<?xml version="1.0" encoding="US-ASCII"?>
<!-- Generated by DFIN XBRL Schema Document - http://www.dfinsolutions.com/ - on 31-08-2026 09:14:53 PM -->
<!-- Copyright(c) 2026 Donnelley Financial Solutions, Inc. All Rights Reserved. -->
<schema targetNamespace="http://www.tcw.com/20260904" elementFormDefault="qualified" xmlns:fnd="http://xbrl.sec.gov/fnd-cef/2025" xmlns="http://www.w3.org/2001/XMLSchema" xmlns:tsifi="http://www.tcw.com/20260904" xmlns:link="http://www.xbrl.org/2003/linkbase" xmlns:rr="http://xbrl.sec.gov/rr/2021" xmlns:dtr="http://www.xbrl.org/2009/dtr" xmlns:ref="http://www.xbrl.org/2006/ref" xmlns:xbrldt="http://xbrl.org/2005/xbrldt" xmlns:xl="http://www.xbrl.org/2003/XLink" xmlns:dei="http://xbrl.sec.gov/dei/2025" xmlns:xbrldi="http://xbrl.org/2006/xbrldi" xmlns:dtr-types="http://www.xbrl.org/dtr/type/2024-01-31" xmlns:xbrli="http://www.xbrl.org/2003/instance" xmlns:cef="http://xbrl.sec.gov/cef/2025" xmlns:xlink="http://www.w3.org/1999/xlink">
    <annotation>
        <appinfo>
            <link:linkbase>
                <link:roleRef roleURI="http://xbrl.sec.gov/cef/role/N2" xlink:type="simple" xlink:href="https://xbrl.sec.gov/cef/2025/cef-2025.xsd#N2"/>
                <link:roleRef roleURI="http://xbrl.sec.gov/cef/role/RiskOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/cef/2025/cef-2025.xsd#RiskOnly"/>
                <link:roleRef roleURI="http://xbrl.sec.gov/cef/role/SecurityOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/cef/2025/cef-2025.xsd#SecurityOnly"/>
				<link:roleRef roleURI="http://xbrl.sec.gov/cef/role/CoregistrantOnly" xlink:type="simple" xlink:href="https://xbrl.sec.gov/cef/2025/cef-2025.xsd#CoregistrantOnly"/>
				<link:arcroleRef arcroleURI="http://xbrl.org/int/dim/arcrole/domain-member" xlink:type="simple" xlink:href="http://www.xbrl.org/2005/xbrldt-2005.xsd#domain-member"/>
				<link:presentationLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/cef/role/N2">	
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/cef/2025/cef-2025.xsd#cef_AllCoregistrantsMember" xlink:label="AllCoregistrantsMember"/>
					<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="DebtInstrumentNameDomain"/>
					<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_CommonSharesMember" xlink:label="CommonSharesMember"/>
					<link:presentationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="ClassOfStockDomain" xlink:to="CommonSharesMember" order="1.0" />
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/cef/2025/cef-2025.xsd#cef_AllRisksMember" xlink:label="AllRisksMember"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_MarketRisksMember" xlink:label="MarketRisksMember"/>
					<link:presentationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="AllRisksMember" xlink:to="MarketRisksMember" order="1.0" />
					<link:loc xlink:type="locator" xlink:href="#tsifi_LiquidityRiskMember" xlink:label="LiquidityRiskMember"/>
					<link:presentationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="AllRisksMember" xlink:to="LiquidityRiskMember" order="2.0" />
					<link:loc xlink:type="locator" xlink:href="#tsifi_InterestRateRisksMember" xlink:label="InterestRateRisksMember"/>
					<link:presentationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="AllRisksMember" xlink:to="InterestRateRisksMember" order="3.0" />
					<link:loc xlink:type="locator" xlink:href="#tsifi_MortgageBackedAndOtherAssetBackedSecuritiesRiskMember" xlink:label="MortgageBackedAndOtherAssetBackedSecuritiesRiskMember"/>
					<link:presentationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="AllRisksMember" xlink:to="MortgageBackedAndOtherAssetBackedSecuritiesRiskMember" order="4.0" />
					<link:loc xlink:type="locator" xlink:href="#tsifi_DerivativesRisksMember" xlink:label="DerivativesRisksMember"/>
					<link:presentationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="AllRisksMember" xlink:to="DerivativesRisksMember" order="5.0" />
					<link:loc xlink:type="locator" xlink:href="#tsifi_CreditRisksMember" xlink:label="CreditRisksMember"/>
					<link:presentationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="AllRisksMember" xlink:to="CreditRisksMember" order="6.0" />
					<link:loc xlink:type="locator" xlink:href="#tsifi_CounterpartyRiskMember" xlink:label="CounterpartyRiskMember"/>
					<link:presentationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="AllRisksMember" xlink:to="CounterpartyRiskMember" order="7.0" />
					<link:loc xlink:type="locator" xlink:href="#tsifi_USTradePolicyRiskMember" xlink:label="USTradePolicyRiskMember"/>
