SYSTEM AND METHOD FOR MANAGING TRANSMISSION FLUID TEMPERATURE

A system and method for managing transmission temperature includes a transmission housing enclosing transmission components for transmitting kinetic energy and transmission fluid, and a heat exchanger within the transmission housing.

FIELD

The present disclosure relates to a system and method for managing transmission fluid temperature.

INTRODUCTION

Modern motor vehicle transmissions use several quarts or liters of transmission fluid or hydraulic oil. The transmission fluid serves several purposes. First the fluid lubricates the numerous moving and rotating parts within the transmission. Second the fluid serves as a heat transfer mechanism to maintain an appropriate operating temperature and third is the use in a hydraulic control system for the transmission.

Attempts at maintaining transmission fluid temperatures within an acceptable operating range have relied upon a transmission oil cooler or warmer remotely located from the transmission which acts to dissipate or absorb heat. A portion of the flow of transmission fluid in the transmission is diverted from the operational flow within the transmission to the external cooler/warmer.

During cold weather starts, the cold transmission fluid can have a high viscosity which can significantly reduce the operating efficiency of the transmission, such as, for example, parasitic frictional losses or resistance to pumping. Depending upon the ambient temperature, it can take a significant amount of time before the transmission fluid temperature rises into a range where operational efficiency is improved to a satisfactory level. This delay is primarily due to the fact that frictional heating from the components within the transmission itself is the only source of heat for raising the transmission fluid temperature. During this time, operational efficiency can be significantly reduced, resulting in, for example, degraded fuel economy.

It is therefore apparent that improved control of the temperature of transmission fluid is desirable.

SUMMARY

A system for managing transmission fluid temperature includes a transmission housing enclosing transmission components for transmitting kinetic energy and transmission fluid, and a heat exchanger within the transmission housing. A method for managing transmission fluid temperature includes providing a transmission housing enclosing transmission components for transmitting kinetic energy and transmission fluid, and providing a heat exchanger within the transmission housing. In this manner, the heat exchanger may be placed within the operational flow path of the fluid, rather than merely in a diversionary flow path in which only a portion of the fluid flow may be exposed to a heat exchanger. In this manner a much larger portion of the flow of transmission fluid, if not the entire flow, in the transmission housing can be exposed to the heat exchanger. This greatly improves the capacity for heat transfer by the heat exchanger, which improves the rate at which heat may be transferred into or from the transmission fluid. For example, the presence of the heat exchanger within the transmission enables the transmission fluid to be heated much more quickly during cold startup conditions which can greatly increase the efficiency and operational effectiveness of the transmission during the cold startup conditions. Similarly, the greater capacity to transfer heat from the transmission provides for a much more effective system of transferring heat away from the transmission to maintain the temperature of the fluid within a preferred range of operating temperatures.

The present invention is in stark contrast to systems which may provide a transmission fluid heat exchanger external to the transmission housing and, therefore, can only send a portion of the flow of transmission fluid to the external heat exchanger, which limits the heat transfer capability of the heat exchanger and the rate at which heat may be exchanged. For example, an externally mounted heat exchanger may only receive about one third of the volume of fluid that flows through the transmission. Further, positioning the heat exchanger outside of the transmission housing requires that a portion of the normal, operational flow of fluid be shunted off a new or different path that is not otherwise necessary to the operation of the transmission. Mounting the heat exchanger within the transmission housing enables positioning of that heat exchanger directly in the path of the normal flow of fluid through the transmission that would have occurred even in the absence of a heat exchanger. This further provides the opportunity to optimize the configuration of the heat exchanger to minimize and/or avoid any disruption in the flow of transmission fluid through the transmission.

Additionally, positioning the heat exchanger outside of the transmission requires the addition of fluid communication channels between the transmission and the remotely mounted heat exchanger. This increase in the path for the transmission fluid requires additional energy to cause the fluid to flow through this additional path. In some instances, this may even require not only additional valving, but may also require a secondary pumping system to force that portion of fluid through this additional path. All of these factors increase the amount of energy required to take advantage of the remotely mounted heat exchanger and reduce the efficiency of the transmission. Mounting the heat exchanger within the transmission housing in accordance with an exemplary embodiment of the present invention obviates the necessity of these structures and, therefore, significantly increases the overall efficiency of the transmission.

