ESP control function ASR

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a Suction line

c Depressurized

g Pilot pressure (brake pressure circuit)

d Pilot pressure (charging circuit)

f High pressure

ASR pressure build-up control mode

(The control process or valve positions shown in the example relate to the RR brake).

If one or both drive wheels tends to spin when starting off or accelerating, the ESP control module introduces the ASR pressure build-up control mode.

At the start of ASR control the rear axle switchover solenoid valve (y19) and the pressure-holding solenoid valve (Y10) are closed.

The ASR/ESP charging pump (M15) charges the high-pressure/return pump (p2) to 3-15 bar via the charging piston unit (14) and therear axle precharge solenoid valve (y17).

The pressure produced by the high-pressure/return pump (p2) is led to the RR wheel brake via the open pressure-holding solenoid valve (y12).

The pressure limiting valve (approx. 160 bar) integrated in the rear axle switchover solenoid valve (y19) is required for high pressure limiting.

The charging pressure is also applied to the actuated (closed) pressure-holding solenoid valves (y6 and y8) of the front axle via the open front axle switchover solenoid valve (y18).

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a Suction line

b Brake pressure

f High pressure

g Pilot pressure (brake pressure circuit)

c Depressurized

d Pilot pressure (charging circuit)

ASR pressure-holding control mode

(The control process or valve positions shown in the example relate to the RR brake).

The ASR pressure holding control phase mode starts if a more powerful brake intervention is no longer required to prevent drive slip.

The pressure-holding phase is initiated by actuating (closing) the pressure-holding solenoid valve (y12). The pressure reduction solenoid valve (y13) remains closed in this control phase.

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a Suction line

c Depressurized

f High pressure

g Pilot pressure (brake pressure circuit)

d Pilot pressure (charging circuit)

e Reduced pressure

ASR pressure reduction control mode

(The control process or valve positions shown in the example relate to the RR brake).

The ASR pressure reduction control mode starts if the brake pressure required to prevent drive slip is too high. The pressure reduction phase is introduced by actuating (opening) the pressure reduction solenoid valve (y13). The pressure-holding solenoid valve (y12) remains closed. The ASR/ESP charging pump (M15) and high-pressure/return pump (p2) are also actuated in this control phase. The switchover solenoid valve (y19) is closed and the

solenoid valve (y17) is opened.

The brake fluid flows back to the charging pressure circuit via the open charging solenoid valve (y17).
The brake fluid returned at the same time by the high-pressure/return pump (p2) is also fed back into the charging pressure circuit of the rear axle by the pressure limiting valve (160 bar) integrated in the switchover solenoid valve.