Vehicle slide rail device

1. A slide rail device of a vehicle, comprising:

a lower rail which extends in a forward-and-rearward direction and is provided with a large number of lock grooves, which are arranged in the forward-and-rearward direction, said lower rail being immovable relative to a floor of the vehicle;

an upper rail which is slidable in said forward-and-rearward direction relative to said lower rail and is provided with a plurality of forward-and-rearward movement restriction grooves which are arranged in the forward-and-rearward direction;

a lock spring, which is slidable together with said upper rail relative to said lower rail, provided with a locking portion which includes a pair of front and rear locking sections which are respective positioned within said forward-and-rearward movement restriction grooves and can selectively enter into, and escape from, said lock grooves; and

a lock release lever, supported by said upper rail, which is rotatable between a locked position, at which said locking sections are allowed to engage with said lock grooves by a biasing force of said lock spring, and an unlocked position, at which said lock release lever presses said lock spring in a direction such that said locking sections escape from said lock grooves against said biasing force,

wherein a rear surface of the front locking section and a front surface of the rear locking section, of said locking portion, contact inner surfaces of corresponding said lock grooves, respectively,

wherein a distance between a front surface of the front locking section and a front surface of a first forward-and-rearward restriction movement groove of said forward-and-rearward movement restriction grooves is narrower than a distance between the rear surface of the front locking section and a rear surface of said first forward-and-rearward movement restriction groove, and

wherein a distance between a rear surface of the rear locking section and a rear surface of a second forward-and-rearward movement restriction groove of said forward-and-rearward movement restriction grooves is narrower than a distance between the front surface of the rear locking section and a front surface of said second forward-and-rearward movement restriction groove.

2. The slide rail device of a vehicle according to claim 1 , wherein said lock spring comprises a plurality of said locking portions, which are provided at different positions in the forward-and-rearward direction,

wherein said locking portions include:

at least one positioning locking-portion, in which a rear portion of the front locking section thereof and a front portion of the rear locking section thereof both contact inner surfaces of corresponding said lock grooves, respectively, and

at least one spaced-apart locking portion, in which a rear portion of the front locking section thereof and a front portion of the rear locking section thereof are both spaced apart from inner surfaces of corresponding said lock grooves, respectively,

wherein a distance between a front surface of the front locking section of said positioning locking-portion and a front surface of a corresponding forward-and-rearward movement restriction groove is narrower than a distance between a front surface of a front locking section of said spaced-apart locking portion and a front surface of a corresponding forward-and-rearward movement restriction groove; and

wherein a distance between a rear surface of the rear locking section of said positioning locking-portion and a rear surface of the corresponding forward-and-rearward movement restriction groove is narrower than a distance between a rear surface of the rear locking section of said spaced-apart locking portion and a rear surface of the corresponding forward-and-rearward movement restriction groove.