ELECTRONIC THROTTLE CONTROL OF SNOWMOBILE WITH TWO-STROKE INTERNAL-COMBUSTION ENGINE

An electronic throttle-control system that includes: an electronic control unit (ECU) including a processor and a memory storing a throttle-control translation map; a throttle-input sensor in electrical communication with the ECU and configured to sense an input from an operator-actuated throttle device; and a 2-stroke internal-combustion engine. The 2-stroke internal-combustion engine may include: an electronic throttle-valve actuator in electrical connection with the ECU; a throttle body for controlling airflow to combustion chambers of the engine and defining first and second throttle bores; first and second throttle valves in the bores; and a throttle valve control shaft coupled to the throttle valves and the actuator, such that movement of the actuator causes the throttle valve control shaft to rotate and move the first and second throttle valves; and a throttle-position sensor in electrical communication with the ECU sensing an actual position of the first and second throttle valves.

BACKGROUND

As compared to snowmobiles with 4-stroke internal-combustion engines, snowmobiles with 2-stroke internal-combustion engines are much lighter and maneuverable, and provide greater power-to-weight ratios. Further, snowmobiles with 2-stroke engines may start easier in cold weather. For these and other reasons, many consumers choose 2-stroke snowmobiles over 4-stroke snowmobiles. However, unlike modern 4-stroke snowmobiles which employ electronic throttle control (ETC), known 2-stroke snowmobiles still utilize mechanical throttle controls, such as a throttle cable connecting the operator throttle lever to the throttle valve in the engine throttle body. Consequently, 2-stroke snowmobiles cannot provide the many advantages offered by ETC.

SUMMARY

Embodiments of the present disclosure include an electronic throttle-control system for a snowmobile. In one such embodiment, the electronic throttle control system includes: an electronic control unit (ECU) including a processor and a memory device storing at least one throttle-control translation map; a throttle-input sensor in electrical communication with the ECU and configured to sense an input from an operator-actuated throttle device; and a 2-stroke internal-combustion engine. The 2-stroke internal-combustion engine may include: an electronic throttle-valve actuator in electrical connection with the ECU and having an actuator motor and gear train; a throttle body for controlling airflow to one or more combustion chambers of the 2-stroke internal-combustion engine, the throttle body defining a first throttle bore and a second throttle bore; a first throttle valve in the first throttle bore and a second throttle valve in the second throttle bore; and a throttle valve control shaft coupled to the first throttle valve and the second throttle valve, and to the gear train, such that movement of the actuator motor and gear train causes the throttle valve control shaft to rotate and move the first and second throttle valves; a throttle-position sensor in electrical communication with the ECU and configured to sense an actual position of the first and second throttle valves. Further, the ECU may be configured to receive a signal representing a throttle-position input from the throttle-input sensor and to determine a throttle-demand position corresponding to a position of the first throttle valve in the first throttle bore and a position of the second throttle valve in the second throttle bore, based on the throttle-position input and throttle-control translation map.

Another embodiment of the disclosure is a method of controlling a starting mode of snowmobile having an electronic-control unit (ECU) with a processor, and a 2-stroke combustion engine with an electronic throttle body having a first throttle valve, a second throttle valve, a throttle-position sensor, and an actuator for actuating the first and second throttle valves. The method includes the steps of: determining whether an electronic throttle body drive-voltage generated by the 2-stroke combustion engine is above a threshold voltage; determining whether an engine speed of the 2-stroke combustion engine is above a first engine-speed threshold; when the generated voltage is at or above the critical threshold voltage and the speed of the 2-stroke combustion engine is above a threshold engine-speed threshold, setting a throttle position of the first throttle valve and the second throttle valve to a neutral-throttle position; after a predetermined period of time, determine whether the engine speed is greater than a second engine-speed threshold; and when the engine speed is greater than the second engine-speed threshold, changing a position of the first throttle valve and the second throttle valve from the neutral-throttle position to an initial throttle-operating position, by controlling the actuator with the processor of the ECU.

Yet another embodiment of the disclosure includes a method of controlling a snowmobile having an electronic-control unit (ECU) with a processor, a memory storing one or more throttle-control translation maps, and a 2-stroke combustion engine with an electronic throttle body having a first throttle valve, a second throttle valve, a throttle-position sensor, an actuator for actuating the first and second throttle valves, and an engine-speed sensor. In this embodiment, the method includes: storing a predetermined idle-speed throttle-valve position and the one or more throttle-control translation maps in the memory; determining with the ECU a throttle-demand valve position, the throttle-demand valve position corresponding to a throttle-demand valve effective area of the first and second throttle valves; comparing the throttle-demand valve position to the predetermined idle-speed throttle-valve position; receiving at the ECU, an output of the engine-speed sensor indicating an actual engine speed of the 2-stroke internal-combustion engine; comparing the actual engine speed with a predetermined engine-idle speed; selecting a throttle-control translation map stored in the memory when the throttle-demand position effective flow area is greater than the predetermined idle-speed throttle position effective flow area and when the actual engine speed is greater than the predetermined idle engine speed; controlling the actuator using the ECU to set a first position of the first throttle valve in the first throttle bore and a first position of the second throttle valve in the second throttle bore based on the selected throttle-control translation map; determining whether an engine fault is present and controlling the actuator using the ECU to set a second position of the first throttle valve in the first throttle bore and a second position of the second throttle valve in the second throttle bore when a fault is present; and determining whether a ground speed or engine speed exceeds a maximum speed limit and controlling the actuator using the ECU to set a third position of the first throttle valve in the first throttle bore and a third position of the second throttle valve in the second throttle bore to reduce ground speed or engine speed to be less than the maximum speed limit.

The above summary of the various representative embodiments of the invention is not intended to describe each illustrated embodiment or every implementation of the invention. Rather, the embodiments are chosen and described so that others skilled in the art can appreciate and understand the principles and practices of the invention. The figures in the detailed description that follow more particularly exemplify these embodiments.

DETAILED DESCRIPTION

For the purposes of understanding the disclosure, reference will now be made to the embodiments illustrated in the drawings, which are described below. While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all combinations, modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims.

Electronic throttle control (ETC), while prevalent on 4-stroke powersports products, has never successfully been implemented on a 2-stroke snowmobile. Over time, more safety features are being implemented on 2-stroke snowmobiles, and their versatility is growing. However, conventional methods for manipulating the feel and/or use of the snowmobile, as well as means of power limiting the snowmobile, have not risen to the level to provide for a true multipurpose 2-stroke snowmobile. Dual-bore, on-throttle, electrically-driven ETC systems herein directed to a 2-stroke snowmobile allow for reduced mass, more precise control and faster response, in addition to reduced throttle-pull effort, thereby providing significantly improved vehicle-feel manipulation, speed limiting, power limiting, start and idle improvements as compared to cable-driven mechanically-actuated throttle-body systems of known 2-stoke snowmobiles.

Further, the ability to create a plurality of drive modes on a 2-stroke engine facilitates implementation of more effective vehicle and engine speed-limiting options to control the power output of the engine to meet the needs of riders of a wider range of skill levels. For example, a reduced maximum-throttle opening with a slower ramp between input and output command can serve as an operational mode for entry-level or inexperienced riders while a 1:1 translation between input and output can serve as a operational mode for experienced riders. Furthermore a throttle map in which the throttle opens further than the user command at certain operating conditions can be used for racing or mountain applications to enhance throttle response. Additionally, the use of ETC can serve as a user-adjustable speed-limiting function that can be used with or without a parental-lock passcode through the gauge to limit vehicle speed so that the operator can use the vehicle according to one of the aforementioned throttle-control modes up to a programable vehicle speed, at which point the throttles will begin to close to maintain the speed.

Furthermore, the use of ETC can be used as a vehicle power-limiting function for circumstances such as: engine overheat, exhaust temperature overheat, transmission low range operation, detonation protection, low-fuel operation and vehicle speed limiting for track durability. Embodiments of snowmobiles with 2-stroke ETC as described herein increase the operational capacity of a single vehicle that is usable for a wide range of operators from the inexperienced to the expert.

