The present invention relates generally to electric vehicles (EVs), fuel cell electric vehicles (FCEVS) and hybrid electric vehicles (HEVs), and specifically to a method and system to disconnect an electric motor/generator powertrain from the vehicle driveline system.
The need to reduce fossil fuel consumption and emissions in automobiles and other vehicles predominately powered by internal combustion engines (ICEs) is well known. Vehicles powered by electric motors attempt to address these needs. An alternative solution combines a smaller ICE with electric motors into one vehicle. Such vehicles have the advantages of an ICE vehicle and an electric vehicle and are typically called hybrid electric vehicles (HEVs). See generally, U.S. Pat. No. 5,343,970 to Severinsky.
The HEV is described in a variety of configurations. Many HEV patents disclose systems where an operator is required to select between electric and internal combustion operation. In other configurations, the electric motor drives one set of wheels and the ICE drives a different set.
Other, more useful, configurations have developed. For example, a series hybrid electric vehicle (SHEV) configuration is a vehicle with an engine (most typically an ICE) connected to an electric generator motor. The generator motor, in turn, provides electricity to a battery and a second motor, a traction motor. In the SHEV, the traction motor is the sole source of wheel torque. There is no mechanical connection between the engine and the drive wheels.
A parallel hybrid electrical vehicle (PHEV) configuration has an engine (most typically an ICE) and a motor that work together in varying degrees to provide the necessary wheel torque to drive the vehicle. Additionally, in the PHEV configuration, the motor can be used as a generator to charge the battery from the power produced by the ICE.
A parallel/series hybrid electric vehicle (PSHEV) has characteristics of both PHEV and SHEV configurations and is sometimes referred to as a xe2x80x9cpowersplitxe2x80x9d configuration. In one of several types of PSHEV configurations, the ICE is mechanically coupled to two electric motors in a planetary gear-set transaxle. A first electric motor, the generator, is connected to a sun gear. The ICE is connected to a carrier. A second electric motor, a traction motor, is connected to a ring (output) gear via additional gearing in a transaxle. Engine torque can power the generator to charge the battery. The generator can also contribute to the necessary wheel (output shaft) torque if the system has a one-way clutch. The traction motor is used to contribute wheel torque and to recover braking energy to charge the battery. In this configuration, the generator can selectively provide a reaction torque that may be used to control engine speed. In fact, the engine, generator motor and traction motor can provide a continuous variable transmission (CVT) effect. Further, the HEV presents an opportunity to better control engine idle speed over conventional vehicles by using the generator to control engine speed.
The desirability of combining an ICE with electric motors is clear. There is great potential for reducing vehicle fuel consumption and emissions with no appreciable loss of vehicle performance or driveability. The HEV allows the use of smaller engines, regenerative braking, electric boost, and even operating the vehicle with the engine shutdown. Nevertheless, new ways must be developed to optimize the HEV""s potential benefits.
One such area of electric powertrain development (not only for the HEV, but any electric powered vehicle) is the need for powertrain/driveline disconnect systems. An electric motor disconnect system would provide added reliability and functionality for the vehicle and powertrain. The disconnect system in an electric powertrain configuration would be useful in a number of vehicle conditions such as a rear-end accident, motor seizure, unmitigated over-torque conditions, unmitigated motor over-temperature/current conditions, and vehicle operating modes such as flat towing (or neutral tow) the vehicle, four wheel, and two wheel drive control in vehicles that are configured as four wheel drive.
Systems to switch off electric motor power from a powertrain are known in the prior art, but systems to disconnect the electric motor driveshaft from the wheels are not known. In HEVs with electric motor drives, an inertia switch, known in the prior art, can be used to disconnect the motor from the high voltage power supply. An inertia switch can have two functions. It can stop fuel supply to the engine and high voltage power to the electric motor(s). This works well in situations such as a rear-end collision. Nevertheless, in the case of an electric drive with a permanent magnet (PM) electric motor, this strategy does not always result in reliable vehicle operation. PM motors/generators rotate at high speeds and are capable of generating very high voltages. For example, if a PM motor is operated at high speeds, traveling down a hill, and is involved in a rear-end accident, the vehicle speed can be forced above a maximum safe vehicle speed. In this condition, while the inertia switch will turn off the high voltage, turning off the high voltage power supply is not adequate. The PM motor and powertrain will continue to be connected to the vehicle driveline system and will continue to rotate and generate high voltages in the motor windings and at the motor terminals. The resultant high voltage developed at the motor terminals in this condition can cause fires or permanent damage within the powertrain such as its electronic circuit boards, capacitors, diodes, motor windings, etc.
