Driving force transfer apparatus for four-wheel drive vehicle

A driving force transfer apparatus for a four-wheel drive vehicle having mainly driven road wheels and secondarily driven road wheels, and a vehicular power transmission with an output axle, comprising:

• a) an input axle connected to said output axle of said vehicular power transmission;
• b) a first output axle operatively connected to said mainly driven road wheels;
• c) a second output axle operatively connected to said secondarily driven road wheels;
• d) a sub transmission mechanism having mesh clutching means for operatively switching at least between a relatively high-speed gear range position and a relatively low-speed gear range position, said sub transmission mechanism being arranged and constructed to transmit a driving force from said power transmission via said input axle to said first output axle according to the switched position set through said mesh clutching means;
• e) a two-wheel-and-four-wheel drive switching mechanism having frictional clutching means and working fluid pressure varying means, a clutching force of said frictional clutching means being varied according to a working fluid pressure applied thereto from said working fluid pressure varying means so that the driving force transmitted to said first output axle is distributed to the second output axle at a torque distribution ratio determined according to the clutching force of the frictional clutching means;
• f) detecting means for detecting a running condition of the vehicle;
• g) controlling means for outputting a control signal to said working fluid pressure varying means to vary the working fluid pressure applied to said frictional clutching means on the basis of a result of the detection of the vehicle running condition;
• h) first and second dog clutches for forcefully connecting the first output axle to the second output axle so that the four road wheels are forced into a four-wheel drive state during the low-speed gear range position switched through the sub transmission mechanism;
• i) smoothly meshing means for smoothly meshing said first and second dog clutches to lower the chance of impinging said first and second dog clutches,
• wherein said mesh clutching means of said sub transmission mechanism comprises:
• j) a high-speed shifting gear formed on the input axle;
• k) a low-speed shifting gear arranged and constructed to transmit the driving force with a revolution of said input axle reduced through a speed-reduction mechanism interlocked with said input axle;
• 1) a four-wheel driving gear arranged and constructed to forcefully set the four road wheels into a four-wheel drive state;
• and
• m) a shift sleeve coupled to said first output axle in a spline coupling form to mesh with the high-speed shifting gear at the high-speed gear range position and to mesh with the low-speed shifting gear and with the four-wheel driving gear at the low-speed gear range position so that the vehicle is forced into the four-wheel drive state, wherein when said sub transmission mechanism is switched from the high-speed gear range position to the low-speed gear range position through said mesh clutching means, said shift sleeve is meshed with the low-speed shifting gear and, thereafter, is meshed with the four-wheel driving gear;and
• n) revolution stopped state detecting means for detecting whether a revolution of said output axle of the power transmission is halted and wherein said smoothly meshing means includes clutching force suppressing means for reducing the clutching force of said frictional clutching means through said controlling means by a predetermined value when said revolution stopped state detecting means detects that the output axle of said power transmission is stopped to help the meshing of said first and second dog clutches.

A driving force transfer apparatus for a four-wheel drive vehicle having mainly driven road wheels and secondarily driven road wheels, comprising:

• a) a power transmission associated with a vehicular engine, said power transmission having an output axle;
• b) an input axle connected to said output axle of said power transmission;
• c) a first output axle connected operatively to said mainly driven road wheels;
• d) a second output axle connected operatively to said secondarily driven road wheels;
• e) a sub transmission having a low-speed and high-speed gear range position switching mechanism arranged and constructed to transmit a driving force transmitted from said power transmission to said first output axle through mesh clutching means provided in said switching mechanism;
• f) a two-wheel-and-four-wheel drive switching mechanism having a frictional clutch arranged and constructed to provide a suitable clutching for said frictional clutch so that said second output axle is coupled to said first output axle at a required torque distribution ratio,
• wherein said sub transmission further includes:
• g) a high-speed shifting gear formed on said input axle,
• h) a low-speed shifting gear arranged and constructed to transmit a speed-reduced revolution of said input axle through a speed reduction mechanism interlocked with said input axle, and
• i) a shift sleeve spline coupled to said first output axle, which is meshed with the high-speed shifting gear when moved to a predetermined high-speed gear range position, and meshed with said low-speed shifting gear and a four-wheel driving gear when moved to a predetermined low-speed gear range position so that the vehicle is forced into a four-wheel drive state and wherein, when said shift sleeve is moved from the high-speed gear range position to the low-speed gear range position through said switching mechanism, said shift sleeve is meshed with said four-wheel driving gear after said shift sleeve has meshed with the low-speed shifting gear;
• and
• j) frictional clutch temporary junctioning means for temporarily junctioning said frictional clutch so that the driving force transmitted to said first output axle is transmitted to said second output axle at a predetermined torque distribution ratio via said frictional clutching means when said shift sleeve is not meshed with the four-wheel drive gear means but only meshed with the low-speed gear means.