Embodiments of the disclosure, and as described in further detail below, include a snowmobile with a 2-stroke internal-combustion engine having a dual bore electronic throttle body with a single shaft connecting the two plates/valves to an electric motor output drive that is used to control the airflow going into the engine. A handlebar mounted throttle-input sensor is used to determine throttle input by the user. An ECU is then able to translate this user input to a throttle body command through a plurality of throttle-control translation maps that are used to alter the performance characteristics of the engine. The plurality of translation maps are used to alter the feel of the vehicle by limiting engine airflow and/or rate at which throttle is applied relative to the users input. A map which features a smoother translation between the user input and the throttle output can be utilized to enhance low speed drivability when towing or navigating tight operating conditions. Additionally, ETC can be used for vehicle speed limiting on mountain snowmobiles equipped with deeper lug tracks as a means of preventing or mitigating the delamination of the track lugs causing track failure.

ETC can also serve as an effective means of power limiting and can be used independently or in conjunction with utilization of the exhaust valves as a means of controlling the airflow through the engine and therefore, the power output of the engine. In the case of elevated engine water or exhaust gas temperature, the exhaust valves may be forced down to limit airflow of the engine or could be used in conjunction with the ETC to force operation of the engine into a region more likely to mitigate this circumstance; usually by limiting power of the engine to reduce heat production both through heat rejection to the cooling system and heat generation through combustion. In the case of engine detonation, instead of forcing the exhaust valves down, a progressive drop in maximum operating throttle position can be implemented to mitigate detonation while still allowing the maximum power allowable for the given circumstances which allows for a less intrusive means of power limiting and engine protection. In the case of a sensor or vehicle fault, a maximum allowable throttle position that overrides the translation maps to allow the rider to limp home for the purpose of repairs or diagnostics to minimize the potential for engine failure may be implemented. For example, sensors may sense and indicate low-fuel pressure, or other engine faults. Vehicle faults may include non-engine related faults, including faults caused by operation of snowmobile10, such as certain brake-throttle interactions, such as operating the throttle while applying the brakes for period of time.

Furthermore, the use of ETC allows for variable throttle angle to be used for starting of the engine to control the flare of the engine in starting conditions according to elevation of operation. Additionally, the ETC can be used as closed loop idle control mechanism to control the engine speed according to a calibratable setpoint.

Referring toFIGS.1-3, an embodiment of snowmobile10includes chassis or frame assembly12having front frame portion14and rear frame portion16. Front frame portion14is supported by skis18, and rear frame portion16is supported by endless track20. Front skis18are operably coupled to front suspension assembly22, and endless track20cooperates with rear suspension assembly24during operation of snowmobile10. Snowmobile10also includes seat assembly26having a seating portion for at least a driver and an optional seating portion for a passenger positioned rearward of the driver portion.

Snowmobile10further includes body assembly28comprised of multiple body panels covering certain components and systems of snowmobile10, including portions of frame assembly12, front suspension assembly22, and powertrain assembly30.

Referring specifically toFIG.3, frame assembly12includes a bulkhead32coupled to a tunnel34extending along a longitudinal axis L of snowmobile10. Bulkhead32supports a steering assembly48.

As will be understood by those of ordinary skill in the art, two-stroke or 2-stroke (sometimes referred to as “2-cycle”), internal-combustion engine50includes various systems and components, such as an engine block with a combustion chamber, pistons, intake and exhaust valves, a fuel system, which may be an electronic fuel-injection (EFI) system, an electrical system, a cooling system, an exhaust system, and various sensors, such as a throttle position sensor, engine-speed sensor, crank position sensor, and so on. Various embodiments of snowmobiles, snowmobile engines, systems and so on are known in the art and are described in U.S. Pat. No. 8,590,654, issued Nov. 26, 2013 and entitled “Snowmobile,” in U.S. Pat. No. 8,733,773, issued May 27, 2014 and entitled “Snowmobile Having Improved Clearance for Deep Snow,” in U.S. Patent Pub No. 2014/0332293A1, published Jul. 23, 2014 and entitled “Snowmobile,” and in U.S. Pat. No. 11,110,994, issued Sep. 7, 2021 and entitled “Snowmobile,” all of which are assigned to Polaris Industries Inc., and all of which are incorporated herein by reference in their entireties.

Powertrain assembly30also includes a drivetrain assembly52comprising a countershaft or jackshaft54and a track driveshaft56. Jackshaft54is operably coupled with the transmission and, in embodiments using a continuously variable transmission (“CVT”), is operably coupled with the secondary or driven pulley. Jackshaft54also is operably coupled to driveshaft56through a belt/chain drive assembly58. Belt/chain drive assembly58includes a drive sprocket60, a driven sprocket62, and a belt or chain64rotatably entrained with drive and driven sprockets60,62. Driven sprocket62is coupled with driveshaft56. In operation, the crankshaft (not shown) of engine50drives the transmission, thereby causing the transmission to output power (e.g., rotation) to jackshaft54. Jackshaft54then drives driveshaft56through belt/chain drive assembly58. As a result, driveshaft56rotates within a portion of tunnel34.

Driveshaft56engages an inner surface of track20, such that as jackshaft54drives driveshaft56, through belt/chain drive assembly58, driveshaft56causes track20to rotate and move snowmobile10.

An engine50speed is controlled, at least in part, by the operator controlling throttle-input device80, which may be a throttle lever or similar. A position of the throttle-input device81may be detected by a throttle-input sensor140(discussed further with respect toFIG.7) that senses a position of throttle-input device80.

Snowmobile10also includes brake system70, which may be a dry or wet brake system controlled by brake lever82. In an embodiment, brake system70is a hydraulic disc-brake system, and is coupled to the transmission. Brake system70may be directly coupled to jackshaft54, or to other portions of the transmission.

In the embodiment depicted, 2-stroke, internal-combustion engine50is a two-cylinder engine, with two combustion chambers and two pistons, though it will be understood that 2-stroke, internal-combustion engine50may comprise a single-cylinder engine, or may comprise more than two combustion chambers, based on various engine factors, including engine size and desired engine power output.

Referring also toFIG.5, electronic throttle-control system88configured for a 2-stroke, internal-combustion engine includes throttle body90defining a pair of throttle bores92, depicted as first throttle bore92aand second throttle bore92b, a pair of throttle valves94, depicted as first throttle valve94aand second throttle valve94b, throttle valve actuator96with actuator motor98and actuator gear train100, and actuator shaft102. Electronic throttle-control system88also includes a throttle-valve position sensor142(seeFIG.7) for detecting a position of throttle valves94.

In the embodiment depicted, throttle body90defines two throttle bores92and two throttle valves94, one for each combustion chamber, though in other embodiments, throttle body90may define a single throttle bore92with a single throttle valve94, or more than two throttle bores with valves, depending on various engine design factors, including the number of combustion chambers defined by engine50. In an embodiment, throttle body90defines one bore92with one throttle valve94, for each combustion chamber of engine50.

As will be understood by those of ordinary skill in the art, each throttle bore92forms a passageway or channel for combustion air to flow into engine50combustion chambers. In embodiments, each throttle bore92defines a generally cylindrical through passageway, with a circular opening. Each throttle bore92, including bores92aand92b, may be of substantially equal size, with a same or similar-sized opening. In an embodiment, a diameter D of each throttle bore92may be in a range of about 30 mm to about 50 mm.

Throttle valves94, including valves94aand94b, in an embodiment, comprise butterfly valves that may form a substantially flat, circular disc or plate. Each butterfly valve94fits at least partially within an interior portion of its respective bore92, depending on the rotated position of the valve. Each butterfly valve94may also define a minimum-air flow, or idle-air flow, hole104, including holes104aand104b, to allow for some airflow through valve94, even when the valve is in a closed position. Each throttle valve94is centered within its respective throttle bore92, such that when each throttle valve94is in a closed position, as depicted inFIGS.4and5, with the exception of air flow through holes104, minimal or no air flows through throttle bore92. In other words, the edges of throttle valves92abut or are very near, inside surfaces defining throttle bodies92such that very little or no air passes around throttle valve94when in the closed position.

