Selector lever downshifts - RA27057229210X(27-9210)

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Fig 1: Selector Lever Downshift From "D" To "3" With Idle Throttle Braking Shift

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Selector lever downshift from "D" to "3" with idle throttle braking shift

When the selector lever is moved from position "D" to "3", the governor pressure "R-D" at the selector valve (1) is switched to zero outlet. The command valve (12) snaps to the right irrespective of vehicle speed. The 4 → 3 downshift is activated.

At the same time, the locking valve RV2 (55) is pushed to the left by the spring (d) after:

the governor pressure "R-D" at the end face (b) and at the annular surface (c) is switched to zero outlet via the selector valve (1).
the end face (a) is pressureless. No pressure can build up downstream of the restrictor (e) in the idle throttle position with the outlet cross-section (VL2) open.

When in its lefthand position, the valve (55) shuts off the line to the reaction valve (RV2). This simulates a closed reaction valve. As soon as the downshift has been initiated and the working pressure passes to the shift side (B2S) the release valve (60) switches the release side of the brake band piston to zero outlet. See also Downshifts when accelerating (function of reaction valves) "C" "4 → 3 Downshift when accelerating".

Brake band B2 is fully engaged, irrespective of vehicle speed and engine speed.

Fig 2: Selector Lever Downshift From "3" To "2" With Idle Throttle Braking Shift

Courtesy of MERCEDES-BENZ OF NORTH AMERICA.

Selector lever downshift from "3" to "2" with idle throttle braking shift

Selector lever downshift "3" to "2" with idle throttle braking shift

When the selector lever is moved from position "3" to "2", the governor pressure "RD-3", which is acting on the end face of the command valve, is switched at the selector valve (1) to zero outlet. The command valve (4) snaps to the left, irrespective of vehicle speed. The 3 → 2 downshift is activated.

At the same time, the braking shift locking valve (61) has moved to the left as a result of the spring force after

the working pressure "AD-3" has been connected to the zero outlet at the selector valve (1), and additionally
the pressure VL2 at the control pressure piston (46) is switched to the zero outlet. No pressure can build up downstream of the restrictor (a) and thus at the end face of the valve (61) in the idle throttle position and when the outlet cross-section "VL2" is open.

When valve (61) is in its lefthand position, the lefthand end face of the locking valve RV1 (62) is connected to the zero outlet. The locking valve RV1 (62) switches to the left and shuts off the connection to the reaction valve (RV1). This simulates a closed reaction valve.

Working pressure flows to the control valve piston B1 (39) and pushes this together with the control valve B1 (38) to the left. The control valve (38) cannot control any contact pressure for the brake band piston B1, but immediately allows the working pressure "A2-4" to act on the piston B1. See also Downshifts when accelerating (function of reaction valves) "B" "3 → 2 Downshift when accelerating".

Brake band B1 is fully engaged, irrespective of vehicle speed and engine speed.