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We probe the dusty environment of the archetypical type-1 AGN in NGC 4151with comprehensive IR reverberation mapping over several decades, in J($\sim1.22\mu$m), H ($\sim1.63\mu$m), K ($\sim2.19\mu$m), L ($\sim3.45\mu$m)and N-band ($\sim10.6\mu m$), plus multiple measurements at 20--40 $\mu$m. At1--4$\mu$m, the hot dust reverberation signals come from two distinct dustpopulations at separate radii ($\sim$0.033 pc and $\sim$0.076 pc), withtemperatures of $\sim$1500--2500 K and $\sim$900--1000 K, consistent with theexpected properties of sublimating graphite and silicate dust grains. Thedomination of the torus infrared output by carbon and silicate grains neartheir sublimation temperatures and radii may account for the general similarityof AGN near-IR spectral energy distributions. The torus inner edge defined bythe hottest dust remains at roughly the same radius independent of the AGNoptical luminosity over $\sim$25 years. The emission by hot dust warmeddirectly by the optical/UV AGN output has increased gradually by$\sim$4\%/year, indicating a possibly growing torus. A third dust component at$\sim$700 K does not seem to participate directly in the IR reverberationbehavior and its emission may originate deep in the circumnuclear torus. Wefind a reverberation signal at $\sim10\mu$m with an inferred radius for thewarm dust of $\sim$2.2--3.1 pc. The lack of variability at 20--40$\mu$mindicates the far-IR emission comes from even more extended regions. The torusproperties revealed by dust reverberation analysis are inconsistent withpredictions from pure clumpy torus models. Instead, the longer wavelengthemission possibly originates in a flared torus or the polar wind.

The Dusty Heart of NGC 4151 Revealed by $\lambda\sim$1-40 $\mu$m Reverberation Mapping and Variability: A Challenge to Current Clumpy Torus Models