First and second throttle valves94aand94bare distributed along a lateral axis A, separated by a center-to-center pitch distance P. In an embodiment, pitch P is in a range of about 100 mm to 200 mm; in another embodiment, pitch P is in a range of about 130 mm to 140 mm; in another embodiment, pitch P is approximately 130 mm. Pitch P may be increased to accommodate larger 2-stroke engines which may have larger cylinders and combustion chambers that have centers spaced further apart laterally.

Actuator shaft102extends from actuator gear train100along lateral axis A, and is mechanically coupled to each of throttle valves94aand94bvia a pair of fasteners95, as depicted. Actuator shaft102may comprise a single shaft, or multiple mechanically-joined shafts. Portions of actuator shaft102may be flat, as depicted, to conform to flat outer surfaces of throttle valves94.

Throttle-valve actuator96, including actuator motor98, is in electrical communication with, and controlled by, the snowmobile ECU, as will be described further below with respect toFIG.7. Actuator motor98is an electric actuator motor powered by an electrical power system of snowmobile10, controlled by the ECU, and is coupled to actuator gear train100. Movement of actuator motor98is translated through actuator gear train100, causing actuator shaft102to rotate about axis A in a clockwise or counter-clockwise direction. Rotation of actuator shaft102in turn causes throttle valves94aand94bto move between a closed throttle position and an open throttle position. In an embodiment, each of throttle valves94aand94bare rotatable in a range of 0 (closed throttle position as depicted) to 90°, fully open throttle position. In other embodiments, each of throttle valves94aand94bare rotatable through a larger range, which may be from fully-closed to fully-open.

Referring also toFIGS.6A and6B, schematic illustrations of a throttle valve94in a closed throttle position and the throttle valve94in an open throttle position are respectively depicted. Referring specifically toFIG.6A, a portion of throttle body90defining a throttle bore92with throttle valve94in a closed position is depicted. Throttle bore92and throttle valve94are representative of any or both of bores92a,92band valves94a,94b. Fasteners95connect throttle valve94to actuator shaft102. Actuator102is in a rotational position that causes throttle valve94to be in a closed throttle position. In this “closed” throttle position, throttle valve94is at a 0° rotational position relative to axis A, which also corresponds to a 0% open throttle position, i.e., not open or closed position. This closed throttle position also corresponds to a minimum valve effective area or minimum throttle-demand effective flow area, meaning that the open area of the valve in the bore is minimized.

Referring specifically toFIG.6B, the same portion of throttle body90defining throttle bore92with throttle valve94therein is depicted. In this position, shaft102and connected throttle valve94are rotated into a fully open throttle position. In this “open” throttle position, throttle valve94is at a 90° rotational position relative to axis A, which also corresponds to a 100% open throttle position. This open throttle position also corresponds to a maximum valve effective area or maximum throttle-demand effective flow area, meaning that the open area of the valve in the bore is maximized.

In an embodiment, throttle valve94is rotatable between the fully-closed throttle position (minimum throttle-demand effective flow area) and the fully-open throttle position (maximum throttle-demand effective flow area), and a plurality of positions between the closed throttle position and the open throttle position, by throttle-valve actuator96, as controlled by ECU128(FIG.7), using actuator motor98, actuator gear train100and actuator shaft102. In an embodiment, each throttle valve94may be positioned to a number of predetermined discrete throttle positions between the closed and open throttle positions. Such throttle positions may be described in terms of throttle-demand effective flow area, e.g., a flow area measured in mm2, percentage of maximum throttle-demand effective flow area, e.g., 0% of maximum throttle-demand effective flow area to 100% of throttle-demand effective flow area, angular rotation of throttle valve94about axis A in degrees. e.g., 0° up to 360° or 0° up to 90°, angular rotation of throttle valve94about axis A as a percentage. e.g., 0% (minimum flow) to 100% (maximum flow). Embodiments may also include assigning a numerical value or level to various throttle positions, with a smallest number corresponding to a closed or minimum throttle-valve demand effective area, such as “level 1” and a largest number corresponding to a fully open or maximum throttle-valve demand effective area, such as “level 100”, such that a range of minimum to maximum throttle-demand effective flow area ranges from level 1 to level 100, with incremental positions therebetween, e.g. 1, 2, 3, 4 . . . 100.

Referring toFIG.7, a block diagram of snowmobile10is depicted. In this embodiment, snowmobile10includes operator inputs120with mode-control input device122and select input device124; display126; electronic control unit (ECU)128with engine control system130and security control system132; sensors that may include vehicle-speed (ground-speed) sensor134, gear-position sensor136, throttle-input sensor138, engine-speed sensor140, throttle-position sensor142and other engine sensors144; throttle-valve actuator96; 2-stroke engine50; transmission53, which may be a continuous variable transmission or CVT53as described above; one or more drive shafts56; and endless track20.

Operator inputs120include various devices and means for an operator of snowmobile10to control and interface with snowmobile10and ECU128. Operator inputs120may include a device for selecting an operating mode of snowmobile10and its 2-stroke engine50, i.e., mode control122, such as an electrical or mechanical switch, or a graphical button on a display device, such as display126. Operator inputs120may also include select input device124for selecting displayed operational settings or options. Other operator inputs120associated with a gauge of snowmobile may be included. In one such embodiments, and as discussed further below, an operator may interface with the gauge to enter a maximum speed limit, or other information intended to limit a ground speed, engine speed, or other vehicle operation limit.

Operator inputs120may collectively comprise a human-machine interface and may include display device126. Display126may be configured to display various information to an operator of snowmobile10, such as ground speed, engine speed, which may be measured in revolution per minute (RPM), engine temperature, outside temperature, and so on. In an embodiment, display126may comprise a touchscreen display configured to receive input from the operator, as well as being configured to display information to the operator.

Electronic control unit (ECU)128functions as a vehicle controller and though depicted as a single ECU, may in some embodiments comprise one or more ECUs having processors and memory for controlling electrical systems or subsystems of snowmobile10. Additional controllers or ECUs not depicted may also be present, such as those specific to control operating systems, including engine50and security-related devices, and/or other connected devices. Functions of ECU128may be performed by hardware and/or computer instructions saved on memory devices, such as non-transient, computer-readable storage mediums.

Memory devices, in an embodiment, includes computer-readable media in the form of volatile and/or nonvolatile memory and may be removable and/or non-removable. Embodiments include random access memory (RAM), read only memory (ROM), electronically erasable programmable read only memory (EE-PROM), flash memory, optical or magnetic storage devices, and/or other medium that can be used to store information and can be accessed by electronic devices. Memory devices are configured to store various types of vehicle data and executable computer-program instructions.

ECU128is in electrical communication with operator inputs120and display126, receiving input from the operator of snowmobile10and displaying or otherwise communication information to the operator.

ECU128may include a controller or control system130to directed to controlling 2-stroke engine50, and a controller or control subsystem132directed to controlling security devices and systems. ECU128with its engine control130is configured to control various operations of 2-stroke engine50, including electronic throttle-valve actuator96, as described above, and as described further below with respect toFIGS.8-16.

The various sensors, including sensors134-144are in electrical communication with ECU128. Vehicle-speed sensor134detects and indicates a ground speed of snowmobile10. Gear-position sensor136detects and indicates a gear position of snowmobile10. In an embodiment, gear-position sensor136indicates whether snowmobile10is in a low gear. Throttle-input sensor138detects and indicates a position of user-actuated throttle input device80. The position of throttle input device80generally indicates a throttle input that is requested by the operator. In an embodiment, throttle-input sensor138is located at or near throttle-input device80. Sensor138detects the requested throttle position and communicates that to ECU128. Engine-speed sensor140detects and indicates an engine speed, which may be measured in RPMs. Throttle-position sensor142detects and indicates an actual position of one or both of throttle valves94. In an embodiment, throttle-position sensor142may be located at or near throttle-valve actuator96. Other engine sensors144may also be present and in communication with ECU128. Other engine sensors144may include one or more fault sensors, engine-temperature sensor, exhaust-temperature sensor, an outside-air temperature sensor, barometric-pressure sensor, fuel-pressure sensor, low-fuel sensor, ECU-voltage sensor, brake sensor, e.g., to detect whether brakes are engaged, and other such sensors.

