Importance

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Abstract

This invention concerns an electric drive system (200) for driving an output. The electric drive system comprises: a first electric motor (250) arranged to drive a first input shaft (230) at a first angular velocity, ω₁, and a second electric motor (260) arranged to drive a second input shaft (240) at a second angular velocity, ω₂. A gear mechanism (210) is provided and is arranged to transmit angular rotation of the first (230) and second (240) input shafts to drive the output (220) at an output angular velocity, ω_out, such that ω_out is proportional to aω₁-bω₂, where a and b are constants. The electric drive system (200) further comprises a controller (270) arranged to control operation of the first (250) and second (260) electric motors. When the output (220) is to be driven from ω_out=0, the controller (270) is arranged to control the first (250) and second (260) electric motors to drive the first (230) and second (240) input shafts. The input shafts are driven in a first phase to primary first and second angular velocities, ω_1,p and ω_2,p, such that aω_1,p≈bω_2,p. The input shafts are also subsequently driven in a second phase in which the first angular velocity, ω₁, or the second angular velocity, ω₂, or both are varied such that aω 1≠b_ω2 and the output is driven from ω_out=0. The result of this is that the motors run in a more efficient part of their output profile, even whilst the vehicle is at rest, pulling off (especially in situations of high output load such as on off-road or otherwise difficult terrain), or moving at low velocity.

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First Claim