ZF Ecomat

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The ZF Ecomat automotive transmission was specifically designed by ZF Friedrichshafen AG primarily for city-buses and motorcoaches. It has several generations – all of the automatic transmission type, and many variants. The latest variants use a lock-up torque converter along with a retarder. Some variants are listed below.

History[]

The ZF Ecomat automatic gearbox was launched in 1978. The basic model is called 4HP500 — "4" refers to the number of forward wave gears, with four, five and six front-speed versions; "500" represents the upper limit of the input torque that the gearbox can withstand. It is divided into 500, 590 and 600 grades, corresponding to 1100Nm, 1250Nm and 1400Nm respectively. In the 2000s, ZF launched Ecomat 2/2 Plus and Ecomat 4 successively, and the gearbox version is also reflected in the suffix of the model name - for example, the "4C" after 6HP604C represents the gearbox type.

Description[]

Like a typical fully automatic gearbox, the ZF Ecomat gearbox is mainly composed of a torque converter and a planetary/epicyclic geartrain.  After the engine power is doubled by the torque converter, it is multiplied by the gear ratio of the planetary gear set to obtain the torque finally transmitted to the transmission shaft (ignoring the angle drive); when the hydrodynamic transmission was introduced before, it was once  Explained that the torque converter's torque ratio is continuously variable and is highest when the output shaft is stationary (called stall ratio).  Therefore, the multiplication of the two makes a wave start with a stepless speed change effect, which can save a wave of large gear ratios like the SCG gearbox.  When the vehicle starts to accelerate to a certain speed, in order to reduce power loss, the lock-up clutch attached to the torque converter will lock the pump wheel and the turbine (that is, "direct connection"), and the transmission will be purely mechanical.  In addition, the Ecomat gearbox is also equipped with a built-in retarder (integral retarder), which operates hydraulically and can provide deceleration assistance without mechanical wear in any frequency band.

ZF Ecomat's planetary gear set consists of three sets, the same as the one-to-three-wave design of the SCG four-speed gearbox.  The front end of the gear set is equipped with three sets of clutches A, B and C, so that the input shaft can be connected to the main shaft of the gear set, the two-wave planetary gear carrier or the three-wave sun gear respectively, so that Ecomat can make six fronts with only three sets of planetary gears.  A combination of the last, unlike the SCG gear box, each gear except the highest wave has a set of planetary gears.

When Clutch A is closed, the input shaft is connected to the main shaft of the gear set, and the operation principle of the first to third waves is the same as that of the SCG gearbox, which will not be repeated here;

When there are four waves, Clutch A and B are engaged at the same time, so that the input shaft and the entire series planetary gear set rotate together, the ratio is 1:1;

During the fifth wave, Clutch B engages the input shaft with the second wave planetary gear carrier (connecting the first wave gear ring and the third wave gear ring at the same time), and the third wave sun gear is braked by Brake D, so that the main shaft of the gear set (that is, the first wave sun gear)  The rotation speed is higher than a wave gear ring (connected to the input shaft), and the final wave of the planetary gear carrier responsible for the output also rotates faster than the input shaft to achieve an overdrive effect;

The six-wave is similar to the five-wave, but the two-wave ring gear is locked instead of the three-wave sun gear with Brake E, which makes the main shaft of the gear set and the first-wave planetary carrier rotate faster, and the final gear ratio is also smaller;

Clutch C is only used in the rear wave, connecting the input shaft to the three-wave sun gear, while Brake F brakes the one-wave ring gear (connected with the two-wave planetary gear carrier and the three-wave ring gear), and the three-wave planetary gear carrier (at the same time as two  The rotation of the wave gear ring) drives the main shaft of the gear set (that is, a wave of sun gears) to rotate in the opposite direction, and the output shaft (a wave of planetary gear carriers) also rotates in the opposite direction.