Snowmobile10may also include a CANBUS or other vehicle network connecting the various controllers and electrical devices of snowmobile10.

As also described above with respect toFIGS.1-3, 2-stroke engine50, drives CVT53, which in turn powers drive shafts56, which turn endless track20, thereby propelling snowmobile10.

Referring toFIG.8, an embodiment of a control diagram for controlling and determining a throttle demand or throttle position for snowmobile10is depicted. Generally, in operation, ECU128receives inputs from snowmobile10sensors and the operator/user of snowmobile10, determines a throttle mode, dynamically determines an appropriate throttle positions, then issues throttle commands to the throttle-valve actuator to attain that determined throttle position, thereby controlling flow of air and fuel to 2-stroke engine50.

More specifically, in this embodiment, ECU128receives vehicle speed input160, operator throttle input,162and engine speed164from vehicle-speed sensor134, throttle-input sensor138and engine-speed sensor140, respectively. “Input” may comprise electrical signals or data transmitted from the respective sensors or associated sensors and controllers. The operator of snowmobile10interfaces with operator inputs120(see alsoFIG.7), which includes gauge166, requesting a particular throttle mode, causing a mode-command message to be sent to ECU128.

In an embodiment, mode-change interlocks168prevent a throttle mode from being changed during operation, or when certain engine and/or vehicle criteria are not met. Such criteria may include, but not be limited to, being below a predetermined threshold vehicle speed or engine speed, being at or below a predetermined throttle position, and other criteria. Mode-change interlocks168may comprise one or more software algorithms stored in memory associated with ECU128, and executed by a processor of ECU128.

In an embodiment, ECU128may transmit information, a “request message” to gauge166and/or display126(FIG.7) relating to a requested throttle mode. Such information may advise an operator of a requested throttle mode, a current throttle mode, or of an inability to implement a requested throttle mode due to an interlock condition.

In this control embodiment, based on vehicle and engine speed, throttle input and user selection, ECU128determines or confirms a throttle mode. As described briefly above, a “throttle mode” corresponds to a selectable, predetermined throttle-control translation map. A throttle-control translation map “translates” or correlates an operator-requested throttle input, such as throttle-input162, to a throttle output, or throttle position as determined by ECU128. Generally, for any particular throttle input, the throttle map identifies an associated throttle output corresponding to throttle valve positioning. Such a throttle output might be the same as the requested throttle input in a first throttle mode, might be less than a requested throttle input in a throttle-limiting mode, or may be greater than a requested throttle input in a third throttle mode. Such throttle modes might respectively be labeled or identified by various labels, such as a standard throttle mode, limited throttle mode, and a dynamic or race throttle mode. Throttle-control translation maps are discussed in greater detail below with respect toFIG.12.

After determining or selecting the throttle-control mode at step170, ECU128then issues throttle commands172to control throttle-control actuator96and a position of throttle valves94according to the selected throttle-control mode and associated throttle-control translation map. In this particular embodiment, no throttle position sensing input or output filtering occurs. A lack of filtering on input/output signals allows for faster response without latency. In an alternate embodiment that employs limited or reduced filtering, the number of filtering samples is less than 10 samples. In one embodiment, ECU128utilizes a PID loop of less than 1 kHz with a greater than 1 kHz calculation loop. In one such embodiment, ECU128utilizes a 500 Hz PID loop with 2 kHz calculation loop to continuously determine throttle commands172. Such embodiments reduce latency and improve throttle response, such that the throttle response of ETC system88resembles that of a mechanically-operated throttle.

Referring toFIG.9, another embodiment of a control diagram for controlling and determining a throttle output for 2-stroke snowmobile10is depicted. This embodiment is similar to the embodiment depicted inFIG.8, though in the embodiment ofFIG.9, additional security and performance-limiting features are included.

As depicted, in this embodiment, ECU128receives vehicle speed input160, throttle input162and engine speed input164from vehicle-speed sensor134, throttle-input sensor138and engine-speed sensor140, respectively. In this embodiment, ECU128also receives gear-position input174from gear-position sensor136, indicating whether snowmobile10is in a low-gear position. As such, ECU128also takes into account a gear ratio of snowmobile10, and adjusts throttle output and throttle valve94positions accordingly. In other embodiments, ECU128may also receive data and input from other vehicle and engine sensors when determining an appropriate throttle output or throttle position.

Similar to the operation described inFIG.8, ECU128receives user input from gauge166or operator inputs120, and prevents mode changes via interlocks at step168, makes a throttle mode determination at step170, and outputs necessary throttle commands at step172. However, in this embodiment, ECU128, as part of the electronic throttle-control system, determines throttle modes and specific throttle commands, at least in part, based on additional system controls.

More specifically, in this embodiment of a control method and system, such system controls include vehicle speed-limit throttle control176, geofencing control178, user-mode lockout180and user passcode control182. Such controls may be used to limit performance and speed of snowmobile10, including limiting access to high-performance throttle modes, provide passcode protection for inexperienced operators, and limit geographical use via geofencing.

Control of speed-limits may be implement with vehicle speed-limit throttle control176. In an embodiment, an operator, which may be a parent or adult, for example, may interact with operator inputs120to enter a desired speed-limit control, which may be a maximum speed limit. ECU128with speed-limit throttle control176saves the selected speed limit input in a memory, monitors snowmobile10ground speed with vehicle-speed sensor134, and electronically limits a position of throttle valves94to maintain a speed at or below the selected speed.

In an embodiment, to implement a vehicle speed limit as described above, a passcode is required, as indicated by user passcode control182. In one such embodiment, a passcode must be entered by an operator via operator inputs120or gauge control166, before limitation on vehicle speed may be entered, and/or before a speed limitation may be removed. As such, a parent, owner or other responsible person may use the passcode to ensure snowmobile10with a potentially inexperienced operator, or any other operator, does not exceed the selected speed limit.

User mode lockout control180allows an operator to define a user profile, which may include the functionality of enabling or disabling one or more available throttle-control modes. For example, a performance-limited youth user mode may be defined, and a performance-enhanced or race-oriented mode may be disabled by an operator interacting with user inputs120. In an embodiment, ECU128causes throttle-control modes to be displayed at gauge166or display126, such that the operator may view and select those throttle-control modes to be enabled or disabled for a particular user or operator profile. In an embodiment, the operator may be required to input a passcode to make changes to change user or throttle modes.

Geofencing control178may be included to create a virtual geographic fence or boundary, within which, operation of all or some functions of snowmobile10is available to an operator. However, outside the virtual boundary, operation is restricted. In one such embodiment, geofence boundaries may be entered via operator inputs120, defining an area in which an inexperienced or youthful operator may operate snowmobile10. Outside the defined boundaries, however, operation of snowmobile10may be restricted to low speed limits, to particular modes, or to even cease operation.

Embodiments of speed-limit throttle control176, geofencing control178, user-mode lockout180and user passcode control182may comprise dedicated hardware components and one or more software algorithms stored in memory associated with ECU128, and executed by a processor of ECU128, or a processor in communication with ECU128.

Referring toFIGS.10and11, embodiments of a low-flow start-and-idle throttle control process, and a high-flow start-and-idle throttle-control process for a 2-stroke snowmobile10, are respectively depicted.

Referring specifically to the graph ofFIG.10, the x axis or abscissa indicates time and the y axis or ordinate indicates three quantities: engine speed ES (solid line), voltage V (long-short dashed line) and throttle position TP (dashed line).

Engine speed ES may be measured in RPMs, as detected by engine-speed sensor140and communicated to ECU128.

