There is a scissors gear (sub-gear) on the driven gear of the camshaft for the compact DOHC which serves to reduce gear noise associated with changes in torque. The sub-gear is pushed toward the rotational direction by the spring at all times and the scissors gear reduces the backlash of the gear by meshing with the drive gear, in order to prevent the noise. Backlash Backlash is the gap between the gear contact surfaces and due to this tolerance in the design and assembly, wear and seizure are prevented.

1. Description

The piston in the power cylinder is positioned on the rack, and the rack moves due to fluid pressurized by the vane pump acting on the piston in either direction. Fluid pressure leakage is prevented by a seal ring on the piston. Also, there is an oil seal on both sides of the cylinder to prevent external leakage of the fluid. The control valve shaft is connected to the steering wheel. When the steering wheel is in the neutral (straight-ahead) position, the control valve is also in the neutral position, so the fluid from the vane pump does not act on either chamber but flows back to the reservoir tank. However, when the steering wheel is turned in either direction, the control valve changes the passage so the fluid flows into one of the chambers. The fluid in the opposite chamber is forced out and flows back to the reservoir tank by way of the control valve. Currently, there are three different types of control valves which perform this changeover action of the passage; spool valves, rotary valves and flapper valves. All types have a torsion bar between the control valve shaft and pinion, and the control valve functions in accordance with the amount of twist applied to the torsion bar.

2. Type of control valve

A control valve is located in the gear housing. The gear housing houses a rackand- pinion type power steering mechanism or a recirculating- bail type power steering mechanism. The control valve is one of three types: a rotary valve type, a spool valve type, or a flapper valve type. Currently, rotary valve types are used in many models.

3. Construction

Here, the rotary valve type is explained. The control valve in the gear housing determines to which chamber the fluid from the vane pump goes. The control valve shaft (to which steering wheel torque is applied) and the pinion gear are connected by means of a torsion bar. The rotary valve and pinion gear are secured by a pin and rotate integrally. If no vane pump pressure is applied, the torsion bar is fully twisted and the control valve shaft and pinion gear make contact at the stopper so the control valve shaft torque is applied directly to the pinion gear.

4. Operation

A restriction in the hydraulic circuit is formed by rotary movement of the control valve shaft in relation to the rotary valve. When the steering wheel is turned to the right, pressure is restricted at orifices X and Y. When it is turned to the left, a restriction is formed at X’ and Y’. When the steering wheel is turned, the control valve shaft rotates, turning the pinion gear via the torsion bar. In contrast to the pinion gear, as the torsion bar twists in proportion to road surface force at this time, the control valve shaft rotates only to the extent of the amount of twist, and moves to the right or left in relation to the rotary valve. Thus orifices X and Y (or X’ and Y’) are formed and a difference in hydraulic pressure between the right and left cylinder chambers is created. In this manner, rotation of the control valve shaft directly performs changeover of the passages and regulates the fluid pressure. The fluid from the vane pump enters from the outer circumference of the rotary valve, and the fluid returning to the reservoir tank passes between the torsion bar and the control valve shaft.

(1) Neutral position

As the control valve shaft does not revolve, it is in a neutral position in relation to the rotary valve. Fluid supplied by the pump returns to the reservoir tank through port “D” and chamber “D”. The right and left chambers of the cylinder are slightly pressurized but as there is no pressure difference between the two, no power steering assist occurs.

(2) Turning right

When the vehicle makes a right turn, the torsion bar is twisted and the control valve shaft revolves to the right accordingly. Fluid from the pump is constricted by orifices X and Y of the control edge in order to stop flow to ports “C” and “D”. As a result, fluid flows from port “B” to sleeve “B” and then to the right cylinder chamber, causing the rack to move to the left and resulting in power steering assist. At the same time, the fluid in the left cylinder chamber flows back to the reservoir tank via sleeve “C” -> port “C” -> port “D” -> chamber “D”.