At present, the common gear ratios of Ecomat gearboxes are 3.43:1 for the first wave, 2.01:1 for the second wave, 1.42:1 for the third wave, 1:1 for the fourth wave, 0.83:1 for the fifth wave, 0.59:1 for the sixth wave, and -4.84:1 for the rear wave.  There is no difference in structure between 5HP and 6HP versions, it is purely the difference in the computer software settings of the gearbox, so the 5HP version can modify the software to unlock the six waves;  The frame is changed to connect to the three-wave sun gear (Clutch B of 4HP is actually equivalent to Clutch C of 5HP/6HP in function, please do not confuse the two "Clutch B"), so it is impossible to achieve super ratio wave, and the highest gear ratio is limited to 1  :1.

However, Ecomat only had a close ratio version when it was first launched, with a gear ratio of 2.81:1 for the first wave, and 1.84:1 for the rest of the gears, 1.36:1 for the third wave, 1:1 for the fourth wave, and 1:1 for the second wave.  The fifth wave is 0.8:1, and the second wave is -3.97:1. There are only 4HP and 5HP versions. Hong Kong's "Leng Lan" also used this version of the Ecomat gearbox.  As for a version with a wide ratio of 3.43:1, it only appeared in the mid-1980s. The difference between the two is the number of teeth in a wave of gear sets - the close ratio version is 85 teeth on the ring gear and 18 teeth on the planetary gear.  , the sun gear has 47 teeth, while the sparse-ratio version of the sun gear has only 35 teeth.

In addition, the Ecomat gearbox also has an "extended" version, adding a set of planetary gears at the output end of the gearbox, extending the basic planetary carrier and the main shaft of the gear set, and adding a set of gear ratios of 5.6:1.  One wave with a large gear ratio, the gear ratios of other gears are not affected.  The highest wave is five waves 1:1 or six waves 0.83:1, which are equivalent to the four and five waves of the basic sparse-tooth ratio version.

Between the torque converter and the clutch of the planetary gear set, there are also two important components - the oil pump and the hydraulic reducer (retarder).  The gear that drives the oil pump is connected to the torque converter pump wheel housing and rotates together with the engine output shaft, so it can provide the oil pressure necessary for the operation and lubrication of the gearbox even when it is empty.  This gear is also responsible for driving the optional PTO (power take-off) device. For example, the air-conditioning version of the Olympian equipped with the Cummins engine relies on the PTO of the Ecomat gearbox to drive the three compression pumps of the Denso air-conditioning system.

As for the hydraulic reducer, the pump impeller is connected to the clutch main shaft, and the turbine is fixed in the gearbox casing, which is responsible for bearing the reaction force.  During normal driving, there is only air in the reducer, and the resistance is negligible; when the reducer takes effect, the gearbox oil is injected into the reducer, and the deceleration force generated is multiplied by the gear ratio of the current wave gear and then transmitted to the drive shaft.  The torque of the hydraulic reducer is proportional to the fluid density, and is also proportional to the square of the speed of the pump wheel.  Therefore, in order to maintain a stable deceleration force output, the amount of oil in the reducer needs to increase as the speed decreases.  At the same time, the centripetal force of the circular motion is also proportional to the square of the rotational speed, which means that the pressure exerted by the oil on the outer circumference of the inner wall of the reducer is also proportional to the torque output by the reducer.  Therefore, by connecting the pressure valve to the outer circumference of the reducer through the oil circuit, the deceleration force can be controlled by adjusting the oil pressure.

There is a retarder accumulator outside the Ecomat gearbox, which usually stores part of the gearbox oil.  When the reducer starts, the electric control oil valve inside the gear box connects the oil circuit between the pressure accumulator and the reducer, and the oil circuit of the gear box oil cooler (oil cooler) is also changed from the connection to the torque converter to the  Reducer; at the same time, an air pressure regulated by a pressure reducing valve (from the auxiliary cylinder in the air system) is applied to the pressure accumulator to maintain the oil pressure in the reducer at the specified level.  This pressure varies with the depth of the brake pedal. Taking Leyland Olympian as an example, the oil pressure of the reducer is controlled in two stages—when the driver gently presses the pedal and the brake system pressure has not reached the effective level, the pedal triggers the switch, and the electric control  The valve inputs the air pressure of 1.2 bar into the pressure accumulator, and the oil pressure of the reducer is controlled at the level of 2 bar; when the depth of the foot switch reaches the level where the brake system is effective, the air pressure in the brake air path will trigger another group of switches and valves, the pressure accumulator  Air pressure and reducer oil pressure were increased to 3 bar and 4 bar respectively.  Whenever the reducer stops working, the air pressure in the pressure accumulator is released, and the gearbox will make a deflation sound, which is the unique mark of the Ecomat gearbox.

