Patent Application
20190093547
The present disclosure relates to a method and system for coolant temperature control in a vehicle propulsion system.
This introduction generally presents the context of the disclosure. Work of the presently named inventors, to the extent it is described in this introduction, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against this disclosure.
Vehicle propulsion systems may include thermal management systems which regulate the temperature of the prime mover such as an internal combustion engine and the like. Temperature management of an internal combustion engine may be important to optimize fuel economy, efficiency, reliability, and durability of, not only the engine, but also of the overall system.
Many thermal management systems for vehicle propulsion systems rely upon a flow of coolant passing through the engine that is regulated by a very simple thermostat. The ability of such a system to accurately and reliably maintain a desired, or target temperature for the engine is very crude. Response to temperature changes can be very slow and only control the temperature within a very wide range.
In an exemplary aspect, a vehicle propulsion system includes a prime mover having a coolant inlet and a coolant outlet, a coolant control valve having a valve inlet in communication with the prime mover coolant outlet, a first valve outlet, and a second valve outlet, a bypass flow path in communication with first valve outlet and the prime mover coolant inlet, a heat exchange flow path in communication with the second valve outlet and the prime mover inlet, a heat exchanger in the heat exchange flow path, a first temperature sensor in the bypass flow path for generating a first temperature signal, a second temperature sensor in the heat exchange flow path for generating a second temperature signal, and a controller in communication with the first temperature sensor for receiving the first temperature signal, the second temperature sensor for receiving the second temperature signal, and the coolant control valve for providing a coolant control valve command signal to the coolant control valve. The controller is a closed loop controller with a gain coefficient, and the controller normalizes the gain coefficient.
In another exemplary aspect, the closed loop controller is a proportional/integral closed loop controller.
In another exemplary aspect, the gain coefficient is one of a proportional gain coefficient and an integral gain coefficient for the proportional/integral closed loop controller.
In another exemplary aspect, the controller normalizes the gain coefficient based upon a ratio of a predetermined difference in values between a first temperature signal and the second temperature signal and a current difference in values between a first temperature signal and the second temperature signal.
In another exemplary aspect, the predetermined difference in values between a first temperature signal and the second temperature signal correspond to a first temperature signal value and a second temperature signal value which both correspond to the gain coefficient.
In another exemplary aspect, the second temperature sensor is downstream of the heat exchanger in the heat exchange flow path.
In another exemplary aspect, the bypass flow path and the heat exchange flow path combine to form a prime mover coolant inlet flow path at the prime mover coolant inlet.
In another exemplary aspect, the third temperature sensor is positioned in the prime mover coolant inlet flow path.
In this manner, thermal management of a prime mover in a vehicle propulsion system may be greatly improved and provide more reliable, responsive, and accurate control of temperature. The system temperature may then be continually optimized over a wide range of operating conditions. This enables more confidence which permits a prime mover to operate closer to a potential threshold temperature while reducing the risk of deviating from a target temperature. In turn, this enables improved fuel economy, efficiency, performance, reliability and durability of the components of the system. Further, this also significantly reduces the calibration workload that might be otherwise required.
Further areas of applicability of the present disclosure will become apparent from the detailed description provided below. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure.
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.
The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein:
Thermal management of a prime mover, such as, for example, an engine, motor, battery pack and/or the like, in a vehicle propulsion system may be critical for obtaining optimal performance, reliability and durability.
The thermal management system 100 may operate in accordance with instructions generated by a control architecture. For example, the coolant control valve controller 112 may receive a first temperature signal, T1, from a first temperature sensor 124 that is positioned in the bypass flow path 116 and which senses the temperature of coolant flowing through the bypass flow path 116. The coolant control valve controller 112 may also receive a second temperature signal, T2, from a second temperature sensor 126 that is positioned in the heat exchange flow path 118 and which senses the temperature of coolant exiting the heat exchanger 122 in the heat exchange flow path 118. The coolant control valve controller 112 may further receive a third temperature signal, T3, from a third temperature sensor 128 that is positioned at the engine coolant inlet 120.
Based upon the first temperature signal, T1, the second temperature signal, T2, and the difference between the third temperature signal, T3, and a target engine coolant temperature the coolant control valve controller 112 may control the coolant control valve 110 in a manner that results in a split in the volume of flow between the bypass flow path 116 and the heat exchange flow path 118 which approaches a target temperature, T3, of the coolant entering the engine coolant inlet 120. In an exemplary embodiment, the coolant control valve controller 112 may operate as a proportional/integral closed loop controller The coolant control valve controller 112 may operate the coolant control valve 110 in accordance with the following:
dV=Kp×T
error
+Ki×∫
t−1
t
T
error
dt (1)
Where dV is the controller-determined change in the volume split between the bypass flow path 116 and the heat exchange flow path 118, Kp is a proportional coefficient, Terror is the difference in temperature between the target inlet temperature and the actual inlet temperature, and Ki is an integral coefficient. Terror may be determined according to:
T
error
=T
target
−T
3 (2)
Where Ttarget is the desired or targeted coolant temperature at the engine coolant inlet 120 and T3 is the actual coolant temperature at the engine coolant inlet 120.
