Patent Application
20150089934
This disclosure relates to the field of hydraulic controls for a vehicle powertrain. More particularly, the disclosure pertains to a system to store and release pressurized fluid.
Many vehicles are used over a wide range of vehicle speeds, including both forward and reverse movement as well as stationary periods. Internal combustion engines, however, are capable of operating efficiently only within a narrow range of speeds. Consequently, transmissions capable of efficiently transmitting power at a variety of speed ratios are frequently employed. When the vehicle is at low speed, the transmission is usually operated at a high speed ratio such that it multiplies the engine torque for improved acceleration. At high vehicle speed, operating the transmission at a low speed ratio permits an engine speed associated with quiet, fuel efficient cruising. The most common type of automatic transmission has a set of clutches and brakes. The various speed ratios are selected by supplying pressurized hydraulic fluid to various subsets of the clutches and brakes.
In order to reduce the fuel consumption of vehicles, some vehicles are configured to turn off the engine when the vehicle is stopped at a light. When the driver releases the brake pedal, the engine is automatically restarted. To satisfy the driver's demand to accelerate, it is important that the engine be restarted and an appropriate transmission ratio be engaged in a very short period of time. In many vehicles, the source of hydraulic pressure to engage the transmission is a pump driven by the engine. Any delay between the engine reaching idle speed and engagement of a suitable transmission ratio contributes to the total delay before vehicle acceleration so this delay must be minimized or eliminated. Some existing vehicles use an electrically driven auxiliary pump to maintain hydraulic pressure while the engine is off. This technique requires significant additional hardware and draws electrical power for the entire period that the engine is stopped with the vehicle in drive. An alternative system, using a hydraulic accumulator to rapidly re-pressurize the clutch engagement hydraulic circuits, has been developed. This accumulator system requires a high flow valve to quickly reengage the clutches in the transmission and a check valve connected to the pump to re-pressurize the accumulator after each use.
A pressurized fluid storage system includes a manifold and a reservoir fluidly connected by a passageway. An engine driven pump may supply pressurized fluid to the manifold. The manifold may, in turn, supply pressurized fluid to a hydraulic control system of a vehicle transmission. The reservoir may be, for example, a piston-type accumulator having a piston that slides within a cylinder defining a fluid cavity and a spring that applies force to the piston to maintain pressure in the fluid. A plug within the passageway passively blocks flow when the pressure in the reservoir exceeds the pressure in the manifold and passively permits flow from the manifold to the reservoir whenever the pressure in the manifold exceed the pressure in the reservoir. The plug may be, for example, a check ball that is forced against a seat by pressure in the reservoir and forced away from the seat by pressure in the manifold. An actuator actively forces the plug into a position that permits a high flow rate from the reservoir to the manifold in response to a control signal. The actuator may include a cylinder containing a piston with a protrusion that pushes the plug. Fluid pressure on one side of the piston pushes the piston toward the plug while a spring pushes the piston away from the plug. In one exemplary embodiment, a binary valve controls the fluid pressure pushing the piston towards the plug. In one position of the binary valve, the chamber pushing the piston towards the plug is fluidly connected to the reservoir. In the opposite position of the binary valve, the chamber pushing the piston towards the plug is vented. In another exemplary embodiment, the chamber pushing the piston towards the plug is fluidly connected to the reservoir while the chamber pushing the piston away from the plug is fluidly connected to the manifold. The piston area is set such that these forces nearly balance the forces on the plug, permitting a relatively low force actuator to directly push the piston.
A hydraulic control system includes a single passageway fluidly connecting a reservoir to a manifold, a check valve within the passageway, and an actuator configured to override the check valve in response to a control signal. The system may also include an engine drive pump configured to deliver pressurized fluid to the manifold. The hydraulic control system is useful for rapidly re-engaging transmission clutches as the vehicle engine is restarted, permitting the vehicle to shut the engine off during periods when the vehicle is stationary, such as while waiting at a traffic light. The reservoir is filled while the engine is running by flow past the check valve when pressure in the manifold exceeds pressure in the reservoir. The check valve maintains the reservoir charge when the engine is stopped. As the engine is restarted, the actuator overrides the check valve allowing fluid from the reservoir to rapidly re-engage transmission clutches.
Embodiments of the present disclosure are described herein. It is to be understood, however, that the disclosed embodiments are merely examples and other embodiments can take various and alternative forms. The figures are not necessarily to scale; some features could be exaggerated or minimized to show details of particular components. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention. As those of ordinary skill in the art will understand, various features illustrated and described with reference to any one of the figures can be combined with features illustrated in one or more other figures to produce embodiments that are not explicitly illustrated or described. The combinations of features illustrated provide representative embodiments for typical applications. Various combinations and modifications of the features consistent with the teachings of this disclosure, however, could be desired for particular applications or implementations.
Fuel consumption can be reduced by stopping the engine when the vehicle is stationary, such as when waiting at a red light. However, it is important to be able to quickly restart the engine when the driver releases the brake pedal so that the vehicle begins accelerating as soon as the driver depresses the accelerator pedal. When the engine is off, the pump does not provide pressurized fluid to keep the transmission engaged, so the transmission is effectively in neutral. Upon restarting the engine, there is a delay before the pump provides enough pressurized hydraulic fluid to re-engage the transmission clutches. To avoid delay in vehicle acceleration, it is desirable to store pressurized fluid in reservoir 20 while the engine is running and release that fluid to rapidly re-engage the transmission clutches while the engine is being re-started.
The components of the hydraulic control system that control the flow into and out of reservoir 20 are illustrated in
To release the pressurized fluid from the reservoir to engage transmission clutches, the control system moves on/off valve 36 to the open position as shown in
Once the pump is supplying sufficient fluid, on/off valve 36 is moved to the closed position and the system returns to the state shown in either
Prior systems include at least two passageways between the reservoir and the manifold. In these systems, one passageway utilizes a check valve and sometimes an orifice to control flow from the manifold to the reservoir. A second passageway utilizes a high flow valve to control flow from the reservoir to the manifold. This configuration, on the other hand, requires only one passageway between the reservoir 20 and the manifold 28.
Another embodiment is illustrated in
The disclosed system may also be used in other applications that require periodic, relatively short duration supply of pressurized hydraulic fluid. For example, some transfer cases need high pressure and high flow only during a change between low range and high range. With the disclosed system, a small low-flow pump would be able to charge the reservoir between range transitions and the reservoir would provide high flow for the event.
While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms encompassed by the claims. The words used in the specification are words of description rather than limitation, and it is understood that various changes can be made without departing from the spirit and scope of the disclosure. As previously described, the features of various embodiments can be combined to form further embodiments of the invention that may not be explicitly described or illustrated. While various embodiments could have been described as providing advantages or being preferred over other embodiments or prior art implementations with respect to one or more desired characteristics, those of ordinary skill in the art recognize that one or more features or characteristics can be compromised to achieve desired overall system attributes, which depend on the specific application and implementation. These attributes can include, but are not limited to cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, serviceability, weight, manufacturability, ease of assembly, etc. As such, embodiments described as less desirable than other embodiments or prior art implementations with respect to one or more characteristics are not outside the scope of the disclosure and can be desirable for particular applications.