Voltage V is a voltage generated by an electrical system of snowmobile10, and specifically from a power-generating device of the electrical system, such as a magneto or alternator. In an embodiment, snowmobile10does not include a battery or electric motor starter, but rather, includes a pull cord or rope operable to rotate engine50crankshaft and magneto (or other electrical-generating component). Pulling the cord rotates the crankshaft and magneto, generating power, which may be measured in generated voltage V. In some embodiments, 2-stroke snowmobile10may include a battery powering a starter motor, which in turn rotates the crankshaft and magneto, thereby generating voltage V.

Throttle position TP corresponds to a position of throttle valves94, ranging from a closed or minimum-air flow position to a fully-open or maximum air-flow position, and positions therebetween. Throttle position TP may be indicated or measured as a percentage of a fully-open position, such as a 0% open position to a 100% open position.

At time T0, 2-stroke engine50is not yet started or operating; throttle position TP is closed, i.e., throttle valves94are in a fully-closed or minimal air-flow position, or at a 0% open position; engine speed ES is zero; and voltage V is zero.

Generally, throttle position TP is determined and controlled by electronic throttle-control system88, including ECU128. However, until ECU128and system88is sufficiently powered, throttle position TP is not actively controlled. In this low-flow start embodiment, throttle position TP is initially closed, pending actuation by throttle-valve actuator96as controlled by ECU128.

At time T1, an operator initiates an engine-start sequence, such as by pulling a start cord or depressing a start button causing a battery to power a starter motor of snowmobile50. Initiating the engine-start sequence causes pistons, crankshaft, magneto or alternator, of 2-stroke, internal-combustion engine50to rotate. As such, engine speed ES begins to increase at time T1.

At time T2, rotation of engine50generates sufficient power such that voltage V rises above 0 volts to a threshold voltage V1. In an embodiment, voltage V2at time T3is sufficient to turn on an H-bridge electronic circuit of the electrical-generation system of snowmobile10, such that throttle-valve actuator96is sufficiently powered to begin opening throttle valves94.

After time T2, and as time approaches T3, engine50rotation continues as a result of initiation of the engine start sequence. Voltage V rises above V1, while engine speed ES also continues to increase.

At time T3, the generated power and corresponding voltage is sufficient to allow normal electrical operations, such that ECU128commands throttle position TP to increase rapidly through TP1up to TP2at time T4.

At time T4, voltage V is near a maximum voltage V3as engines speed increases. Throttle position TP is at TP2, which is above a necessary air flow for engine idle. Electronic throttle-control system88with ECU128initiates an idle control sequence to change throttle position TP to a position appropriate for engine idle. As such, electronic throttle-control system88with ECU128processes engine sensor inputs, such as those described above, and begins to close throttle valves94. i.e., changes the throttle position to approach TP1in the time interval of T4to T5. Initially increasing throttle position TP to TP2to allow for relatively high air flow, followed by reducing air flow at TP1, allows the engine speed to rise above idle speed and then settle to the target so that it can more effectively burn the fuel used for the starting event to reduce smoke, improve idle consistency and minimize spark plug fouling.

At time T5, engine speed ES is at a predetermined idle speed, which in an embodiment may be in a range of 1,000 RPM to 1.500 RPM. Voltage V is in a steady state at V3. From time T5to T6, electronic throttle-control system88with ECU128holds throttle position TP at idle position TP1.

At time T6, electronic throttle-control system88with ECU128initializes an “idle” proportional-integral-derivative (PID) control loop, which is then actively executed starting at time T6and extending thereafter to time T7and beyond, and until an operator or ECU128calls for operation above engine idle.

Consequently.FIG.10depicts a low-flow start-up sequence for snowmobile10with a 2-stroke internal-combustion engine that includes the steps of: ECU128commanding a throttle position of throttle valve94at a first, low-flow or minimal flow position; causing rotation of an electricity-generating device of the 2-stroke engine50, such as rotation of a magneto or rotor of an alternator; generating a voltage produced by rotation of the electricity-generating device; when the generated voltage exceeds a predetermined voltage threshold, commanding opening throttle valve94to a throttle position that is greater than a throttle idle position, such that an effective area of throttle valve94is greater than an effective area when in the minimal flow position, and such that air flow through throttle valve94is increased and greater than air flow needed for an engine idle state; closing throttle valve94to decrease an effective valve area and corresponding air flow, to an idle-state effective valve area and air flow; controlling a throttle valve94position to maintain a predetermined engine idle speed.

Referring toFIG.11, a high-flow start-up sequence for snowmobile10with a 2-stroke internal-combustion engine is depicted. The start-up sequence ofFIG.11is similar to the start-up sequence ofFIG.10, though the initial throttle positions are markedly different. In the embodiment ofFIG.10, at start up, the one or more throttle valves94are initially at a minimal air flow or minimal valve effective-area position TP0, followed by throttle valves94being ramped up or opened to a high-flow position, TP2, followed by closing valves94to an idle position. In contrast, in the embodiment ofFIG.11, throttle valve position TP is initially at a relatively high-flow, or large valve-effective-area position TP2.

In an embodiment, throttle valves94may be held in throttle position TP2by a biasing spring, then held in that position until time T4when voltage V has surpassed threshold voltage V1, and initialization of the PID idle loop is initiated. At time T4, electronic throttle-valve control system88with ECU128commands actuation of throttle valves94, which counters the spring bias, and actuates throttle valves94to an idle throttle position TP1, which is then maintained.

Referring toFIG.12, a chart depicting throttle input and throttle output (throttle position) vs. time is depicted. Time is represented on the x axis, or abscissa, and ranges from time T0to T6, while throttle input and throttle output are represented by the y axis or abscissa, ranging from TP0to TP7, which corresponds to 0% throttle output (minimum air flow and maximum open position of throttle valves94) to 100% throttle output (minimum air flow and maximum open position of throttle valves94).

The time period of T0to T1represents a star-up time period; time period T1to T2represents a first engine-idle state or control period; time period T2to T3represents a first position-based throttle control period, where an operator selects or inputs a throttle position and a throttle output or actual throttle position is determined by electronic throttle-control system88and ECU128; time period T3to T4represents a fixed-state output; time period T4to T5represents a second position-based throttle control period; and time period T5to T6represents a second engine-idle control period.

The dashed line indicates throttle input, corresponding generally to an amount of throttle requested by an operator of snowmobile10operating throttle-input device80. In an embodiment, throttle input corresponds to a selected position of throttle-input device80, which also corresponds to a detected mechanical position of throttle-input device80as sensed or detected by throttle-input sensor138. In one such embodiment, throttle input may range from a minimum input of zero, to a maximum requested throttle input of 100%. In an embodiment, and as depicted inFIG.12, throttle input ranges from a throttle neutral position TP0, or 0% throttle input, to a maximum throttle input of TP7, or 100% throttle. The dashed-line throttle input set may also correspond to a first set of throttle outputs, such that a 1:1 relationship exists between throttle input and throttle output for time periods T2and beyond (after start up). For example, a throttle input of 50% of maximum may correspond to a throttle output of 50% of maximum throttle, or 100% throttle input corresponds to 100% throttle output.

The solid line and the long-dash-short-dash line depicted inFIG.12each correspond to a range of actual throttle positions TP. As described with respect toFIGS.10-11, each throttle position TP corresponds to, or represents, a particular throttle valve94position as determined by electronic throttle-control system88. The various throttle positions TP may also be referred to as a “throttle output” as each throttle position is a result of a requested throttle input. Consequently, the chart ofFIG.12refers to “throttle inputs” and “throttle outputs.”

The solid line represents a second set of throttle positions TP corresponding to a race throttle mode and a second throttle-control translation map, while the long-dash-short-dash line represents a third set of throttle positions TP corresponding to a limited throttle mode and a third throttle-control translation map. The second and third sets of throttle positions TP are determined, at least in part, by the throttle input. Generally, for the second set of throttle positions TP corresponding to a race throttle mode, each throttle position TP is equal to, or greater than a corresponding throttle input, and for the third set of throttle positions TP corresponding to the limited throttle mode, each throttle position TP is equal to, or less than, a corresponding throttle input.

