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Continuously variable transmission system with power boost

Continuously variable transmission system with power boost description/claims

This disclosure relates generally to continuously variable transmission (CVT) systems, and more specifically to a system and method for boosting power to a continuously variable transmission (CVT).

Many propelled vehicles and work machines, particularly earth working machines, use a continuously variable transmission (CVT) to drive wheels or tracks which propel the vehicle or work machine. A CVT provides an infinite number of transmission ratios to generate an output at any speed in its operating range. One example of a CVT is a hydrostatic transmission consisting of a variable speed hydraulic pump and a hydraulic motor. An example of such a hydrostatic transmission is disclosed in U.S. Pat. Nos. 6,385,970 and 6,424,902 to Kuras et al. The speed output of such a transmission can be continuously varied by controlling the displacement of the hydraulic pump.

Another example of a CVT is an electric motor and inverter as is used in hybrid-electric systems such as in hybrid-electric cars. A hybrid-electric system generally includes an internal combustion engine that is mechanically coupled to drive an electric generator that creates electrical power. The power from the electric generator is then consumed by an electric motor. An inverter contains the power electronics that control the output speed and torque of the electric motor—thus the transmission ratio is adjusted electronically by the inverter. The electric motor provides torque to drive a load, such as the wheels or tracks of a propelled vehicle. Hybrid-electric systems can be used in a variety of applications, such as automobiles, earth-working machines, or other machinery.

One problem encountered in CVT systems is that the inertia of the motor (hydraulic or electric) and the associated system components can be quite large. When the inertia is large, the acceleration response of the motor is limited. In other words, if the inertia is large, it will be difficult to accelerate the motor quickly unless the engine is sufficiently powerful. A limited motor acceleration response may be unacceptable, especially for certain applications such as construction machines like wheel loaders or utility tractors driven by the CVT system. More power can be provided to the motor simply by installing a more powerful engine and generator. This is often undesirable, however, because a more powerful engine may also be larger, heavier, and result in a less efficient system.

U.S. Pat. No. 6,726,594 to Mizuno discloses a control system for a vehicle. A controller detects whether an acceleration of a vehicle is requested. If acceleration is requested, a final target engine output power is calculated based on the accelerator pedal position and the vehicle speed. The engine speed at which the target output power can be generated with the minimum fuel consumption is calculated. A target engine torque is calculated based on the target engine output power and engine speed. A transient operating point is then determined by calculating ranges of engine torque and engine speed which can be achieved within a predetermined time. The controller then controls the speed ratio of a continuously variable transmission so as to operate the engine at the transient operating point.

Controlling the speed ratio of a CVT may not provide sufficient acceleration if the rate of fuel consumption in the engine is not increased to boost engine power output. What is needed is a system and method for improving motor acceleration in a CVT system without requiring the installation of a larger engine. What is further needed is a system and method for boosting power to a motor in a CVT system without damaging the engine. The disclosed system is directed to satisfying one or more of the existing needs in the industry.

In accordance with one aspect of the disclosed system, a method is provided of boosting power to a continuously variable transmission having a motor. The continuously variable transmission is powered by an engine. The method includes selectively adjusting a power output of the engine above a steady state power output rating of the engine when an acceleration of the motor exceeds an acceleration threshold value.

According to another aspect of the disclosed system, a method is provided of boosting power to a continuously variable transmission having a motor. The continuously variable transmission is powered by an engine. The method includes determining an acceleration of the motor. A power boost map is selected when the acceleration exceeds an acceleration threshold value, and a baseline map I selected at other times. The power boost map and baseline map represent engine power output as a function of engine speed. A speed of the engine is sensed and at least one parameter of the engine is adjusted to control the rate of fuel combustion in the engine to provide an engine power output in accordance with the selected map at the sensed engine speed.

According to another aspect of the disclosed system, a method is provided of boosting power to a continuously variable transmission having a motor. The continuously variable transmission is powered by an engine. The method includes determining an acceleration of the motor. A first engine underspeed threshold is selected when the acceleration exceeds an acceleration threshold value. A second engine underspeed threshold is selected at other times. A speed of the engine is sensed and at least one parameter of the engine is adjusted to control the rate of fuel combustion in the engine to provide an engine power output in accordance with an engine power map, wherein the engine power map represents engine power output as a function of engine speed.

According to another aspect of the disclosed system, a continuously variable transmission system is provided including an engine and a continuously variable transmission powered by the engine. The continuously variable transmission includes a motor. A controller is operative to selectively adjust a power output of the engine above a steady state power output rating of the engine when an acceleration of the motor exceeds an acceleration threshold value.

FIG. 1 depicts a block diagram illustrating a hybrid-electric system in accordance with an exemplary embodiment of the present disclosure;

FIG. 2 depicts a flow chart illustrating a scheme for boosting power to a continuously variable transmission in accordance with an exemplary embodiment of the present disclosure;

FIG. 3 depicts an example of a power boost map and a baseline map;

FIG. 4 depicts a flow chart illustrating an alternate scheme for boosting power to an continuously variable transmission in accordance with an exemplary embodiment of the present disclosure;

FIG. 5 depicts a built-in power boost map showing engine power vs. engine speed in accordance with an exemplary embodiment of the present disclosure;

FIG. 6A depicts a simulation showing engine speed over time during motor acceleration using the baseline, power boost, and built-in power boost engine maps;

• Provisional Patent
• Utility Patent

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