(3) Turning left

In the same manner as for a right turn, when the vehicle makes a left turn, the torsion bar is twisted and the control shaft rotates to the left accordingly. The fluid sent from the pump is constricted by orifices X’ and Y’ of the control edge in order to stop flow to ports “B” and “D”. As a result, fluid flows from port “C” to sleeve “C” and then to the left cylinder chamber, causing the rack to move to the right and resulting in power steering assist. At the same time, the fluid in the right cylinder chamber flows back to the reservoir tank via sleeve “B” -> port “B” -> port “D” -> chamber “D”.

Each gear condition is explained using the solenoid valves and shift valves.

1. 1st gear

For gear shift from neutral to 1st gear, the fluid passage to C1 is opened by switching the manual valve. Since the No. 1 solenoid valve is on and the No. 2 solenoid valve is off, the fluid passage to C0 is opened. (No.1 solenoid valve is on, and No.2 solenoid valve is off.) The operation of C1 and F2 creates the fluid passage for 1st gear. In the “D” and “2″ ranges, the engine brake is not applied because of the operation of F2. In the “L” range, the passage to B3 is opened and the engine brake is applied.

Hydraulic pressure to the planetary gear unit

C1 from manual valve

C0 from 3-4 shift valve

B3 from 2-3 shift valve

2. 2nd gear

The No. 2 solenoid valve is switched from off to on according to signals from the ECU. (No.1 solenoid valve is on, and No.2 solenoid valve is on.) The hydraulic pressure applied on the top of the 1-2 and 3-4 shift valves is discharged and the 1-2 shift valve is moved up by the force of the spring. Therefore, the fluid passage opens to B2. The operation of C1 and B2 (F1) shifts up to 2nd gear. In the “D” range, the engine brake is not applied because of the operation of F1. In the “2″ range, the fluid passage to B1 is opened and the engine brake is applied.

Hydraulic pressure to the planetary gear unit

C1 from manual valve

C0 from 3-4 shift valve

B2 from 1-2 shift valve

B1 from 1-2 shift valve

3. 3rd gear

The No. 1 solenoid valve is switched from on to off according to signals from the ECU. (No.1 solenoid valve is off, and No.2 solenoid valve is on.) The hydraulic pressure starts to be applied on the top of the 2-3 shift valve, moving down the 2-3 shift valve. Therefore, the fluid passage opens to C2. The operation of C1 and C2 shifts the gear up to 3rd gear.

Hydraulic pressure to the planetary gear unit

C1 from manual valve

C0 from 3-4 shift valve

B2 from 1-2 shift valve

C2 from 2-3 shift valve

4. O/D gear

The No. 2 solenoid valve is switched from on to off according to signals from the ECU. (No.1 solenoid valve is off, and No.2 solenoid valve is off.) The hydraulic pressure starts to be applied on the top of the 1-2 and 3-4 shift valves, moving down the 3-4 shift valve. (The line pressure from the 2-3 shift valve is applied at the bottom of the 1-2 shift valve, so 1-2 shift valve does not move.) Therefore, the fluid passage that had been acting on C0 to B0 is switched and the gear is shifted up to the O/D gear. When the overdrive main switch is OFF, it cannot shift up to the O/D gear. Because the ECU does not send the signal to turn off the No.2 solenoid valve.

Hydraulic pressure to the planetary gear unit

C1 from manual valve

B0 from 3-4 shift valve

B2 from 1-2 shift valve

C2 from 2-3 shift valve

Description

The shift lever corresponds to the gear shift lever of the manual transaxle. The driver can select the driving mode – forward or reverse travel, neutral, and park – by operating this lever. There are the following types of shift levers. The shift lever used depends on the vehicle and grade.

1. Straight type

2. Column type

3. Gate type

4. Straight type with E-shift system

HINT:

The overdrive main switch may also be called the overdrive OFF switch or the transaxle (transmission) control switch. The E-shift type can shift the gear up or down with the transaxle/transmission shift switch.

