The present invention relates to a rotational unit having a mechanical rotational device; an electric rotational device, which is coupled to the rotary shaft of the mechanical rotational device and functions as at least one of a motor and a generator; and a rotational member, which is coupled to the rotary shaft and has a power transmitting mechanism located at the periphery of the rotational member for transmitting power between the rotational unit and an external device.
Japanese Laid-Open Utility-Model Publication No. 6-87678 discloses such a rotational unit.
In the rotational unit disclosed in the publication, the rotary shaft of a mechanical rotational device (the compression mechanism of a hybrid compressor) is coupled to an electric rotational device (a motor). A rotational member (a pulley) is also coupled to the rotary shaft for transmitting power from an external device (an engine). An electromagnetic clutch is located between the rotational member and the rotary shaft to selectively transmit power.
As the electromagnetic clutch is engaged and disengaged, the mechanical rotational device is driven by the force of the engine and the rotor of the electric rotational device is rotated to generate electricity, and the mechanical rotational device is driven by the force of the electric rotational device.
The rotational member is coupled to a power transmitting mechanism. A belt is engaged with the power transmitting mechanism to transmit power of the engine to the rotational member. The electric rotational device is displaced from the power transmitting mechanism in the axial direction of the rotary shaft.
The rotor of the electric rotational device includes permanent magnets. The electric rotational device also includes a stator part, which is formed with a conductor wire. The electric rotational device is driven by electricity supplied from a battery connected to the conductor wire. Also, the battery is charged with electricity generated by the electric rotational device.
Although the electric rotational device is axially displaced from the power transmission, the radial dimension of the electric rotational device is not increased to increase the power. Also, since the electromagnetic clutch is formed with relatively large members such as electromagnets, the size of the rotational member is increased. When the electromagnetic clutch is engaged or disengaged, the clutch is controlled by external electric signals, which complicates the structure.
When the mechanical rotational device is driven by the engine, the rotor is dragged along and rotated. At this time, since the rotor includes permanent magnets and magnetic force of the rotor acts on the stator, heat is generated due to excitation loss of the stator, which causes energy loss. When the rotor is dragged along and rotated, the force between the permanent magnets and the stator changes due to changes in distances between the poles of the permanent magnets and the poles of the stator. This fluctuates the torque acting on the rotary shaft and thus generates rotational vibration.
Current generated by the electric rotational device may be smoothed. To smooth the current, a capacitor may be connected to the battery in parallel. Even if the battery is disconnected from the capacitor by a relay when the battery need not be charged, the electricity continues to be generated as long as the rotor is dragged along and rotated. Accordingly, the voltage between the terminals of the capacitor becomes excessive, which may damage the capacitor. Therefore, the voltage between the terminals of the capacitor needs to be controlled such that it does not become excessive, which complicates the structure.
Accordingly, it is a first objective of the present invention to provide a compact and simple rotational unit that permits the size of an electric rotational device to be increased regardless of the size of a power transmitting mechanism to increase the power of the electric rotational device. A second objective of the present invention is to provide a rotational unit that reduces energy loss when a mechanical rotational device is driven by an external drive source and suppresses rotational vibrations of a rotary shaft.
To achieve the foregoing and other objectives and is accordance with the purpose of the present invention, a rotational unit having a mechanical rotational device, a rotary shaft, an electric rotational device, a rotational member, a one-way clutch is provided. The mechanical rotational device has a housing. The housing includes a front wall. The rotary shaft has an end portion that protrudes from the front wall of the housing. The electric rotational device is coaxial with the rotary shaft. The electric rotational device is coupled to the end portion of the rotary shaft and functions as at least one of a motor and a generator. The rotational member is coupled to the rotary shaft and has a power transmitting mechanism for transmitting power between the rotational unit and an external device. The a one-way clutch is located in a power transmitting path between the rotary shaft and the rotational member. The one-way clutch is located inward of the rotational member. The electric rotational device is located on or forward of the front wall of the housing. At least part of the electric rotational device is located outside the outer dimension of the power transmitting mechanism.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.