In operation, and as will be described further below, ECU128receives throttle input in the form of data or a signal from throttle-input sensor138, based on operator interaction with throttle-input device80. ECU128then translates the received throttle input to a throttle body command through one of a plurality of throttle-control translation maps that are used to alter the performance characteristics of engine50. In an embodiment, the plurality of translation maps are used to alter the feel of snowmobile10by controlling engine air flow through throttle valves94and/or controlling a rate at which throttle is applied relative to the operator's input. For example, a reduced maximum throttle opening with a slower ramp between input and output command can serve as an operational mode for entry level or experienced riders, such as the “limited” throttle mode depicted by the long-dash-short-dash line ofFIG.12. A 1:1 translation between input and output can serve as an operational mode for more experienced riders (dashed line). Furthermore, a map in which the throttle opens further than the operator commands via throttle-input device80at certain operating conditions can be used for racing or mountain applications to enhance throttle response, i.e., the “race” throttle mode corresponding to the solid line set of throttle positions TP ofFIG.12.

In the embodiment depicted, throttle input during the start-up period of T0to T1is relatively constant at TP0. During the first idle state period of time T1to T2, throttle input is increased to TP1, which is an idle input. In an embodiment, during the start-up period and first idle period, throttle output may be predetermined, with little or no consideration of an actual throttle input so as to initialize operation of snowmobile10and engine50at start up. More specifically, and in this embodiment, from T0to T2, all actual throttle positions TP for each available throttle mode may be substantially the same. In the embodiment ofFIG.12, throttle positions TP during start-up from T0to T1and during idle from T1to T2are the same as the “low-flow” start start-up sequence ofFIG.10(where time period T0to T2ofFIG.12corresponds to time period T0to T7ofFIG.10). In other embodiments, a high-flow start-up control sequence, such as the one depicted and described with respect toFIG.11may be utilized.

After engine idle is established, and after time T2, throttle output is determined based on the position of throttle-input device80and a corresponding throttle-control translation map, e.g., the map for 1:1 map, or limited mode. As such, throttle output during time period T2to T3is referred to as “position-based” throttle control. Between time T2and time T3, throttle input and throttle position TP corresponding to a 1:1 throttle-control translation map increases from throttle position TP1, to TP6at time T3.

However, unlike the first set of throttle positions corresponding to selection of the 1:1 throttle map, when an operator selects the second or race map, electronic throttle-control system88and ECU128controls throttle valves94to exceed an operator-requested throttle input. For example, when throttle input is at approximately 50%, which in a 1:1 mapping would correspond to a 50% throttle output at throttle position TP4, the throttle output is approximately 75% at throttle position TP5. In other words, the throttle output at TP5is 1.5 times the throttle input of TP4, i.e., a 1:1.5 translation. A difference between throttle outputs for throttle input/1:1 map as compared to the race map is measured as Δ1. In an embodiment, this throttle-output difference Δ1may vary with throttle input, such that a non-linear relationship between throttle input and throttle output is defined by the second or race map, as depicted. As will be understood by those of ordinary skill, a relationship between throttle input and throttle output may be defined in many different ways by a throttle-control translational map.

Conversely, when an operator selects the third or limited map, electronic throttle-control system88and ECU128control throttle valves94to be below an operator-requested throttle input. For example, when throttle input is at approximately 50%, which in a 1:1 mapping would correspond to a 50% throttle output at throttle position TP4, the throttle output is approximately 35% at throttle position TP3. In other words, the throttle output at TP3is 0.7 times the throttle input of TP4, i.e., a 1.33:1 translation. As can be seen by the long-dash-short-dash line corresponding to the third and limited translational map, throttle output is less than throttle input for most requested throttle inputs.

At time T3, throttle input is nearly at a maximum input, and throttle position demand is at TP6for the given map selection. Shortly after time T3, throttle input is at maximum input, or 100%, and throttle-input device80is held by an operator at a mechanical stop. Throttle position TP is controlled by a fixed-duty cycle. From approximately time T3to time T4, throttle control is no longer position based since the throttle input is at the maximum setting.

Rather, throttle control is now based on predetermined parameters saved in electronic throttle-control system88, such as maximum throttle position TP7.

At time T4, throttle input is at a maximum and throttle position TP still at TP7. After time T4, throttle input decreases below a maximum throttle input based on operator control of throttle-input device80, as sensed by throttle-input sensor138, and as communicated to ECU128. Consequently, from time T4to time T5, throttle control is once again position based, i.e., based upon a position of throttle-input device80.

At time T5, a second idle PID control loop is implemented, with throttle output TP being set to idle throttle output TP1.

Referring to the flow charts ofFIGS.13and14, additional detail regarding throttle control is depicted and described.

Referring specifically to the flow chart ofFIG.13, an embodiment of a process200for controlling a throttle for a 2-stroke snowmobile engine50is depicted and described. At step202, a processor of ECU128is initialized. At step204, electronic throttle-control system88determines whether a voltage V generated by snowmobile10at start-up (as described above) is greater than a predetermined threshold voltage. Referring also toFIG.10, in an embodiment, the predetermined threshold voltage may be voltage V1. If generated voltage V is not above the predetermined threshold voltage, then the process reverts back to step202.

If generated voltage V is at or above the predetermined threshold voltage, then the power supplied by the stator is sufficiently high to provide the necessary current to throttle valve actuator96to ensure position accuracy and no loss of other vehicle function occurs due to voltage drops. Consequently, sufficient power will be available to continue the start-up process, then at step206, actual engine speed ES, which may be measured in RPMs, is compared to a first predetermined engine-speed threshold, ES1. In an embodiment, engine speed is monitored by ECU128, which receives input from engine-speed sensor140(seeFIG.7). If the actual engine-speed ES is greater than the predetermined engine-speed threshold ES1, then the process proceeds to step208, and ECU128actuates throttle valve actuator96to set throttle valves94to a predetermined throttle start position TP. Referring also toFIG.10, in a low-flow start-up control sequence, this predetermined throttle start position refers to throttle position TP0, which in an embodiment may be less than TP1. In a high-flow start up control sequence, such as the one described inFIG.11, a predetermined throttle start position TP may be greater than throttle position TP1, such as TP2. In an embodiment corresponding toFIG.10with a low-flow start, ECU128and electronic throttle-control system88ramp up or open up throttle position TP from TP0to TP2, then reduce to TP1for idle, as engine speed ES increases.

If the engine speed ES is not above the predetermined engine-speed threshold ES1, then monitoring of engine speed ES continues.

After setting throttle position TP to a throttle start position, in an embodiment, electronic throttle-control system88initiates a timer hold sequence, such that at step210a timer is started. At step212, if the tinier time is less than a predetermined hold time, then the timer hold sequence continues, then when the timer is equal to the predetermined hold time, at step214, engine speed ES, which may be measured in RPM, is compared to a second predetermined engine-speed threshold, ES2. In an embodiment, second engine-speed threshold ES2is greater than first engine-speed threshold ES1.

If engine speed ES is greater than second engine-speed threshold ES2, then at step216, electronic throttle-control system88begins controlling throttle position TP in a “normal” operating mode, which may be a position-based operating mode as described above.

However, if engine speed ES is not greater than second engine-speed threshold ES2, then at step218, electronic throttle-control system88decays or reduces that throttle position TP to close down valves94until engine speed ES increases, and electronic throttle-control system88begins controlling throttle position TP in a “normal” operating mode, which may be a position-based operating mode as described above.

Referring to the flow chart ofFIG.14, which includesFIGS.14A to14C, a method240for post-start-up throttle control by electronic throttle-control system88is depicted.

