Hydraulics Quiz No. 3 (second copy): suspension and frequency calculation

In this document

Multiple-choice questionnaire (p. 30)

This document is the Hydraulics Quiz No. 3, presented as "the third of the six Hydraulics quizzes" p. 30, to be returned within a fortnight. The seven questions concern suspension: shock absorption according to flexibility (Q1), the fate of shock energy between sphere and shock absorber (Q2), pressure distribution between spheres (Q3), the installation of height correctors (Q4), the operation of height correction during a load decrease (Q5), whether corrections are systematic or not (Q6), and the filling conditions of a sphere according to its residual nitrogen pressure, with numerical thresholds of 15 bar and 65 bar proposed as answers (Q7) p. 30.

A contact number is indicated: "49 45 43 56", fax "40 11 44 97" p. 30.

Frequency calculation exercise (p. 31)

Page 31 proposes an exercise based on the frequency formula for a mechanical spring suspension, f = 1/(2π) × √(K/m), with K being the spring stiffness and m the applied mass p. 31.

It is requested to calculate this frequency for m = 500 kg and K = 33,360 newton/meter, then to determine the new frequency if the mass increases by 300 kg, with three answers proposed (2 Hz, 1.3 Hz, 1 Hz) p. 31.

The following questions concern the consequence on comfort ("harder", "softer", "identical"), the stiffness to give the spring to maintain the same comfort (with four values in daN/m proposed: 33,360, 53,376, 20,850, 53,321), and finally the behavior of a gas spring suspension when faced with the same mass variation p. 31.

The bottom of the page includes a space for remarks, as well as fields for "Time required", "Signature", "Done at", "on", which remained empty on this copy p. 31.

Context

The principle mentioned here — replacing the metal spring with a volume of pressurized gas in a sphere — refers to the hydropneumatic suspension developed by Paul Magès for Citroën, whose natural frequency varies differently from that of a conventional mechanical spring when the load increases. This contrast between gas spring and mechanical spring is precisely what the exercise seeks to reveal.

This quiz seems to be part of a distance learning system intended for Citroën network technicians, probably in the 1990s, a period when the company formalized the pedagogy of its "Hydraulics Expert Notebooks".

Archivist's perspective

This document constitutes a second copy of Quiz No. 3, identical in content to another copy already listed in the collection. Its presence in duplicate probably illustrates the serial distribution method of these self-training modules, sent to several trainees or kept as a carbon copy as indicated by the final mention "Keep the carbon copy" p. 31.

The frequency exercise p. 31 is particularly revealing of the system's pedagogy: it makes the user concretely manipulate the physical difference between conventional suspension and gas suspension, the heart of the innovation brought by Magès.

This quiz can be compared to Quiz No. 5 and No. 6, as well as the Expert Notebooks welcome booklet, which clarifies the general organization of this six-module training.