outside these predetermined limits jolts on the transmissions are therefore limited but also slipping of the wheels is limited providing for a truly limited slip power transmission structure which has no adverse effects during cornering when the relative speed difference of the two driven wheels is only relatively small the valve housing 48 preferably has a passage 50 of circular cross section and both the control members 52 and 54 are preferably also circular the outer member 54 being a cylinder and the inner member 52 being a spool disposed in the cylinder a somewhat simplified control valve arrangement is shown in fig2 for the lower half of the transmission here the ends of the links directly form the control members 52 and 54 and the pressurized fluid supply and discharge lines 62 64 and 66 are directly connected to the outer control member 54 however since the outer control member is movable with the link 60 the fluid supply and discharge lines are to be flexible functionally both arrangements are identical and the same reference numerals have therefore been used to indicate corresponding parts the present invention has been described in connection with infinitely variable traction roller transmissions but it may be used of course in connection with any transmission with infinitely variable transmission ratio infinitely variable belt type transmissions would be quite suitable for use in connection with the present invention the belt type transmissions may be simply of the v belt friction type or the higher power capacity shim type belt transmissions in which the side walls of the pulleys have radial grooves receiving the ends of the shims of the.