Electricity: motive power systems – Battery-fed motor systems
Reexamination Certificate
2000-01-31
2001-06-05
Nappi, Robert E. (Department: 2837)
Electricity: motive power systems
Battery-fed motor systems
C318S430000, C180S065100, C180S065230, C180S065310, C180S065510
Reexamination Certificate
active
06242873
ABSTRACT:
FIELD OF THE INVENTION
The present invention relays to hybrid electric vehicles and more specifically to an energy management system for such vehicles.
BACKGROUND OF THE INVENTION
Hybrid vehicles generally have an electric drive train, an electrochemical battery as an energy storage device and an internal combustion (IC) engine. Series hybrid vehicles have no mechanical connection between the internal combustion engine and the drive train whereas parallel hybrid systems do have a mechanical cling.
Energy Management Concept and Objectives
The key difference between conventional vehicles, which generally rely solely on an internal combustion engine connected to a drive in for motive power, and hybrid vehicles is that the hybrid vehicles offer a virtually unlimited number of system configurations characterised by their energy flow patterns. The overall efficiency of a conventional vehicle is determined primarily by the combined efficiency of its components. The overall efficiency of a hybrid vehicle is determined by its configuration and the utilisation of the components. For instance, the operation of a hybrid vehicle with an undersized auxiliary power unit (APU) on a highway will result in a much higher energy use and lower efficiency than for a vehicle with a larger APU as the balance of the traction power must come from the battery and be later replenished. On the other hand, an oversized APU in a low speed operation will cause battery overcharging leading to frequent engine restarts. Due to the wide range of road loads encountered by a hybrid vehicle in normal operation, the objective of maximising energy efficiency cannot be achieved with a rigid system designed for average operating conditions. Energy management is a key element to ensure that the vehicle energy resources are utilised in a most effective manner.
The objectives of the energy management system is to minimise the energy consumption and emissions while reducing the component load. In a most common hybrid system configuration, consisting of an IC engine-based Auxiliary Power Unit (APU) and an electrochemical battery the objective is to operate the engine as close as possible to its maximum efficiency point, while eliminating the transients, and to use the battery to supply the power boost during acceleration, hill climbing and other high load driving modes. Since the road load varies widely during the duty cycle, the energy management system must adjust the energy flow to satisfy the road load demand and maintain the battery stale of charge.
Thermostatic (On-Off) Strategy
Early hybrid electric vehicles employed a thermostatic or on-off energy flow control strategy. The concept was based on switching the generator set on when the battery state of charge dropped below a prescribed level and off when the upper allowable state of charge level was exceeded.
The main disadvantage of the above approach is that the battery must be rather large to provide the capability of operating in the electric mode for extended periods of time, often at high loads. In order to provide a reasonable frequency of the engine cycling, the operating range of the battery state-of-charge has to be relatively wide, which results in a high overall energy loss due to the large amount of energy flowing through the battery. The losses are compounded by the fact that the battery discharge rates in the electric mode are higher than in hybrid mode. The need to recharge the battery from a deeper state of discharge in a reasonable time requires also higher charging rates. There is also an issue of the thermal balance of the battery where the large amount of energy dissipated in the battery may lead to battery overheating and loss of functionality of the system.
Load Following Strategy
The second generation of hybrid vehicles addressed the above problems by utilising a load-following control strategy where the auxiliary power unit output is controlled in response to the battery state-of-charge change. In such systems, the battery state-of-charge remains within a narrow range defined as optimum for the given battery type. The load-following approach reduces the energy exchanged with the battery and improves the overall efficiency of the system. However, since the APU operation is not directly correlated with the road load demand, the APU operation occurs at random and, in cases when the APU output does reflect the road load demand, the battery is discharged and charged at high rate, incurring excessive energy losses.
Adaptive Strategy
The ultimate form of hybrid vehicle energy management is an adaptive system where the energy flow is always in balance with the road load demand to ensure minimum energy use, minimum emission and the lowest possible component load at all times. In the ideal implementation, the power split between the battery and the auxiliary power unit is set in such a way that the total energy supplied by the battery and the auxiliary power unit to the wheels is always minimum for any finite time period. That means that the output of the auxiliary power unit must be varied to correspond with the general load pattern and the battery must be used only for a short duration power boost. A typical road load profile consists of a number of cycles that include an initial acceleration phase, cruising phase including one or several sections at approximately constant speeds, separated by short periods of acceleration or deceleration, and the final phase of deceleration to stop. Ideally, the system energy balance on each of such cycles would be such that the battery state of charge at the end of the cycle would be equal to that at the beginning of the cycle. However, this approach is not practical as some of these cycles are very short compared to the time constants of the hybrid drive train components. A finite time period must be used which would allow the system to respond to the read load demand in quasi-steady state manner.
Related Patent Discussion
The inventors are aware of prior patents directed to hybrid electric vehicles where energy management is addressed. Specifically, the energy management in this context is defined as controlling tee battery state of charge.
Early patents such as U.S. Pat. No. 4,187,436 to Etienne issued on Feb. 5, 1980 proposed hardware-based solutions to control the battery state of charge by switching the generator on and off. With tie development of the microprocessor technology in the 1980s, the focus shifted to software-based control systems relying on a microprocessor to implement the control strategy.
In the 1990s, a number of patents were issued that addressed the load-following approach. Two Ford patents, U.S. Pat. No. 5,264,764 to Kuang issued on Nov. 23, 1993 and U.S. Pat. No. 5,318,142 to Bates issued on Jun. 7, 1994, proposed a systems that numerically integrated the battery current and voltage to determine the required auxiliary power unit output. Toyota's U.S. Pat. No. 5,550,445 to Nii issued on Aug. 27, 1996 described a load-following systems where the engine is activated when a heavy motor load is detected to prevent an excessive battery discharge and shut down at low load to prevent the battery overcharging Another patent by Nii (U.S. Pat. No. 5,650,931 issued Jul. 22, 1997), proposed a system that analysed the vehicle's past power demand history and adjusted the generator output in accordance with the most frequent power value. A third patent by Nii (U.S. Pat. No. 5,698,955 issued Dec. 16, 1997) described a system to control the power in series hybrid vehicles where the power demand determined from the analysis of previous time intervals was corrected by several factors such as motor acceleration, battery state of charge trends etc. to reduce the control delay. A fourth patent by Nii (U.S. Pat. No. 5,804,947 issued Sep. 8, 1998) described a similar control system that used battery current rather than the dc link power for determining the power demand. U.S. Pat. No. 5,786,640 to Sakai issued on Jul. 28, 1998 and assigned to Nippon Soken proposed a fuzzy logic approach to improve the co
Drozdz Piotr
Zettel Andrew
Azure Dynamics Inc.
Nappi Robert E.
Smith Tyrone
Townsend and Townsend / and Crew LLP
LandOfFree
Method and apparatus for adaptive hybrid vehicle control does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for adaptive hybrid vehicle control, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for adaptive hybrid vehicle control will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2532010