Accident Law--Impleading of Insurance--Liability of the insurance company arises for the purpose of reimbursement of the amount of compensation found to be payable by the owner of the vehicle insured--It is only in exceptional cases and as provided for under Section 170 of the Act, the insurance company can defend a claim petition--Only on limited grounds it may be permitted to question the quantum of compensation--Motor Vehicles Act, 1988, Section 170.