Patent Description:
In an electric car, efficient use of electrical power is extremely important. There are various different components in a vehicle's drive train, and if any of these components are not operating efficiently the vehicle and its user may be deprived of range, time and power associated with use of the electric vehicle that may otherwise be available. An electric vehicle typically relies solely on stored electric power. Thus, there is a need to convert electric energy to propulsion power as efficiently as possible.

<CIT> discloses a lubricating system for a vehicle transmission component comprising an electrical pump for pumping lubricant from a reservoir to the transmission component and a controller for monitoring a driving condition and, based thereon, configuring the electrical pump to pump a predetermined flow rate of lubricant to the transmission component.

The present application discloses a transmission system for an electric vehicle that improves the efficiency of the power transfer within the transmission system and, thus, provides for increased range, operating time and power for an electric vehicle.

The features, aspects, and advantages of the present invention will become apparent from the following description, and the accompanying exemplary embodiments shown in the drawings, which are briefly described below.

As disclosed herein, a transmission system for an electric vehicle is provided. The vehicle includes a DC power source to supply power to one or more propulsion motors. The transmission may be used to change the speed of the motor shaft to match the desired speed of the shaft driving a wheel of the vehicle. The DC power source in an electric vehicle may be the main battery of the electric vehicle.

<FIG> shows an exemplary electric vehicle <NUM> configured to be driven by a pair of propulsion motors <NUM>, <NUM>. The vehicle may include a rechargeable energy storage system <NUM> (e.g., a battery). The vehicle may also include an engine <NUM> to provide supplemental power. The engine <NUM> may generally refer to any apparatus operable to augment power or range beyond the range associated with power provided by the battery <NUM>. For example, the engine <NUM> may be an internal combustion engine that consumes gasoline. The storage system <NUM> may be, for example (but not limited to) a high-voltage battery, such as a high-voltage lithium ion battery pack. Operation of the vehicle <NUM> may be driven by each power source and/or both. The vehicle <NUM> may include multiple electrical motor/generators <NUM>, <NUM> that may be operated either as drive motors that convert electrical power to rotational mechanical energy or as generators that convert rotational mechanical energy to electrical energy. The motor/generators are at times referred to simply as motors but, as described herein, include the ability to be driven to generate electricity. The motor/generators may be electrically driven and coupled to the engine <NUM> and the storage device <NUM>.

According to various embodiments, the vehicle <NUM> includes a first motor/generator <NUM> that serves as a motor to drive the front wheels <NUM> of the vehicle. In the regenerative braking mode the motor <NUM> may serve as a generator to charge the storage device <NUM>. The vehicle <NUM> further includes a second motor/generator <NUM> (e.g., rear wheel drive (RWD) motor) that engages a drive shaft that turns one or more rear wheels <NUM>. One or more intermediate devices, such as a rear gearbox <NUM> and a rear differential <NUM>, may be provided between the second motor/generator <NUM> and the rear wheels <NUM>. Similarly, the vehicle <NUM> may include a front gearbox <NUM> and a front differential <NUM>, located between the front motor/generator <NUM> and the front wheels <NUM>.

The vehicle <NUM> may further includes a generator <NUM> that is driven by the engine <NUM> and generates power for propulsion or for charging the battery <NUM>. As further described below, the gearboxes <NUM>, <NUM> may be single speed gearboxes or multi-speed gearboxes. The motor/generators <NUM>, <NUM>, <NUM> and the battery <NUM> may be coupled to a common DC bus <NUM>. In some embodiments, the generator <NUM> and motor/generators <NUM>, <NUM> may be AC devices and electric conversion devices such as inverters <NUM>, <NUM>, <NUM> may be coupled between the motor generators and the DC bus <NUM>. The vehicle <NUM> may be operated normally as a RWD vehicle, with the front wheels only powered when needed for additional power or traction.

When the vehicle accelerates or increases energy consumption, speed of the drive motors increase to deliver more power or energy to the wheels <NUM>. The turning of the motors may be reversed to provide regenerative braking, which provides the impression of downshifting the vehicle <NUM>. This also generates energy that may be stored in the battery <NUM>. Accordingly, in some embodiments, the vehicle <NUM> may actuate regenerative braking to slow the vehicle <NUM> rather than causing brake pads (not shown) to slow the wheels when a braking actuator is activated.

The increase in speed of the drive motors when the vehicle accelerates causes a decrease in the efficiency of the operation of the gear box due to the increase and temperature and pressure of the lubricating oil in the gear box. The efficiency decreases due to, for example, churning losses of the lubricating oil, friction losses of the rotating components, and the increase in temperature (i.e., heat dissipation). The disclosed system lowers oil level in a reservoir, and adds oil to the gear box, during a transient event. For example, the disclosed system provides for a system to temporarily add extra oil into the gearbox system during a transient event (e.g. high acceleration event) to provide for increased operational efficiency of the gears, bearings, shafts located in the gear box. The overall volume of the lubricating oil is distributed throughout the system components including the reservoir, gear box, pump and the connecting lines (e. g, pipes, conduits, etc.).