					<link:presentationArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/parent-child" xlink:from="AllRisksMember" xlink:to="USTradePolicyRiskMember" order="8.0" />
				</link:presentationLink>
				<link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/cef/role/CoregistrantOnly">
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/cef/2025/cef-2025.xsd#cef_AllCoregistrantsMember" xlink:label="AllCoregistrantsMember"/>
				</link:definitionLink>
				<link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/cef/role/SecurityOnly">
					<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_DebtInstrumentNameDomain" xlink:label="DebtInstrumentNameDomain"/>
					<link:loc xlink:type="locator" xlink:href="https://xbrl.fasb.org/us-gaap/2025/elts/us-gaap-2025.xsd#us-gaap_ClassOfStockDomain" xlink:label="ClassOfStockDomain"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_CommonSharesMember" xlink:label="CommonSharesMember"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="ClassOfStockDomain" xlink:to="CommonSharesMember" order="1.0"/>
				</link:definitionLink>
				<link:definitionLink xlink:type="extended" xlink:role="http://xbrl.sec.gov/cef/role/RiskOnly">
					<link:loc xlink:type="locator" xlink:href="https://xbrl.sec.gov/cef/2025/cef-2025.xsd#cef_AllRisksMember" xlink:label="AllRisksMember"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_MarketRisksMember" xlink:label="MarketRisksMember"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="MarketRisksMember" order="1.0"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_LiquidityRiskMember" xlink:label="LiquidityRiskMember"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="LiquidityRiskMember" order="2.0"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_InterestRateRisksMember" xlink:label="InterestRateRisksMember"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="InterestRateRisksMember" order="3.0"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_MortgageBackedAndOtherAssetBackedSecuritiesRiskMember" xlink:label="MortgageBackedAndOtherAssetBackedSecuritiesRiskMember"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="MortgageBackedAndOtherAssetBackedSecuritiesRiskMember" order="4.0"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_DerivativesRisksMember" xlink:label="DerivativesRisksMember"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="DerivativesRisksMember" order="5.0"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_CreditRisksMember" xlink:label="CreditRisksMember"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="CreditRisksMember" order="6.0"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_CounterpartyRiskMember" xlink:label="CounterpartyRiskMember"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="CounterpartyRiskMember" order="7.0"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_USTradePolicyRiskMember" xlink:label="USTradePolicyRiskMember"/>
					<link:definitionArc xlink:type="arc" xlink:arcrole="http://xbrl.org/int/dim/arcrole/domain-member" xlink:from="AllRisksMember" xlink:to="USTradePolicyRiskMember" order="8.0"/>
				</link:definitionLink>
				<link:labelLink xlink:type="extended" xlink:role="http://www.xbrl.org/2003/role/link">
					<link:loc xlink:type="locator" xlink:href="#tsifi_CommonSharesMember" xlink:label="CommonSharesMember"/>
					<link:label xlink:type="resource" xlink:label="label_CommonSharesMember" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">Common Shares [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="CommonSharesMember" xlink:to="label_CommonSharesMember"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_MarketRisksMember" xlink:label="MarketRisksMember"/>
					<link:label xlink:type="resource" xlink:label="label_MarketRisksMember" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">Market Risks [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="MarketRisksMember" xlink:to="label_MarketRisksMember"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_LiquidityRiskMember" xlink:label="LiquidityRiskMember"/>
					<link:label xlink:type="resource" xlink:label="label_LiquidityRiskMember" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">Liquidity Risk [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="LiquidityRiskMember" xlink:to="label_LiquidityRiskMember"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_InterestRateRisksMember" xlink:label="InterestRateRisksMember"/>
