors collect data indicating this change of status to the engine controller.  Additionally, the operator indicates that the vehicle should operate with a reduced fuel consumption rate. The engine controller takes the engine sensor data and the operator input to determine that the backlash can be increased, as well as the amount by which the backlash should increase.  The controller then signals the actuator to move the platform and the idler gear further away from the crank gears.  A translation sensor and/or a pressure sensor confirm that the idler gear has moved away from the crank gears.

[0031] The vehicle is driven at a constant speed for some time, and the engine heats up.  The engine sensors detect this, and the engine controller determines that the temperature increase is enough to warrant movement of the idler gear to compensate. The actuator moves the idler gear until a pressure/resistance sensor or location sensor indicates that the idler gear and crank gears have appropriate backlash.  The appropriate amount of backlash for each type of engine status can be determined by the engine controller based upon stored data.  The stored data can include gear center to center distances, pressure values, and/or resistance values for each vehicle speed range, engine temperature range, load range, and operator input.

[0032] The operator slows the vehicle and drives through a parking lot or other area where the vehicle speed is limited to about 10 miles per hour (about 16 KPH).  The engine sensors detect this change in status, the engine controller determines that the backlash should be adjusted and signals the actuator.  The actuator then moves the idler gear to reduce the backlash in the gear train, thus reducing engine noise.