Patent Description:
Grass mowing machines such as riding greensmowers, trim and surround mowers and fairway mowers may include internal combustion engines to power a hydrostatic traction drive circuit and hydraulic mowing circuit. The internal combustion engine may produce maximum power at maximum engine speed, but it may be desirable to run the engine at lower speeds to achieve better economy or noise reduction. Power requirements needed to maintain the desired ground speed may increase in sloping terrain or other conditions. Additionally, power requirements for hydraulic mowing circuits may increase in wet grass, verticutting or other conditions.

An engine speed control system for a mower is needed that can run at low power in economy or low noise modes, but can increase power if the mower encounters terrain or other circumstances with greater power requirements. An engine speed control system is needed that allows operators to only run the engine at speeds required for the work being done, and can adapt the engine speed when necessary. An engine speed control system is needed that reduces fuel consumption and noise levels experienced around the mower. An engine speed control system is needed that does not require sensors to measure hydraulic pressure of the hydrostatic traction drive circuit and/or hydraulic mowing circuit to determine power requirements.

<CIT> shows an electronic engine speed control system for a grass mowing machine powered by an internal combustion engine includes a microcontroller providing an output signal to an engine speed actuator for the engine, a pedal position sensor connected to a foot pedal and providing a voltage input signal to the microcontroller based on the position of the foot pedal, a PTO clutch switch or sensor providing a signal input to the microcontroller indicating if a PTO clutch is engaged, and a lever position sensor connected to a hand lever and having a range of positions including an Automatic mode position and a plurality of Manual mode positions.

An adaptive engine speed control method for a grass mowing machine according to claim <NUM> is provided, with an internal combustion engine providing power for an engine operating mode of a grass mowing machine within a pedal based engine speed control range. A controller commands the engine to run at an engine speed above the pedal based engine speed control range based on a traction feedback signal from a hydrostatic traction drive circuit, for an adaptive engine speed control range above the pedal based engine speed control range.

The adaptive engine speed control system allows the mower to run at low power in economy or low noise modes, but can increase power if the mower encounters terrain or other circumstances with greater power requirements. The system allows operators to only run the engine at speeds required for the work being done, and can adapt the engine speed automatically based on need. The system also helps reduce fuel consumption and noise levels experienced around the mower, thus improving operator comfort and reducing noise pollution, but does not require sensors to measure hydraulic pressure of the hydrostatic traction drive circuit and/or hydraulic mowing circuit to determine power requirements.

In an embodiment shown in <FIG>, adaptive engine speed control (AESC) system <NUM> may be on riding greensmower <NUM> having three or more reel cutting units, or on a trim and surround mower or fairway mower with multiple reel cutting units. The mower may be powered by internal combustion engine <NUM>, and may have a hydrostatic traction drive circuit <NUM>, and/or hydraulic mowing circuit <NUM>, and a hydraulic lift and lower circuit for the cutting units. The AESC system may be included as software in vehicle controller <NUM> that provides PID control to the engine, also referred to as a PID controller.

In an embodiment of the invention shown in <FIG>, AESC system <NUM> may provide adaptive engine speed control to the internal combustion engine based on traction feedback output percent <NUM> from the hydrostatic traction drive circuit, PID control <NUM>, and pedal based engine speed <NUM>. Each of the traction feedback output and pedal based engine speed which may be expressed as a percent. The AESC system also may use other information available to the PID controller including enable status, speed lock/cruise status, actual vehicle speed, desired vehicle speed, PTO switch position, maximum pedal based engine speed percent, minimum pedal based engine speed percent, pedal based engine speed percent, maximum adaptive engine speed percent, and traction feed forward output percent.

In an embodiment of the invention shown in <FIG>, the AESC system may increase engine speed above a pedal based engine speed control range. For example, the pedal based engine speed control range with the PTO off, for an engine mode designed to provide fuel economy or reduced sound, may be from <NUM> rpm at a pedal position of <NUM>%, up to a maximum of <NUM> rpm at a pedal position of <NUM>%. The AESC system may use the traction feedback output to determine when to increase engine speed above the pedal based engine speed control range to a higher adaptive engine speed control range. For example, the AESC system may increase the engine speed up to <NUM> rpm or higher, which may be a high idle speed.

In the embodiment of <FIG>, the AESC system may be used with an internal combustion engine having one or more engine operating modes and one or more pedal based engine speed control ranges. For example, an economy mode may have a pedal based engine speed control range for transport when the PTO switch is off. Each engine operating mode may have a maximum allowed pedal based engine speed when pedal position is <NUM>%. The AESC system also may be used with one or more engine operating modes having fixed engine speeds, such as <NUM> rpm for mowing when the PTO switch is on. Additionally, the AESC system may be used with engines having cruise control or speed lock features in which a fixed engine speed may be set by the operator.

In the embodiment of <FIG>, the AESC system may command engine speed based on traction feedback output, also referred to as feedback current offset, from the hydrostatic traction drive circuit.

The traction feedback output may be a percent based on load, which may be actual external load the hydrostatic traction drive circuit is experiencing or any variation in system parameters that cause the traction feed forward output to produce less output than desired based on pedal position. The traction feedback output may be the amount of current the controller adds or subtracts from the open loop traction feed forward current to the valves for the hydrostatic wheel motors. In normal conditions, actual vehicle speed may be close to desired vehicle speed. However, if traction drive load changes based on conditions, actual vehicle speed may decrease below the desired vehicle speed based on pedal position. As a result, the traction feedback output adds current to the open loop feed forward current. The AESC system of the present invention uses the traction feedback output to increase engine speed to satisfy power requirements.

