Patent Application
20070037651
The present invention relates to the field of planetary gearsets and their use in continuously variable transmissions.
Hydrostatic units are a common way of achieving a stepless transmission for use in an automobile. Stepless transmissions are desirable because they are steplessly adjustable over a wide range, and can provide improved efficiency in packaging and fuel economy. A common way to achieve stepless gearing is through the use of a hydrostatic unit. Hydrostatic units consist of a pump, with a variable displacement volume, and a motor, which is driven by the pump, having either a fixed or variable displacement volume. A power source coupled to the transmission provides power to a planetary gearset, which in turn splits the power between the hydrostatic unit and the output.
One problem that exists in current continuously variable transmissions that utilize hydrostatic units is that there is no “mechanical neutral,” meaning that when a neutral condition is desired, there is no complete disconnect from the power source to the transmission. In most current designs, neutral is achieved by adjusting the swashplate of the pump in the hydrostatic unit such that no power is transferred to the motor. One major drawback to this design is that residual drag torque in the transmission can still transfer a small amount of torque to the output, thereby not allowing for a true neutral position; also, any deviation in the tolerance of the displacement volumes in the hydrostatic unit may also cause a small amount of torque to be transferred through the transmission, which would also negate the vehicle being in neutral.
Another problem with current designs using a hydrostatic unit involves trying to achieve a reverse gear. This is accomplished by reversing the operation of the hydrostatic unit. In the reverse configuration, the motor acts as the pump, and the pump acts as the motor. The drawback in this method of achieving reverse comes from the displacement volumes of the pump and motor in the hydrostatic unit being configured to provide the proper amount of torque when the vehicle is going in a forward direction. In reverse, a very small amount of torque is transferred through the hydrostatic unit to drive the gearset, resulting in the vehicle moving very slow, and with little power. Also, when in reverse, because of the displacement volumes in the hydrostatic unit, the engine may run at very high rpm to achieve reverse using this method, making it very inefficient.
The present invention is directed toward overcoming these and other problems associated with using a hydrostatic unit in a continuously variable transmission. The present invention allows for a “mechanical neutral,” as well as a more efficient reverse configuration to be achieved. The present invention has a dual sun planetary gearset, as well as a dog clutch or other type of shifting device, which allows for the hydrostatic unit to operate in a reverse direction in similar fashion to how it operates in a forward direction, thereby increasing efficiency and torque in the reverse direction. The gearset of the present invention has a first sun gear having one or more planetary gears that are mounted on a carrier. These planetary gears are connected to a second set of planetary gears, also mounted on a carrier, and driving a second sun gear. The second sun gear is connected to another gear, which is in mesh with a gear connected to the pump. The second sun drives the pump of the hydrostatic unit, which is turn drives the motor. The motor is connected to the carrier through a gearmesh. The carrier and output are combined to transmission output in forward. The dual sun planetary gearset provides two powerflow paths through the transmission, the first as described for forward direction. The second, for reverse direction, drives the motor (as a pump) and outputs the pump (as a motor) to drive the second sun gear and transmission output. When the shifting device is moved to either the forward or reverse position, the hydrostatic unit increases the speed of the vehicle without increasing the speed of the input, providing a stepless power transfer through the transmission.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein:
The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
A schematic diagram of the present invention is shown
The hydrostatic unit 12 is of the type that is well known in the art and commonly used. The pump 32 hydraulically drives motor 34, which is connected to motor gear 36. The pump 32 circulates fluid back and forth between the pump 32 and motor 34, driving the motor 34 to rotate. The stepless gearing is achieved through the use of the motor 34 in the hydrostatic unit 12. As the angle of the swashplate inside the motor changes relative to motor gear 36, the amount of torque and power transferred through the hydrostatic unit 12 changes as well. Changing this angle also effects the final drive ratio of the planetary gearset 66. When the swashplate in the hydrostatic unit is at a maximum angle relative to the motor gear 36, the result is the planetary gearset 66 will behave in similar fashion to first gear in a typical automatic or manual transmission. As the swashplate in the motor 34 moves toward a parallel position relative to the motor gear 36, less torque is generated, and the planetary gearset 66 will have the effect on the final output of a drive or overdrive gear in a common automatic or manual transmission.
The power flow path for the various positions of the dog clutch will now be described. When the dog clutch 58 is positioned so that it connects to the carrier 50, the planetary gearset 66 propels the vehicle forward. The first sun gear 46 drives the set of first planet gears 48, which in turn rotate carrier 50. The carrier 50 is connected to the gear 56, and the gear 56 drives the pump gear 30, and is also engaged with the dog clutch 58, which drives the output shaft 64. The hydrostatic unit 12 provides power delivered back into the planetary gearset 66 and also provides the stepless ratio change by motor gear 36 meshing with the gear 60. The gear 60 is operably connected to second sun gear 54, that is in mesh with second planetary gear 52. The second planetary gears 52 are mounted on carrier 50, which as previously stated, drives gear 56. The end result is that the power transmitted to the gear 56 from the engine 62 being split between the planetary gearset 66 and the hydrostatic unit 12, and the hydrostatic unit 12 providing power input back into the planetary gearset 66, as well as providing a stepless ratio change comparable to that of common five and six speed transmissions.
Reverse is achieved by sliding the dog clutch 58 into a position such that it is connected to the second sun gear 54. Power from the engine 62 is still split between the planetary gearset 66 and the hydrostatic unit 12. However, the power is transferred from the first sun gear 46, to the planetary gears 48 and onto the carrier 50. The second sun planetary gear 52 is engaged with and receives power from the carrier 50. The second sun gear 54 is meshed with the second sun planetary gears 52 and passes the power flow onto the dog clutch 58, and finally, to output shaft 64. Because of the dog clutch 58 engaging the second sun gear 54, instead of the gear 56, the planetary gearset 66 drives the final output shaft 64 in a reverse direction, but allows for hydrostatic unit 12 to still act in the same manner as if the vehicle was going in a forward direction. This provides the necessary amount of torque required to move the vehicle in reverse, and acts similarly reverse gears in typical automatic and manual transmissions.
The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.