The above features and advantages, and other features and advantages, of the present invention are readily apparent from the detailed description, including the claims, and exemplary embodiments when taken in connection with the accompanying drawings.

DETAILED DESCRIPTION

FIG. 1is a schematic illustration of a propulsion system100in accordance with an exemplary embodiment. The propulsion system100includes an engine102providing kinetic energy via a coupling104to a transmission106. The transmission106may be connected to the coupling104via a torque converter108. The torque converter108in turn is coupled to a plurality of kinetic energy transmitting devices110. The kinetic energy transmitting devices110may be, for example, friction clutches and brakes arranged with planetary gear sets or the like. The transmission106includes a housing112that encloses the components of the transmission106along with transmission fluid or transmission oil that lubricates and cools/warms the components within the transmission106. In an automatic transmission, the transmission fluid may also be used to operate clutches to selectively engage gear sets in a hydraulic control system (not shown).

In accordance with an exemplary embodiment, the transmission housing112also encloses a heat exchanger114. The heat exchanger114is positioned within the transmission housing112to enable heat transfer to and/or from the transmission fluid enclosed within the transmission housing112. The heat exchanger114may be in fluid communication using fluid heat transfer medium capable of circulating within the heat exchanger114and of flowing to and from the heat exchanger114via passages extending through walls of the transmission housing112to a thermal management system116located external to the transmission106. For example, a thermal management system116may be positioned external to the transmission106and serve to distribute and manage the transfer of heat between multiple components within an automobile.

The thermal management system116inFIG. 1includes a heat exchanger118which may be associated with the engine102and/or another thermally active device such as, for example, a radiator120. The thermal management system116may include any number of heat exchangers which may exchange heat with, for example, the radiator120, an engine block within the engine102, an exhaust manifold, exhaust system of the engine, power steering systems, and/or the like. The present invention is not limited to any specific structure of a thermal management system, other than that the system be capable of circulating a heat exchanging medium through the heat exchanger114within the transmission106.

The heat exchanger118may be in selective fluid communication with the heat exchanger114. The flow of fluid to the heat exchanger114being controlled via a fluid switching system, an example of which is schematically illustrated as a valve122. Another example of a fluid switching system may include a thermostat The thermal management system116further may include a controller124that controls the flow of fluid to the heat exchanger114based upon, for example, a signal received from a temperature sensor126positioned within the transmission housing112. In this manner, the controller124can selectively switch the flow of fluid to the heat exchanger114to, for example, provide heat to the heat exchanger114to increase the temperature of the transmission fluid as may be desirable in a cold start condition, or the controller124may selectively switch the flow of fluid to the heat exchanger114to, for example, remove heat from the heat exchanger114to maintain the temperature of the transmission fluid within a desired range of temperatures.

In the exemplary transmission106schematically illustrated inFIG. 1, a pump/filter128may also be located within the transmission housing112. The pump/filter128motivates the transmission fluid to circulate within the transmission housing112to provide lubrication, heat management, and/or for use within a hydraulic control system to selectively engage clutches and/or gear sets within the transmission in an automatic transmission. In the exemplary embodiment ofFIG. 1, the heat exchanger114is positioned near and/or adjacent to an inlet to the pump/filter128such that a substantial majority of the flow of transmission fluid being circulated through the transmission contacts heat exchanging surface of the heat exchanger114. In this manner, the efficiency of heat transfer between the heat exchanger114and the transmission fluid is maximized, which, thereby, increases the heat transfer capacity and may significantly reduce the amount of time it takes to change the temperature of the transmission fluid to within a desired operating range of temperatures. Additionally, the configuration of the heat exchanger114may be adapted to optimize or maximize the contact of the transmission fluid to the heat exchanger114before it enters the inlet of the pump/filter128as will be explained in accordance with exemplary heat exchangers below.

FIG. 2shows a cross-sectional perspective view of a sump200of an exemplary transmission202. The sump200is typically filled with transmission fluid (not illustrated) to a level204such that the components located within the sump200are immersed in the transmission fluid. The transmission202includes a transmission housing206having walls208defining the outer extent of the transmission housing206and which enclose the components within the housing206and maintain the transmission fluid within the housing206. A transmission fluid filter210is positioned within the sump200of the transmission202. The transmission fluid filter210includes an inlet212that receives transmission fluid from the sump200. The filter210may form a portion of a pump or may be in fluid communication with a pump (not shown) which motivates the fluid to flow into the inlet212and through the filter210. In another exemplary embodiment, the transmission sump200may not include a filter210, but may only include a pump (not shown). In any case, transmission fluid is drawn from the sump200for use elsewhere in the transmission.

