| 摘要 |
A control unit (50) makes a single control signal available for driving the through-flow control valves (TEV1, TEV2) (51, 52). Through-flow valve (TEV2) has a larger maximum through flow than through-flow control valve (TEV1). A delay circuit is indicated by the phantom outline (52') and is mounted at the valve stage TEV2 (52). The delay circuit includes an electric delay element (53) with the aid of which the original control signal is delayed in time by an amount DELTAt1 relative to the control signal of control valve (TEV1). The resulting delayed signal is supplied to an AND-gate (54) together with the original control signal. Accordingly, a control signal is present at the output of the AND-gate for the control valve (TEV2). The time delay makes possible the exclusive activation of the through-flow control valve (TEV1) (51) at low pulse duty factors. In this way, a high small quantity meterability is achieved. Starting at a specific pregivable switch-in time, the control valve (TEV2) (52) is switched in so that a very large through flow is possible. The invention thereby makes possible excellent meterability at low as well as at high through flows.
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