  We present the observational results from a detailed timing analysis of the
black hole candidate EXO 1846-031 during its outburst in 2019 with the
observations of Insight-HXMT, NICER and MAXI. This outburst can be classfied
roughly into four different states. Type-C quasi-periodic oscillations (QPOs)
observed by NICER (about 0.1-6Hz) and Insight-HXMT (about 0.7-8Hz) are also
reported in this work. Meanwhile, we study various physical quantities related
to QPO frequency.The QPO rms-frequency relationship in three energy band 1-10
keV indicates that there is a turning pointing in frequency around 2 Hz,which
is similar to that of GRS 1915+105. A possible hypothesis for the relationship
above may be related to the inclination of the source, which may require a high
inclination to explain it. The relationships between QPO frequency and QPO
rms,hardness,total fractional rms and count rate have also been found in other
transient sources, which can indicate that the origin of type-C QPOs is
non-thermal.
