Patent Application
20100113202
This patent disclosure relates generally to continuously variable transmissions and, more particularly to continuously variable transmission having a clutchless input that does not require a torque converter.
When a powered machine is accelerated, i.e., “launched,” from a standstill to a forward or reverse speed, the primary mover, e.g., the engine, of the machine transitions from a disengaged state to an engaged state. Whenever the engine is in the engaged state, its speed is generally related to the speed of the machine by a transmission ratio. However, this relationship is approximate in that a clutch or torque converter is generally employed to smooth the transition from the disengaged to the engaged state. Without the clutch or torque converter, the engine could stall or, at best, lug severely.
Although a number of types of transmissions are usable in such machines, a continuously variable transmission (“CVT”) is often used for its ability to provide a wide range of ratios and to smoothly vary the transmission ratio. One traditional CVT type is a split path transmission which includes an input for the primary mover as well as for two motors. The two motors, working in cooperation, set the ratio of the transmission. However, while providing smooth operation and a wide range of transmission ratios, the motors also contribute size, weight, and expense to the final transmission assembly.
Although single motor CVTs have been attempted, none has been of a design and configuration sufficient to substantially ameliorate the foregoing problems.
In one aspect, the disclosed principles pertain to a single motor drive train system for propelling a host machine, the drive train system comprising an engine, a motor, and a lossless buffer receiving the engine output and the motor output, and having a buffer output, such that the lossless buffer provides a range of transmission ratios between the rotational engine output and the rotational buffer output, wherein the range of transmission ratios includes a zero transmission ratio. It should be noted that in the context of this disclosure, the term “lossless” does not mean that the entity in question experiences, or has imposed upon it, no loss of energy whatsoever. Rather, the term “lossless” denotes the absence of intentional frictional losses/slippage such as may be present in clutches and torque converters.
Continuing with this aspect of the disclosure, the transmission input is linked directly to the rotational buffer output, and has a rotational transmission output linked to a propulsion means to propel the host machine. Thus, rotation of the transmission input rotates the transmission output, causing the propulsion means to propel the host machine.
In another aspect, a machine is provided for rendering clutchless engagement of a transmission without the use of a torque converter. The machine comprises an engine for propelling the machine, a transmission having a transmission input and a transmission output, and a lossless buffer between the engine and the transmission, wherein the lossless buffer employs a single electric motor to provide ratios in a range including zero between the engine output and the transmission input.
In yet another aspect of the disclosure, a buffer system is provided for managing the transmission of power between an engine and a transmission in the absence of a torque converter or clutch between the engine and the transmission. The buffer system comprises a mechanical buffer receiving as input an output of the engine and providing as output an input to the transmission, and a single electric motor controlling the input-to-output transmission ratio of the mechanical buffer to allow the mechanical buffer to provide such ratios in a range including zero. The system also includes a controller for controlling the single electric motor to modify the transmission ratio of the mechanical buffer.
Other aspects and features will be apparent from the detailed description, taken in conjunction with the drawings, of which:
This disclosure relates to machines requiring a transmission to link a power source to a final ground-engaging mechanism, e.g., wheels, tracts, etc. Examples of such machines include machines used for mining, construction, farming, transportation, and other industries and endeavors known in the art. For example, the machine may be an earth-moving machine, such as a wheel loader, excavator, dump truck, backhoe, motor grader, material handler or the like. Moreover, an implement may be connected to the machine. Such implements may be utilized for a variety of tasks, including, for example, loading, compacting, lifting, brushing, and may include, for example, buckets, compactors, forked lifting devices, brushes, grapples, cutters, shears, blades, breakers/hammers, augers, and others.
A motor 103, e.g., an electric motor is provided having a motor output 107. It will be appreciated that the motor 103 may consume electrical energy to provide a torque or may be driven while providing a reactive force, thus generating electricity for storage in a battery (not shown) or other storage element. A lossless buffer 109 is interposed between the motor 103 and engine 101, and a transmission 111. For driving a load, the lossless buffer 109 provides at a buffer output 113 to the transmission 111 a weighted combination of the rotation of the engine 101 and the rotation of the motor 103.
The details of the lossless buffer 109 will be discussed in detail below with reference to
The power train system 100 exhibits three primary states. The first occurs when the engine 101 is running, but the machine is not moving. In this state, the torque provided to the transmission 111 by the engine 101 via the engine output 106 is essentially reflected to the motor 103 via the motor output 107, whereupon the energy is either stored, e.g., via a battery, or dissipated, e.g., via a resistive grid. In the second state, usually occurring when the machine is being launched from the first state, the engine 101 provides torque to the lossless buffer 109 via the engine output 106, the machine is moving at least slightly, and the motor 103 is being driven by the lossless buffer 109 via the motor output 107, but is providing a reactive torque to accelerate or move the machine.
In other words, in this second stage, the motor 103 resists movement, and as such, the buffer output 113 of the lossless buffer 109 moves or accelerates under the force of the engine 101. In the third stage, the engine 101 provides torque to the lossless buffer 109 via the engine output 106 and the motor 103 provides proactive torque to the lossless buffer 109 via the motor output 107. In this state, the rotational speed of the buffer output 113 is a weighted average of the rotational speed of the engine 101 and the motor 103. The effective transmission ratio of the lossless buffer 109 relative to the engine output 106 is controlled by the rotational speed of the motor output 107, i.e., the rotational speed of the motor 103. Thus, for example, if the engine speed and motor speed are of equal magnitudes but opposite directions, the transmission ratio of the lossless buffer 109 is zero. Moreover, fractional or overdrive ratios between the engine output 106 and the buffer output 113 can be provided by varying the speed of rotation of the motor output shaft 107.
