Honda Prelude -- Transmission

OVERVIEW
A 5-speed manual transmission is standard on the Prelude. An automatic transmission is also available for the standard Prelude (the Type SH is only available with a manual transmission).

The automatic transmission is a new design and is the first Honda automatic transmission to be used with a DOHC VTEC engine in the United States.

Design and performance goals for both transmissions centered around having them contribute to the new Prelude's sporty, fun-to-drive mission. Something an enthusiast would use and appreciate.

ELECTRONICALLY CONTROLLED 4-SPEED AUTOMATIC TRANSMISSION WITH SEQUENTIAL SPORTSHIFT
The available electronically controlled 4-speed automatic transmission used on the Prelude is compact, smooth operating, fast shifting and efficient. Its Sequential SportShift mode allows it to be manually upshifted and downshifted in order to enhance the Prelude's performance.

Specific changes to the transmission include a wider range of ratios, a larger, faster microprocessor, linear hydraulic control for the clutches, a revised lockup torque converter, Sequential SportShift and the addition of Honda's Grade Logic Control System.

As on the previous design, 4th gear is an overdrive gear. Overdrive improves fuel economy and helps reduce engine wear and noise at highway speeds.

AUTOMATIC TRANSMISSIN DESIGN
Like all Honda-designed automatic transmissions, this latest Prelude automatic is a constant-mesh type, with three parallel shafts: input, intermediate and output. Shifting is electronically controlled and hydraulically actuated. Shift management is controlled by a new 16-bit microprocessor. The new microprocessor's greater capacity is used to control two new linear-shift solenoids, that in turn controls hydraulic pressure to the gear clutch packs. The older transmission used a combination of several non-linear (on/off) solenoids, springs and accumulators to control this function. Since the new control is linear, clutch engagement is more progressive. The result is smoother shifting and power transmission over a greater variety of power and gear settings. This is especially noticeable on full-throttle upshifts.

A newly added centrifugal hydraulic cancellation mechanism improves shift control by minimizing centrifugal hydraulic pressure in the clutch packs. As a result, shifts are smoother, with less shift shock.

The new, more powerful electronic control unit also receives throttle-position data electronically, making it possible to eliminate the throttle-cable-actuated hydraulic control used on previous Prelude transmissions. Eliminating the cable helps lighten throttle-pedal spring pressure, which helps minimize driver foot and leg fatigue. In addition, the elimination of the throttle/transmission cable allows for a shorter pedal stroke with better feel.

In addition to shifting more smoothly, the new transmission also shifts 10% faster than its predecessor.

The low-gear hold function of the previous transmission is now incorporated into the new transmission's Sequential SportShift, so the one-way clutch and low-hold clutch eliminated. The new transmission fits in a 25mm-shorter case than its predecessor and is almost two pounds lighter. An additional support bearing in the idle-gear shaft reduces transmission gear noise under load.

The lockup torque converter helps minimize fluid-coupling slippage by mechanically coupling the engine to the transmission during certain driving modes, such as steady-state cruising. The benefit is better mileage. The lockup feature works in 2nd and 3rd gears as well as 4th and also maintains lockup in 2nd, 3rd and 4th gears during deceleration. The design absorbs vibration and judder better during engagement and allows for an extended lockup zone. The result is a smoother engagement and also a slight increase in efficiency, and therefore slightly higher mileage.

GRADE LOGIC CONTROL SYSTEM
The Prelude automatic transmission is the first Prelude transmission to use Honda's Grade Logic Control System. Grade Logic differs from more conventional computer-controlled shift programming in two important ways: It can determine certain vehicle driving situations and then, based on stored "shift maps," select the appropriate shift points for 3rd-gear/4th-gear upshifts and 4th-gear/3rd-gear downshifts. This feature is especially useful when driving up and down long grades and when performance-driving.

