VW LMi is the tightest known quadruple system with 2+2 hierarchy .
It consists of a W UMa-type eclipsing binary ( P _ { 12 } = 0.47755 days ) and another detached non-eclipsing binary ( P _ { 34 } = 7.93 days ) orbiting around a common center of mass in about P _ { 1234 } = 355 days .
We present new observations of the system extending the time baseline to study long-term perturbations in the system and to improve orbital elements .
The multi-dataset modeling of the system ( 4 radial-velocity curves for the components and the timing data ) clearly showed an apsidal motion in the non-eclipsing binary at a rate of 4.6 degrees/yr , but no other perturbations .
This is consistent with the nearly co-planarity of the outer , 355-day orbit , and the 7.93-day orbit of the non-eclipsing binary .
Extensive N-body simulations enabled us to constrain the mutual inclination of the non-eclipsing binary and the outer orbits to j _ { 34 - 1234 } < 10 degrees .