Automatic transmission

The invention concerns an automatic transmission with a bell housing in which a torque converter hub is in contact with a pump rotor.

It appears that in some powertrains (combination of engine and transmission) , bending frequency are excited at idle speed (about 600 rpm) and amplified in a frequency range around 220 to 280 Hz which corresponds to the second harmonics of pump orders and its side bands. This mode leads to a high noise and vibration level which is very obvious and disturbing for the driver at idle speed. The main path for the vibration is the torque converter hub directly in contact with the pump rotor. This specific noise is called "Moan" noise.

The objective of the present invention is to provide an automatic transmission with less pump noise and vibration which should at the same time be easy to manufacture.

This objective is attained according to the present invention in that the pump rotor is centered in the bell housing.

The present invention is based on the concept that according to the prior art, the pump rotor can translate a few millimeters along the Y and Z axes due to torque converter hub displacement (leading by a powertrain resonance in the case presented above) and that some of the noise and vibration are due to these small translations. By centering the pump rotor in the bell housing, those degrees of freedom are suppressed for the pump rotor and the noise and vibration are significantly reduced. First measurements have shown that up to 4.5 dB improvement at the pump main order and up to 10 dB improvement at the pump harmonics which are the main causes for the Moan noise can be achieved with the present invention.

According to a preferred embodiment of the invention, the surface of contact between the torque converter hub and the rotor is reduced to the tangs, the minimum which is necessary to spin the pump rotor.

According to another embodiment of the invention, the pump rotor is provided at its end which is in contact with the bell housing with a centring element.

Furthermore, due to the centring of the rotor itself directly in the bell housing, an intermediate piece between the pump rotor and the bell housing can be suppressed. This facilitates production logistics and maintenance costs.

In the following, the invention is described in detail with reference to the drawings in which

FIGURE 1 shows the general environment of the invention,

FIGURE 2 shows the prior art solution,

FIGURE 3 shows the solution according to the present invention.

FIGURE 1 shows the bell housing 1 which is closed by the pump cover 2 onto which the pump tower 3 is mounted. The stator shaft 4 extends through the pump cover 2 and the pump tower 3. Inside the bell housing 1, the torque converter hub 5 and the torque converter drive plate 6 are represented. The torque converter hub 5 drives the pump rotor 7 by the tangs 12. It can be seen that the pump rotor 7 according to the prior art is essentially a ring with 13 slots for the 13 vanes 8 and two pump rotor tangs 12 in its inner diameter used for making it spin, and the pump rotor 7 is centred (supported) by the torque converter hub 5 as shown in FIGURE 2b.

The pump vane 8 and the pump slide 9 are also shown in FIGURE 1.

It can be seen from FIGURE 2 that according to the prior art, a part 10 is arranged between the pump rotor 7 and the bell housing 1. This part 10 is used to center the pump rotor 7 in the pump system when the torque converter is not yet installed in the transmission during assembly of the transmission at the plant.

FIGURE 3 shows the arrangement according to the present invention. The pump rotor 7 has still its general form but is provided at its end with a small shoulder 11. This shoulder 11 is used to center the pump rotor 7 in the bell housing 1. With this design, the shoulder 11 supports (centers) the pump rotor 7 in the good driving position so that the contact surface between torque converter hub 5 and the pump rotor 7 can be minimized by increasing the pump rotor inner diameter by 1 mm. At the same time the main path for vibration coming from the powertrain resonance is suppressed thereby reducing significantly noise and vibration, especially at pump main order (13 ^th order) and at the pump harmonics (24 ^th , 26 ^th and 28 ^th order) .

Due to this different conception of the pump rotor 7, the pump rotor 7 according to the present invention is centered without play in the bell housing 1 and the small translations of a few millimeters which are possible to the pump rotor 7 according to the prior art are efficiently suppressed.

As shown in FIGURE 3, the part 10 is no more needed in the arrangement according to the present invention so that a cost reduction can be achieved with the present invention.