There are various types of planetary gear units. Here, typical planetary gear units are:

1. 3-speed + O/D type (FF vehicles)

By combining a 3-speed planetary gear unit with an O/D gear unit, four forward gear ratios and one reverse gear ratio are generated.

2. 3-speed + O/D type (FR vehicles)

3-speed x O/D type (FR vehicles)

The O/D gear unit for FR vehicles is placed between the torque converter and 3-speed planetary gear unit, which location is different from that of FF vehicles.

However the configuration is the same as for FF vehicles. Therefore four forward gear ratios and one reverse gear ratio are generated. Also, in the A350, the 1st gear and the O/D gear are combined to produce the 2nd gear. In this way, five forward gear ratios and one reverse gear ratio are generated.

3. 4-speed + O/D type (FR vehicles)

A center planetary gear is placed between the front planetary gear and the rear planetary gear. By combining these with the O/D gear unit, five forward gear ratios and one reverse gear ratio are generated.

4. 5-speed type (FR vehicles)

A center planetary gear is placed between the front planetary gear and the rear planetary gear. Also, the front planetary gear has two pinion gears arranged between the ring gear and the sun gear. By combining these planetary gear unit, five forward gear ratios and one reverse gear ratio are generated.

5. 4-speed CR-CR type (FF vehicles)

Four forward gear ratios and one reverse gear ratio can be generated with two planetary gears. A CR-CR planetary gear is a type of planetary gear unit that joins the front and rear planetary carriers to the ring gear.

6. 4-speed ravigneaux type (FF vehicles)

A long pinion and short pinion are placed between the ring gear and the front sun gear. The long pinion also meshes with the rear sun gear. Four forward gear ratios and one reverse gear ratio can be generated.

7. 3-speed + U/D type (FF vehicles)

One planetary gear is placed on the counter shaft. This operates as an “under-drive” reduction unit. The same as the 3-speed + O/D type, four forward gear ratios and one reverse gear ratio are generated. The gear ratio for the top gear is same as O/D for the total reduction ratio including the differential gear ratio.

8. 4-speed + U/D type (FF vehicles)

A 4-speed CR-CR type planetary gear unit is placed on the input shaft and an “under-drive” reduction unit is placed on the counter shaft. With these, five forward gear ratios and one reverse gear ratio are generated.

The overdrive gear unit is an independent planetary gear unit with a gear ratio less than 1.0 (approx. 0.7-0.8). It is combined with a conventional 3-speed planetary gear unit and is equivalent to the 4th speed gear. The overdrive gear unit consists of the planetary gear set, brake (B0), clutch (C0), and one-way clutch (F0). The power is input to the overdrive carrier and output from the overdrive ring gear. Normally, when the vehicle speed goes over 40 km/ h in the “D” range, shifting up to the overdrive gear becomes possible. It is also possible to drive without shifting up to the overdrive gear if that suits the driver.

HINT:

The illustration on the left is for a 3- speed planetary gear unit with an overdrive gear unit added (A140 series).

“P” or “N” Range

When the shift lever is in “N” or “P”, the forward clutch (C1) and direct clutch (C2) do not operate, so input from the input shaft is not transmitted to the differential drive pinion shaft. In addition, when the shift lever is in “P”, the parking lock pawl engages with the parking gear to which the differential drive pinion shaft is splined, thus preventing the vehicle from moving.

NOTICE:

Parking lock mechanism for FR vehicles

When the shift lever of an automatic transmission for a FR vehicle is in the “P” range, the parking lock pawl is engaged with the front or rear planetary ring gear, which is splined with the output shaft, preventing movement of the vehicle. However, on FR- based 4WD vehicles, the movement of the vehicle cannot be prevented if the transfer mechanism is in neutral, even if the automatic transmission is in “P”. For this reason, be sure to set the parking brake when parking.

