Alternating Relay Delay for Stop-Start Overvoltage
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Solution Overview
Problem
Existing engine starting devices for the Stop & Start function in vehicles face challenges in achieving high reliability while maintaining cost-effectiveness and ease of maintenance, particularly in managing overvoltage and minimizing the risk of unwanted engine startups.
Innovation Solution
The solution involves an engine starting device with two relays controlled by an electronic control unit (BCM) that alternately exchanges delay settings between the relays for successive startings, distributing overvoltage risks evenly and ensuring both relays are used with the same reliability, thus minimizing failure risks and costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If two relays are used in series for controlling the Stop and Start function, then reliability is improved, but the risk of overvoltage damage during relay closing increases
Solution Approach 1:
The control unit implements a timing mechanism that closes the second relay (KR2) before closing the first relay (KR1). This preliminary action of closing KR2 first prepares the circuit in a controlled sequence, preventing overvoltage spikes that would occur if both relays closed simultaneously. The delay parameter (DELAY) is specifically designed to create this time gap between relay operations.
Solution Approach 2:
The control unit alternates the closing sequence of the two relays between different engine starting operations. In one operation, KR2 closes before KR1; in the next operation, the sequence is reversed. This periodic alternation distributes the overvoltage stress evenly between the two relays over time, preventing any single relay from bearing excessive cumulative damage while maintaining the series connection for reliability.
2Speed
If relays are closed simultaneously to start the engine, then starting speed is improved, but overvoltage damage risk increases
Solution Approach 1:
The control unit closes the second relay (KR2) with a delay (DELAY) before closing the first relay (KR1). This preliminary closing of KR2 prepares the circuit path in advance, allowing the engine starting process to begin without significant delay while avoiding the simultaneous closure that causes overvoltage spikes. The delay is calibrated to be minimal yet sufficient to prevent harmful voltage transients.
3Reliability
If one relay is assigned to handle all overvoltage risks, then reliability of individual relay is improved, but the overall system becomes less cost-effective and more complex
Solution Approach 1:
The control unit alternates the closing sequence of the two relays between successive engine starting operations. During one operation, KR2 closes before KR1; during the next operation, KR1 closes before KR2. This periodic reversal distributes the overvoltage stress evenly across both relays over time, ensuring they experience equal cumulative stress and have equal probability of failure. This eliminates the need for one relay to be specially designed to handle all overvoltage risks, maintaining component simplicity and cost-effectiveness while achieving balanced reliability.
Data Source
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AI summary
The present invention relates to an engine starting device for the stop and start function in a vehicle, comprising: a first relay (RL1) with main line connected to an ignition switch (KEY); a second relay (RL2) with the main line connected to the main line of said first relay and to an ignition circuit of a starter (SM), said main lines of said first and second relay when they are close they determine the activation of the starter for the engine starting; an electronic control unit (BCM) comprising controlling means (DR1, DR2) of said first and second relay, so that, when there are the conditions for an engine starting by means of the stop and start function (S&S), they determine the closing of said main lines of said first and second relay with a first delay from each other, so that it is possible to exchange the delay between said relays for alternate successive startings.