The disclosed innovative transmission system accomplishes this increase in efficiency (or, reduces the amount of decrease in deficiency) by temporarily adding a portion of lubricating oil from a reservoir to the gear box in order to increase efficiency of the gear box during a high acceleration event. The size or volume of the portion of the lubricating oil is relatively small and depends on the size of the various components of the transmission system including, for example, the overall volume of oil located in the gear box. For example, the present system preferably adds about <NUM> of lubricating oil from the reservoir toward the gear box when a high acceleration event is detected. Alternatively, the amount of oil removed from the reservoir may be between <NUM>-<NUM> or other suitable amount. The normal volume of oil in the reservoir may be about <NUM> liters. Thus, during a transient situation of high acceleration the disclosed system removes approximately20 percent of the volume of oil from the reservoir and pumped toward the gear box. Substantially all of the oil removed from the reservoir is added to the gear box. The added volume of oil may range from about <NUM> to <NUM> percent of the total volume of oil used during standard operating conditions depending on the size of the gear box, reservoir and oil system.

In another example, the normal volume of oil in the reservoir may be <NUM> liters and the system may be configured to transfer <NUM> of oil to the system and gear box. Thus, the transferred quantity of oil is approximately <NUM> percent of the system volume.

<FIG> discloses an alternative exemplary embodiment of a power train for an electric vehicle <NUM> configured to be driven by a pair of propulsion motors <NUM>, <NUM>. Although not shown in <FIG>, the vehicle may be an all-wheel drive (AWD) vehicle and include two or four motors and the capability of driving all four wheels simultaneously. The vehicle <NUM> shown in <FIG> operates in the same basic manner as the vehicle of <FIG> and may include the same variations and embodiments of the system and components described above.

The vehicle <NUM> may include a rechargeable energy storage system <NUM> (e.g., a battery). The vehicle may also include an engine <NUM> to provide supplemental power. The engine <NUM> may generally refer to any apparatus operable to augment power or range beyond the range associated with power provided by the battery <NUM>. For example, the engine <NUM> may be an internal combustion engine that consumes gasoline. The storage system <NUM> may be, for example (but not limited to) a high-voltage battery, such as a high-voltage lithium ion battery pack. Operation of the vehicle <NUM> may be driven by each power source and/or both. The vehicle <NUM> may include multiple electrical motor/generators <NUM>, <NUM> that may be operated either as drive motors that convert electrical power to rotational mechanical energy or as generators that convert rotational mechanical energy to electrical energy. The motor/generators are at times referred to simply as motors but, as described herein, include the ability to be driven to generate electricity. The motor/generators may be electrically driven and coupled to the engine <NUM> and the storage device <NUM>.

According to various embodiments, the vehicle <NUM> includes a pair of motor/generators <NUM>, <NUM> that serve to drive the front wheels <NUM> of the vehicle. In the regenerative braking mode the motors <NUM>, <NUM> may serve as a generators to charge the storage device <NUM>. The vehicle <NUM> may include a gearbox <NUM> located between the motor/generators <NUM>, <NUM> and the front wheels <NUM>. The gearbox <NUM> may be configured to be a split gear box (i.e., drive each wheel independently from separate motors), or an integrated gear box that allows one of the two motors <NUM>, <NUM> to drive both wheels <NUM> together.

The vehicle <NUM> may further include a generator <NUM> that is driven by the engine <NUM> and generates power for propulsion or for charging the battery <NUM>. As further described below, the gearbox <NUM> may be single speed gearboxes or multi-speed gearboxes. The motor/generators <NUM>, <NUM>, <NUM> and the battery <NUM> may be coupled to a common DC bus <NUM>. In some embodiments, the generator <NUM> and motor/generators <NUM>, <NUM> may be AC devices and electric conversion devices such as inverters <NUM>, <NUM>, <NUM> may be coupled between the motor generators and the DC bus <NUM>. The vehicle <NUM> may be operated normally as a FWD vehicle.

<FIG> discloses an exemplary transmission system <NUM> to be used in an electric vehicle, such as those vehicles described above. However, the innovative transmission system disclosed herein is not limited to those exemplary embodiments of electric vehicles disclosed in the present application.

The disclosed transmission system <NUM> includes an oil reservoir <NUM>, which can be, for instance, a dedicated oil sump for the transmission system or a sump shared with other systems that use the same lubricating fluid. The system includes a pump <NUM> driven by a motor <NUM>. The pump <NUM> may be any suitable type such as centrifugal, positive displacement (e.g., screw type, piston type, etc.). A screw type pump is preferred. The motor <NUM> includes a controller <NUM> for controlling operation of the motor <NUM> and, thus, the pump <NUM> as well. The pump may operate to move the lubricating fluid or oil either toward or away from the components to be lubricated. The system may include various valves (not shown) to prevent the flow of oil in an undesirable direction when the pump is not operating.

