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2-Speed Accessory Drives

2-Speed Accessory Drives Crankshaft Pulley

Why 2-speeds?

There are a number of benefits in specifying a 2-speed front end accessory drive (FEAD) system for IC engines:

Reduction of parasitic loses - accessories such as air conditioning compressors and alternators are sized for low engine speed performance and therefore run faster than necessary at high engine speeds. By using a 2-speed crank pulley the accessories can be slowed down at higher engine speeds thus reducing parasitic losses of the system and improving fuel economy.

Smaller accessories - another way to reduce parasitic losses is to specify smaller accessories which are driven faster at low engine speed via a 2-speed crank pulley. This also offers scope to reduce package size, weight and cost.

Reduced engine idol speed - the minimum idle speed in some applications is determined by the performance requirements from the engine driven accessories. By using a 2-speed crank pulley and increasing the drive ratio at low engine speed, the idle speed can in some cases be reduced for improved fuel economy without loss of accessory functions (subject to their being no other constraints such as gearbox or lubrication requirements or other factors that may affect idle stability).

2-speed crank pulley

Antonov is developing a patent pending 2-speed crankshaft pulley which incorporates a planetary gear system with 2 drive ratios. The clutch is electro-hydraulically controlled with oil feed from the engine to avoid the need for a separate pump with keeps parasitic losses and cost to a minimum.

The clutch can be activated on demand depending on the required strategy which can be speed or accessory load demand. A shut off valve protects the engine lubrication system from pressure loss and a disconnect feature can be included for such applications as stop start.

Antonov Mechanical Module (AMM)

The Antonov Mechanical Module (AMM) is a self controlling 2-speed automatic shift system based on one of the Antonov original patents. The AMM utilises internal mechanical forces created by torque and speed to effect a smooth shift between two gear ratios. The AMM can be used to boost the performance of engine driven accessories at low engine speed then revert to direct drive at high engine speed. The AMM can be incorporated into the FEAD system in several ways. It can be integrated with a single accessory, but be incorporated into the FEAD system in several ways. It can be integrated with a single accessory, be a standalone unit within the belt run, or even incorporated into the crank nose pulley so that all engine accessories can be driven at 2-speeds.

As well as optimising the performance and efficiency of engine accessories, the AMM could be used as an automatic transmission for recreational vehicles such as ATVs and boats, and it lends itself particularly well to military applications where not having an electronic control system would be an advantage.

The AMM principle of operation is to control a gear shift from a speed increasing ratio (typically between 1,2x and 1.7x) and direct drive, through the use of mechanical forces generated within the unit by speed and torque. Axial force generated by centrifugal weights acts against spring preload and axial force generated by torque on helical gears. The input speed to the AMM increases and at a particular speed, which can be tuned for each application, the axial force from the the centrifugal weights overcomes the other two forces and the unit shifts from the over speeding ratio to direct drive. Conversely, as the input speed decreases, the axial force generated by the centrifugal weights decreases to a point where it can no longer overcome the spring and gear axial forces, and the AMM shifts to the over speeding ratio. Because of hysteresis in the system, there is a 200-330rpm difference between the up shift and the downshift. This means that the AMM does not hunt between the two ratios and is always positively in one ratio or the other.