The wave transfer mode of the Ecomat gearbox is changeable. In theory, each wave gear can have two states of "oil pressure" and "direct connection". The former relies on the torque converter to double the power, and the driving is smooth but the power loss is large; the latter uses the lock  The -up clutch transmits power directly, which is highly efficient but is prone to stumbling when the oil is withdrawn at low speed.

Taking the four-speed basic model as an example, depending on the gear box settings, there are three wave turning modes from starting acceleration to four-wave, each with its own advantages and disadvantages:
①: One wave of hydraulic pressure -> One wave of direct connection -> Two waves of direct connection -> Three waves of direct connection -> Four waves of direct connection
②: 1st wave of hydraulic pressure -> 2nd wave of hydraulic pressure -> 2nd wave of direct junction -> 3rd wave of direct junction -> 4th wave of direct junction
③: 1st wave of oil pressure -> 1st wave of straight knot -> 2nd wave of oil pressure -> 2nd wave of straight knot -> 3rd wave of straight knot -> 4th wave of straight knot

Mode ① Advances the lock-up time, which can reduce power loss, but sacrifices the smoothness of the turning wave (the engine speed difference is very large during a wave of lock-up), and the deceleration of the oil collection when the wave is straight will cause a violent setback (especially the old ones).  The reason why Ecomat is believed to be the mismatch between the gearbox torsional damper and the rest of the powertrain, and the fact that the old engine uses mechanical rather than electronic throttle control).

On the contrary, mode ② prolongs the time of hydraulic transmission, with lower efficiency but smooth starting (small engine speed fluctuation), and because of the blade design of the torque converter, it has a one-way transmission characteristic, and it is closed in the oil pressure section.  When oil is running, the vehicle will "freewheel" without being affected by the braking effect of the engine, and the engine speed will drop immediately without being dragged up by the speed of the vehicle.

As for mode ③, some gearboxes are set to use this mode every time they start; and even if the gearbox is preset to use mode ① or ②, it will automatically change whenever the driver deeply presses the accelerator to start (kick-down mode).  Use mode ③.  The first and second waves of this mode are divided into four sections. The second wave hydraulic section is used to fill the gear ratio gap between the first wave and the second wave, while maintaining the engine speed at a high level to provide better climbing.  Oblique power, but the fuel consumption also rises.

The torque converter of the Ecomat gearbox is not only used at the start, but also often intervenes when turning low waves.  For example, when driving with three waves straight and low revs, increase the throttle to re-accelerate, or when the power is insufficient when the three waves go up, the gearbox will not go directly to the second wave, but will temporarily release the lock-up clutch and enter the second wave.  Hydraulic section, and then return to direct mechanical transmission.  In this way, the acceleration force can be enhanced by the torque converter in the oil pressure section, and the third wave to the second wave can be avoided due to the wide gear ratio difference when the full throttle is directly carried over (the multi-plate brake bite force is also adjusted to the highest).  Frustration.

When decelerating, depending on the gearbox version, the timing of switching to hydrodynamic mode will vary.  For example, the old-style Ecomat decelerates from four waves to a stop, and it will turn waves in the order of four waves straight -> three waves straight -> three waves of oil pressure -> two waves of oil pressure -> one wave of oil pressure; as for the later Ecomat, and Ecomat  2/2 Plus/4, it will drag the wave all the way to the second wave in the direct mode, and then go to the oil pressure section.  The difference between the two is that the speed from the second wave of oil pressure to the first wave of oil pressure only happens when it comes to a stop.  Therefore, if you drive slowly on a traffic-congested road without stopping, and then re-accelerate after slowing down, it will start with a second wave of hydraulic pressure.

