Motor vehicles – Power – Electric
Reexamination Certificate
2000-03-20
2001-05-01
Camby, Richard M. (Department: 3618)
Motor vehicles
Power
Electric
C180S065100
Reexamination Certificate
active
06223844
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to fuel cell powered vehicles in which the propulsion motor receives electrical power from a fuel cell stack and, more particularly, to a fuel cell vehicle engine in which the propulsion motor is operatively connected to a device associated with the supply of a fluid stream to a fuel cell stack.
BACKGROUND OF THE INVENTION
Electrochemical fuel cells are an attractive power source for electric vehicles, including wheeled vehicles, trains, marine vessels and airborne vehicles. Electrochemical fuel cells convert a fuel and an oxidant to produce electric power, which can be used to power an electric propulsion motor in a vehicle. Thus, in a fuel cell engine, fuel- and oxidant-containing reactant streams are supplied to a fuel cell stack in order for it to operate. Typically a coolant fluid stream is also supplied to the fuel cell stack. Fuel cell stacks typically include inlet ports and manifolds for directing a fuel stream and an oxidant stream to the anode and cathode, respectively, and corresponding exhaust manifolds and outlet ports for expelling unreacted fuel and oxidant streams and reaction products. Stacks also usually include an inlet part and manifold for directing a coolant fluid to interior channels within the stack, as well as an exhaust manifold and outlet port for coolant fluid exiting the stack. As used herein, the term fuel cell stack refers to a plurality of fuel cells, regardless of the nature of their configuration or electrical interconnection.
In conventional fuel cell powered wheeled vehicles, one or more fuel cell stacks are used to electrically power an electric propulsion motor which is directly coupled, optionally via a speed reducer (single or multiple ratio transmission), to the vehicle drive shaft. In addition, the fuel cell stack provides independent electric power to numerous separate motors which drive auxiliary devices including pumps and heaters, such as, for example, an oxidant air compressor, fuel pump, power steering pump, air brake compressor, air conditioning compressor, cooling fans, and the like. Typically, when the vehicle is stationary, the propulsion motor does not rotate, and therefore auxiliary devices cannot be driven by the propulsion motor when the vehicle is stationary.
The separate motors for the auxiliary devices add significantly to the weight, volume, cost and complexity of a fuel cell engine. In particular, each motor in the system generally requires a motor controller or inverter (for example, for each synchronous AC motor) and associated control system, thus many duplicate components and subassemblies are required.
A fuel cell engine and its associated control systems can be simplified considerably by coupling the propulsion motor to mechanically drive one or more auxiliary devices in the vehicle.
It is particularly advantageous to couple the propulsion motor to mechanically drive one or more devices associated with the supply of a fluid stream to the fuel cell stack. For example, when the propulsion motor is coupled to drive a device for directing a reactant stream into the fuel cell stack a synergistic effect arises which can simplify and stabilize the engine control system. The electrical power output of a fuel cell stack is related to the rate of supply of fuel and oxidant to the fuel cells of the stack. As the vehicle requires more propulsive power the propulsion motor (at any specific torque) will demand more electric power from the fuel cell stack to increase its speed. As the speed of the propulsion motor increases so will the speed of a reactant supply device mechanically coupled to it, thus increasing the rate of reactant delivery to the stack in concert with the demand for increased electrical power output.
Similarly with stack cooling fluids, an inherent increase in the rate of coolant circulation as the propulsion motor demands more electric power, may be beneficial. One or more of the fuel cell stack cooling pumps may be coupled to be driven by the propulsion motor. Typically the stack generates more heat as it produces more power so, provided the increased rate of coolant circulation results in greater cooling, this arrangement can be advantageous.
SUMMARY OF THE INVENTION
In the present approach, an electric motor drives the propulsion system of the vehicle and the same motor is coupled to drive at least one device associated with the supply of a fluid stream into the fuel cell stack, and optionally other auxiliary devices in the vehicle, via a power take-off mechanism.
A fuel cell engine for a vehicle comprises at least one fuel cell stack for producing electric power from a fuel and an oxidant, a propulsion motor for propelling the vehicle, the motor being connected to receive electric power from the at least one fuel cell stack and operatively connected to mechanically drive a device for directing a fluid stream into the fuel cell stack. In preferred embodiments, the at least one fuel cell stack is a solid polymer fuel cell stack.
The propulsion motor is preferably coupled for propelling the vehicle via a transmission. In most terrestrial vehicles it is preferable to couple the electric propulsion motor to the vehicle drive shaft via a multi-ratio transmission or continuously variable ratio transmission, which may be automatic or manually controlled. The transmission can modify the propulsion motor r.p.m. and torque to meet the instantaneous propulsion power requirements of the vehicle. If the instantaneous torque requirement of the vehicle cannot be met at a particular propulsion motor speed because the engine power is limited (for example, because of a limit in the rate of delivery of a reactant stream into the fuel cell stack by a device mechanically coupled to the propulsion motor), then the transmission allows the ratio of the propulsion motor speed to vehicle speed to be adjusted to meet the torque requirement (correspondingly adjusting the reactant stream flow rate to better match the fuel cell power output requirement). Further, if a particular propulsion motor speed causes a reactant stream to be directed into the stack at too high a rate, then again the ratio between the propulsion motor speed and vehicle speed can be reduced via the transmission. Thus, through a transmission the propulsion power output may be adjusted somewhat independently of the requirements of a fluid delivery device, or any other auxiliary devices, coupled to the propulsion motor.
A further advantage is realized by having a transmission when the propulsion motor is mechanically coupled to drive a device for directing a reactant stream to the fuel cell stack. If the engine power demand cannot be met at a particular propulsion motor speed and the transmission reduces the ratio between vehicle speed and propulsion motor speed, the reactant supply device may be accelerated by the vehicle's inertia, thus assisting the fuel cell stack to respond more quickly to meet the increased power demand. In conventional systems, when fuel cell power demand increases, the energy required to accelerate a reactant supply device is derived only electrically from the fuel cell itself, thus the system may be slower to respond, due to limitations in the capability of motor and/or inverter of the device and in the fuel cell power output.
It is preferable that the propulsion motor be coupled for propelling the vehicle via a selective coupling mechanism, particularly in wheeled vehicles. This enables the propulsion motor to continue to drive auxiliary loads when the vehicle is idling and its speed is zero, and enables the motor and auxiliary loads to be driven slower when the vehicle is coasting (for example, downhill). The selective decoupling mechanism may comprise, for example, a clutch or torque converter. It is preferable that the decoupling device be capable of transmitting maximum motor torque while slipping, for substantial durations, during acceleration. The selective coupling mechanism may be part of the transmission system. A selective coupling mechanism may not be necess
Corless Adrian J.
Greenhill Craig J.
Merritt Robert D.
Mufford W. Edward
Camby Richard M.
McAndrews Held & Malloy Ltd.
Xcellsis GmbH
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