Electromagnetic suspension system

An electromagnetic suspension system comprising:

• an electromagnetic suspension unit which is provided for a wheel of a vehicle and which is disposed between a body-side portion and a wheel-side portion of the vehicle, said electromagnetic suspension unit including (a) a hydraulic shock absorber and (b) an electric actuator that is configured to apply a vertical force between the body-side portion and the wheel-side portion;
• and
• a performance-change detecting device including an actual absorber-expansion/contraction-related amount obtaining portion configured to obtain an actual value of an absorber-expansion/contraction-related amount upon application of vibration to said electromagnetic suspension unit in a vertical direction, the absorber-expansion/contraction-related amount including at least one of amount and velocity of expansion/contraction of said shock absorber in the vertical direction,
• wherein said performance-change detecting device is configured to detect change of performance of said electromagnetic suspension unit, based on the actual value of the absorber-expansion/contraction-related amount obtained by said actual absorber-expansion/contraction-related amount obtaining portion,
• wherein said hydraulic shock absorber and said electric actuator are disposed between the body-side portion and the wheel-side portion, in series with each other via an intermediate member,
• wherein said actual absorber-expansion/contraction-related amount obtaining portion includes an actual expansion/contraction-related-amount calculating portion that is configured to obtain an actual value of the absorber-expansion/contraction-related amount, based on an actual value of a sprung/unsprung-portions-distance-related amount and an actual value of an electric-operation-related amount,
• wherein the sprung/unsprung-portions-distance-related amount includes at least one of amount and velocity of change of a distance between the body-side portion and the wheel-side portion, while the electric-operation-related amount includes at least one of amount and velocity of operation of said electric actuator,
• and wherein said performance-change detecting device includes:
• (a) an absorber-expansion/contraction-related amount estimating portion that is configured to obtain an estimated value of the absorber-expansion/contraction-related amount;
• (b) a portion that is configured to detect that a performance of said electric actuator is changed such that said electric actuator becomes closer to a free state, when a value related to an average of an absolute value of a difference between the estimated value and the actual value of the absorber-expansion/contraction-related amount over a predetermined time period is larger than a predetermined threshold value, and a value related to an average of an absolute value of a difference between the estimated value and the actual value of the sprung/unsprung-portions-distance-related amount over the predetermined time period is larger than a particular threshold value;
• and
• (c) a portion that is configured to detect that a performance of said shock absorber is changed such that resistance acting against the expansion/contraction of said shock absorber is increased, when the value related to the average of the absolute value of the difference between the estimated value and the actual value of the absorber-expansion/contraction-related amount over the predetermined time period is larger than the predetermined threshold value, and the value related to the average of the absolute value of the difference between the estimated value and the actual value of the sprung/unsprung-portions-distance-related amount over the predetermined time period is not larger than the particular threshold value.