					<link:label xlink:type="resource" xlink:label="label_InterestRateRisksMember" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">Interest Rate Risks [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="InterestRateRisksMember" xlink:to="label_InterestRateRisksMember"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_MortgageBackedAndOtherAssetBackedSecuritiesRiskMember" xlink:label="MortgageBackedAndOtherAssetBackedSecuritiesRiskMember"/>
					<link:label xlink:type="resource" xlink:label="label_MortgageBackedAndOtherAssetBackedSecuritiesRiskMember" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">Mortgage Backed and Other Asset Backed Securities Risk [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="MortgageBackedAndOtherAssetBackedSecuritiesRiskMember" xlink:to="label_MortgageBackedAndOtherAssetBackedSecuritiesRiskMember"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_DerivativesRisksMember" xlink:label="DerivativesRisksMember"/>
					<link:label xlink:type="resource" xlink:label="label_DerivativesRisksMember" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">Derivatives Risks [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="DerivativesRisksMember" xlink:to="label_DerivativesRisksMember"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_CreditRisksMember" xlink:label="CreditRisksMember"/>
					<link:label xlink:type="resource" xlink:label="label_CreditRisksMember" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">Credit Risks [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="CreditRisksMember" xlink:to="label_CreditRisksMember"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_CounterpartyRiskMember" xlink:label="CounterpartyRiskMember"/>
					<link:label xlink:type="resource" xlink:label="label_CounterpartyRiskMember" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">Counterparty Risk [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="CounterpartyRiskMember" xlink:to="label_CounterpartyRiskMember"/>
					<link:loc xlink:type="locator" xlink:href="#tsifi_USTradePolicyRiskMember" xlink:label="USTradePolicyRiskMember"/>
					<link:label xlink:type="resource" xlink:label="label_USTradePolicyRiskMember" xlink:role="http://www.xbrl.org/2003/role/label" xml:lang="en-US">US Trade Policy Risk [Member]</link:label>
					<link:labelArc xlink:type="arc" xlink:arcrole="http://www.xbrl.org/2003/arcrole/concept-label" xlink:from="USTradePolicyRiskMember" xlink:to="label_USTradePolicyRiskMember"/>
				</link:labelLink>
			</link:linkbase>
		</appinfo>
	</annotation>
	<import namespace="http://www.xbrl.org/2003/instance" schemaLocation="http://www.xbrl.org/2003/xbrl-instance-2003-12-31.xsd"/>
	<import namespace="http://www.xbrl.org/2003/linkbase" schemaLocation="http://www.xbrl.org/2003/xbrl-linkbase-2003-12-31.xsd"/>
	<import namespace="http://xbrl.org/2005/xbrldt" schemaLocation="http://www.xbrl.org/2005/xbrldt-2005.xsd"/>
	<import namespace="http://xbrl.sec.gov/dei/2025" schemaLocation="https://xbrl.sec.gov/dei/2025/dei-2025.xsd"/>
	<import namespace="http://www.xbrl.org/dtr/type/2024-01-31" schemaLocation="https://www.xbrl.org/dtr/type/2024-01-31/types.xsd"/>
	<import namespace="http://xbrl.sec.gov/cef/2025" schemaLocation="https://xbrl.sec.gov/cef/2025/cef-2025.xsd"/>
	<import namespace="http://xbrl.sec.gov/cef-pre/2025" schemaLocation="https://xbrl.sec.gov/cef/2025/cef-2025_pre.xsd"/>
	<import namespace="http://xbrl.sec.gov/fnd-cef-pre/2025" schemaLocation="https://xbrl.sec.gov/fnd/2025/fnd-cef-2025_pre.xsd"/>
	<element name="CommonSharesMember" id="tsifi_CommonSharesMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="MarketRisksMember" id="tsifi_MarketRisksMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="LiquidityRiskMember" id="tsifi_LiquidityRiskMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="InterestRateRisksMember" id="tsifi_InterestRateRisksMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="MortgageBackedAndOtherAssetBackedSecuritiesRiskMember" id="tsifi_MortgageBackedAndOtherAssetBackedSecuritiesRiskMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="DerivativesRisksMember" id="tsifi_DerivativesRisksMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="CreditRisksMember" id="tsifi_CreditRisksMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="CounterpartyRiskMember" id="tsifi_CounterpartyRiskMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
	<element name="USTradePolicyRiskMember" id="tsifi_USTradePolicyRiskMember" type="dtr-types:domainItemType" substitutionGroup="xbrli:item" abstract="true" nillable="true" xbrli:periodType="duration"/>
</schema>