A heat exchanger214is also positioned within the sump200of the transmission housing206. The heat exchanger214is configured to optimize the exposure of the transmission fluid being drawn from the sump200and into the inlet212to the heat exchanging surfaces of the heat exchanger214. For example, as may be more easily understood with reference toFIGS. 3A and 3B, the heat exchanger214may form a u-shape in order to substantially surround the inlet212such that substantially the entire flow (see flow lines220) of transmission fluid from the sump200into the inlet212contacts heat exchanging surfaces of the heat exchanger214, thereby maximizing the capacity of the heat exchanger214to transfer heat to and/or from the transmission fluid.

As illustrated inFIGS. 3A and 3B, the heat exchanger214is a configuration that includes a stacked set of crescent-shaped plates222. The plates222are hollow to provide flow of heat transfer fluid media within the plates222. The surface of the plates222may include surface features (not shown) such as dimples, guides, or ridges to affect the flow of the fluid across the heat transfer surfaces and/or to improve or maximize the surface area or heat transfer characteristics of the interaction between the transmission fluid and the heat transfer surfaces of the heat exchanger214to improve the capacity of heat transfer between the transmission fluid and the heat exchanger214. The surface features may also be designed to minimize the pressure drop of the flow across the heat exchanging surfaces and/or to improve heat transfer characteristics between the oil and heat exchanging surfaces.

The heat exchanger214includes a baffle216which may serve to guide the flow of transmission fluid from the sump200into contact with heat exchanging surfaces of the heat exchanger214. Alternatively, the baffle216may be configured to prevent or block the flow of transmission fluid from the sump200to the inlet212via a flow path that might not otherwise come into contact with the heat exchanging surfaces of the heat exchanger214. Such a baffle216may be useful in those instances where there may be insufficient space to provide heat exchanging surface of the heat exchanger214such as where, for example, the inlet212may be positioned very close a wall208of the transmission housing206.

The heat exchanger214includes an inlet passage218and an outlet passage220which extend through corresponding passages224in the walls208of the transmission housing206. In this manner, the heat exchanger214may be in fluid communication with the outside of the transmission to enable flow of a fluid heat transfer media provided and/or controlled by, for example, an exemplary thermal management system116.

FIG. 4illustrates another exemplary sump area400in a transmission402. The transmission sump area400includes a pump406, a filter408and the heat exchanger214. The inlet to the filter408is close to a wall410of the transmission housing sump area400. Therefore, there is not enough space to position heat transfer surfaces of the heat exchanger between the inlet and the wall410. In this instance, the baffle216serves block the flow of the fluid from the sump400into the inlet where heat exchanging surfaces of the heat exchanger are not located. Rather, the baffle216redirects the flow of fluid into the inlet such that the fluid contact heat exchanging surfaces of the heat exchanger214before entering the inlet.

FIGS. 5A and 5Billustrate another exemplary embodiment of a heat exchanger500that includes a central opening502that is surrounded by heat exchanging surfaces of annular-shaped plates504. This heat exchanger500may be positioned within a transmission housing such that the central opening502receives a fluid inlet. In this manner, the heat exchanging surfaces of the annular-shaped plates504substantially surround the central opening502which requires the flow of fluid into an inlet positioned in the central opening to contact the heat exchanging surfaces of the annular-shaped plates504. Other alternative embodiments of a heat exchanger may be adapted to the environment and/or structures within the housing to provide for heat transfer to and/or from the transmission fluid and remain within the scope of the present invention. For example, a heat exchanger may be configured as a tube assembly or any other structure.

The heat exchanger may be positioned anywhere within the transmission housing so long as at least some heat transfer enabling contact is provided between the heat exchanger and the transmission fluid within the transmission housing. For example, the heat exchanger may be positioned in an area within the transmission housing where transmission fluid may be splashed onto the heat exchanger or the heat exchanger may sit in its own sump area (not shown) to accommodate other considerations such as packaging and/or space limitations.