The need to reduce fossil fuel consumption and emissions from automobiles and other vehicles predominately powered by internal combustion engines (ICEs) is well known. Vehicles powered by electric motors attempt to address these needs. Another alternative solution is to combine a smaller ICE with electric motors into one vehicle. Such vehicles combine 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 motor called a generator. The generator, in turn, provides electricity to a battery and another motor, called 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 an electric 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 “split” parallel/series 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 with the engine “off”, 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 speed 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 drivability. 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 HEV development involves improvement of the vibration damping characteristics of the HEV powertrain mounting system. The ICE can be frequently started and stopped throughout a drive cycle. Vibration characteristics of an ICE during idle are different than during its normal operating speed. Automotive powertrain systems are generally suspended on a vehicle by support members usually called mounts. These mounts generally can be classified into two categories including rubber mounts and hydraulically damped rubber mounts. Each type has different anti-vibration characteristics.
A rubber mount, known in the art, utilizes a rubber element to achieve a desired anti-vibration characteristic. A hydraulically damped powertrain mount, known in the art, utilizes a rubber element, two fluid chambers, and a fluid de-coupler to achieve desired anti-vibration characteristics. The de-coupler can essentially be an orifice or other type of flow path that allows transfer of a fluid from one chamber to another. A larger orifice or shorter flow path allows easier fluid transfer and is useful for idle and start-up speeds. A smaller orifice or longer flow path restricts the fluid flow providing increased damping for normal engine running modes. See for example, U.S. Pat. No. 4,277,056 to Ticks.
Also known in the art are switchable powertrain mounts having a rubber element, two fluid chambers, two de-couplers, and a means to switch from one de-coupler to the other. The switching means can be vacuum controlled. This allows the same mount to achieve two sets of desired anti-vibration characteristics to minimize engine vibration felt by the vehicle occupants. One set of characteristics is designed to minimize vibration felt during engine idling, and the other set of characteristics is designed to minimize low-frequency vibration felt during driving. See for example, U.S. Pat. No. 5,642,873 to Kato. In these switchable mounts, the mount is simply controlled by the vacuum line. No controller or control logic is used to control the switchable mount.
In an HEV, a controller is useful to determine when to switch the mount to accommodate different vibration characteristics. For example, U.S. Pat. No. 4,161,304 to Brenner et al. uses a vibration sensor to determine the amount of spring rate of a mount. Nevertheless, a controller is unknown in the art to address the unique characteristics of an HEV powertrain. This controller would need to accommodate frequent engine start and stops in the typical HEV drive cycle.