Transmission drive unit 150 Nm

Jefa 150 Nm transmission autopilot drive unit
The Jefa transmission drive is one of the most compact autopilot drives in the world. It's as strong as a human being (the max. output torque of 150 Nm is equivalent to 30 Kg on the rim of a 1 meter wheel) and is build for 24 hours per day continuous operation with a total weight of only 6 Kgs. The combination of the specially designed electric motor with the ultra efficient 3 stage planetary gearbox results in an extremely efficient drive unit to keep the battery charging time to the minimum. The drive can be used on boats from 30 to 50 foot (or with a rudder torque up to 300 KgM) equipped with a Jefa transmission steering system. Please click on the pictures for a larger view.
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Main dimensions
The Jefa transmission drive is very compact with a length of 162 mm and a maximum diameter of 158 mm. As space is always a problem on sailing yachts, the compact drive unit can be integrated into the steering system even when a very limited space is available. The drive can be mounted on the BG11 and BG14 bevel gearboxes or directly on the RG10 reduction gearboxes. Please remind that a preparation for the autopilot integration is required when ordering the steering system. 
The mounting possibilities:

The transmission drive can be mounted on every (prepared) bevel gearbox in the steering system or directly on the RG type reduction boxes with multiple input shafts.
The construction:

The above assembly drawing shows a transmission drive mounted on a bevel gearbox. The drive can be separated in 3 main parts: The electric motor (1), the three stage planetary gearbox (2) and the electro-magnetic clutch (3). The Jefa transmission drive has multiple advantages over existing integrated drive units. These advantages will be explained per section of the drive:

Electric Motor: The flat wound electric motor (pancake motor) used in the Jefa drive units is carefully selected for this application. Pancake motors have multiple advantages over normal electric DC motors:

  • A large flat wound rotor to achieve a high starting toque and an immediate response to the autopilot speed control signal.
  • A motor efficiency of 72,5% to achieve a minimal power consumption and maximal mechanical power output (compared to max. 50% efficiency of a normal DC motor).
  • Compact main dimensions compared to achievable output.
  • Aluminium motor housing in stead of sheet steel plate to avoid corrosion.

Planetary gearbox: To achieve a correct rudder travel speed (hard over time) the electric motor has to be reduced in speed with a factor 486:1. Some autopilot drive producers use a worm reduction box, but the efficiency is extremely low as the gears rub each other. Some producers use a combination of a planetary gearbox with a 2 stage spur gear set (one small gear and one big gear), but this creates a much bigger unit with an offset to the centre and much heavier loaded gears. The best way to achieve this high reduction in combination with a high torque is a 3 stage planetary gearbox. It's also the most expensive way as every gear step has 4 gears in stead of 2 gears but the huge advantages overrule the higher price:

  • The highest possible efficiency compared to any other gearbox.
  • All forces are equally spread over 3 gear teeth in stead of one allowing a much compacter and stronger solution.
  • The forces and torques from the motor to the output shaft remain in the centre line of the drive unit, resulting in a higher efficiency and extremely reduces the loads on the housing and other internal parts.

Electro magnetic clutch: On the moment the transmission steering system on the yacht is manually operated, the autopilot drive has to be disconnected from the steering system. This is achieved with the electro-magnetic clutch (4) and controlled automatically by the autopilot junction box. Jefa has developed a unique and patented engagement clutch. The solution is based on two electrically operated spring loaded clutch pins that engage and disengage the outer gear ring of last planetary gear step. This solution has multiple advantages over the existing friction plate clutches:

  • Less friction to back drive the unit.
  • Lower power consumption (1.3 Amp. at 12 Volt, 0.7 Amp at 24 Volt). When the clutch isn't powered, it's disengaged and engaged when powered.
  • The clutch doesn't wear in time.
  • More compact than any friction clutch.
  • When the autopilot is switched off, the helmsman isn't suddenly confronted with the full rudder torque, but has to put loading on the wheel to equalise the forces so the the clutch can disengage, making the manual take over much safer. 
The performance

This performance table shows the relation between the consumed power and the output power. The red line shows the output torque against the needed amperage for the 12 volts transmission drive. The blue line shows the output speed of the drive relative to the output torque. Also visible is the strength of the drive unit related to man power. The unit is much stronger than a human being and can last much longer but one should note that when the unit is operated in the red zone, something is wrong with the trim of the boats and the sails should be adjusted to achieve lower rudder torques. The above table shows that the Jefa transmission drive will steer the yacht even in the worst possible conditions. As the drive will mostly operate in the left green zone and will not continuously rotate, the average power consumption on 12 volts is 1.5 amps.
Connections:

This illustration shows the minimal components for a working autopilot configuration. Jefa autopilot drives work together with all mayor autopilot electronics. The connection of the Jefa autopilot drive to the autopilot junction box is quite simple. The two 0.75 mm˛ red and black wires have to be connected to the plus and minus of the autopilot clutch line. This will make sure that when the autopilot user engages the autopilot on the control screen, the clutch will engage and allow the autopilot motor to drive the steering system. The two 2 mm˛ red and black wires have to be connected to the autopilot drive output connection. Now the Jefa autopilot drive is integrated into the system.
Compatibility in 12 Volts. (not available in 24 volts*1)
Following table shows the maximum rudder torques at midships and full rudder that can be generated by the Jefa 150 Nm transmission drive in combination with various autopilot junction boxes and reduction gearboxes. As the transmission drive drives the steering system, the maximum rudder torque depends on the type of reduction box used in the system. The hard over time (HO-time) states the time it takes the drive to travel the full 72 degrees of rudder travel when the speed control of the pilot is set to maximum speed.
Autopilot junction box 12 Volt version. Max. output (Amp.) BRG10-50 & RG10-50 midships (KgM) BRG10-50 & RG10-50 full rudder (KgM) RG10-70 midships (KgM) RG10-70 full rudder (KgM) BRG10-67 midships (KgM) BRG10-67 full rudder (KgM)
HO-time no load   14 sec. 14 sec. 19 sec. 19 sec. 18 sec. 18 sec.
HO-time max. load   26 sec. 26 sec. 37 sec. 37 sec. 36 sec. 36 sec.
Simrad AC10 12 123 233 172 327 165 313
Simrad AC20 20 169 321 237 449 226 430
Simrad AC40 40 Overpowered, do not use
B&G h1000*˛ 25 169 321 237 449 226 430
B&G h2000 ACP-1 25 169 321 237 449 226 430
B&G h2000 ACP-2 40 Overpowered, do not use
Raymarine S1 15 158 299 220 419 211 401
Raymarine S2 20 169 321 237 449 226 430
Raymarine S3 30 Overpowered, do not use
*1: This drive isn't available in 24 volts. This voltage is only usable with a Simrad junction box which can accept 24 volts input and can be set to 12 volts output.
*˛ Please use part number h1000-CUW specially made for Jefa drives, equipped with dynamic braking. Don't use the standard h1000.
Pricing

Jefa transmission drive units

Part No.

Description

Price in Euro

DU-TS150-12

Transmission autopilot drive unit 250 Nm 12 Volts

€ 1.546