[en] Differential cross sections for π⁺p and π^-p elastic scattering have been measured at 12 energies in the region 277-640 MeV. The data were obtained in the angular range THETAsup(*)π = 40⁰-176⁰, with a typical accuracy of 2-5%. The results for 288 MeV and 292.9 MeV are in good agreement with the data of Bussey et al. Using the data obtained, isopin bounds have been calculated for the charge-exchange scattering. It is shown that the charge-exchange cross sections at large angles are grouped near the bottom isospin limit, and at energies larger than 490 MeV they lie beyond the region allowed by isospin invariance. The comparison was carried out with the predictions of different phase-shift analyses. It is shown that the existing phase-shift analyses do not describe all the set of the new data. A new energy-independent phase-shift analysis has been carried out at 12 energies in the region 240-700 MeV. (orig.)