unselect the selected rows in a datatable

I'm working on a datatable with a single selection mode.My problem is that when I refesh the page , the same selected rows before refreshing stay refreshed. Any idea on how unselecting all datatable rows in this case. I appreciate helping me with this issue.

This is my datatable code:

    <p:dataTable id="cars1" var="car"   widgetVar="carsTable" value="#{typePrimeManager.tprimes}" editable="false" style="margin-bottom:20px"  paginator="false"  selectionMode="single" selection="#{typePrimeManager.selectedtype}" rowKey="#{car.idPrime}">
    <p:ajax event="rowSelect" update=":form:cars2" />
    <p:ajax event="rowUnselect" listener="#{typePrimeManager.setSelectedtype(null)}" update=":form:cars2"/>
    <p:ajax event="rowUnselect" listener="#{typePrimeManager.setSelectedtype(null)}" update=":form:cars2"/>
    <p:column headerText="intitule des types">  
    <h:outputText value="#{car.intitulePrime}" />
    </p:column>
    </p:dataTable>