Less sophisticated automatic transmissions use only throttle position (engine load) and road speed to determine the appropriate shift point. In addition, only one shift-point map is used. As a result, there are certain situations that can "fool" the computer. For example, when driving up a long hill with the shift lever in "D" and the transmission in 4th gear, a conventional automatic transmission could end up in an inappropriate mode that causes it to continually "hunt" between 3rd and 4th gear as the driver changes throttle position. When driving down a long grade, a conventional transmission may select 4th gear, when the advantage of 3rd-gear engine braking would have been more useful.

The Grade Logic Control System used on the Prelude automatic transmission performs better in these situations, because in addition to throttle position and road speed, it also uses rate of deceleration and rate of acceleration to determine special driving conditions. Grade Logic then chooses the appropriate shift points from any of six different shift maps.

For example, when driving uphill, Grade Logic will sense a large throttle opening without any increase in speed. Based on this, Grade Logic will determine that the Prelude is going uphill and it will determine how steep the grade is. It then chooses a shift map that will downshift and hold 3rd gear, thereby eliminating hunting between gears.

Grade Logic also uses brake-pedal application as a control input. For example, if it receives a closed-throttle signal and a brake-pedal activation signal, Grade Logic will determine that the Prelude is driving downhill. It then selects a shift map that will downshift and hold 3rd gear to allow the Prelude to utilize engine braking.

Similarly, Grade Logic can use a rapid deceleration signal and closed throttle to determine that the Prelude is entering a tight curve, or a corner. It then chooses a shift map that downshifts and then delays upshifting during acceleration for more responsive performance.

This same set of inputs occur in stop-and-go city traffic, when abrupt braking is followed by quick, hard acceleration. Here again, the transmission will improve the Prelude's performance by downshifting and holding 3rd gear when braking and accelerating.

SEQUENTIAL SPORTSHIFT
An innovative, new feature on the Prelude automatic transmission is Honda Sequential SportShift. It combines the ease and convenience of an automatic transmission with the shift-it-yourself fun of a manual. When the transmission shift lever is in the "D" mode, the transmission operates like any other Honda automatic transmission. However, when the driver wants more performance and faster shifting, they can place the transmission in the sequential mode and control the transmission shift points. The shifter operates sequentially; the driver merely pushes the gear-change handle repeatedly in one direction for upshifts and in the opposite direction for downshifts, much like a motorcycle or racingcar gear selector. A large LED display in the tachometer (where the driver can quickly see it), indicates what gear the transmission is in.

When in the sequential mode, the transmission will not upshift until the driver selects the next higher gear. When downshifting, the transmission will not change to a lower gear until it receives a command from the driver and the engine rpms have dropped below the point where overrevving would occur. If, for example, the Prelude is in 3rd gear, approaching a 2nd-gear corner, the driver can preset the transmission by downshiffing once. The transmission will automatically downshift (within a second) when engine speed drops. The Prelude will arrive at the corner in 2nd gear without any more attention to shifting by the driver.

If the Prelude comes to a stop while in the sequential mode and in a higher gear--4th, 3rd or 2nd, for example--it will automatically shift into 1st gear.

When driving up or down a steep grade in 4th gear, in the sequential mode, the Grade Logic Control System in the automatic transmission will automatically override the Sequential SportShift mode, and the transmission will downshift to 3rd.

The transmission's electronic control will not let the transmission operate in the sequential mode until the hydraulic transmission fluid has warmed up.

5-SPEED MANUAL TRANSMISSION
A cable-operated, 5-speed manual transmission is standard on the Prelude and Prelude Type SH (the automatic transmission is not available on the Type SH). Double-cone synchronizers on 2nd gear help minimize shift effort. In addition, clutch-pedal effort has been reduced, thanks to a new clutch lining. The lining's higher coefficient of friction allows for a reduction in lining diameter, without any sacrifice in durability. The smaller-diameter clutch reduces clutch-pedal effort.

Prelude 5-speed Manual Transmission Gear Ratios
(Prelude and Prelude Type SH)

1st Gear: 3.285
2nd Gear: 1.956
3rd Gear: 1.344
4th Gear: 1.034
5th Gear: 0.812
Reverse: 4.266
Final Drive: 4.266
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