Referring specifically toFIG.14A, at step242, ECU128determines whether electronic throttle-control system88is enabled. If enabled, at step246, a throttle position TP as demanded by ECU128based on throttle input (“TPS Demand”) is compared to a predetermined idle throttle position (“Idle TPS Conditional”) and engine speed ES is compared to a predetermined engine-idle speed (“Idle Speed Conditional”). When the ECU-demanded throttle position TP is less than the predetermined idle throttle position and engine speed ES is less than the predetermine engine-idle speed, then at step248, ECU128determines whether an electronic throttle control (ETC) idle PID control loop is enabled.

When the electronic throttle control (ETC) idle PID control loop is not enabled, then electronic throttle-control system88controls throttle valve actuator96and throttle valves94according to a fixed-state output based on a throttle-closed duty cycle. In other words, the throttle position is set to a fixed position which is substantially closed.

When the electronic throttle control (ETC) idle PID control loop is enabled, then after an idle control transition time, such as described at steps210and212of the method ofFIG.12, electronic throttle-control system88controls throttle valve actuator96and throttle valves94according to an idle PID control loop executed by ECU128and electronic throttle-control system88.

At step246, when the ECU-demanded throttle position TP is not less than the predetermined idle throttle position and engine speed ES is not less than the predetermine engine-idle speed, then at254, a throttle-control translation map (“throttle map”) is selected. As described above, a throttle map describes a relationship between a plurality of throttle-inputs and a plurality of corresponding throttle outputs. A throttle may be selected by an operator of snowmobile10interacting with operator inputs120, which is them implemented by ECU128, or may be selected by ECU128based on operator input, prior selected maps, a predetermined stored default throttle map, saved throttle-map selection history, and/or other factors.

At step256, a throttle position TP1is set by electronic throttle-control system88based at least in part on the selected throttle map.

At step258, ECU128receives input from gear sensor136(see also,FIG.7) to determine whether a gear position of snowmobile10is in a low position. When the gear position is in the low position, at step260, the throttle position TP is set to a throttle position corresponding to a low-gear throttle position, which may be different than the throttle position TP as set at step256before the low-gear check; and when the gear position is not in the low position, the throttle position remains as set at step256.

At step264, a series of faults are checked by ECU128. If any faults are detected, then at step266, throttle position TP is set to a predetermined throttle position setting based on the particular fault detected. ECU128may be configured to determine whether any of a number of faults relating to engine50or other snowmobile10systems have occurred. Such faults may include: low ECU voltage, low or high engine temperature, problematic spark/detonation, oil pump operation or pressure, unrealistic barometric pressure, unrealistic outside air temperature, high exhaust temperature, low fuel pressure, riding with brakes on, and other faults.

Referring also toFIG.14B, if no faults are detected, then at step268, ECU128receives vehicle ground speed data from vehicle-speed sensor134, and determines whether a detected ground speed is greater than a ground-speed limit, and when the gear position is also detected as being in a low position, then at step270, changing the throttle position TP, i.e., TPS Demand, to reduce air flow through throttle valves94so as to achieve a target maximum low-gear ground speed for snowmobile10.

Otherwise, at step272, ECU determines whether the vehicle ground speed is greater than a predetermined allowable ground speed. When the vehicle ground speed is greater than the predetermined allowable ground speed, then at step274, ECU128and electronic throttle-control system88changes the throttle valve position to reduce air flow to achieve a target maximum allowable vehicle ground speed. In an embodiment, the target allowable vehicle ground speed may be controlled by an operator interacting with operator inputs120, which may include gauge166.

When the vehicle ground speed is not greater than the predetermined allowable ground speed, then at step276, ECU128compares the current TPS Demand or throttle position TP to a throttle position maximum threshold. When the ECU demanded throttle position is greater than a maximum throttle position threshold. ECU128and electronic throttle-control system88controls the throttle according to a fixed state pout control based on a throttle-open duty cycle. In other words, when an operator actuates throttle-input device80to request maximum throttle, and ECU128determines a corresponding throttle position TP, if that demanded throttle position exceeds a predetermined maximum throttle position, then electronic throttle-control system88and ECU128set the throttle position according to a predetermined fixed position corresponding to an open position of throttle valves94.

At step280, when TPS Demand is not greater than the TPS Demand maximum threshold, then ECU128determines whether an actual throttle valve position detected by throttle-position sensor142is greater than the throttle position demanded or determined by ECU128plus a hysteresis factor, for a predetermined period of time, and also whether a throttle-safety switch is active for a predetermined period of time. If yes, this indicates a fault in engine throttle control, such as a throttle valve94being stuck in an open position, and fuel and engine ignition are cut so as to cease operation of engine50.

Referring also toFIG.14c, when such conditions are not met at step280, then at step284, a throttle safety switch is checked by ECU128. If the throttle safety switch is active, meaning a throttle fault, is active for a predetermined threshold period, then at step286, fuel flow and ignition are cut, and in some embodiments, a code indicated that a throttle set position was not achieved may be stored and/or displayed.

When ECU128does not detect the safety switch conditions of step284, then at step288, another check by ECU128is conducted. At step288, ECU128determines whether engine speed ES is above a predetermined maximum engine speed. If it is, then at step290, ECU128and electronic throttle-control system288reduces throttle, i.e., changes a throttle position TP to reduce air flow, so as to achieve the predetermined target maximum engine speed.

When engine speed ES is not above the predetermined maximum engine speed, then at step292, ECU128determines whether the demanded throttle position is greater than an allowable maximum throttle demand. If not, at step296, the throttle demanded or throttle position TP determined by ECU128is left unchanged. However, if the demanded throttle position is above the maximum, then at step294, electronic throttle-control system88controls and reduces the throttle position such that the throttle position corresponds to the predetermine maximum throttle position.

Following either of steps294or296, the process reverts to step256(FIG.14A), where electronic throttle-control system88continues to monitor and set the throttle position as described above with respect toFIGS.14A-14C.

Referring toFIG.15, an engine-idle PID controller and control loop method350for electronic throttle control implemented by electronic throttle-control system88is depicted and described. Engine-idle PID loop350embodies methods of controlling engine50idle at or near the idle set point, which includes methods of controlling electronic throttle-control system88to dynamically position throttle valves94to control air flow through throttle body90. Executable instructions for the method steps may be saved in a memory of electronic throttle-control system88, including ECU128, with a processor executing the saved instructions.

As will be understood by one of ordinary skill, engine-idle speed is the process variable to be measured and controlled. Consequently, engine-idle speed target or set-point value356, which may be defined in engine RPM, is input into comparator354. Actual or sensed engine-speed is also input into comparator354, although initially, a first or initial engine-idle speed at step358is input for the first calculation. In an embodiment, sensed engine-idle speed at step356is transmitted from engine-speed sensor140and received by ECU128for processing as part of the idle PID control loop.

Comparator354compares sensed engine-idle speed with the target engine-idle speed352, and outputs engine-idle speed error360. The function of comparator354may be performed by a processor of ECU128, as will be understood by one of ordinary skill in the art.

Proportional, integral and differential gains362,364and366are determined based on the respective proportional, integral and differential components of error360, then summed at step368to determine a corrected throttle position at step370which is intended to achieve the target engine-idle speed. At step372, the corrected throttle position is compared to a maximum idle throttle position.

At step374, when the corrected throttle position is greater than a predetermined throttle position that achieves a maximum engine-idle speed, then the throttle position is set to the throttle position to cause maximum engine-idle speed in ECU128, and electronic throttle-control system88adjusts a throttle position to the throttle position to achieve maximum engine-idle speed.

At step376, when the corrected throttle position is not greater than a predetermined throttle position that achieves a maximum engine-idle speed, then the throttle position remains set to the corrected throttle position and electronic throttle-control system88adjusts a throttle position to the corrected throttle position.

Engine-speed is checked again at step356, and analyzed by comparator354, and the loop analysis is repeated.

The following clauses illustrate the subject matter described herein.