When turning waves under different conditions, the oil pressure provided to the multi-plate clutch/brake controlling the planetary gear set also needs to be changed accordingly, so as to adjust the appropriate turning wave strength to avoid slipping and wear due to too little force when the accelerator is too large.  , When the throttle is firmly engaged and the turning wave is not smooth, etc.  Therefore, the Ecomat gearbox has a load sensor that is linked with the engine fuel injection pump, or directly obtains the throttle signal through the CAN bus system (only applicable to gearbox models with a suffix "C"  version), to determine the wave-turning strength.

The throttle pressure valve in the Ecomat gearbox oil circuit system, its electronically controlled oil valve can vibrate with different frequencies to control the oil pressure rising speed provided to the clutch/brake, this process is called pressure modulation.  Each group of clutch/brake is operated by its own piston and electronically controlled oil valve, and the flow rate of oil entering the piston from the valve is not only controlled by the main oil pressure, but also affected by the oil pressure output by the throttle pressure valve - the higher the pressure  High, the faster the flow rate, the faster the occlusal force rises to the full pressure state.  The electronically controlled oil valve of the Throttle pressure valve only operates during the wave entry process. The stronger the vibration, the more the oil pressure is reduced. It lasts for about 1.5 seconds. After the vibration is stopped, the full pressure is applied to the clutch/brake.  The lock-up clutch also has a similar control mechanism, but it is directly determined by the oil pressure in the torque converter, because this oil pressure represents the torque that the lock-up clutch will bear.

Gear ratios Ecomat I (1980–1985)[]

1	2	3	4	5	R
2.82	1.84	1.36	1.00	0.80 (optional)	4.84

Gear ratios Ecomat I/II/IV (1985–Present)[]

1	2	3	4	5	6	R
3.43	2.01	1.42	1.00	0.83 (optional)	0.59 (optional)	4.84

1st generation — Ecomat (1980–2002)[]

All generations of the Ecomat series are no longer in production.

• 4HP500 / 5HP500 / 6HP500 — four-, five- or six-speed; maximum input torque of 1100 Nm
• 4HP590 / 5HP590 / 6HP590 — four-, five- or six-speed; maximum input torque of 1250 Nm
• 4HP600 / 5HP600 / 6HP600 — four-, five- or six-speed; maximum input torque of 1400 Nm

2nd generation — Ecomat 2 (1997–2007)[]

All generations of the Ecomat series are no longer in production.

• 4HP502/C / 5HP502/C / 6HP502/C — four-, five- or six-speed; maximum input torque of 1,100 newton-metres (811 lbf⋅ft)
• 4HP592/C / 5HP592/C / 6HP592/C — four-, five- or six-speed; maximum input torque of 1,250 newton-metres (922 lbf⋅ft)
• 4HP602/C / 5HP602/C / 6HP602/C — four-, five- or six-speed; maximum input torque of 1,600 newton-metres (1,180 lbf⋅ft)

3rd generation — Ecomat 4 (2006–2016)[]

All generations of the Ecomat series are no longer in production.

• 5HP504/C – five speed for lighter buses up to 13 ton; maximum input torque of 850 newton-metres (627 lbf⋅ft)
• 5HP504/C / 6HP504/C — five- or six-speed; maximum input torque of 1,100 newton-metres (811 lbf⋅ft)
• 5HP594/C / 6HP594/C — five- or six-speed; maximum input torque of 1,250 newton-metres (922 lbf⋅ft)
• 5HP604/C / 6HP604/C — five- or six-speed; maximum input torque of 1,750 newton-metres (1,291 lbf⋅ft)

Use in rail vehicles[]

In addition to its use in road vehicles, the Ecomat transmission is also employed in the Class 172 lightweight diesel multiple unit (DMU) trains in service with various operators in Great Britain, in major refurbishments of in the Czech Republic, CAF built C4K in Northern Ireland and the ABB Scandia built IC3 (DSB Class MF) DMUs in Denmark.

See also[]

• List of ZF transmissions
• The succeeder of the ZF Ecomat

References[]

• "ZF Ecomat – Driveline Technology in City Buses". ZF Friedrichshafen AG. ZF.com. Retrieved 24 November 2009.
• "Volvo B10M Mk I Operator's Manual, Volvodemort version, Specifications Section:". ZF Friedrichshafen AG. ZF.com. Retrieved 14 February 2013.

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