The system may further include a heat exchanger <NUM> for cooling the lubricating fluid. The heat exchanger may include a cooling fluid <NUM> carried through the heat exchanger to remove heat from the fluid or oil. The lubricating fluid is provided to the gear box <NUM>, described further below.

The system <NUM> includes a controller <NUM> for the motor <NUM>. The controller <NUM> may be configured to send a receive data to other vehicle components. For example, the controller <NUM> may be connected to the vehicle CAN bus <NUM> or other similar data carrying system. The CAN bus <NUM> carries information from various vehicle components and sensors such as an inertia measuring unit (e.g., an acceleration sensor in x, y and/or z directions), a vehicle speed sensor (e.g., a wheel speed sensor), a propulsion motor speed sensor, a steering angle sensor. The CAN bus carries information regarding the acceleration of the vehicle to the controller. Here, the controller <NUM> is configured to determine the acceleration of the vehicle based on the information received from one or more of the vehicle sensors mentioned above, concretely from a propulsion motor speed sensor.

The controller <NUM> is configured so that when the vehicle acceleration is determined to be greater than a predetermined value, the controller directs the motor <NUM> to drive the pump <NUM> to remove oil from the gear box <NUM>. The first predetermined value may be in a range of <NUM>. <NUM> to <NUM>. Preferably, a set point of <NUM> is used for the first predetermined value. The pump <NUM> only operates to remove a relatively small amount of oil from the gear box for the amount of time that the vehicle acceleration is taking place. Once the vehicle acceleration has returned below a second predetermined value the pump operates to return the removed quantity of oil to the gear box from the reservoir <NUM>. The second predetermined value is preferably in the range of3. <NUM> to <NUM>. The preferred value of the second predetermined value is. Thus, the lubrication of the components in the gear box is not jeopardized due to the small volume of oil removed, the short time duration of reduction of volume of oil in the gearbox, and the relative high pressure of the oil remaining in the gear box during the high acceleration event.

<FIG> shows the internals of an exemplary gear box <NUM>. In the exemplary embodiment, a propulsion motor (<NUM>, <NUM>, <NUM>, <NUM>) includes a drive shaft <NUM> that drives a motor gear <NUM>. Each motor gear <NUM> drives a larger gear <NUM> that is connected to a smaller gear <NUM> that engages a wheel gear <NUM> that is connected to drive shaft <NUM> for each of the wheels. The drive shaft may alternatively be connected to a differential (<NUM>, <NUM>). In alternative embodiments, the gear box may container more gears depending on the use of the vehicle (e.g., grades encountered, top desired speed, etc.). The split gear box shown in <FIG> is exemplary only. In alternative embodiments, the gear box may be cross-connected internally to allow one motor to drive both wheels.

As utilized herein, the terms "approximately," "about," "substantially", and similar terms are intended to have a broad meaning in harmony with the common and accepted usage by those of ordinary skill in the art to which the subject matter of this disclosure pertains. It should be understood by those of skill in the art who review this disclosure that these terms are intended to allow a description of certain features described and claimed without restricting the scope of these features to the precise numerical ranges provided. Accordingly, these terms should be interpreted as indicating that insubstantial or inconsequential modifications or alterations of the subject matter described and claimed are considered to be within the scope of the invention as recited in the appended claims.

The terms "coupled," "connected," and the like as used herein mean the joining of two members directly or indirectly to one another. Such joining may be stationary (e.g., permanent) or moveable (e.g., removable or releasable). Such joining may be achieved with the two members or the two members and any additional intermediate members being integrally formed as a single unitary body with one another or with the two members or the two members and any additional intermediate members being attached to one another.

References herein to the positions of elements (e.g., "top," "bottom," "above," "below," etc.) are merely used to describe the orientation of various elements in the figures.

Claim 1:
A transmission system (<NUM>) for an electric vehicle (<NUM>, <NUM>) comprising:
a gear box (<NUM>, <NUM>) containing gears (<NUM>, <NUM>, <NUM>, <NUM>) and a lubricating fluid;
a reservoir (<NUM>) for storing lubricating fluid; and
a pump (<NUM>) for moving lubricating fluid into and out of the reservoir (<NUM>), wherein operation of the pump (<NUM>) is controlled by a controller (<NUM>), characterized in that the controller (<NUM>) is configured to
determine acceleration of the vehicle (<NUM>, <NUM>) based on information received from a propulsion motor speed sensor and to
control the pump (<NUM>) so that a portion of the lubricating fluid is transferred from the gear box (<NUM>, <NUM>) into the reservoir (<NUM>) when a value for the acceleration of the vehicle (<NUM>, <NUM>) is greater than a predetermined value.