Patent Application
20120111955
The present invention generally relates to a thermostat and more particularly, to a vehicular thermostat for transmission oil. The present invention employs a bimetal element to cause opening and closing the flow of oil through a heat exchanger rather than a wax motor.
The automatic transmission of a motor vehicle requires cooling, which is achieved by flowing the automatic transmission fluid (ATF) through a transmission oil cooler. However, it is desirable to be able to control the flow of oil through said cooler, because cooling the ATF when it is cold enough can be detrimental, causing the oil to become too viscous for the proper operation of the transmission. It is desirable to allow the ATF to flow through the cooler only when cooling is actually required. At all other times the ATF should be recycled back to the transmission without flowing through the oil cooler. The present invention provides a reliable and cost-effective method to automatically bypass the ATF back to the transmission when the ATF does not require cooling.
Efforts have been made in the past to use a wax element to control the flow of ATF. However, this approach has reliability issues, because the high temperature and the high pressure under which an oil thermostat operates make it prone to failure. Even in more traditional uses, such as in water thermostats for engines, which typically operate a lower temperatures and lower pressures than the transmission, the wax thermostat is a failure-prone component because of the tendency of the wax to leak out of the wax capsule. In an oil application the use of a wax motor is even riskier.
It is an object of present invention to provide a thermostat that eliminates the wax element failure mode.
It is another object of present invention to provide a thermostat that is rugged and more reliable than conventional transmission thermostats.
It is still yet another object of present invention to provide a transmission oil thermostat with all the above benefits.
According to one particular aspect, the present teachings provide a transmission thermostat for controlling the flow of automatic transmission fluid between a transmission and a transmission oil cooler. The thermostat includes a temperature-sensitive mechanism. The temperature-sensitive mechanism may include at least one bimetallic coil.
The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
Corresponding reference numerals indicate corresponding parts throughout the several views of the drawings.
At the heart of the device of
The bi-metallic oil thermostat is a device that controls and directs the flow of oil from the transmission to either the transmission oil cooler, or back to the transmission when no cooling is required.
Under a cold oil condition, the bimetal coil (3) rotates the shaft (4), causing plates (7) and (8) to open and plates (9) and (10) to close. When plates (7) and (8) are open, the oil flows back to the transmission (TRANS) through port (11) with minimal impedance. Therefore the thermostat is in by-pass mode, preventing the oil to reach the transmission oil cooler (TOC).
As the oil temperature rises and the hot oil condition is reached, the bimetal coil (3) rotates the shaft (4) closing plates (7) and (8) while simultaneously opening plates (9) and (10). When orifices (21) and (22) are open, the oil communicates with port (12); thus flowing toward the transmission oil cooler (TOC). Oil then circulates through the heat exchanger, and returns to the housing (1) through port (13), then continues through port (11) with minimal impedance back to the pumping source.
When orifices (23) and (24) are closed in a hot condition, no oil is bypassing the cooler circuit. When orifices (21) and (22) are closed in a cold condition, no oil is allowed to flow through the cooler circuit. In thermal transition, all plates (7),(8), (9) and (10) are partially open allowing a modulated portion of oil to flow to the cooler circuit via port (12) and a portion to be bypassed through port (11).
The plates are designed in a balanced way, so that for instance when the oil pressure tries to close plate 41, it simultaneously tries to open plate 42, creating a zero net torque on the connecting shaft. The balanced design is key to this thermostat, because it allows the bimetal coil to control the rotation of the shaft with the relatively small torque exerted by the coil, which would be insufficient to overcome the high oil pressure forces if such a balanced approach was not used. The balanced design cancels the forces created by the oil pressure, allowing the bimetal coil to rule.
The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.