1. In overdrive

In overdrive, the O/D brake (B0) locks the O/D sun gear, so when the overdrive pinion gears revolve clockwise around the overdrive sun gear while rotating around the pinion shafts. Therefore, the overdrive ring gear rotates clockwise faster than the overdrive carrier. The length of the arrow shows the rotational speed and the width of the arrow shows the torque. The longer the arrow, the greater the rotational speed and the wider the arrow, the greater the torque.

2. Not in overdrive

The overdrive planetary gear set acts as a direct drive mechanism, rotating as a single unit to output the input power (rotating speed and torque) as is. The length of the arrow shows the rotational speed and the width of the arrow shows the torque. The longer the arrow, the greater the rotational speed and the wider the arrow, the greater the torque.

In automatic transaxle vehicles, the planetary gear unit handles deceleration, reverse, direct connection, and acceleration. The planetary gear unit consists of the planetary gears, clutches, and brakes. The front planetary gear set and the rear planetary gear set are connected to the clutches and brakes that connect and disconnect the power. They switch the input section and fixing elements and produce various gear ratios and neutral.

HINT:

The illustration on the left is for a 3- speed planetary gear unit (A130 series). Basically, this model will be used to explain operations of the planetary gear unit.

Construction

The planetary gears have three types of gears – the ring gear, pinion gears, and sun gear – and the planetary carrier. The planetary carrier is connected to the center shaft of each pinion gear and makes the pinion gears revolve. With this set of mutually connected gears, the pinion gears resemble planets revolving around the sun, so they are called the planetary gears. Normally, plural planetary gears are combined in the planetary gear unit.

Principle of Operation

By switching the input, output, and fixing elements, it is possible to decelerate, reverse, directly connect, and accelerate. The outline of these operations is explained below.

1. Deceleration

Power input: Ring gear

Power output: Planetary carrier

Fixed: Sun gear

When the sun gear is fixed, only the pinion gear rotates and revolves. Therefore, the output shaft decelerates in proportion to the input shaft only by the rotation of the pinion gear. The length of the arrow shows the rotational speed and the width of the arrow shows the torque. The longer the arrow, the greater the rotational speed and the wider the arrow, the greater the torque.

2. Reverse

Power input: Sun gear

Power output: Ring gear

Fixed: Planetary carrier

When the planetary carrier is fixed in position and the sun gear turns, the ring gear turn on its axis and the rotational direction is reversed. The length of the arrow shows the rotational speed and the width of the arrow shows the torque. The longer the arrow, the greater the rotational speed and the wider the arrow, the greater the torque.

3. Direct connection

Power input: Sun gear, ring gear

Power output: Planetary carrier

As the ring gear and sun gear rotate together at the same speed, the planetary carrier also rotates at the same speed. The length of the arrow shows the rotational speed and the width of the arrow shows the torque. The longer the arrow, the greater the rotational speed and the wider the arrow, the greater the torque.

4. Acceleration

Power input: Planetary carrier

Power output: Ring gear

Fixed: Sun gear

When the planetary carrier turns clockwise, the pinion gear revolves around the sun gear while turning clockwise. Therefore, the ring gear accelerates based on the number of teeth on the ring gear and sun gear. The length of the arrow shows the rotational speed and the width of the arrow shows the torque. The longer the arrow, the greater the rotational speed and the wider the arrow, the greater the torque.

1. Construction

The shift and select lever shaft are set at right angles to the fork shafts on top of the transaxle case. A double-meshing prevention mechanism and reverse gear mis-shift prevention mechanism are adopted. Also, a shift detent mechanism and reverse detent mechanism are adopted on the shift fork shaft.

2. Double-meshing prevention mechanism

This mechanism prevents possible shifting into two gears at the same time. When two shift forks are moved at the same time, they catch during selecting and the gears are doublemeshed. As a result, the gears do not turn, the vehicle acts as though the brakes have been jammed on, and the tires lock up causing a very dangerous situation. The shift fork lock plate is prevented turning by a bolt which allows the shift and select lever shaft to slide only in the select direction.