In this manner, the thermal management system 100 may control the amount of heat removed from the prime mover 102 by diverting proportions of a stream of coolant exiting the prime mover 102 into two streams, the relative proportions of those streams may be adjusted with a closed loop controller that operates based upon an error or difference between a target coolant inlet temperature and an actual coolant inlet temperature. However, the effectiveness of this thermal management system 100 is based upon proportional and integral coefficients which are determined by calibrating those coefficients for a specific set of conditions. As those conditions change from that specific set of conditions, the coefficients which correspond to optimized prime mover performance at a new set of conditions also change. Any reduction in temperature control of the prime mover as a result of a change in operating conditions may have adverse effects on the fuel efficiency, economy, durability, reliability, and performance of the prime mover. In an attempt to address the changing conditions, multiple different sets of coefficients may be determined which each correspond to a different set of operating conditions. However, determining these multiple different sets of coefficients requires a significant amount of calibration workload. Further, the operating conditions of a prime mover may vary widely and it becomes increasingly difficult to obtain a set of coefficients for each different set of operating conditions. Any increase in the resolution of the operating conditions for which coefficients are determined, requires a corresponding increase in calibration workload to obtain those coefficients.
In accordance with an exemplary embodiment of the present disclosure, the thermal management system may significantly improve the ability to accurately control the temperature of the prime mover for a wide range of varying operating conditions by using a leveraged normalization factor. The inventors discovered that by comparing the energy balance across the thermal management system at a reference temperature to the energy balance of the thermal management system at actual temperatures across a wide range of operating conditions enables a scaling of the control system coefficients which accurately and reliably controls the prime mover temperature to a target temperature. In this manner, the control system coefficients may be continuously optimized across a wide variety of operating conditions while simultaneously obviating a large calibration workload.
The inventors discovered that the temperature of the heat exchanger 122 has a large impact upon the effectiveness of the heat exchanger 122 to reject heat and, therefore, its impact upon the temperature of the coolant entering the prime mover 102. For example, when the heat exchanger 122 is cold the impact of the heat exchanger 122 upon the coolant temperature is larger than when the heat exchanger 122 is warm. When the heat exchanger 122 is colder than the temperature at which the control system coefficients were determined, then any controller determined adjustment in the proportional volume between the two streams 116 and 118 may have a larger impact upon the temperature of the coolant at the inlet 120 than intended. This may lead to a potential overshoot in temperature and an instability in the temperature. In contrast, when the heat exchanger 122 is warmer than the temperature at which the control system coefficients were determined, then any controller determined adjustment in the proportional volume between the two streams 116 and 118 may have a smaller impact upon the temperature of the coolant at the inlet 120 than intended. This may lead to a significant increase in the delay with which the actual temperature of the coolant at the inlet 120 approaches the target temperature. In other words, this may result in an overdamped system.
To address and overcome these deficiencies, the inventors created a leveraged and normalized factor which scales the coefficients such that they are continuously optimized to provide improved control over the coolant temperature at the inlet 120. The inventors devised a coolant control valve leverage factor, Fccv, which is determined based upon:
Where (T1−T2)standard is the difference between the first temperature, T1, and the second temperature, T2, at a predetermined set of operating conditions and (T1−T2)current is the difference between the first temperature, T1, and the second temperature, T2, at current or actual conditions. Preferably, the operating conditions and corresponding temperatures, T1 and T2, are the same operating conditions and temperatures, T1 and T2, at which the control system coefficients were determined. For example, during a calibration procedure the prime mover 102 may be operated in an actual vehicle propulsion system and those coefficients which provide a desired and/or optimized control over the prime mover temperature for a given set of conditions may be determined and the temperatures, T1 and T2, for that set of conditions may then be set as the standard temperatures with which a value for (T1−T2)standard is stored and used for the calculation of Fccv.
Using Fccv, the coefficients for the control system may be continuously optimized. For example, in a control system using a proportional gain coefficient and an integral gain coefficient, the gains may be adjusted and/or compensated using:
K
PC
=K
P
×F
ccv; and (4)
KIC=KP×Fccv (5)
Where KP is the proportional gain coefficient that was obtained during calibration, KI is the integral gain coefficient that was obtained during calibration for a proportional/integral control system, KPC is the compensated proportional gain coefficient, and KIC is the compensated integral gain coefficient, where Fccv is determined as described above.
Control over the coolant control valve 110 may then be based upon the following:
dV=K
PC
×T
error
+K
IC×∫t−1tTerrordt (6)
Where dV is the change in volumetric flow rate between the bypass flow path 117 and the heat exchange flow path and Terror is determined in the same manner as explained above with reference to equations (2) and (3). dV may then be used to control the position of the coolant control valve.
These oscillations may further have an adverse impact upon the durability and reliability of the coolant control valve. Every time the temperature at the inlet fluctuates in
In stark contrast, the response of the thermal management system in accordance with an exemplary embodiment of the present disclosure which uses the leveraged and normalized factor, FCCV, as described above to adjust or compensate the control system coefficients provides an improved temperature response 208 which better follows the target temperature 204. This further reduces and/or eliminates the requirement for the coolant control valve to continuously adjust. The coolant control valve may be accurately and appropriately positioned immediately and/or much sooner which significantly reduces the wear and improves the reliability and durability of the coolant control valve.
This description is merely illustrative in nature and is in no way intended to limit the disclosure, its application, or uses. The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent upon a study of the drawings, the specification, and the following claims.