Other types of powertrain failures in electric powered vehicles must also be anticipated. All electric powered vehicles are subject to electric motor/generator seizure and rotor lock-up due to failures that can occur internal and external of the motor/generator. Internal failures that can cause seizure include foreign debris, broken components, and coil insulation failure. External failures include sensor failure, low inverter voltage, control module failure, communications failure, and motor speed calculation failure. When these failures occur, over-current and over-temperature conditions internal to the electric motor/generator can occur, and if not caught in time, can lead to seizure and lock-up of the electric motor. In this condition, the vehicle can be forced to an unexpected and abrupt stop. Monitors and controls are known in the prior art that can mitigate these types of failures. Unfortunately, if these monitors and controls fail, severe electric motor/generator and powertrain damage can occur. For example, U.S. Pat. No. 6,135,914, to Yamaguchi et al., addresses the problem of motor speed control after a generator accident. Unfortunately, this control system assumes electronic controls are still available. Further, it does not address motor/generator over voltage and the issues related with PM motor/generator applications. Over-torque conditions can also exist in an electric vehicle such as when the torque supplied is greater than the torque requested. Too much torque can cause excessive and unexpected acceleration to occur.
Therefore, a system and method needs to be developed to monitor the electric motor and sense when lock-up occurs, disconnect the electric motor/generator and powertrain from the driveline system and allow the driver to come to a controlled stop. In cases where monitors and controllers for over-torque and over-temperature conditions fail, a powertrain disconnect needs to be developed. Ideally, this system and method can be developed using existing component technologies. Additional advantages to this disconnect system could allow a flat tow of the electric powered vehicle and to provide a four wheel or two wheel drive control.
Accordingly, the present invention provides wheel-end and center axle disconnects for a vehicle with an electric motor/generator powertrain attached to the vehicle driveline system, such as an electric vehicle (EV), fuel cell electric vehicle (FCEV), and hybrid electric vehicle (HEV). The present invention can monitor the electric motor/generator and sense when lock-up or failures occur, and disconnect the electric motor/generator powertrain from the driveline system. This can allow the driver to come to a controlled stop. In cases where monitors and controllers for over-torque and over-temperature conditions fail, the disconnects function as a redundant fail-safe.
The present invention in its preferred embodiment is able to use existing component technologies. Additional advantages to this disconnect system would allow neutral tow and four wheel/two wheel drive control of an electric powertrain vehicle.
Specifically, the present invention is a method and system to disconnect at least one drive wheel from the vehicle driveline system, with an electric generator/motor powertrain connected to the driveline system. The powertrain and driveline system can include an electric motor mechanically connected to an output shaft, the output shaft mechanically connected to at least one axle, the axle mechanically connected to at least one drive wheel; the axle further comprising a means to mechanically disconnect the output shaft from at least one drive wheel; a vehicle system controller comprising monitors for input from an inertia switch and electric motor/generator conditions which can activate the means to mechanically disconnect the output shaft from the drive wheels in predetermined vehicle conditions. The predetermined vehicle conditions can include activation of the inertia switch such as during a rear-end collision, or abnormal electric motor/generator conditions such as over-torque, over-temperature, or over-current. The invention can also be configured to monitor driver demand for four wheel drive, two wheel drive, and neutral tow and activate the means to mechanically disconnect the output shaft from at least one drive wheel to meet that demand.
The means to mechanically disconnect the output shaft from the drive wheels comprises of a disconnect actuator and a joint attached to an axle. The disconnect actuator can be electric or vacuum powered. The disconnect joint(s) can be positioned in a center axle or wheel-end configuration. The type of disconnect configuration used for the present invention is determined by the type of axle used in the vehicle. If the axle is a conventional type axle and open differential, it will use single or center axle disconnect. Those vehicles that use limited slip differential axle, or a transaxle will require two disconnects in a wheel-end configuration.
Other objects of the present invention will become more apparent to persons having ordinary skill in the art to which the present invention pertains from the following description taken in conjunction with the accompanying figures.