3. Operation of double-meshing prevention mechanism

The shift fork lock plate fits into two of the three shift fork head slots at all times and locks all shift forks except for the gear to be used. For example, when the shift lever is put into 1st or 2nd gear, the shift fork lock plate and shift inner lever No. 1 move to the right as shown in the diagram on the left. The shift fork lock plate prevents the 3rd/4th and 5th/reverse shift fork heads from moving so that only the 1st/2nd shift fork head can move.

4. Reverse mis-shift prevention mechanism

If the transaxle is shifted into reverse gear while the vehicle is running, this can break the clutch and the manual transaxle and at the same time lock up the tires, causing a very dangerous situation. Therefore, this mechanism is set up so that the driver must shift into the neutral position before shifting into reverse gear.

5. Operation of reverse mis-shift prevention mechanism

(1) When selecting the gear When the gear shift lever is moved to the 5th/reverse selection position (the neutral position between 5th and reverse gears), the shift inner lever No. 2 moves in the “5th/reverse” direction, turning the reverse restrict pin in the direction as shown by arrow A.

(2) Shifting into 5th gear When the transaxle has been shifted into 5th gear, shift inner lever No. 2 rotates in the direction shown by arrow B, releasing the reverse restrict pin. As a result, the reverse restrict pin is returned to its original position by a return spring.

(3) Attempted shifting from 5th gear into reverse If gear shifting is attempted directly from 5th gear into reverse (as shown by arrow C), the shift inner lever No. 2 hits the reverse restrict pin, preventing the transaxle from shifting into reverse from 5th gear.

(4) Shifting into reverse gear After the gear shift lever is once returned to the neutral position between 3rd and 4th gears and then moved to the 5th/reverse selection position, shift inner lever No. 2 and the reverse restrict pin will be in the configuration as shown in the left. In this configuration, shifting into reverse rotates shift inner lever No. 2 in the direction shown by arrow D without any interference from the reverse restrict pin.

6. Reverse one-way mechanism

The reverse idler gear moves only when the transaxle is shifted into reverse. When it is shifted into 5th gear, the reverse idler gear is kept in the neutral position.

Reverse one-way mechanism operation

(1) Shifting into 5th gear When the transaxle is shifted into 5th gear, the shift fork shaft No. 3 is moved to the right, causing balls to be pushed into the grooves of shift fork shaft No. 2.

(2) Shifting into reverse When the transaxle is shifted into reverse, the reverse shift fork is moved to the left by the snap ring which is fitted onto the shift fork shaft No. 3.

(3) Shifting from reverse into neutral The shift fork shaft No. 3, the balls and reverse shift fork are all moved integrally to the right.

7. Shift detent mechanism

There are three grooves on each shift fork shaft, and the detent ball is pushed into the groove by the spring when shifting gears. This not only prevents the transaxle from jumping out of gear, but also gives the driver a better feel for the gear engagement.

8. Hub sleeve function

To prevent the gear from jumping out, the spline between the hub sleeve and the speed gear is tapered to form a chamfer shape and improve the meshing of the hub sleeve and speed gear. For the same purpose, the teeth of the input, idler, and reverse gears are also slightly tapered.

(1) When the driving force is transmitted from a gear to the hub sleeve The splines on the gear mesh with all the hub sleeve splines.

(2) When the driving force is transmitted from the hub sleeve to a gear (during engine breaking) A lower number of gear splines meshes with the hub sleeve. This causes the meshing pressure of the hub sleeve and the gear to increase, thus preventing the transaxle from jumping out of gear.

SERVICE HINT:

If the hub sleeve spline chamfer portion is worn, the transaxle jumps outof gear.

9. Reverse detent mechanism

There is also a groove on the upper surface of the reverse shift fork into which the lock ball is pushed by a spring. When the transaxle is not shifted into reverse, this groove prevents the reverse idler gear from moving.