The illustrated configuration thus allows the machine to be launched from a stationary state to a moving state without clutches or torque converters between the engine 101 and the split torque transmission 103, while also allowing a wide range of effective transmission ratios. This provides the benefits of allowing a compact and simple installation, while avoiding excess expenditures on equipment and maintenance.
As can be seen, the engine output 106 is connected to the at least one sun gear 201, such that rotation of the engine 101 serves to rotate the at least one sun gear 201 at a like speed and in a like direction. Also shown, the motor output 107 is linked to the at least one ring gear 203. In this way, the torque of the at least one ring gear 203 is transferred to second input 107 and hence to the motor 103. Likewise, the torque of the motor 103 is transferred via the motor output 107 to the at least one ring gear 203. Finally, in the illustrated embodiment, the at least one planet gear/planet gear carrier assembly 205 is linked to the buffer output 113. In this way, the engine output 106, motor output 107, and buffer output 113 are interconnected and their rotational speeds are interrelated.
It will be appreciated that the tooth counts used to reach these ratios are not critical, and that the ratios used in any particular implementation need not match the example given above to fall within the disclosed principles of operation.
Referring to
Thus, for example, at the time of transition from the idle mode to forward or reverse motion of the machine, the motor 103 transitions from being a strictly driven element to providing an active or reactive torque at the second input 107. The active or reactive torque can be generated by supplying a voltage input to the motor 103 in a direction the same as or opposite to (for reactive torque) the induced current, with the polarity of voltage determining the direction of the applied torque and the magnitude of the voltage determining the extent of the torque on the motor output 107.
It is also expected to use the illustrated configuration to provide a braking force to the buffer output 113, e.g., to decelerate the host machine.
As shown in the example environment of
The process executed by the controller 105 in regulating and coordinating the lossless buffer 109, engine 101 and motor 103 is shown via the process 600 of
The initial state of the host machine prior to execution of process 600 is idle, i.e., the engine 101 is running but the host machine is not moving. At stage 601 of the process 600, the controller 105 receives an acceleration command, e.g., from a physical or electrical user interface element. Pursuant to the command received at stage 601, the controller 105 first optionally connects the motor 103 to a motor controller at stage 603 if the motor 103 had been providing electrical power to a battery or the like during idling. At stage 605, the controller 105 increases fuel flow to the engine 101 to increase its output power, while also increasing the reactive torque provided by the motor 103 via the motor controller. These actions have the net effect of increasing torque at the buffer output 113 to accelerate the host machine.
Once a desired speed is attained, e.g., further acceleration is not requested, the controller 105 may continue to increase the speed of the motor 103 while decreasing the speed of the engine 101 at stage 607. This increases the effective transmission ratio of the split torque transmission 103 to conserve fuel and allow the engine 101 to operate within an optimal operating range.
At stage 609, the controller 105 receives a retarding command, again optionally resulting from interaction of the user with a user interface element. At stage 611, in response to the retarding command, the controller 105 idles the engine 101 and shunts the motor inputs so that the motor now supplies electrical energy to a battery or dissipater. This action tends to reduce the speed of the machine. If need be, the controller 105 may optionally apply the service brakes of the machine at stage 613.
The present disclosure is applicable to driven machines having transmissions for imparting motion to the machine. In particular, the disclosed principles provide a mechanism for omitting a clutch and torque converter from the machine drive train while maintaining the ability to start and stop the host machine without lugging or stalling the engine 101. This system may be implemented in on-highway or off-highway machines, construction machines, industrial machines, etc. Although many machines that may benefit from the disclosed principles will be machines used at least occasionally for transport of goods, materials, or personnel, it will be appreciated that such transmissions are used in other contexts as well, and the disclosed teachings are likewise broadly applicable.
Using the disclosed principles, a lossless buffer 109 is disposed in the machine drive train system 100 between driving elements, e.g., engine 101 and motor 103, and a transmission. The buffer provides zero, fractional, and overdrive ratios between the engine 101 and the transmission to allow start up from full stop with the engine 101 running and to allow stopping from forward motion without stalling the engine 101. It will be appreciated that this description provides examples of the disclosed system and technique. However, it is contemplated that other implementations of the disclosure may differ in detail from the foregoing examples. Moreover, the references to examples herein are intended to reference the particular example being discussed at that point and are not intended to imply any limitation as to the scope of the disclosure more generally. All language of distinction and disparagement with respect to various features is intended to indicate a lack of preference for those features, but not to exclude such from the scope of the disclosure entirely unless otherwise indicated. Although the motor 103 has been referred to herein as an electric motor, it will be appreciated that the motor 103 may instead be a hydraulic motor or other non-electric motor without departing from the scope of the disclosed principles.
Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. All methods described herein can be performed in any suitable order and from any suitable step unless otherwise indicated herein or otherwise clearly contradicted by context.