In one embodiment, the AESC system may include software logic shown in <FIG>. The AESC system may be enabled in blocks <NUM>-<NUM>. In block <NUM>, the operator may actuate an enable switch or the PID controller may automatically activate the AESC system if the operator selects an engine operating mode that is enabled, such as economy mode, having a maximum allowed pedal based engine speed percent that is limited and is below the maximum adaptive engine speed. In block <NUM>, if the AESC system is not enabled, the output of AESC system, expressed as a percent, may be the same pedal based engine speed.

In one embodiment shown in <FIG>, the AESC system may determine PID reset conditions in blocks <NUM>-<NUM>. For example, if there is a transition observed on the PTO switch, from OFF to ON in block <NUM>, or from ON to OFF in block <NUM>, the PID may be reset in block <NUM>. If the PTO switch is OFF for transport in block <NUM>, and the pedal based engine speed percent reaches or exceeds the maximum pedal based engine speed percent in block <NUM>, the PID may be reset in block <NUM>. Or if the traction feed forward output is zero in block <NUM>, or the cruise control/speed lock is switched from OFF to ON in block <NUM>, the PID may be reset in block <NUM>.

In one embodiment shown in <FIG>, the AESC system may determine the PID input to the engine in blocks <NUM>-<NUM>. If the vehicle is moving forward, the AESC system may use the traction feedback output percent as the adaptive engine speed PID input in block <NUM>. If the vehicle is moving in reverse, the AESC system may use the traction feedback output percent as the adaptive engine speed PID input in block <NUM>, after reversing the sign from negative to positive. The AESC system determines if the vehicle is moving in reverse if the traction feed forward output percent is less than zero in block <NUM>, or if the vehicle speed is less than zero in block <NUM>. Traction feed forward output percent is the open loop signal to the wheel motors of the hydrostatic traction drive circuit, based on pedal input from the operator. Traction feedback output percent is the closed loop feedback output signal. In block <NUM>, the AESC system may filter the adaptive engine speed PID input using a first order low pass filter.

In one embodiment shown in <FIG>, the AESC system may include PID input override logic in blocks <NUM>-<NUM>. For example, the AESC system may preload zero for the integral term of the PID input in block <NUM>, or the previous PID output for the integral term in block <NUM>, or the pedal based engine speed percent for the integral term in block <NUM>. The AESC system also may reset the PID input as zero in block <NUM>. The override logic may be based on the status of the PTO switch (transport or mow) in blocks <NUM>, <NUM> and <NUM>; the status of cruise control or speed lock in block <NUM>; if pedal based engine speed percent has reached or exceeded the maximum engine speed limit percent in block <NUM>; and if the traction feed forward output percent is zero in blocks <NUM> and <NUM>.

In one embodiment shown in <FIG>, the AESC system may provide PID control in blocks <NUM>-<NUM>. In block <NUM>, the AESC system may use the AESC PID input from blocks <NUM>-<NUM>, PID reset from blocks <NUM>-<NUM>, integral preload from blocks <NUM>-<NUM>, and Gain Scheduling, to determine the AESC PID output. Gain Scheduling may dynamically calculate the gain values for the P, I or D terms in the PID over a linear region of the control input. Gain scheduling may be used for a given system if different control efforts may be desired depending on the operating range, and may be achieved by having different gain values in the operating range. Block <NUM> may provide a first order low pass filter, along with a filter override to pass through the unfiltered PID output.

In one embodiment, the AESC system may use mow feedback output percent from the hydraulic mowing circuit to change engine speed. The mow feedback output percent may be the amount of current the PID controller adds or subtracts from feed forward current to the valves for the hydraulic reel motors. The controller may send open loop feed forward current signals to the valves to provide flow rates for desired reel speeds based on speed settings of the cutting units. In normal conditions, actual reel speeds may be close to desired reel speeds. However, if mowing load changes based on conditions, actual reel speed may decrease below the desired reel speed. As a result, the controller may determine the feedback output current offset that must be added or subtracted from the feed forward current for the desired reel speed. The adaptive engine speed control system may use the feedback current offset to estimate if and how much to increase engine speed to satisfy power requirements.

In one embodiment, the AESC system may automatically increase engine speed above the pedal based engine speed control range if increased load is detected for the hydrostatic traction drive circuit and/or hydraulic mow circuit. The AESC system may use the feedback current output from the hydrostatic traction drive circuit, and/or the feedback current output signal from the hydraulic mowing circuit, to detect and estimate the increased load and engine speed. The AESC may provide PID output to increase engine speed above the maximum allowed pedal based speed if there is an increase in power demand due to an increase in tractive load and/or mowing load. The AESC system may sum the estimated power requirements of the hydrostatic traction drive circuit and hydraulic mowing circuit, and use the total to change the engine speed to meet the power requirements of the vehicle. The AESC system may eliminate the need and cost for additional sensors that measure hydraulic pressure of the hydrostatic traction drive circuit and/or hydraulic mow circuit.

Claim 1:
An adaptive engine speed control method for a grass mowing machine (<NUM>), the machine (<NUM>) comprising:
an internal combustion engine (<NUM>); and
a controller (<NUM>) commanding the engine (<NUM>),
wherein the engine (<NUM>) is providing power for an engine operating mode within a pedal
based engine speed control range,
wherein the controller (<NUM>) is commanding the engine (<NUM>) to run at an engine speed above the pedal based engine speed control range,
characterised in that the commanding step is based on a traction feedback signal from a hydrostatic traction drive circuit (<NUM>).