*5.1. Experimental scheme*

In order to validate the effectiveness of the Autogram, an experiment was executed on a swashplate axial plunger pump with a center spring wear fault. The rotational speed of the pump was set as at 1470 r/min. The pressure transducer was set at the pump outlet, and the fluid pressure of the outlet was set as 10 MPa. The fluid pressure signal of the outlet was sampled at 10 kHz. The center spring wear fault feature frequency was 24.5 Hz [37].

The swashplate axial plunger pump experiment systems are shown in Figure 11.

(c) (d)

**Figure 11.** Swashplate axial plunger pump experiment systems. (**a**) Schematic diagram; (**b**) Swashplate axial plunger pump; (**c**) Data acquisition equipment; (**d**) Invalidation spring and the normal spring.

*5.2. Center spring wear fault signal of fluid pressure*

The center spring wear fault signal of fluid pressure in the frequency domain is shown in Figure 12.

**Figure 12.** Spectrum of the center spring wear fault signal.

It can be seen from Figure 12 that the fault feature information on center spring wear at fault feature frequency 24.5 with some harmonics is not obvious, and the amplitude values are very small. Thus, the fault feature information is contaminated by a lot of background noise.