Clause 1. An electronic throttle control system that includes: an electronic control unit (ECU) including a processor and a memory device storing at least one throttle-control translation map; a throttle-input sensor in electrical communication with the ECU and configured to sense an input from an operator-actuated throttle device; and a 2-stroke internal-combustion engine. The 2-stroke internal-combustion engine may include: an electronic throttle-valve actuator in electrical connection with the ECU and having an actuator motor and gear train; a throttle body for controlling airflow to one or more combustion chambers of the 2-stroke internal-combustion engine, the throttle body defining a first throttle bore and a second throttle bore; a first throttle valve in the first throttle bore and a second throttle valve in the second throttle bore; and a throttle valve control shaft coupled to the first throttle valve and the second throttle valve, and to the gear train, such that movement of the actuator motor and gear train causes the throttle valve control shaft to rotate and move the first and second throttle valves; a throttle-position sensor in electrical communication with the ECU and configured to sense an actual position of the first and second throttle valves. Further, the ECU may be configured to receive a signal representing a throttle-position input from the throttle-input sensor and to determine a throttle-demand position corresponding to a position of the first throttle valve in the first throttle bore and a position of the second throttle valve in the second throttle bore, based on the throttle-position input and throttle-control translation map.

Clause 2. The electronic throttle control system of clause 1, further comprising an engine-speed sensor in electrical communication with the ECU and configured to sense a speed of the 2-stroke internal-combustion engine.

Clause 3. The electronic throttle control system of clause 2, wherein the ECU is configured to control the actuator during a start mode to decrease the throttle output when a sensed speed of the 2-stroke internal-combustion engine is less than an engine-speed threshold.

Clause 4. The electronic throttle control system of clause 1, wherein the ECU is configured to limit a throttle-demand position based on ground speed, engine speed, and/or user-selected limit parameters or fault-state limit positions.

Clause 5. The electronic throttle control system of clause 1, wherein a bore diameter of the first throttle bore is substantially the same as a bore diameter of the second throttle bore and a throttle-bore pitch of the first throttle bore to the second throttle bore is greater than twice the bore diameter.

Clause 6. The electronic throttle control system of clause 5, wherein the bore pitch is in a range of 100 mm to 200 mm.

Clause 7. The electronic throttle control system of clause 6, wherein the bore pitch is in a range of 130 mm to 140 mm.

Clause 8. A snowmobile, comprising the electronic throttle control system of any of clauses 1-7.

Clause 9. Another embodiment of the disclosure is a method of controlling a starting mode of snowmobile having an electronic-control unit (ECU) with a processor, and a 2-stroke combustion engine with an electronic throttle body having a first throttle valve, a second throttle valve, a throttle-position sensor, and an actuator for actuating the first and second throttle valves. The method includes the steps of: determining whether an electronic throttle body drive-voltage generated by the 2-stroke combustion engine is above a threshold voltage; determining whether an engine speed of the 2-stroke combustion engine is above a first engine-speed threshold; when the generated voltage is at or above the critical threshold voltage and the speed of the 2-stroke combustion engine is above a threshold engine-speed threshold, setting a throttle position of the first throttle valve and the second throttle valve to a neutral-throttle position: after a predetermined period of time, determine whether the engine speed is greater than a second engine-speed threshold; and when the engine speed is greater than the second engine-speed threshold, changing a position of the first throttle valve and the second throttle valve from the neutral-throttle position to an initial throttle-operating position, by controlling the actuator with the processor of the ECU.

Clause 10. The method of clause 9, further comprising initializing the processor of the ECU.

Clause 11. The method of clause 9, wherein in the neutral-throttle position, an effective area of each of the first throttle valve and the second throttle valve is greater than a respective effective area of the first throttle valve and the second throttle valve in the initial throttle-operating position.

Clause 12. The method of clause 11, further comprising setting a position of the first throttle valve and the second throttle valve to the neutral-throttle position using a spring to bias the first and second throttle valves.

Clause 13. The method of clause 12, wherein changing a position of the first throttle valve and the second throttle valve from the neutral position to an initial throttle-operating position comprises the processor controlling the actuator to move the first throttle valve and the second throttle valve to the initial throttle-operating position in opposition to a force exerted by the biasing spring.

Clause 14. The method of clause 9, wherein in the neutral-throttle position, an effective area of each of the first throttle valve and the second throttle valve is less than a respective effective area of each of the first throttle valve and the second throttle valve in the initial throttle-operating position, and changing a position of the first throttle valve and the second throttle valve from the neutral-throttle position to the initial throttle-operating position includes further increasing the effective area of the first throttle valve and the second throttle valve while the voltage is increasing and below the critical voltage threshold.

Clause 15. Yet another embodiment of the disclosure includes a method of controlling a snowmobile having an electronic-control unit (ECU) with a processor, a memory storing one or more throttle-control translation maps, and a 2-stroke combustion engine with an electronic throttle body having a first throttle valve, a second throttle valve, a throttle-position sensor, an actuator for actuating the first and second throttle valves, and an engine-speed sensor. In this embodiment, the method includes: storing a predetermined idle-speed throttle-valve position and the one or more throttle-control translation maps in the memory; determining with the ECU a throttle-demand valve position, the throttle-demand valve position corresponding to a throttle-demand valve effective area of the first and second throttle valves; comparing the throttle-demand valve position to the predetermined idle-speed throttle-valve position; receiving at the ECU, an output of the engine-speed sensor indicating an actual engine speed of the 2-stroke internal-combustion engine; comparing the actual engine speed with a predetermined engine-idle speed; selecting a throttle-control translation map stored in the memory when the throttle-demand position effective flow area is greater than the predetermined idle-speed throttle position effective flow area and when the actual engine speed is greater than the predetermined idle engine speed; controlling the actuator using the ECU to set a first position of the first throttle valve in the first throttle bore and a first position of the second throttle valve in the second throttle bore based on the selected throttle-control translation map: determining whether an engine fault is present and controlling the actuator using the ECU to set a second position of the first throttle valve in the first throttle bore and a second position of the second throttle valve in the second throttle bore when a fault is present; and determining whether a ground speed or engine speed exceeds a maximum speed limit and controlling the actuator using the ECU to set a third position of the first throttle valve in the first throttle bore and a third position of the second throttle valve in the second throttle bore to reduce ground speed or engine speed to be less than the maximum speed limit.

Clause 16. The method of clause 15, further comprising controlling the first and second throttle valves to maintain an engine idle speed when the throttle-demand position effective flow area is less than the predetermined idle-speed throttle position effective flow area and when the actual engine speed is less than the predetermined idle engine speed.

Clause 17. The method of clause 15, further comprising determining whether a gear position of the snowmobile is a low-gear position, and setting a position of the first and second throttle valves to a low-gear throttle position when the gear position of the snowmobile is a low-gear position.

Clause 18. The method of clause 15, further comprising setting a position of the first and second throttle valves to a fixed-state throttle position when a throttle-demand effective flow area exceeds a throttle-demand maximum threshold.

Clause 19. The method of clause 15, further comprising comparing an actual throttle position of the first and second throttle valves as indicated by the throttle-position sensor to a throttle-demand position, and causing the ECU to cease engine fuel flow and/or ignition when the actual throttle position effective flow area is greater than the throttle-demand position effective flow area for a predetermined period of time.

Clause 20. The method of clause 15, further comprising determining, when the snowmobile includes a safety switch, that the safety switch is active for greater than a predetermined period of time, and in response, causing the ECU to cease engine fuel injection and/or ignition.

Clause 21. The electronic throttle control system of clause 1, wherein the bore diameter is in a range of about 40 mm to about 60 mm.

The embodiments above are intended to be illustrative and not limiting. Additional embodiments are within the claims. In addition, although aspects of the present invention have been described with reference to particular embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention, as defined by the claims.

Persons of ordinary skill in the relevant arts will recognize that the invention may comprise fewer features than illustrated in any individual embodiment described above. The embodiments described herein are not meant to be an exhaustive presentation of the ways in which the various features of the invention may be combined. Accordingly, the embodiments are not mutually exclusive combinations of features; rather, the invention may comprise a combination of different individual features selected from different individual embodiments, as understood by persons of ordinary skill in the art.